IOBC/WPRS
Working Group "Integrated Control in Field Vegetable Crops"
OILB/SROP
Groupe de Travail "Lutte lntegree en Culture de Legumes"
PROCEEDINGS WORKING GROUP MEETING
Vienna (Austria) 28-30 October 1991
Edited by S. Finch & J. Freuler
IOBC/WPRS Bulletin Bulletin OILB/SROP 1992/XV/4 INTRODUCTION
From about the time of the 1988 Meeting in Tune (Denmark) andduring the 1990 Meeting in Braunschweig (Germany) [which unfortunately was not published], there has been a gradual transition in the work of Group Members from pest controi relying almost entirely on commercially-produced pesticides to methods based on non chemical methods of control. The major constraint to the implementation of anynew method of pest control is that while reductions in crop yield will be acceptable in certain crops, reduction in crop quality·wilJ not. Group Members have concentrated mainly on twoapproaches. The first has been to develop pest forecasting systems so that pesticide is applied only when absolutely necessary. Only after the amounts of pesticides applied to crops has been reduced to a minimum will it be possible to screen adequately biologkal control agents under truly commercial conditions. The second approach has been to abandon systems of "clean crop" cultivation in favour of intercropping vegetables with various other plants to deter pest insects frominfesting the crops. Although the advantages of such systems have been stressed by Coaker in England (1975) and Theunissen in the Netherlands (1980), it is only in the last two years that Theunissen hasdeveloped the system to a stage where it may now be acceptable to commercial growers. Therefore, the papers presented in this Bulletin descnbe how elements normallyassociated with classical Integrated Pest Management {1PM), such as cultural control, microbial control, the augmentation of predators/parasitoids, and resistant crop varieties could possibly be integrated into future systems of pest control. Although some systems are now being tried in the field, others are still at the research stage. The numbers of scientists wishing to take part in collaborative projects appears extremely encouraging for the future success of the Group.
The meeting in Vienna was appreciated greatly by all participants. I therefore take this opportunity to thank Professor Kurt Russ forhis generous hospitality and Dr Andres Kahrer forall he did with the local arrangements to make our meeting in Vienna so enjoyable.
Finally, I thank my secretary, Mrs S K Proctor, forthe invaluable help she gave during the production of this Bulletin, and in particular for the marvellousjob she made of re-typing all manuscripts into a standard format.
S. Finch Wellesbourne, July 1992
I LIST OF PARTICIPANTS Numbers m parentheses ( ) are the Codes for each Country
Dr M Ahlstrom-Olsson Swedish University of Agricultural Sciences Department of Plant and Forest Protection Box44 S-230 53 Alnarp TEL: (46) 40 41 50 00 SWEDEN FAX: (46) 40 46 21 66
Dr N Birch Scottish Crop Research Institute !nvergowrie Dundee DD2 5DA Scotland TEL: (44) 382 562 731 UNITED KINGDOM FAX: (44) 382 562 426
Dr J Blood-Smyth ADAS March :High Street March CAMBRIDGE PE15 9LT TEL: (44) 354 53931 UNITED KlNGDOM FAX: ( 44) 354 50082
Dr :KBooij Jnstituut PlantenziektenkundigOnderzoek - !PO Binnenhaven 12 Postbus 9060 6700 GW Wageningen TEL: (31) 8370 76261 TIIENETHERLANDS FAX: (31) 8370 10113
Ms A Brugner NOVO NORDISK A/S Argentinierstrasse 21 A-1040 Wien TEL: (43) 222 505 4757 AUSTIUA FAX: (43) 222 505 0888
III Dr E Brunel Institute Nationalde la Recherche Agroncmique Laboratoire deRecherches de la Chaire do Zoologie Domaine de la Motte au Vicomte BP 29 - 35650 leRheu TEL: (33) 99 28 51 60 FRANCE FAX: (33) 99 28 51 50
DrR Collier EntomologySection Horticulture ResearchInternational Wellesboume Warwick CV35 9EF TEL: (44) 789 470 382 UNITEDKINGDOM FAX: (44) 789 470 552
Dr M Cruzde Boelpaepe Centre Nacional de Proteccao de Producao Agricole INIA-ER Tapada da Ajuda P-1300Lisbon TEL: (351) 363 40 54/57 PORTUGAL FAX: Not available
Dr J Ellenberg Royal Veterinary and Agricultural University Sectionfor Zoology Biilowsvej 13 DK-1870 Fredricksberg C Copenhagen TEL: (45) 35 28 26 92 DENMARK FAX: (45) 31 37 31 93
Dr PR Ellis EntomologySection HorticultureResearch International Wellesbourne Warwick CV35 9EF TEL: {44) 789 470 382 UNITEDKINGDO M FAX: (44) 789 470 552
IV Professor P Esbjerg RoyalVeterinary and Agricultural University Section for Zoology Biilowsvej 13 DK-1870 Fredricksberg C Copenhagen TEL: (45) 35 28 26 60 DENMARK FAX: (45) 35 28 26 70
Dr S Finch Head, Entomology Section Horticulture Research International Wellesbourne Warwick CV35 9EF TEL: (44) 789 470 382 UNITED KINGDOM FAX: (44) 789 470 552
Dr R Forster Biologische Bundesanstalt fiir Land- und Forstwirtschaft lnstitut fiir Gemiisebau Messeweg 11/12 D-3300Braunschweig TEL: (49) 531 399 1 GERMANY FAX: (49) 531 399 239
Dr J Freuler Station Federale de Recherches Agronomiques de Changins CH-1260 Nyon TEL: (41) 223 63 43 85 SWITZERLAND FAX: (41) 223 62 13 25
Dr MHommes Biologische Bundesanstalt fiir Land- und Forstwirtschaft lnstitut fiir Pflanzenschutz im Gemiisebau Messeweg 11/12 D-3300Braunschweig TEL: (49) 531 399 1 GERMANY FAX: (49) 531 399 239
V DrJ PHonnay Institute for the Encouragement of Scienfitic Research in Industry and Agriculture IRSIA-IWONL De Crayerstraat6 1050Brussels TEL: (32) 2 643 25 25 BELGIUM FAX: (32) 2 643 24 32
DrB Humi Eidg. Forschungsanstaltfiir Obst- Wein- und Gartenbau CH-8820 Wadensw11 TEL: (41) 1783 6111 SWITZERIAND FAX: (41) 1780 6341 Dr S Johnsen Royal Veterinaryand Agricultural University Department of Ecology and Molecular Biology Section: Zoology 13Biilowsvej DK-1870 Fredricksberg C Copenhagen TEL: (45) 35 28 26 TI DENMARK FAX: (45) 35 28 20 79 Dr B Jonsson Vaxtskyddscentralen Plant Protection Centre Box44 S-23 053 Alnarp TEL: ( 46) 40 415 OOO SWEDEN FAX: ( 46) 40 462 166
Dr A Kahrer Bundesanstaltfiir Pflanzenschutz Trunnerstrasse 5 A-1020 Wien TEL: (43) 222 211 13 255 AUSTRIA FAX: ( 43) 222 21 60 825
Dr V Kostal Institute of Entomology Czechoslovak Academy of Sciences 370 05 Ceske Budejovice Branisovska 31 TEL: (42) 38 817 CZECHOSWVAKIA FAX: (42) 38 436 25
VI Ms V Langer Royal Veterinary and AgriculturalUniversity Department of Ecology & Molecular Biology Section of Zoology Biilowsvej 13 DK-1870 Fredricksberg C Copenhagen TEL: (45) 35 28 26 84 DENV.i.ARK FAX: (45) 35 28 26 70
Dr R G McKinlay Edinburgh School of Agriculture West Mains Road EDINBURGH EH9 3JG Scotland TEL: (44) 31 667 1041 UNITED KINDOM FAX: (44) 31 667 2601
Dr R Meadow Statens Plantevem (Norwegian Plant Protection institute) Department of Entomologyand Nematology Fellesbygget N-1432 As TEL: (47) 994 9296 NORWAY FAX: (47) 994 9226
Dr W Miiller-Fietrallia BiologishceBundesanstalt fiir Land- und Forstwirtschaft Institut fiirPflanzenschutz in Gemiisebau Messeweg 11/12 D-3300 Braunschweig TEL: (49) 531 399 1 GERMANY FAX: (49) 539 399 239
Dr A Percy-Smith Zoological Department Research Centre for Plant Protection Lottenborgvej 2 DK-2800Lyngby TEL: (45) 4587 2510 DENMARK FAX: ( 45) 4587 1028
VII Dr A Poelking Bfologische Bundesanstalt fiir Land- und Forstwirtschaft lnstitut fiirPflanzenschutz in Ackerbau und Griinland Messeweg 11/12 3300Bnumscbweig TEL: (49) 531 399 525 GERMANY FAX: (49) 531 399 239
Dr G Taksdal Saerheim Research Station N-4062 Klepp Station TEL: (47) 44255 44 NORWAY FAX: (47) 442 56 96
Dr J Theunissen lnstituqtPlantenziektenkundig Onderzoek - IPO PO Box42 Binnenhaven 12 NL-6700Wageningen TEL: (31) 8370 76255 TIIE NETIIERLANDS FAX: (31) 8370 10113
Dr A Vainio Agricultural Research Centre of Finland Institute of Plant Protection SF-31600Jokioinen TEL: (358) O 708 5367 FINLAND FAX: (358) 0 708 5463
Dr F Vande Steene Centrum voo:rOndenpek op Groentegewassen Faculteit van de Landbouwwetenschappen Coupure Unks 653 B-9000Gent TEL: (32) 91 646 155 BELGIUM FAX: (32) 91 244 093
VIII TABLE OF CONTENTS
Introduction l list of Participants m
Theunissen,J, Supervised control in field vegetable crops in Europe. 1
!Uood Smyth, J.A.,Davies, J., Emmett, B.J., Lole,M ., Paterson, C. & Powel!, V. Supervised control of aphid and caterpillar pests in Brassica crops. 9
Croz de Boelpaepe, M.O., Form,M.R. & Fernandes, J.E. Aphid pests of vegetable crops and aphidophagous insects caught in a suction trap in the Algarve, Portugal. 16
Kah:rer,A. Monitoring the timing of peak flight activity of Thrips tabaci in cabbage fields. 28
Percy-Smith,A. & Philipsen, H. Implementation of carrot fly monitoring in Denmark. 36
Jonsson, B: Forecasting the timiiig of dainageby tne carrot fly. 4:,
Finch, S. An introduction to integrated pest management in field vegetable crops. 49
Taksdal, G. Aspects of the biology of brassica root flies (Delia jloralis andD. radicum) in relation to IPM in south-west Norway. 53
McKin.lay, R.G. & Birch,A.N.E. Integrated conaol of root flies in swedes. 62
Miiller-Pietrallia, W., Hommes, M. & Sondgeratb, D. Using an extended Leslie modelto forecast the development of Delia radicum I. Populations. 68
Collier, R.H., Finch, S. & Phelps, K. The feasibility of using models to forecast carrotfly attacks in commercial carrot crops. 69
Meadow, R. A Nordic project on the cabbage root fly and the turnip fly (1991-1994). 77 " Esbjerg, P. Temperature and soil moisture - two major factors affecting Agrotissegetum Schiff. (Lep., Noctuidae) populations and their damage. 82
IX Johnsen, S. Age-specific, temperature-dependent mortalityin Agrotis segetwn: an,explanatorymodel. 92
Ems, P.R. Sources of resistance in brassicas to cabbage root fly. 94
Langer, V. The use of a living mulch of white clover on the control of the cabbage root fly (Delia radicum) in white cabbage. 102
Theunissen, J., Booij, C.1.H., Schelling, G. & Noorlander, J. Intercropping white caobage with clover. 104
Honunes, M. Simple control thresholds for foliage pests of leek. 115
Freuler, J. Guidelines and scouting methods in integrated production of field vegetable crops; the situation in Switzerland. 122
Forster, R. & Hommes, M. Supervised control of lepidopterous pests in white cabbage. 127
Ellenberg,J., Philipsen, H. & Bresciani, J. Ecologicalinteractions between insect pathogens and insect pests of cabbage. 138 Delia ViinuJmm,li ., Va!nio, A. & Jaakkola, S. Attempts to control spp. with entomopathogenic nematodes. 143
Kostru,V. Characteristics of plants thatinfluence host-plant finding/acceptance by the cabbage root fly. 154
Van De Steene,F., Benoit, F. & Ceustennans, N. The use of covers to reduce cabbage root fly and caterpillar damage in white cabbage crops. 155
Bru.ne}, E. Work carried out at Rennes during 1990 and 1991 on pest insects of field vegetable crops. 168
Ahlstrom-Olsson, M. & Jonasson, T. Mustard meal mulch· a possible cultural method forattracting natural enemies of brassica root flies into brassica crops. 171
Finch, S. & Eiliott, M.S. Predation of cabbage root flyeggs by carabidae. 176 lFinch,§. Collaborative projects for 1992 and 1993. 184
X Supervised cont!"ol in field vegetable crops in Europe
J. Theunissen
ResearchInstitute for Plant Protection (/PO), Wageningen, The Netherlands
Summary Supervised control is being implemented gradually in a number of field vegetable crops in Europe. Methods of supervised control are in various stage of development, that range from basic research to independent application by commercialgrowers. This paper contains an inventoryof "the state of the art" in westernEurope. The crops involved arein decreasingorder of importancebrassicas, carrots, leek, peas.beans andlettuce. Thestage of development of supervised controlin these crops has been placed arbitrarily in three classes. In addition. an overview is presented of the prioritiesin pest/disease controlin several crop situations and thevarious approaches that can be applied to solve them. Finally, the general trendsand major problems facingthe widespreadintroduction of superlised control into commercial field vegetable production in the near future are discussed
lntrod,u:tio.m Supervised control methods are being introduced, slowly but surely, into commerciaifield vegetable growing in westernEurope. Thedevelopment of these methods varies according to local conditions and the problems involved. Supervised control is a method used to determine whether, or not, it is necessary to control a pest, or disease, in a givensituation. When control is necessary, it should be carried out preferably by the most appropriate method available. For instance, in greenhouse vegetable crops in the Netherlands supervised control involves using stickytraps to monitor pest populatio!lS. This informationis thenused to decide when parasitoids should be introduced. In contrast, in field vegetables crops most control depends on the application of pesticides. Supervised control is based on a combination of simple sampling/monitoring systems to assess pest populations on an individualfield level, and on a set of criteria to indicate what levels of pest infestation can be tolerated and what cannot. Such criteria (named tolerance levels or action thresholds) are considered to be dynamic as separate criteria are often used for different growth stages of the crop. Theabove criteria should be expressed in the unit in which the insects are sampled/monitored in the field Although the sampling/monitoring method should be accurate, it should alsobe as simple as possible to minimize both the man hours involved and the equipment costs. One question that arises regularly is: who should run the su�rvised control system. the grower or the AdvisoryService? The answer to this question obviously has a considerable bearing on the way in which the system is implemented and presented to the grower. In this.paper an up-to-date view will be presented of the development and use of supemsed control in field vegetables in Europe.
1 Methods The different phases in the development/implementation of supervised control have been arbitrarily indicated by 1, 2 or 3 in Table 1. Explanation: 1 Supervised control method{s) still in the research phase. Such methods are not yet operational in grower'sfields. 2 Operational supervised control methods. Such methods are being tested in growers' fields but are not yet applied independently by growers. 3 Supervised control proper. Already applied either by a) growers; or b) on a commercialbasis. Since cropping practises and the structure of the Advisory Services differgreatly from country to country,many combinations are possible. In the above classification, "commercial" means that the growers pay for their information andadvice, regardless of whether the adviser is employed by a commercial company or by the Government. When the grower makes independent decisions he is supposed to have incorporated supervised control methods within his regular cropping practice. Operational methods are those that are technically sound and simple to use in practice. However, they may not yet have been implemented on a wide-scale into existing cropping systems. Any methods that are still being run byresearchers or AdvisoryService personnel,and arenot yet commercial, are indicatedby 2. Methods in the stage of research and field testing are shown as 1. The development and implementation of supervised controlfor vmous crop-pest situations within a country can differ considerably. Such situations are indicated by symbols such as 2/3. To increase the value of this overview, short descriptions will be included for eaeb eotHltfy3f tbe-eurrent--supervised--eontrol programmes.
Results The current state of research and development of supervised controlin Europe is shown in Table 1. The indications are strictly qualitative. Therefore, they do not indicate the extent of the implementation, nor for example the number of farmers who have adopted a particularsystem. In Austria, research is being carried out to monitor populations of Thrips tabaci m cabbage crops. Areas have been identified, for the processing industry, in which Psi/a rosae does not occur and hence carrots can be grown without pesticide. Numbers of the garlic fly,Suillia univittata, are being monitored to develop a pest warning system. In Belgium, research has been reported on the development of supervised control systems for use in Brassica crops against Delia radicum,Mamestra brassicae, Pierisrapae and Plutellaxylostella; in leek against Thrips tabaci; and in beans against Hylemya cilictura. In Switzerland, operational systems are available for supervised control of Delia radicum, Thrips tabaci, Brevico,yne brassicae and caterpillarsin cabbage and cauliflower crops; of Psila rosae in carrots crops; and of Thrips tabaciin onion crops (Freuler & Fischer, 1991a,b). Growers also use supervised control against carrot fly on a regular basis. Research is being carried out also on supervised control of Thrips tabaci and Acrolepiopsis assectella (leek moth) in leek.
2 Table 1: Overview or development and implementation or supervised conm>I in fteld vegetable crops in Europe
CROP PEST(S) COUNTRY s A B CH D DK GB NL Brassica CRF, caterpillars 1 2 2 1 1/2 aphids, diseases 2/3
Carrot 1 2/3 2 1 Psilarosae 2/3 2/3 3 Pea, bean Pea moth 1 2/3 3 aphid, midge Lettuce aphids 2 Leek, onion, Leek moth 1 1 1/2 1 1 1/2 garlic thrips, diseases Various Agroti.sspp. 2 2 2 various
1 = research; 2 = operational, not yet commercial; 3 = applied by growers Code for countries: A Austria, B Belgium, CH Switzerland, D Germany, DK Denmark, GB England, NL the Netherlands, S Sweden
In Germany, operational methods of supervised control are available foruse in brassicacrops against Deliaradicum, caterpillars and cabbageaphids; in carrot crops againstPsila rosae; and in leek crops against leek moth and Thrips tabaci. In brassica and carrot crops, limited numbers of growers use egg-traps and yellow stickytraps, respectively. Pheromone traps for monitoring populations of Plutella xylostella, Mamestra brassicae,Plusia gamma and Acrolepiopsisassectella are commercially available, but it is not clear whether they are actually used by growers. Extension services of the various republics (Lander) provide growers with regional warnings on tbe occu_rrence of major vegetable pests. Research is carried out on forecasting methods forDelia radicwn in brassica crops, forPsila rosae in carrot crops and for Thrips tabaci on leek crops. In Denmark, vegetable growers can subscnbe to a supervised control system for the carrot rust fly and Agrotis segetum that is operated by the Advisory Service (Esbjerg et al., 1988; Esbjerg, 1988; Philipsen, 1988). The carrot fly system is based on the numbers of flies caught on yellow sticky traps. The farmer puts traps into his fields, collects them after a given interval and then sends the traps back to the
3 Advisory Service for the insects to be counted. The results are then conveyed to the grower. Regional early warnings, based on weather data, are sent to growers when Agrotis segetum infestations are expected. Research is being done to improve the existing forecasting system forA. segetum, and to study monitoring of Deliaradicum and D. flora/is in brassicacrops. In England the extension service (ADAS) plays an important role in the implementation of supervised control in field vegetables. Operational systems are available for forecasting spraying dates for pea moth (Cydia nigricana) and cutworms (Agrotis segetum). Carrot fly (Psi/a rosae) infestations are monitored using yellow sticky traps; cabbage root fly (Delia ra.dicum) by taking soil samples; and lettuce aphids by the use of yellow water traps. Monitoring systems based on pheromone traps are used forFlutella xylostella andother Lepidoptera. Coloured sticky traps in decision making for Thrips tabaci (blue) and pollen. beetle (yellow), and coloured water traps (yellow)for Thrips tabad and Ceutorrhynchusspp. These systems arerun by ADAS persollI!el. A number of growers and commercial crop consultants use their own. non-validated, methods of supervised control in brassica crops. Some pea growers operate pheromone traps for pea moth and also record the appropriate temperatures foregg hatch in order to calculate the correct spraying dates. Carrot fly monitoring is carried out by private consultants and ADAS. Research on developing and validating cabbage root fly (Finch & Collier, 1988, Collier et al, 1991) and carrot fly forecasis has now been completed. In 1992, the Horticultural Development Council, which collects an annual levy from all large growers, will pay Wellesboume to send weekly pest forecasts, based on data from the closest meteorological station, !o over 200 growers. Forecasts will be sent out to a similar number of growers to indicate when pollen beetles will migrate from the soil beneath crops of oilseed rape andinvade susceptible crops of cauliflower and calabrese. In Sweden, farmers pay crop consultants to monitor carrot flyinfestations using the methods developed by the Danish advisoryservice. Carrot processing companies either monitor their own fields or hire crop consultants. Regionalphenologkal data and crop damage are collected by the Extension Service. Cabbage root fly oviposition is not monitored because only soil-applied insecticides are used. Pea processfr1g companies use pheromone traps to monitor pea moth (Cydia nigricana) infestations. Scouts arehired to sample fields for pea aphid (Acy.thosiphon pisum) infestations and crop rotation is applied to avoid infestations by the pea midge ( Contarinia pisi) (.!onsson, 1988). For carrots and red beet, processing companies hire crop consultants to apply the Danish systems for for!!casting cutworms (Agrotis segetum) attacks. Growers organizations payfor a pheromone trapping system of A. segetum around carrot fields m central and south Sweden. In the Netherlands, supervised control of caterpillars and cabbage aphids in Brussels sprouts is carried out by about 70 - 80% of all commercial growers. The number of sprays applied have been reduced from7.3 in 1981 to their current levels of 3-4 on farmers' conveutionai farms and 1-2 on farms where supervised control is practiced. Savin� on unnecessary pesticide applications in this- crop amount to about Dfl. 1 million/year. In white and red cabbage, similar supervised control methods have beeu developed and are now widely used by growers. For a series of other brassica crops (cauliflower, spring cabbage, broccoli, savoy cabbage) sets of tolerance levels have been worked out, but they have not yet been tested in commercial brassica-growing areas. These methods consist of a set of tolerance levels, based on the growth stage of the crop, and a simple method for sampling the pest infestation (systematic or sequential sampling)(Theunissen & den Ouden, 1985, 1987, 1988;
4 Theunissen, 1988). A monitoring system for carrot fly (Psila rosae) was developed using yellow stickytraps similar to those used in the Danish and Swiss systems (den Ouden & Theunissen, 1988). A crude tolerance level was calculated from the correlation between accumulated fly catches and the percentage of carrots damaged alongside the traps. This method still needs further validation and hence is not yet operational under field conditions. In onions, the onion fly (Delia antiqua), has been treated commercially with sterile flies since 1980. Presently sterile insects are released into about 1500 ha of the Polders. In leek, research is being carried out to develop supervised control against Thrips tabaci, Acrolepiopsis assectella,Puccinia allii and Phytophthora porri. This includes monitoring methods, tolerance levels, and simple sampling systems (Theunissen & Legutowska,1991a, 1991b; Theunissen & Schelling, 1991).
General trends
The development and implementation of supervised control systems is determined largely by external factors. Such factors may either stimulate or restrict the adoption of such systems. Although several factors can be named, their effects are difficult to quantify. They originate largely from changes in public opinion towards the current methods of crop production and from the political translation of these changes in terms of research priorities and funding. These factors include: increased public and political pressure for 1PM. increased awareness of growers to the environmental impacts of their production systems. increased awareness of consumers to the safety of the prooucts and the. methods of production. Consumers are becoming more critical of residues in products and the environmental impacts of current production systems. interest of both growers and general public in methods of sustainable crop production. Much of crop protection research is now aimed at developing such methods. increased demand by growers for supervised and biological control methods. The first step in reducing the usage of pesticides is supervised control. This has tc be fol!owed by integrated systems that also include biological control. resistant vai:ieties, and appropriate cultural practices etc. The increased interest of growers for such approaches is a logical step towards sustainable agriculture. existing conventional control practises are converging with supervised control methods in terms of pesticide use. Without adopting supervised control methods officially, many growers are now becoming more careful about applying sprays as more information on supervised control penetrates into growers' communities. Modern growers who employ supervised control methods are often used as examples by their neighbours and by other growers within their region. Effective information by extension services plays an important role in the dissemination of this type of information. in spite of the stimulating developments to date, the process of translating research results into simple methods which can be applied by growers remains difficult. Thisis the case in both Europe (Theunissen & den Ouden, 1988) and in the United States (Stoner et al, 1986). More attention should be given ta this part of the system.
5 Priorities
In view of the increased demand from growers and the public formore acceptable control methods, priorities must be set in each countryto make .the most effective use of the information available from research and development. The major priorities in the most important field vegetable crops in westernEurope are: brassicas: Delia radicum,D. jloralis, Thrips tabu.ci, various caterpillar species, Brevicoryne brassicae, fungal diseases, Contarinia nasturtii. carrots: Psi/a rosae, aphids, nematodes. leek: Thrips tabaci, Puccinia allii, Phytophthora porri,Acrolepiopsis assectella. lettuce: aphids. swedes: Delia spp. In countries where a particular crop-pest combination is important, different priorities may be set. The priorities with respect to the technical research and development of supervised control can be summarized as follows: 1. Problem definition. Define the most important pests and diseases, based on: a) the economic importance of the produce. b) the current level of pesticide use. How much can be saved on pesticide treatments. c) the presence of a pest/disease complex. It is more realistic and rewarding to develop methods which can be used, at least partly, to develop supervised control for several concurring pests or diseases. It is importan,to present to the grower a recipe which is as simple ruid wide-ranging as possible. For example, we have developed in leek a systematicsampling method which can be used for Thrips tabaci, leek moth (Acrolepiopsis assectella), rust (Puccinia allii) andleafspot (Phytophthora porri). If just one sampling plan can be used forall problems, then it is more likely to be accepted. d) the time required to achieve minimum pesticide usage. It is important to produce results as soon as possible, as the availability of suitable methods has both a technical/economical and a psychological effect. e) the impact in a particular sector. It can be important to achieve a breakthrough in a sector which previously has been reluctant to adopt supervised control. For example, floriculture in the glasshouse industry in the Netherlands always considered supervised control to be impossible because of the zero-tolerance levels required in most crops. Recently this position has changed and research has now been started on supervised control. This major breakthrough needs to be consolidated. 2. Develop effective sampling and monitoring methods. Determine where, when, and how to estimate pest population densities in a reliable and simple manner. This is the first requirement for supervised control systems. 3. Investigate the damage function(s). The criterion of what pest infestations can be tolerated in a crop at any specific growth stage depends on the amount of economic damage that will result at harvest. This is the second requirement for supervised control systems. 4. Translate the research results into simple systems that can be used directly by growers. The difficulties in this problem are greatly underestimated.
6 Application of supervised control and integrated control methods in field vegetable crops in Europe is increasing. Consultation and cooperation within Europe and the relevant IOBC Working Groups must continue if the current high momentum of this important development is to be sustained.
Acknowledgement
I thank all the colleagues in Europe who have provided me with information concerning the state of affairs in their respective countries. Their co-operation made this paper possible.
R�sum�
La Jutte dirig� en culture I�gumi�re de pleine terre en Europe
La Jutte dirigee est graduellement introduite dans un nombre croissant d'especes des cultures maraichereseuropeennes. Lesmethodes pour y parvenir sont a des stades de developpement variables, depuis la recherche de base jusqu'a !'application independante par le producteur. Cet article comprend un inventaire de "l'etat de la question" en Europe de l'ouest. Les cultures concemees sont, dans l'ordre d'importance decroissant, les Brassica, carotte, poireau, pois, haricot et laitue. L'etat d'avancement de la lutte dirigee dans ces cultures a ete arbitrairement classe en 3 categories. En plus. un aper� des priorites.de. }utter contr.e.Jes.ra'!ageurs. et . maladies est presente pour plusieurs conditions culturales, ainsi que Ies diverses approches envisageables. Enfin, Ies tendances generales et les problemes majeurs s'opposant, a court terme, a une large introduction de la Jutte dirigee dans la production commerciale de legumes sont discutes.
References
Collier, R.H., Finch, S. & Phelps, K (1991). A simulation model for forecasting the timing of attacks of Delia radicum on cruciferous crops. EPPO Bulletin :n: 419-424. Den Ouden, H. & Theunissen,J. (1988). Monitoring populations of the carrot rust fly, Psila rosae, for supervised control. In: Working Group "Integrated control in fieldvegetable crops'; WPRS Bulletin, IOBC, 1988/Xl/1: 26-32. Esbjerg, P., Philipsen, H. & Perey-Smith, A (1988). The significance of carrot fly (Psila rosae) in Denmark. In: Working Group "Integrated control infield vegetable crops", YIPRS Bulletin, IOBC, 1988/XI/1: 14-25. Esbjerg, P. (1988). Integrated pest management in Danish carrot fields: Monitoring of the turnip moth (Agrotis segetum Schiff., Lepidoptera: Noctuidae). In: "Progress on pest management in fieldvegetables'; Balkema, Rotterdam, 177-186. Finch, S. & Collier, R.H. (1988). Development of traps for monitoring populations of the carrot fly. In: Working Group '1ntegrated control infield vegetables� WPRS Bulletin, IOBC, 188/XI/1: 1-7. Freuler, J. & Fischer, S. (1991). Methodes de controle et utilisation des seuils de
7 tol�rance pour les ravageurs des cultures marakheres de pleine terre. 2e edition, Revue suisse Vitic. Arboric. Hortic., 23(:?): 101-124. Freuler, J. & Fischer, S. (1991b). Kontrollniethoden und Anwendung von Schaden schwellen fur die Schiidlinge im Freilandgemiisebau. LandwirtschaftSchweiz 4(TJ: 341-364. fonsson, B.G. (1988). An ecological approach to management of the pea ·midge, Contariniapisi (Winn.), in vining peas. Plant ProtectionReports, Dissertation 17, Dept. Plant and Forest Protection, Swedish University of Agricultural Sciences. Philipsen, H. (1988). Monitoring teclwJques forthe carrot fly (Psi/a rosae). In: Working Group Hlntegrated control in fieldvegetable crops'� WPRS Bulletin, IOBC, 1988/XI/1: 8-13. Stoner, K.A, Sawyer, AJ. & Shelton, AM. (1986). Constraints to the implementa tion of !PM programs in the U.S.A: a course outline. Agric., Ecosystems and Environm. 17: 253-268. Theunissen, J. (1988). Sequential sampling of insect pests in Brussels sprouts. !n: Working Group "Integrated control in field vegeiab!e crops� WPRS Bulletin, IOBC, 1988/XI/1: 111-117. Theunissen, J. & Den Ouden, H. (1985). Tolerance levels for supervised control of insect pests in Brussels sprouts and white cabbage. J. Appl Ent. 100: 84-87. Theunissen, J. & Den Ouden, H. (1987). Tolerance levels and sequential sampling tables for supervised control in cabbage crops. Mitt. Schweiz. Ent. Gesel/schaft 60: 243-248. Theunissen, J. & Den Ouden, H. (1988). Implementation of supervised control in commercial cabbage growing. In: Working Group '1ntegrated control infield vegetable crops'; WPRS Bulletin., IOBC, 1988/XI/1: 127-131. Theunissen, J. & Legutowska, H. (1991a). Thrips tabaci Lindeman (Thysanoptera, Thripidae) in leek: symptoms, distribution and population estimates. J. Appl. Ent. 112: 163-170. Theunissen, J. & Legutowska, H. (1991b). Thrips tabaci Lindeman (Thysanoptera, Thripidae) in leek: within-plant distribution. J. Appl Ent. 112: 309-316. Theunissen, J. & Schelling, G. (1991). Within-plant distribution of Thrips tabaci Lindeman on untreated leeks (Allium ponum L). Med. Fae. Landbov:ww. Rijksurw.1. Gent, 56/3b: 989-994.
fOBC/WP�WorldngQ'royp Meetjng "Integrated Control in Field Vegetables".Vienna. 2§:30Oct 1991
8 Supervised control of aphid and caterpillar pests in Brassica crops
J.A Blood Smyth(l>, J. Davies, BJ. Emmett, M. Lole C. Paterson & V. Powell
(t) AgricultW'alDevelopment and Advisory Service, MAFF, High Street, March, Cambridge, PE15 9LT, UK
Sl!mmary
Simple damage thresholds were tested for cabbage aphid (Brevico,yne brassicae) and cabbage caterpillars ( e.g. Pierisrapae) in crops of cabbage, calabrese and Brussels sprouts. In half the experiments, the systematic sampling method used by Hommes et aL (1988) was adopted. In the remainder, a combination of systematic and sequential sampling methods were tested. There was a 23% reduction in number of sprays used, where pest control was based on threshold values in comparison to routine sprays applied every two weeks. However, in two trials the percentage of unmarketable heads fromsupervised plots was unacceptable for supermarkets, which have a "nil tolerance" for pest presence and damage. Tentative conclusions fromthe firstyear's work suggest that damage thresholds need to be lowered as soon as the marketable parts, e.g. start of·cabbage heading, button hritiation, of the crop-begintcrappear:
introduction
Supervised control in brassica crops has been practiced in the Netherlands for several years following research work on sampling methods and tolerance levels (Theunissen & Den Ouden, 1985). In the United States variable intensity sampling methods have been investigated (Hoy et al., 1983). The IOBC/WPRS - Working Group on Integrated Control in Field Vegetables undertook a joint project to test simple damage thresholds for cabbage caterpillars and cabbage aphid on cabbage in five European countries (Hammes et aL, 1988). The aim was to encourage implementation of supervised control methods in practice. Following the publication of this work and with the encouragement of entomologists at HRI (Horticulture Research International)Wellesboume, a project was set up between entomologists fromADAS (Agricultural Development and Advisory Service) and horticulturalists from ADAS and HRI, funded by MAFF (Ministry of Agriculture, Fisheries and Food). The aim of this three-year project is to evaluate sampling methods for monitoring foliar pestson brassica crops and to establish a series of robust threshold levels. In this paper the results of most of the first year's experiments (1991) are presented (some trials have yet to be harvested).
9 Materials and methods
Three sites were used and three types of brassicas were tested (Table 1), in the field plots at research centres and at one commercial farm (Cottenham). The two damage thresholds used for both pests were that plants were treated if 10% of the samples plants were infected during the first two inspections and if 5% of the plants were infected in the remaining samples until harvest. In each field trial there were three treatments, except at Cottenham where there were four. A minimum plot size of 200 sq m was used except in the Arthur Rickwood EHF cabbage trial where plots were much smaller.
Table 1. Sites and types of brassica tested
Organisation Site Type of Brassica
ADAS Arthur Rickwood, EHF, Cambs Cabbage, calabrese
ADAS Cottenham, Cambs Cabbage
HRI Kirton, Llncs Brussels sprouts, cabbage, calabrese
HRI Stockbridge House, Yorks Brussels sprouts
Treatments were as follows:-
1) Untreated, control 2) Routine treatment - sprayed at two week intervals with a tank mix of deltamethrin (5 ml a.i./ha) and pirimicarb (75 g a.i./ha) 3) Supervised treatment - insecticides and doses as above, applied singly or as a tank mix only when thresholds were reached. 4) 1PM - Bocillw thuringiensis (Thuricide, 1 kg/ha) and pirimicarb (75 g a.i/ha) applied either singly or in a tank mix, but only when threshold(s) reached.
Sampling of the supervised and 1PM plots started two weeks after tr,u1splanting and was repeated at two-week intervals until harvest. Two methods of sampling were used. For the cabbage trial sites at Arthur Rickwood EHF and Cottenham and the Brussels sprouts trial site at Stockbridge, the systematic method used by the IOBC Working Group (Hammes et al, 1988) was adopted. On each sampling occasion, 50 plants were examined from each plot (10 sampling points of 5 plants, regularly distributed over the whole plot). In the remaining trials and in one replicate at Stockbridge, the systematic sampling method (Fixed number of plants) was combined with a sequential sampling method (variable number of plants), based on a sampling chart and a list of random numbers. The numbers of plants infested with caterpillars and aphids were recorded on the supervised plots. At harvest, aphid and caterpillar damage was recorded on 30 -
10 50 plants/plot and the number of marketable heads, (spears or buttons) recorded (Table 2).
Table 2. Damage classes for aphid, caterpillar and marketing assessments
1. Clean, no pest or damage on wrapper/outer leaves or bead 2. Pests or damage only on wrapper/ outer leaves or head 3. Pests or damage on head; plant unmarketable 4. Numbers of plants in standard marketing categories 5. Post-harvest quality assessment
Results and Discussion
In 1991, in sharp contrast to the two previous years, there was an extremely late migration of cabbage aphid. At three sites, the threshold for cabbage aphid was never reached (Table 3). At the other sites, thresholds were reached between July and September. Spray treatments were reduced from 6.6 on the routinely treated plots to 1.3 on the supervised plots (Table 5).
Table 3. Infestation levels of the cabbage aphid recorded in the supervised plots (1991)
% plants infested with cabbage aphid Site and crop Sample No. 1 2 3 4 5 6 7 8 9
(Threshold values%)------10 10 5 5 5 5 5 5 5 Arthur Rickwood EHF cabbage 5 5 1 <1 0 calabrese 0 0 0 0 1
Cottenham cabbage 0 0 0 0 0 0 0 2 0
HRI Kirton B. sprouts 0 0 <1 0 3 4 4 15 15" cabbage 1 8 6 4 19 calabrese 0 0 0 <1 0 0 8 2 7• HRI Stockbridge B. sprouts 0 0 0 0 0 0 2 6 18*
• to end of September
11 Table 4. Infestation levels of the cabbage caterpillars recorded in the supervised plots (1991)
% plants infested with cabbage caterpillars Site and crop Sample No. 1 2 3 4 5 6 7 8 9 (Threshold values%) 10 10 5 5 5 5 5 5 5 ------··--..------Arthur Rickwood EHF cabbage 5 5 14 3 85 calabrese 0 0 0 0 1
Cottenham cabbage 0 0 0 0 0 0 0 HRIKirton B. sprouts 0 0 0 3 13 0 <1 <1 <1" cabbage 0 0 3 6 <1 0 0 0 1" calabrese <1 1 6 0 <1
HRI Stockbridge B. sprouts 0 0 0 12 4 4 12 12*
ie to end of September
Similarly, there was a late build up of cabbage caterpillars,especially Pieris rapae (Table 4). Spray treatments was reduced from a mean of 6.6 on the routinely treated plots to 1.7 on the supervised plots (Table 5). For both aphid and caterpillar control at Cottenham, sprays was reduced from 9 on the routine to 1 on the 1PM plot. The major problems were caused by diamond-back moth, Plutellaxy!.ostella, which were sometimes difficult to detect when sampling, especially when hidden amongst calabrese spears. At the time this paper was presented only four out of seven trials had been harvested. The calabrese from the site at Arthur Rickwood EHF suffered little attack, as it was harvested before the main migration of cabbage aphid and build-up of cabbage caterpillars. By contrast, there was unacceptable damage on cabbage from the supervised plots, that were harvested two months later. Pieris rapae caterpillars caused devastating ciamage on one replicate of the supervised treatment plots. There was una�ceptable damage by caterpillars on the- cabbage fromthe supemsed plot at Cottenham, despite only small infestations. Tentatively, it tan be concluded Lliat the thresholds tested need to be lowered from the beginning of head (spear and button) formation onwards. The British supermarkets operate a "nil tolerance" for presence of insects in marketable fresh produce. One aphid on a sprout button is unacceptable. Similarly, pest damage, e.g., holes caused by caterpillars feeding, is unacceptable. The supermarkets may reject ctamageq produce and/or cancel the contract with the grower or cooperative.
12 Table 5. Number of sprays applied to control aphids and catero.illars on the routinely treated and the supemsed control plots and the percentage of crop classified s marketble. Control = untreated plots.
Site and N!l, Qf 5J!r� annli�d Marketable crop heads Aphid Caterpillar
Arthur RickwoodEHF cabbage untreated 0 0 91 routine 5 5 89 supervised 2 3 72 calabrese untreated 0 0 99 routine 4 4 100 supervised 0 0 99
Cottenham cabbage untreated routine 9 9 100 supervised 0 1 90 1PM 1 1 92
HRI Stockbridge Brussels sprouts* untreated 0 0 routine 8 8 supervised 1 3
HRIKirton Brussels sprouts"' untreated 0 0 routine 8 8 supervised 2 2 cabbage* untreated 0 0 routine 9 9 supervised 0 2 calabrese+ untreated 0 0 88-- routine 3 3 95 supervised 0 1 93
'" still to be harvested + caterpillars and aphids detected in crowns of untreated and supervised harvested speari, at 27% and 12% respectively
13 The systematic sampling method (Hommes et al, 1988) proved to be practical, straight forward and less time-consuming than the other method, where a combination of systematic and sequential sampling methods was adopted. Thelatter was time-consuming especially when attempting to use random plant numbers to sample a Brussels sprout crop. With a more practical path through the plot, while retaining a sequential method, it may be possible to reduce the time taken. However, this may not be possible when infestation levels are low. There was a considerable reduction in the number of sprays used on the supervised plots. The leading supermarkets and the public wish fewer insecticides to be used on fresh produce. However, produce must satisfy the quality requirements. For growers to accept and adopt supervised control of foliar pests on brassica crops, damage thresholds must be robust, sampling procedures practical and not time consuming, while enabling the production of top quality vegetables.
Conclusion
The interim results of the first year of a three-year project have been presented and the conclusions at this stage are only tentative. Because of the stringent supermarket requirements and "nil tolerance" forpest presence/damage, the damage thresholds foraphid and caterpillar need modifying. Thus from the "head formation" stage the threshold may need to be lowered to 1 %. The sequential sampling method with variable number of plants can be less time-consuming that!systematic methods. The method adopted in this first year needs to be simplier, both to reduce time spent inspecting the plants ai,d to make the system morereadily -adoptable by the grow.er_ In._spiteof...th.epresent problems,.there is considerable and growing interest amongst UK growers, consultants and the supermarkets in supervised control.
