ZOBODAT - www.zobodat.at

Zoologisch-Botanische Datenbank/Zoological-Botanical Database

Digitale Literatur/Digital Literature

Zeitschrift/Journal: Denisia

Jahr/Year: 2002

Band/Volume: 0004

Autor(en)/Author(s): Stewart Alan J.A.

Artikel/Article: Techniques for sampling Auchenorrhyncha in grasslands 491-512 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Techniques for sampling Auchenorrhyncha in grasslands

ALAN J.A. STEWART

Abstract

The relative merits of different techni- They can be used to give estimates of ques for sampling the Auchenorrhyncha absolute population density in grasslands community in grasslands are reviewed. As and tend to sample the epigeal species bet- is the case when studying many other ter than sweep nets. However, a true pic- invertebrate groups, no single technique ture of the species living in the lowest can be relied upon to reveal the full range vegetation stratum or close to the soil sur- of species at a site or provide unbiased face can best be obtained by using pitfall estimates of population density for all spe- traps. A comprehensive inventory of spe- cies. Nevertheless, with moderate effort cies would therefore need to combine pit- and inexpensive equipment and if due fall trapping with either sweep netting or attention is paid to the importance of stan- suction sampling. Brief discussions are dardising sampling procedures to allow also presented of techniques for sampling comparisons across both space and time, the aerial fauna and for estimating disper- reliable estimates of both relative and sal and movement between populations. absolute population density can be achie- ved. Sweep-netting is an inexpensive and Key words: Auchenorrhyncha, sam- simple method for providing relative esti- pling, grasslands, sweep-netting, suction mates of population density but it is hard samplers, pitfall traps, population estima- to standardise and it under-samples the tes, standardization. epigeal species. The conventional D-Vac suction sampler has now been largely superseded by a variety of smaller and cheaper hand-held suction devices that have been developed by modifying devices Denisia 04, that are sold for collecting garden refuse. zugleich Kataloge des OÖ. Landesmuseums, Neue Folge Nr. 176 (2002), 491-512

491 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Introduction red to closely grazed or regularly mown gras- slands where the vegetation remains generally The Auchenorrhyncha form an important short (MORRIS 2000). For this reason, the component of the invertebrate fauna of most Auchenorrhyncha community is a good temperate grasslands. The group has a number reflection of the intensity of grassland mana- of properties which make it very suitable for gement, responding both rapidly and precisely monitoring the biotic conditions and assessing to any changes in the management regime the conservation status of a range of grassland such as the imposition or cessation of grazing types (HILDEBRANDT & NICKEL in press): (MORRIS 1981a, 1981b; MORRIS &. PLANT (i) Population densities in grasslands often 1983). exceed those of other key invertebrate taxo- (v) At a more practical level, there are nomic groups such as the Heteroptera and well tested and widely accepted techniques for Coleoptera and can reach remarkably high sampling the Auchenorrhyncha community 2 levels (in excess of 1,000 individuals per m ; in grasslands, although there is no technique WALOFF 1980). Potential species richness is that will suit all circumstances, nor one that is high enough to be a useful ecological indica- devoid of sampling bias. Nevertheless, reliable tor, with individual grassland sites often sup- population estimates can be generated using porting in excess of 40 species (MORRIS 1971). simple, inexpensive and portable equipment. (ii) The autecology of many grassland In general, at least in Europe, the taxonomy of Auchenorrhyncha is well studied in terms of the group is well documented, stable and sup- host plants, habitat associations and responses ported by high quality identification keys. to management. It is therefore possible to pro- When embarking upon a programme of vide a detailed ecological interpretation of the research on the ecology of grassland Auche- community from data on species occurrence or norrhyncha, one of the first questions to be relative abundance. answered will be: what sampling technique (iii) The Auchenorrhyncha perform an should be used? This deceptively simple que- important functional role in the grassland stion turns out to be remarkably complex to community as herbivores, by tapping into the answer, as the rest of this paper will show. phloem or xylem sap or extracting the con- Field entomologists have shown considerable tents of the mesophyll cells of their host ingenuity in developing a wide variety of plants. When population densities are high, collection and sampling methods, responding this action induces a substantial photosynthe- to the considerable range of habitat associa- tic drain on the plants and may influence the tions and behaviour patterns exhibited by this outcome of competition between plant species group of insects. Most field research program- and hence the course of succession (BROWN et mes will initially be concerned with tackling al. 1988). The transmission of plant pathogens two primary questions: what species occur in a by many Auchenorrhyncha may compound habitat and at what densities? Faced with this such effects. Removal of plant sap followed by challenge, selection of the most appropriate excretion of soluble waste material by these sampling technique is not always straightfor- insects will undoubtedly have significant ward. There is no universally applicable sam- effects on nutrient cycling within the gras- pling technique that will suit all purposes. Fur- sland ecosystem, although this effect has thermore, all techniques are selective to some received rather less attention than it deserves. degree, the extent of the bias being dependent on a number of factors. Reliable estimation of (iv) The structure and composition of population density may require employing grassland Auchenorrhyncha communities several techniques in combination. generally reflect a combination of the species composition and physical structure of the The researcher who is faced with deciding vegetation (BROWN et al. 1992). Auchenorr- which sampling techniques to employ has to hynchan species richness tends to be much take a number of considerations into account. greater in undisturbed and lightly grazed gras- The most important of these is sampling effi- slands where the vegetation is taller, compa- ciency: the effectiveness with which the tech-

