52 Plant Protection Quarterly Vol.10(2) 1995 Halliday, R.B. (1991). Taxonomic back- ground of the redlegged earth mite The biology and behaviour of redlegged earth mite Halotydeus destructor (Tucker) (Acarina: Penthaleidae). Plant Protection Quar- and blue oat mite on crop plants terly 6, 162-5. Jack, R.W. (1908). The earth flea: A com- Garrick McDonaldA, Kylie MoritzA, Eve MertonB and A.A. HoffmannB mon pest of winter vegetables. The Ag- A Plant Sciences and Biotechnology, Agriculture Victoria, La Trobe ricultural Journal of the Cape of Good Hope 32, 615-20. University, Bundoora, Victoria 3083, Australia. B James, D.G. (1995). Biological control of School of Genetics and Human Variation, La Trobe University, Bundoora, earth mites in pasture using endemic Victoria 3083, Australia. natural enemies. Proceedings of the sec- ond national workshop on redlegged Summary earth mite, lucerne flea and blue oat Earth mites are one of the major deter- the redlegged earth mite (Halotydeus de- mite, pp. 69-71. rents to the successful establishment of structor Tucker) although blue oat mite Löhr, B., Varela, A.M. and Santos, B. winter oilseeds, particularly canola. In (Penthaleus major Duges), true wireworms (1990). Exploration for natural enemies order to understand how crop manage- (Fam. Elatridae), false wireworms (Fam. of the cassava mealybug, Phenacoccus ment practices may impact on mites and Tenebrionidae), cutworms (Agrotis infusa) manihoti (Homoptera: Pseudococcidae), their damage, we have commenced a and slugs are also important. in South America for the biological con- study of the relationships between the The aim of our research is to evaluate trol of this introduced pest in Africa. mites and oilseed, grain legume and ce- various cultural control and plant resist- Bulletin of Entomological Research 80, real crop plants. Halotydeus destructor ance options to minimize the impact of 417-25. were shown not to be attracted to lupins, pests on the establishing crop, particu- Meyer, M.K.P. (1981). Mites pests of crops wheat or oats, and their survival and fe- larly canola (Brassica napus). We are, for in southern Africa. Science Bulletin, De- cundity were significantly lower on example, interested in how different rota- partment of Agriculture and Fisheries, Re- these than on other plant types. This tion sequences may affect the build up in public of South Africa 397, 1-92. suggests that such crops, particularly lu- earth mite populations prior to a canola Narayan, D.S. (1962). Morphological, bio- pins, used in rotations prior to canola, planting. logical and ecological studies on the could minimize the in-paddock infesta- Earth mites are regarded as ubiquitous winter grain mite, Penthaleus major tions of mites. Preliminary screening pests of most field crops including cereals (Duges), Penthaleidae: Acarina Part 1. tests for H. destructor resistance has also although there is anecdotal evidence that Journal of the Zoological Society of India shown that some northern hemisphere H. destructor has a low preference for the 14, 45-63. varieties of Brassica napus are prone to latter. Thus, a crop rotation sequence with Newman, L.J. (1931). The principle insect significantly less cotyledon damage wheat preceding canola should reduce pests of tobacco. Journal of the Depart- than local varieties. Notably, survival mite populations, possibly to below dam- ment of Agriculture of Western Australia and fecundity of H. destructor on age threshold levels, for subsequent 8, 520-41. B. napus was low even on susceptible crops. Another pest management option Qin, T.K., Gullan, P.J., Beattie, G.A.C., varieties, indicating that the species al- for mites in winter oilseeds may be the Trueman, J.W.H., Cranston, P.S., ready has a level of partial resistance. development of resistant plant varieties. Fletcher, M.J. and Sands, D.P.A. (In On the one variety tested (Oscar), In this paper, we summarize our progress press). The current distribution and Penthaleus major caused only half the in laboratory studies of the relationships geographical origin of the scale insect damage of H. destructor. between mites and crop and crucifer Ceroplastes sinensis (Hemiptera: weed plants. We include preliminary re- Coccidae). Bulletin of Entomological Introduction sults from feeding/choice studies of mites Research. Winter oilseeds are highly vulnerable to on oilseed, legume and cereal crop plants, Tucker, R.W.E. (1925). The black sand pest damage during the first weeks after studies of H. destructor population growth mite: Penthaleus destructor n. sp. Ento- germination. The most significant pest is characteristics on crop and pasture plants, mology Memoirs, Department of Agricul- ture, Union of South Africa 3, 21-36. 3.5 Wallace, M.M.H. and Mahon, J.A. (1971). Distribution of Halotydeus destructor 3 and Penthaleus major (Acari: Eupodidae) in relation to climate and land use. Aus- 2.5 tralian Journal of Zoology 19, 65-76. Womersley, H. (1933). On some Acarina from Australia and South Africa. Trans- 2 actions of the Royal Society of South Aus- tralia 57, 108-112. 1.5 Womersley, H. (1941). The redlegged earthmite (Acarina: Penthaleidae) of 1