R�sume
Lutte dirig� en culture 14 migre tres tard dans les cultures, de sorte que les seuils n'ont pas ete depasses dans plusieurs experimentations. Le nombre moyen de pulverisations a ete de 5.7 dans les parcelles traitees d'une maniere routiniere, alors qu'il n'a ete que de 0.7 dans celles OU la lutte dirigee avec seuil a ete appliquee. Le nombre de chenilles, notamment celles de Pieris rapae, a considerablement augmente en fin de la saison. Le nombre moyen de pulverisations etait dans ce ,;as de 6.1 (routine) contre 1.4 (lutte dirigee). Le nombre de tetes non commercialisables a depasse les 9% dans deux essais. La teigne des cruciferes (Plutellaxylostella) a pose un probleme important dans les pommes de broccoli, car les magasins de grande surface prescrivent une tolerance zero pour ce ravageur. Au terme de ces premieres annees d'essais, il semble qu'il faille abaisser les seuils actuels. De plus, les methodes d'echantillonnage devraient etre reevaluees pour determiner les mieux adaptees aux conditions pratiques. L'application combinee des methodes d'echantillonnage systematique et sequentielle a exige un temps considerable dans les cultures de chou de Bruxelles. La methode de Hommes et aL s'avere en revanche plus facile et presente ainsi plus de chances d'etre adoptee par les producteurs. Il y a un interet considerable, parmi les producteurs et les conseillers du Royaume-Uni, pour !'introduction de systemes bases sur la lutte dirigee. References Hommes, M., Dunne, R., Ellis, P.R., Fischer, S., Freuler, J., Kahrer, A, & Terretaz, C. (1988). Testing damage thresholds for caterpillars and aphids on cabbage infive european countries - report on a collaborative project done in 1985 and 1986. International Organisationfor Biological and Intergrated Control of Noxious Animals and Plants. Working Group "Integrated Controlin Field Vegetable Crops" 118-126. Hoy, C.W., Jennison, G., Shelton, AB. & Andaloro, J.T. (1983). Va.riable - intensity sampling: a new technique for decision making in cabbage pest management. Journal of &onomic Entomology 76: 139-143. Theunissen, J. & Den Ouden, H. (1985). Tolerance levels for supervised control of insect pests in Brussels sprouts and white cabbage. Zeitschriftfur angewandte Entomologie 100: 84-87. IOBC/WPRS-WorkingGroup Meeting "IntegratedControl in Field Vegetables".Vienna, 28-30 Oct 1991 15 Aphic! pests of vegetable crops and aphidophagous insects caught in a suction trap in the Algarve, Portugal M.O. Cruz de BoelpaepeCl), M.R. Forra<2> & J.E. Fernandes<2> <1> !NIA, CentroNacional de Protecr;iio da Produr;iioAgricola, Tapada da Ajuda, Edijicio 1, 1300 Lisboa, Portr,,1,gal <2> Direcr;iio Regional de Agricultura do Algarve, Apartado 282, 800 Faro, Portugal Summary A survey was made in 1989 and 1990 of the aphid pests of vegetable crops and aphidophagous insects caught in a suction trap operating close to ground level (1.5 m high) at Silves in the Algarve. The suction trap was sited in a plum orchard surrounded by fields containing crops of beans, peas, tomatoes, potatoes and some protected vegetables. The seasonal abundance of Aphis craccivora Koch, A fabae Scopoli, A. gossypii Glover, A. nasturtii Kalt., Brevicoryne brassicae L and Myzus persicae (Sulzer) are described. Numerical response of parasitoids to prey density are shown forAphidius Nees against M. persicae;Diaeretiella Stary against B. brassicae/M. persicae; and for Lipopfexis Foster/Lysiphlebus Forster/TrioxysHalidey_ againstAphis spp. 1n some instances predatory Chrysopids, were the most abundant biological control agents captured. Identificationof the periods when the aphids were controlled most effectivelyby aphidophagous insects, show clearly the advantage of using pesticides in a rational manner. Introduction Aphid control in vegetable crops should be based on the rational use of insecticides. The kinds of insecticides used a.'ld the timing of applications must take into account economic thresholds (Tatchell, 1982) and the impact of natural enemies on aphid populations during specific periods of the year (Mack & Smilouitz, 1980). Suction traps, operating near to ground level in agricultural areas have been used to monitor aphids flying in the locality and to determine whether such aphids are v,rus vectors (Plumb, 1975). Since 1989, the authors have used this approach in the Algarve. Suction traps catch aphids as they migrate between host-plants and therefore represent a differentstage- in life-cycle-ofthe aphids- to those found infesting the crop piac'lts (Tatchell, 1982). Attempts are being made to relate the numbers of aphids caught in the traps to crop damage (Forrest et al., 1973) and to indicate when aphids are likely to 8pread virus from one crop to the next. This paper describes the seasonal changes in the !lumbers of alates of the main aphid pests of vegetables and relates this to the numbers of aphidophagous insects trapped during 1989-90. 16 Materials and Methods From early March until the end of November (excepting August) in both 1989 and 1990, a suction trap, positioned 1.5 m above ground level, was continuously used to sample the aerial fauna. The trap was sited in a plum orchard at Silves in the Algarve. The plum orchard was surrounded by lemon orchards, peach orchards, by intensive cultivations of horticultural crops. According to the statistics from the Regional Directory of the Algarve in the neighbourhood of Silves in 1989, extensive areas represented 42.8% from the total area of horticultural crops (215.6 ha), from which melon was one of the most important crop (17.9 ha). Horticultural crops were also cultivated intensively in fields or plots under a plastic cover {2.7 ha), in vegetable gardens (31.6 ha) and under greenhouse {3.2 ha). Although broad beans and peas were the main vegetable crops, many field crops of tomato, potatoes (16.4 ha) and cabbage were also grown. The main crops grown under greenhouse conditions were, in descending order of importance, tomato, beans, lettuce and cucumbers. Generally two crops were grown each year on each field, or in each greenhouse. The aphid samples were taken from the suction trap at 10.00h and 17.00h each day, and were placed in 70% alcohol to preserve the insects. In the laboratory, the aphids and aphidophagous insects were separated from the 'non-target' insects. identified and counted. Results and Discussion Seasonal abundanceof alateaphid species The aphid species, caught in the suction trap during 1989 and 1990, that cause direct damage to vegetable crops by sucking plant sap, or indirect damage by transmitting viruses, are shown in Table 1 together with their vegetable host-plants and the viruses they are known to transmit. Among the species listed, Aphis craccivora, A. fabae, A. gossypii,A. nasturtii,Brevicoryne brassicae and Myzuspersicae were the most abundant caught during the two years. The mean monthly aerial abundance of A. craccivora and M. persicae are shown in Fig. 1. Similar data, but sub-divided into four classes to represent four different aphid densities are shown in Fig. 2 for B. brassicae,A.nasturtii, A. gossypii and A. fabae. M. persicae, an efficient virus vector, is normally considered to be dioecious, alternating between a woody primary host (e.g. Prunus persica {L) and many secondary hosts, which include a wide range of vegetable crops. However, mild winters in the Algarve allow anholocyclic clones of this aphid to survive. The spring flight of M. persicae occurred in March and, as most of these aphids had clavate siphunculi, they must have originated from herbaceous, rather than woody, plants. Following a decrease in aphid numbers in April, the numbers of alates caught increased again in May. This peak of activity was followed by a sharp decline in numbers between early June and September (Fig. 1). The decline in aphid numbers can be explained by adverse conditions, such as the deterioration of the host plants, the lethal effects of high summer temperatures and the mortality caused by aphidophagous insects. 17 Table 1: Aphid species caught by the suction trap togethei" with the vegetable host plants of the aphids and the viruses the aphids can transmit APHID SPECIES VEGETABLE HOST PLANTS VIRUSES TRANSMI1TED Acyrthosiphon Leguminosae(pea, bean. broad Pea enation mosaic, bean pisum (Harris) bean) yellow mosaic, bfan common Cruciferae mosaic, alfalfa mosaic virus, cauliflower mosaic Aphis craccivora Leguminosae {bean, broad Bean yellow mosaic, alfalfa Koch bean) mosaic virus Aphisfabae Scopoli Leguminosae (bean, broad Alfalfa mosaic virus, bean bean) yellow mosaic, potato Y, beet Solanaceae(potato) mosaic, cucumber mosaic I Chenopodiaceae (beet) Aphis gossypii I Cucurbitaceae (cucumber) Cucumbe:rmosaic, bean Glover Leguminosae(bean. bro1d yellow mosaic, bean common bean) mosaic, potato Y, pole.to Solanaceae (potato) aucuba mosaic, cauliflower Piperaceae (pepper) mosaic, celery mosaic, lettuce mosaic, beet mosaic �phirnasturtii Solanaceae (potato) Potato-A,-potato Y, potato Kaltenbach aucuba mosaic, potato leaf roll, cucumber mosaic, bean common mosaic Aulacorthum solani Solanaceae (potato) Potato leaf roll, potato Y, Kaltenbach Cruciferae(cabbage) tomato aspermy, cauliflower Chenopodiaceae (beet) mosaic, beet mosaic, so;ybean Compositae (lettuce) mosaic, cucumber mosaic, Leguminosae(soybean) pea mosaic Brevicoryne Cruciferae( cabbage, rape) Cabbage black rir.g spot, brassicae (L) cabbage ring necrosis, rape savoy, cauliflower mosaic, cucumber mosaic, bean I common mosaic Cavariella aegopodii Umbelliferae(carrot) Carrot motley dwarf, bean (Scopoli) yellow mosaic, pea mosaic Hyperomyzys Compositae (lettuce) Cauliflower mosaic, beet lactucae L mosaic 18 APHID SPECIES VEGETABLE HOST PLANTS VIRUSES TRANSMI1TED Macrosiphum Solanaceae (potato, tomato) Potato A, potato Y, potato euphorbiae Cruciferae (cabbage) aucuba mosaic, potato (Thomas) Chenopodiaceae (beet) spindle tuber, potato leaf roll, tomato aspermy, iomaio yellow net, tomato yellow top, cabbage black ring spot, bean common mosaic, pea mosaic, onion yellow dwarf, lettuce mosaic Myzus persicae Solanaceae (potato) Potato A, potato aucub& (Sulzer) Cruciferae (radish, cabbage) mosaic, potato !eaf roll, Chenopodiaceae (beet) potato spindle tuber, potato Compositae (lettuce) Y, radish yellows, cebbege Piperaceae (pepper) black ring spot, �abbage ring necrosis, cauliflower mosaic, celery mosaic, beet mosiac, beet mild yellowing, cucumber mosaic, alfalfa mosaic virus Megoura vidae Leguminosae (broad bean) Bean yellow mosaic, pea Buckton mosaic, cucumber mosaic Nasonovia n7:iisnigri Cfuciferae (cabbage) (Mosley) Compositae (lettuce) Smynthurodes betae Solanaceae (potato) Westwood Chenopodiaceae (beet) Leguminosae Rhopalosiphoninus Solanaceae (potato) Potato leaf roll lalysiphon (Davidson) Therioaphis trifolii Leguminosae Bean yellow mosaic, alfaifa (Monell) mosaic virus Therioaphis riehmi Leguminosae Sean yellow mosaic, alfalfa (Bomer) mosaic virus The numbers of aphids caught began to rise again in October and reached peak numbers in November. This migrant autumn population was made up of alate exules, sexuparae and males (17% of the total aphids caught). The alate exules migrate to Prunus persica to mate. As no oviparae were found in leaf samples collected from a number of Prunus trees, it appears that many aphids overwinter on herbaceous plants (anholocyclic) in this region of Portugal. Inspection of aphids indicated that the first risk of virus spread into vegetable 19 crops occurred in March with the migration of the aphids from the overwintering herbaceous plants. These alate exules disperse readily and increase the risk of both viral infection and direct damage until the end of June. Although virus is not a problem during the summer and autumn, outbreaks of virus infection often occur in late November due to the build-up of large numbers of aphids on the overwintering vegetable crops. Similarly, M. persicae, the most abundant species of Aphis caught in the region, namely A. craccivora, A. fabae, A. gossypii and A. nasturtii, had conditions to exist parthenogenetically on herbaceous plants. MEAN NUMBERS OF APHIDS 1989-90 300 � MYZUS PERSICAE 0 APHIS CRACCIVORA 200 100 # MARCH APRIL MAY JUNE JULY SEPT. OCT. NOVEMBER Fig. 1: Tn.e mean mm1thly aerial ebundance of M.persicae &nd A cruccivora caught at a height of 1.5 m In a suction trap operaOng at Silves, in the Algarve, Portuga! Catches of A. craccivora increased fromMarch to May, declined during the summer, and increased again to maximum numbers during September (Fig. 1). In addition to the effects of natural enemies, poor condition of the host plants and high temperatures may have been partly responsible for the decline in the population of this aphid during the summer. The risk of the spread of virus by this aphid increased with increasing aphid numbers. Although A. gossypii behaved similarly to A. craccivora, the numbers of A. gossypii remained higher during the summer (Fig. 2) and hence this aphid was more likely to transmit virus at this time. The seasonal distribution and the frequency distributions of the density classes of A. fabae and A. nasturtii were identical. From March. to April/May, there was an increase in the frequencies of several density classes for both species, followed by a 20 slight decline in summer and a resurgence in early autumn (Fig. 2). All four species of the genera Aphis were common during the summer months, probably because of the large number of plants that can be used as hosts by these four species of Aphis. In contrast,B. brassicae was the least numerous of the common aphids captured, possibly a direct result of the small number of cabbage plants growing in the area. Brevico,yne numbers tended to increase from March to June and then decline through the summer and autumn (Fig. 2). The risk of Brevico,yne damaging crops and spreading disease from one crop to another was therefore greatest during the spring. Predator - preyinteractions The reactions of predators to changes in the density of their prey can be examined by calculating either functional or numerical responses (Kuchlein, 1966). Functicnal responses quantify the changes in food consumption by the predators in response to increasing prey numbers, whereas numerical response indicate how changes in the numbers of prey are related to changes in the numbers of predators. The latter was used in the present study, as it is an important factor in deciding which insecticide to select for use in systems of integrated pest management (Hodek et aL, 1966). The inventory and relative abundance of aphidophagous insects caught in the suction trap during 1989-90 are summarised in Table 2. The mean predator/parasitoid-prey ratio's for the main aphid pests of vegetables are shown in Table 3. Under optimum conditions, the predator/prey ratio should approach unity. When the ratio are close to zero, or well above unity, the aphidophagous species are either not present in sufficient number or are present in excessive numbers, respectively. In the first case, it is generally considered that the synchronisation of the predator and the prey is poor and the second situation generally signifies that the predator has a wide range of prey (polyphagous). Parasite - host relationship The genera Aphidius and Diaeretiella contain important parasitoids of the green peach aphid M. persicae. The parasitoid/prey ratios calculated during 1989- 1990 (Table 3), indicated that species of Aphidius might be more effective parasitoids of M. persicae than species of Diaeretiella. High rate of parasitism indicated that Aphidiusmatricariae was highly effectiveagainst M. persicae on peppers under glasshouse conditions _(Khristova, 1973). Aphidius was likely most effective at controlling aphids during the period from March to June (Table 3). When high numbers of aphids occurred during May and November, the parasitoid was relatively ineffective. According to Kuchlein (1966), this phenomenon is common and seems related to the reduction in the fecundity and increased mortality of parasitoids or predators at very high densities of the aphid prey. 21 Table 2: !nventocy of aphidophagous insects caught by the suction trap (1989-19�0) PARASITES Diptera Cediomyiidae Hymenoptera Aphidoletes aphidimyza Aphidiidae Rondani ++ Aphidiw Nees +++ Diaeretiella Stary +++ Syrphidae Ephedrus Haliday + Episyrphw; balteatus De Geer + Lipoplexis Forster ++ Syrphw auricolis Mg. + Lysiphlebw Forster ++++ Syrphw corollae Fabricius + Monoctonus Haliday ++ Praon Haliday + Toxares Haliday + Neuroptera Trioxys Haliday ++ Chrysopidae Anysochrysa albolineata Kill + Anysochrysa baetica Holzel +++ Hyperparasites Anysoch,ysajlavifrons Brauer + Chalcididae Anysoch,ysa inomata Navas + Pteromalinae Anysoch,ysa ventralis Curtis + Asaphes Walker + Anysoch,ysa ventralisprasina Pachyneuron Walker + Burmeister +++ Ch,ysopaformosa Brauer +++ Proctotrypirlae Ch,ysopa septempunctata Lygocerus Forster + Wesmael + Chrysoperla camea Stephens ++++ PREDATORS Hemerobi!dae Co!eoptera Boriomyia spp. + Coccinellidae Hemerobiw spp. + Coccinella septempunctata Micromw; spp. + Linnaeus + Chilocorus bipwtulatus Linnaeus + Lasia Mulsant + Platinaspis Redt. + Propylaea quatuordecim- -punctata Llnnaeus + Scymnw; subvillosw Goeze + Number of specimens caught: 0-30; 30-100; 100-500; + + + > 500 + = ++ = + + + = + = 22 Table 3: Predator/prey ratios of the numbers oi' aphidophagous Insects and their prey caught during 1989-90 - Mar Apr May Jun Jul Sept Oct Nov Parasitoid/prey Aphidius/M. persicae 0.9 1.8 0.5 4.0 0.7 0.3 0.2 0 Diaeretiella/M. persicae 1.3 3.5. 0.9 0.6 0 0.1 0 0 Lysiphlebus/A craccivora 0.3 1.9 6.7 5.2 6.6 0.1 1.7 0.3 Lipoplexis/A. craccivora 0.1 0.3 0.2 0.1 0.1 0 0.6 0.1 Trioxys/A. craccivora 0.2 0.3 0.2 0 0.1 0 0.2 0 Predator/prey C. camea/M. persicae 0.5 1.3 2.2 19.5 71.2 8.5 0.7 0 C. formosa/M. persicae 0.1 0.5 0.5 0.6 10.5 6.7 0.2 0 A. ventralis + A. ventralis 0.2 0.2 0 1.1 12.1 7.5 0.2 0 prasina/M. persicae A. baeticajM. persicae 0.2 0.1 0.1 1.0 28.4 11.0 0.4 0 C. camea/A. craccivora 0.2 0.5 0.9 11.0 16.9 0.3 4.3 0.2 C. formosa/A. craccivora 0.1 0.2 0.3 1.1 2.3 0.1 0.1 0 A. ventralis + A ventralis 0.1 0.1 0 0.6 2.9 0.2 0.1 0 prasina/C. craccivora A. baetica/A. craccivora 0.1 0.1 0 0.7 5.7 0.2 0.7 0 Diaeretiella appeared to be effective against M. persicae during the period from March to May (Table 3). Analysis of the relationship between B. brassicae and Diaeretiella showed that parasitoid numbers increased with aphid numbers until May (Fig. 2). According to Paetzold & Yater (1966), Diaeretiella rapae (McIntosh) is the main parasitoid emerged from mummies of B. brassicae. In June, when the numbers of prey were at their maximum, there was a decline in the parasitoid populations. However, the seasonal changes in Diaeretiella numbers closely reflected the changes in the number of their prey. Numerical responses indicated that Diaeretiella was better synchronized with B. brassicae populations than with M. persicae populations (Cruz de Boelpaepe et al., in press). Species of Lysiphlebus, Lipoplexis and Trio"XJS that were caught in the suction trap are known parasitoids in Aphis spp. (Stary, 1964). In spring the parasitoid/host ratios between Lysiphlebus species and A. craccivora and A. gossypii increased from 23 March to May and declined during June-July, along with the decline in aphid numbers (Table 3). In September, the lowest parasitiod/host ratio occurred during the period of maximum aphid numbers (Table 3). The close synchronisation between the spring and summer flights of both aphids and parasitoid indicates that the parasitoid are probably helping to regulate field populations of A. craccivora and A.gossypii. The effectiveness of Lysiphlebus spp. in controlling A. gossypii has already been demonstrated under glasshouse conditions (Chekmenen & Zhikhareva, 1978). Both Lipoplexis and Trioxys were not well synchronized with changes in prey numbers during the course of this study (Table 3, Fig. 2). The changes in the numbers of both parasitoidswere closely related to the changes in numbers of A. fabae during the spring and summer, whereas Lipoplexisnumbers followed those of A. nasturtii during the autumn. Parasitoid/prey ratios were invariably low during early spring (Table 3), when aphid numbers are low and when the rate of development of the parasitoids is also low because of the low ambient temperatures (Kuchlein, 1966). Predator-preyrelationships Chrysophids were one of the most abundant predators caught in the suction trap during 1989-1990 (Table 2). According tc Johnson (1950), such traps are ideal for catching small or light insects namely chrysophids. Predator-prey ratios were calculated for the most abundant species of Chrysophld ( Chrysoperla carnea; Chrysopafomiosa; Anisochrysa ventralis + A ventrais prasina; Anisochrysa baetica) caught and the main aphid species found in vegetable crops. Catches of Chrysoperla camea, the most numerous lacewing caught in the traps, increased during April and May, with the increase in the numbers of M. persicae, and reached a maximum during �arly June, when the numbers of aphids caught began to decline. From summer to early autumn, the numbers of predators decreased and fewestpredators were found in November when aphids numbers were at their peak (Table 3). The two chrysophids Chrysopaformosa and Anisochrysa baetica responded in a similar manner to changes in M. persicae as Chrysoperla cam.ea. Anisochrysa ventralis and its sub-species A. ventralis prasina decreased at the times (May - November) large numbers of M. persicae were caught and were highest (June - October) when few M. persicae were caught (Table 3). The predator/prey ratios of C. camea and Chrysopa formosa indicate that these two predators appear to be more closely synchronized with populations of A. craccivora and A. gossypii than v.ith populations of other species of Aphis. Although changes in the predatur and prey populations were similar during the spring months, the predators were not able to keep up with the increase in aphid numbers that occurred during September (Table 3).- Seasonal. changes of the ahO¥e.two chrysophids may also help to regulate field populations of B. brassicae (Fig. 2). Changes in the numbers of A. ventralis (including its subspecies) and A. baetica did not appear to be related with changes in the numbers of Aphis species caught in the locality (Fig. 2; Table 3). 24 MEAN NUMBERS OF PREDATORS/ 1989·90 PARASITOIDS 50 .... * ...... •\ FREQUENCY: : 12 ** BREVICORYNE BRASSIC-AE 150 8 4 0 0 /���l.t�.l 0 APHIS NASTURTII 12 600 8 4 400 0 APHIS GOSSYPII 12 8 4 APHIS FABAE 30 8 20 4 10 Fig. 2: Histograms of the monthly frequency distribution of four density classes • A (0 < x < 5), B (5 < ::t < 10), C (10 < x < 20), D (x > 20) • of alate aphids. Aerial abundance of the parasites Diaeretiella spp. * * , Lysiphlebus spp. 0-G , Lipoplexis spp. //////// , Triazys, spp...... and predators C camea ,,,,,,,;, , C jonnosa [:I , A. ventralis + A ventralisprasina . � caught at a height of I.Sm in a suction trap operating at Silves in the Algarve, Portugal 25 Conclusions Knowledge on the seasonal abundance of alate aphids helps to indicate the periods when field vegetables are at risk from virus infections. Greater accuracy in forecasting would be possible if aphid numbers could be correlated directly to crop damage. Estimation of the predator/parasitoid-prey relationships indicated the times at which aphidophagous insects showed "potential" ability for regulating pest aphid populations. Such times coincided with high predator/parasitoid-prey ratios. The word "potential" indicates that the evaluation was based on suction trap catches and not on the insect fauna recorded in the crop. Whenever possible, insecticides that are harmless to aphidophagous insects should be selected for those periods of the year when the predator/prey ratio remains high and yet aphid numbers do not decline. Such insecticides should be alternated with less selective chemicals during periods of scarcity of aphidophagous insects, which occur invariably towards the start of aphid infestations. Acknowledgement The authors are greatly indebted to Dr Stan Finch, Head of the Entomology Section of Horticulture Research International, Wellesbourne (UK) for the valuable help given in the revision of this manuscript. Resum� Fucerons ravageurs des cultures legumi�res et insectes aphidiphages pieges par un pi�ge lk sucdon en A!garve Durant 1989 et 1990, un releve des pucerons ravageurs des cultures legumieres et des insectes aphidiphages a ete dresse a !'aide d'un piege a succion installe a 1.5 m du sol dans un verger de prunier entoure de cultures de haricot, de pois, de tomate, de pomme de terre et de quelques cultures protegees, a Silves en Algarve. Lafrequence saisonniere d'Aphis craccivora Koch, A. fabae Scopoli, A. gossypii Glover, A. nasturtii Kalt., Brevicoryne brassicae L. et Myzus persicae Sulzer est presentee. La reponse numerique des parasitoides a la densite de proies est demontre pour Aphidius Nees a l'egard de M. persicae; pour Diaeretiella Stary a l'egard de B. brassicae/M. persicae, ainsi que pour Lipoplexis Foster/Lysiphlebus Foster/Trioxys Haliday a l'egard d'Aphis spp. Dans certains cas, les Chrysopides predateurs ont ete les auxiliaires les plus frequemment pieges. L'identification des periodes durant lesquelles les pucerons sont combattus le plus efficacement par les insectes aphidiphages demontre clairement l'avantage de !'utilisation rationnelle des pesticides. 26 References Chekmenen, S.Y. & Zhik.hareva, Z.L (1978). Biological protection of vegetable crops. Rast. Zashch. 4: 58-59. Cruz de Boelpaepe, M.O., Fernandes, J.E. & Forra, M.R. (in press). Insectos uteis capturados pela armadilha de suc�ao num pomar de Silves - sincronismo cias flutua�oes numericas afidffago - presa. Presented at Symposium Auxiliares e Produtos Fitofarmaceuticos, Lisbon, 9-10 May 1991. Organised by Sociedade Portuguesade Filiatriae Fitofarmacologia: 8pp. Forrest, J.M.S., Hussain A & Dixon, AF.G. (1973). Growth and wilting of radish seedlings, Raphanussativus, infested with the aphid Myzus persicae. Ann. appl Biol 15: 267-274. Hodek, L, Holman, J., Novak, K, Skuhravy, V., Stary, P., Weismann, L & Zeleny, J. (1966). The present possibilities and prospects of integrated control of Aphis fabae Scop. In: "Ecology of aphidophagous insects", 360pp, (ed. Hodek, I.), Academic publ. House, Prague: 331-343. Johnson, C.G. (1950}. A suction trap for small airborne insects which automatically segregates the catch into successive hourly samples. Ann. appl Biol 37: 80-91. Khristova, E. (1973). An efficient parasite of Myzus persicae in the greenhouse. Rast. Zashch. 21(10): 13-14. Kuchlein, J.H. (1966). Some aspects of prey-predator relation. In: "Ecology of aphidophagous insects", 360pp, (ed. Hodek, 1.), Academic publ. House, Prague: 237-242. Mack, T.P. & Smilowitz, Z. (1980). The development of a green peach aphid natural enemy sampling procedure. Environ. Entomol 2(4): 440-445. P-aetzold; U; & Vater, G. (1966). Population dynamics of the parasites and hyperparasites of Brevicoryne brassicae (L). In: "Ecologyof aphidophagous insects", 360pp, (ed. Hodek, 1.), Academic publ. House, Prague: 279-281. Plumb, R.T. (1975). Barley yellow dwarf virus in aphids caught in suction traps, 1969- 73. Ann. appl Biol 83: 53-59. Stary, P. (1964). Food specificity in the Aphidiidae (Hymenoptera). Entomophaga 9(1): 91-99. Tatchell. G.M. (1982). The interpretation of suction trap samples and aphid forecasting in Britian. In: Euraphid Gembloux 1982, 91pp. (ed. Bernard, J.), Gembloux Stn. Zool Appl: 63-68. IOBCIWPRS-WorkingGroup Meeting "IntegratedControl in Field Vegetables". Vienna,28-30 Qs;t 1991. 27 Monitoring the timing of peak flight activity of Thrips tabaci in cabbage fields A Kahrer FederalInstitute for Plant Protection, Trunnerstrasse 5, 1020 Vienna, Austria Summary Theflight activity of Thripstabaci was monitored to obtain a better understanding of its population dynamics and to determine the most appropriate time to apply insecticidal sprays for its control. The Thrips tabaci were caught in white-coloured water traps. Traps were sited in a cabb':lgefield in Seibersdorf 50 kmsouth-east of Vienna during both 1990 and 1991. Peak flight activity was recorded on 29 June 1990 and 13 July 1991. Maximumflight activity occurred at about the time growersharvest their rape crops but before they started to harvest their cereal crops. Introduction The damage caused to cabbage heads by Thrips tabaci is one of the most serious probiems in cabbage production in Austria. The Thrips live in the cabbage heads in the small spaces between the layers of the leaves. Hence, they are well protected against both adverse environmental conditions and sprays of insecticide. One way to overcome this problem is to plant cabbage varieties that are resistant to T. tabaci. Another way is to improve the current insecticidal treatments. However, insecticidal sprays are effective only if the spray droplets contact the target insects. Hence, it is important to determine when, during their life-cycle, T. tv.haci occur on the outside of cabbage heads. This could be a result of invasion from other fields or from natural swarming behaviour. North-American workers (Shelton, 1986; North, 1986) generally believe that when adjacent crops of wheat, clover and alfalfa are harvested, T. tabaci moves in large numbers into brassica crops. This paper describes how T. tabaci populations were monitored to determine if mass flights also occur in mid-Europe. Materials and Methods The experimental work was carried out in a 2 ha field at Seibersdorf, located about 50 km south-east of Vienna. This area has a pannonian climate, which is characterized by dry, hot summers. The main field crops are cereals, cabbage and to a lesser extent rape. A local variety of late cabbage was planted in the middle of April. At the beginning of June, the experimental field was treated twice with a mixture of Pirimiat.rb and Deltamethrin. It was treated again with beltamethrin in mid-August. The flight periods of T. tabaci .were monitored using 2 white-coloured water traps 28 (dimensions 20 cm x 30 cm) placed on the ground. A few drops of detergent were added to the water to lower the surface tension and hence help considerably in trapping Thrips tabaci. The traps, put out in the middle of June, were emptied every day until the end of August. The trapped insects .were preserved in alcohol, and identified using a dissecting microscope. Samples that did not contain apparently Thrips tabaci were discarded. The remaining samples (Thysanoptera looking like Thrips tabaci) were prepared for inspection by heating the insects in lactic acid for 15 minutes and then embedding them in a mixture of chloralhydrate, glycerol and gum arabic (Andre'S medium). This was done initially with the insects caught during 12 days distributed evenly throughout the monitored time-period. As only occasional thrips were found among these that were not T. tabaci, the trap contents of the other days were identified using a microscope, without being embedded first. The times at which field crops (especially cereals) in the locality of the experiment were harvested were the dates at which the crops were taken into the local storehouse. Results Figure 1 shows the flight activity of Thrips tabaci in 1990 and 1991. In both years, there was a clearly defined peak. Peak flight activity was recorded on 29 June in 1990 and on 13 July in 1991. The maximum number of T. tabaci caught/trap/day was 315 in 1990 and 155 in 1991. The period of flight activity lasted for about 10 days. Figure 5 shows the period of flight activity and the times of harvest of crops from neighbouring fields. In both years, peak flight activity coincided with the harvest of the rape crop (Fig. 2) but occurred well before the harvest of the cereal crops (Barley - Fig3; Wheat - Fig.4; Rye - Fig. 5). Discussion This present investigation gave an indication of the numbers of Thripstabaci flying at various times in cabbage fields. Czencz (1985) showed that, in a range of field crops, different coloured water traps were equally effective at catching T. tabaci. Hence, the numbers of T. tabaci caught do not appear to be affected greatly by the colour of the trap. In this investigation high numbers of T. tabaci (315/trap in 1990 and 155/trap in 1991) were caught on certain days. These figures are much higher than those reported by Shelton (1986) and North (1986). However, the numbers of T. tabaci caught outside the main peak of activity are similar to those reported by Shelton (1986) and North (1986). This raises the question of whether we were all monitoring the same phenomenon. Perhaps, I recorded natural swarming behaviour. Peak flight activity occurred either at the end of June (1990) or in mid-July (1991). The time of peak flight activity appears to depend on weather factors. However, data collected during only two seasons of monitoring are not sufficient to test any specific theory. This was true of the data collected in both years, in which there was some agreement between the flight activity of Thrips tabaci and the harvest of cereals. However, this is only a temporal coincidence and need not be interpretedas the cause of the effect. Whatever the reason, the peak flight activity of Thrips tabaci occurred before the harvest of cereals, and at about the time that the rape crop was being harvested. 29 350 300 250 1990 Thrips 200 /trap /day 150 100 50 0J-����+1-1-+1-J.L..l.w4\IQ+��H4>..x•11TI1A=Pt4TI++i=i+Ill=+F""i t-�t'f'nl 160 1-40 120 1991 100 Thrips /trap 80 /day 60 -40 20 Fig. 1: Flight activity of Thrips tabaci monitored in cabbage fields in Seibersdorf (eastern Austria) during 1990 (above) and 1991 (below) 30 160 350 140 1990 300 120 250 Crop 100 200 Thrips harvest Th rips Rope harvest (1000 80 /trap /day tons) 150 60 100 40 20 50 0 0 !J qO qO 0 t,f t, 91) 300 160 1.«I 250 1991 120 200 Crop 100 Thrips harvest Thrips Rape harvest (1 OOO 150 80 /trap tons) /day 100 60 40 50 20 Fig. 2: Flight activity of Tluipstabad monitored in cabbage fields in 1990 and 1991, and its relationship to the harvest of rape 31 2500 350 1990 300 2000 250 Crop 1500 harvest· 200 Thrips (1000 Thrips Barley harvest /trap 1so /day tons) 1000 100 500 50 �11!1Pi,f'l,H4A=l'f'l'.+l+f,�ffl'l�m'1�m-t+I- 0 O 1 c;i '1,4:,•• DATE 2500 1991 140 2000 120 100 p 1500 Cro Thrips harvest Thrips Barley harvest ao /trap (1000 /day tons) 1000 60 500 20 Fig. 3: Flight activity of Thrips tahaci monitored in cabb.age fields in 1990 and 1991, and its relationship to harvest of barley 32 2000 350 1800 1990 300 1600 1400 250 Crop 1200 200 Thrips harvest Wheat harvest 1000 Thrips /trap (1 OOO 1so tons) /day 800 600 100 2500 HO 1991 140 2000 120 Crop 1500 100 Wheat Thrips harvest Thrips (1000 harvest 80 /trap tons) /day 1000 60 40 SOO 20 0 q,' q,\ ' q,' · � 1� �· · ,,�· '};.�El q,'.I ' ').'!>· o 'l.O"�' DATE Fig. 4: Flight activity of Thripstabaci monitored in cabbage fields in 1990 and 1991, and its relationship to the harvest of wheat 33 350 350 300 1990 300 250 250 Crop 200 200 Thrlps harvest Thrips Rye harvast (1 OOO /trap tons) 150 150 /day 100 100 50 50 250 160 1991 140 200 120 100 Crop 150 Thrips harvest Thrips Rye harvest ao /trap (1000 tons) /day 100 60 Fig. 5: Flight activity of Thripstabaci monitored in cabbage fields in 1990 and 1991, and its relationship to the harvest of rye 34 R�sum� D�termination du moment de l'activit� de vol maximalede Thripstabad dans les cultures de choux L'activite du vol de Thrips tabaci a ete suivi pour mieux en comprendre la dynamique de population et determiner le moment adequat d'applications insecticides destinees a le combattre. Les T. tabaci ont ete captures dans des cuvettes a eau de couleur blanche placees, en 1990 et 1991, dans une culture de chou a Seibersdorf, a 50 km au sud-est de Vienne. L'activite de vol maximale a ete observee le 29 juin 1990 et le 13 juillet 1991. Ces periodes correspondent a peu pres a la recolte du colza, mais precedent les moissons. References Czencz. K. (1985). The role of coloured traps in collecting Thrips fauna. In: Population Structure, Genetics and Taxonomy of Aphids and Thysanoptera, {eds Holman, J., Pelikan, J., Dixon, AF.G., Weismann, L) ISBN 90-5103-001-0. pp 426-435. North. R.C. & Shelton, AM. (1986). Ecology of Thysanoptera within cabbage fields. Env. Ent. 15: 520-526. Shelton, AM. & North, R.C. {1986). Species composition and phenology of Thysanopterawithin field crops adjacent to cabbage fields. Env. Ent. 15: 513-520. IOBC/WPRS-Workin,i GroupMee ting "IntegratedControl inField Ve getables· Vienna. 28-30Oct 1991 35 Implementation of carrot fly monitoring in Denmark 1 2 A Percy-Smifu< ) & H. Philipsen< ) <1> Dept. of PestManagement, Research Centre for PlantProtection, Lyngby,Denmark <2> Inst. Ecology Molecularand Biology, Agricultural University, Copenhagen, Denmark Summary A system formonitoring carrot fly(Psila rosae)attacks hasbeen set up in Denmark. Growers are contacted initially by the Advisory Service. Participation in the system has to be paid for by the growers. On average, one set of disposable yellow sticky traps are used for every 10 ha of carrots. Communication has been given an extremely high priority. Hence, recommendations are sent each week to individual growers, whilst more general regional and national warnings are sent out by the Advisory Service. The possible risk of damage is evaluated by taking into consideration such factorsas: site history, d�,te of drilling, date of harvest, source of carrot fly and extent of shelter at the individual site. Use of the system has progressed despite an incompiete understandingof certain factors. The monitoring system has strengthened the growers' confidence in manipulating various aspects of their pest management strategies, and allowed them to rely less on chemical treatments. Introduction The carrot fly, (Psi/a rosae ), is one of the main pests of field vegetables in Denmark. Yellow stick traps are now being used as the basis of a system for monitoring carrot fly attacks in Denmark. The system has been in operation since 1984 and has prcgressed througha series of steps, each of which has posed new, and often unforeseen, problems. Initially, advisors and growers had reservations about identifying carrot fly. These have now been overcome, only to be replaced by other problems. Both technical and practical matters have been reviewed regularly and adapted to meet new needs. The monitoring system is now used routinely in practice and is widely-accepted. Materials and Methods The commercially available disposable, sticky traps, of a specific yellow hue (RebellR, Wadenswil, Switzerland) are used for monitoring carrot fly. Growers are contacted initially by the advisory service and participation in the schemeis voluntary. In contrast to other Danish monitoring systems that operate in 36 large scale agricultural crops, growers have to pay a fee to participate in the relatively small-scale monitoring systems that have been developed for pests of field vegetables; Once a grower has paid his fee, a scientist from the Research Centre for Plant Protection, or a trained person from the advisory service, visits the grower to set-up the traps. The optimum siting for the traps is discussed in detail with the grower, to determine the most likely place to catch flies. Information obtained from the grower is collated with the numbers of insects caught to produce a risk evaluation. This evaluation takes into account site hist01y, date of drilling and date of harvest, as well as source of carrot fly and extent of shelter belts at the individual site. A set of traps consists of five sticky traps with a net mounted over each trap to keep out larger non-target insects (Philipsen, 1988). Traps are placed 40 cm above the soil surface or, later in the season, immediately above the crop canopy. Traps placed over bare soil catch fewer flies than traps placed in the crop (Philipsen, 1985). Hence, it is important to place the traps above an even stand of the host crop. The row of traps are placed about 10 m away from the shelter belt and with the flat surface parallel to the edge of the field. The five traps are placed about 10 - 20 m apart and serviced once a week. Results A system for monitoring carrot fly attacks is now used in practice. General warnings, at both regional and national levels, are distributed by the Advisory Service (Fig. 1). SUMMARY OF CARROT FLY CATCH 1990 Print date: 13-08-90 Region: 2 Participant no. 310 Name: Cians Holm Clausen Town: Fa\revejle Date from Date to Ave./ Recommendation Date Insecticide used trap/day sprayed 11-07-90 19-07-90 0.00 No treatment recommended 19-07-90 27-07-90 0.00 No treatment recommended 27-07-90 05-08-90 0.00 No treatment recommended 05-08-90 12-08-90 0.00 No treatment recommended Participant no. 384 Nnme: Mogens Olsen Town: Farevejle Date from Date to Ave./ Recommendation Date Insecticide used trap/day sprayed 11-07-90 19-07-90 0.20 No treatment recommended 19-07-90 27-07-90 0.32 Treatment recommended - Pyrethroid as soon as possible 27-07-90 05-08-90 0.02 No treatment recommended 28-07-90 Sumialpha 05-08-90 12-08-90 0.05 No treatment recommended Fig. 1: A typical report for carrot fly catch sent to advisors (English translation) (after.Murali.& Percy-Smith,1991) 37 Weekly recommendations are sent directly to individual growers (Fig. 2). Results from the monitoring study are incorporated into the Plant Protection Information System at the Research Centre for Plant Protection (RCPP). The pest and disease monitoring information is being integratedwith detailed information on plant protection, including spraying techniques; pesticide information; biology of pests and insect etc.; into a large database. Ministry of Agriculture Danish Institute of Plant and Soil Science Research Centre for Plant Protection CATCH OF CARROT FLY 1990 Print date: 28-07-90 Catch in period from 19-08-90 10 27-07-90: Total Ave./trap/ Trap no. catch day i 3 4 5 2 3 1 2 5 13 0.32 EVALUATION: 384 As a resull of the catch in !his period Mr. Mogens Olsen TREiITMENTis RECOMMENDED. Fa""revejle- A PYRETHROID (e.g. Sumialphn) should be used as soon as possible. Department of Pest Management Alex Percy-Smith, Tel. 45 87 25 10, l'xl. 233 •Poul 80rge S0rensen Ave.: 0.08/lrap/day No treatment recommended •Erik S0rcnsen Ave.: 0.15/lrap/day No treatment recommended Fig. 2: A typical recommendation card sent to carrot growers (Eng!ish translation) (at'lei"Murnii & Percy-Smith, 1991) The early Danish work on monitoring carrot fly was described by Philipsen (1983) who concluded that yellow sticky traps had considerable potential for monitoring carrot flypopulations. After a steady initial increase in interest, a sharp rise in interest occurred in 1987 as a result of the involvement of two processing companies. Since then further developments have taken place. Monitoring of carrot flyis now organised in one of three different ways, the way being determined largely by the numbers of growers in the region. Firstly, the closeness of the Research Centre to a large concentration of growers producing freshmarket carrots, on the drained area of Lammefjorden, N W 38 Zealand, means it is possible for a person from the Research Centre to service these traps. Secondly, on the island of Funen, there is a concentration of carrots grown for processing. Here the monitoring is carried out collaboratively by the AdvisoryService and by the processing companies, using the system developed by RCPP. The processing companies insist that their growers use the system and they also give a contribution to the cost of the grower's participation. Finally, it is too time consuming for the RCPP, or advisors, to service traps at the remaining carrot growers who are widely-spread throughout the country. Therefore, a system has been devised whereby the growers send their traps to the Research Centre each week so their flies could be counted. Gradually the work bas become routine. As a consequence, monitoring was decentralised in 1990 and now traps are sent to members of the local Advisory Service, who carry out the monitoring and advisory work in their particular regions. The Research Centre for Plant Protection in Denmark bas recently provided information and advice enabling advisors in Southern Sweden to start their own monitoring system. In 1989, yellow sticky traps were used to monitor carrot fly at 163 sites in Denmark (Table 1), a density of about one set of traps for each 10 ha of carrots. Dnc to the decentralisation of the monitoring system, comparable statistics are not currently available for the last two years. However, through close contact to the Advisory Service, it is believed that the number of participants has now stabilised at around 160. Monitoring individual fields is the strength of the system. Although this level of monitoring is likely to be maintained, it is unlikely that any further development will occur in the near future. Table 1: Number or participants in the monitoring and warning system for carrot Dy (Psi!arosae) run by the Research Centrefor Plant Protection, Denmark Serviced Processing Serviced Sent Year by Factories by to Sweden TOT.A.L Advisors RCPP RCPP 1984 14 - - - - 14 1985 24 - - - - 24 1986 33 - - - - 33 1987 46 50 - - - 96 1988 12 56 32 38 6 144 1989 31 69 30 26 8 163 1990 0 0 33 9 0 42 1991 0 0 34 6 0 40 Growers had, previously, been extremely uncertain if and when there had been a need to treat. This resulted in both poor timing of treatments and many unnecessarytreatments. In the 1970s and early 1980s, most growers treated their crops on a routine basis. Growers indicated that it was not uncommon to treat from 10 to 15 times during a growing season. Yellow sticky traps have demonstrated the variation in fly numbers from site to site, both in time of activity and size of 39 population (e.g. Esbjerg et aL, 1988). Use of sticky traps has provided a suitable method for correctly timing insecticide treatments. Use of the monitoring system has strengthened the growers' confidence in evaluating damage risks by considering factors such as site history, date of drilling, date of harvest, source of carrot fly and extent of shelter belts. Thispest management strategyhas permitted growers to apply fewer insecticide treatments. This is important, as there seems to be considerable variation in efficacy of the insecticides available for carrot fly control. Growers have changed their treatment strategies. The monitoring system provide an improved way of managing the carrot fly. Treatments are now rarely applied againstcarrot flyin processing carrots forslicing, as such crops are in the ground for only a relatively short period. Such carrots are usually grown in the period between the two flygenerations and hence avoid attack. However, processing carrots for dicing are sown early and harvested relatively late in the year. Therefore control is often necessary in such crops (Percy-Smith, 1988). In addition, crops considered to be at risk are now harvestedas early as possible to avoid damage in the clamps, where temperature is difficult to control. Considerable variation, fromsite to site, in need for treating fresh-market carrots has meant that individual recommendations have been an essential part of the monitoring system (Percy-Smith, 1990). Growers andadvisors are well aware of the risk areas, and now include them in their management strategies. For example, carrots from edges of field are ha..--vestedearlier and not stored; and fields of early and main-crop carrots are kept as far away from each other as possible. Disccssion The use of yellow sticky traps has improved the basis for decision making in crop protection in carrot crops. Diffusionhas progressed relatively slowly and as a result has ensured that confidence in the system has remained high. Growers now appreciate that the monitoring system is of considerable assistance, despite some present limitations. Communication has been given an extremely high priority in the monitoring system. The aim is to send weekly bulletins to advisors and growers, to keep everyone informed of the current situation. Personal contact has been important and possible, largely because many crops are grown by a relatively few growers. Annual meetings for growers and advisors have also been of considerable value for discussing the organisation of the monitoring system, carrot fly biology and pest management strategies. These meetings have also provided good opportunities for maintaining participants' interest L11 the monitoring system, as well as motivating other growers to adopt the system. A constraint on the use of yellow sticky traps, is the need for a certain·degree of training in the identification of carrot fly. This has been overcome by ensuring either people from the Research Centre, or from the Advisory Service, count the flies. The selectivityresulting fromthe use of net-covered trnps is a pre-requisite forquick servicing of the yellow sticky traps-.- The problem of the sticky traps losing their sticky properties due to emulsification of the adhesive in wet weather (Finch & Collier, 1989) is not encountered if traps are serviced at weekly intervals. 40 Time and resources must be allocated for implementation of monitoring and warning systems to make them available to the growers and advisors. The development of this system has progressed despite an incomplete understanding of certain aspects. Although the time of flight activity can be identified with a reasonable degree of accuracy, it is unfortunate that an appropriate insecticide cannot "e recommended. It is essential to investigate the effect of various insecticides against carrot fly. However, traditional pesticide field trials have severe limitations, largely because carrot fly infestations are not regularlydistributed. By using small field and laboratory techniques, it should be possible to carry out pesticide tests under well defined conditions. A source of carrot fly is needed. Sites with large populations of carrot fly could provide the necessary material. Otherwise, laboratory cultures must be started. Work has been started at the Research Centre to establish a carrot fly culture to provide material for laboratory and small field trials. Nevertheless, there is still a need to improve our understanding of the use of yellow sticky traps e.g. their positioning in the field; reducing the monitoring period, with the aid of temperature sums, to the relevant period; knowledge of area covered by information from one set of traps; work on thresholds. R�sum� Mise en oeuvre c:i'un reseau de surveillance de la mouche de le carotte au Danemark Un systeme d'avertissement pour Jes attaques de la mouche de la carotte (Psi/a rosae) a ete mis sur pied au Danemark. Lesproducteurs sont initialement contactes par le service d'avertissement et la participation au systeme est payante. En moyenne, un jeu de plaquettes jaunes engluees a jeter est utilise par 10 ha de carotte. Lapriorite absolue a ete donnee a la communication: ainsi, les producteurs re�oivent chaque semaine des recommandations personalisees, alors que les avertissements a caractere general, pour une region ou le pays entier, sont diffuses par le Service d'avertissement. Le risque probable de degits est evalue en considerant divers facteurs, tels que l'historique de la localite, les dates de semis et de recolte, la source d'infestation par la mouche de la carotte, ou l'etendue des abris, et cela individuellement pour chaque site. Le systeme d'avertissement s'est repandu malgre une comprehension incomplete de ce1tains facteurs. 11 a renforce la confiance du producteur dans la possibilite de jouer sur divers aspects des strategies de limitation des organismes nuisibles, le rendant ainsi moins dependant des traitements chimiques. 41 References Esberj, P., Philipsen, H. & Percy-Smith, A (1988). The significance of carrot fly (Psi/a rosae) monitoring in Denmark. In: Integratedcontrol infield vegetable crops, IOBC/WPRS Bulletin, 1988, XI/1: 14-25. Finch, S. & Collier, R. (1989). Effects of the angle of inclination of traps on the numbers of large Diptera caught on sticky boards in certain vegetable crops. Entomologia experimentalis et applicata 52: '13-27. Murali, N.S. & Percy-Smith, A (1991). Database Management System for Monitoring and Warning of Codling moth (Cydia pomonella) and carrot fly (Psi/a rosae). Comput. ElectrorL Agri. Percy-Smith, A (1988). Gule limplader i anvendelse - til vurdering af risiko for angreb af gulerodsflur (Psi/a rosae (F)). (Yellow sticky traps in use - to assess the risk of attack by carrot fly (Psi/a rosae (F.)) - Summary in English). 