492 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at nique reveals all the individuals in the target ring on which sampling techniques are most area. This will vary between species, habitats, appropriate in different circumstances. These seasons, environmental conditions and, to a include: lesser extent, between field workers. Cost is i) Vertical stratification of species: always a major consideration. It includes not Many species select particular strata wit- just the cost of the materials and the time nee- hin the vertical structure of grassland vegeta- ded to sample, but also the time required to tion (DENNO 1980; DENNO et al. 1980). This process any material collected. The latter is demonstrated particularly clearly by the use includes separation of the insect specimens of different techniques (e.g. pitfall trapping, from plant material and other debris inadver- suction sampling and sweep netting) that sam- tently collected during the sampling process, ple different subsets of the total fauna (AND- identification of specimens and curation of RZEJEWSKA 1965; PAYNE 1981; PETER 1981; the samples or selected voucher material for TÖRMÄLÄ 1982; NOVOTNY 1992; CHERRILL & future reference. The time required to do this SANDERSON 1994). Furthermore, there is evi- post-sampling work is often under-estimated. dence that this stratification changes seaso- For quantitative studies, it must be possible to nally (ANDRZEJEWSKA 1965) and diurnally standardise the technique, so that it can be (ROMNEY 1945). replicated with confidence over both space ii) Sexual differences in activity patterns: and time. Not all techniques lend themselves These may result in biased sex ratios in the to this. Other considerations such as the amo- catches produced by particular techniques. For unt of training required and the extent to example, pitfall trap catches of certain species which sampling is weather-dependent may tend to be dominated by males (LEQUESNE & also have to be built into the selection pro- MORRIS 1971; PAYNE 1981; TÖRMÄLÄ 1982), cess. Generally, the final choice is based on a possibly because the females are more seden- balance of the appropriateness of the techni- tary. que measured against time and cost. iii) Differences in sampling efficiency bet- Programmes for sampling Auchenorrhyn- ween life history stages: cha in grassland must be guided by these gene- The same technique may not be appro- ral principles. Here, I review the techniques priate for all life history stages, even within that have been developed or adapted to sam- the same species. This may be because, for ple these insects in the grassland habitat and example, nymphs and adults inhabit different comment on their effectiveness. The review is parts of the host plant (overwintering nymphs concerned solely with the efficacy of the tech- of certain species typically reside close to the niques themselves; issues relating to the stati- soil surface) or have different susceptibilities stical design of field sampling programmes to being caught. SlMONET et al. (1979) con- (HURLBERT 1984; EBERHARDT & THOMAS cluded that the D-Vac was the most appro- 1991; DUTILLEUL 1993) and subsequent analy- priate technique for sampling adults of the sis of the data (see summary of key references potato leafhopper, Empoasca fabae; however, in POTVIN & TRAVIS 1993) have been covered nymphs were more efficiently extracted by in general terms elsewhere. SOUTHWOOD placing excised branches of the plant for 24 hr (1978), DENT (1991) and KUNO (1991) consi- in containers with small Dichlorvos squares der the application of general principles speci- (SlMONET et al. 1978). fically to sampling insect populations. Techni- iv) Diurnal changes in behaviour: ques for sampling the predators and parasitoids Whilst diurnal periodicities in leafhopper of Auchenorrhyncha (many of which are the flight activity have been known for some time same as for their hosts) are not dealt with (LEWIS & TAYLOR 1965), rather little is known here, but are covered fully by POWELL et al. about whether analogous changes occur in (1996). other behavioural traits. DONDALE et al. As is the case in other invertebrate groups, (1972) and SCHAEFER (1973) report diurnal certain features of the ecology and behaviour changes in pitfall trap catches, whilst PAYNE of Auchenorrhyncha have an important bea- (1981) has suggested that these changes differ