Australia. Transactions of the Royal Soci- Multiplication index ety of South Australia 65, 292-4. 0.5 Weeks, A., Fripp, Y.J. and Hoffmann, A.A. (1995). Population structure of redlegged earth mite and blue oat mite 0 vetch faba field canola lupins wheat oats populations in Victoria. Proceedings of medic beans peas the second national workshop on redlegged earth mite, lucerne flea and Figure 1. Net reproductive rate of H. destructor on various crop and pasture blue oat mite, pp. 33-5. hosts. The dotted line indicates the net population replacement rate. Plant Protection Quarterly Vol.10(2) 1995 53 and screening experiments for H. destruc- Experiments B. napus hybrids, if hybridization proves tor resistance in a variety of oilseed Feeding preferences. Choice and no possible. Ten seedlings of each line/spe- brassicas and weedy crucifers. choice experiments, replicated six times, cies were grown in each of ten replicate were conducted with H. destructor and containers and maintained for one week Methods P. major on common vetch, canola, lupins, at 25°C. Mites were collected from a local wheat, medic and capeweed. The experi- pasture and 100 H. destructor were added Assay methods ments were conducted in petri dishes to each pot, except for five pots of var. Single mite and small cohort experi- containing a thin layer of moistened fine Oscar which received 100 P. major each. ments. A technique to study single or white sand, five young adult mites and Damage scores on the cotyledons were re- small numbers of mites over protracted the test leaf/leaves. In the no-choice ex- corded after 2, 5 and 8 days. periods was developed using 7 cm petri periment, the mites were offered a single dishes with leaf cuts and mite(s). The leaf section (4–8 cm), cut from a fully de- Results dishes were lined with fine grade filter veloped leaf of the test plant. In the choice paper containing a moisture pad (a experiment, a leaf cut of vetch and the Feeding preferences gauze-covered vial cap containing cotton host plant were offered. The number of In the absence of a choice of hosts H. de- wool) and were sealed with parafilm. mites on or off the plant was recorded structor spent significantly (P<0.001) Whole plant experiments. Plants were every five minutes for an hour. more time feeding from vetch, medic and grown in a sterilized potting mix in 10 cm Population growth characteristics on capeweed (>50% of total time) than on pots. A 9 cm diameter clear plastic dome, crop plants. H. destructor survival and re- canola, lupins or wheat (<10% of total constructed from the middle and upper productive rate were measured on each of time) (Table 1). When H. destructor were section of a 1.25 L polyethylene seven host plants (canola, lupins, faba offered vetch as a choice to any of the terephthalate (PET) bottle, was firmly fit- beans, field peas, wheat, oats, white clo- other hosts, significantly more time ted into the rim of a pot by means of self ver). Four plants of each species were (P=0.05) was spent feeding on canola and adhesive urethanefoam tape. The dome grown in ten replicate 10 cm pots until capeweed (>20% of total time) than on contained four 5 cm diameter gauze they were about 14 days old (10–15 cm lupins, wheat or medic. In both series of vents. Each pot was watered by keeping it high). Fifty young adult H. destructor experiments, the mites were attracted to in an 11 cm diameter saucer (plastic food were placed on each plant. After 10 days the lupins and wheat for less than 10% of container) which was partly filled with and 14 days, the number of eggs laid and the time. P. major had less distinct prefer- water once weekly. The resistance screen- the surviving mites were counted and the ences. The mites spent significantly more ing experiments were also undertaken in latter removed. After a further 28 days, time (P<0.01) on capeweed than on the PET bottles, but these had the bottom re- the next generation of mites and their other tested plants, and showed least tained and the neck removed. Sterilized eggs were counted. The experiments were preference for vetch. When offered vetch potting mix (10 cm) was added and the concluded after six weeks when host as a choice to each of the test plants, seeds were sown directly. The tops were quality had declined. P. major spent significantly less time on sealed with perforated cling wrap plastic. Resistance screening experiments. Six lupins than on medic or capeweed All experiments, except the resistance