5. DanskePlontevaemskonference 1988, Sygodomme og Skadedyr.: 319-328. Percy-Smith, A (1990). Udvikling ai varslingssystemer for skadedyr i. frilandsgr0nsager. (Summary in English). 7. Danske Plantenvaemskonference 1990, Sygdomme og Skadedyr.: 301-313. Philipsen, H. (1983). Brug af gule limplader til vurdering af risiko for angreb af gulerodsfluen (Psi/a rosae F.). (The use of yellow sticky traps to estimate risk of attack by the carrot fly (Psi/a rosae). Tidsskrift for planteavl 1663 87(4): 389- 397. Philipsen, H. (1985). Integrated Pest Management in Danish Carrot fields: monitoring carrot fly (Psi/a rosae F.) by means of yellow sticky traps. !n: Progress on Pest Management in Field Vegetables. Proceedings of the CEC/IOBC &jJertsrGroup meeting, Rennes, W-23 November 1985: 169�175. Philipsen, H. (1988). Monitoring techniques for the carrot fly (Psila rosae F.). In: Integrated controlin field vegetable crops, IOBC/WPRS Bulletin, 1988 Xi./1: 8- 13. IOBC/WPRS-WorkingGroup Meeting "Integrated Control in fieldVegetables", Vienna.28-30 Oct 1991 42 Forecasting the timing of damage by the carrot fly B. Jonsson SwedishBoard of Agriculture, Plant Protection Centre, Alnarp, Sweden Summary The relationship between flight activity of the carrot flyPsila rosae and crop damage was studied in Sweden. These and other data were studied to assess the potential of using accumulated temperature to forecast when fly damage should occur in carrot crops. Activityof the carrot fly was monitored in carrot fields during 1987-1991 using yellow traps. !n fieldsin which high numbers of flieswere caught, the percentage of carrots damaged was assessed at weekly intervals. Temperatures were accumulated as air temperatures recorded above a temperature threshold of 3°C. The temperature accumulations were started as soon as the number of flies caught during the second generation exceeded 1 fly/trap/week and were continued until crops damage rose above 10%. The number of D0 required forthe development of P. rosae egg and larval 0 stages prior to 10% crop damage was found to be 500 ± 48 D • The results show the potential of accumulated temperatures for forecasting when crop damage will occur. With this system, it should be possible to advise growers to harvest infested fields, or part of fields (e.g. borders), before carrot flylarvae reduce crop quality. Introduction The carrot fly,Psila rosae (F.), can be a serious pest of carrots in Sweden. Carrot is the most important field vegetable in Sweden and is grown currentlyon about 1700 ha per year. In the major carrot producing areas of southern and central Sweden. the carrot fly has two generations. Damage by larvae of the first generation is seldom a problem except in very early-sown crops grown for summer consumption. Such crops represent less than 10% of the total carrot hectareage. The main crops of carrots, however, is harvested during September and October. About 25% of this crop is used for the fresh market and the remainder is placed into cold stores. Larval damage by the second generation of the carrot fly can cause considerable loss of quality in main crop carrots, particularly in crops harvested towards the end of the season. By delaying sowing of carrots by 2-3 weeks, damage by the first generation of the fly was reduced considerably (Coaker & Hartley, 1988; Ellis & Hardman. 1988). Damage by the second generation can also be avoided by harvesting the carrots before the larvae began to cause feeding damage on the main roots of the carrot plants (Taksdal, 1981). Chemical control is necessaryonly in carrot crops intended for late harvest and in which the carrot fly has already laid eggs. The activity of the flies can be monitored using yellow sticky traps and the numbers of flies·caught can 43 be used to decide whether or not to apply chemical control (Hofsvang & Lien. 1986; Esbjerg et al., 1988; Den Ouden & Theunissen, 1988). However, as the development of the carrot fly is temperature dependent, it is possible to forecast the timing of fly emergence and peak fly activityfrom accumulated temperatures (Collier & Finch, 1988). A system based on accumulated temperatures should be useful for forecasting the time when larvae attack the carrot crop. According to Dufault & Coaker(1987), the first- and second-larval instars, which la'it a few days and 2-3 weeks respectively, restrict their feeding to the side roots and hence do not damage the main tap root of the carrot. By being able to predict the time when the third (final) instar larvae move to feed on the tap roots, it should be possible to advise growers of when to harvesttheir carrots to avoid crop damage. In the present study, the relationship between flight activity (oviposition) of the carrot flyand crop damage was studied in carrot crops in southern and central Sweden. A method for using accumulated temperatures to forecast crop damage was also evaluated. Material and Methods Carrot fly activity was monitored in carrot fields in southernand central Sweden using yellow traps. Water-traps were used in 1987 and 1988 and sticky-traps (.RebellR), placed under green netlon-covers(Philipsen. 1988), were used in 1989- 1991. The 2-4 traps used in each field were situated in places where high numbers of flies were e>..-pected, i.e. in protected areas of the field and close as possible to ari. emergence site. The numbers of flies caught were recorded weekly. r.nfields in which high numbers of fleis were caught (1 field fn 1987 & 1989, 2 fields in 1989, 5 fields in 1990 and 3 fields in 1991) the percentage of carrots with larval damage was assessed by taking between 2 to 4 samples/week, each sample containing 50 carrots. The carrots were sampled from alongside the traps. The first carrots were sampled 3- 4 weeks after the flies of the second generation became active. Sampling was continued until the beginning of November in 1987 but only until late September in 1991. A threshold temperature of 3°C was used as the base above which to accumulate the number of day-degrees required for the development of the egg-stage and 'the first- and second-larval instars. This threshold was an average calculated from the results of earlier workers(Stevenson, 1981; McLeod et al., 1985), who indicated that the threshold for egg development was 4.1°C & 4.5°C and for larval development 2.0"C. Accumulated temperatures were calculated(sine-wave method) fromair temperature obtained from regional meteorological stations. Calculations were made from the date(date between weekly recordings) when the numbers of second generation flies exceeded 1 fly/trap/week until the time damage in the SO plant carrot samples, exceeded 10%. Results and Dist!!ssion The timing of second generation carrot flyactivity in southern and central Sweden varied considerable between years and localities(Table 1). The date on which larval damage rose above the threshold level was also highly variable. 44 ° Table 1: Day0degrees (D") accumulated above 3 C for development of egg and larval stages-Of the carrot fly (Psila ro.sae).0 D calculated from the date trap catches of the second generation exceeded 1 fly/trap/day to when larval damage exceeded 10% of the carrots samples Date Date Year Region (locality) >l fly/ damage Accumulated D0 trap/day exceeded exceeded 10% 1987 Southern(Bjuv) 26/8 4/11 528 1988 Southern(Bjuv) 3/8 14/9 511 1989 Southern(Farhult) 2/8 12/9 520 1989 Southern (Borgeby) 16/8 27/9 492 1990 Southern (Farhult) 18/7 29/8 603 1990 Southern(Borgeby) 25/7 29/8 505 1990 Southern (Oland) 25/7 1/9 535 l 1990 Central(Gotland) 8/8 CJ/9" 4� 1990 Central (Odeshog) 25/7 29/8 469 1991 Southern (Farhult) 8/8 13/9 456 1991 Southern (Oland) 10/8 15/9 409 1991 Central (Skara) 12/8 2/10 480 500 ± 48 D0 1n 1987, an extremely cold season, the first peak {>l fly/trap/day) of activity of second generation flies did not occur until late August (Fig. la). Damage remained below 10% in each of the first 5 carrot samples but then suddenly increased to nearly 40% during the two first weeks of November. The date at which damage increased was estimated to be 4 November. Fig. lb shows the data collected during 1990, a warm season. In a field in southern Sweden in 1990, carrot fly catches exceeded 1 fly/trap/day on 18 July. The increase of larval damage was dramatic in 1990 and occurred during the last week of August (week 35 - Fig. lb). In 1991 carrot flies of the second generation became active in southern Sweden at the beginning of August and exceeded 1 fly/trap/day at Farhult on 8 August (Fig. le). Damage increased considerably during the second week of September (week 37 - Fig. le). 45 1 a. BJUV 1987 3-r------60 ••••0-••• % damaged carrots > ea "O number of flies -- 2 --1 1/) Q) E;: 0 1 cii E ::, C 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 week 1 b. FARHULT 1990 3.----::----,----,��-----,------�60 ····s-··· % damaged carrots --- number of flies ... "O-- l�J-... e· --c. 2 ( 1/) Q) . � 0 cii . E ::, C . .j---,_.;:::.,..-..-<-1--...... --.-3"+-...-.....--...... �------I- 0 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 week 1 c. FARHULT 1991 � 3.-••-•• --.-••- - ______------60 ,;. o/codamaged carrots --- number of fiies r, / ; . ..,e .i-:...... ,.....,_,..�;::::;::::;:::..,i��-;::;:� ...... -��--1 0 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 week Fig. la-c: Numbers of carrot flies caught/trap/day in southernSweden together with the percentage of carrots damaged during the second generation flyattack. The flies were caught in yellow water-traps in 1987 and on yellow sticky-traps in 1990 & 1991. 46 The number of day-degrees accumulated from oviposition to 10% crop damage was found to be 500 ± 48 D0 (Table 1). The D0 accumulated up to the critical event was close to 500 D0 for 10 out of the 12 fields studied. The results from the remaining two fields, one in 1990 and one in 1991, were more variable. However, considering the calculations were based on recordings made only once a week, and on air temperatures from regional meteorological stations, the results are extremely promising. They show clearly that there is considerable potential for using accumulated temperatures to forecast when larval damage should occur in carrot fields. The method would probably be improved if the flycatches were recorded more frequently and if temperature-recordings were made directly in the carrot fields. Using an upper temperature threshold (Allen, 1976) when calculating day degrees, might also improve the accuracy of the forecast. A method for forecasting the timing of larval damage in carrot fields will i>e of great value to carrot growers. With such a forecast, it should be possible to advise growers when to harvest infested fields, or part of fields ( e.g. borders), before carrot fly larvae cause any substantial loss in crop quality. In areas where the growers are organised, or carrots are grown on contract, it should be possible to reduce the overall carrot flyinfestation by harvesting infested fields before the predicted date of larval attack. Crops from fields free of carrot fly (low or zero catches in yellowtraps) are those that should be selected for late harvest and/or storage. Resume PnMsion de l'apparition des degats de la mouche d� la carotte La relation entre l'activite des adultes de la mouche de la carotte Psila rosae et les degits dans les cultures a ete etudiee en Suede. Parmi d'autres, ces donnees ont ete analysees afin d'evaluer la possibilite d'utiliser les sommes des temperatures pour pronostiquer !'apparition des degats de la mouche dans les cultures. L'activite de l'adulte dans les cultures a ete suivie de 1987 a 1991, au moyen de pieges jaunes. Le pourcentage de carottes attaquees a ete determine une fois par semaine dans les parcelles oii un grand nombre de mouches a ete capture. Les temperatures de !'air depassant le seuil de 3°C ont servi a calculer la somme des temperatures sitot que les captures ont depasse une mouche par piege et par semaine, pendant la deuxieme generation, et jusqu'a ce que les degats dans les cultures aient excede 10%. Lasomme des temperatures necessaire au developpement embryonnaire et larvaire de P. rosae jusqu'a !'apparition de 10% de degats dans les cultures, est de 500 ± 480 DJ.. Les resultats prouvent le reel interet des sommes des temperatures pour predire le moment d'apparition des degats dans les cultures. Grace a ce systeme, il devrait etre possible de conseiller aux producteurs de recolter entierement, ou partiellement (p. ex. bordures) les cultures infestees, avant que les larves ne provoquent une baisse de la qualite de la recolte. 47 References Allen, J.C. (1976). A modified sine wave method for calculating degree days. Environmental Entomology 5: 388-396. Coaker, T.H. & Hartley, D.R. (1988). Pest management of Psila rosae o� carrot crops in the eastern region of England. IOBC/WPRS Bull XI/1: 40-52. Collier, R.H. & Finch, S. (1988). A preliminary forecasting system for carrot fly in the UK. Brighton Crop Prot. Conf.: 257-262. Den Ouden, H. & Theunissen, J. (1988). Monitoring populations of the carrot rust fly, Psi/a rosae, for supervised control. IOBC/WPRS Bull Xl/1: 26-32. Dufault, C.P. & Coaker, T.H. (1987). Biology and control of the carrot fly, Psi/a rosae (F.). Agr. Zool Rev. 2: 97-133. Ellis, P.R. & Hardman, J.A (1988). Non-insecticidal contributions to an integrated programme forthe protection of carrots against carrot fly. IOBC/WPRS BulL XI/1: 33-39. Esbjerg, P.; Philipsen, H. & Percy-Smith, A (1988). The significance of carrot fly (Psi/a rosae) monitoring in Denmark. IOBC/WPRS Bull XI/1: 14-25. Hofsvang, T. & Li.en, H.M. (1986). Gulrotflue,Psi/a rosae (Fabricius), varsling av av angrep ved bruk av gule limfeller. Forskn. Fors. Landbr. 37: 71-79. McLeod, D.G.R.; Wnistlecraft, J.W. & Harris, C.R. {1985). An improved rearing procedure for the carrot rust fly (Diptera: Psilidae) with observations on life history and conditions controlling diapause induction and termination. Can. Ent. 117: 1017-1024. Philipsen, H. (1988). Integrated pest management in Danish carrot fields: Monitoring carrot fly (Psi/a rosae F.) by means of yellow sticky traps. In: ''Progress on pest management infield vegetables", (ed;- Cavaltoro, R. & Peterents; C)� AA Balkema, Rotterdam: 169-175. Stevenson, A.B. (1981). Development of the carrot rust fly, Psila rosae (Diptera\: Psilidae), relative to temperature in the laboratory. Can. Ent. 113: 569-574. Taksdal, G. (1981). Varsling om sverrnetiderog fttaksstyrka av gulrotfluge. Aktuelt fra Statensfagtjenste for landbruket. 1: 45-52. IOBC/WPRS-WorkingGroup Meetine: "IntegratedControl in FieldVegetables", Vienna. 28-30Oct 1991 48 An introduction to integmted pest management in field vegetable crops S. Finch HorticultureResearch International, Wellesboume, Warwick CV35 9EF, UK Summary At a recent IOBC meeting held at Veldhoven, TheNetherlands, I was invited as convener of this Working Group to present a paper describing the current situation in Integrated Pest Management (IPM) in field vegetables in Europe. I would like to repeat the first part of this paper here, in an attempt to ensure that during any subsequent discussions, we all use the same meaning whenever we refer to, or mention, IPM. By adopting this approach, I hope we can avoid spending time discussing semantics and instead concentrate solely on making critical assessments of the recent scientific advances in pest management in field vegetable crops. Introduction to IPM During the last 30 years the attitude towards pest, disease and weed control in horticultural crops has changed, partly as a result of pressures from conservationists and, more recently, from the biased ways in which information media influence public opinion. Since the early 1960s, it has not been sufficient to produce a chemical only to kill the targetorganism. Additional information has been required on the effect of the chemical on the environment in general, and on beneficial insects in particular. Hence, although the implementation of integrated control systems is slow, progress has to be viewed in the light of the vast amounts of information, education and political manoeuvres required to make such systems work. Integrated pest management In vegetable growing, two factors operate against the use of classical "integrated pest management": the transience of the crop due to rotation, and the demand for increasingly high-quality produce. These two factors are complementary for, in the short-term relationship between pest and crop, the natural enemies of the pest have insufficient time to establish their superiority before the crop is damaged and no longer of high quality. Consequently, Dunn and Coaker (1965) suggested that combinations of biological agencies and chemical treatments, now commonly referred to as "integrated pest management", had little application when dealing with pests of vegetables. They proposed that "rational control" was more suitable, since it implied using the existing information on crop culture, pest control, and the biology of the pest, to determine the minimum amount of the appropriate insecticides to produce the required level of pest control. Hence, by the same token, if growers apply more 49 insecticide than is required to control the pest, then this approach can be considered to be "irrational control". Unfortunately, during recent years, many authors have defined IPM in extremely loose terms. As a consequence, the editors (Bum et al., 1987) of a recent multi-authored book on Integrated Pest Management in Europe, had considerable difficulty in defining what is now understood by integrated pest management and left the readers to form their own opinions. Such a situation is far from satisfactory, as many authors now consider "rational control" to be synonymous with 1PM. Although to some people such differences may appear to be only semantic, I prefer to keep the two approaches separate. Hence, I consider that the "rational" approach is based on using pesticides as the basis of the overall control measures, whereas integrated pest management (1PM) in the classical sense is biologically-based and uses pesticides only to improve the level of control in those instances where it is essential to avoid large crop losses. In preparing for the Veldhoven meeting, I sent a circular to many of you to ascertain how XPM wasbeing used commercially in vegetable production in your particular countries. With the exception of the work on the onion fly (Delia antiqua) in The Netherlands (Loosjes, 1976), classical 1PM in other countries appears still to be largely, though not solely (see Theunissen - this bulletin), at the research/ development level. I do not find this surprising, as pesticides are not only highly effective control agents but are also relatively cheap. In addition, for many of the biological control agents to be used as a substitute fora particular pesticide, the biological agent often needs a pesticide-free environment and this can rarely be achieved under present field situations, where a particular crop may be subjected to attacks from a wide range of pests and diseases {Finch, 1987; 1989). Therefore, the way to progress initially is to identify the minimum amounts of pesticicfes required to control the pests/diseases that attack a particular crop. Only after this has been achieved, and it could take many years, will it be possible to obtain a true assessment of the detrimental effects of pesticides on the environment, and to screen adequately biological control agents under truly commercial conditions. It should also be remembered that scientists are currently being asked to develop systems of "natural" control foruse in large monocultures which, although now regular features of our landscape, are extremely "unnatural" systems. Discussion Most of the contributions being presented at this meeting can be placed into one of two groups. The first group is concerned with developing methods, such as supervised control (Blood-Smyth; Forster; Freuler; Hommes) and pest forecasting {Collier; Cruz de Boelpaepe; Esbjerg; Johnsen; Jonsson; Muller-Pietrallia; Percy Smith), to reduce the amounts of insecticide currently applied to vegetable crops. The second group is concerned with methods of control, such as intercropping (Langer; Theunissen), plant resistance {Ellis), fungal pathogens {Eilenberg), parasitoids {Ahlstrom-Olsson; Vainio) and predators (Finch), that might one day prove to be viable alternatives to commercially-produced insecticides. Neither of these two approaches should be considered to be 1PM, as the first system is still totally dependent on commercially-available insecticides and the second relies on an "alternative" rather than on an "integrated" system of control. 50 Some systems of 1PM are, however, being attempted. They include, for example, the contributions of Taksdal and McKinlay in which resistant cultivars are being used to ensure that the appropriate level of crop protection can be achieved with reduced amounts of insecticide. A good example of this approach is the work of Thompsonet al., (1980) who showed that the carrot fly (Psi/a rosae) could be controlled by integrating a resistant cultivar with only one third of the insecticide required fora comparable level of control on a susceptible cultivar. Although this can be considered truly to be 1PM, as the major part of the control is biologically based, an insecticidal input is still needed, as the plant resistance alone does not give the level of pest control required to produce a crop of high quality. R�sum� Introduction a la protection int�gree des cultures maraich�res La plupart des contributions presentees a cette reunion peuvent etre classees dans deux groupes. Le premier concerne des methodes en voie de developpement. telles la lutte dirigee (Blood-Smyth; Forster; Freuler; Hommes) et la prevision d'attaque par les ravageurs (Collier, Cruz de Boelpaepe; Esbjerg; Johnsen; Jonsson; Milller-Pietrallia; Percy-Smith), dans le but de reduire les quantites d'insecticides couramment utilisees en culture marakhere. Le deuxieme conceme les methodes de lutte, telles les cultures mixtes (Langer;Theunissen), la resistance des plantes (Ellis), les charnpignonsentomopathogenes (Eilenberg), les parasitoides (Ahlstrom-Olsson; Vainio) et predateurs (Finch), susceptibles de devenir un jour des alternatives viables aux insecticides industriefs. Aucune des deux approches ne peut etre consideree comme protection integree, car la premiere est encore entierement dependante des insecticides du commerce et la deuxieme s'appuie plus sur une "alternative" que sur un systeme "integre" de lutte. Toutefois, quelques systemes de protection integree sont tentes. Ainsi, p. ex., les contributions de Taksdal et McKinlay dans lesquelles des varietes resistantes sont utilisees, afin d'assurer que le niveau desire de protection de la culture est obtenu tout en utilisant moins d'insecticides. Un bon exemple de cette approche est le travail de Thompson et aL (1980) qui montre que la mouche de la carotte (Psila rosae) peut etre maitrisee en integrant une variete resistante a l'emploi d'un tiers seulement de !'insecticide necessaire a la protection comparable d'une variete sensible. Meme si ce procede peut etre considere comme protection integree vraie puisque la lutte presente une base biologiquemajoritaire, un apport d'insecticide reste necessaire, car la seule resistance varietale ne montre pas le niveau de protection necessaire pour produire un legume de haute qualite. Acknowledgement I thank the Ministry of Agriculture, Fisheries and Food for supporting this article through their funding of MAFF Project FOSB. 51 References Burn, AJ., Coaker, T.H., & Jepson, P.C. (1987). Integrated Pest Management. Academic Press: London, 474pp. Dunn, J.A & Coaker, T.H. (1965). Rational control of vegetable crop p�sts. Annals of AppliedBiology 56, 342-345. Finch, S. (1987). Horticultural Crops. In: IntegratedPest Management {eds AJ. Burn, T.H. Coaker, P.C. Jepson}, pp. 257-293: London Academic Press, 474 pp. Finch, S. (1989). Ecological considerations in the management of Delia pest species in vegetable crops. Annual Review of Entomology 34, 117-137. Loosjes, M. (1976). Ecology and genetic control of the onion fly,Delia antiqua (Meigen). Centre forAgricultural Publishing and Documentation, Wageningen, The Netherlands. 179pp. Thompson, AR., Ellis, P.R., Percival!, AL. & Hardman, J.A {1980). Carrot fly. Integrated control using insecticides with carrot cultivars of differing susceptibility. Report of the National Vegetable Research Station for 1979, pp. 30. I0BC/WPRS-Workin°Group Meeting 'Integrated Controlin Field Vegetables', Vienna, 28-30Oct 1991 52 Aspects of the biology of brassica root flies G. Taksdal Saerheim Research Station, N-4062 Klepp St., Norway Summary Samples of brassica root fly pupae were collected from a range of localities in south-west Norway. The times for 50% emergence of D. jloralis adults under field conditions at Saerheim varied considerably. Emergence varied by up to a month and 461 accumulated day-degrees C in populations of pupae collected from up to 300 km apart. Differences occurred even between populations collected from less than 10 km apart. D. radicum comprised 2-6% of the root fly population at Saerheim during 1980 to 1986, but increased to 11% in 1987 and 56% in 1988. Sowing sw·edes late reduced damage from first generation D. radicum, and, when combined with half dose of chlorfenvinphos in early July, also reduced subsequent damage by both root fly species. To study the effect of brassica crop movement, in 1991 eight fieldexperiments were sited 3 m to 550 m away from a brassica field that had been infested with root fliesin 1990. The mean egg recovered per plant during the season varied from 477 to 1960. The index of damage of the most resistant of three swede cultivars varied from 49 to 66. Therelative resistance to D. floralis of five swede cultivars changed with increasing fly infestation. At low levels of attack, the most resistant cultivars gave satisfactory control. A half dose of insecticide was sufficient to protect these cultivars at higher levels of pest infestation. Introduction In attempts to protect cruciferous crops with reduced inputs of pesticides, basic knowledge is required on the biology of brassica root flies and on the '!cological situation within particular farming areas. Thus the patterns of emergence of root fly populations in an area must be known if models are to be used to forecast the most appropriate times to apply insecticide (Finch & Collier, 1983). In many parts of northern Europe, the turnip root fly (Delia flora/is) and the cabbage root fly (D. radicum) occur in the same locality. This complicates control problems (Finch & Collier, 1988), especially as the relative proportions of the two species can change radically within a short period of time (Johansen & Hals, 1990). In many areas of Norway, the agriculture consists mainly of small farm groups which are separated in terms of their geography and climate. In such situations, controlling these two fly pests by growing crops in isolated areas or by planned movement of crops ov�r either appropriate distances or naturally-occurring barriers, can be tested. 53 As control from plant resistance is independent of the problems mentioned above, partial plant resistance can possibly be integrated with a number of other control methods (Ellis, 1988; Birch, 1989) to give an ev�n higher level of pest control. This paper presents investigations related to many of the above problems. Experiments Emergence periods or adults or D. flora/is Each November from 1980 through 1984, samples of pupae (44 in total) from 21 localities in south-west N01way, were placed under natural field conditiora in the soil at Saerheim Research Station. Shortly before the expected timeof first emergence of D. radicum adults in the following spring, emergence boxes were placed over the soil in which the pupae were buried. The numbers of flies that emerged were then recorded three times each week. Air temperatures, recorded at a weather station, were used to calculate accumulated day-degrees C. TI1e times at which the flies emerged from the earliest and latest populations indicated clearly the greatvariation in fly emergence (Fig. 1 ). In three years, the dates to 50% emergence differed by about one month. Thelargest difference in 0 accumulated day-degrees,461 D , was recorded in 1980. There was a tendencyfor the late-emergingpopulations to be near the coast, and for the early-emerging populations to be from further inland or from higher elevations. Differences occurred between populations sampled less than 10 km apart. Sowingdates and pesticide doses AlthoughD. radicum comprised only 2-6% of the total root flypopulation at Saerheim during1980 to 1986, it increased to 11% in 1987 and to 56% in 1988 (Fig. 2). When this occurred, the fieldcrops were damaged considerably by the unexpectedly high firstgeneration population of D. radicum. The time of fly emergence from pupae collected from swede fields during the autumn of 1990 (Fig. 2), indicated ihat late sowings might avoid early attack by D. radicum. This was tested in 1991 in a split-plot field experiment in which three sowing dates were combined with 0, 0.5, and normal (2.5 kg a.i. per ha) doses of chlorfenvinphos granules, applied as a band treatment in early July. Both sowing date and dose of chlorfenvinphos affected (P < 0.001) the percentage of swede roots with early damage. Chlorfenvinphos also affected Llie late index of damage (ID) (Taksdal,. 1992). Interactions between sowing dates and doses of chlorfenvinphos were significant (P < 0.05) both for early and late damage (Fig. 3). Applications of chlorfenvinphos had no noticeable effect on the amount of early plant damage following the first sowing. On later sowing, however, the first half dose of chlorfenvinphos had a significant effect. Similar effects were recorded for all sowing dates when the estimates were based or. late damage. Normal dose of chlorfenvinphos did not improve the effecton root damage compared to half dose. 54 1- rJ) 25 1132 ::> 1259 1181 c., 15 ::> < 98 0 1134 1M9 ., 1062 99 3 848 w z 25 867 ::> 876 845 866 725 800 "") 829 15 727 75 3 75 3 rJ) 659 5 645 w 643 6'46 < 541 O 601 r 25 504 i5 r 45 6 412 5 19 8 O 1981 'l 1982 198 3 1984 YEARS Fig. 1: The ea!"liest and latest emergence at Saerheim of &dult D. jloralis each year (1980-1984) from pupal samples of local populations. Accumulated day-degrees are given for the periods, and for date of 50% fly emergence (o). 60 E ::, A u "g 40 ftl c I- z 20 0 0::: w Q. 90 82 83 84 86 87 88 89 1 91 80 81 85 YEAR Fig. 2: Percent of D. rodicum recorded in the adult emergence boxes at Saerheim from 1980 to 1990. For 1991, the percent of D. rodicum was assessed from pupae collected from swede fields; (A) sown 15 May and; (B) planted 28 June 55 w fu! j q d 0 w n ates 0: 15 May w 60 < 100 -----0 --0 :I: 60 <...I t:: LL s: 0 � 40 wCl) 8, 0 a:: C I- 20 z wz 0 � � O·I ' ' -0 1.25 2.5 0 1.25 2.5 CHLORFENVIN PHOS KG A. I. PER HA Fig. 3: Percent :roots w!th esriy damage and indices of late damage at three sowing d2tes and different applications of chlorlenv.nphos m 1991 Crop movement and roott1y attack To study the possible effects of crop movement, in 1991 eight field e�riments were sited from3 m to 550 m away from a field that had contained a high infestation of fly in 1990. In each experiment, three swede varicttes (Table 1), with differing susceptibility to rcot fly, were planted in three randomized hlocks. Cauliflowers were also planted as an easy way to sample the relative numbers of eggs laid at the eight sites (Hughes & Sru.ter, 1959). At the distances of 400 m and 550 m fromthe earlier infestation, eggs were laid by flies from a neighbour's field. Therefore, i:hese results are not included in this paper. The numbers of eggs recovered bet',veen sites, varied considerably both with respect to distance from the earlier infestation and to the presence of natural barriers (Fig. 4, Table 1). The different egg numbers recovered from the three sites in the field of adult emergence (3 m, 87 m and 90 m) may have been caused by the strong wind blowing predominantly from the NNW. The reductions recorded in oviposition, both with distance and with the presence of natural barriers, were most pronounced during peak oviposition. The low numbers of eggs in part of July reflect the gap between the end of the first generation of D. radicum, and the start of the combined population of D. floralis and the second generation of D. radicum. Most flyeggs were recovered fromthe plot situated 90 m fromthe earlier infestations (Table 1 ). Reductions in egg number by a factor of 2.2 at the 97 m site and by 23 at the 300 m site did not affect the indices of damage. When egg numbers were reduced by a factor of 4.1 at the 200 m site, the lowest index of damage for all sites was recorded fromthe �s S-7.7.90 and Ruta. 56 Table 1: Damage to three swede cultivars, and the mean egg numbers recovered per cauliflower plant, at different distances from an earlier root fly infestation Distances (m) 3 87 90 97 200 300 X Cultivar S- 7.7 90 66 57 53 63 49 58 56 Vige 74 57 53 69 60 68 64 Ruta 74 68 68 71 61 68 67 Significance ns • • ns • • •• LS.o.<1> 0.05 7 10 8 4 4 Mean eggs/plant<2> 1411 1842 1960 885 477 835 8 l) Least significantdifference ( = P < 0.05; •= = P < 0.01; ••• = P < 0.001) 2> Accumulated from 28 May to 19 September o m s s Windbreaks sot � � I I I I 1 • I I I I I 200m SSE Windbreaks 57 Resistance of swede cumvars to D. ftorali.s at different levels of attack Attempts to control D. floralis by a combination of chlorf�nvinphos and partial resistance in swedes was investigated in split-plot field experiments starting in 1987 (Taksdal, 1992). As the 1987 experiment was separated by 200m including two windbreaks and some housing from the nearest 1986 crop, fly attacks were low. At low levels of attack, damage gradually increased fromthe partially-resistant cvs Melfort, Angus, and Vige through to the susceptible cvs Gry and Ruta. In 1998 and 1989, the experiment was repeated in the same field and the levels of attack were considerably higher. The relative resistance of the cultivars changed with higher levels of attack. Thus the resistance of Vige in 1987 broke down in 1988, and was even less apparent in 1989. In contrast,Gry which, in the absence of a chemical treatment, was susceptible in 1987, was resistant in 1989. At the lowest level of attack, plant resistance alone gave satisfactory control with Melfort, Angus and Vige. Even at high levels of attack, a half dose of cblorfenvinphos was sufficient to protect Melfort and Angus. Discussion The variation in fly emergence between populations of D. flora/is in south-west Norway would make it necessary to identify the emergence pattern of root flies in each locality to be able to make use of pest forecasting systems. The research and development costs would seem to prohibit such an approach, as the emergence patterns of D. radicum populations would also have to be incorporated into the forecasts. The results (Fig. 1) illustrate clearly the protracted emergence that occurs in field populations of D. flora/is. In contrast, most populations of D. radicum have short, sharp periods of emergence (Collier & Finch, 1985; Finch et al., 1988). Forecasting the time of emergence is probably more useful forcontracted than for the protracted patterns of fly emergence. Similar differences in emergence patterns, which are common between the univoltine D. flora/is and the bivoltine D. radicum, have been recorded for the carrot fly (Psila rosae) (Ausland, 1957). Adults from pupae of the second generation of carrot fly emerged over about ten days in the spring, while adults from the univoltine part of the population emerged over 30-50 days. Knowledge about local emergence patterns of a species is a prerequisite for accurate pest forecastingsystems. The experiment in which varying sowing dates were combined vtith various doses of chlorfenvinphos was carried out largely to counteract the changes in the fly population, from one containing almost exclusively late emerging D. flora/is to one containing about equal numbers of both species. A similar change in dominance, between the two species, was recorded in northern Norway during the late 1970's (Johansen & Hals, 1990). The work on different sowing dates and doses will be continued, and in future will include also partially-resistant cultivars. In the crop movement experiment, there was no obvious relationship between the numbers of eggs recovered and crop damage (Table 1). Thesites at 97 m and 300 m, which had the highest damage, were the two most sheltered sites. Except for 2 one site, the area of cruciferous crops at each site was only 91 m • At the 200 m site, the area used was 0.2 ha, the same size as the source of root flies in 1990. Swede cvs 58 Vige and Ruta were included in identical field experiments at the two sites in 1990 and 1991. The differences in ID values and yield (Table 2) indicate that there is an advantage in moving crops. This advantage is likely to increase in localities where 1PM is practised. Table 2: Root fly damage (ID), and grade 1 yields of two swede cvs grown at a site on which swedes had been grown for 4 years, and at a new site Vige Ruta Yield Grade 1 Yield Grade 1 ID %(1) tonnes ID % tonnes /ha /ha At source of pupae 1990 66 32 1.7 74 13 0.7 At the 200 m site 1991 51 46 3.3 59 34 3.2 <1> Percent "Grade 1• of total yield Manyaspects of crop movement were not studied sufficiently in the present investigation. For example, the source of root fly adults may also be a source of natural control agents. Thus a fungus disease that had not been recorded previously was found in root fly eggs collected at the site of emergence of the flies (Eilenberg & Philipsen, 1992). Elsewhere the investigation will be discussed in relation to root fly dispersal (Finch & Skinner, 1975; 1982), and mortality of immature stages (Finch & Skinner, 1988). For a detailed discussion of the resistance of swede cultivars to the turnip root flyat different levels of fly infestation, the paper of Taksdal (1992) should be consulted. The conditions for agriculture in south-west Norway, and the coexistence and varying dominance of D. radicum and D. floralis indicate that forecasting times of attack from accumulated day-degrees would be difficult. Control methods which do not require a detailed knowledge about the local root flypopulations appear more promising. Delaying sowing or planting dates, use of resistant crop varieties and crop rotation are only a few of the many strategies that need further development. 59 Resume Quelques aspects de la biologie de la mouche des cruciteres (Deliaflora/is et U radicum) P.l! relation avec la protection integr� au sud-ouest de !a Norv�ge Des echantillons de pupes des mouches des cruciferes ont ete recueillis dans diverses localites du sud-ouest de la Norvege. A Saerheim. le moment ou 50% des adul,es de Deliajloralis eclosent en conditions naturelles, varie considerablement. Cette variation peut atteindre un mois et 461 degres-jours pour des lots de pupes preleves a la distance maximum de 300 km. Des differences sont meme apparues entre des populations separees de moins de 10 km. La proportion de Delia radicum dans la population a ete de 2-6% a Saerheim de 1980 a 1986, puis a augmente a 11% en 1987 et a 56% en 1988. Un semis tardif des rutabaga a reduit les degtits dus a la premiere generation de D. radicum. En addition, un traitement effectue au debut juillet avec une demie dose de chlorfenvinphos, a diminue les degats dus conjointement auxdeu.-c especes. Pour etudier l'effet de la distribution des cultures de Brassica, 8 essais, distants de 3 a 550 m d'une c ..dture de Brassica infestee par les deux especes en 1990, ont ete implantes en 1991. Le nombre moyen d'oeufs retrcuves au pied des plantes au courant de la saison variait de 477 a 1960. L'indice d'attaque du cultivar de rutabaga le plus resistant parmi les trois en culture variait de 49 a 66. La resistance relative de cinq cultivars de rutabaga a l'egard de D. flora/is a change conjointement a une pression croissante du ravageur. Aun niveau d'attaque faible, les cultivars resistants ont montre un comptJTtement satisfaisant. Une demie dose d'insecticide s'est averee suffisante pour proteger ces cultivars dans des conditions d'infestations plus severes. References Ausland, 0. (1957). The carrot fly (Psi/a rosae Fabr.). !nvestigations on its biology iq Norway (Norwegian, English summary). Meld. Stat. PL Vem 14: 68pp. Birch, AN.E. (1989). Inkractions between root flies and brassica roots - clues to alternative control strategies. Aspects Appl. Biol 22: 289-295. Collier, RH. & Finch, S. (1985). Accumulated temperatures forpredicting the time of emergen,;e in the spring of the cabbage root fly, Delia radicum (L.) (Diptera: Anthomyi.idae). Bull Ent. Res. 75: 395-404. Eilenberg, J. & Philipsen H. (1992). Ecological interactions between insect pathogens and pest populations in cabbage. WPRS/IOBC Bulletin (This Bulletin). Ellis, P.R. (1988). The impact of exploiting plant resistance to pests in agriculture. Aspects Appl Biol 17: 321-329. Finch, S., Bromand, B., Brunel, E., Bues, M., Collier, R.H., Dum1e, R., Foster, G., Freuler, J., Homrnes, M., Vankeymeulen, M., Mowat, DJ., Pelerents, C., Skinner, G., Stadler, E. & Theunissen, J. (1988). Emergence of cabbage root flies from puparia collected throughout northern Europe. Proceedings of the CEC/IOBC E'- 60 brassica crops: Major factors influencing the accuracy of the forecast and the effectiveness of control. Proceedings of the CEC/IOBC Experts Group Meeting, Rennes, 20-22 November 1985, pp. 49-54. Finch, S. & Skinner, G. (1975). Dispersal of the cabbage root fly. Annals of Applied Biology 81: 1-19. Finch, S. & Skinner, G. (1982). Upwind flight by the cabbage root fly,Delia radicum. PhysioL Ent. "i: 387-399. Finch, S. & Skinner, G. (1988). Mortality of the immature stages of the cabbage root fly. Proceedings of the CEC/IOBC Experts Group Meeting, Rennes, 20-22 November 1985, pp. 45-48. Hughes, R.D. & Salter, D.D. (1959). Natural mortalityof Erioischiabrassicae (BoucM) (Diptera, Anthomyiidae) during the immature stages of the first generation. J. Anim. EcoL 28: 231-241. Johansen, TJ. & Hals, A (1990). The biology of Delia radicum and D. flora/is Fallen (Diptera: Anthomyiidae) in northern Norway (Norwegian, English summary). Norsk. Landbr. Forsk. 4: 337-350. Taksdal, G. (1992). The complementary effects of plant resistance and reduced pesticide dosage in field experiments to control the turnip root fly,Delia flora/is, in swedes. J. Appl Biol 120: (in press). IOBC/WPRS-WockiQiGroup Meeting "IntegratedControl in Field Vegetables". Vienna, 28-30Oct 19')1 61 Integrated control of root flies in swedes R.G. McKinlay<1> & AN.E. Birch<2> <1> The ScottishAgricultural College, WestMains Road, Edinburgh EH9 3JG, UK 2 < > Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK Summary Cabbage root fly (Delia radicum) and turnip root fly (D. floral.is) damage can be difficult to prevent when insecticides are used as the sole method of fly control. At the Scottish Crop Research Institute, Dundee, swedes (Brassica oleracea var. napobrassica) have been screened fortheir resistance to root fly species in both field and field-cage experiments. Detailed glasshouse and laboratory studies, on selected swede cvs and swede breeding lines, have shown that resistance is primarily due to antixenosis, or reduced egg laying. Field experiments o,,er two years at The Scottish Agricultural College, Edinburgh, indicated that it is possible to reduce insecticide inputs by 50% on partially resistant swedes and still obtain good root flycontrol. The prospects for developing 1PM systems based on resistant cultivars is dis�d.. Iniroductfon The cabbage root fly (Delia radicum) and the turnip root fly(D. flora/is) are two of the most important pests of swedes (Brassica oleracea var. napobrassica) in northern Europe. Even a small amount of larval feeding damage on culinary swedes reduces the value of the crop. The keeping quality of the crop is also reduced considerably by secondarypathogens that enter the roots through the areas damaged by the fly larvae. Because of the extended period of attack by D. flora/is ( three months per year) and D. radicum (five-six months per year), two or three carefully timed insecticide applications are required to protect the crop adequately throughout the growing season (McKinlay, 1986). Problems of controlling root flies using insecticides are exacerbated by the flies laying at differenttimes in different localities (Finch, Collier & Skinner, 1986) and by microbial degradation of some widely-used carbamates in certain soils (Suett, 1986). We have been screening swedes for their resistance to root flies since 1985. A small number of cvs and breeding lines have been selected to study the mechanism of the resistance (Birch, 1988; 1989). The main objective, however, was to determine whether root flies could be controlled on swedes by combining partially resistant cultivars with reduced rates of insecticides. This paper summarises the progress made to date. 62 Materials and Methods Field experiments were carried out in 1985 using the swede cvs Doon Major, Angus and Melfort. In 1986, the cv. Sator Otofte was also included in the trial so that egg-laying, pupal development, and crop damage could be estimated in the absence of insecticides. Fly eggs were sampled weekly, taking 12 five-plant samples per cv. over 30 randomised plots. Subsamples of eggs were hatched to identify larvae. Root damage was assessed, using a four-category system, on 60 roots per cv., to calculate a mean root damage index (RDI). Pupae were extracted fromthe soil beneath the same roots at harvest and were then identified and counted (Finch et al, 1978). In 1988, 12 potted plants of each-swede genotype were randomised in a 3 m x 3 m x 1 m high 'Tygan' tunnel and exposed to 450 D. floralis adults. Egg counts were made after seven days, using egg-traps (Freuler & Fischer, 1983). Theplants were exposed to attack for a further eight weeks before assessments were made of root damage and pupal numbers. During 1988 and 1989, two cultivars of swedes (Angus - a partially resistant cv. and Ruta Otofte - a relatively susceptible cv.) were tested with and without insecticides. Chlorfenvinphos granules (10% w/w; Birlane Granules; Shell) were applied to all plots at 70 g/100 m of row for control of the first generation of the cabbage root fly. The insecticidal treatments tested against the second generation of the cabbage root fly and the single generation of the turnip root flywere: 1) manufacturers recommended rate (mrr) of carbofuran granules (5% w/w; Yaltox; Bayer) at 12.5 g/10 m row; 2) one half of mrr of carbofurangranules; 3) two sprays of chlorfenvinphos ec {24.8% w /w; Birlane 24; Shell) in 1988 and two sprays (24.3% w/w; Sapecron 240 EC; Ciba-Geigy) in 1989 at mrr of 31/ha each spray; 4) two sprays of chlorfenvinphos ec at one half of mrr each spray; and 5) untreated. During 1988, the carbofuran granules were applied on 27 July; and the two sprays of chlorfenvinphos on 27 July and 10 August, respectively. The corresponding dates for applying insecticide in 1989 were 25 July and 10 August. The experiments were sown on 10 May 1988 and 28 April 1989 and harvested on 25 November 1988 and 11 December 1989. Each plot was four rows wide (rows were 51 cm apart in 1988 and 65 cm apart in 1989) x 5 m long with 15 cm spacing between seeds in the row. In both years, the treatments were replicated 6 times within a randomised block. A 1.5 m length of row was harvested from the middle two rows of each plot. In 1988 and 1989, the incidence of cabbage root flydamage was assessed on 10 and 20 randomly chosen roots, respectively. Because of the low fly infestation in 1988, only the presence/absence of damage was recorded. The percentages of damaged roots were then subjected to an angular transformation and analysed by analysis of variance. In 1989, root damage from cabbage root fly attack was scored and analysed after McKinlay (1986). The damage by turnip root fly was too low in. both 1988 and 1989 for meaningful assessment. Results During the 1985 experiment, the population of D. floralis was large: 3 to 4 times as many D. floralis females were caught than D. radicum. In the 1986 experiment, although similar numbers of the two species were caught, fly numbers 63 were lower thanin 1985. Thenumbers of eggs recovered, root damage index and pupal numbers are shown in Table 1. The field results indicated that reduced egg-laying (antixenosis) by cabbage root flyand turniproot fly, was the most important component of resistance in cvs Angusa...,d Melfort. This was confirmed in field-cage experiments (Birch, 1989). The results for GRL agaa and forcvs Angus, Melfort, Doon Major and Sator Otofte are shown in Table 2. Table 1. Relative resistance/susceptibilityof swedes to attack by cabbage (CRF) and turnip (TRF) root flies in the field Cultivar CRF eggs TRF eggs RDI CRF pupae TRF pupae (/5-plant sample) {1-4) /root /roo� Doon Major 1985 57 2.8 2.7 11.2 1986 12 20 2.7 1.9 1.7 Sator Otofte 1986 20 20 2.2 1.7 1.1 Angus 1985 26 1.2 1.2 1.8 1986 1 4 1.8 1.5 0.2 Melfort 1.3 1985 16 1.4 OA 1986 5 6 1.8 1.2 0.4 Significance 1985 * • NS • 1986 **"' �·· ..... NS ,::. - = egg numbers too small foranalysis; RDI = root damage index; NS = not significant; "' = P<0.05; �" = P Theresults of the field experimentsinvolving insecticides are shown in Tables 3 and 4. During 1988, the percentage of swede plants damaged by the cabbage root fly did not differ {P > 0.05) between cv. Ruta Otofte + full rate carbofuran and.cv. Angus + half rate carbofuran. In contrast, cv.Ruta Otofte + fullrate chlorfenvinphos reduced (P < 0.05) the percentage of damaged plants compared to cv. Angus + half rate chlorfenvinphos (Table 3). During 1989, cv. Angus + half rate chlorfenvinphos reduced (P < 0.05) the damage to swede roots by cabbage root flylarvae compared to cv. Ruta Otofte + full rate chlorfenvinphos. Similarly, cv. Angus + half rate carbofuran reduced (P < 0.05) damage when compared to cv. Ruta Otofte + full rate carbofuran (Table 4). 64 Table 2. Fie!d-cage assessment of D. flora/is egg-laying, pupal development, and root damage to swedes Cultivar/ Eggs/plant Pupae/root RDI % roots breeding line marketable GRLagaa 16 3.1 2.4 58 Angus 26 4.6 3.2 33 Melfort 30 12.5 2.8 33 Doon Major 51 19.3 4.0 0 Satar Otofte 40 24.6 3.8 8 Significance *** •• • "'* RDI = root damage index Table 3. Percentage of swedes dam&ged by cabbage root ilyin the 1�88 1ield experiment Treatments % p!ants Duncan's Multiple damaged+ Range Test++ Ruta Otofte no insecticide 77 a Angus no insecticide 60 a C Angus 2 x half-rate chlorfenvinphos 48 b C e Ruta Otofte 2 x half-rate chlorfenvinphos 40 b C e g Ruta Otofte 2 x full-rate chlorfenvinphos 33 b d e Ruta Otofte full rate carbofuran 32 b d e g Angus half-rate carbofuran 32 b d e g Angus 2 x full-rate chlorfenvinphos 32 b d e g Ruta Otofte half-rate carbofuran 23 b d f Angus full rate carbofuran 15 b d f h + assessed only as presence or absence of damage ++ means with the same letter do not differ significantly (P > 0.05) 65 Table 4. Scores of root damage to swedes cacsed by cabbage root fly in the U89 field experiment Treatments Rooe Damage + Duncan's Mu!tiple Score Range Test++ Ruta Otofte no insecticide 26 a Ruta Otofte half-rate chlorfenvinphos 24 a C Ruta Otofte full-rate chlorfenvinphos 20 a C e Ruta Otofte half-rate carbofuran 16 b d f g Angus fu!l-rate chlorfenvinphos 14 b d f g h Ruta Otofte full-rate carbofuran 14 b d f g h i Angus no insecticide 13 b d f "'a h i j Angus half-rate chlorfenvinphos 12 b d f g h i j k Angus full-rate carbofuran 11 b d f g h i j k l A..ngus half-rate carbofuran 10 b d f g h i j k l + higher scores = poorer control + + means with the same letter do not differsignificantly (P > 0.05) Discussion Field experimentsshowed that the swede rultivars Angus and Melfort were partiallyresistant to turnip root fly and cabbage root fly. Antixenosis was found to be the major mechanism of resistance. Between 2-5 times as many D. floralis eggs were laid on the susceptible cv. Doon Major as on the resistant cv.Angus. The degree of antixenosis againstD. radicum was variable in 1985, due to low numbers of flies. However in 1986, D. radicum laid 15 times as many eggs on cv. Sator Otofte as on cv. Angus. Field-cage results confirmed field results and indicated that the Scottish Crop Research Institute breeding line GRL agaa had a high degree of antixenosis to D. floralis. Recent field and laboratory experiments have shown that GRL agaa is also resistant to D. radicum. The overall objective of the programme is to develop a system, based on the combination of partially resista:qt cultivars and reduced rates of insecticides, for the integrated ccntrol of root flies on culinary swedes. It is promising, therefore, to note the similar degree of control given by cv. Angus + half rate carbofuran to cv. Ruta Otofte + full rate carbofuran in 1988; and the better control given by cv. Angus when combined with half rates of the insecticides than by cv. Ruta Otofte when combined with full rates of the insecticides in 1989. In practice, the market is likely to dictate whether integrated approaches will be adopted. If growers are unable to market partially resistant cultivars, integrated approaches such as those reported in this paper will not be adopted. At present, the market forswede cultivars resistant to root fly attack is small compared to the large 66 market forthe agronomically desirable cultivars that are currently susceptible to damage. Therefore, research should identify the resistance factor in cultivars such as· Angus with a view to isolating the genes responsible and incorporating them into cultivars preferred by the market. R�sum� Protection int�� contre les dipt�res des racines sur rutabaga La mouche du chou (Delia radicum) et la mouche du radis (Deliaflora/is) provoquent des degdts qu'il est difficile de prevenir lorsque les insecticides constituent le seul moyen de lutte. Au Scottish Crop Research Institute de Dundee, divers rutabagas (Brassica oleracea var. napobrassica) ont ete testes en champ et en cage exterieure quant a leur qualite de resistance a l'egard des dipteres des racines. Des etudes detaillees en serre et en laboratoire sur des cultivars et des lignees selectionnees de rutabagas ont revele que la resistance est avant tout du type antixenose, a savoir la reduction de la ponte. Des experiences en plein champ, conduites durant deux ans a Edimbourg, au Scottish Agricultural College, ont montre qu'il est possible de reduire les traitementsinsecticides de 50% sur les rutabagas partiellement resistants, tout en assurant une bonne efficacite sur les dipteres ravageurs. Les perspectives pour developper des systemes de protection integree bases Sur des cultivars resistants sont discutees. References Birch, AN.E. (1988). Field and glasshouse studies on components of resistance to root fly attack in swedes. Ann. appl Biol 113: 89-100. Birch, AN.E. (1989). A field cage method for assessing resistance to turnip root fly in brassicas. Ann. appl Biol US: 321-325. Finch, S., Collier, R.H. & Skinner, G. (1986). Local population differences in emergence of cabbage root flies from south-west Lancashire: implications for pest forecasting and population divergence. Ecol Ent. 11: 139-145. Finch, S., Skinner, G. & Freeman, G.H. (1978). Distribution and analysis of cabbage root fly pupae populations. Ann. appl Biol 88: 351-356. Freuler, J. & Fisher, S. (1983). Description d'un piege a oeufs pour mouche du chou, Delia brassicae. Bull de la Soc. Ent. Suisse 55: 77-85. McKinlay, R.G. (1986). Insecticidal control of cabbage and turnip root flies in swede turnips. Tests of Agrochemicals and Cultivars No 7 (Ann. appl Biol 108 supplement), pp. 34-35. Suett, D.L (1986). Accelerated degradation of carbofuran in previously treated field soils in the United Kingdom. Crop Prot. 5: 165-169. IOBC/WPRS-WorkingGroup Meeting "Integrated Control in FieldVegetables", Vienna. 28-30 Oct 1991 67 Using an extended Leslie model to forecast the development of .Ilelia radicum I. Populations l 1 2 W. Miiller-Pietrallia( >, M. Hommes < ) & D. SondgerathC ) (l) BiologischeBundesan.stalt Jar Land- und Forstwirtschaft, InstitutJar Pjlanzenschutz in Gemusebau, Messeweg11/12, D-3300 Braunschweig, Gennany <2> Technical UniversityBrav.n.schweig, Institute of Geoecology Summary This report describes a simulation model for forecasting cabbage root fly emergence. The simulation is based on an extended Leslie model and couples together one Leslie process for each stage of insect development. The coupling of the Leslie processes is done via time-dependent transition probabilities which reflect the state of development of the individual insects. The state of development is described by the biological age of the insects, under a range of different environmental conditions. The simulation models show close agreement with rlata collected from i) laboratory experiments (controlled conditions) and ii) field er.perhnents (variable conditions). It is hoped that a system to predict fly attack and ts- optimise control procedurescan be developed from this- modelling approach. R�sum� L'utilisstioi. d'1m modMe Leslie �tendu pour la p�vision du d�veloppement de populations de Deliaradicum L. Le travail decrit un modele de simulation pour la prevision de l' emergence de la mouche du chou. La simulation est basee sur un modele Leslie etendu et assemble ur. processus de Leslie pour chaque stade de developpement de l'insecte. Le couplage t:!e ces processus est opere via des probabilites de transition dependant du temps, refletant li: stade de developpement des insectes pris individuellement. Le stade de d�veloppement est decrit par l'fige physiologique des insectes soumis a une serie de differentes conditions environementales. Les modeles de simulation mcntrent une bonne conccrtlance aussi bien avec des donnees provenant du laboratoire (conditions contrblees) que du plein champ (conditions variables). Par cette approche de modelisation, on espere developper un systeme pour la prevision d'attaque de la mouche du chou et pour optimaliser des mesures de lutte. IOBC{WPRS-WorkjngGroup Meetin� "In�gratedControl in FieldVegetables", Vienna. 28-30Oct 1991 68 The feasibility of using models to forecast carrot fly attacks in commercial carrot crops R.H. Collier, S. Finch & K. Phelps HorticultureResearch International, Wellesboume, Wwwick, CV35 9EF, UK Summary Simulation models to forecast the timings of flyemergence and egg laying by the carrot fly (Psila rosae) were run in 1991 using weather data collected weekly fromeight weather stations in the UK (Latitude51-54 °N). The models were run using data derived from the daily maximum and minimum air temperatures and from soil temperatures at a depth of 10 cm. Forecasts indicated that insect activity was earliest at Wellesboume and Mepal (central and eastern England) and latest at Aughton (north west England). The carrot flyforecasts were validated using data obtained fromfly samples collected from Wellesboume field plots and from commercial carrot crops in easternEngland. "Forecast" and "observed" insect activity were separated into generations and compared on a cumulative percentage basis, so that differencesin the times to 10% and 50% fly-emergence and egg-laying could be compared. Generally, the "forecasted" activities of the flies were accurate to within one week of the observed activities of the flies. The reproducibility of the carrot fly forecast depended on simulating the development of a population of more than 50 flies and ideally, 100-250flies. The model :,howedclear!y that a minimum of 50 - 100flies must be caught per generation if information from insect traps is to be used to advise growersof the most apprnpriate time to apply insecticide. Advice on the timing of carrot fly attacks, based on fewer flies, is meaningless. Introduction Although relatively persistent insecticides can be applied to the soil at drilling or transplanting to control fly larvae that feed on the subterranean parts of vegetable crops, such chemicals are usually effective only against one generation of the pest fly. Therefore, supplementary sprays have to be applied to established crops to control subsequent generations of flies. As the effects of such sprays persist generally for only short periods, the sprays need to be applied at precise times if they are to be effective. Unfortunately, the timing of insect generations varies considerably from region-to-region and year-to-year (Esbjerg et al, 1988; Collier & Finch, 1988). Therefore, it is necessary to know exactly when peak periods of pest attacks occur if supplementarysprays are to be effective. Although routine monitoring of pest 69 populations allows the increases and decreases in insect numbers to be recorded. such information does not provide advanced warning of when an attack is likely to cccur. However, a pest forecasting system, based on local weather data, should give early warning of when to apply control treatments. The simulation model, developed primarily to forecast the timing of cabbage root fly attacks on swede crops (Collier et al, 1991), is based on a series of equations which describe how the rates of insect development change with temperature. The parameters forthese equations were established under controlled-environment conditions in the laboratory. The model includes a simple method, also derived from laboratory experiments, that incorporated the variability that occurs naturally within the population of the fly. A similar model has now been developed for forecasting the timing of attacks by carrot fly. This model was run in 1991 to examine the feasibility of providing carrot fly forecastsfor several regions from a central location. Data, obtained weekly from colleagues with access to appropriate weather stations, were used to update the carrot flyforecasts. Copies of the revised forecasts were then sent each week to regional entomology advisers in ADAS. The accuracyof such forecasts can be assessed by validating the expected insect activitygenerated by the model against the actual insect activity recorded under field conditions. However, as carrot flies are mobile insects that attack ephemeral crops, the numbers of insects sampled often change dramatically from one generation to the next. This paper describes the feasibility of using models to forecast carrot fly attacks in commercial vegetable crops. Materials and Metb.ods Running thecarrot fly forecasts Meteorologicaldata Theforecasts were run using data from eight weather stations, located close to the major areas of vegetable production. Daily records of maximum and minimum air temperatures and the soil temperature at a depth of 10 cm recorded at 09.00 h were obtained from each station. Each Monday, the appropriate weather data were forwarded to Wellesbourne by telephone or fax from the eight weather stations. These data were then transferred to the computer so that the complete set of data from 1 February 1991 to the last data entry was available for use in the model. Empirical equations, derived at Wellesboume, were then used to estimate, foreach day, the maximum and minimum soil temperature at 6 cm (Collier et al, 199:i), the mean depth at which larvae are found in the soil. Hourly soil and air temperatures were also estimated from the maximum and minimum temperatures using a variant of the method devised by Parton & Logan (1981). Finally, the weather data were extrapolated beyond the date of the last 1991 entry by adding data collected at Wellesbourne during the corresponding week in 1989, a relatively warm year. It was hoped, by using this data for the extrapolation, the forecasts would err on the side of "earliness" and hence anticipate the actual insect attacks. Theweather data could have been extrapolated equally-well by using long term averages or climatological data. 70 On receipt of the weather data, the carrot flymodel was run. Theforecasts for the eight localities were then listed in order of latitude from south to north and summarised on an information sheet. This sheet, which also contained information on the current state of development of the pest population, was sent by fax to consultants, advisors and growers. Insect monitorin�data Thefield activity of carrot fly was monitored using orange RebellR traps (Collier & Finch, 1988). Results Runnini:t he carrotfly forecasts Table 1 shows the carrot fly forecasts issued on Monday 5 August 1991. The forecasts mdicate the percentage of second generation flies that had emerged from the soil and the percentage of eggs that had been laid. It was estimated that by Sunday 4 August, 43%of the second generation flies had emerged at Mepal (Lat 52.2°N) and 22% at Aughton (Lat 53.3°N). Similarly, although egg-laying had not started at Aughton, 14%of the eggs of the second fly generation had been laid at Wellesboume. As described earlier, the forecasts were extended beyond 4 August using weather data collected at Wellesboume in 1989. It was estimated that 10% egg-laying occurred by 3 August at Wellesboume and would occur by 9 August at Aughton. Similarly, 50%of the eggs would be laid by 17 August at Wellesboume and by 27August at Aughton. Table 1. CarrotDy forecasts issued on 4 August 1991 % %of Estimated(b)date of eggs Met Station Latitude emergence eggs of 2nd generation ON of flies (a) To end of actual weather data (b) Includes weather data from 1989 71 The model predicted that 50% activity of the first and second carrot fly generations should occur between 25-31 May and 16-27 August, respectively. The forecasts indicated that fly activity was earliest at Wellesbourne and Mepal (central and easternEngland) and latest at Aughton (north west England). Validation of the forecasts Fig. 1 shows typical curves for real and forecast carrot fly activity at Mepal during 1991. Toe data have been plotted as percentage of the total number of insects simulated (expected)/monitored (observed) throughout the whole season. Although the peaks of expected and observed activity agree quite closely, it is difficult to measure the level of agreement. Fig. 2 shows the same data plotted on a cumulative percentage scale in which fly activity, instead of being expressed forthe whole season, has been separated into generations. With this "scaled" approach, it is easier to measure the accuracy of the forecastand to estimate, for example, differences in the times to 10% and 50% egg-laying. Using the above approach, forecasts were run for sites where appropriate insect monitoring data and weather data were available. In general, the mean difference between the forecasted and actual times of 50% egg-laying was approximately 7 daysfor the carrot fly. The influence of sample size Once the simulation models reflect the actual ffeld activity of the flies, the models can be used to inspect the properties of the overall sampling procedures. For example, they can be used to determine the amount of data required for the simulation to produce estimates of a given level of accuracy. To determine the number of samples needed to give the required level of sampling precision, the carrot fly simulation model was run using the weather data collected at WeUesbourne in 1991. The model was run 10 times foreach sample, using sample sizes of 10, 50, 100, 250 and 500 flies or eggs. Different random numbers were used for each simulation and the times for 10% and 50% activity were compared. When only 10 flies were used, the shape of the simulated egg-laying curve varied considerably between runs (Fig. 3) and hence the sample size was clearly not sufficiently large to give meaningfulresults. When the times to 10% and 50% egg laying by the second fly generation were calculated for each run of the model, the dates of 10% and 50% egg-laying ranged from 25 July to 13 August (19 days) and 6 August to 3 September (28 days), :respectively. As expected, the spread of times to 10% and 50% egg-laying decreased with increasing sample size (Table 2). To produce a consistent estimate of the timing of carrot fly activity ( error less than ± 1 week) it was necessary to use a sample of 100-250 flies (Table 2). 72 % flies trapped 25 20 ••••.. I I f 15 I I ,, , I ,, , I ,,I , I I I I , I I , I , I I , , I I , I I , I I 10 , I I ' I I , I , I \ , I \ , I \ , I \ ,, I \ 5 , I ,, I ,, , , 0 1 Apr 1 May 1 Jun 1 Jui 1 Aug 1 Sep 1 Oct Fig. 1: Actual (-) and forecast(- - -) carrot fly activity at Mepal during 1991, plotted as a percentage of the total number of flies moniiored/simulated during the season Cumulative % flies (scaled) 100 , ,,,,,,-·· ,, 80 ,, ,, 60 40 20 1 Apr 1 May 1 Jun 1 Jui 1 Aug 1 Sep 1 Oct Fig. 2: Actual(-) and forecast (- - -) carro! fly activity at Mepal during 1991 plotted on a cumulative percentage scale, with the flyactivity separated into the first and second generations 73 Cumulative % flies 100 · /�··············· .. ,,····· · · 80 I I I I I I 60 :. I : • I : 'I / : I /: I 40 : f;. ?," t.: • i ,• 20 : :/, : f 1 :. �i •fi··1 I/ J 0 L----.:.i··----...L...---...L...---...L...---...L...--- 1 Aug 1 Sep 1 Oct 1 Nov 1 Dec Fig. 3: Simulation of second gel!eration �arrot fly egg-laying fttWe1lesbourne in 1991. Four simulations on a population of 10 flies Table 2. Range of simulated times io a) 10% and b) 50% egg laying by second generation carrot flies at Wellesbourne in 199L Each simulation was run 10 times using different ra!ldom number seeds a) 1Q% �g� laying Population size Range of estimates Days Mean 10 25 Jul-13Aug 19 31 Jui 50 29 Jui- 6 Aug 8 2Aug 100 31 Jui- 6 Aug 6 3 Aug 250 2Aug- 6 Aug 4 3Aug 500 2 Aug- 5 Aug 3 3Aug b) 50% ,gg la)dng Population size Range of estimates Days Mean 10 6 Aug- 3 Sep 28 16Aug 50 14 Aug-28 Aug 14 20Aug 100 16 Aug-28 Aug 12 21Aug 250 17Aug-25 Aug 8 21Aug 500 19 Aug-22Aug 3 21Aug 74 Discussion The carrot fly simulation model indicates the numbers of flies "available" for trapping on a particular day, but does not have any component that relates how the weather (temperature, rainfall, wind) on the day of sampling affects pest activity. The numbers of flies caught/trap, reflect not only the numbers of insects present but also the activity of the insects during the sampling period. Although there will be differences on a day-to-day basis between simulated and forecastactivity, these will generally even themselves out over time. The accuracy of the comparisons being made between observed and forecasted insect activity are also constrained by the frequencywith which the insects are sampled in the field. To validate the model, it was considered more appropriate to sample many sites at weekly intervals,rather than a few sites at more frequent intervals. Hence, the comparisons being made between observed and forecasted activity cannot expect to have an accuracy of much less than one week. The carrot fly model was run with a range of sample sizes to indicate the size needed to produce a repeatable simulation. This technique also gives guidelines on the numbers of flies that have to be trapped under field conditions, if the data are to be of use in validating the forecasting model. For example, a sample of 10 fliesper generation cannot produce a reliable estimate of fly activity in the field, as 10 iterations on samples of 10 carrot flies produced estimates of 50% activitythat differedby as much as 20 days. Minimum sample size has a bearing not only on the amount of data required to validate the pest forecasting model. but also on the direct use of monitoring data to determine spray timings. The data in Table 2 show that at least 50 flies should be trapped/generation to provide a meaningful estimate of fly activity in the fiefd: Even when 50 fliesare trapped (Table 2), times of 10% and 50% egg laying may only be expected to estimate the true population to within ± 1 week, which is close to the standard sampling interval of one week. Ideally, 100-250 flies should be sampled in each generation. These results show that the importance of using effective insect traps cannot be over-emphasised, both for model validation and for using fly trapping data as the indicator of whether or not to apply insecticide sprays to established vegetable crops. Thesimulation model developed to forecast the timing of carrot fly attac1'.s has been validated for many site/year combinations and the forecasts are generally accurate to within one week. Models can only be validated at those sites where sufficient insects have been sampled during the course of a generation. Because the carrot fly forecastssimulate insect activity throughout development, they can be used in a number of ways to provide growers with advanced warnings of periods of high insect activity. Hence, pest-insect forecasts have considerable scope for exploitation. Acknowledgements We are grateful to Dr J Blood-Smyth of ADAS, Cambridge for providing the insect monitoring data from Mepal. This work was funded by the Horticultural Development Council as part of project FV13a. 75 Resume La possibilite d'utilisation de modeles pour la prevision d'attaque de ravageurs dans Jes cultures maraicileres commerciales Des modeles de simulation pour la prevision des epoques d'emergence et de ponte de la mouche de la carotte (Psila rosae) et de la mouche du chou (Delia radicum) ont fonctionne en 1991 sur la base des releves meteorologiques hebdomadaires provenant de huit stations du Royaume-Uni (latitude 51-54° N). Ces modeles utilisent des donnees derivees du maximum et du minimum des temperatures joumalieres de l'air, ainsi que du sol a 10 cm. Lesprevisions indiquent que l'activite des insectes est la plus precoce i\Wellesboume et Mepal (centre et partie orientale de l'Angleterre) et la plus tardive a Aughton (nord-ouest de l'Angleterre). Les previsions pour la mouche du chou et la mouche de la carotte ont ete validees par echantillonnage de mouches et d'oeufs dans des parcelles experimentales de Wellesbourne et dans des cultures commerciales de Brassica et de carottes de I'Angleterre orientale. L'activite calculee et reelle de l'insecte a ete separee selon Jes generations, puis comparee sur la base d'un pourcentage cumule, faisant ressortir les differences temporelles pour atteindre 10% et 50% d'emergence des mouches ou de l'oviposition. En general, l'activite calculee des mouches s'est montree sernblable a celle observee, l'ecart se maintenant a rnoins d'une semaine. La reproductibilite de la prevision pour la mouche de la carotte depend de la simulation du developpement d'une population depassant 50 individus. La simulation de l'activite des populations de la mouche du chou en regime d'eclosion precoce ne requiert que .50 individus, cependant que celles en regime d'eclosion tardive necessite plus de 100 insectes. l..esm�les demontrent clairement qu'il faut pieger un minimum de 50- 100 insectes par generation si !'information fournie par piegeage est destinee a l'avertissement des producteurs sur le moment opportun de traitement. Tout conseil relatif a la periode d'attaque des mouches qui serait base sur un nombre d'individus plus faible est denue de sens. References Collier, R.H. & Finch, S. (1988). A preliminary forecasting system forcarrot flyin the UK. 1988 Brighton Crop Protection Conference - Pests andDiseases. 257- 262. Collier, R.H., Finch, S. & Phelps, K. (1991). A simulation model for forecasting ilie timing of cabbage root fly attacks on cruciferous crops. EPPO Bulletin 21: 419- 424. Esbjerg, P., Philipsen, H. & Percy-Smith, A (1988). The significance of carrot fly (Psila rosae) monitoring in Denmark. Integrated Control in Field Vegetable Crops IOBC/WPRS Bulletin/Ja/I: 14-25. Parton, WJ. & Logan, J.A (1981). A model for diurnal variatio!l in soil and air temperatures. Agricultural Meteorology 23: 205-216. Phelps, K., Collier, R.H. & Finch, S. (1992). Validation of the model for forecasting the timing of cabbage root fly attacks on field brassica crops. Computer science and mathematical methods in plant protection. IOBC/WPRS International Workshop, Parma 1990: (in press). IOBC/WPRS-Workjnw;Group Meeting"Integrated Control in Field Vegetables",Vienna, 28-30 Oct1991 76 A Nordic project on the cabbage root fly and the turnip fly (1991-1994) R. Meadow Department of Entomology and Nematology, Norwegi.anPlant Protection Institute, N-1432 As, Norway Summary A project involving researchers in all of the Scandinavian countries was started in 1991 under the auspices of the Nordic Joint Committee for Agricultural Research. The purpose of the project is to promote, coordinate and integrate research activity aimed at reducing the use of chemical insecticides in brassica vegetable and root crops. Thefocus of the project is on control of the cabbage root fly (Delia radicum) and the turnip fly (D. jloralis). The research covers different approaches to environmentally-sound control of these pests, with certain aspects being emphasized in the different countries. Several aspects will be integrated as the project progresses. The approaches covered by the project can be grouped as follows: forecasting, warning and economic thresholds; reduced dosages of insecticides/ alternative insecticides; alternative cultural techniques; plant resistance to insect damage; beneficial organisms. The first research season as a group was 1991. However, several ofthe researchers involved have already had one or two seasons of preliminaryinvestigatio ns, and some of this work is described elsewhere in this bulletin. !ntroduction The Nordic Joint Committee forAgricultural Research began a project in 1991 to investigate possibilities for reducing the amount of insecticides used in the production of brassica vegetable and root crops. Several of the countries involved now have an officially stated goal of reducing the use of pesticides. As the root flies that attack brassicas a1."e the cause of most use of chemical insecticides in these crops m the Scandinavian countries, the current studies focus on the cabbage root fly (Delia radicum (L)) and the turnip fly (D. j[oralis (Fallen)). The five Scandinavian countries (Denmark, Finland, Iceland, Norway and Sweden) cover a large area in which brassica crops are grown in a region spanning from about 55°N to 70°N. This includes a wide variety of local climates, as well as differences in the importance of the two fly species. The turnip fly has not been found in Iceland (Olafsson, pers. com.), but is often the more prevalent species in Norway and northern regions of Sweden and Finland, and can also be important in northernmost Denmark. This species has shown considerable local variability in thermal requirement for emergence of adults (see Taksdal, this bulletin), and this may be even more extreme over the large region investigated by the current project. 77 Investigations The major approaches covered by the project, include pest forecasting, warning and economic thresholds, reduced dosages of insecticides/ alternative insecticides, alternative cultural techniques, plant resistance to insect damage and beneficial organisms. The various approaches are emphasized differently in the different countries. The sub-projects are listed in Table 1, together with the countries involved and the names of the major participants. Tab!e 1. Overviewof the subject areas investigated in the Nordic project 1YPE OF STUDY LOCATION & PARTICIPANTS Forecasting, Monitoring, Economic Denmark: Percy-Smith Thresholds Norway: Meadow Insecticide Dosage Denmark: Percy-Smith Norway: Meadow, Taksdal Resistant Cultivars Nnrway: Taksdal Beneficial organisms: Entomogenous Neir.atodes Finland: Hokkanen, Vainio, Vanninen Beneficial organisms: Insect Pathogenic Fungi Denmark: Ellenberg Beneficial organisms: Predators, Parasitic insects Sweden: Jonasson, Ahlstrom-Olsson keland: Halldorsson, Olafsson, Gudmundsson Cultural Techniques: Living Mulch Denmark: Langer Norway: Meadow Cultural Techniques: Trap Crop Norway: Meadow Cultural Techniques: Mustard Mulch Sweden: Jonasson, Ahlstrom-Olsson Basic Biological Studies: Delia radicum Iceland: Halldorsson, Olafsson, Gudmundsson Basic Biological Studies: Deliaflora/is Norway: Taksdal, Johansen Modelling of Interactions Denmark: Johnsen 78 Forecasting, Monitoring, Economic Thresholds In Denmark and Norway, monitoring techniques are being refined to predict the best time for control actions. Previous studies on monitoring in Denmark (Bromand, 1988) provide a good basis for this work. Where both fly species occur together, monitoring changes in pest numbers is more complicated. Recent studies on the biologyof the flies under local conditions (Johansen & Hals, 1990; Taksdal, this bulletin) have shed light on this problem and are being continued in cooperation with the current project. Workers in the IOBC group and others (e.g. El Titi, 1979) have attempted to establish damage thresholds with limited success. Thecurrent Nordic project will also address this problem. Reduced dosages of insecticides/alternat ive insecticides Studies investigating the possibility for using lower dosages of currently-used insecticides are being conducted in several of the countries involved. Cooperative trials will help to avoid unnecessary duplication of effort. Biorational and novel insecticides are also included in this work. Plantresistance to insect damage Plant cultivars exhibiting partial resistance to damage from the flies are being selected in swedes. Several promising cultivars have already been identified and are being incorporated into breeding programs (see Taksdal, this bulletin). These cultivars will be combined with other damage reducing techniques (e.g. low dosage of insecticide) to limit damage to that which is economically acceptable. &ploiting beneficialo rganisms In cooperation with J0rgen Eilenberg of the Royal Veterinaryand Agricultural University in Copenhagen, fungal pathogens of the root flies will be identified and considered forexploitation. Naturally occurring predators and parasites will be evaluated by project cooperators at the Swedish Agricultural University in Alnarp, Sweden. Special strains of entomogenous nematodes are being evaluated at the Agricultural Research Centre in Jokioinen, Finland, for their effect in controlling root flies. After further selection, suitable nematode strains will be tested in fieldtrials in several of the cooperating countries. Very little is known about the natural enemies of cabbage root flies in Iceland. Studies will be done by the Agricultural Research Institute in Reykjavik to investigate the occurrence of natural enemies and to evaluate their importance as control agents. Biological studies on the cabbage root fly in Iceland will also be continued, building on investigations from the past decade (Halld6rsson, 1989). 79 Cultural techniQyes: Livingmylch/Mystard mulch/Trap cropping Reduction in damage from cabbage root flies by intercropping or living mulch has been demonstrated (see Theunissen et al., this bulletin). Studies in cooperation with the Nordic project are being carried out in Denmark with clover living mulch and cauliflower (see :Langer, this bulletin). Similar studies are being done in Norway, using clover and swedes, where both species of flies are found together. Spreading mustard seed meal in brassica plots has demonstrated an effect on the cabbage root flyand its predators/parasitoids (see Ahlstrom-Olsson & Jonasson. this bulletin). The meal appears to change the oviposition pattern of the flies, and to attract alternative hosts for staphylinids, increasing their numbers at the most appropriate time in respect to cabbage root flyoviposition. These interactions are being studied at the Swedish Agricultural Universityin Alnarp as a part of the project. The use of highly attractive host plants as trap crops for pests can provide an alternative to treating the main crop with insecticides (Hokkanen. 1991). This technique shows most promise in areas where cropE are grown on a relatively small scale. Trials using turnip varieties known to be highly attractive to both species of flies are being carried out in swede crops in Norway. These studies are aimed at eliminating the need to spray the main crop or the trap crop. Simulation modelling A model for simulating the phenology of the cabbage root flyand of cauliflower has been developed by SteffenJohnsen of the Royal Veterinaryand Agricultural Universityin Copenhagen (Johnsen et al., 1990). This model will incorporate some of the information collected in the current project and will be used to predict the time of emergence of the flies and the impact of the various other control techniques on fly mortality. Conclusion By supporting this four year project, the Nordic Joint Committee for Agricultural Research has contributed to a substantial increase in the amount of research activity on enviromnentally-sound control of vegetable pests. TI1e project also allows for better coordination of this research within the Scandinavian countries than was possible in the absence of formalised cooperation. A major challenge for the project group will be to integrate the various techniques now being investigated. Ar.knnwledgements This project is being funded by the Nordic Council, the Danish Ministry of Agriculture, the Finnish Academy, the Nornegian Agricultural Research Council, the Swedish Council for Forestry nnd Agricultural Research and the Oil-seed-rape Growers' Association of Southern Sweden. 80 R�sum� Un projet nordique sur la moucbe du chou et la mouche du radis (1991-1994) Un projet impliquant des chercheurs de tous les pays de la Scandinavie a debute en 1991 sous les auspices du Nordic Joint Committee for Agricultural Research. Le but est de promouvoir, de coordonner et d'integrer les activites de recherche ayant pour objet de reduire !'utilisation des insecticides synthetiques dans les cultures legumieres de Brassica. Le projet se concentre sur la lutte contre la mouche du chou (Delia radicum) et la mouche du radis (Deliafloralis). La recherche couvre differentes approches d'une lutte contre ces dipteres compatibles avec l'environnement, avec des points forts dans les differents pays. Plusieurs aspects seront integres au fur et a mesure de l'avance du projet. Les approches traitees peuvent �tre classees comme suit: prevision, avertissement et seuils economiques, dosages reduits d'insecticides/insecticides "alternatifs"; techniques culturales alternatives;resistance des plantes aux dega.ts d'insectes; organismes auxiliaires. 1991 fut la premiere saison de recherche dans le cadre de ce groupe. Toutefois, plusieurs chercheurs affiliesavaient deja conduit des investigations preliminaires pendant une ou deuxsaisons. Certains de ces travaux sont egalement rapportes dans ce bulletin. References Ahlstrom-Olsson, M. & Jonasson, T. {1992). Mustard meal mulch (Sinapis alba) - a possible cultural agent for attracting natural enemies of brassica rootflies_ (Deliafloralis and D. radicum). This bulletin. Bromand, B. (1988). Three years experience of using a warning system to predict the times of attack by the cabbage root fly (Delia radicum). Bulletin SROP/WPRS 1988 XI/ 1: 77-88. El Titi, A (1980). A contribution towards the •economic threshold· of Hylemia bra.ssicae. BulletinSROP /WPRS 1980 III/1: 35-42. Halld6rsson, G. (1989). The Cabbage Root Fly and its Control. (In Icelandic). RALA Report no. 134: 65 pp. Hokkanen, H.M.T. (1991). Trap cropping in pest management. Annu. Rev. Entomol 36: 119-138. Johansen, TJ. & Hals, A (1990). The biology of Delia radicum L. and D. jloralis Fallen (Diptera: Anthomyiidae) in northern Norway. (In Norwegian, English summary). Norsk landbruksforskning 4: 337-350. Johnsen, S.; Guterierrez, AP. & Freuler, J. (1990). The within season population dynamics of the cabbage root fly (Delia radicum [L.]). A simulation model. Mitt. Schweiz. Ent. Ges. 63: 451-463. Langer, V. (1992). The use of white clover living mulch as a control method of cabbage root fly (Delia radicum) in white cabbage. This bulletin. Taksdal, G. (1992). Some aspects of the biology of brassica root flies in relation to IPM in south-west Norway. This bulletin. Theunissen, J.; Booij, CJ.H.; Schelling, G. & Noorlander, J. (1992). Intercropping white cabbage with clovers. This bulletin. IOBC/WPRS-WorkingGroyp Meeting "IntegratedControl in Field Vegetables".Vienna 28-30Oct 1991 81 Temperature and soil moisture • two major factors affecting Agrotis segetum Schiff. (Lep., Noctuidae) populations and their damage P. Esbjerg Section for Zoolog;, Royal Veterinaryand Agricultural University, Bulowsvej 13, DK-1870 Frederiksberg C, Denmark Summary- Several times this century, damage by Agrotissegetum has been great in many countries throughout NW Europe. The common factor appeared to be the weather, with cutworm damage being high in dry hot summers. Earlier literature suggested that lack of precipitation helped cutworms to survive. During the late 1970s, this explanation was changed and was replaced by a model in which cutworm survival was negatively related to the number of rainy days (and amount of rain) during (May) + June + July and related positively to high July temperature. Investigations have been carried out during the last 10 years to determine how such a mechanism could be operating. The most important finding of this investigation was that Li and Li were extremely sensitive not only to high soil moisture but also to lmv temper&ures. 1nese abiotic factorsacting on Li and Lz appear to be the key factors regula.ting cutworm populations. The practical importance is these finding are now being used commercially. The work implies that biological/ecological details may be vital and should not always be discarded in favour of simple spray thresholds. Introduction Major outbreaks of Agrotissegetum have occurred in Denmark and other part,; of NW Europe several times this century. The most notable outbreaks were recorded in 1917, 1934, 1959 and 1976, when attacks by larvae (cutworms) of A. segetum reached severe levels. The catastrophic attack of 1917 was described from Germany (Kleine, 1919, Muller & Molz, 1919) and Denmark (Statens Plantepat. Fors0g, 1917) and, as a consequence of this attack, investigations on the biology of A. segetum were started in Germany (Herold, 1919, 1920, 1923). The 1934 outbreak was described from Denmark (Bovien & Stapel, 1935) and was also reflected in renewed investigations on the biology of A. segetum in Germany (Fiedler, 1936). Twenty-five years later, in 1959, severe attacks were again widespread in Denmark (Statens Plantepat. Fors0g, 1959, Thygesen, 1968). Similar attacks were also reported from the late GDR (Noll, 1961). In 1976, following widespread attacks in 1975, there was, according to the many reports (Statens Plantepat. Fors0g, 1976; Zethner, 1977; Ramson et al, 1977; Schmidt, 1977; Criiger, 1978; Hulbert & Siiss, 1983), what is likely to be the most 82 severe A. segetum attack of the 19th century. Weather and cutworm attacks The common factor for the four outbreak years and several locally similar situations(e.g. Estonia(Zolk, 1930)) was that the summers were extremely warm and dry. As early as 1935, Bovien and Stapel (1935) concluded from their limited knowledge that "lack of precipitation during May and June was reason for severe cutworm attacks". Thygesen (1968) came to the same conclusion based on records collected over the following 32 years. However, Zethner & Esbjerg (1978) arrived at a differentconclusion. After analysis of 70 years of insect records(Stapel, 1977; cf. Fig. lA) and the monthly weather records for the comparable periods, Zethner & Esbjerg (1978) concluded that excess precipitation in May + June + July lowers the risk of cutworm attack. Their main support for their conclusions is shown in Fig. lB. This conclusion was supported further by Mikkelsen and Esbjerg (1981), who, by using a linear regression model, were able to explain 64% of the variation in attack that occurred over the 70 year period ( cf. Fig. lA). Among eight parameters, the most important ones that correlated, either positively ( +) or negatively (-), with .the amount of cutworm damage were 1) the level of damage in the previous year( +); 2) the temperature in July ( + ); 3) the number of days of precipitation in June(-); and 4) the number of days of precipitation in July(-). PrCW = 8.61 + 0.35*CWL + 0.42*T7 - 0.02*P234-0.04*P5-0.31*PD6-0.24*PD7 - 0.06*PD8- O.OI*PIIL � 2 CD ID ... N 0 1960 Fig 1A: Levels of cutworm attack estimated between 1906-76 by Stapel (!977); and between 1977-79 by Mikkelsen & Esbjerg (1981). The linear regression derived from the same data by Mikkelsen & Esbjerg (1981) is shown above the baT �hart. PrCW = level of predicted cutworm attack. The numericai sum.x in the variable nam.es refer to the month in the year of observation. TI,for example, is the mean temperature for July, and P234 is the total precipitation (mm) during February, March and April. L refers to the preceding year. PllL is the precipitation in November last year, and CWL is the cutworm attack last year. 83 N _____..__, ______._, __ ___.1.._1 ____--l- ,_ ,--1 I X X X I o_ 1E 1E - 10 "'" 1 X X 1+ - I tU iE 10 X X X X I z I I I X X X X X X X N_ I XXX * :oocx X - X X X - X X • lOC X X I 0------..___1 __ -I- I ,--I ---rI -,------I 50 100 150 200 250 Total precipitation (mm) for May + June + July Fig. lH: The reiationship, estimated by Stapel (1977), between precipitation in May+June+Ju!y and cuiY1orn:attack. (Modified after Zethner& Esbjerg.1n8). Ecological details Themost recent ecological information has allowed a relatively crude cutworm forecast to be issued. This forecast is based on a combination of sex trap catches and weather conditions (Esbjerg & Zethner, 1980). However, the detailed understanding of the abiotic factors regulating A. segetum populations is weak. Hence, more specific information is needed to develop the forecast to the state where it will'be abk. to predict accurately as well the request/non request for control as the best time to apply control treatments. The following describe briefly a series of investigations on the influence of soil moisture and temperature on A. segetum. Such information will form .!Il integral part of the final forecast. I) Soil mo!sture as mortaU!y facto'° According to t.l).e literature, cutworms in the Ll (larval instar 1) and 12 stage remain on the foliage of plants (Bovien & Stapel, 1935; Thygesen, 1968) and hence can be washed down onto the soil and drowned by rain. Similarly, A. segetum eggs were considered to be extremely robust in Denmark whereas Hiilbert and Suss {1983), referring to the work of Herold (1919), claimed that humid conditions caused high egg mortality. The following three aspects of larval survivalhave been studied (Esbjerg et al., 1986): 84 A) Relative humidity. Larvae were not killedby either high (100% and 85%) or low (45% and 25%) relative humidities. B) Artificial (lysimeter) rain showers each of 15 mm. No differences was found between 1-5 showers. However, far more cutworms survived on sandy than on clay soil. C) Soil moisture: 1) partly caged L1 - IA cutworms in medium-size pots; and on 2) L1 and U cutworms caged around the canopy of single carrots in small pots (Fig. 2) were highly sensitive; particularly the youngest larvae, to soil moisture. In this situation, 50% of the larvae died over a 10-14 day period in the moist soil compared to 23% when the soil was dry (cf. Fig. 2). The behaviour of L1 and U cutworms was studied using the same set up (Fig. 2) as that used in the previous experiment. The results showed that when the soil is dry, young cutworms spend most of the day in the upper 2-3 mm of the soil and move to the foliage of the crop for 2-3 brief feeding periods. However, when the soil is moist, the young cutworms remain on the foliage throughout the day. When this occurs, both feeding frequency and development rate are reduced, and cutworm mortality is increased (Esbjerg, 1988). I A 8 Fig. 2: Experimental design used to investigate the influence of soil moisture on Li and L2 cutworms (Esbjerg etal., 1986). A = "Pot design": Th� vertical lines illustrate caging by a plastic cylinder. B = "Honey cup design": C = cap with ventilation game, D = Honey cup, E = sandy soil around carrot, F = paraffin wax which prevents water transportbetween the sandy soil a11d the soil in the pot below the paraffin wax. 85 A further experiment, in which cutworms were among carrots growing into buckets confirmed that moist soil is a major mortality factor, particularly to young cutworms. Furthermore, root damage by larger cutworms was reduced when the soil was wet (Esbjerg, 1990). There was �.lso an indication that mortality increased at low temperatures (14°C). No humidity related mortality effects could be demonstrated for the egg stage. The overall egg mortality was 14% (Esbjerg, in prep.). II) Temperature effedi: on development rate and mortality rate It was assumed that high temperature would increase development rate and hence allow young cutworms to pass the moisture (precipitation) sensitive (Ll and U) part of the life-cycle more rapidly (Mikkelsen & Esbjerg, 1981). Mortality directly due to temperature was thought to occur only at extremely high and low temperatures. However, lower root damage than forecast in 1984 and 1985 (Esbjerg, unpublished) lead to a more thorough investigation of the effect of temperature on cutworm mortality. The influence of temperature was studied in two ways: A) Data for a large scale set-up, involving 11 experiments at temperatures ranging from 12° to 35°C as shown in Table 1. Time until death, time to pupation, weight of pupae, and moth emergence were recorded individually for all insects. B) In a smaller and more detailed set-up, the individual duration of egg development (from oviposition to hatching), and the de•,elopment of larval instars 1-3 were recorded and the days on which individual insects died were noted. The development rate of A. segetum is temperature dependent (Fig. 3; Esbjerg & Johnsen, in prep.). The shape of the temperature-related mortality curve (Fig. 4) also indicates that mortality of A. segetum is temperature dependent and age specific. Particularly important is the high sensitivity of the L1 and U stages to low temperatures (12°-15°C) (Esbjerg & Johnsen, in prep.). In contrast, large larvae and pupae are sensitive only to high temperature. In addition, there was no temperature dependent mortality of eggs at temperatures 15° and 28°C (Esbjerg, in prep.). The mean pre-oviposition period, the mean oviposition period and the mean egg production per female have. also been determined for the model, but only at 20"C (Esbjerg, in prep.). The results obtained above have been summarized according to their position in the life-cycle of A. segetum. Factors important to the field situation, such as trapping moths and deciding when to apply insecticide treatments, are also mentioned to illustrate the overall knowledge required to produce an accurate forecast. 86 Table 1: Temperature combinations employed in 11 experiments on developmental time and mortality or Agrotissegetwn larvae. In brackets after the exp-number is shown the number or larvae in that particularexperiment ° ° ° ° ° ° Exp/temp. 12 15 17" 20 25 28" 33 35 . , < = - r. . :::.!-�- • �·---- - ....�.,�� .... 1 (150) * * * 2 (150) * 0 * 3 (150) * • * 4 (150) * * * 5 (375) • * • 6 (400) * $ • 7 (400) • * 8 (500) • • • 9 (250) • • • 10 (250) • • • 11 (375) • • • • Sex trapping ror rorecasting Sex ratio 1 : 1 (Esbjerg, unpublished data from 10 years of collecting and rearing the insects in the laboratory). Only 80% of the females are productive (Esbjerg, in prep.) - Pre-oviposition period = 3.7 days, oviposition period = 5.7 days (Esbjerg, in prep.). Mean egg number per female = 400 (SD 385) (Esbjerg, in prep.). Compared to 800 (Thygesen, 1968) and 1000 (J0rgensen, 1984). Mean egg mortality = 14% (Esbjerg, in prep.). L1 and 12 growth rates depend on temperature. According to Esbjerg & Johnsen (in prep.), growth rates in Denmark differfrom those recorded by Hiilbert & Siiss (1983). L1 and 12 mortality rates depend on soil moisture (Esbjerg et aL, 1986) Treatment L3 - L6 growth rate and mortality rates depend on temperature (Esbjerg & Johnsen, in prep.). L3 - L6 mortality rates, and crop damage, depend on soil moisture and temperature (Esbjerg, 1990). 87 Damage Pupal development rates and mortality rates depend on temperature (Esbjerg & Johnsen, in prep.). To obtain a greater understanding of the population dynamics of A. segetum, information is still needed on the factors governing:- Winter mortality (partly known from Hansen (in prep.). Diapause and the emergence of moths from the overwintering phase (under investigation by Johnsen & Esbjerg). 0.04 l ,., l / 0.03 ...... ,,... 0.02 1ij c.. Q) E a.. 0 1i5 0.01 0.00 s 10 15 20 25 30 Temperature °C Fig. 3: The rate oi'development of Agrotissegetum for all larval instars (soHd line), and for 1st instar larvae (dashed line). Concluding Remarks The above results indicate that temperature and soil moisture during Ll-12 stages are the key factors regulating cutworm survival. This has important practical consequences. Furthermore, as sufficient informationhas now been obtained for compuier modelling of the overall system (Johnsen, this bulletin), it should be possible to simulate future changes in cutworm populations and the associated 88 variations in crop damage. Detailed research on the basic biology of pest insects is an essential part of accurate pest forecasting systems. It is important to emphasize this point as the growinginterest in 1PM has led to the unfortunate belief that simple pest thresholds based directly on counts, samples or catches of insects - can be used to make accurate decisions concerning pest control. Only in a limited number of cases is there likely to be a direct (linear) relationship between trap catches of adult insects and subsequent crop damage. The sources of variation in pest growth rates and mortalities described in this project illustrate clearly the dangers, both from a scientific and a practical viewpoint, of relying to a heavily on using simple insect counts as the basis for deciding whether or not insecticides should be applied to field vegetable crops. 80% Percentage larval m<>rtality so% 40% 20% L---�------ Temperature °C Fig. 4: The influence of temperature on the mortalityof all larval instars of Agrotis segetum Acknowledgements This research has been supported financially by the Danish Council for Veterinary and Agricultural Research and by the HoffmannsgaveFoundation. 89 R�sum� La tem�.-atu.re et l'humidit� du sol - deux racteurs majeurs inffuen�ant les populations d'.Agrotissegetum et leurs d�Ats Durant ce si�cle, Agrotis segetum a provoque a plusieurs reprises de grosdegAts dans plusieurs pays du nord-ouest de l'Europe. Les conditions meteorologiques sont apparues comme etant le facteur de relation directe avec des degAts de vers gris importants durant les etes sees et chauds. La litterature ancienne suggere que le manque de precipitations aide les vers gris a survivre. Pendant la findes annees 1970, cette explication a ete modifiee et remplacee par un modele dans lequel la survie des chenilles est correlee negativement avec le nombre de jours de precipitations (et l'intensite de celles-ci) pendant les mois de (mai) + juin + juillet, et positivement avec des temperatures elevees au mois de juillet. Des investigations ont ete menees durant les dix dernieres annees, afin de determiner comment un tel mecanisme pourrait operer. Le resultat le plus important est que les larves des stades Li et Li se sont montrees extremement sensibles non seulement a l'humidite elevee du sol, mais egalement aux basses temperatures. Ces facteurs abiotiques agissant sur les jeunes stades larvaires se revelent etre les facteurs-cles de regula'tion des populations de vers gris. L'importance pratique de ces resultats est attestee par leur utilisation commerciale actuelle. Le travail demontre que des details biologiques/ecologiques peuvent etre vitaux et ne devraient pas etre systematiquement ecartes en faveur de simples seuils d'intervention. References Bovien, P. & Stapel, C. (1935). Knopormeangrebet 1934. DanishJ. Plant & Soil Sci., 40: 599-621. Criiger, G. (1978). Beobachtungen zum starken Erdraupenauftreten (Agrotis spp.) im Jahre 1976. Nachrichtenbl. Dtsch. Pjlanzenschutzd. 30: 17-19. Esbjerg, P. & Zethner, 0. (1980). Knopormevarsling baseret p.i registrering af vejrlig og p.ifangst af agerugler (Agrotis segetum) i feromonfrelder. Proc. Nordisk Plantevremskonf. 5-1 marts 1980. Esbjerg, P., Nielsen, J.K., Philipsen, H., Zethner, 0. & 0g.ird, L (1986). Soil moisture as mortality factor for cutworms,Agrotis segetum Schiff. (Lep., Noctuidae). J. Appl. Ent. 102: 277-287. Esbjerg, P. (1988). Behaviour of lst-2nd instar rutworms (Agrotis segetum Schiff., Lep., Noctuidae) - the influence of soil moisture. J. Appl. Ent. 105: 295-302. Esbjerg, P. (1989). The influence of soil moisture on mortality and on the damaging effect of 2nd to 6th instar cutworms (Agrotis segetum Schiff, Lep.: Noctuidae). Acta OEcologica. OEcol. Applic. 