distantly related lines of B. napus and (P<0.01). These experiments are being re- screening, used mites from a culture seven other crucifer species were tested peated using plant tissue and mites in maintained at 11 and 18°C (Ridsdill- for mite resistance. The latter include various stages of growth, and using mites Smith 1991) on common vetch (Vicia weeds which are being evaluated as a collected from different hosts and with sativa cv Blanchefleur) (K. Gaull personal source of disease resistance in breeding different clonal forms of P. major (Weeks communication). programs and which will be used in et al. 1995). Table 1. The amount of time Halotydeus destructor and Penthaleus Population growth characteristics of major spent on six test plants in choice and no choice H. destructor on crop plants experiments. There were major differences in H. de- Test plant Average time spent (mins) (± SEM) feeding/resting on a test plant structor response to the various host plants. Vetch and faba beans were rela- when offered the test plant alone when offered choice of test tively good hosts; juvenile and adult sur- (no choice) plant and vetch vival and oviposition rate were signifi- H. destructor P. major H. destructor P. major cantly higher (P<0.05) than on other hosts Vetch 31.2 ± 4.7 9.3 ± 2.4 na na (Table 2). However, we observed that the Canola 5.3 ± 2.8 15.7 ± 1.8 12.0 ± 5.1 7.7 ± 3.8 rate of juvenile development was slower Lupins 2.7 ± 1.4 24.5 ± 3.6 3.0 ± 1.6 1.0 ± 0.6 on faba beans than on vetch. At the con- Wheat 6.7 ± 1.6 14.0 ± 2.8 0.5 ± 0.3 7.8 ± 1.6 clusion of the experiment (six weeks), the Medic 31.7 ± 2.0 23.0 ± 2.6 2.3 ± 1.0 14.2 ± 4.0 second generation mites on vetch were Capeweed 37.2 ± 2.8 35.8 ± 5.1 12.7 ± 5.7 19.8 ± 2.9 mature and had laid large numbers of eggs; on the faba beans most mites na = not applicable were deutonymphs or immature adults. Table 2. Population growth characteristics for Halotydeus destructor maintained on various crop/ pasture plants. Vetch Faba beans Field peas Lupins White clover Canola Wheat Oats Adult survival after 10 d (%) 56.0cd 55.0cd 41.0bc 30.0ab 63.0d 23.0ab 27.0ab 20.0ab Adult survival after 14 d (%) 49.0cd 54.0d 34.0bc 18.0ab 48.0cd 3.0a 9.0a 11.0a Oviposition (eggs/week) 4.6cd 5.3d 1.8ab 0.8ab 1.9ac 1.6ab 0.0a 0.1a Juvenile survival (%) 65.0 54.0 78.0 5.0 84.0 0.0 na 0.0 na = not applicable Numbers with the same letters across the rows are not significantly different (P<0.05). 54 Plant Protection Quarterly Vol.10(2) 1995 Table 3. Average mite numbers and damage scores (±SEM) on six Brassica i. the particular crop of wheat, chickpeas napus lines and seven crucifer weeds. or lupins contained a heavy weed infes- tation (as in Merton et al. 1995), thereby Mites on plant Damage score providing mites with acceptable alter- B. napus variety native hosts for breeding; Oscar (H. destructor only)A 34.5 ± 4.1 4.15 ± 0.16 ii.the mites were surviving and breeding Oscar (P. major only)A 9.0 ± 2.6 2.66 ± 0.12 on other non-vascular plants such as al- Narendra (WA)A 26.9 ± 4.6 4.08 ± 0.12 gae, fungi or mosses in or on the soil Jet Neuf (French) 24.3 ± 5.3 2.88 ± 0.17 surface (we have preliminary evidence Bronowski (Polish)A 26.2 ± 5.8 3.52 ± 0.16 which suggests that at least juvenile Chituzen (Japanese) 25.9 ± 4.8 2.07 ± 0.21 survival is possible on non-vascular Cyclone (Danish)A 21.3 ± 5.1 2.84 ± 0.21 plants); iii.these crop plants become more accept- Crucifer weeds able to the mites in the post-vegetative H. incana 3.2 ± 0.8 2.71 ± 0.14 stages. The first two options are more B. juncea 26.5 ± 1.4 2.46 ± 0.18 probable and are being investigated S. arvensis 8.9 ± 2.3 0.65 ± 0.15 further. S. alba 31.4 ± 1.3 1.75 ± 0.11 The initial screening of lines of B. napus B. tournefortii 10.2 ± 1.8 1.83 ± 0.12 with H. destructor showed extensive vari- B. carinata 14.5 ± 4.1 1.44 ± 0.06 ability in resistance; some varieties re- E. sativa 33.0 ± 3.1 2.61 ± 0.12 ceived less than half the damage of com- Least significant difference (P<0.01) for mite number = 17.3, damage = 0.66. mercial varieties such as Oscar. A further A low glucosinolate levels in seed. promising outcome was the demonstra- tion that B. napus var. Oscar may be sig- Relative to vetch, survival of adults and Discussion nificantly less susceptible to P. major than oviposition rate on field peas was signifi- Our results, while being preliminary, H. destructor, although this work is pre- cantly lower; survival of juveniles was have shown the potential of two separate liminary. Considering that even suscepti- higher while their development rates were approaches for minimizing mite impact ble cultivars of B. napus are poor hosts to also slower. Survival of adults and juve- on canola: the use of lupins or wheat in both species of mite, it should not be diffi- niles on white clover were