10: 335-347. Fiedler, R (1936). Die wichtigsten schadlichen Erdraupen der Gattung Agrotis (Lep., Noct.). Dtsch. Ent. Ztschr.: 113-179. Herold, W. (1919). Zur kenntnis von Agrotis segetum Schiff. (Saateule ). I. Das Ei und die jugendliche Larve. Ztschr. angew. Ent. 5: 47-60. Herold, W. (1920). Zur kenntnis vonAgrotissegetum Schiff. (Saateule). II. Die heranwachsende Raupe. Ztschr. angew. Ent. 6: 302-329. Herold, W. (1923). Zur kenntnis von Agrotis segetum Schiff. (Saateule). m. Feinde 90 und krankheiten. Ztschr. angew. Ent. 9: 306-332. Hiilbert, D. & Suss, A (1983). Biologic und wirtschaftliche Bedeutung der Winter Saateule, Scotia (Agrotis) segetum Schiffermiiller. Beitr. Ent., Berlin. 33(2): 383- 438. Johnsen, S. (ibid.). Agespecific, temperature dependent mortalityin Agrotis segetum. An explanatorymodel. J0rgensen, J. (1984). Landbrugszoologi. DSR, K(Jbenhavn, 1984: 1-238. Kleine, R. (1919). Die Wintersaateule Agrotis segetum und ihre Bedeutung als landwirtschaftlicherSchiidling. Ztschr. angew. Ent. 6: 247-269. Mikkelsen, S. & Esbjerg, P. (1981). Theinfluence of climatic factors on cutworm (Agrotis segetum) attack level, investigated by means of linear regression models. DanishJ. Plant & Soil Sci. 85: 291-301. Muller, M.C. & Molz, E. (1917). Beobachtungen iiber das Auftreten der Erdraupen der Saateule (Agrotis segetum) im Jahre 1917. Ztschr. angew. Ent. 5: 43-46. Noll, J. (1961). Uber die Ursachen der Massenvermehrung der Erdraupen der Wintersaateule (A. segetum Schiff.). NachrichtenbL Dtsch. Pjlanzenscutzzd. 15: 253-291. Ramson, A., Erfurth, P. & Herold, H. (1977). Das Auftreten der wichtigsten Schaderreger in der Pflanzenproduktion der DDR im Jahre 1976 mit schlussfolgerungen fiir die weitere Arbeit im Pflanzenschutz. NachrichtenbL Pjlanzenschutz DDR 31: 65-84. Schmidt, J. (Im). Spezielle Pflanzenschutzprobleme 1976. Rhein. Monatsschr. Gemuse, Obst, Schnittblumen 65: 53-54. Stapel, C. (1977). Den 0konomiske betydning af plantesygdommenes og skadedyrenes bekrempelse i landbruget. Ugeskr.f. agron. hort. & lie. U2: 735- 746. Statens PlantepatologiskeFors0g. (1917}. Mfuiedsoversigter over plantesygdomme 1917. Statens Plantepatologiske Fors0g. (1934). Mfuiedsoversigter over plantesygdomme 1934. Statens PlantepatologiskeFors0g. (1976). Mfuiedsoversigterover plantesygdomme 1976. Thygesen, T. (1968). Iagttagelser over biologiensamt resultater af bekrempelsesfors0g 1959-1966. Danish l Plant& Soil Sci. 71: 429-443. Zethner, 0. (1977). Losses caused by cutworms (Agrotis segetum Schiff.) and approaches to their control in Denmark. Proc. British Crop Prot. Conf.,Pests & diseases.: 271-277. Zethner, 0. & Esbjerg, P. (1978). Cutworm attacks in relation to rainfall and temperature during 70 years. KlimatologiskeMeddr . .4: 103-108. Zalk, K (1930). Die Wintersaateule (Agrotis segetum Schiff.) und ihre Bekiimpfung. Tartu OlikooliEntomoloogia-Katsejaama Teadaanded 10: 1-49. IOBC/WPRS-Working GroypMeet ing "IntegratedControl inField Vegetab)es".Vienna. 28-30 Oct 1991 91 Age-specific, temperature-dependent mortality in Agrotis segetam: an explanatory model S.Johnsen Section of Zoology, Royal Veterinaryand Agricultural University, Bulowsvej13, DK-1870 Frederiksberg C, Denmark Summary Within the framework of the age-specific, time-varying life table approach, temperature dependent mortality of A. segetum larvae was modelled as a submodel, coupled to a phenological model. Laboratory data collected by P. Esbjerg presented at this meeting, showed that the younger larval stages suffered larger mortalities at lower temperatures (in the range of 12-20"C), and the older larvae at higher temperatures (25-33°C). This agrees with the finding that the lower threshold for development of the younger larvae is higher ( about 11° C) that that for older larvae (about 7°C). Survivorship in the submodel is assumed to be a function of the temperature dependent net intake of food. Net intake is modelled to be an upward bellshaped function of temperature, which arises as a result of a functional response model increasing with temperat.ire to level offat an optimum, and respiration cost function increasing exponentially with temperature. The submodel operates with two such functions; one for younger and one for older larvae, with optima at 28°C and 20"C respectively. Daily mm1ality rates are modelled as linear functions of daily net intake. In accordance with laboratory observations, a delay is incorporated between the action of the mortality and the actual death of the larvae. This delay is short at very low net intakes and longer when food intake is higher. Applied as an attrition function in a distributed delay phenological model, this submodel reproduces laboratory data very well. The submodel is part of a larger modelling system forthe field population dynamics of A. segetum, currrently being developed by the author in collaboration with P. Esbjerg. Resume L'influence de Page specilique et de la temperature sur la mcrtalitd! chez.Agrotis segetum: un mod�fa explicatii En considerant l'age specifique et le temps dans le cadre d'une approche de table de survie, la monalite d'Agrotis segetum dependant de la temperature a ete fommleeen sousmodele combine a un modele phenologique. Des donnees rle laboratoire rec-.i.eillies par P. Esbjerg et presentees lors de cette reunion mcntrent que les jeunes stades larvaires subissaient de plus grandes mortalites a des temperatures inferieures (cntre 12-20°C) et les stades plus ages a des temperatures superieures (entre 25-33°C). Ceci est en accord avec les 92 observations prouvant que le seuil inferieur de developpement des jeunes larves (environ l1°C) est plus eleve que celui des larves iigees (environ 7°C). Le taux de survie dans le sousmodele semble etre une fonction de !'absorption nette de nourriture, elle-meme dependante de la temperature. L'absorptionnette, en modelisation, prend la forme d'une courbe de Gauss en "cloche renversee", qui est fonction de la temperature; le tout resulte d'un morlele de reponse fonctionnelle augmentant avec la temperature et atteignant un niveau optimal, ainsi que d'une fonction des depenses respiratoires augmentant de maniere exponentielle avec la temperature. Le sousmodele opere avec deux de ces fonctions, l'une pour les jeunes larves et l'autre pour les stades plus ages avec les optima a 28°C et 20"C respectivement. Les taux de mortalite joumaliere sont modelises comme fonctions lineaires de !'absorption joumaliere nette. Conformement aux observations en laboratoire, un delai entre !'action de la mortalite et la mort effective des larves est incorpore au modele. Ce delai est court quand !'absorption nette est tres faible, et s'allonge quand celle-ci est plus elevee. Applique sous forme d'une fonction a taux instantane de perte (attrition) dans un modele phenologique a delai reparti (distributed delay model), ce sous modele reproduit assezfidelement les donnees rlu laboratoire. II fait partie d'un systeme de modelisation plus etendu pour la dyna.mique de populations naturelles d'A. segetum actuellement en cours de developpement par l'auteur en collaboration avec P. Esbjerg. IOBC/WPRS-Workin,gGroup Meeting "Integrated Control in FieldVegetables". Vienna, 28-30Oct 191}1 93 Sources of resistance in brassicas to cabbage root fly P.R. Ellis Horticulture Research Intemationril, Wellesboume, Warwick; CV35 9EF, UK. Summary Progress is reported on the identification of sources of resistance to cabbage root fly,Delia radicum. . Field and laboratory studies at Wellesbourne have shown that low levels of resistance to cabbage root fly exist in all crops studied, while moderate resistance has been discovered in some glossy cabbage and glossy cauliflower lines. The growing of partially-resistant varieties improved insecticide performance when compared with chemical treatments applied to susceptible varieties. Introduction The cabbage root fly,Delia radicum L., is a serious threat to brassica crops, despite routine treatments with a range of insecticides. Hence, there is an urgent requirement for alternative control measures. The use of pest-resistant varieties of brassicas offers a long-lasting and en�ironmentally-acceptable method of reducing cabbage root fly damage. The literature on this subject has been reviewed in several publications (Ellis & Hardman. 1975; Ellis, Hardman, Crisp & Johnson, 1976; Hardman & Ellis, 1978; Ellis, 1988). Host plant resistance to cabbage root fly is currently under investigation at Wellesbourne, England; Dundee, Scotland (Birch, 1988); Switzerland (Freuler, Gagnebin & Strasser, 1990); and the United States of America (M. Dickson, personal communi�ation). This paper describes the results of recent studies at Wellesboume. Resistance in individual brasska crnps 1. Cabbage, Brassica oleracea L. var. capitata (L.) Alep. At Wellesboume cabbage varieties were tested in a series of experiments over eight seasons. In each experiment cabbage plants were raised in 4.3 cm3 peat blocks in trays in a cool glasshouse. Prior to transplanting the plants were hardened off in frames. The cabbage plants were transplanted in rows 60 cm apart and 45 cm within the row in randomised block experiments. Maggot damage to roots was assessed by lifting plants, shakingthem free of soil and assigning them to one of four grades, according to the severity of attack ( clean, slight, moderate and severe damage). Using this data it was possible to calculate a root damage grade, the % undamaged and the % slightly damaged roots, all three assessments being internationally recognised by members of the IOBC Working Group on 'Integrated Control in Field Vegetable Crops' (Thompson, 1980). The results of five years experiments are shown in Table 1 which lists a sample 94 of the varieties tested on each occasion. Certain red cabbage varieties were less damaged than others but were not sufficiently promising to warrant selection for breeding programmes, confirming findings of earlier workers (Matthewman & Lyall, 1966; Prokopy, Collier & Finch, 1983). In 1984, cabbage lines bred for their resistance to caterpillar attack were received from Dr M. Dickson, New York State Agricultural Experiment Station, Geneva, New York, USA and tested against cabbage root fly. Two of these lines (NY 10127 and 10128) were less damaged than any of the other material included in experiments in the years, 1984-1988 (Table 1). Seed from the least damaged plants of the promising lines were saved for use in future experiments. Unfortunately, both are glossy cabbages and will require considerable improvement if they are to be developed into commercially-acceptable varieties. in 1985, two cabbage varieties one susceptible ('Resistant Danish') and one partially-resistant ('Red Drumhead') to cabbage root fly were compared in plots which were either untreated or treated with granules of chlorfenvinphos (Birlane 10% a.i., Shell Chemicals UK Ltd.). The results (Table 2) showed that there was a complementaryeffect of combining host plant resistance with insecticide, 96% of 'Red Drumhead' plants compared with 89% of 'Resistant Danish' plants remaining free of attack followingtreatment. Table 1: Cabbage root fly attack expressed as a mean damage grade (1 = no attack llri> to 4 = all plants severely damaged) on cabbage varieties and breeding lines at Wellesbourne Varietyor Year breeding line 1981 1983 1984 1986 1988 (5)<•> (50) (12) (8) (12) NY 10127 - - 1.9 2.5 25 NY 10128 - - 2.0 2.8 - Couve Pence de Pavoa - - - - 2.9 'Red Drumhead' 2.7 1.8 2.8 2.7 2.9 'Super Red' - 23 23 2.8 3.1 'Yates Giant Red' 2.4 1.6 - - - 'Late Purple Flat Poll' 2.3 2.2 2.9 - - 'Golden Acre Progress' 2.9 2.4 2.6 3.3 3.1 'Super Green' - - 3.0 2.9 - 'Late Flat Dutch' - 2.4 2.9 - - 'Gourmet YR' - 2.4 25 3.0 2.9 Number of plants 5 10 40 50 40 per replicate <•> Total number of varieties in experiment 95 Table 2: Complementary effects or partial resistance and insecticide in controlling cabbage root fly on cabbage at Wellesboume in 1985 (mean of 40 plants per treatment) % of roots in each category 'Resistant Danish' 'Red Drumhead' Cabbage root fly grade (susceptible) (partially-resistant) Untreated + Insecticide Untreated + Insecticide 1 Undamaged 0.2 89.3 7.1 95.6 2 Slight damage 343 10.7 57.7 4.4 3&4 Moderate & 65.5 0 35.5 0 severe 2. Cauliflower.Bras.sica oleracea L var. botrytis L There are numerous reports in the literature of cauliflower varieties being tested against cabbage root fly but no resistance was discovered prior to 1970 (Ellis, Hardman. Crisp & Gray, 1985). in 1978, Freuler investigated cabbage root fly attack on 34 cauliflower varieties in Switzerland and although he demonstrated that there was great variation within varieties he could not identify any highly resistant varieties. In subsequent work, he studied antixenosis (non-preference) resistance in cauliflower and made selections fromfield experiments involving a range of varieties. Selection and testing has continued in alternate years and has produced breeding lines with higher levels of resistance than the parental materif'J (Freuler. Gagnebin &Strasser. 1990). At Wellesbourne cauliflower varieties have been evaluated for resistance to cabbage root fly using similar techniques to those described earlier for cabbage. Experiments on 12 varieties of cauliflower in 1972 & 1973 demonstrated significant differences in their attractiveness for egg-laying. Resistance appeared to be related to the vigour of the root system. Five generations of breeding for enhanced resistance in the Flora Blanca variety 'Asmer Hylite' did not produce material with levels of resistance higher than that of the parental variety. Four of the selections from this variety were compared with a highly susceptible variety ('Finney's 110') at Wellesbourne in 1983. ftJthough there were differences in root damage indices and root weights, they were not sufficient to warrant further breeding (Table 3). In 1977, 173 cauliflower varieties were evaluated for their resistance to cabbage root fly in the fieldat Wellesboume. There were significantdifferences between and within cauliflower groups. the two least damaged groups being of the Roscoff and Le Cerf types. Several generations of breeding showed that recombinants possessed greater resistance than either parent. However, selection did not lead to further improvements in resistance (Ellis et al, 1985). One of the varieties. 'All Year Round', which was least damaged in 1977 was grown alongside a highly susceptible variety 'Erfort Matra RS' in plots which were either untreated or treated �th a recommended dose of granular chlorfenvinphos insecticide (Birlane 96 10% a.i., Shell Chemicals UK Ltd.). This experiment showed that there were complementary affects of combining partial plant resistance with insecticide, the chemical being more effective in protecting partially-resistant than highly susceptible plants (Table 4). T2ble 3: Comparison of cabbage root fly attack on 5 cauliflowerlines at Wellesbourne in 1983 (mean or five 10-plant p!ots per treatment) Llne Number of eggs Root damage Dryroot weight per 10-plant plot index (g) A 864 41.9 2.59 B 673 52.5 2.48 C 902 47.3 2.70 D 1071 47.3 2.54 'Finney's 110' 1174 74.6 2.13 LS.D. (P = 0.05) N.S. 11.5 0.18 Table 4: Compiememaryeffects or partial resistance and insecticide in rontrolling cabbage root fly on cauliflower at Wellesbourne in 1985 (mean or 40 plants per treatment) % of roots in each category 'Erfurt Matra RS' 'All Year Round' Cabbage root flygrade (susceptible) (partially-resistant) Untreated + Insecticide Untreated + Insecticide 1 Undamaged 1 63 14 90 2 Slight damage 43 32 62 9 3&4 Moderate & 56 5 24 1 severe In more recent work, several cauliflower lines bred for their resistance to caterpillar attack by Dr M. Dickson, Geneva, USA, were tested against cabbageroot flyat Wellesboume in 1984, 1987 and 1988. Two of these breeding lines, G 9120 and G 7802, were as resistant as 'All Year Round' in 1987 and 1988 (Table 5). Both lines are glossy cauliflowers and will require considerable improvement, if they are to be bred into commercially-acceptable varieties. 97 3. Brusselssprouts. Brassica oleracea L var. gemmifera Zenk. Eight varieties of Brussels sprouts were tested against cabbage rootfly in the field at Wellesbourne in 1971 and a further 12 varieties in 1972. Although none of the varieties possessed promising levels of resistance, the least preferred and least damaged plants fromeach variety were selected and seeded. Subsequent work indicated that the progeny had not responded to selection. Six accessions were tested in a glasshouse experiment in 1976, in which plants were inoculated with root flyeggs produced in a laboratory culture (Finch & Coaker, 1969). All accessions were damaged. Table 5: Cabbage root Dy damage, expressed as a mean damage grade (l = ao attack up to 4 = all plants severely damaged), on cauliffowervarieties and breeding lines at Wellesboume Varietyor Year breeding line 1984 (12)<•> 1987 (5) 1988 (11) G 9120 2.2 1.2 2.6 G7802 2.9 1.2 2.9 'Asmer Hylite' 2.4 - - 'All Year Round' - 2.2 2.9 'White Rock' - 2.0 - 'Perfection' - 2.2 3.1 Number of plants 40 40 40 per replicate C•> Number of varieties tested r . Brassica oleracea L var. italica Plenck. 4. Calab ese, sproutinr,broccoli At Wellesboume in 1982. 1� calabrese accessions. representing a wide range of genetic material, were grown at different spacings in the field. Consistent resuits were obtained and two HRI breeding lines (Numbers 61 & 62), as well as 'Hybrid Gem·, were less damaged than the rest. However, none of the calabrese accessions was sufficiently resistant to warrant further study. 5. .Ilu:nm,Brassica campestris L Ten different turnip varieties were evaluated in the field over several seasons in Finland. The variety'Zwaans Brabo' was consistently less damaged than the rest, but was noi considered sufficiently resistant to make a significant contribution to 98 cabbage root fly control (Varis, 1958). Turnips have not been tested at Wellesboume. 6. � or rutabagaBrassica napus L Recently interest has focused on swede varieties, bred for resistance to Delia flora/is Fallen, in countries where both species of root fly severely damage swede crops. Field trials in two years showed that the varieties 'Angus' and 'Melfort' possessed antixenosis resistance. In one experiment, cabbage root flies laid 34 times more eggs on the susceptible variety 'Sator Otofte' than on 'Angus' (Birch, 1988). These results have also been confirmed at Wellesboume (Ellis, unpublished). Further investigations are in progress. 7. � Brassica oleracea L var. acephala DC. Four lines of kale bred for different isothiocyanate content at the Institute for Grassland and AnimalProduction, Aberystwyth, Wales, were tested against cabbage root fly at Wellesboume in 1974. The kale line possessing the highest concentration of isothiocyanates was least preferred, possibly because the level was so high as to be repellent. In contrast, the egg-laying preferences of the other three lines was positively correlated with isothiocyanate content. In 1981, the variety 'Tall Green Curled' was grown alongside cabbage varieties in the field at Wellesboume. This kale variety was significantly less damaged than any cabbage variety tested at Wellesboume. 8. .wildBrassica species Few workers have evaluated wild Brassica species for their resistance to cabbage root fly. Theliterature on screening wild crucifers was reviewed by Nair, McEwen & Alex (1973) but none of the plants tested in early work included Brassica species. In a study of the potential host plants of this pest Finch & Ackley (1977) included two wild Brassica species, B. juncea (L) Czem. and B. nigra (L.) Koch, which supported few cabbage root flies when young plants were inoculated with eggs. These results suggest that a search for resistance among wild species may be worthwhile. Prospects for the future The aim of this work is to exploit sources of resistance to reduce the grower's dependence on chemical control of cabbage root fly. However, the market will not accept lower standards arising out of crop blemishes. Therefore, it is no use increasing levels of resistance at the expense of quality or yield. Ideally, high levels of resistance are required in crops where the marketed part of the plant can be damaged by the insect. This includes such crops as swede, turnip,radish and the buttons of Brussels sprouts. In most leaf and flower brassica crops, where cabbage 99 root flydamages the root system, the plants can tolerate certain levels of attack without crop quality being affected. In such crops, partial resistance may be valuable. The results discussed in this paper indicate that high levels of resistance to cabbage root fly have not yet been found in any commercially-acceptable -horticultural brassicas. Two wild Brassica species supported few root flies in laboratory experiments (Finch & Ackley, 1977) and this evidence suggests that additional species should be examined forsources of resistance. With this in mind, a range of wild Brassica species has now been collected at Wellesboume. It is hoped that transferring genes for resistance from such distant relatives to cultivated lines of crop plants will be simplified following recent advances in genetic engineering. Moderately high levels of resistance to cabbage root fly exist in glossy breeding lines of cabbage and cauliflower; and in certain varieties of kale. However, considerable work is needed to determine how best to utilise this resistance in horticultural brassica crops. Although partial resistance to cabbage root fly exists in all types of cultivated brassica crops, resistance alone is not sufficient to provide control even in leaf brassica crops. The experiments at Wellesboume, where partial resistance hasbeen combined with insecticides, have revealed that higher levels of protection are possible where such combinations are used. It would be worthwhile evaluating most commercially-acceptable horticultural brassicas for their resistance status, so that the concentration of routine insecticide applications could be adapted to cater for the inherent plant resistance. In this way existing varieties of brassicas could be used more effectively. Resume Soul!'ces de resist1mces chez les Brassica l l'egard de ia mouche du choii La resistance de Brassica a. l'attaque de la mouche du chou est en etude a Wellesboume, faisant partie d'un programme destine a reduire la dependance des producteurs al!X insecticides. La recherche a pour but d'identifier les sources de resistance chez les Brassica et d'exploiter cette resistance dans des programmes integres de Jutte contre la mouche du chou. Des essais ont montrc que plusieurs facteurs. tels la couleur, l'age et la taille, le stade phenologique de la plante et meme le degre de colonisation par des rnicroorganismes de cette derniere influencent le niveau de resistance. 11 existe a l'interieur du pool genetique des Brassica une grande variatbn dans la reaction a l'attaque de la mouche du chou. 11 est ainsi possible de classer les differentes cultures de Brassica dans l'ordre d'une tolerance croissante a l'attaque. Une resistance partielh a ete de,::ouverte chez diverses varietes et ligneesde cbou pomme, chou-fieur et rutabaga. Elle a ete confirmee durant ';}lusieurs saisons et dans differents pays. Les n.iveaux de resistance ont ete ameliores par des programmes de selection. Toutefois, les tentatives d'utiliser la resistance chez le chou-fle1.1r pour completer des traitements insecticides ont produit des resultats variables. Lesperspectives d'identification de sources supplementaires de resistance pour la selection de Brassica montrant de hauts niveaux de resistance et les possibilites d'exploitation de ces sources dans des-programmes de protection integere contre la 100 mouche du chou sont discutees. References Birch, AN.E. (1988). Field and glasshouse studies on components of resistance to root fly attack in swedes. Annals of Applied Biology 113: 89-100. Ellis, P.R. (1988). Investigations of resistance in vegetable crops to root-feeding dipterous pests. Acta Horticulturae 219: 31-37. Ellis, P.R. & Hardman, JA (1975). Laboratory methods for studying non-preference resistance to cabbage root fly in cruciferous crops. Annals of Applied Biology 79: 253-364. Ellis, P.R., Hardman, JA, Crisp, P. & Gray, AR. (1985). Investigations of resistance in cauliflowers to cabbage root fly attack. Proceedings of the 'Better Brassicas 84' Conference, St Andrews, pp. 202-206. Ellis, P.R., Hardman, J.A, Crisp, P. & Johnson, AG. (1976). Laboratory studies of non-preference resistance to cabbage root fly in radish. Annals of Applied Biology 84: 81-89. Finch, S. & Ackley, C.M. (1977). Cultivated and wild host plants supporting popuations of the cabbage root fly. Annals of Applied Biology 85: 13-22. Finch, S. & Coaker, T.H. (1969). A method for the continuous rearing of the cabbage root flyErioischia brassicae (Bouche) and some observationson its biology. Bulletin of EntomologicalResearch 58, 619-627. Freuler, J. (1978). Glasshousestudies of the effectsof cabbage root fly larvae,Delia brassicae (Hoffm.) (Dipt. Anthomyiidae) on cauliflower varieties. Z-eitschriftfur Angewandte Entomologie 85: 98-105. Freuler, J., Gagnebin, F. & Strasser, R. (1990). Current studies on resistance to cabbage root fly (Delia radicum)in caulilfower. In: Breeding for Resistanceto Insects andMites. IOBC/WPRSBulletin 1990 XIU/6, pp. 4-12 Hardman, JA & Ellis, P.R. (1978). Host plant factors influencing the susceptibility of cruciferous crops to cabbage root fly attack. Entomologia experimentaliset applicata 24: 393-397. Matthewman, W.G. & Lyall, LH. (1966). Resistance in cabbage to the cabbage maggot. Hylemya brassicae (Bouche). Canadian Entomologist 98: 59-69. Nair, K.S.S., McEwen, F.L & Alex, J.F. (1973). Oviposition and development of Hylemya brassicae (Bouche) (Diptera: Anthomyiidae) on cruciferous weeds. Proceedings of the EntomologicalSociety of Ontario 104: 11-15. Prokopy, RJ., Collier, R.H. & Finch, S. (1983). Leaf color used by cabbage root flies to distinguish among host plants. Science 221: 190-192. Thompson, AR. (1980). The assessment of damage caused to cruciferous crops by larvae of Hylemya brassicae in soil. !n: IOBC/WPRS Bulletin 1980/UI/1, p. 19- 26. Varis, A-L, (1958). On the susceptibility of the different varieties of big-leafed turnip to damage caused by cabbage maggots (Hylemyia spp.). Journalof ScientificAgriculture Society of Finland 30: 271-275. IOBC/WPRS-WorkingGroup Meeting "IntegratedControl in FieldVegetables". Vienna. 28-30Oct 1991 101 The use of a living mulch of white clover on the controi of the cabbage root fly (Delia radicum) in white cabbage V. Langer Section of Zoology, Royal Veterinary and Agricultural University Bulowsvej 13, DK-1870 Frederiksberg C, Denmark Summary Earlier studies of the influence of living mulch/intercrops on cabbage root fly (CRF) behaviour showed that intercrops reduced the number of CRF eggs, larvae and pupae recovered from crops and also reduced crop damage. In most cases, the reduction in CRF numbers and damage were accompanied by large reductions in yield, which resulted from the competition between the intercrop and the cruciferous crop plants. In this experiment, strips of white clover (var. "Kent") were used as the intercrop between rows of transplanted (1990) or sown (1991) autumn white cabbage (var. "Olympiade"). Treatments were clean cultivation, spring-sown clover, and clover established in the previous August. The clover was kept low by mowing it 4-6 times during the growing season. No herbicides or other pesticides were used. In both seasons, the fall-sown clover proved too competitive foruse in commercial production. Hence the remaining results are concerned solely with the effects of the spring-sown clover. The numbers of eggs recovered from the clover plots on two sites in 1990 and on one site in 1991 were 55%, 70% and 43% lower, respectively, than those recovered from the clean plots. Similarly, pupal numbers were reduced by about 72% in the clover plots. Pupal parasitism was about 45% on one site in 1990, and ranged from 37-58% on the other site. Parasitism was highest by Aleochara (30-34%) in the clean plots and by Trybliographa in the clover plots. Thelower numbers of eggs recovered from the plots is probably a direct result of the stressed smaller cabbage plants growing in the intercrop being less preferred by the adult flies. Egg counts on newly-transplanted similar-sized plants showed less pronounced differences between clean and clover plots. In 1990, the total yield of cabbage in the spring-sown clover was only 33% of that in the clean plots. However, due to high levels of CRF damage in the heads of the cabbage harvested fromthe clean plots, only 53% of the heads were marketable. Therefore, the yield of marketable heads in the clover plots was 59% of that in the clean plots. In 1991, CRF damage did not occur in the heads of the cabbage. Consequently, the total head yield and yield of marketable heads in the clover intercrops were only 40% of those recorded from the clean plots. The results from two years show that, although this method lowers the numbers of pest insects in the crop, it also has a potentially detrimental effect on yield. The method will only be attractive to growers provided ways can be foundof growing the cabbage crop so that it shows no apparent signs of stress, or loss of vigour, from competing with the clover intercrop. 102 Resume L'utilisation d'une couverture vegetate de trefle blanc pour la luUe contre la mouche du chou (Deliaradicum) sur chou blanc De preredents essais sur !'influence d'une couverture vegetate intercalaire sur le comportement de la mouche du chou (CRF) ont montre une reduction du nombre d'oeufs, de larves et de pupes de CRF echantillonnes dans la culture, ainsi que des degllts sur celle-ci. Dans la plupart des cas, la reduction du nombre de CRF et de degllts allait de pair avec de fortes diminutions de la recolte par l'effet de competition entre culture intercalaire et culture de cruciferes. Dans cet essai, des bandes de trefle blanc (var. "Kent") ont servi de culture intercalaire entre des lignes de chou blanc d'autornne (var. "Olyrnpiade") plante (1990) ou seme en place (1991). Les variantes comprenaient: temoin sans trefle, trefle seme au printemps et trefle installe en aout de l'annee precedente. Le trefle a ete maintenu basen le fauchant 4 a 6 fois pendant la saison de croissance. Aucun herbicide ni autre pesticide n'a ete applique. Durant les deux saisons d'essais, le trefle seme en fin d'ete s'est avere trop competitifen culture commerciale. Pour cette raison, seuls les resultats concemant l'effet du trefle seme au printemps sont rapportes ici. Le nombre d'oeufs retrouve dans les variantes a trefle, dans deux sites en 1990 et dans un site en 1991, a ete inferieur de 55%, 70% et 43% respectivement, par rapport aux temoins. De mame le nombre de pupes a diminue d'environ 72% dans les variantes "trefle". Le parasitisme des pupes etait d'environ45% a un emplacement en 1990 et variait de 37%-58% a l'autre emplacement. Aleochara etait le parasite le plus actif avec un taux de parasitisme de 30-34% dans les variantes "temoin", alors que Trybliographa dominait dans les procedes avec trefle. La plus faible quantite d'oeufs retrouves dans ces parcelles resulte sans doute de la baisse d'attractivite exercee sur la mouche adulte par des choux en "stress", de petite taille. Le decompte d'oeufs sur de jeunes plants fraichement transplantes et de mame taille montre des differences moins prononrees entre les temoins et les procedes avec trefle. En 1990, la recolte totale de choux dans la variante "trefle"n'atteignait que 33% de celle du temoin. Toutefois, en raison du niveau eleve d'attaque de CRF, seules 53% des tates recoltees dans le temoin etaient commercialisables. De ce fait, la recolte commercialisable de la variante "trefle" atteignait 59% de celle du temoin. En 1991, aucune attaque de CRF dans les tates de choux n'a eu lieu; en consequence, la recolte totale et la recolte commercialisable des parcelles en trefle ne representaient que 40% de celle des parcelles "temoin". Ainsi que les resultats de ces deux annees le montrent, la technique de couverture intercalaire reduit le nombre d'insectes ravageurs dans la culture, mais elle peut avoir un effet prejudiciable sur le rendement. Elle ne deviendra attractive pour les cultivateurs que dans la mesure ou il sera possible d'assurer la croissance des choux sans signes de "stress" ou de baisse de vigueur imputables a la competition avec la culture intercalaire de trefle. IOBC/WPRS-WorkingGroup Meeting "Integrated Control in Field Vegetables".Vienna. 28-30Oct 1991 103 !nterc:ropping white cabbage with clover J. Theunissen, C.J.H. Booij, G. Schelling & J. Noorlander Research Institutefor Plant Protection (/PO), PO Box 9060, 6700 GW Wageningen, TheNetherlands Summary Intercropping fresh-market white cabbage with white clover (Trifoliwnre pens) or subterranean clover (Trifolium subterraneum)reduced considerably many pest insect populations. Reductions were found in larval cabbage moth (Mamestra brassicae) numbers and their feeding damage; in oviposition and subsequent damage by cabbage root fly (Delia radicum); and in infestation of harvested cabbage heads by thrips (Thrips tabaci). No differences were found in infestation of cabbage heads by cabbage gall midge (Contarinia nasturtii) or flea beetles (Phyllotreta spp.). More aphid parasitiods, carabid and staphylinid ground beetles, and spiders, were recorded from the clover intercropped plots than from the monocropped plots. Significant differences were found between the treatments in crop yield, crop quality and in the economic value of the final produce. Introduction lntercropping and mixed cropping are used widely in the tropics. Reductions in pest numbers resulting fromintercropping have been reported by several authors (Perrin, 1977; Theunissen & den Ouden, 1980; Kenny & Chapman, 1988, Tingey & Lamont, 1988). Similar reductions have been reported also from mixed cropping systems, where two, or more, main crops were planted in the same field (Satpathy et al, 1977; van Rheenen et al., 1981; Tukahirwa & Coaker, 1982; Uvah & Coaker, 1984; Martin et al, 1989; Bach & Tabashnik, 1990). Adoption of such systems in the temperate zone, with its large area of arable and intensive field vegetable crops, requires methods which not only fit into the exii;ting cropping patterns but which also provide a distinct advantage to the grower. At present, many constraints limit the use of intercropping on a large scale. However, the decreas-:: in etfectiveness of certain pesticides coupled with the increased public and political pressure to limit the use of pesticides are considerable incentives to find new methods of control based on applying less pesticide. Once suitable methods have been four..d, it wiil be necessary to develop methods acceptable to commercial growers and suitable for use on a large scale. This paper described how intercropping white cabbage with two species of clover affected pest-insect populations, numbers of parasitoids and predators of crop pests, and the final yields of cabbage crops. 104 Material and Methods Material The main crop was fresh market white cabbage cv. Minicole. Tw� species of clover were used as the intercrop: Trifolium repens cv. Pertina and Trifolium subte"aneum cv. Geraldton. The clover seeds were mixed with appropriate strains of Rhizobium bacteria, and were drilled by machine on 25 March. The amounts of clover seed used were 10 kg/ha of T. repens and 20 kg/ha T. subte"aneum. The cabbage plants were transplanted into the clover intercrops during 1-4 May. The cabbage plants were spaced 0.5 m apart within the row and 0.75 m apart between the rows. Emergence of T. repens seedlings was slow and patchy but eventually the clover formed a dense, green carpet which grew as high as the cabbage plants. In contrast, an even stand of T. subte"aneum emerged within 10-14 days. The young plants of this clover can withstand frost. They grew only half as tall as the T. repens plants. During the experiment, the T. subte"aneum intercrop matured and died, leaving behind a 1-2 cm deep mulch of brown stems which covered the soil. Plants that germinated from the seeds shed by the mature crop emerged before the end of theexperiment to form a new intercrop of yellowish-green clover. Methods The experi..ment was carried out in 1990 and repeated in exactly the same way in 1991. As the results for both years were similar, only the 1991 results will be described in detail. The experimental design was a randomised block with three treatments(cabbage without clover(monocrop); cabbage intercropped with T. repens; cabbage intercropped with T. subte"aneum ), each replicated four times. Each square 2 plot was 571 m • No pesticide was used in the experiment. Fertilizer was applied at the rate of 1000 kg NPK 12-10-18/ha. This was achieved by applying 28.5 kg/plot directly after transplanting; applying an additional 14 kg/plot two weeks later; and a final application of 14 kg/plot on 21 June. The same amount of fertiliser was applied to each plot( applied per individual plant to minimize fertilizer influence). The crop was harvested on 20 August. Thefrequency of sampling and the data collected were as follows: 1) Each week 20 plants/plot were sampled at random to record numbers of eggs, eggmasses, and small caterpillars( < 13), large caterpillars( > 13) and pupae of Mamestra brassicae, Pierisrapae, Plutella xylostella and Plusia gamma. Pieris brassicae was not considered as it was rare in the experimental area. Similarly, the experiment was carried out at the time of year (March-August) when Evergestisforficalis occurs only in low numbers, so this species also was not recorded. 2) Cabbage aphid infestations were estimated on the same 20 plants in each plot. The plants sampled were classified as: 1 = clean(no aphids found), 2 = light (1-10 aphids/plant), 3 = medium (11-100 aphids/plant), and 4 = heavy(> 100 aphids/plant). 3) Samples were collected weekly of the soil from around the stems of 5 randomly selected plants/plot. Each sample was immersed individually in 105 water and the cabbage root fly (Delia radicum) eggs and pupae floated up after thorough stirring and were then counted and recorded. 4} Epigeic insects and spiders were trapped in 6 pitfall traps/plot. The tiapped insects were collected weekly, identified, and separated into the most important groups of predators. 5) Each week, marked plants were inspected to record when plants became infested with disease and bow rapidly the diseases spread. 6) The amount of feeding injury by caterpillars was recorded three weeks before harvest. All plants in all plots were scored according to the qualityand quantityof feeding injury. Three categories were used: a. no injury, b. economically-unimportant injuryand c. economically-important injury (damage). During the experiment, colleagues fromthe Center for Agro-Biological Research (CABO) made routine assessments of the growth of both the main crop and the clovers, of the weeds present in the intercrops, and of the competition between the main crop and the intercrops. These data are not discussed here. At harvest 25 cabbages/plot were harvested, using a pre-determined grid pattern that avoided the border rows of the plots. The weight and quality of each cabbage was recorded. The quality criteria used were those of commercial growers who sell their produce at die Dutch auction. In this system, quality classes 1 and 2 are marketable, but class 3 is not. The reason for non-marketability was recorded for all plants placed into class 3. For some blemishes, such as those caused by thrips and cabbage gall midge, removal of a number of leaves made class 3 cabbages marketable but at a much reduced price. The mean price at Dutch auctions for fresh-market white cabbage on the day thecrop was harvested was used to calculate the economic value of the yields from the various plots. Results In the monocrop plots, populations of M. brassicae larvae were larger than in the clovers plots (Fig. 1). During 1991, fewlepidopterous eggs were found and the populations of P. rapae, Plutellaxylostella and Plush!gamma were low. Also populations of Brevicoryne brassicae (the cabbage aphid) were low, but when aphids were found they tended to be in the monocrop. In general, the plants in the monocrop had more individuals of pest species than the intercrops, but the overall number of species was much lower. Clear differences occurred between the monocrop and the clovers with respect to the abundance of life. For example, a greater diversity of aphid parasitoids and more aphid parasitoids were found in the clover intercropped plots than in the monocropped plots. Similarly, more staphylinid ground beetles, carabid ground beetles and spiders were trapped in the clover plots. In 1990, more carabid beetles were caught in the clover plots, particularly during early summer (Fig. 2), and the two clovers had similar effects. In 1991, although the numbers of predators caught were much lower, their patterns of occurrence were similar to those recorded in 1990. In particular, carabid species of the genera Amara and Harpalus, and staphylinid species of the genus Philonthus, were favoured by the presence of clover. A more detailed analysis of the effects of the clover intercrop on 106 predators will be published elsewhere. Oviposition of the cabbage root fly (Delia radicum) was influenced considerably by the presence of the clovers. This phenomenon has been discussed elsewhere (Theunissen & Schelling, 1992). The assessment, three weeks before harvest, of feeding injury by caterpillars, indicated that economic damage would be much greater in the monocrop than in the clovers (Fig. 3). To test our sampling method, especially sample size, the accumulated number of caterpillars found up to that moment in each plot were regressed against the economically important feeding injury per plot. At harvest the weights of cabbages from the monocrop were higher than those from the clover plots. However, from the economic viewpoint, quality is all important. On the day of harvest (20 August), the mean price for class 1 and 2 cabbages was Dfl. 0.305/kg and for class 3 was Dfl. 0.137/kg. The harvest results are shown in Table 1. Table 1: Yield data and estimated value or harvested crops Plot type Percentage of Mean weight of Value of marketable marketable crop(a) cabbages cabbage (kg) (Dfl./ha) Monocrop 29 1.97 4,648 T. repen.s 72 1.63 9,570 T. subte"aneum 70 1.63 9,308 (a) including marketable class 3. From a crop protection point of view, the reasons why cabbages had to be rejected were extremely interesting. Three of the main reasons were cabbage maggot (Delia radicum) tunneling in the head; the presence on, and discolouring of, the head by thrips (Thrips tabaci); and feeding injury in the cabbage head by caterpillars. Non marketability due to these causes is shown in Fig. 3. Other reasons for rejection included the presence of cabbage aphids; feeding injury fromPhyllotreta spp.; and the presence or feeding symptoms of cabbage gall midge (Contarinia nasturtii). The last three factors were not important in our study. Similarly, there was no crop loss due to disease. 107 Mamestra brassicae small catarpillars number of cater illars 40 30 20 10 34 42 48 55 62 69 76 83 90 97 104 111 119 DAT (days after transplanting) - monocrop c:::J T. repens c::J T. subt. Mamestra brassicae large caterpillars number of cater lllars 35 30 25 20 15 34 42 48 55 62 69 76 83 90 97 104 111 119 DAT (days after transplanting) - monocrop C::J T. repens c::J T. sub!. Fig. 1: Mean numbers (4 replic2tes) of Mamestrabrossicae caterpillars recorded weekly during the gromng season in plots of monocroppet! cabbage and jn cabbage plots intercropped with the clovers. Trifolium repens and T. subtenwieum. The weekly records are shown as days afte.transplanting - DAT. 108 Discussion One of the ideas behind the introduction of intercropping is that diversity in the agro-ecosystem provides a more stable cropping situation in which the development of pest populations is reduced by natural antagonists. If suc.h a reduction can be realized within commercial crop growing, the use of pesticides can be minimized or eliminated. Way (1976) argued that the notion "diversity is stability" has a limited validity. Although this may be the case, it cannot be denied that many experiments with mixed cropping or intercropping have demonstrated useful reductions of pest populations in intercropped versus monocropped fields (Perrin, 1977; Altieri & Letourneau, 1982). Even in situations where a significant reduction in pest populations cannot be demonstrated, the effects in terms of yield and financial results show promises for use in 1PM and integrated production systems. However, not all results are easy to interpret. For example, the distribution of egg-masses and caterpillars of Mamestra in 1990 differed considerably from those in 1991. In 1990 a significantly higher oviposition of M. brassicae was observed in the monocrop, whereas in 1991 very few egg-masses were found at all. In contrast. although the larval populations did not differ between the clovers and the monocrop in 1990, they did (P = 0.05) in 1991 (Fig. 1). In both years, however, the yields were better in the plots in which the cabbages were intercropped with clover. Hence, seasonalvariability during the cropping period can obscure the effects of intercropping on pest populations. The assessment of caterpillar feeding injury and damage prior to harvest demonstrated the difference between the appearance of the plants in the field and real damage. Because no pesticides were used in this experiment, many plants showed signs of caterpillar feeding (monocrop: 42.3%, T. repens: 17.4%, T. subterraneum: 36.3%). From this total, however, only the following proportion were expected to cause loss of quality at harvest (monocrop: 17.6%, T. repens: 2.8%, T. subterraneum: 7.0%) (Fig. 2). The results obtained at this assessment. reflected accurately the actual resultsobtained three weeks later when the crop was harvested. Rejection because of caterpillar feeding occurred on 17%, 2% and 4% of the plants from the monocrop, T. repens, T. subterraneum plots, respectively. These data stress the importance of assessing field situations on real damage rather than merely on visual appearance. Fewer cabbages were rejected as non-marketable from the clover plots than from the monocrop plots. The economic advantage of this situation is shown in Table 1. Cabbages from the monocrop plots were generally larger and heavier, but less tightly packed, than cabbages from the clover plots. In addition the cabbages from the monocrop plots were often infested by pests, or showed severe symptoms, that lead to them being declassified. It is clear from Fig. 3 that scoring the reasons for rejection reflects the overall effects of intercropping on the various pest populations. The data suggest that the infestations by cabbage root fly were reduced by about 50%; that thrips populations were reduced considerably in the clover plots; and that caterpillar damage was reduced by about 80%. These findings are particularly important for the cabbage root fly and thrips as both pests are extremely difficult to control with insecticides late in the cropping season. Effects of intercropping clover on the oviposition of cabbage root fly have been described earlier (O'Donnell & Coaker, 1975; Ryan et al, 1980; Tukahirwa & Coaker, 1982). The effect of intercropping on thrips populations was surprising. even though Satpathy et al (1977) 109 had earlier described how intercropping reduced crop damage because the thrips fed mainly on the intercropped species. In the clover-cabbage case, however, it was clearly evident that the thrips populations were much larger in the monocrop plots and that damage was more extensive at harvest in such plots than in the intercropped plots. As the difference in quality attained from reducing thrips infestations saved the crop financially (see Fig. 4), this seems a convincing argument for using intercropping systems in sustainable horticulture. It is uncertain to what extent the increased numbers of insect antagonists in the intercropped plots contributed to the reduction of pest infestations. Most of the antagonsists are known to have a variable impact on the numbers of cabbage root fly, aphids and caterpillars. However, it is the seasonal abundance and the combined effects of the whole range of predators and parasitoids that is crucial in the overall suppression of pest insect populations. Since the intercropping effects on predator numbers were more apparent in early summer, the main effect of the predators will be to reduce the early build-up of pest populations. One major point of concern is whether the differences recorded in the current experimental plots will be maintained when int.ercropping is attempted on a large field scale. carabid beetles/ trap/ week 60 40 20 May June July Aug � monocrop �;;;,;?�;J T.subterraneum- T.repens Fig. 2: Seasonal changes in the numbers of carabid beetles caught in pitfall traps placed in cabbage monocrop and cabbage/dove, intercrop systems. The data are shown as numbers of beetles caught per trap, expressed as 3-weekly running means. 110 One obvious limitation of the present experiments is that the effects of intercropping on pest populations and crop yield have been made only in a "no pesticide" situation. To assess intercropping as a production system, the current system will have to be tested against insecticide-treated monocropped cabbages. Such a comparison should reveal whether intercropping can suppress pest populations to levels where less insecticide can be applied. The present paper demonstrates clearly the potential for reducing pest populations in fresh-marketwhite cabbage by intercropping with clovers. The development of methods for using intercropping in sustainable agriculture is the next step. percentage plants with feeding symptoms 50 40 30 20 10 0 monocrop T. repens T. subt. i) % injury ii) btmml % damage Fig. 3: Result of caterpillar feeding injury three weeks prior to harvest.· Plants with feeding symptoms were assigned to the following two categories. i) Plants with feeding symptoms (injury) that did not affect crop quality at harvest. This injury was noi: considered to be damage. ii) Plants in which caterpillar feeding did affect crop quality at harvest, and led to financial losses. This injury was considered to be damage. 111 mean no. rejected plants/sample 15 iO 5 monocrop T. repens T. subt. 11111 rootfly l�Uj thrips EEi[] cater- pillars Ffg. .f: Reasons for non-marketability or cabbage lieads (25 pfants/piot) at fiarvest. Themean number or plants rejected for three pests are shown foreach treatment. The differences in thrips infestation a:.1d damage between monocropped plants and plants intercropped with ciover are shown clearly in the results. Resume Culture mixte de trefle et de chou blanc Un essai a ete conduit en 1990 et 1991 pour evaluer les effets de la culture mixte sur des populations de ravageurs. Deux especes de trefle, Trifolium repens et T. subterraneum ont ete cultivees avec du chou blanc cv 'Minicole'. L'essai s'est deroule sur la meme parcelle experimentale durant les deux ans. Les parcelles elementaires mesuraient toutes 23 r.. 24 m. Chacune des trois variantes (chou blanc seul, avec T. repens, avec T. subterraneum) a ete repliquee quatre fois. Aucun pesticide n'a ete applique. Des observationssur les principaux ravageurs, notamment la noctuelle du chou (Mamestra brassicae), la petite pieride du chou (Pierisrapae), le puceron cendre du chou (Brevicoryne brassicae) et la mouche du chou (Deliaradicum) ont ete effectuees chaque semaine. De plus la pedofaune epigee a ete echantillonnee avec la meme frequence par 6 pieges pitfall par parcelle elementaire. 