similar to those rotation prior to canola to reduce popula- cult to develop, through selection, ad- on vetch but oviposition rate was signifi- tion pressures of earth mites, and the equate resistance to prevent crop loss. cantly lower. development of mite resistance in Alternatively, the other crucifer species Canola, lupins, wheat and oats were all B. napus. tested also showed promising levels of re- inferior hosts. Adult and juvenile survival H. destructor is not attracted to wheat sistance to H. destructor. Some of these were consistently low on these plants and and will not survive or breed on it, mak- species have been successfully hybridized there were few if any eggs laid. Of these ing this species an ideal crop to plant be- with B. napus to introduce resistance to hosts, the highest oviposition rate was on fore canola. Despite the anecdotal evi- the disease ‘blackleg’. This program may canola, and most eggs were laid on the dence that P. major has a preference for also permit the incorporation of earth cotyledons. However, none of the neonate graminaceous plants (Jeppson et al. mite resistance. larvae survived. Once the cotyledons had 1975), including wheat, this preference senesced, no further eggs were laid. No was not evident in our studies. They Future directions eggs were laid on wheat. were, however, more attracted to wheat Some productive areas for future research than lupins. The disadvantage of using include: Resistance screening experiments wheat prior to canola in crop rotations is i. development of H. destructor and P. ma- There was significant variation in damage that canola requires high soil nitrogen, so jor resistant cultivars by screening sev- scores across the varieties: var. Chitzen pasture or grain legumes are generally eral thousand lines of B. napus had a significantly lower damage rating preferred. Thus, lupins may be a promis- germplasm held in the Australian (P=0.01) than all other varieties. Var. Cy- ing alternative in crop rotations. Unlike Oilseeds Collection at Horsham, clone and var. Jet Neuf had significantly the other grain legumes tested, lupins ii.assessment of the role and tissue-spe- less damage than Oscar, the Western Aus- were not attractive to H. destructor and the cific activity of glucosinolates in the tralian variety Narendra or var. poor survival and fecundity of mites most promising of these lines, and Bronowski. P. major caused significantly should result in a rapid decline in popula- iii.determining the mode of inheritance of less damage to var. Oscar than did H. de- tion densities in the season prior to the this resistance. structor. There was no significant differ- canola crop. Field data appear to support ence between H. destructor numbers re- this (Merton et al. 1995). Chickpeas are a Acknowledgments corded on each B. napus variety on day 2, possible alternative to lupins in a crop ro- We wish to thank James Ridsdill-Smith although there were significantly fewer tation prior to canola. Thackray (1995) has and his team for their early advice in our P. major than H. destructor on var. Oscar observed that chickpeas are not colonized mite research, and Phil Salisbury, Dennis (Table 3). by H. destructor, in the presence or ab- Ballinger and Dave Robson, Victorian In- Of the other weed and agronomic sence of other host species. stitute for Dryland Agriculture, Horsham crucifer species, H. incana, S. arvensis, Farmers and advisers often question re- for their provision of seed and advice on B. tournefortii and B. carinata had signifi- sults such as the above. They cite exam- resistance screening. We are grateful for cantly fewer mites on their leaves than ples of young canola crops, planted into the assistance provided by Erica Hajdu, did the other species. Cotyledon damage paddocks previously cropped in wheat, Ken Lu and Lisa Orth in the behaviour ex- scores also varied widely although none lupins or chickpeas, but in which H. de- periments. This work was supported by of the species were damaged as much as structor infestations had turned out to be the Grains Research and Development B. napus. S. arvensis, S. alba, B. carinata, severe. There are various possible expla- Corporation. and B. tournefortii had the lowest damage nations for the higher than expected scores. populations: Plant Protection Quarterly Vol.10(2) 1995 55 References Jeppson, L.R., Keifer, H.H. and Baker, Biological control of redlegged earth mite and lucerne E.W. (1975). ‘Mites injurious to eco- nomic plants’. (University of California flea by the predators Anystis wallacei and Press, Berkeley). Merton, E., McDonald, G. and Hoffmann, Neomologus capillatus A.A. (1995). Cultural control of redlegged earth mite, blue oat mite and Phil Michael, Department of Agriculture, Baron-Hay Court, South Perth, lucerne flea in canola. Proceedings of Western Australia 6151, Australia. the second national workshop on redlegged earth mite, lucerne flea and Summary following the presentation of research blue oat mite, pp. 87-9. Anystis wallacei preferred redlegged findings at the previous National Work- Ridsdill-Smith, T.J. (1991). Laboratory earth mite and Neomulgus capillatus shop (Michael et al. 1991a). The new ob- rearing of Halotydeus destructor preferred lucerne flea in the insectary. jectives became: (Tucker) (Acari: Penthaleidae). Journal Feeding tests showed that 100 i. to determine the impact of the two of the Australian Entomological Society 30, A. wallacei per square metre can kill predators on the pests in the insectary 313. 