112 Les degats dus aux chenilles ont ete evalues pour chaque plante trois semaines avant la recolte et les tetes triees selon leur caractere comrnercialisable ou non. A la recolte, 25 plantes par parcelle, choisies a l'aide d'une "grille" d'echantillonnage ont ete pesees individuellement et leur qualite evaluee. Tous les choux places en classe 1 et 2 sont commercialisables. ll leur a ete attribue le prix moyen des mises hollandaises du jour de la recolte en 1990 et 1991, afin de faire intervenir le facteur economique dans nos resultats d'essais. Les choux, situes en classe 3, sont invendables. Les raisons de cette depreciation ont ete relevees en 1991, a la recolte. Durant la saison, des differences significatives entre les populations de ravageurs sur chou seul et sur chou avec trefle ont ete trouvees; cependant, il n'y en a pas eu entre les deux types de trefle. Meme si les poids des choux en monoculture sont legerement plus eleves qu'une polyculture, la difference qualitative occasionne un benefice financier significatif en faveur de la culture mixte. Apres analyse des causes de non-commercialisation, il s'avere que, significativement, un nombre plus eleve de plantesprovenant de la monoculture sont rejetees en raison des degats dus au thrips, a la mouche du chou et aux chenilles. Les populations de thrips sont nettement plus basses dans les parcelles en polyculture. Du faitde la difficulte de !utter chimiquement rontre les thrips ou une attaque tardive de la mouche du chou, la reduction des populations de ces deux ravageurs par la culture mixte revet un interet considerable. References Bach, C.E. & Tabashnik, B.E. (1990). Effects of non-host plant neighbours on population densities and parasitism rates of the Diamondback moth (Lepidoptera: Plutellidae). Environmental Entomology, 19: 987-994. Kenny, GJ. & Chapman, R.B. (1988). Effects of an intercrop on the insect pests, yields, and quality of cabbage. New Zealand Journal of Experimental Agriculture, 16: 67-72. Martin, R.C., Amason, J.T., Lambert, J.D.H., Isabelle, P., Voldeng, H.D. & Smith, D.L. (1989). Reduction of European cornborer (Lepidoptera: Pyralidae) damage by intercropping corn with soybean. Journal of Economic Entomology, 82: 1455-1459. O'Donnell, M.S. & Coaker, T.H. (1975). Potential of intracrop diversity for the control of brassica pests. Proceedings 8th British Insecticide Fungicide Conference, 1975: pp. 101-105. Perrin, R.M. (1977). Pest management in multiple cropping systems. Agro Ecosystems, 3: 93-118. Rheenen, HA van, Hasselbach, O.E. & Muigai, S.G.S. (1981). The effect of grov.,ing beans together with maize on the incidence of bean diseases and pests. NetherlandsJournal of Plant Pathology, 87: 193-199. Risch, SJ., Andow, D. & Altieri, M.A (1983). Agroecosystem diversityand pest control: data, tentative conclusions, and new research directions. Environmental Entomology U: 625-629. Ryan, J., Ryan, M.F. & McNaeidhe, F. (1980). The effect of interrow pant cover on populations of the cabbage root fly,Delia brassicae (Wiedemann). Journalof 113 Applied Ecology, 17: 31-40. Satpathy, J.M., Das, M.S. & Naik, K {1977). Effect of multiple and mixed cropping on the incidence of some important pests. Journal of Entomological Research, 1: 78-85. Theunissen, J. & den Ouden, H. (1980). Effects of intercropping with Spergula. arvensis on pests in Brussels sprouts. Entomologia experimentalis et applica.ta., 27: 260-268. Theunissen, J. & Schelling, G. (1992). Cabbage-clover intercropping: oviposition of Delia radicum. Proc. Exper. & Appl. Entomol. NetherlandsEntomological Society 3: 191-196. Tingey, W.M. & Lamont, W J. (1988). Insect abundance in field beans altered by intercropping. Bulletin of Entomological Research, 78: 527-535. Tukahirwa, E.M. & Coaker, T.H. (1982). Effect of mixed cropping on some insect pests of brassicas;reduced Brevico,yne brassicae infestationsand influences on epigeal predators and the disturbance of oviposition behaviour in Delia brassicae. Entomologia experimentalis et applicata, 32: 129-140. Way, MJ. (1976). Pest and disease status in mixed stands versus monocultural: the relevance of ecosystem stability. In: "Origins of pest, parasite, disease and weed problems", (J.M.Cherrett & G.R.Sagar, Eds.), Blackwell, Oxford, UK: 127-138. IOBC/WPRS-WorkingGroup Meeting "IntegratedControl in Field Vegetables".Vienna. 28-30Oct 1991 114 Simple control thresholds for foliage pests of leek M. Hom.mes Federal Biological Research Centre, Institutefor Plant Protection in Horticulture, Messeweg11-12, D-3000 Braunschweig, Germany Summary Thrips (Thripstabaci Lind.),leek moth (Acrolepiopsis assectellaZ.) and caterpillars of several species of noctuid moths are important foliage pests of leek (Allium porrum L) in Germany. Thrips tabaci is by far the most important pest. Infestation by this insect can cause severe losses in plant quality and considerable reductions in average plant weight. Experimentswith control thresholds forthrips (50% infested plants) and leek moth (5% infested plants),based simply on the presence/absence of the pests, gave highly effectivecontrol and involved only small amounts of insecticide. In contrast, spraying plants every two weeks, or when an extremely low threshold (1 % of plants infested by thrips or leek moth)was exceeded, used considerably more insecticide and failed to increase the proportion of marketable heads or their average weight. The tolerance levels describedabove should be regarded only asguides. Such thresholds have to be adjusted, forspecific situations such as those that occur when the market will accept only the highest quality produce or if the control treatment used by the groweris not the most effectivetreatment available. Introduction Supervised control, based on action thresholds or tolerance levels, is one of the major aspects of integrated pest management that could be introduced into practice relatively easily. In contrast, the development of non chemical methods of pest control, involving biological control agents or resistant varieties, will require extensive long-term development if they are ever to be introduced into practise. After the success of using supervised control to combat foliage pests of cabbage (Hom.mes et al, 1988; Forster et al, 1991), investigations have been started to develop a similar system for pests of leek. In Germany, leek is a major field vegetable crop and its cultivation is characterised by intensive spraying during the summer months to control infestations of thrips and leek moth. Materials and Meihods The investigations were carried out in the experimental fields of the Federal Biological Research Centre at Braunschweig, and at Hotzum, a locality 10 km south of Braunschweig. Leek plants, grown in a plant nursery, were transplanted into 115 25 m x 40 m experimental plots. Plants were spaced 20 cm apart within the row, and 62.5 cm apart between the rows. Toe pest sampling techniques that were used had been developed earlier for pests of cole crops (Hommes et al, 1988). At two-week intervals, subsamples of 5 leek plants were checked at each of 10 points distributed regularly over the plot. The heart and the leaves of each plant were inspected carefully for living thrips and for freshfeeding mines, or larvae, of the leek moth. Based only on presence/absence sampling, the number of plants infested by thrips or leek moth were recorded. The percentages of infested plants were recorded separately for thrips and leek moth and then compared with the threshold values. The tolerance levels tested in the field experimentsare listed in Table 1. Thelevels chosen were based on the experience gained fromseveral years of pest control studies on leek and cabbage. Crops were sprayed as soon as the observed infestation levels exceeded the tolerance levels. Sprays of deltamethrin (12.5 g a.i./ha) were applied in 1989 and 1990 and sprays of cypermethin (30 g a.i./ha) in 1991. Apart from the 1990 experiment at Braunschweig, in all other experiments spray threshold plots were compared both with unsprayed plots (no insecticide) and with intensively sprayed plots (Table 2). In the first two years, intensive spraying was equivalent to a routine spray every two weeks. In 1991, it wasequivalent to an insecticide spray whenever at least 1 % of the plants were infested. Table 1: Tolerance levels tested rox- ieek pests 25% and 50% plants infested by thrips (125% and T50%) 5% and 10% plants infested by leek moth (LS%and L10%) 1 % plants infested by thrips or leek moth (TL1%) At harvest, 100 plants from each treatment were checked individually for damage. In 1989 and 1990, damage by thrips was graded on a scale of 1 to 4 (in which 1 = clean, no damage; 2 = slight damage; 3 = moderate damage; 4 = severe damage). In 1991, an extended scale from 1 to 9 (1 = no damage ... 9 = very severe damage) was used to obtain more detailed information. Records were also taken of the number of ieaf blades and leaf stalks damaged by caterpillars. Plants were classified as not marketable if the damage grade for thrips was 3 or 4 in !989 and 1990, and 5 or above in 1991. All plants with obvious feeding damage by caterpillars were graded as unmarketable. 116 T&ble 2: Results of field experiments involving control thresholds for pests of leek Site % plants marketable showing No. Relative Year/Crop crop loss due to of yield Treatment sprays thrips leek-moth noctuids cutworms Bra111lli!.;hw,ig 1990/autumn leek untreated 33 48 56 87 - 100 thresholds T50/LM5% 97 100 99 100 2 116 1991/summer leek untreated 50 89 87 90 - 100 thresholds T25/I.M5% 100 100 100 100 4 104 intensive/TU% 100 100 100 100 5 110 Hotzum 1989/winter leek untreated 69 47 -- 100 thresholds T50/LM5% 100 96 - - 3 145 intensive/routine 100 100 - - 7 145 1990/winter leek untreated 55 67 100 100 - 100 thresholds T50/LM5% 100 100 100 100 2 122 intensive /routine 100 100 100 100 7 130 1991/autumn leek untreated 22 83 65 98 - 100 thresholds T25/LM5% 99 99 93 100 2 110 thresholds T50/LM10% 98 100 100 100 2 105 intensive/TU% 100 100 100 100 6 110 Mean (1989-1991) untreated 46 67 77 94 - 100 thresholds T50/LM5% 99 99 100 100 2 122 intensive 100 100 100 100 6 124 Results and Discussion In 1990, the percentage of plants infested by thrips and leek moth in the plots at Braunschweig and Hotzum are shown in Figs. 1 and 2. At both sites, only the thrips infestation exceeded the tolerance level. At both sites, two sprays were needed 117 to control this pest. Infestations of leek moth were low, probably a direct result of the two applications of deltamethrin. The insecticide sprays were highly effective against thrips, and were characterized by a steep decline in the numbers of plants infested by thrips during the two weeks following application. During the summer months, the effect of the sprays did not last as long. Four weeks after the first insecticide spray, the thrips population again exceeded the threshold value. Fig. 3 shows the infestation level recorded in 1991 in an early autumn crop of leeks at Braunschweig. As this crop was harvested at the end of August, during the main period of infestation by thrips, the tolerance level was reduced from 50% to 25% to ensure the leeks were of high quality. In the middle of June, the attack by leek moth exceeded the 5% tolerance level and an insecticide had to be applied. This was the only instance during the three years of the experiments, that a leek moth infestation exceeded the spray threshold. Usually, insecticide had to be applied only to control thrips. This indicated that the time of occurrence of other pests on leek corresponded with the insecticide application against thrips. As three sprays were required to control thrips during July and August, no larvae of the leek moth was found during this period. Thefirst treatment against thrips could have been avoided if the 50% tolerance level had been used. % plant� lnfeatad by thrlp0 by leek moth 100,...... ,.==--======cr-������-,25 90 80 20 70 60 15 SOIHHH'HHH 0 14.5 28.5 11.6 25.6 9.7 23.7 6.8 20.8 3.9 17.9 1.. 10 Fig. 1: Level of pest attack in threshold plot (Braunschweig, 1990) The situation at Hotzum in 1991 (Fig. 4) was similar to that of 1990. Two sprays during the main infestation period (middle of July - middle of September) were sufficient to give excellent control of thrips. No difference was found between the number of sprays required when the tolerance level was set at either 50% or 25% infested plants. This indicated that the tolerance level can be wide without increasing the risk of losses in yield. The probable explanation for this, is that large increases in 118 infestation levels (up to 100%) are required before thrips cause serious damage (Theunissen & Legutowska. 1991}. At this site, leek moth infestations remained below 5% throughout the season and hence have not been included in the Figure. % planta Infested by thrlps by le ..k moth 100 25 90 80 20 70 60 15 l+;i;1,a.,-. ,,;•;;;,;•,a.: 50 40 10 30 20 5 10 0 9.7 23.7 6.8 20.8 3.9 17.9 1.10 15.10 29.10 Fig.2: Level ot pl?st attack in threshold plot (Hotzum, 1990) ,c. plant• Infested by tlulpa by leek moth 100.....-������---,,...._...��---==,,..,,...... ,,,.....,,..,,...,,,.,,,...,,,.....,,,.."""'""�...,,,.....,,,.."""'""...,,,.,,,,..,..,25 *thrlpa 90 20 80 70 15 60 50 10 40 30 20 5 10 0 0 8.5 21.5 4.6 18.6 1.7 15.7 29.7 13.8 27.8 10.9 Fig. 3: Level of pest attack in threshold plot (Braunschweig, 1991) 119 The results of the five field experiments carried out from 1989 to 1991 are summarized in Table 2. From the proportion of marketable plants in the untreated plots, it is obvious that thrips was the main cause of crop loss. On average, more than 50% of the leek plants were unmarketable due to severe feeding symptoms on their leaves. Beside the considerable loss in quality, average plant weigh� were reduced by up to 45%. Such losses can be explained only by thrips attack. Decreases in yield due to thrips have been recorded previously for onions (Edelson et al, 1986; 1989). % plantc lnfeat.,d by thrlp• iOO,-,...,======�==..,.,,,,..====='=',,,.,.,,-,==,--������, 90 80 V Ina. appl. 25 '6 plot 70 60 EiO 40 30r+���"���;�;�.�s;,��-�•�.. 20 10 18.6 9.7 23.7 6.8 20.8 3.9 17.9 1.10 15.10 Fig. 4: Level of thrips attack in threshold plots (Hotzum, 1991) Attack by leek moth was another important source of crop loss. At harvest, about one third of the plants had distinct leek moth damage. This can be distinguished easily from the damage caused by noctuid caterpillars. The relative high damage fromcaterpillars was surprising. Feeding on the leaves averaged about 25%. Damage to the shaft below the soil surface, caused by cutworms, was recorded on up to 13% of the plants. Caterpillars of the following species were recorded in the field plots: Mamestra brassicae L., Autographagamma L, and Agrotissegetum D. No significant differences were obtained in the marketable yield of leeks from the intensiveiy sprayed plots and the threshold plots. While the intensively sprayed plots always gave 100% marketable plants, the values of the threshold plots were only marginally lower. These slight (1-2%) losses are acceptable to the farmer and are far outweighed by the considerable reduction in the number of insecticide sprays required. On average, four sprays could be saved by basing leek pest control on tolerance levels. The experiments have shown that simple control, or action, thresholds can be used to allow growers to apply less insecticide to control the main foliage pests of leek. The thresholds are easy to use and sufficiently reliable to ensure that the farmer obtains both high yields and good quality. In most cases, it is sufficient to concentrate only on attack by thrips, provided thrips infestations regularly 120 occur at high levels in the field, and insecticides are not used that kill only thrips. The present thresholds should be regarded only as guides. They have to be adjusted for specific situations such as those that occur when the market will accept only the highest quality produce or when the grower does not apply the most effective insecticide spray available. R�sum� Des seuils d'interventio!l simples pour les ravageurs a�riens du poireau Le thrips (Th.rips tabaci Llnd.), la teigne du poireau (Acrolepiopsisassectella Z.) et les chenilles de plusieurs especes de noctuelles sont des ravageurs importants du feuillage du poireau (Allium porrum L) en Allemagne. T. tabaci est de loin l'insecte le plus nuisible. Par ses infestations, il peut occasionner de graves pertes en diminuant la qualite et le poids moyen de la plante. Des essais sur des seuils d'intervention pour le thrips (50% de plantes attaquees) et pour la teigne du poireau (5% des plantes attaquees), bases simplement sur la presence ou !'absence des ravageurs, ont ete tres concluants tout en exigeant que peu d'insecticides. Par contre, en traitant toutes les deux semaines ou en appliquant un seuil tres bas (1 % de plantes infestees par le thrips ou la teigne du poireau) avec une utilisation considerable d'insecticides il n'a pas ete possible d'augmenterni la proportion de ruts commercialisables ni le poids moyen de la plante. Ces seuils de tolerance n'ont qu'une valeur indicative et doivent !tre ajustes aux situations particulieres prevalantes lorsque le marche n'accepte qu'une qualite de recolte tres elevee ou si le producteur n'applique pas,le- meilleur traitement disponible. References Edelson, J.V., Cartwright, B. & Royer, TA (1986). Distribution and impact of Thrips tabaci (Thysanoptera: Thripidae) on onion. L EcorL EntomoL 79: 502-505. Edelson, J.V., Cartwright, B. & Royer, TA (1989). Economics of controlling onion thrips (Thysanoptera: Thripidae) on onions with insecticides in South Texas. L &orL EntomoL 82: 561-564. Forster, R., Hildenhagen, R. & Hammes, M. (1991). Bekampfung von Kohlschadlingen nach Bekampfungsschwellen. Deutscher Gartenbau 45: 564- 566. Hommes, M., Dunne, R., Ellis, P.R., Fischer, S., Freuler, J., Kahrer, A & Terratez, C. (1988). Testing damage threshold for caterpillars and aphids on cabbage in five European countries - Report on a collaborative project done in 1985 and 1986. WPRSBulletin 1988/XI/1, 118-121. Theunissen,J. & Legutowska, H. (1991). Thrips tabaci Llndemann (Thysanoptera, thripidae) in leek: symptoms, distribution and population estimates. L Appl Ent. 112: 163-170. IOBC/WPRS-WorkingGroup Meeting "IntegratedControl in FjeldVegetables•. Vienna. 28-30Oct 1991 121 Guidelines and scouting methods in integrated production of field vegetable crops; the situation in Switzedand J. Freuler Station Federale deRecherches Agronomiques de Chan.gins, CH-1260Nyon, Switzerland Summary Approximately three years ago, a working group was started within the Swiss Vegetable Union to set up guidelines for integrated production (IP); in the first instance to consider field vegetables and later to consider glasshouse crops. This working group includes not only representatives from cantonal, federal and commercial vegetable organisations but also growers, advisors and researchers. !nitially, a catalogue was made of the requirements for each component of integrated production. Such components included crop rotation, fertiliser requirements, soil tillage, cropping techniques, plant protection strategies and the optimum metllods for harvesting and storing the crops. The catalogue was used to produce the guidelines concerning the requirements acceptable at present, future requirements, and the methods available to achieve such requirements. For example, in the section on plant protection, there is information on spraying equipment, on the use and handling of pesticides and on pest, disease and weed control. The guidelines are now being tested on about 15 pilot farms, in a range of different vegetable growing areas. This work is being carried out to determine the acceptability of the requirements and to accumulate more data. The aim is to demonstrate the effectiveness of such systems rather than to do furtherexperimental work. At present, no financial compensation is given to growers who adopt the guidelines. Nevertheless the office for the coordination of Integrated Production, within the Ministry of Agriculture, has started a national project to determine how much more labour is used in integrated farming systems than in traditional farming systems. At the same time, groups of growers from several regions have introduced "integrated production" techniques on at least some of their fields. These growers are assisted by advisors, who in some regions are subsidised by cantonal and federal funds. Simple experimentation takes place and the information gained is spread rapidly between the members of the group. Recommendations have been produced in the form of working sheets for most crop situations as the growers may find the guidelines too general and therefore difficult to follow. These recommendations still require further validation. Specific regional practices is sometimes allowed if the proposed recommendation proves difficult to implement. 122 The final goal is to award a national label to growers who satisfy the requirements laid down for integrated vegetable production. To do this, a grower has to be member of a regional IP organisation, has to satisfy the minimum requirements of the guidelines and has to keep a diary of his farm practices and an up-to-date summary of his crop working sheets. This labelling by regulation will come into force in 1993. Thestatutory body will be the National Label Commission, which will both supervise the admission of growers into the scheme and the subsequent inspection of all farms. The new system will be involved in the IP scheme funded by professionalorganisations, by the cantonal and federal governments, by commerce, and by a levy for the label. The Ministry of Agriculture seeks to promote IP by increasing the price of the products from such farms, by paying compensation for lower yields or higher inputs, by generating contracts for specific products, by supporting pilot farms and by regulating imports and exports. To satisfy present and future requirements in plant protection, simple scouting methods are required to determine the best time to apply sprays and whether or not sprays should be applied (action thresholds). A second edition of a French publication describing the progress made in entomological scouting methods has been published recently (Freuler & Fischer, 1991a) and a German version is also available (Freuler & Fischer, 1991b). For the carrot rust fly,Psila rosae, the vertical double-sided yellow stickytrap 229 is still in use, but for practical reasons we also recommend traps inclined at 45° to the vertical with the stickysurface facing downwards, as described by Finch & Collier (1989). Results of a co-operative experiment on the efficiency of the two traps showed that both traps caught similar numbers of flies except in the Rhone valley, where at some locations the double-sided trap caught more flies than the inclined trap. More data are needed on the best position for the inclined trap. Tolerance thresholds, based on cumulated captures of carrot rust fly, valid only for the region around Yverdon, had to be adapted for other growing regions. They were adapted according to the meteorological conditions and in particular to soil surface temperature, an important egg mortality factor (Overbeck, 1978). When compared to the theoretical egg survival rate from Yverdon, acting as reference, egg survival in Geneva in 1990 and in the southern part of Switzerland, in the canton of Tessin during 1991 was much higher. The spray thresholds therefore have been lowered in the localities around Geneva and in the canton of Tessin. The time to start scouting cruciferous crops in the spring to look for caterpillars and the cabbage aphid, Brevicorynebrassicae L, is indicated by pheromone trap catches of the cabbage moth, Mamestra brassicae L The trap consists of a water trap designed by Bues (pers. comm.). Crop scouting starts two weeks after the first cabbage mqth is caught. The efficacy of the cabbage moth trap is improved considerably if the water in the traps is maintained at a constant level by means of a reservoir (Fig. 1, Table 1 ). To carry out supervised control of the above pests, we employ first event sampling (Berchtold & Freuler, 1988). In this method, all parts of the field are inspected, written observations are kept to a minimum and, as attack increases, less time is required to arrive at the appropriate decision. 123 1.3m 1cm H Fig. 1: Phe;:omone water trap fo;:the cabbage moth, Mamestrabrassicae L. The Bues-trap (pers. comm.) wi.h an s.dditiona! reservoir of water. 124 Table 1: Comparison or th� efficacy of the pheromone water trap for the cabbage moth, Mamestrabrassicae L. without and with an additional water reservoir Numbers of cabbage moth caught Date (1991) Trap without reservoir Trap with reservoir 29 July 25 29 5 August 33 49 9 August 23 17 16 August 33 34 23 August 42 97 26 August 24 39 2 September 36 74 9 September 21 57 16 September 1 2 23 September 0 2 Total 238 400 R�sum� Dii'ective:. et m�thodes de surveillance des ravageurs de ple!ne tene ea production m&raicMre int�gr&; la situation helvit!tlque Des directives pour la production integree en culture maraichere de pleine terre ont ete elaborees en se basant sur des exigences minimales pour chaque element oomposant: sol, rotation des �ltures, fertilisation, travail du sol, techniques culturales, protection des piantes, recolte, conservation. Elles sont testees sur des domaines pilotes, et des groupes regionaux de producteurs interesses sont etablis. Le reglement qui regit l'attribution d'un label national est en voie d'!tre signe par l'Union Suisse du Legume. n est propose des ameliorations concemant les methodes de surveillance de la mouche de la carotte, Psi/a rosae, (plaquettes engluees et grille des seuils de tolerance), de la noctuelle du chou, Mamestra brassicae, (piege a pheromone a eau) et des ravageurs aeriens des cultures de cruciferes, c'est-a-dire les chenilles diverses et le puceron cendre du chou, Brevicoryne brassicae, (methode d'echantillonnage du premier evenement). References Berchtold, W. & Freuler, J. (1988). First even sampling. A new technique for estimating insect attack, using the onion miner fly,Liriomyza nietzkei, as test insect. Entomol exp. appl 49, 251-257. Finch, S. & Collier, R.H. (1989). Effects of the angle of inclination of traps on the numbers of large Diptera caught on sticky boards in certain vegetable crops. 125 EntomoL exp. appL 52, 23-27. Freuler, J. & Fischer, S. (1991a). Methodes de controle et utilisation des seuils de tolerance pour les ravageurs des cultures maraicheres de pleine term. 'ie edition. Revue suisse Vitic. Arbortic. Hortic. 23(2), 101-124. Freuler, J & Fischer, S. (1991b). Kontrollmethoden und Anwendung von Schadenschwellen fiir die Schadlinge im Freilandgemiisebau. Landwirtschaft Schweiz 4(7), 341-364. Overbeck, H. (1978). Untersuchungen zum Eiablage- und Befallsverhalten der Mohrenfliege,Psila rosae F. (Diptera: Psilidae), im Hinblick auf eine modifizierte chemische Bekampfung. Mitt. Biol Bundesanst. Land- u. Forstwirtsch. Berlin-Dahlem, 183, 1-145. IOBC/WPRS-WorkingGroup Meeting 'IntegratedControl in Field Vegetables', Vienna. 28-30Oct 1991 126 Supervised control of lepidopterous pests in white cabbage R. Forster & M. Hommes Federal Biological Research Centre, Institutefor Plant Protectionin Horticulture, Messeweg11/12, 3300 Braunschweig, Gennany Summary During 1987 to 1991 a system of supervised control was tested, improved, and established officially for use in German cole crops. This paper describes investigations on the occurrence, dispersal and damage by lepidopterous pests in white cabbage crops. During the test period, the percentage of plants infested by the three key species were: 71% for Plutella xylostella (Lepidoptera: Plutellidae), 45% for Pieris rapae (Lepidoptera: Pieridae) and 40% for Mamestra brassicae (Lepidoptera: Noctuidae). The test plants were infested less frequently, by Autographa gamma(Lepidoptera: Noctuidae) [16% ], Evergestisforficalis (Lepidoptera: Pyralidae) [6%] and Pieris brassicae (Lepidoptera: Pieridae) [2%]. P. rapae (52%), P. xylostella (26%) and M. brassicae (20%) accounted for 98% of the damage that occurred on head leaves. These three species were dominantin all regions. In late cabbage they were most damaging from the beginning of heading until harvest. Losses in untreated plots from minor blemishes were more important than losses in crop weight (up to 39% and 5%, respectively). All three species caused damage of economic importance. Specific differences, especially those concerned with the sites of feeding and amount of leaf area lost, were also obvious. The results again confirm that, although differentthresholds have to be used for the different growth stages of the plant, the pest species involved do not have to be identified. The thresholds, based on the simple presence/absence of caterpillars on 50 plants (heart; head leaves and 6 upper leaves) per field,proved reliable. This improved procedure reduced the amount of insecticide applied by 65% compared to the spray regime applied routinely to white cabbage crop. In addition, it is less time consuming than the former supervised control procedure and also has economical and ecological benefits. Introduction Between 1987 and 1990, various action thresholds against caterpillars and cabbage aphid were tested at 95 locations and on more than 150 ha in Germany (Forster et al., 1991). Tests on the occurrence of caterpillars, indicated that considerable modifications were needed to the procedure used by Hommes et al. (1988) in five European countries during an earlier two year field trial. The main purposes of the present project was to introduce supervised control into practice and 127 to test action threshold for caterpillars to reduce the number of applications of insecticides. The main objectives of the current work were: to introduce spray thresholds for caterpillars, to assess accurately crop losses due to caterpillar infestations, to investigate regional occurrence, within-plant distribution, levels of infestation, and damage of the various species of caterpillars infesting cole crops. Materials and Methods Tests and investigations were carried out in several major growing areas in Germany between 1987 and 1990. Observations were started two weeks after the late cabbage crop was transplanted (end of May) and were continued until harvest (end of October). A) Tests of supervised control procedures in practke Fifty plants (heart or head leaves and 6 upper leaves) were inspected at 2- week intervals. An insecticide was applied once the infestation exceeded the action threshold. At harvest, fifty plants were weighed and graded for quality. The parameters studies are shown in Table !. They include:- !) Inspection of the head, heart leaves, and 6 uwer leaves, to determine the level of pest infestation. 2) The relative risk of crop damage during the different phases of plant growth (particularly its impact on the final weight and quality of the crop). 3) Spray thresholds. 4) Thedifference in crop quality required for fresh-market and industrial processing. 5) The reduction in the number of sprays needed to produce marketable crops. B) Investigations on the occurrence of, and damage hy, �aterpillars The numbers of caterpillars found on 50 whole plants were recorded every2 weeks on the plots without insecticide treatments. Fifty plants were also assessed at harvest for crop quality and crop yield. Result! A) Tests of supervised control procedures in practice To check whether action thresholds, without first identifying the different caterpillar species, worked in practice, records were taken at 2-week intervals of the levels of caterpillar infestations on the plants. A final check for damage was made at harvest. This test included different levels of infestation and information from several 128 growing regions. The comparison of crop quality and crop yield (Table 2) indicates the effectiveness of supervisedcontrol systems in cole crops. The proportion of cabbage heads suitable for fresh market/storage and for the sauerkraut industry, as well as their average weights, were similar following both supervised control and the routine control practice. However, the number of insecticide applications was reduced considerably in the supervised control plots. In addition to the present studies, the results of 1991 field trials indicated that different action thresholds should be used for at least three different periods of crop growth (Table 3). Table 1: The two different spray thresholds used for controlling cate11>illars in whlte cabbage crops between 1987 and 1990 Year Sampling unii Spray threshold Plant growth until:- Market [% infestation] 1987 Whole plant 10%: 5% 4 weeks after Fresh : Storage transplanting : harvest 1988 heart or head & 10%: 5% 4 weeks after Fresh : Storage 6 upper leaves transplanting : harvest 1989 heart or head & 20%: 5% heading : harvest Fresh: Storage 6 upper leaves 1990 heart or head & 50%: 5% heading : harvest Fresh : Storage 6 upper leaves heart or bead & 50%: 10% heading : harvest Industrial 6 upper leaves processing Thethree periods of plant growth that should be considered are:- 1) from transplanting until the 8th leaf is produced; 2) from production of the 9th leaf until the beginning of heading • to minimize severe defoliation and subsequent loss in crop weight; 3) from heading until harvest - to minimize damage of the head leaves and associated loss of quality. A fourth period, starting at the time of head fill, could be profitable for the sauerkraut industry, as considerable superficial damage is tolerated for this market. 129 Table 2: Quality, weigh� and numberor insecticide sprays applie Treatment Fresh market : Industrial Mean weight Mean no. of applied Storage processing (kg) of insecticide [sauerkraut] cabbage heads sprays Untreated 61 88 2.9 a Supervised 88 98 3.1 2.1 Routine 91 99 3.1 6.0 Table 3: Th2four diffeent spraythresholds used for controllingcaterpillars in white cabbage crops iD 1991 Sample Unit Spray threshold Plant growth<1> until: Market [% infestation] heart or head & 25% : 50% : 5% : 5% 8th leaf : heading : Fresh : 6 upper leaves head fill : harvest Storage heart or head & 25% : 50% : 15% : 25% 8th leaf: heading : Industrial 6 upper leaves head fill : harvest processing <1> For the definition of plant growth see Buhtz et al. (1990) B) Investigations on the occurrence and damage of caterpil!ars Information was collected for the common caterpillars species of their regional occurrence, within-plant distribution, levels of infestation, and damage. Such data were collected to test whether the procedure was sufficiently reliable for a range of infestations. The most common species of caterpillars on cabbage crops were (in alphabetical order): Autographagamma (Silver Y Moth) Evergestisforficalis (Garden Pebble moth) Mamestra brassicae (Cabbage Moth) Pieris brassicae (Large White Butterfly) Pieris rapae (Small White Butterfly) Plutella xylostella (Diamondback Moth) The frequency of infested cabbage between 1987 and 1989 are shown in Fig. 1. 130 %infested plants 100 years 90 g 1987 - 1989 80 CJ 1989 70 m 1988 [lilll 1987 60 50 40 30 20 10 0 P.xyfostella P.rapae M.brasslcae A.gamma E.forflcalls P.brasslcae species Fig. 1: Frequency or plants infested with caterpillars ;n late cabbage crops (1987- 1989). Most plants were attacked by P. xylostella, P. rapae and M brassicae (71%, 45% and 40%, respectively). Thethree remaining species A gamma, E. forficalis and P. brassicae infested fewer plants (16%, 6% and 2%, respectively). Thefrequency of distribution of infested plants during three different periods of plant growth are shown in Fig. 2. While the proportion of infested plants was low during the first sampling period, andmoderate during the second, all species reached their highest levels of attack after the beginning of heading. Hence, crop losses were more likely to be due to reductions in quality rather than to the reductions in quantity (weight). P. xylostella (diamondback moth), P. rapae (small white butterfly)and M brassicae (cabbage moth) were the most abundant pests in all regions (Fig. 3). In all regions, A. gamma (silver Y moth), E. forficalis (garden pebble moth) and P. brassicae (large white butterfly) were less abundant. Important differences concerning the level of infested plants are obvious in northern part of Germany. In contrast to the west and the south, infestation by M brassicae was less frequent in the north. Greater numbers of plants infested with E. forficalis caterpillars were recorded only in the west of Germany. Fig. 4 shows the amount of leaf area the caterpillars consumed from the lower, upper and head leaves. The amount of leaf lost from both the lower and upper leaves indicates that such damage should not have a major impact on crop weight. However, feeding damage on head leaves reduced marketability, and hence was important. 131 %Infested plants 100 90 P.xylostella -D P.rapae 80 M.brassicae llillilll A.gamma 70 - D E. forllcalis 60 P.brassicae 50 40 30 20 10 0 transplan tlng-8.leaf 9.leal-headlng heading-harvest Fig. 2: Frequency or plants infested with caterpillars during three periods or plant growth, in late cabbage crops during �88 and 1989. %Infested plants 100 90 80 70 P.xylostella 60 CJ P.rapae 11m M.brasslcae 50 A.gamma 40 D E.forflcalls P.brassicae 30 20 10 North West South Fig. 3: Frequencyor plants infested with caterpillars in the North, West and South or Germany (1987-1989). 132 100% defoliation 25% -llillilil 20% 75% BI 10% D 5% 1% CJ- 0% 50% lower upper head lower upper head tower upper head 1987 1988 1989 Fig. 4: Loss of leaf area due .:o natural infestations of caterpillars (lower, upper and head leaves) during 1987 to 1989. Toe within-plant distribution of the different species of caterpillars reveals their typical feeding sites. While P. rapae preferred to feed on the upper and head leaves (70% of the P. rapae-larvae), most A. gamma (87%) fed on the outer leaves. The most abundant species P. xylostella, P. rapae and M. brassicae, as well as E. forftcalis, fed frequently on the cabbage heads (Fig. 5). Fig. 6 shows the relative loss of leaf area from the lower, upper, and head leaves of cabbage plants following feeding by the three most abundant caterpillar species. When assessed on the amount of foliage consumed from the lower and upper leaves, M. brassicae (59%, 65%) seemed to be a more troublesome pest than P. rapae (40%, 64%) or P. xylostella (44%, 45%). When assessed on the numbers of feeding holes recorded on the cabbage heads, all three species caused similar levels of damage (M. brassicae 44%, P. rapae 43% and P. xylostella 38% ). Table 4 shows the impact of natural infestations of caterpillars on the quality and weight of cabbage plants in untreated plots. TRble 4: Impact of caterpillars on the quality and weight of white cabbage (expressed as percentage of supervised controlplots = 100) harvested from untreated plots of white cabbage between 1987 and 1990 Fresh market : Storage Industrial processing Head weight Crop losses ( % ) 39 12 5 13:) In fas tati on P.rapae E.forficalis P.xylostella M.brasslcae P.brasslcae A.gamma D lower leaves m upper leaves 1!1!!111 heart or head leaves Fig. 5: Within-plant-distribution of several caterpillar species on white cabbage during 1988 and 1989. 100% defoliation 25% liliillil- 20% 75% 10% -D 5% 1% -D 0% 50% lower upper head lower upper head lower upper head P.xylostella P.rapae M.brasslcae Fig. 6: Losses of leaf area due to feeding by �aterpillars of P. xylosteJJa. P. rapae and M. brassk:ae (the most abundant species) on white cabbage during 1988 and 1989. 134 In general, during 1988 to 1990, caterpillars made 32% of heads unmarketable for fresh market/storage and 10% unmarketable for industrial processing. In contrast, their feeding damage caused only a 5% loss in crop weight. Because of the high proportion of cabbage head infested by P. rapae (Small white butterfly),P. xylostella (Diamondback moth) and M. brassicae (Cabbage moth), caterpillars of all three species are regarded as the serious pests (Fig. 7). Caterpillars of A. gamma, (Silver Y moth), E. forficalis (Garden pebble moth) and P. brassicae (Large white butterfly) were found less frequently on head leaves. P.rapae 51,5 other species 2,6 Fig. 7: Proportions of the caterpillar species causing infestation of head leaves on v1hUe cabbage during 1988 and 1989 Discussion Theimproved procedure reduced the amount of insecticide applied to 35% of that applied in the "routine" crop protection practice without reducing plant marketability. The early insecticidal sprays are the ones that are most frequentlynot required. Furthermore the new procedure is less time consuming that the one Hommes et al. tested in 1985 and 1986 (Hommes et al., 1988) as only heart or head leaves, plus 6 upper leaves, have to be inspected. Depending on the plant variety involved, the new system required up to 75% less time and also had both economical and ecological benefits. In 1985, Sears et al. tested several partial-plant sampling procedures in the USA and Canada. They confirmed substantial savings in scouting time but had considerable reductions in marketability, particularly for fresh-market cabbage. When combined with a lower spray threshold at the beginning of heading, a sampling method similar to the one developed by Sears et aL proved satisfactory under German conditions. The dominant pest species P. xylostella, P. rapae and M. brassicae all caused crop damage of economic importance in different vegetable-growing regions of Germany. These findings agree with those recorded in the West of Germany by Hommes (1983). In untreated plots, losses in plant quality are more important than losses in plant weight (up to 39% & 5%, respectively). The results indicate that 135 damage at different stages of plant growth, especially the beginning of heading, are critical in supervised control systems, whereas the actual caterpillar species involved is relatively unimportant. These findings agree with the basic assumptions proposed earlier by Theunissen and den Ouden (1985). To determine plant growth accurately, the phenology of the plants. is more reliable than using "weeks after transplanting" which was proposed earlier by Theunissen & den Ouden (1985), Hommes et al. (1988) and others. Andaloro et al. (1983) and Buhtzet al. (1990) carried out some basic studies on plant phenology. Buhtz et al. (1990) proposed the use of a decimal-code to describe different plant growth stages. This coding, which can in practice be applied easily to all varieties, was included in the new procedure. The present investigations indicated that there are three to four periods of plant growth that need to be considered. Thefirst three periods are: 1) from transplanting to production of the 8th leaf; 2) fromthe production of the 9th leaf until the start of heading; and 3) from heading until harvest - to minimise damage on the head leaves and subsequent loss of crop quality. A fourth period, starting at the time of head fill, could be profitable for the sauerkraut industry, as considerable superficial damage to the head leaves can be tolerated for this market. This improved system has now been established officially in Germany forthe production of cole crops. R�sum� L2 lutte dirigee conire Jes l�pidopt�res su:I:' chou bianc De 1987 a 1991, un systeme de lutte dirigee a ete teste, ameliore et officiellement introduit dans les cultures de choux en Allemagne. Ce travail decrit les investigations menees sur !'apparition, la dispersion et le degfit provoque par les lepidopteres dans les cultures de chou blanc. Durant la periode experimentale, le pourcentage de plantes attaquees par !es trois ravageurs-cles etait le suivant: 71 % pour Plutellaxylostella (Lepidoptera : Plutellidae), 45% pour Pieris rapae (Lepidoptera: Pie.:idae) et 40% pour Mamestra brassicae (Lepidoptera : Noctuidae). Le taux d'infestation par Autographagamma (Lepidoptera: Noctuidae), Evergestisforficalis (Lepidoptera : Pyralidae) et Pieris brassicae (Lepidoptera : Pieridae) etait inferieur, se limitant a 16%, 6% et 2% respectivement. Les degfits sur les tetes ont ete occasionnes pour 98% par les trois ravageurs cles avec la repartition suivante: 52% pour P. rapae, 26% pour P. xylostella et 20% pour M. brassicae. Ces memes especes sont dominantes dans toutes les regions et tres dommageables au chou tardif des le debut de la formation de la tete et jusqu'a la recolte. Dam; les parcelles non traitees, les pertes dues a des morsures mineures etaient plus importantes que les pertes de poids de recolte (iusqu'a 39% et 5% respectivement). Les trois especes ont occasionne des degfits economiques. Des differences specifiques concernant specia!ement le site des morsures et la perte de surface foliaire sont egalement evidentes. Les resultats confirment de nouveau qu'il n'est pas necessaire d'identifier les especes presentes, bien que des seuils differencies selon le stade phenologique de la plante doivent etre utilises. Ceux-ci, bases sur une simple presence/absence de chenilles sur 50 plantes (coeur; feuilles formant la tete et les 6 136 suivantes) par champ se sont reveles fiables. Grace lice procede ameliore, la quantite d'insecticides appliquee a pu etre diminuee de 65%, en comparaison d'un regime de traitements routiniers appliques sur chou blanc. be plus, cette methode de controle exige moins de temps que celle proposee anterieurement et presente des avantages economiques et ecologiques. Referencfs Andaloro, J.T., Rose, K.B., Shelton, AM., Hoy, C.W. & Becker, R.F. (1983). Cabbage growth stages. New Yorks Food andLife Science Bulletin 101: 4pp. Buhtz, E., Boese, L, Grunert, C. & Hamann, W. (1990). Koordinierter Dezimalcode (KDC) der phanologischen Entwicklung fiir landwirtschaftliche Kulturpflanzenarten, Gemiise, Obst und Sonderkulture. Felversuchswesen 12 7 Jahrgang, Heft 1: 57-58. Forster, R., Hildenhagen, R., Hommes, M. & Schorn-Kasten, K (199891). Bekampfung von Kohlschadlingen nach Bekampfungsschwellen. Deutscher Gartenbau 9: 564-566. Hommes, M. (1983). Untersuchungen zur Populationsdynamikund integrierten Bekampfung von Kohlschadlingen. Mitteilungender BBA 213; 210pp. Hommes, H., Dunne, R., Ellis, P.R., Fischer, S., Freuler, J., Kahrer, A & Terretaz, C. (1988). Testing damage thresholds for caterpillars and aphids on cabbage in five European countries. Report on a collaborative project done in 1985 and 1986. WPRS Bulletin 11(1): 118-126. Sears, M.K, Shelton, AM., Quick, T.C., Wyman, JA & Webb, S.E. (1985). Evaluation of partial plant sampling procedures and corresponding action thresholds formanagement of lepidoptera on cabbage. J. EcoTL EntomoL 78: 913-916. Theunissen, J. & den Ouden, H. (1985). Tolerance levels for supervised control of insect pests in Brussels sprotus and white cabbage. Z. angew. Ent. 100: 84-87. IOBC/WPRS-WorkingGroup Meetin& "Integrated Controlin FieldVegetables·. Vienna.28-30 Oct 1991 l.37 Ecological interactions between insect pathogens and insect pests of cabbage J. Ellenberg, H. Philipsen & J. Bresciani Department of Ecology and MolecularBiology, Royal Veterinary and Agricultural University, DK-1870 Frb.C, Denmark Summary In Denmark, studies were carried out on pathogens of cabbage pests, especially on fungal pathogens of adult cabbage root flies (Delia radicum). Major events of the life-cycle of three fungal pathogens of D. radicum (Entomophthora muscae, Strongwellsea castrans and Beauveria bassiana) are presented schematically. Factors that are important in the development of fungal epidemicsare discussed. Preliminaryobservations on other pathogens of cabbage pests are also presented. Introduction Before attempting to control pest insects by applying microbial agents, it is important to obtain a good ecologicalunderstanding of how microorganisms help to regulate pest insect populations under field conditions. We have chosen cabbage, as our model crop, fora three year study that started in 1991. The main pest in this study is the cabbage root fly,Delia radicum, and the main pathogens are entomogenous fungi. In an earlier study, two fungi Entomophthora muscae and Strongwellsea castrans were shown to be important naturally-occurring mortality factors of D. radicum in Denmark, (Ellenberg, 1991). Within cabbage crops, information will be gathered on the occurrence of insect pathogens, with special emphasis being placed on fungal pathogens. The study will also include sampling and incubation of living insects from the field (Eilenberg and Philipsen, 1988) and isolation, using Tenebrio molitor larvae, of microorganisms from soil samples (Zimmermann, 1986). In 1991 samples were collected from several crops in three localities: "H0jbakkegaard", Tastrup (cauliflower), "Hegnstrup", Slangerup (white cabbage, brussel sprouts, cauliflower a.o., grown organically) and "I..angvad", Roskilde (several types of cabbage). A brief outline of some ecological aspects of this project are given below. Proposed life-cycles of fungal pathogens oi Delia radicum A proposed schematic diagram of the life-cycle of Entomophthora muscae, a common pathogen of D. radicum, is shown in Fig. 1. When insects are killed by this fungus they become fixed to the top parts of the foliage of plants. 138 3. Infected D.r. fly in the field 1. Fungus-killed D.r. attach to 2. C infect plants and ini adult D.r. 1 tiate C discharge 4. Fungus-killed 6. R produce C D.r. with R drop 5. R stay in the which infect o.r. to soil surface soil until spring emerging from pupal stage Fig. 1: Schematic diegram of events in the proposed life-cycle of Entomophthora muscae, a pathogen of adult cabbage root flies (Deliaradicum). D.r. = Delia radk:um; C = conidia; R = resting spores. Horizontal shaded line indicates surface of soil Thespores are discharged from these elevated positions and hence the disease is transmitted horizontally. Towards the end of the season. certain flies that are killed contain resting spores instead of conidia. Such flies do not climb to the tops of plants but instead drop to the soil surface. Theresting spores remain in the soil during the winter and in the following spring infective units, the conidia, are produced fromthe resting spores. A proposed schematic diagram of the life cycle of Strongwellsea ca.strans is shown in Fig. 2. Infection in the adult fliesproduces a depression in the abdomen. from where conidia are discharged to infect other insects. Infected flies help to spread the fungus as they are still able to fly around for several days after the depressed area in their abdomen. With this fungus also, resting spores are produced towards the end of the season. inside infected individuals. When such flies fall to the soil the spores remain dormant throughout the winter and give rise to the infective units in the following spring. Thus it appears that the overall life-cycles forE. mwcae and S. ca.strans are similar. Delia radicum is considered to be a major host for both pathogens, although occasionally other Diptera within the Anthomyiidae may also be hosts. The soil is important as a winter reservoir forresting spores of both E. mwcae and S. castrans. It is only during their emergence in the spring that the adult flies become infected at the soil surface. During the rest of the year, infection occurs while the insects are flying or in the crop foliage. 139 J. Infected D.r. fly in the field 1. Infected D.r. develop abdominal 2. c infect hole from which adult D.r. C are discharged 4. Fungus-killed 6. R produce C D.r. with R drop 5. R stay in the which infect D.r. to soil surface soil until spring emerging from pupal stage Fig. 2: Schematic diagram of events in the proposed life-cycle of Suongwellseu. costrans9 a pathogen of adult cabbage root. flies (Delia radicwn). D.r. = Delia rr:ulicum; C = conidia; R = resting spores. Horizon.ta! shaded line indicates surface of soil During 1991, Beauveriabassiana was recorded for the first time, and from several locations, as a natural pathogen of adult cabbage root flies. Thisfungus is a well-known pathogen of many soil-inhabiting insects. Our proposed life-cycle of how this fungus affects cabbage root flyis shown in Fig. 3. 