16 000 redlegged earth mites in one pest and in the field, Thackray, D.J. (1995). Developing tech- generation. Two types of field trials ii.to assess the effect of the predators on niques for mass rearing redlegged earth were conducted using a novel barrier pasture production and quality, mites. Proceedings of the second na- system. The addition of both predators iii.to develop techniques for continuous tional workshop on redlegged earth into ungrazed plots reduced peak pest small-scale predator rearing, mite, lucerne flea and blue oat mite, pp. numbers by more than two thirds, while iv.to determine predator survival after 45-8. vegetative and seed yields were more treatment with insecticides commonly Weeks, A., Fripp, Y.J. and Hoffmann, A. than doubled. Pest numbers were low in used on pasture, A. (1995). Population structure of mown plots but peak populations of v.to monitor predator survival and redlegged earth mite and blue oat mite redlegged earth mite and lucerne flea spread at release sites. populations in Victoria. Proceedings of were reduced by 80 and 60% respec- the second national workshop on tively. A. wallacei was reared in field Methods redlegged earth mite, lucerne flea and cages for two years at greater densities blue oat mite, 33-5. than naturally occurring in the field. Insectary feeding trials Predators survived in much greater In view of the large range of possible prey numbers than pests after sprays of com- types and combinations of prey for the mon pesticides. feeding preference work, only simple testing of a few prey types was under- Introduction taken. This was performed in small tubes, Control of redlegged earth mite allowing careful counting of the indi- (Halotydeus destructor) and lucerne flea vidual predators and prey as they were (Sminthurus viridis) would increase pas- added and as they were recovered after ture, animal and crop production but the feeding period. Predators were sepa- farmers have largely decided against the rated and starved 24 hours prior to test- chemical control option. Continuously ing. A second method was to count operating and compatible control strate- redlegged earth mite and A. wallacei into gies such as resistant varieties and bio- boxes with growing pasture plants. The logical control would be the ideal alterna- invertebrates were removed with a suc- tive to chemical control. tion sampler at the end of the test. Condi- Wallace (1981) collected Anystis wallacei tions in the insectary were standardized Otto and Neomolgus capillatus (Kramer), for all the testing at 13°C and 70% humid- releasing them separately in a few loca- ity. tions in Western Australia. He had ob- served them as predators around the Field trials testing predator effectiveness Mediterranean where they coexist in The two types of field trials set up to de- some areas. He examined the effects of termine the effects of the predators on each introduced predator in Australia and pest populations and pasture were com- concluded that they are useful control plete block designs with four replications agents of redlegged earth mite and lu- and the same treatments: chemical con- cerne flea. trol, untreated and biological control. It was demonstrated that colonies of i. The ‘Addition’ trial had 2 × 2 m plots these predators could be established in which were separated so that they new areas where they would spread could be managed totally from the out- slowly. Evidence that the predators re- side. The same plots were used over duced pest numbers was also reported two years. Predators were collected (Michael et al. 1991a). from elsewhere and counted before This project was commenced with the adding them to the biological control major objective of accelerating the spread treatment. of the two predators. Further assessments ii.The ‘Elimination’ trials had contiguous on predator effectiveness were also 10 × 10 m plots separated only by a planned and sites for this had been estab- common barrier. One of these trials lished. However the emphasis of was located on an area colonized by this project was altered substantially A. wallacei and the other was on an area