6. Infected D.r. l fly in the field 1. Fungus-killed D.r. 4. Care released 5. D.r. get infected drop to soil surface by fungus-killed � by C during emerging and release C insects from pupal stage l i 2. C join the pool 3. Soil inhabiting of Bb spores in ��> insects recieve the soil infection by C Fig. 3: Schematic diagram of events in the proposed life-cycle of Beauveriabassia:ntl (Bb), a pathogen of adult cabbage root fiies (Deliaradicum). D.r. = Delia radicum; C = conidia; R = resting spores. Horizontal shaded line indicates surface of soil 140 Flies are infected by B. bassiana after eclosion and during the period in which they use the ptlilinum to force their way through the upper layers of soil and onto the soil surface. Flies killed by this fungus fall to the soil. The spores that are released then add to the pool of B. bassiana infective units already in the soil. In infested soil, B. bassiana has a wide range of insect hosts, one of which is D. radicum. B. passiana was found mainly on flies from Hegnstrup. At this locality, several strains of B. bassiana were isolated from soil samples. Apart fromE. muscae and S. castrans, certain other members of the Entomophthorales were found on adults of D. radicum. These included Conidiobolus spp. and Zoophthora radicans during 1988 and 1989 (Eilenberg, 1991) and E,ynia sp. during 1991. However, each species was found in only 1-2 specimens. Occurrem:eo! pathogens on other cabbage pests Individuals of Brevico,yne brassicae were found to be infested by three pathogens: E,ynia neoaphidis,Entomopthhora planchoniana and Conidiobolus obscurus. E. neoaphidis was the only species that was common, being found mainly during October at Hegnstrup. AlthoughPhyllotreta spp. were sampled throughout the season, fungal infections were never detected. Fungal pathogens were also not detected in Pieris rapae sampled during August and September. In contrast, E,ynia virescens was found in individuals of Agrotis segetum that were sampled at Hegnstrup. The plant insect-pathogen intemction in cabbage The figures show that the life-cycles of the three main fungal pathogens of D. radicum contain several events that are critical for both disease transmission and the development of fungal epidemics. The present research aims to study in detail the factors that influence such events. In addition to further sampling in the field, this work will include studies o!l l} infection processes (electron microscopy); 2) basic parameters such as the time to kill; 3) how infection influences the behaviour of the flies and; 4) characterization of fungal strains. The methods of crop cultivation used in vegetable crops may also influence the events in the life-cycle of the pathogens. For example, intercropping may enha..,ce fungal infection because of a more stable microclimate around the plant. 1n contrast, crop rotation and soil treatment may reduce the reservoir of fungal spores in the soil. The detailed life-cycles of the three fungi are not similar. Furthermore, there are several pest insects of cabbage that are attacked by pathogens. Therefore, changes in cultivation methods may have adverse effects on certain insect-pathogens. Hence, general conclusions on how insect pathogens could regulate pest insect populations in cabbage cannot be made at present. In future, it may be possible to enhance fungal epidemics to a level at which they could control root flies. Whether intercropping will help in the production of epidemics of entomopathogenic fungi within cabbage crops remains to be seen. 141 R�sum� Interactions �ologiques entre des entcmopathog�nes et des insectes a:avageurs du chou Au Danemark, des etudes sur des pathogenes de ravageurs du chou, particulierement sur des champignons pathogenes des adultes de la mouche du chou (Delia radicum) ont ete entreprises. Les caracteristiques principales du cycle evolutif de trois d'entre eux (Entomophthora muscae, Strongwellsea castrans et Beauveria bassiana) sont presentees schematiquement. Les facteurs importants au developpement epidemique des maladies fongiques sont discutes. Des observations preliminaires sur d'autres pathogenes de tavageurs du chou sont egalement presentees. References Ellenberg, J. (1991). Entomophthorales on adult cabbage root flies (Delia radicum). /OBC/WPRSBulletin 14, 46-48. Ellenberg, J. & Philipsen, H. (1988). The occurrence of Entomophthorales on the carrot fly (Psi/a rosae F.) in the field during two successive seasons. Entomophaga 33, 135-144. Zimmermann, G. (1986). The "Galleria bait method" for detection of entomopathogenic fungi in soil. l Appl EntomoL 102, 213-215. IOBC/WPRS-WorkingGroup Meeting "IntegratedControl in FieldVegetables". Vienna. 28-30Oct 1991 142 Attempts to control Delia spp. with entomopathogenic nematodes I. Vanninen, A Vainio & S. Jaakkola Agricultural Research Centre, Institute of PlanJ Protection, SF-31600 Joldoinen, Finland Summary Under laboratory conditions Steinemematid nematodes penetrated cabbage root fly larvae (Delia radicum), and also developed and reproduced in their cadavers. The rate of success, however, was low. Many times the juveniles seemed unable to kill the pest larvae. Instead, small spots of brown pigmentation occurred on the fly larvae, indicating that the pest's defence mechanisms probably included an encapsulation process. In a greenhouse experiment, one Finnish isolate of Steinernema feltiae was more effective than seven other isolates tested against D. radicum. Nevertheless, in fieldtrials in 1987 and 1990 this isolate, used at the rate of 12,000- 18,000 infectives per plant,did not protect cabbage and cauliflower plants against rootfly attacks. A dry period during July may have been the reason for poor control in 1990. However in 1987 the summer wasvery wet, so there should have been adequate moisture for the nematodes. Nematodes applied at the rate of 35,000 infectives per plant in 1990 protected cauliflowertransplants to some degree. Theyields from the nematode treated plants in the experiment were twice as large as those fromthe untreated plants. In the summer of 1991, attempts were made to improve control by applying the nematodes to coincide with the start of egg-laying by the root flies. The moisture conditions of the soil were recorded using a tensiometer. Soil moisture remained in excess of 60% throughout the growing season, a level assumed to be adequate for nematode survival. Highest crop yields were obtained from the insecticide-treated (diazinon) plots. However, crop yields fromthe nematode treated plots were higher than those from the untreated plots. Introduction In Finland, the brassica root flies (Delia radicum and D. jloralis) are the most serious pest insects of Brassica vegetable crops. On cabbage, Brussels sprout and cauliflower, yield losses in the past have been mainly quantitative ones. However, recently in Finland larvae have been found in the foliar parts of plants, and this has led to qualitative losses. Chemical control of cabbage maggots is often inadequate. Soil insecticides applied at planting do not remain effective sufficiently long to control D. flora/is larvae, which appear in the field in the middle of July, or the second generation of D. 143 radicum, which are present from the end of July onwards (Havukkala et al, 1984). The number of growers that cultivate cabbage plants organically is increasing, and there is a considerable demand for non-chemical methods to control brassica root flies. Crop covers can be used, but they have not been accepted widely because they are difficult to apply, particularly to large fields. Insect pathogenic nematodes have been tested against the cabbage· root flies on several occasions and with varying results (Bracken, 1990; Georgis et al, 1983; Hellqvist et al, 1988; Hommes, 1988; van Sloun, 1989; van Sloun & Sikora, 1986; Welch & Briand, 1961). In general, the level of control achieved bas been poor. Choice of nematode isolate or strain,and timing of application are probably the best ways to improve control results against cabbage maggots (Bracken, 1990; Hellqvist et al, 1988). We chose the cabbage root fly as the target against which to test Finnish isolates of Steinememafeltiae. This insect was chosen because of its importance as a crop pest in Finland. Materials and Methods Nematode& used in the experiments The Finnish S. fe/tiae isolates were obtained during a survey carried out in 1986-87 (Vanninen et al, 1989). Nematodes used in the experiments were multiplied in Tenebrio molitoriarvae. Infectives were less than 4-weeks old when used and were stored at 4°C prior to use. The commercial nematode strain "Nemo S" (Steinemema sp.), used in the field experiment in 1991, was obtained from Christian Hansen's Biosystems in Denmark. Greenhouse experiment The efficacy of the eight S. feltiae isolates was tested againsI D. radicum using 5-weeks old chinese cabbage seedlings as host plants. The plants were grown individually in 1 litre plastic pots filled with commercially-available compost. Fresh eggs (max 48 hrs old) of D. radicum were obtained from a laboratory culture (Finch & Coaker, 1969). Twenty eggs were placed on the soil around each seedling, and then nematodes, a: the rate of 20,000 per plant were pipetted onto the soil in 5 ml of water. The concentration of the isolate SFS20 was 17,500 per plant, and isolate SFS7 was tested at both 15,000 and 20,000 infectives per plant. Ten seedlings were treated with each nematode isolate, and ten plants were left untreated. Theplants were kept in a greenhouse at 23°C on trays. All pots with the same nematode isolate were kept on the same tray to avoid cross contamination. The plants were watered by flooding the trays. After a month, any fly pupae were washed from the soil and root damage was assessed on a scale of 0-3 (0 = undamaged; 1 = 1-25% damaged; 2 = 25-50% damaged; 3 = over 50% damaged). Survival of the nematodes was checked by baiting the soil with T. molitorlarvae in three pots in each treatment. Observations were made in the laboratory of how. infectives of isolate SFS22 attacked and penetrated late instar larvae of D. radicum. 144 Attempts to control .Ilclia spp. with entomopathogenic nematodes I. Vanninen, A Vainio & S. Jaakkola AgriculturalResearch Centre, Institute of Plant Protection, SF-31600 Jokioinen, Finland Summary Under laboratory conditions Steinemematid nematodes penetrated cabbage root fly larvae (Delia radicum), and also developed and reproduced in their cadavers. The rate of success, however, was low. Many times the juveniles seemed unable to kill the pest larvae. Instead, small spots of brown pigmentation occurred on the fly larvae, indicating that the pest's defence mechanisms probably included an encapsulation process. In a greenhouse experiment, one Finnish isolate of Steinemema feltiae was more effective than seven other isolates tested against D. radicum. Nevertheless, in field trialsin 1987 and 1990 this isolate, used at the rate of 12,000 - 18,000 infectives per plant, did not protect cabbage and cauliflower plants against root fly attacks. A dry period during July may have been the reason for poor control in 1990. However in 1987 the summer was very wet, so there should have been adequate moisture for the nematodes. Nematodes applied at the rate of 35,000 infectives per plant in 1990 protected cauliflower transplants to some degree. Theyields from the nematode treated plants in the experimentwere twice as large as those from the untreated plants. In the summer of 1991, attempts were made to improve control by applying the nematodes to coincide with the start of egg-layingby the root flies. The moisture conditions of the soil were recorded using a tensiometer. Soil moisture remained in excess of 50% throughout the growing season, a level assumed to be adequate for nematode survival. Highest crop yields were obtained from the insecticide-treated ( diazinon) plots. However, crop yields fromthe nematode treated plots were higher than those from the untreated plots. Introduction In Finland, the brassica root flies (Delia radicum and D. floralis) are the most serious pest insects of Brassica vegetable crops. On cabbage, Brussels sprout and cauliflower, yield losses in the past have been mainly quantitative ones. However, recently in Finland larvae have been found in the foliar parts of plants, and this has led to qualitative losses. Chemical control of cabbage maggots is often inadequate. Soil insecticides applied at planting do not remain effective sufficiently long to control D. floralis larvae, which appear in the field in the middle of July, or the second generation of D. 143 radicum, which are present from the end of July onwards (Havukkala et al, 1984). The number of growers that cultivate cabbage plants organically is increasing, and there is a considerable demand fornon-chemical methods to control brassica root files. Crop covers can be used, but they have not been accepted vvidely because they at'.e difficult to apply, particularly to large fields. Insect pathogenic nematodes have been tested against the cabbage· root files on several occasions and with varying results (Bracken, 1990; Georgis et al, 1983; Hellqvist et al., 1988; Hammes, 1988; van Sloun, 1989; van Sloun & Sikora, 1986; Welch & Briand, 1961). In general, the level of control achieved has been poor. Choice of nematode isolate or strain, and timing of application are probably the best ways to improve control results against cabbage maggots (Bracken, 1990; Hellqvist et al, 1988). We chose the cabbage root flyas the target against which to test Finnish isolates of Steinemema feltiae. This insect was chosen because of its importance as a crop pest in Finland. Materials and Methods Nematodes used in the experiments The Finnish S. feltiae isolates were obtained during a survey carried out in 1986-87 (Vanninen et al, 1989). Nematodes used in the experiments were multiplied in Tenebri.o molitor larvae. lnfectives were less than 4-weeks old when used and were stored at 4°C prior to use. The commercial nematode strain "Nemo S" (Steinemema sp.), used in the field experiment in 1991, was obtained from Christian Hansen's Biosystems in Denmark. Greenhouse experiment The efficacyof the eight S. feltiae isolates was tested against D. radicum using 5-weeks old chinese cabbage seedlings as host plants. The plants were grown individually in 1 litre plastic pots filled with commercially-available compost. Fresh eggs (max 48 hrs old) of D. radicum were obtained from a laboratory culture (Finch & Coaker, 1969). Twenty eggs were placed on the soil around each seedling, and then nematodes, at the rate of 20,000 per plant were pipetted onto the soil in 5 ml of water. The concentration of the isolate SFS20 was 17,500 per plant, and isolate SFS7 was tested at both 15,000 and 20,000 infectives per plant. Ten seedlings were treated with each nematode isolate, and ten plants were left untreated. TI1e plants were kept in a greenhouse at 23°C on trays. All pots with the same nematode isolate were kept on the same tray to avoid cross contamination. The plants were watered by flooding the trays. After a month, any fly pupae were washed from the soil and root damage was assessed on a scale of 0-3 (0 = undamaged; 1 == 1-25% damaged; 2 = 25-50% damaged; 3 = over 50% damaged). Survival of the nematodes was checked by baiting the soil with T. molitor larvae in three pots in each treatment. Observations were made in the laboratory of how infectives of isolate SFS22 attacked and penetrated late instar larvae of D. radicum. 144 Table 1. Efficacy of Steinernema-isolates against Delia. spp. in greenhouse and field tests. In treatment column no. of nematodes per plant is as follows if not otherwise stated in brackets after the isolate code: greenhouse experiment 20,000 mfestives/piant; field experiment in 1987 !2,000 /piant; field test in 1990 35,000 !nfectives/plan� at Piilldine, and 18,000 infectives/p!ant at Ruukid. s� text ro� �rue of root damage, s.d. = standard deviation. Experiment and No. of No. of Root damage index Yield/plot, treatment test pupae/plant g plants mean s.d. scale mean s.d. mean s.d. Greenhouse: " Untreated 10 3.3abcd 1.12 0-3 2.6abc 0.53 SFS20 (17,500) 10 4.78 2.95 2.3bc 0;82 ab SFS4 10 4.l 1.97 2.'Z' 0.63 SFS7 (15,000) 10 4.0"bc 1.49 2.1•bc 0.48 SFS26 10 3.9* 2.42 2.gab 0.30 SFS7 10 3.4abcd 1.90 2.4abc 0.52 SFS25 10 2.2bcde 1.39 2.4abc 0.53 SFS8 10 2.()""e 2.45 3.0" 0.00 SFS24 10 1.s means with the same letters do not differ from each other (Duncan's multiple range test (P = 0.05), ANOVA-procedure/SAS). total no. of plants/treatment in 1990 was 100 in both locations; plants killed by bugs are excluded from the analysis. 147 Field test in 1987 The amount of rainfall in June and August 1987 was double the long term average for the area in which the experiment was carried out, and in July it equalled the long term average (see Table 2). Throughout the whole growing season, the weather was wetter and cooler than normal. Of the pupae recovered from the soil, 95% were D. flora/is. Neither the root damage index nor the number of pupae found around nematode-treated plants differed from the untreated controls (Table 1) (ANOVA/SAS: F = 0.18, P < 0.833, and F = 0.98, P < 0.392, respectively). Table 2. Weather conditions in the experimental sites in 1987 and 1990 (Ilmatieteen laieos. Kuakausikatsaus Suomen ilmastoon/The Me:eorofogical Institute of Fin!and. Monthly weather records). Average monthly Soil temperature in Precipitation, mm Location air temperature °C depth of 20 cm (range), °C June July Aug June July Aug June July Aug Eurajoki,1987 12.2· 14.5 11.7 1.s·· 12.6 10.9 93• 69 129. (grid 61'10", - - - 21'45") 11.7 15.3 13.8 Palkane, 1990 14.5 15.6 15.6 9.0.. 14.5 12.5 25 67 43 (weather - - - station nearby) 14.5 16.5 16.5 (grid 61'20", 24'15") Ruukki, 1990 12.9 15.2 14.1 11.0 14.5 13.5 43 94 60 (Weather - - - station nearby) 13.5 15.5 16.5 (grid 64'40", 25'05") values from the nearest weather station in Kokemaki (grid 61'15", 22'18") were used for air temperature and precipitation, as there is no weather station in Eurajoki. values from Jokioinen weather station (grid 60'48", 23'30") were used for soil temperatures for Pfilkane and Eurajoki, as soil temp:!rature is not recorded at all weather stations. 148 Field test in 1990 June and August were hotter and drier in 1990 than on the average. Both at Palkane and Ruukki least rain fell in June (Table 2). Rainfall was particularly low at Palkane and, in June and August, amounted to only half the long term av�rage for that time of year. It also rained less than average at Ruukki, but as the rainfall is generally higher in this area, the experimental site still received more water than the site at Pfilkane. The attack by brassica root flylarvae was severe in both places. One third of the untreated plants were killed during the growing season. A third of the nematode treated plants were killed at Ruukki, whereas only 20% were killed at Pfilkane. In contrast, only 2% of the transplants treated with diazinon died at Palkane. As expected, diazinon was not as effective at Ruukki (Table 3) as this was a peat soil. Table 3. Qualityor cauliflowers at the two experimental sites in :S.990. Location Percentage of cauliflowers in different quality classes and treatment Dead in the Blind (growth Heads with early stage point destroyed symptoms Healthy Total by bugs) of rotting Palkane: Untreated 31 3 28 38 100 SFS22 21 5 25 49 100 Diazinon 2 3 0 95 100 Ruukki: Untreated 37 2 0 61 100 SFS22 37 1 3 59 100 Diazinon 14 6 1 79 100 The rotting brown or greyish spots on the cauliflowers were not caused by cabbage maggots, but by bacteria and fungi that attacked either healthy or wounded spots on the heads. We cannot explain why the proportion of these heads was so low in diazinon treated plants at Pfilkane. The mean yield per plants was small in both localities, as the cauliflowers were harvested all at one time rather than waiting until each cauliflower was ready for harvest. The cauliflowers treated with diazinon were larger than those from the untreated plots and from the plots treated with nematodes (Table 1; ANOVA/SAS F 155.8, P < 0.0001 for Pfilkane, and F 48.3, P < 0.001 for Ruukki). There was no= statistical difference between the mean= yields/plant of untreated and nematode treated cauliflowers. However, at Palkane the cauliflowers treated with SFS22 were twice as heavy as the untreated cauliflowers. The total yield (all quality classes included) from each treatment was as follows: at Palkiine, 58.3 kg/diazinon treatment, 10.9 kg/SFS22 treatment, and 4.8 kg/untreated plants. The figures for Ruukki were 26.0 kg/diazinon, 9 kg/nematode, and 8.7 kg/untreated plants. 149 Field test in 1991 The temperatures in 1991 at Piilkii.ne were similar to those in 1990, but rainfall was higher. Plant bugs destroyed 14-20% of the cauliflowers during June. The damage was spread evenly over all experimental plots. Owing to deaths from cabbage root flyattacks, the percentage of dead plants had risen to 25-37% by harvest. Consequently, the yield values are based on 6-8 cauliflowers/plot rather than on 10 cauliflowers. The effect of irrigation on the ability of the polymer to keep the moisture content of the soil high could not be studied, because rainfall was heavy throughout the growing season. Hence the moisture content of the soil remained at 80-90% for most of the summer. There was no difference in yield between irrigated and non-irrigated plots, or between plots that were and were not treated with the polymer. In this experiment, when the yield of untreated plants was given an index of 100, diazinon was shown to increase yield by 60% and the nematode treatments by 11-27%. However, yields fromthe nematode-treated plants did not differ fromthose from the untreated (control) plants. The average number of cabbage root flypupae recovered per plant varied between 15 and 21. The highest number of pupae were recovered from the plants treated with diazinon (n = 32 plants/treatment). 75% of the pupae were D. floralis, 15% D. radicum, and the rest were unidentifiedDelia-species. The root damage indices did not differ between treatments. The proportion of heavily damaged roots (index 3 or higher on scale 0-5) was similar for the diazinon-treated and the untreated plants (25% and 31%, respectively). In plants treated with nematodes the value ranged from27% to' 52%. In September, steinernematid nematodes could be isolated from all plots, including the untreated and the diazinon-treated plots. Nematodes were found most frequently in plots treated with SFS22. Discussion Control of brassica root flies with steinemematid nematodes is difficult. The la.-vae seem to be innately resistant to the infectives. Morris (1985) tested S. Jeltiae against 31 agricultural insect pests and found that dipterous pests, D. radicum among others, were not as easily infected by nematodes as lepidoterous larvae. Both Bracken (1990) and van Sloun (1989) found that at best only about 30% of the larvae of D.radicum were killed by nematodes in laboratory tests. Van Sloun (1989) hypothesized that it is more difficult for the infectives to enter D. radicum larvae because the larvae are relatively small and their mouth opening - through which the infectives often enter - is smaller than that of lepidopterous larvae. Our observations on the appearance of pigmented spots on D. radicum larvae exposed to nematodes indicated that physiological resistance mechanisms, e.g. encapsulation, may also protect the larvae against steinemematids. Two of the present experiments indicated that the nematodes gave some control of brassica root maggots. The greenhouse experiment demonstrated a difference between S. Jeltiae isolates in their efficacy against D. radicum. The field experiment at Piilkane in 1990 indicated that isolate SFS22 gave some protection to 150 cauliflower transplants against brassica root maggots. However, the degree of control was much lower than that achieved with diazinon. Ineffective isolates, low application rates and low soil temperatures in 1987 may help to explain why the nematodes failed to control root fly larvae. At Ruukki in 1990, the rate of 18,000 infectives per plant was low compared to the 35,000 applied per plant at Palkiine. In addition, at Ruukki the infectives migrated to untreated and diazinon treated soils during the summer, which must have lowered the nematode population on the nematode-treated plants towards the middle of July, when D. floralis, the dominant fly species in the area, laid eggs. In 1990 at Palkiine, the success of the SFS22 infectives may have been prevented by the dry weather at the end of June and beginning of July, which led to rapid drying of the sandy soil (irrigation was applied when needed, rather than trying to keep the soil moisture at a predetermined level). No nematodes were found in soil samples taken in the autumn. In the moist year of 1991, nematodes were isolated fromsoil samples fromall treatments. In general, the survival of SFS22 in soil was good. Vainio (unpublished) has studied the persistence of SFS22 .in the field at Jokioinen, since it was introduced in 1989. This isolate was still present in the field in the summer of 1991. Why the SFS22 infectives were not effective against cabbage root fly larvae in 1991, when moisture conditions were good is difficult to explain. Applying the nematodes at the beginning of the egg-laying by D. radicum did not improve the level of control. The application rate of 20,000 infectives per plant was probably too low. This lower application rate, rather than 35,000 infectives/plant, was selected because it would be economic in cauliflower production. The polymer used in the 1991 experiment can hold 250 times of its own weight of water when mixed with soil. At its presence price, however, this polymer is not an economically viable proposition for use in cabbage crops. It was used merely to try to make moisture conditions more favourable for nematodes. We have not yet studied whether the polymer affects the behaviour of steinemematid infectives. According to the literature, the factors that can improve the effectiveness of entomoparasitic nematodes against brassica root fly larvae are 1) improved strains or isolates (Bracken, 1990); 2) correct timing of application (apply when the flies are laying eggs) (Hellqvist et.al., 1988); 3) application method (apply to the soil, not to the root ball at planting) (Hellqvist et al., 1988); 4) keeping the soil sufficiently moist for the nematodes to be active throughout the growing season. Our studies have shown that practically nothing is known about the interaction of steinemematid nematodes and larvae of D. radicum or D. floralis in the soil. How does the cabbage plant affect the nematodes? Are the infectives repelled by the chemicals emitted when the plant roots are damaged by maggots? Would any strain, or isolate, be attracted to the chemicals? Lei et aL (1989) showed in laboratorytests, that differences exist between Heterorhabditis heliothidis strains in their attraction to dead, frozen D. radicumlarvae. However, nematodes were neither attracted to or repelled from seedlings of radish and rutabaga. Whether there were differences between Steinemema species in their attraction to live cabbage root fly larvae, or their host plants, has not been studied. According to Bracken (1990), cabbage root fly larvae are relatively safe from nematodes once they have burrowed into the plant (in his tests, a piece of rutabaga). Is the time just after hatching the only period when nematodes can infect cabbage root fly larvae, or can the nematodes also attack them later, as the fly larvae do not 151 burrow very deeply into cabbage and cauliflower roots? Despite the fact that the levels of control obtained with steinemematids are not predictable, growers that cultivate Brassica using organic systems are highly interested in using nematodes. Toe market price of organically-grown cabbages and cauliflowers is 2-3 times that of conventionally-grown produce (Nikkila, 1�91). Increase in yield of 50% (Palkane 1990) or 10-27% (Pfilkane 1991), above the yield from untreated plants, would be of considerable value to organic farmers, if they have no other way of controlling infestations of brassica root flies. Rtsum� Tentatives de Jutte contre Delia spp. au moyen de n�matodes entomopathogenes En laboratoire, des nematodes Steinemematidae ont penetre des larves de ia mouche du chou (Delia radicum) et se sont developpes et reproduits dan.s les cadavres de l'Mte. Neanmoins, le taux de succes etait bas. Plusieurs fois, les formes juveniles ne semblaient pas capables de tuer les larves du ravageur. L'apparition de petites taches brunes sur l'Mte amenait a l'bypothese d'une reaction de defense impliquant probablement un processus d'encapsulation. Un isolat finlandais de Steinemema feltiae s'est revele dan.s un essai en serre plus efficace que sept autres isolats contre D. radicum. Toutefois, utilise a une dose de 12'000 a 18'000individus infectieux par plante, cet isolat n'est pas parvenu, durant les essais en champ de 1987 a 1990, a proteger des plantes de chou et de chou-fleur contre des attaques de la mouche du chou. Une periode secbe en juillet pourrait etre a l'origine de cette faible efficacite en 1990. En 1987, l'ete a cependant ete tres humide, de sorte que les conditions auraient dl1 etre favorables aux nematodes. A une dose de 35'000 individus infectieux par plante, les jeunes plants de cbou-fleur ont ete quelque peu proteges en 1990. La recolte des plantes traitees aux nematodes etait deux fois plus elevee que celle des plantes non traitees. En ete 1991, des tentatives ont ete faites pour ameliorer l'efficacite en appliquant les nematodes au moment du debut de la ponte de la moucbe du chou. L'humidite du sole ete enregistree avec un tensiometre. Elle s'est maintenue avec un excedent de 60% durant toute la periode de vegetation, soit ii. un niveau suppose favorable a la survie du nematode. Les recoltes les plus elevees ont ete obtenues des parcelles traitees a l'insecticide (diazinon). Cependant, les recoltes provenant des parcell�s traitees au nematode etaient superieures a celles des ternoinsnon traites. References Bracken, G.K (1990). Susceptibility of first-in.star cabbage maggot, Delia radicum (L) (Anthornyiidae: Diptera), to strains of the entomogenous nematodes Steinemema feltiae Filipjev, S. bibionir (Bovien), Heterorhabditis bacteriophora Poinar, and H. heliothidis (Khan, Brooks & Hirschmann). Can. Ent. 122: 633- 639. Finch, S. & Coaker, T.H. (1969). A method for the continuous rearing of the cabbage root flyErioischia brassicae (Bch.) and some observations on its 152 biology. Bull Ent. Res. 58: 619-627. Georgis, R., Poinar, G.O. Jr & Wilson, AP. (1983). Practical control of the cabbage root maggot, Hylemia brassicae (Diptera; Anthomyiidae) by entomogenous nematodes. IRCS Med. Science 11 322. Havukkala, I., Holopainen, J.K. & Virtanen, M. (1984). Flying periods and oviposition of cabbage root flies in southern and central Finland. Ann. Agric. Fenniae 23: 1-7. Hellqvist, S., Johansson, L& Burman, M. (1988). Neoaplectana carpocapsae (Nematoda} mot stora koalflugan(Delia floralis). Vaxtskyddsrapporter, Jordbruk 53, Sveriges Lantbruksuniversitet: 44. Lei, Z., Webster, J.M. & Rutherford, T.A (1989). Behaviour of entomopathogenic nematodes in the presence of Delia radicum and its host plant seedlings. l NematoL 21: 571. Morris, O.N. (1985). Susceptibilityof 31 species of agricultural insect pests to the entomogenous nematodes Steinemema feltiae and Heterorhabditis bacteriophora. Can. Ent. 117: 401-407. Nikkila, M. (1991). Luonnonmukaisesti tuotetut elin tarvikkeet vahittaishinnat ja markkinarakenne. Kuluttajatutkimus Keskuksenjulkaisu 13. van Sloun, P. & Sikora, R.A (1986). Control of Agrotis segetum and Delia brassicae with species of Steinemema and Heterorhabditis. In: Fundamental and applied aspects of invertebrate pathology. Proceedings of the Fourth International Symposium of InvertebratePathology, 18-22 August 1986, Veldhoven, The Netherlands, p. 318. van Sloun, P. (1989). Bekampfung der kleinen Kohlfliege Delia radicum Lund der Wintersateule Agrotis segetum Schiff. mit entomophagen Nematoden der Gattungen Steinemematidae und Heterorhabditidae sowie Einfluss biotischer Faktoren auf das Verhalten der Nematoden. Diss., Institute fur Pflanzenkrankheiten der Rheinischen Frieddch-Wilhelms Universitiit zu Bonn. 121pp. Vanninen, I., Husberg, G.-B. & Hokkanen, H. (1989). Occurrence of entomopathogenic fungiand entomoparasitic nematodes in cultivated soils in Finland. Acta Ent. Fenniae 53: 65-71. Welch, H.E. & Briand, L.B. (1961). Field experiment on the use of a nematode for the control of vegetable crop insects. Proc. ent. Soc. Ont. 91: 197-202. IOBCIWPRS-WorkimiGroup Meeting "IntegratedControl in Field Vegetables".Vienna. 28-30Oct 1991 153 Characteristics of plants that influence host-plani finding/acceptance by the cabbage root fly V. Kostal Institute of Entomology, CzechoslovakAcademy of Sciences, 370 05 CeskeBudejovice, Branisovska 31, Czechoslovakia Summary Various physical characteristics of the host-plant that influence host-plant acceptance by cabbage root fly were studied under laboratory conditions. No-choice bioassays confirmed that only combinations of physical and chemical stimuli elicited normal oviposition by the fly. The chemical nature of the host-plant was the factor most important for host acceptance. fu addition, although various-shaped objects stimulated responsive flies to lay, stem-shaped objects were the most effective. Although the colour and shape of leaf models wasnot important in no-choice bioassays, in choice bioassays cabbage root flies distinguished between some leaf shapes and colours. Flies were less selective when deprived of an oviposition site. Thefemales probably perceived the shape of the leaf during their post-alightment behaviour. There appeared to be four main regions of the spectrum that influenced oviposition by the cabbage root fly. Oviposition appeared to be positively correlated with the levels of violet-blue and orange-red wavelengths and negatively correlated with the levels of UV and green-yellow wavelengths reflected from plant models. Resume Carad�rlstiques vegetales influen<;ant la d�ouverte et l'acceptation de la plante-Mte par la mouche du thou Differentes caracteristiques physiques de la plante-Mte influen<;ant son acceptation par la mouche du chou ont ete etudiees dans des conditions de laboratoire. Des biotests sans choix ont confirmeque seules des combinaisons de stimuli physiques et chimiques provoquent une ponte nonnale chez l'insecte. La nature chimique de la plante-hi>te s'est averee le facteur le plus important pour l'acceptation de l'Mte. De plus, m!me si des objets de forme variable stimulent des mouches pr!tes a pondre, des objets en forme de tige s'averent les plus efficaces. Bien que la couleur et la forme des feuilles artificielles ne soient pas importantes en condition de tests sans choix, les mouches ont fait la distinction entre quelques formes et couleurs de feuille dans des tests avec choix. Privees de lieu de ponte, elles se soot montrees moins selectives. Les femelles per<;oivent la forme de la feuille probablement pendant la phase comportementale qui suit leur arrivee sur une plante. Quatre plages principales du spectre semblent influencer l'oviposition de la mouche du chou, qui parait !tre correlee positivement avec le niveau des longueurs d'onde dans le violet-bleu et dans !'orange-rouge et negativement avec celui des longueurs d'onde dans l'UV et dans le vert-jaune reflechi par des plantes artificielles. IOBC/WPRS-WorkingGroup Meeting"Integrated Control in Fie\d Vegetables".Vienna. 28-30Oct 1991 154 The use of covers to reduce cabbage root fly and caterpillar damage in white cabbage crops F. Van De SteeneCl), F. Benoit<2> & N. Ceustermans<2> <1> Centre for research in Vegetable Crops, Section V, LW.O.N.L., Faculty of Agricultural Sciences, Laboratory of Zoology, Ghent State University, Belgium <2> Centre for research in Vegetable Crops, Section I, Vegetable Research Station, Sint KaJelijne-Waver, Belgium Summary The effectiveness of two polyethylene-nets and two non-woven polypropylene-fleecesin controlling cabbage root flyand caterpillars of M. brassicaeand P. rapae in white cabbage crops was studied during 1990 and 1991. These tests were carried out because varying results had been obtained in recent seasons when the insecticides chlorfenvinphos and carbofuran had been applied to control the cabbage root fly. Four experiments were carried out: twoin the spring crops and two in summer crops. The covers were placed over crops shortly after planting and removed after various intervals of time. During the experiments;the numbers of eggs of the cabbage root fly were assessed using eggs-traps and the numbers of adults of M. brassicae using a light trap. In the spring crops, most of the cabbage root fly eggs were laid between 20 May and 20 June. In the summer crops, eggs were recovered from 15 August to the beginning of September. M. brassicae was caught in the light trap from the beginning of August until 15 September. Protecting white cabbage crops with nets or fleecesis an alternative method for controlling the cabbage root fly should the insecticides chlorfenvinphos and carbofuran lose their effectiveness. The nets and fleeces also produce an effetive control of caterpillars, provided their are no pupae of pest caterpillars overwintering in the soil when the crop covers are applied. Introduction In Belgium, the organophosphorus insecticides bromofos, diazinon, foxim, ethion, chlorpyrifos, fonofos, bromofos-ethyl, chlorfenvinphos and the carbamate insecticides carbosulfan and carbofuran are recommended for application to soil to control root flies in field vegetable crops. Chlorpyrifos, fonofos, bromofos-ethyl (to be withdrawn in 1992), chlorfenvinphos, carbosulfan and carbofuran are widely used for a variety of crops, including cabbages, carrots, leek and celery. Unfortunately, the efficacy of chlorfenvinphos and carbofuran in controlling larvae of the cabbage root fly is now extremely low because of the reduced persistence of those insecticides in 155 the soil (Van De Steene & De Smet, 1988; Van De Steene, Melkebeke & Verstraeten, 1990). These two insecticides have been applied in successive years and repeatedly in small fields at certain areas. Under such conditions, highly active microbial populations can develop that are able to degrade rapidly the insecticide. This phenomenon is commonly called 'enhanced' or 'accelerated' degradation (Walker & Suett, 1986). Enhanced degradation of carbofuranhas been reported by several authors during recent years (Felsot & Maddox, 1981; Read, 1983; Camper et al., 1987; Chapman et al., 1985). The result of enhanced degradation is a failure of the insecticide to control adequately the target insect. This paper reports the effectiveness of four different crop covers in preventing damage by cabbage root fly and cabbage caterpillars. Materials and Methods Four covers were compared with the insecticide chlorpyrifos for their relative effectiveness at controlling larvae of the cabbage root fly. The covers were also tested for their effectiveness in preventing caterpillar damage. During 1990 and 1991, four experiments were carried out at St. Katelijne-Waver in spring and summer crops of white cabbage. Plot design and layout Each plot consisted of two rows of 13-15 plants. Each cover tested, each insecticide treatment, and each untreated plot, was represented once only within each block. The positions of the plots within the three replicated blocks were randomised. The remaining experimental details are shown in Table 1. Treatments Immediately after planting, all covers were placed over the cabbage crops. the covers were removed at various times (see Table 2) during the season. The characteristicsof the test covers were: ''Lanet" gauze: polyethylene with a mesh of 1.35 mm square; weight = 20 g/m2 "Uco" gauze: polyethylene with a mesh of 1 x 1.8 mm; weight = 75 g/m2 "Pl 7" fleece: non-woven polypropylene; weight = 17 g/m2 "PlO" fleece: non-woven polypropylene; weight = 10 g/m2 A few days after planting, 100 ml of an aqueous suspension of the insecticide chlorpyrifos were applied to the base of each insecticide-treated plants. 156 Table 1: Experimental details of planting procedures and the dates when insect damage and crop yield were assessed Details of the 4 1990 1991 experiments Vegetable White cabbage White cabbage Spring crop Summer crop Spring crop Summer crop Variety Castello Struktion Castello Bison Sowing date 22 March 29 June 22 March 26 June Planting date 18 April 18 July 25 April 17 July Plant spacing 50 X 60 cm 50 x 60 cm 50 X 60 cm 50 X 60 C1Il No. of 11 7 12 12 treatments No. of 3 3 3 3 replications No. of 28 30 26 26 plants/plot Total no. of 924 630 930 930 plants Assessment of 29 May & 4 Sept. & 24 May, 16 Aug. cabbage root fly 6 July 8Nov. 10 June 13 Sept. damage & 5 July & 7 Oct. No. of plants 15 15 15 15 assessed Assessment of 6 July 8 & 18 Sept. 18 July 4 Sept. caterpillar 9 & 23 Oct. 7 & 24 Oct. damage Harvest of 30 6 July 30 Oct. 18 July 28 Oct. cabbage Assessmentof cabbage root fly and caterpillar damage In the 1990 experiments, cabbage root fly damage to the roots of cabbage was assessed both 5-6 weeks after planting and at harvest. In 1991, similar assessments were carried out 4 and 6-7 weeks after planting and at harvest. In each experiment, damage to the cortex of the roots of 15 randomly selected plants was assessed on a five category scale: 1 = clean (0% damage); 2 = 1 to 3 mines in the stem; 3 = more than 3 mines in the stem; 4 = stem and root moderately damaged (50%); and 5 = stem and root completely damaged (100%). A mean root damage index (R.D.I.) was 157 calculated for each treatment using the formula: la+2b + 3c + 4 d+ Se a+b+c+d+e where a, b, c, d and e are the respective numbers of plants having damage scores of 1, 2, 3, 4 and 5. The mean numbers of larvae and pupae were also recorded on the plants assessed for root damage. Damage by caterpillars was assessed on a three category scale: 1 = no feeding on the wrapper leaves: no feeding on head 2 = feeding on the wrapper leaves: no feeding on head 3 = feeding on the wrapper leaves: feeding on hea.d [unmarketable cabbage] In the spring crop, caterpillar damage was recorded at harvest;whereas in the summer crop damage was recorded immediately after the crop covers were removed. For all experiments, the mean head weight(± S.E.) of the cabbage plants was calculated from samples of 30 cabbages per plot. Table 2: List pf crop covers used and the times they were taken offthe crops 1990 1991 Treatments Spring crop Summer crop Spring crop Summer crop Untreated - - - - Chlorfenvinphos 24 April 24 July 11 May 25 July (100 mg a.i./pl) "Lanet" gauze to 4 May 29 Aug. 13 May 16 Aug. "Lanet" gauze to 18 May 12 Sept. 24 May 30 Aug. "Lanet" gauze to 8 June 26 Sept. 10 June 13 Sept. "Lanet" gauze to - - 19 June 4 Oct. "Uco" gauze to 4 May 29 Aug. 13 May 16 Aug. "Uco" gauze to 18 May - 24 May 30 Aug. "Uco" gauze to 8 June - 10 June 13 Sept. "PlO" fleece to 4 May 29 Aug. - 16 Aug. "PlO" fleece to 18 May - - 30Aug. "PlO" fleece to 8 June - - 13 Sept. "Pl7" fleece to - - 13 May - "Pl 7" fleece to - - 24 May - "Pl 7'' fleece to - - 10 June - 158 Table 3: Mean root damage index (R.D.I.) and mean no. of cabbage root fly larvae and pupae recovered per plant (1990) Spring crop Treatments Cover to 1st sample (29 May) 2nd sample (6July) Percent. Mean Mean No. Mean Mean No. Control RD.I. larvae/pi RD.I. l+p/pl Untreated - 2.0 3.7 2.2 7.3 - Chlorpyrifos - 1.3 0.4 1.5 1.8 75 ''La.net"gauze 4May 1.9 4.3 2.0 6.1 15 "Lanet" gauze 18 May 1.0 0.0 1.7 2.5 65 "La.net" gauze 8 June 1.0 0.0 1.3 0.7 90 "Uco" gauze 4May 2.4 6.2 2.0 7.0 4 "Uco" gauze 18May 1.0 0.0 1.8 1.7 77 "Uco" gauze 8June 1.0 0.0 1.1 0.3 96 "PlO" fleece 4May 2.1 4.8 1.9 3.5 51 "PlO" fleece 18May 1.0 0.0 1.6 2.8 61 "PIO" fleece 8 June 1.0 0.0 1.0 0.0 100 Summer crop Treatments Cover to 1st sample (29May) 2nd sample (6July) Percent. Mean Mean No. Mean Mean No. Control RD.I. larvae/pi RD.I. l+p/pl Untreated - 2.0 5.2 3.2 14.7 - Chlorpyrifos - 1.1 0.3 1.7 2.5 85 "Lanet" gauze 29 Aug. 1.0 0.0 2.1 6.2 58 "Lanet"gauze 12 Sept. 1.0 0.0 1.7 3.9 73 "Lanet" gauze 26 Sept. 1.0 0.0 1.1 0.4 97 "Uco" gauze 29 Aug. 1.0 0.0 2.0 4.5 69 "Uco" gauze - "Uco" gauze - "PlO" fleece 29 Aug. 1.0 0.0 1.7 2.6 82 "PIO" fleece - "PlO" fleece - 159 Table 4: Mean roo1 damage index (R.D.t) and mean no. of cabbage root fly larvae and pupae recovered per plant (1991) Spring ctop Treatments Cover 1st sample 2nd sample 3rd sample % to (24 May) (10 June) (5 July) Cont Mean Mean Mean Mean Mean Mean RDI larvae RDI larvae RDI l+p Untreated - 1.2 1.6 1.4 2.4 2.6 5.4 - Chlorpyrifos - 1.0 0.0 1.0 0.0 1.2 1.6 70 "Lanet" 13 1.0 0.0 1.5 1.9 2.0 4.1 24 gauze I May "Lanet" 24 1.0 0.0 1.0 0.0 1.6 1.9 65 gauze May I "Lanet" 10 - - 1.0 0.0 2.1 2.4 56 gauze June "Lanet" 19 - - - - 1.0 0.0 100 gauze June "Uco" gauze 13 1.0 0.0 1.2 0.6 2.1 4.7 13 May "Uco" gauze 24 1.0 0.0 1.0 0.0 1.9 1.7 70 May "Uco" gauze 10 - - 1.0 0.0 2.2 2.4 56 June "P17" fleece 10 1.1 0.4 1.7 2.8 2.1 3.6 33 May "P17" fleece 24 1.0 0.0 13 0.7 2.0 3.8 30 May "Pl7'' fleece 10 - - 1.0 0.0 1.8 2.1 61 June 160 Table 5: Mean root damage index (R.D.I.) and mean no. of cabbage root fly larvae and pupae recovered per plant (1991) Summer crop Treatments Cover 1st sample 2nd sample 3rd sample % to (24 May) (10 June) (5 July) Cont Mean Mean Mean Mean Mean Mean RDI larvae RDI larvae RDI l+p Untreated - 1.2 1.6 3.0 11.9 2.9 9.20 - Chlorpyrifos - 1.0 0.0 1.5 2.6 1.7 3.20 45 "Lanet" 16 1.0 0.0 3.0 8.4 3.1 13.20 0 gauze Aug "Lanet" 30 - - 1.0 0.0 1.9 5.80 37 gauze Aug "Lanet" 13 - - 1.0 0.0 1.0 0.00 100 gauze Sept "Lanet" 4 Oct - - - - 1.0 0.00 100 gauze "Uco" gauze 16 1.7 2.9 2.8 13.2 3.0 8.70 Aug "Uco" gauze 30 - - 1.0 0.0 1.7 7.10 Aug "Uco" gauze 13 - - 1.0 0.0 1.0 0.00 100 Sept "PlO" fleece 16 1.0 0.0 2.9 9.6 2.8 10.40 Aug "PlO" fleece 30 - - 1.0 0.0 1.6 4.60 50 Aug "PlO" fleece 13 - - 1.1 0.8 1.0 0.00 100 Sept 161 Table 6: Damage by caterpillars and mean head weight of cabbsge (Spring crop 1990} 6 July 1990 Cover No. of cabbage % Mean weight (g) Treatments to with damage unmarketable per cabbage head score (30 cabbages) ± 1 2 3 S.E. Untreated - 19 9 20 42 1868 ± 50 15 Chlorpyrifos - 26 9 18 2184 ± 53 "Lanet" gauze 4 May 29 12 10 20 2289 ± 62 "Lanet" gauze 18 May 44 6 0 0 2130 ± 54 "Lanet" gauze 8June 50 - 0 0 2091 ± 45 "Lanet" gauze ------ "Uco" gauze 4 May 38 9 2 4 2275 ± 58 "Uco" gauze 18 May 49 3 0 0 2090 ± 45 "Uco" gauze 8 June 47 - 0 0 2000 ±' 45 "PlO" fleece 4 May 29 16 6 12 2330 ± 46 "PlO" fleece 18 May 31 15 1 2 2198 ± 43 "PlO" fleece 8 May 51 - 0 0 1844 ± 46 LS.D. (P = 0.05) 345 v.c. (%) 6 162 Table 7: Damage by caterpillars and mean cabbage weight (spring crop 1991) 18 July 1991 Treatments Cover to No. of % Mean weight (g) cabbage with unmarketable per cabbage head damage score (30 cabbages) ± S.E. 1 2 3 Untreated . 32 l 163 Table 8: Damage by cate.pillars and mean head weight of cabbage (Summer crop 1990) 1st count 2nd count 3rd count (4 Sept.) (18 Sept.) (9 Oct.) Treatments Cover to No. of No. of No. of cabbage cabbage with cabbage with with damage damage score damage score score 1 2 3 1 2 3 1 2 3 Untreated - 48 23 - 37 27 7 24 14 33 Chlorpyrifos - 51 25 - 35 30 11 19 30 27 "Lanet" gauze 29 Aug. 67 1 - 59 6 3 44 19 5 "Lanet" gauze 12 Sept. 73 - - 71 2 - 70 3 - "Lanet" gauze 26 Sept. 74 -- 74 - - 74 - - "Uco" gauze 29 Aug. 73 - - 56 6 1 54 8 1 "PlO" fleece 29 Aug. 69 - - 66 3 - 53 16 - 4th count (23 Oct.) Mean weight (g) Treatments No. of cabbage per cabbage head with damage % (30 cabbages) score unmarketable ± S.E. 1 2 3 Untreated 20 2 49 69 2037 ± 111 Chlorpyrifos 19 0 57 75 1940 ± 118 "Lanet" gauze 40 .3 25 37 2055 ·± 112 "Lanet" gauze 67 3 3 4 1778 ± 90 "Lanet" gauze 72 1 1 1 1241 ± 89 "Uco" gauze 41 10 12 19 1381 ± 66 "PIO" fleece 46 5 18 26 1467 ± 83 LS.D. (P = 0.05) 977 v.c. (%) 33.73 164 Table 9: Damage by caterpillars and mean bead weight of cabbage (Summer crop 1991) 1st count (4 Sept.) 2nd count (7 Oct.) Treatments Cover to No. of cabbage with No. of cabbage with damage score damage score 1 2 3 1 .2 3 Untreated - 36 14 10 6 4 40 Chlorpyrifos - 33 18 9 11 1 48 "Lanet" gauze 16 Aug. 57 3 - 27 9 24 "Lanet" gauze 30 Aug. 60 - - 60 - - "Lanet" gauze 13 Sept. 60 - - 49 2 9 "Lanet" gauze 4 Oct. 60 - - 47 4 9 "Uco" gauze 16 Aug. 58 2 - 21 8 31 "Uco" gauze 30 Aug. 60 - - 53 4 3 "Uco" gauze 13 Sept. 57 3 - 46 0 14 "PlO" fleece 16 Aug. 59 1 - 10 6 44 "PlO" fleece 30 Aug. 60 - - 37 8 15 "PlO" fleece 13 Sept. 60 - - 55 2 3 3rd count (24 Oct.) Mean weight (g) Treatments No. of cabbages % per cabbage head with damage score unmarketable (30 cabbages) 1 2 3 Untreated 3 10 47 78 2116 ± 97.47 Chlorpyrifos 1 8 51 85 2144 ± 99 "Lanet" gauze 11 14 35 58 1836 ± 104 "Lanet" gauze 40 6 14 23 2034 ± 82 "Lanet"gauze 36 4 10 17 1776 ± 76 "Lanet" gauze 39 4 17 28 1340 ± 136 "Uco" gauze 6 17 37 62 1791 ± 95 "Uco" gauze 41 7 12 20 2180 ± 79 "Uco" gauze 42 1 17 62 1874 ± 98 "PlO" fleece 6 12 42 70 1896 ± 55 "PlO" fleece 28 17 15 25 1746 ± 92 "PlO" fleece 54 1 5 83 1694 ± 83 LS.D. (P = 0.05) 505 v.c. (%) 16 Resuhs and Discussion The mean root damage index and the mean number of larvae/pupae per plant for each treatment are shown in Tables 3 (1990 Expt.), 4 and 5 (1991 Expt.). The mean percentages of unmarketable heads and the mean weight per cabbage head in the spring crops are shown in Table 6 (1990) and Table 7 {1991). Thecorresponding data for the summer crops are shown in Table 8 (1990) and Table 9 (1991). In all experiments, the insecticide chlorpyrifos was extremely effective in controlling larvae of the cabbage root fly. Good control was also obtained by the covers removed 4-5 weeks before harvest. The damage by the larvaeof cabbage root fly was low (5-7 larvae & pupae/plant) in the spring crop, but high (15 larvae & pupae/plant) in the untreated plots in the summer crop in 1991. There was no caterpillar damage in the spring crops in either 1990 or 1991. Similarly, in the summer crop, in 1990 little damage occurred in the plots that were left covered until 12 September. However, in the summer crop of 1991, considerable damage occurred on the plots left covered until mid-September. This damage was caused by M. brassicaeadults emerging from pupae that had remained in the soil from September or October of the previous (1990) year. As the moths were trapped under the covers, they had little alternative than to lay on the crop. All covers were equally effective in controlling larvaeof the cabbage root fly and caterpillars. In all experiments, the mean weight of the cabbage heads was similar, indicating that the time covers were removed had no measurable effecton the crop yield. Conclusions Protecting white cabbages crops with nets or fleeces is a method of controlling cabbage root fly without applying insecticide. The covers also prevent damaged by caterpillars of M. brassicae provided the covered soil does not already contain overwintering moth pupae. In Belgium the covers can be removed on 10 June (spring crop-planted in April) or on 10 September (summer crop-planted in July or later}. Acknowledgement We thank the Institute for Encouragement of Scientific Research in Agriculture and Industry (I.W.O.N.L.) for subsidising this work. R�sum� L'utilisation de voHes de couvertures pour reduire les d�gits de la mouche du chou et des chenilles dans les cultures de chou blanc L'efficacite de deux filets en polyethylene et de deux voiles non-tisses en polypropylene pour lutter contre la mouche du chou et les chenilles de Mamestra brassicae et de Pieris rapae dans les cultures de chou blanc a ete etudiee en 1990 et 1991. Les quatre essais, dont deux portaient sur des cultures de printemps et deux 166 sur des cultures d' ete, ont ete entrepris suite a des resultats incertains durant ces dernieres annees avec les insecticides chlorfenvinphos et carbofuran. Les differents types de couverture ont ete places sur les cultures sitl>t la plantation effectuee et enleves a des differents intervalles. Durant les essais, le nombre d'oeufs de la mouche du chou a ete determine a l'aide des pieges a oeufs et le nombre de papillons de M. brassicae au moyen d'un piege lumineux. La plupart des oeufs de la mouche du chou sont pondus entre le 20 mai et le 20 juin pour les cultures de printemps, et du 15 aoftt au debut septembre pour les cultures d'ete. M. brassicae a ete piegee du debut aoftt au 15 septembre. La couverture des cultures de chou blanc par des filets ou des voiles est une methode de lutte contre la mouche du chou qui peut remplacer les insecticides chlorfenvinphos et carbofuran au cas ou ils perdraient leur efficacite. Elle peut egalement eviter les chenilles a condition qu'il n'y ait pas de nymphes hivemantes dans le sol au moment de la mise en place de la couverture. References Camper, N.D., Fleming, M.M. & Skipper, H.D. (1987). Biodegradation of carbofuran in Pretreated and Non-pretreated soils. Bull Environ. Contam. · Toxicol 39: 571-578. Chapman, R.A, Moy, R. & Herming, K (1985). A simple test foradaptation of soil microorganisms to the degradationof the insecticide carbofuran. J. Environ. Sci. Health B20(3): 313-319. Felsot, A.S. & Maddox. J.V. (1981). Enhanced microbial degradation of carbofuran in soils with histories of furadan use. Bull Environ. Contam. Toxicol 26: 781- 788. Read, D.C. (1983). Enhanced microbial degradation of carbofuran and fensulfothion after repeated applications to acid mineral soils. Agriculture, Ecosystemsand Environment 10: 37-46. Van De Steene, F. & De Smet, G. (1988). Chemical control of Delia radicum (L) in brassica crops and accelerated microbialbreakdown of chlorfenvinphos and trichloronate. Bulletin SROP, 1988 XI/1: 136-149. van de Steene, F., Melkebeke, T. & Verstraeten, R. (19090). Breakdown of carbofuran, chlorpyrifos, fonofos and bromofos-ethyl applied to soil from four regions of Belgium. Med. Fae. Landbouww., Rijkruniv., Gent 55/1: 107-116. Walker, A. & Suett, D.L (1986). Enhanced degradation of pesticides in soil: a potential problem for continued pest, disease and weed control. In: Crop Protection in Vegetables, Aspects of Applied Biology, 12: 95-103. IOBC/WPRS-WorkingGroup Meeting 'IntegratedControl inField Vegetables', Vienna, 28-30Oct 1991 167 Work airried oui at Rennes during 1990 and 1991 on pest insects of field vegetable crops* E. Brunel /NRA, Laboratoirede Reserches de la Chairede Zoologie, Domaine de la Motte au Vicomte, BP 29, 35650 Le Rheu, France Summary During 1990 and 1991, pest insect control in field vegetable crops has concentrated on the cabbage root fly (Delia radicum), the artichoke fly( Cheilosia vulpina}, and the carrot fly (Psila rostie). Most work has been carried out on the cabbage root fly, largely because cbelllical control appears to be becoming more and more difficult as this pest find new crops (e.g. oilseed rape) in which to multiply. In addition, with the limited number of soil insecticides available, and even fewer active ingredients, many of the products are used intensively in certain soils. As a consequence of this, many insecticides are now being degraded by soil micro-organisms before they have chance to protect the crop plants from fly infestations. At present, the major emphasis is to develop control methods that are less harmful to the environment than insecticides. In order to do this in a satisfactory manner, it will be essential to obtain a far greater knowledge of the detailed ecology of pest insects. If non-insecticidal methods of control are to be effective, then further information will be required on the population dynamics of the pest, the size of local pest populations, and on factors that regulate diapause. Three new ways of controlling the cabbage root fly have been tested during 199Q and 1991. In the first of these, the insect growth regulator Cyromazine (Trigard, Ciba Geigy) when applied to plants in a similar manner to a soil-insecticide, gave· high levels of fly control in both laboratory and greenhouse trials. Secondly, twelve strains of Bacillus thuringiensiswere tested fortheir effectiveness at killingcabbage root flyadults. Although several strains killed the flies, the bacteria had to be imbibed in the drinking water of the flies to be effective. Obviously, under field conditions it could prove extremely difficult to restrict flies to specific drinking sites. The third approach, that was started only in 1991, will be to rear and release large numbers of the parasitoidAleochara bilineata into fields containing brassica crops in Brittany. This project is being undertaken in collaboration with the Pl�mt Protection Service. The area of intensive vegetable production in the north of Brittany has been chosen as the site for a "large-scale" field trial. Theinitial work is concentrating on developing suitable methods for mass-rearing the pest and its parasitoid, by ma.�g maximumuse of the cultural and environmental conditions available locally . .. Paper. presented by S. Finch 168 The second pest studied, the artichoke fly, has been the subject of a thesis prepared by Cadou under the guidance of Brunel. This thesis, which deals with the biology, and in particular with the factors that influence diapause of this pest syrphid, will be available in 1992. Finally data are available from the carrot fly trapping scheme, in which flies have been trapped in a routine way for each of the last 26 years. The numbers of flies caught in Malaise traps have been compared to the numbers caught in other traps. The data obtained have also confirmed the results of other members of the Working Group concerning the relative effectiveness of water traps and sticky traps. R�sume Recherches poursuivies a Rennes en 1990 et 1991 sur les dipteres ravageurs des cultures legumieres En 1990 et 1991 les recherches ont ete focalisees sur les dipteres ravageurs des cultures legumi�res de plein champs: la mouche du chou (Delia radicum), le syrphe de l'artichut (Cheilosia vulpina) et la mouche de la carotte (Psila rosae). Les principaux travaux concement la mouche du chou, en raison des difficultes rencontrees au niveau de la lutte chimique et du fait que cet insecte trouve chaque annee de nouvelles cultures (colza) pour se multiplier. De plus, malgres le nombre limite de produit insecticide du sol disponible et les faibles quantites de matieres actives employees, certains produits soot utilises de fa�on repetee. Une des consequences de ces pratiques est que ces produits soot degrades par les micro organismes du sol avant meme d'avoirassure la protection de la plante. Actuellement les principaux objectifs soot de developper des methodes de lutte moins nuisibles pour l'environnement que les insecticides. Cela exige l'approfondissement de nos connaissances de l'ecologie des ravageurs. Pour que les methodes de lutte alternative puissent etre efficaces, il faudra reunir des informations sur la dynamique des populations du ravageur, le niveau des populations locales et les facteurs qui regulent la diapause. Trois approaches nouvelles ont ete testees pour lutter contre la mouche du chou: 1) En premier lieu, le regulateur de croissance d'insecte, la cyrnmazine (Trigard, Ciba Geigy), appliquee sur les plantes de la meme maniere qu'un insecticide du sol assure une protection efficace contre la mouche du chou aussi bien en essais de laboratoire qu'en serre. 2) Lanocuite de 12 souches de Bacillus thuringiensis a ete testee sur D. radicum. Quelques souches, incluses dans l'eau de boisson, des adultes soot efficaces. Bien sur, en conditions naturelles, il faudra preciser la possibilite d'attirer les adultes sur des sites specifiques. 3) En 1991, nous avons commence un elevage du parasite Aleoclrara bilineata en vue de lacher inondatif dans les parcelles de Brassica en Bretagne. Ces travaux soot realises en collaboration avec le Service de la Protection des Vegetauxavec qui une zone de culture intensive a ete choisie dans le nord de la Bretagne pour des essais a grande echelle. Ce travail est centre sur l'elevage synchrone du parasite et de son hote et devra tenir compte de l'adaptation aux conditions culturales et environnementales. 169 Le deuxieme ravageur, le syrphe de l'artichaut, fait l'objet d'une these preparee par D. Cadou (sous la responsabilite de Brunel). Ce travail developpe la biologic du ravageur dans les conditions bretonnes et, en particulier, les facteurs qui influencent la diapause. Enfin, le piegeage de la Mouche de la carotte est realise depuis 26 ans de fa�on reguliere et dans les memes conditions. Les captures realisees a la tente malaise sont comparees a celles des pieges jaunes. Les resultats confirment ceux obtenus au moyen des piege a eau et des pieges a glu par les membres du groupe de travail OILB sur l'efficacite de ces deux systemes de capyures. IOBC/WPRS-WorkingGroyp Meeting 'IntegratedControl in FjeldVegetables". Vienna. 28-30 Oct 1991 170 Mustard meal mulch - a possible cultural method for attracting natural enemies of brass!ca root flies into brassica crops M. Ahlstrom-Olsson & T. Jonasson Swedish University of Agricultzual Sciences, Department of Plant & ForestProtection, PO Box 44, S-230 53 Alnarp, Sweden Summary Theadult activityperiod ofAleochara bilineata is well synchronized with the pupal stage of the cabbage root fly (Delia radicum). Hence, the adult beetles generally occur too late in the season to be important egg predators of D. radicum. In contrast, another species, Aleochara bipusiulata, hibernates as an adult and is active at the time of the first generation of D. radicum,when A. bilineata is scarce. If A. bipustulatacan be attracted to fieldscontaining Brassicacrops, it may help to reduce crop damage by eating eggs and larvae of D. radicum. When white mustard meal (Sinapis alba),whose odour is similar to that of a wounded crucifer plant wasused as amulch in fieldexperiments, it strongly attracted species of Aleochara. Themustard meal also attracted large numbers of the bean seed flies D. platura and D. florilega. Thisattraction of the two species of Deliaprovided conditions suitable forA. bipustulatato reproduce, since the adults beetles were able to use the puparia of D. platura and D. florilega as hosts for their progeny while feeding on the eggs of D. radicum. Introduction The Swedish part of the joint Nordic project "Reducing the use of insecticides in Brassica vegetable crops" is to study the possibility of using naturally occurring predators and parasitoids as biological agents for controlling Brassica root flies. The turnip root fly (Delia floralis) and the cabbage root fly (D. radicum), are the two pests being studied. To date, all studies have been concentrated on D. radicum. Two other flies, D. platura and D. florilega, that also live in Brassica crops are primarily saprophagous, and often feed on the dead and decaying plant material that is produced following attacks by D. radicumand D. f/oralis. Staphylinid beetles of the genus Aleochara are an interesting group of natural enemies of Brassica root flies. In addition to the beetles eating eggs and larvae of Delia species, their larvae also develop as parasitoids within Delia puparia (Colhoun, 1953). A. bilineata hibernates in the larval stage within Delia puparia (Fuldner, 1960). The beetle larvae start their development as soon as temperatures begin to rise in early spring and their development is such that the adult activity period of A. bilineata is synchronized well with the pupal stage of D. radicum (Fig 1). Consequently, adults 171 of A. bilineata occur too late in the season to be important egg predators of D. radicum. Aleochara bil/neata &-&-& Delia radicum f \ illfil /i· Aleochara bfpustulata Delia pfatura/fforflega 100 120 160 - 18.0 220 Julian pays Fig. 1: Schematic representatio:i or Ufe-cycles of Delia and AJeochara. The late season generations of adult Deliarodicum and D. platura/Jlorilega are probably only partiaI generations. In contrast to A. bilineata, it is the adults of A. bipustulata that hibernate. Hence, A. bipustulata is active early in the season (Fuldner, 1960) and usually occurs in large numbers during the peak period of oviposition by the first generation of D. radicum. Consequently, it is active too early in the season to be of great importance as a parasitoid of D. radicum (Fig. 1). However, if it could be attracted in sufficiently large numbers to fields, containing Brassica crops, it might help to reduce crop damage by destroying eggs and larvae of Brassica root flies. Experimental Crushed, defatted seed of white mustard (Sinapis alba) has been used as a mulch in field experiments involving Brassica vegetable crops in southern Sweden since 1988. The results indicate that mustard meal applied as a thin layer (225 kg/ha) on the soil within the rows of the crop plants, reduces damage by larvae of Delia radicum (Fig 2). 172 Table 1. Numbers of Aleochara caught in pitfall traps during 1989 and 1990. Differences between the treatments are shown by * = (P = 0.05); 111* = (P = 0.01); n.s. = no significant difference Location Species Plots with Plots without · Statistical (year) of Aleochara mustard meal mustard meal significance Fulltofta A. bilineata 110 81 n.s.• (1989) A bipustulata 355 107 Fulltofta A bilineata 155 121 ••n.s. (1990) A bipustulata 165 31 (I Alnarp A. bilineata 124 59 .. (1990) A bipustulata 286 59 Torslunda A. bilineata n.s. 6 8 • (1990) A. bipustulata 223 54 kg/plot 75 70 65 t;\ffl marketable yield D unmarketable yield 60 55 50 45 40 35 30 25 20 15 10 5 0 control Bir 20 mustard Bir 10 Bas 10 Bas 5 Bas 1.25 kg/plot • kg/ e square meters Fig. 2: Levels of Delia radicumcontrol attained in swedes treated with Birlane G (chlorphenvinphos) 20 kg/ha; Birlane G 10 kg/ha; Basudin EC (diazinon) 10 I/ha, 5 I/ha and 1.25 I/ha; mustard meal 225 kg/ha; and without insecticide. The !ncreased marketable yield reflects the decreased damage by D. radicum. The mustard meal treatment was more effective than two of the Basudin treatments. 173 TheAleochara species are strongly attracted by the mustard meal (Table 1). Toe same is true for D. platura and D. jlorilega. The larvae of these fliesfeed on the mustard meal and have such a rapid rate of larval development that they pupate in the soil around the brassica plants only shortly after D. radicum reaches its peak period of oviposition. This enables A. bipu.stulata to reproduce successfully, as the adult beetles can feed on the eggs of D. radicumand then the puparia of D. platiua and D. jlorilega as hosts for their progeny. Insect activity in a cabbage field treated with mustard meal is comparable to that in a crop heavily infested by D. radicumlarvae. The odour of the decomposing mustard meal is similar to that of a damaged crucifer tissues and arisesfrom isothiocyanates and other metabolites of glucosinolates. Adding the meal to a newly transplanted, completely healthy cabbage plant, makes it smell as if a heavy attack has already started. The most important benefit from applying such mulches is that they attract A. bipu.stulata during the main oviposition period of D. radicum. Manipulating a naturally occurring predator seems a more appropriate method than releasing laboratory-reared insects, as suggested by Bromand (1980). Toe direct effect of mustard meal mulch on D. radicumneeds further study, as there was a tendency for fewer fly eggs to be recovered from around treated plants. IUsumi Les mulch de farine de moutarde O une m�thode culturnle possible pour l'attraction d2s ennemis naturels de la mouche du chou daas les cultures de .Brassica La periode d'activite de l'adulte d'Aleochara bilirieata est bien synchronisee avec le stade pupal de la mouche du chou (Delia radicum). Ainsi, ies coleopteres adultes apparaissent generalement trop tard pour etre des predateurs importants d'oeufs de D. radicum. En revanche, une autre espece, Aleochar"' bipu.stulata, hiveme a l'etat d'adulte et est active durant la premiere generation de D. radicum, alors que A bilineata est rare. A. bipu.stulata pourrait contribuer a la reduction des degfits dans les cultures par son action de predation sur les oeufs et larves de D. radicum, s'il etait possible de l'attirer vers les champs de Brassica. La farine de la moutarde blanche (Sinapisalba), appliquee en mulch dans un champ experimental, attire fortement des especes d'Aleochara par son odeur comparable a celle de plantes de cruciferes blessees. Elle attire egalement en grand nombre les deu.-r especes de mouche grise des semis D. platura et D. jlorilega. Ce dernier effetprocure les conditions propices a la reproduction d'A. bipu.stulata, les coleopteres adultes utilisant les puparia de D. platura et D. jlorilega comme hotes pour leur progeniture, tout en se nourrissant eux-memes des oeufs de D. radicum. References Bromand, B. (1980). Investigations on the biological control of the cabbage root fly (Hylemya brassicae)with Aleochara bilineata. Bulletin SROP 3(1): 49-62. (International organization for biological and integrated control of noxious animals and plants.) Colhoun, E.H. (1953). Notes on the stages and the biology of Baryodma ontarionis, 174 Casey (Coleoptera: Staphylinidae) a parasite of the cabbage maggot, Hylemya brassicae Bouche (Diptera: Anthomyiidae). CanadianEnJomologist 85: 1-8. Fuldner, D. (1960). Beitriige zur Morphologie und Biologie von Aleochara bilineata Gyll. und A bipustulata L (Coleoptera: Staphylinidae). Z. Morph. DkoL Tiere 48:·312-386. IOBC/WPRS-WorkingGroup Meeting 'IntegratedControl inField Vegetables', Vienna. 28-30Oct 1991 175 Predation of cabbage root fly eggs by carabidae S. Finch & M.S. Elliott HorticultureResearch International, Wellesbourne, Wwwick CV35 9EF, U.K Summary Laboratory tests with carabid ground beetles found in soils on the Wellesbourne Research Station,indicated that intermediate-sized beetles such as Bembidion tetracolum and Agonum dorsale were more effective predators of cabbage root fly eggs than small beetles, e.g. Bembidion lampros, Trechusquadristriatus, or large beetles, e.g. Harpalus rufipes,Pterostichus melanarius. Further tests indicated that Agonum dorsale would be an ideal predator, as it can survive up to a month without food, is not killed by Pterostichus, aggregates naturally, eats maximum numbers of cabbage root fly eggs and larvae; and although strictly carnivorous is not cannibalistic. Agonum dorsale is also relatively easy to retain near to the stems of plants by simple barriers. Unfortunately, as insufficientAgonum dorsale were available at the time of the greenhouse and field trial, Bembidion tetracolum, a less favoured beetle, was used. Greenhouse trials with B. tetracolum, indicated that 2 beetles per plant were sufficient during the spring to control the high !evels of cabbage root fly infestation normally encountered in the field at Wellesboume. This species was not as effective, however, when tested in the field during mid-summer. Introduction Work at Wellesbouroe in the late 1950s (Hughes, 1959; Hughes & Salter, 1959) and early 1960s (Hughes & Mitchell, 1960; Wright et al., 1960; Mitchell, 1963; Coaker & Williams, 1963) showed that predators exerted an important check on the populations of the cabbage root fly, with ground beetles alone killing > 90% of the eggs and first-instar larvae produced during the first and second fly generations. In recent years, however, averages of 150 third-instar larvae/plant have occasionally been recorded from certain crops attacked by the first generation of flies. As such numbers are unlikely to represent only 10% of a pest population, it appears that some of the earlier estimates of predation may no longer be appropriate. Recent research has shown that although there can be a 90% mortality during the life-cycle of the cabbage root fly, approximately 30% of this mortality appears to occur at the egg a11dfirst-instar larval stages (Finch & Skinner, 1988). Results indicate that considerable mortality occurs during the later larval stages and is often due to abiotic rather than biotic factors. This paper is concerned primarily with determining whether there are ground beetle species that may be suitable for use as biological control agents against the cabbage root fly. 176 Experimental work Materials and methods In earlier studies, Coaker & Williams (1963) indicated that five of.the ground beetles common in the Wellesboume locality were important predators of cabbage root flyeggs. These five beetles and a further four species were included in the present study (Table 1). An additional factor determining this choice was that the nine beetles could be collected in reasonable numbers from the fields of the Research Station. Once collected, the beetles were separated into species. About 50-100 beetles of a particular species were then maintained in ventilated plastic boxes (28 cm x 16 cm x 9 cm deep) in a room at 18 ± 2°C. Twice weekly the beetles were provided with food and water. Initially the beetles were given corned beef as food, but as this became toxic to some beetle species once it started to decompose, the beetles were fed subsequently on dry cat biscuits (Powell - personal communication). Table 1: Mean numbers or cabbage root fly eggs eaten/day by individuals or the nine test beetles. °Five species tested by Coaker & WHiiams (1963) Bembidion lampros • 6 Trechus quadristriatus• 7 Bembidion tetracolum 32 Amara familiaris 58 Agonum dorsale 55 Harpalus affinis • 18 Nebria brevicollis 2 Harpalus rufipes• 7 Pterostichus melanariu.s• 0 Predation or cabbage root fly eggs Tests were carried out by placing beetles individually into small (12.5 cm x 8 cm x 2 cm deep) ventilated boxes lined with dampened white filter paper. Each beetle was provided with two 1.5 cm filter paper squares each of which contained 60 freshly laid cabbage root flyeggs. The numbers of flyeggs eaten/day were recorded for 10 beetles of each species for a ten-day period (Table 1). Most eggs were eaten by the intermediate-sized beetles such as Bembidion tetracolum, Amu,rafamiliaris and Agonum dorsale. Although earlier workers (Coaker & Williams. 1963) had indicated that Bembidion lampros, Trechus quadristriatus and Pterostichus melanarius were important as predators of cabbage root fly eggs, the first two beetles are small and hence there is a physical limit to the numbers of eggs they can consume in a day and the third beetle is large and does not eat eggs. As chemical tests were used previously to show which beetles had ingested cabbage root 177 fly stadia in their diet, the positive results from tests with Pterostichusmelanarius (Coaker & Williams, 1963) were misleading and probably indicated that this beetle had eaten smaller beetles that had fed on root fly stages. Survival of beetles in no-food sit1nations As many agricultural soils now contain little organic matter during the spring and early summer, there are probably tim:es when beetles are subject to starvation conditions. To determine how long beetles can survive in "no-food" situations, beetles were placed individually into deep open-topped plastic containers in which the walls of the container sloped inwards. One beetle was placed into each container and then half of the containers were kept dry permanently and the other half had water added daily. Table 2: Surviw1l {in days) of test carabid beetles denied food snd kept eithe..- in dry containers or in containers to which water was added oaiJy Dry Wet Bembidion lampros 4 5 Trethus quadristriatus 7 16 Bembidion tetracolum 4 8 Amara familiaris 8 11 Agonum dorsale 9 30 Harpalus affinis 10 24 Nebria brevicollis 9 91 Harpalus rufipes 14 47 Pterostichus melanarius 11 26 The data show that the larger beetles survived 9-14 days without food or water and that two of the smaller beetles survived for only 4 days (Table 2). However, when supplied with water, one of the best predators of cabbage root fly eggs,Agonum dorsale, survived without food forabout 30 days. The Nebria result is atypical because this beetle aestivates during the summer and hence during this quiescent phase it can live for long periods providing it can obtain sufficient water to metabolize slowly its reserves of stored fats. Predation betw�n beetle species Most people describe ground beetles as "beneficial insects" because in "no choice" situations the carnivorous beetles will eat pest insects and the plant-feeding 178 beetles will eat weed seeds. However, as some of these beetles also eat each other, some species may not be of value in pest control terms, particularly if they destroy other beneficial beetles. To determine which beetles kill other beetles, one specimen of Pterostichus melanarius was placed into a plastic arena with one specimen of one of the other test beetles. Each beetle pairing was replicated five times so that forty-five arenas were used for the complete experiment. The experiment was repeated with Harpalus rufipes as the dominant beetle. All beetles were supplied with water but not with food. During the 30 days of the experiment Pterostichus melanarius was not canm"balistic and did not kill Harpalus rufipes or Nebria brevicollis. It fed voraciously, however, on the small- and intermediate-sized beetles and had destroyed all of them within two to five days, except for Agonum dorsale which survived for 18 days and appeared to protect itself by releasing deterrent chemicals. Harpalusrufipes did not eat the other beetles, a clear indication that this beetle feeds primarily on material of plant origin. Maintaining predatory beetles close to plants To determine how many predatory beetles would be required per plant to control cabbage root fly infestations under field conditions, beetles must be retained alongside plants for the duration of the experiment. In the past, galvanized metal barriers have been used for this purpose at Wellesboume (Mitchell, 1963). Such barriers were used in the present experiments to determine whether the beetles could climb out of barriers with outwardly-projecting flanges, from which they were expected to escape, and from barriers with inwardly-projecting flanges(overhangs), fromwhich they were not expected to escape. All barriers over which beetles were expected to escape were painted first with blackboard paint and, while the paint was wet, were sprinkled with dry silver sand to create a rough surface that was easy for beetles to climb. Within 5 minutes of the start of the experiment all beetles had climbed the 5 cm-high barriers coated with sand. Bembidion tetracolum (40%) and Agonum dorsale (60%) even managed to climb over unpainted shiny metal barriers within a day. No beetles escaped out of the barriers in which the flangepointed towards the plant, indicating that while some beetles could scale shiny vertical surfaces, none could overcome the overhang. For this reason, round 15 cm-diameter plastic barriers with a 2 cm overhang facing towards the plants were used to retain predatory beetles alongside brassica plants. However, as such barriers are only deep enough to be pushed about 1 cm into the soil, beetles could escape by burrowing. The arrangement used to determine which beetles could burrow under the barriers is shown in Fig. 1. The three species capable of burrowing under the barriers were Trechus quadristriatus, which normally spends most of its time burrowing alongside the roots of crop plants and Harpalus affinis and H. rufipes, both of which are seed eaters and live mainly in shallow burrows beneath dense matt-forming weeds such as chickweeds (Stellaria spp.) and mayweeds (Anthemis/Matricaria spp.). 179 ARRANGEMENT FOR BEETLE BURROWING EXPERIMENT 15 cm diameter plastic barrier Beetle burrow Water trap Fig. 1: Diagram of arrangement used to determine whether ground beetles coul� burrow under plastic barriers used in attempts to retain predatory beetles near the base of plants infested with cabbage root fly eggs Advantages of l!SingAgonum dorsale as a specific predator A series of experimentswere carried out to determine which beetle, of the nine tested, possessed most of the characteristics considered impcrtant for a predator of the immature stages of the cabbage root fly. In eight of the nine experiments, Agonum dorsale appeared to be the most suitable beetle on which to base future research work in that it consumed maximum numbers of cabbage root fly eggs and larvae, survived forup tc a month without food and was not eaten readily by other beetles, such as the larger species of Pterostichus. Additionally, A. dorsale has certain advantages if attempts are made in the future to rear and release predator beetles, in that although it is strictly carnivorous it is not cannibalistic. It also aggregates naturally and hence maintaining large colonies in a small space should not pose the problems associated with other species. Agonum dorsale should also be relatively easy 180 to retain around the stems of fly-infested brassica plants, as it does not fly out of or burrow under simple barriers. Its only drawback is that it can climb and hence may not stay where it is required for field trials. However, recent advances in intercropping clovers with brassica crops (Theunissen et aL - this bulletin) may provide cropping systems that are more conducive to restricting this speci�s to the vicinity of infested brassica plants. Under natural conditions, A. dorsale is more numerous in crops that provide good ground cover, such as cereals, than in the bare soil situation normally associated with spaced brassica crops. Testing predatory beetles under glasshouse conditions To determine the numbers of beetles required to control cabbage root fly infestations, six-week old cauliflower plants were transplanted into 17.5 cm diameter pots of Levington compost and then each plant was surrounded with a 15 cm diameter beetle barrier (Fig. 1). All the plants were allowed to establish for one week and then 25 of the "barriered" plants were used in each test. No cabbage root fly eggs were added to the five plants used as the "un-infested" control, whereas 40 freshly-laid eggs were added to each of the other twenty plants. Beetles were not added to five of these plants ("infested" control). One, two or four beetles were added to five of each of the remaining plants. As sufficientAgonum dorsale were not available at the time of these experiments, the experiments was carried out with the other two intermediate-sized beetles, Ama,�a familiaris and Bembidion tetracolum. Table 3: Final plant weight and numbers of cabbage root fly (CRF) pupae recovered from brassica plants inoculated initially with 40 cabbage root flyeggs and 1, 2 or 4 individuals of the beetlesAmara familiarisand Bembidion tetmcolum CRF eggs/plant Beetles· /plant Plant wt (g) No. of CRF pupae ·Amarafamiliaris 0 0 89 40 0 5 27 40 1 5 30 40 2 35 18 40 4 50 14 ·nembidion tetracolum 0 0 136 40 0 8 17 40 1 72 8 40 2 131 3 40 4 129 3 181 The results (Table 3) show that although Amarafamiliaris will eat cabbage root fly eggs when given "no-choice" (Table 1), it is normally a saprophagous feeder and hence is not an effective root fly predator when allowed access to alternative sources of food. Nevertheless, the treatments involving 2 and 4 beetles/plant did protect the plants to a certain extent and lowered the numbers of pupae produced. The Bembidion tetracolum result was more promising. With this species, even one beetle/plant gave some protection, and plant growth was not affected. In addition pupal survival was extremely low when either 2 or 4 beetles were retained alongside the base of an infested plant. Conclusions The major problem with carabids, is that despite living forlong periods such beetles are generally only effective predators during the relatively short period when they are maturing/laying eggs. Hence, achieving control under field conditions, they may have to be reared and released at a specific developmental stage, which would probably be difficult and costly to achieve. A simpler alternative to rearing large numbers of ground beetles may be to adopt the approat:h of Theunissen et aL (this bulletin) and alter the cropping system so that increased numbers of predators are arrested at the appropriate time of year within infested brassica crops. This may be feasible against the first (May - early June) generation of the cabbage root fly, as at this time of year Agonum dorsale and Bembidion tetracolum are in the development phase in which they will eat large numbers of the immature stages of the cabbage root fly. Acknowledgement We thank the Ministry of Agriculture, Fisheries and Food for supporting this work as part of MAFF Project F05B. R�sum� Les Carabes, auxiliaires potentiels pour la Jutte contre la mouche du chou Des essais en laboratoire avec des carabes provenant des sols de la Station de recherche de Wellesboume indiquent que les specimens de taille moyenne, tels Bembidion tetracolum et Agonum dorsale sont des predateurs d'oeufs de la mouche du chou, bien plus efficaces que ceux de petite taille comme Bembidion lampros, Trechus quadristriatus, ou de grande taille, tels Harpalusrufipes ou Pterosticlw.smelanarius. D'autres experiences montrent qu'Agonum dorsale pourrait etre un predateur ideal, car il peut survivre quatre semaines sans nourriture, n'est pas tue par Pterostichus, s'agrege naturellement et devore un grand nombre d'oeufs et de larves de la mouche du cbou; bien que strictement carnivore, il ne montre pas de cannibalisme. Il s'avere egalement aise de maintenir Agonum dorsale au voisinage des tiges des plantes au moyen de barrieres simples, car il ne s'envole pas et ne tente ni de grimper, ni de creuser pour s'echapper. 182 Malheureusement, il n'a pas ete possible de recolter en champ Agonum dorsale en suffisance pour effectuer des essais en serre et en plein champ. Par consequent, Bembidion tetracolum, un predateur moins propice, a ete teste en serre au printemps; il s'avere que deux individus par plante seraient suffisants pour combattre des niveaux eleves d'infestations rencontres habituellement dans les parcelles de Wellesbourne. Cependant, cette espece ne s'est pas averee aussi efficace lors d'une experimentation a la mi-ete en champ. Le probleme majeur chez les carabes semble atre le fait qu'ils ne sont, en regle generale et malgre leur grande longevite, des predateurs efficaces que pendant une periode relativement courte, correspondant a la maturation ovarienne et a fa ponte. Ainsi, pour leur utilisation comme moyen de lutte en conditions de pleine terre, ils devraient atre eleves, puis introduits a un Stade de developpement physiologique precis, ce qui serait probablement difficile et onereux a assurer. References Coaker, T.H. and Williams, DA (1963). The importance of some Carabidae and Staphylinidae as predators of the cabbage root fly,Erioischia brassicae (Bouche). Ent. exp. et appl 6, 156-164. Finch, S. & Skinner, G. (1988). Mortality of the immature stages of the cabbage root fly. In: "Progress on Pest Management in Field Vegetables". Eds. R. Cavallaro & C. Pelerents. A A Balkema, Rotterdam. pp. 45-48. Hughes, R.D. (1959). The natural mortality of Erioischia brassicae (Bouche) (Dipt., Anthomyiidae). J. exptl Biol 37, 218-223. Hughes, R.D. and Mitchell, B. (1960). The natural mortality of Erioischia brassicae (Bouche) (Dipt., Anthomyiidae): life tables and their interpretation. J. anim. Ecol 28, 343-357. Hughes, R.D. and Salter, D.D. (1959). Natural mortality of Erioischia brassicae (Bouche) (Dipt., Anthomyiidae) during the immature stages of the first generation. J. anim. Ecol 28, 231-241. Mitchell, B. (1963). Ecology of two carabid beetles, Bembidion lampros (Herbst) and Trechusquadris triatus (Schrank). J. Anim. Ecol 32, 377-392. Wright, D.W., Hughes, R.D. and Worrall, J. (1960). The effect of certain predators on the number of cabbage root fly (Erioischia brassicae (Bouche)) and the subsequent damage caused by the pest. Ann. appl Biol 48, 756-763. IOBC/WPRS-WorkingGroup Meeting "Integrated Control in Field Vegetables", Vienna, 28-30 Oct 1991 183 Collaborative projects for 1992 and 1993 S. Finch HorticultureResearch International, Wellesboume, Wwwick; CV35 9EF, UK Introduction Prior to the meeting, all participants were circulated with brief notes to publicize the work of the IOBC. The notes emphasized that the two main objectives of IOBC Working Groups are to stimulate international c9llaboration between researchers working in the same area, and to develop joint projects. I also stressed that for those Group members attempting to develop possible collaborative projects prior to the meeting, it was advisable to keep the initial project as simple as possible, as many people already have large research programmes. "For such workers, it is often extremely difficult to incorporate anything other than small amounts of "new" work. In contrast, joint projects can be much larger if the major work schedules of two or more researchers in different countries are currently along similar lines. The above points were borne out well in the final discussion concerning collaborative work, in which the main aim was to ensure that all participants were involved in at least one collaborative experiment. In all, twelve topics were suggested and, as to be expected, some were greeted with great enthusiasm whereas others received something of a lukewarm reception, largely because the research area suggested was often the major research thrust of a separate IOBC Working Group. It is inevitable that researchers will base their attendance at a specific Working Group on the commodity being discussed - here Field Vegetables - rather than on their preferred personal research topic, as the former often constitutes the greater part of their job. Proposed Experiments The twelve topics suggested for collaborative experiments are shown below. They are presented in the order they were taken down at the meeting by Bob Ellis. 1. Intercropning Leader: Jan Theunissen (The Netherlands) Intercropping was the topic that appeared to have most current support, and in essence involves controlling pest insects of field vegetable crops by undersowing the crops with variou types of clover (Trifolium spp.). Jan Theunissen was chosen as the leader of the project, as he has done most of the pioneering work on this subject in western Europe. The twelve group members shown in the Table all expressed interest in being involved in this project. 184 Comments Collaborator Country Repeat Mechanisms S Finch/P R Ellis UK • • MHommes D .. F Van de Steene B • • A Kahrer A • V Langer DK • • R Meadows N • J Freuler CH • B Hurni CH • J Theunissen/C Booij NL • • R McKinlay UK • Workers from Belgium, Denmark, The Netherlands and the United Kingdom agreed to repeat the extensive type of field experiments that have been carried out in the Netherlands during the last 2 years (see Theunissen et al - this bulletin). Workers from the remaining six countries intended to do smaller experiments, mainly to determine the mechanisms responsible for deterring pest insects from infestingfield vegetable crops that are growing in clover. Jan Theunissen said that he intended to submit a proposal for EEC funding on this project and Kees Booij agreed to provide Jan with all the assistance possible in preparing the submission. 2. Anh.i.ds Leader: Bob Ellis (United Kingdom) Collaborator Country Collaborator Country A Kahrer A J Theunissen NL M Cruz de Boelpaepe p PR Ellis UK The above 4 scientists agreed to carry out co-operative work on monitoring aphid populations and in particular in studying bow overall aphid mortality is influencedby fungal pathogens and overwinter conditions. Although not mentioned above, I feel that J. Eilenberg should have been included in this project, as fungal pathogens are his current major research interest (see Eilenberg & Philippsen - this bulletin). 185 3. Carrot fiy monitoring Leader: Jost Freuler (Switzerland)/Rosemary Collier (United Kingdom) Collaborator Country Collaborai:o!" Country P Esbjerg DK J Theunissen NL A Percy-Smith DK J Blood-Smyth UK H Philippsen DK R H Collier / S Finch UK B Jonsson s J Freuler CH It was agreed that the members involved in this project should carry out a further years work in 1992, to compare the relative effectiveness of vertical and angled traps. The design of the experiment would be circulated by Jost. It was hoped that Group members could produce a refereed paper on this subject in 1993. In his absence, Alex Percy-Smith suggested that the Danish contingent should ask Holger Philippsen to write up all information that is available on spray thresholds for the carrot fly, using the data from the above members of this collaborative project and fromEtienne Brunel of France. 4. Microbialc onirol Leader: Jorgen Eilenberg (Denmark) Collaborator Country Coilaborator Country - J Eilenberg DK A Vainio F S Finch UK Braunschweig D D Chandler UK Biosis AK A P Richard UK This is one area in which this Working Group would benefit from closer collaboration with other Groups. However, I feel that we need only one or two participants from other Groups, to also attend our meetings, to make this a dynamic part of the Group. This should not be too difficult to achieve, as many of the scientists using microbials as their control agents often work on field vegetables as their main commodity. In addition, Bacillus thuringiensis also comes under the heading of this project, and many group members already use preparations of this bacterium for pest control in vegetable crops. 186 5. Physical barriers for carrot fly Leader: Still to be decided Collaborator Country Collaborator Country J Blood-Smyth UK S Finch UK R McKinlay UK F van der Steene B As can be seen from the table, this is largely a UK problem, and has arisen mainly because large acreages of carrots are now drilled early in the season and covered with polythene to produce early crops. Obviously with the frozen soils of much of mainland Europe, extending the season with polythene covers in much less viable. The three main topics that will be considered in this project are the most appropriate times to apply and remove the barriers, the physiological effects of the barriers on the crop and the effects of the barriers on predatory ground beetles. Thefollowing five projects were being studied currently by only one or two Group members. Nevertheless, they have been included for completeness and to indicate who to contact should anyone wish to start collaborative work on any of these subjects before the next meeting in November 1993. 6. Parasitoidsor pest insects Leader: Stan Finch (United Kingdom) If this work was to be centred on Aleochara, then I am sure that Monika Ahlstrom-Olsson and Etienne Brunel would be willing to become involved in co operative experiments. 7. Predators or pest insects Leaders: Kees Booji (TheNetherlands)/Stan Finch (United Kingdom) 8. Companion planting/trap croppini: Leader: Richard Meadow (Norway) 9. Host-plant resistance Leader: Bob Ellis (United Kingdom) Bob is the current convenor of the IOBC Working Group on this subject. 187 10. Pest controlby cr op isolation Leader: Gudmund Taksdal (Norway) 11. Action thresholdsfor pests or leek Leaders: MartinHommes (Germany)/Jan Theunissen (The Netherlands) Collaborator Country Collaborator Country MHommes D BHurni CH J Theunissen NL F van der Steene B A Kahrer A J Blood-Smyth UK J Freuler CH S Finch UK This again is a topic that produced considerable interest. Thefirst strength of this project is its aim to minimise the amount of crop inspection required before deciding whetheror not, to spray. Its second strength is that it involves an element of integrated crop production, as the scientists involved are considering crop diseases (relatively few in leeks) in addition to crop pests. 12. Supervisedcontrol Leader: Still to be decided Collaborator Country Collaborator Country MHommes D F van der Steene B J Blood-Smyth UK PR Ellis UK This project will continue largely in brassica crops. Jan Theunissen agreed to provide information on this subject as, and when, required. Obviously there is nothing permanent about the above projects, so that anyone who now finds they would like to become involved in a particular subject should contact the appropriate leader. In their concluding remarks, Jan Theunissen and Peter Esbjerg said that they would convey to Council Members that there was a need for a group,which could be separate or involved in an existing Working Group, to find better ways of relaying IOBC results to farmers. NEXT MEETING 1st choice: Switzerland (Erich Stadler/Beat Hurni) Alternatives: Scotland, Portugal, England 188 Resume Projets en collaboration en 1992 et 1993 Avant la reunion, tous les participants ont ete invites a publier leurs travaux executes dans le cadre de l'OILB/SROP. Cette circulaire insistait sur les deux objectifs principaux des groupes de travail OILB/SROP, a savoir la stimulation de la collaboration internationale entre chercheurs dans le meme domaine et le developpement de projets en collaboration. J'ai aussi avise Jes membres du groupe qui tentaient de developper des projets avant la reunion, qu'il fallait maintenir tout projet initial aussi simple que passible, car la plupart des interesses ont des programmes de recherche deja fort remplis. Dans ces cas, ii leur est souvent extremement difficile d'y incorporer autre chose que de petites portions d'une nouvelle matiere. En revanche, les projets en collaboration peuvent etre beaucoup plus amples, car la substance princpale du cahier des charges de deux ou de plusieurs chercheurs de differents pays se trouve etre generalement sur un axe similaire. Les points susmentionnes ont ete bien maintenus dans la discussion finale sur le travail en collaboration ou le but principal etait de s'assurer que tous les participants soient impliques dans au moins un projet en collaboration. En tout, douze sujets ont ete proposes dont quelques-uns, comme on pouvait s'y attendre, furent re1r11s avec un grand enthousiasme, alors que d'autres plut�t avec tiedeur, principalement parce que le domaine de recherche suggere etait souvent la princpale composante d'un autre groupe de travail OILB/SROP. Il est inevitable que les chercheurs frequentent specifiquement un groupe de travail parce qu'on y discute du sujet principal et qu'il constitue la plus grande partie de leur travail - dans notre cas de la culture maraichere de plein champ - et misent moins sur leur domaine de recherche personnel prefere. Les douze sujets proposes pour une experimentation en commun figurent ci apres. Ils sont presentes dans l'ordre tel qu'ils ont ete enregistres pendant la reunion par Bob Ellis. 1. Culturesintercaiaires Coordonnateur: Jan Theunissen (Pays-Bas) Ce theme a re1r11 le plus grand soutien general. En substance, ii consiste a lutter contre les insectes ravageurs de legumes de pleine terre par un entre-semis de trefle. Jan Theunissen a ete choisi comme coordonnateur de ce projet parce qu'il a mene un important travail de pionnier dans ce domaine en Europe de l'ouest. Les douze membres du groupe figurant dans un tableau ont tous exprime leur interet a y participer: 189 Observations Collaborateur Pays Repetition Mecanismes S Finch/P R Ellis UK * * MHommes D * F Van de Steene B * * A Kahrer A * V Langer DK * * R Meadows N * J Freuler CH * BHumi CH * J Theunissen/C Booij NL * * R McKinlay UK * Les collegues de la Belgique, du Danemark, des Pays-Bas et de l'Angleterre se sont mis d'accord pour repeter le vaste type d'experimentation en champ conduit aux Pays-Bas durant les deux demieres annees (voir Theunissen et al. -- dans ce bulletin). Ceux de six pays restants ont l'intention de faire des essais plus redcits sur des cultures intercalaires. Plusieurs de ces essais ont pour objet de determiner les mecanismes responsables de l'eloignement des insectes attaquant les cultures legumieres de pleine terre lorsqu'elles sont cultivees avec des trefles. Jan Theunissen a l'intention de soumettre un projet a la ce pour recevoir des fonds, Kees Booij acceptant de fournirtoute aide necessaire pour preparer cette soumission. 2. Pucerons Coordonnateur : Bob Ellis (Angleterre) Collaborateur Pays Collaborateur Pays A Kahrer A J Theunissen NL M Cruz de Boelpaepe p PR Ellis UK Ces quatre chercheurs susmentionnes veulent collaborer a la surveillance des populations de pucerons. Ils desirent en particulier etudier comment la mortalite globale chez les aphides est influencee par les pathogenes fongiques et les conditions hivemales. Bien que J. Eilenberg ne soit pas mentionne dans la liste, je souhaite qu'il soit inclus dans ce projet, puisque les pathogenes fongiques des aphides forment une part importante de son interet scientifique general (voir Eilenberg & Philippsen - dans ce bulletin). 190 3. La surveillance de la mouche de la carotte Coordonnateurs: Jost Freuler (Suisse)/Rosemary Collier (Angleterre) Collaborateur Pays Collaborateur Pays P Esbjerg DK J Theunissen NL A Percy-Smith DK J Blood-Smyth UK H Philippsen DK R H Collier / S Finch UK B Jonsson s J Freuler CH Il a ete convenu par les membres impliques dans ce projet de conduire une annee supplementaire d'experimentation en 1992 pour comparer l'efficacite relative de pieges droits et inclines. Le plan experimental sera distribue par J. Freuler. Il est souhaitable que les membres du groupe parviennent a elaborer une publication de reference sur ce sujet. Alex Percy-Smith a suggere que les chercheurs danois chargent Holger Philippsen, qui n'a pu assister a la reunion, de rassembler les informations disponibles sur les seuils d'interventionpour la mouche de la carotte, en utilisant les donnees des autres membres du projet et d'Etienne Brunel de France. 4. Luttemicrobiolo2igue Coordonnateur : Jorgen Eilenberg (Danemark) Collaborateur Pays Collaborateur Pays J Eilenberg DK A Vainio F D S Finch UK Braunschweig D Chandler UK Biosis AK A P Richard UK Dans ce domaine, le groupe de travail beneficierait d'une collaboration plus etroite avec d'autres groupes. Neanmoins, je suis sur qu'il suffirait que deux participants provenant d'autres groupes viennent a nos reunions pour dynarniser cette partie du groupe. J'ai l'impression que ceci devrait se realiser relativement facilement, car beaucoup de chercheurs utilisant les microorganismes comme moyen de lutte travaillent principalement en culture marakhere de pleine terre. De plus, Bacillus thuringiensis fait aussi partie de ce projet et plusieurs d'entre nous }'utilise deja en champ. 191 5. Barrib'es m�caniquescontre ia mouche de la carotte Coordonnateur: vacant Collaborateur Pays Coliaborateur Pays J Blood-Smyth UK S Finch UK R McK.inlay UK F van der Steene B Comme l'indique le tableau, ii s'agit d'un probleme essentiellement anglais qui est apparu avant tout parce que de grandes surfaces de carottes sont maintenant semees tot dans la saison et couvertes avec du polyethylene pour hater la culture. II est evident que cette technique est nettement moins adaptee aux sols gelifs de la majorite de !'Europe continentale. Les trois sujets principaux traites par ce projet sont l'etude du moment le plus propice a la mise en place et a l'enlevement des filets, des effets physiologiques des barrieres sur la culture et de leurs influences sur les carabes. Les cinq projets suivants sont generalement etudiespar un ou deux membres du groupe seulement. Neanmoins, ils ont ete inclus par souci d'exhaustivite et pour preciser qui contacter au cas oil l'un ou l'autre chercheur souhaiterait debuter un travail sur un de ces sujets d'ici a notre prochaine rencontre de novembre 1993. 6. Parasitoirlesd'insectes rav a�urs Coordonnateur: Stan Finch (Angleterre) Si ce travail doit s'orienter vers Aleochara, je suis persuade que Monika Ahlstrom-Olsson et Etienne Brunel seraient interesses a s'impliquer dans une experimentation commune. 7. Predateursd'insectes ravageurs Coordonnateurs: Kees Booij (Pays-Bas)/Stan Finch (Angleterre) 8. Plantes associtesI plantes-pi= Coordonnateur: Richard Meadow (Norvege) 9. R�sistance des plantes-hotes Coordonnateur: Bob Ellis (Angleterre) Bob est l'actuel animateur du groupe de travail OILB/SROP qui s'occupe de ce domaine. 192 10. Lutte contreJes rava2eurs par isolation de culture Coordonnateur: Gudmund Taksdal (Norvege) 11. Seuils d'interventionpour Jes ravageurs du poireau Coordonnateurs: Ma rtin Hommes (Allemagne)/Jan Theunissen (Pays-Bas) Collaborateur I Pays I Collaborateur I Pays MHommes D B Hurni CH J Theunissen NL F van der Steene B A Kahrer A J Blood-Smyth UK J Freuler CH S Finch UK Voici a nouveau un sujet suscitant un interet considerable. Le premier point de ce projet consiste a reduire a un minimum le temps consacre a !'inspection de la culture pour estimer la justification ou la non-necessite d'un traitement. Le second point est que le projet inclut un element de production integree, puisque les chercheurs impliques tiennent compte des maladies (generalement limitees sur le poireau) en plus des ravageurs. 12. Lutte dirigte Coordonnateur: vacant. Collaborateur Pays CoHaborateur Pays MHommes D F van der Steene B J Blood-Smyth UK PR Ellis UK Ce projet va se poursuivre principalement dans les cultures de Brassica. Jan Theunissen accepte de fournir des informations a ce sujet, si besoin est. 11 va sans dire qu'il n'y a rien de permanent dans tous ces projets; ainsi quiconque souhaiterait participer a un projet particulier peut contacter le coordonnateur correspondant. Dans leurs remarques de conclusion, Jan Theunissen et Peter Esbjerg ont declare qu'ils souhaitent informer les membres du Conseil OILB/SROP de la necessite de former un groupe, separe ou inclus dans un groupe de travail existant, qui s'efforcerait de trouver de meilleures voies pour transmettre les resultats de l'OILB/SROP aux cultivateurs. Prochaine reunion lere option: Suisse (Erich Stadler/Beat Hurni) Solutions de rechange: Ecosse, Portugal, Angleterre. IOBC/WPRS-WorkingGroup Meeting "Integrated Control in Field Vegetables•, Vienna, 28-30 Oct 1991 l93