493 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

between the sexes. ROMNEY (1945) reports BUNTIN 1988). Where the use of more than diurnal changes in vertical positioning of one sampling technique is unavoidable, an Eutetrix teneüus on beet plants, but this effect attempt should be made to calibrate between has not been widely investigated in other spe- the results (e.g. CHERRY et al. 1977; SlMONET cies. In the light of these possible effects, sam- et al. 1978, 1979; TöRMÄLÄ 1982; BUNTIN pling programmes that involve any sort of eva- 1988). luation of treatment effects (e.g. different gras- It is important to distinguish at the outset sland management regimes) should stipulate between different types of field work. 'Collec- that samples are taken at similar times of day ting', for species inventory work or to obtain to ensure comparability of catches, material, perhaps for experimentation or a v) Spatial distribution patterns: taxonomic investigation, is an essentially The number and location of replicate sam- non-quantitative exercise; there is no particu- ples within a site or experimental plot need to lar interest in determining population size. On be chosen bearing in mind the importance of the other hand, true 'sampling' has the speci- spatial factors in determining abundance. In fic objective of providing an unbiased estima- addition to the possibility of direct spatial te of population density and is by definition autocorrelation (the phenomenon where the quantitative. This paper is concerned primari- similarity between samples is related, positive- ly with techniques to achieve the latter objec- ly or negatively, to their physical distance tive. Of course, most of the techniques used apart (LEGENDRE 1993)), insect species occur- for quantitative sampling can also be used for rence and/or abundance may be highly corre- general collecting. lated with one or more key environmental fac- tors (such as soil conditions, aspect or vegeta- Absolute versus relative populati- tion composition) which are themselves spati- on size estimates ally correlated. Rather few studies on Auche- norrhyncha have tested for such autocorrelati- In quantitative sampling, there is an on (SANDERSON et al. 1995) or attempted to important distinction between estimates of quantify spatial variation in general terms and absolute as opposed to relative population size how this changes temporally (GYÖRFFY & or density (SOUTHWOOD 1978; DENT 1991). KARSAI 1991). An estimate of absolute population density is A comparison of the relative efficiencies a count of the numbers of individuals within a of the different available sampling techniques specified area. As it is an estimate of the actual should be done as part of the preparatory work density, it should be comparable both spatial- for any field study. Failure to do this may result ly and temporally (i.e. with estimates derived in erroneous conclusions based on inappro- from other sites or on other dates). One priate comparisons, for example by comparing should realise however that techniques desi- results from the same technique in different gned to estimate absolute population density, habitats or in different environmental conditi- whether by visual searching or some sort of ons. Such considerations are particularly rele- extraction technique, rarely detect 100% of vant in community studies, where apparent the insects actually present; in fact, extraction differences in the relative abundance of spe- efficiencies are frequently much less than this. cies may simply reflect differences in sampling As the resultant count will therefore be an efficiency. Few community studies address this under-estimate of the true population density, problem, despite TöRMÄLÄ 's (1982) warning caution should be exercised when extrapola- that different techniques for sampling grass- ting from small samples to produce population land faunas produce very different results. estimates for large areas, as the under-estima- Comparative studies should consider not just tes then become greatly magnified. sampling efficiency (the number of insects If areal densities are either inappropriate extracted per unit area) but also the relative or impracticable, the next best estimate of precision of each technique, measured as the absolute density expresses the population variability amongst replicated samples (e.g. count in units of habitat; for the Auchenorr-

494 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at hyncha, this is most appropriately some com- with total counts adjusted accordingly if they ponent of the host plant (e.g. a count of num- differ consistently. bers per leaf, unit leaf area, stem length or Trapping techniques exploit the fact that whole plant). These 'habitat units' will chan- most insects move through their habitat. A ge as the plant grows, so a measure of the num- simple distinction can be made between ber of habitat units per unit area is also needed 'interception traps' that collect insects moving before a true population density estimate can through the habitat as part of their normal be derived. behaviour and 'attraction traps' that provide a When it is impossible to estimate absolute stimulus which draws the insects towards the densities, the field researcher must resort to sampling point. Such techniques are usually relative population estimates. Here, the esti- highly cost-effective as they are generally less mate is no longer a true count of numbers in a time-consuming and require less skill than given area, as the unit of measurement is active sampling techniques (LOTT & EYRE usually unknown. Data from traps generate 1996). They also have the advantage of sam- this type of relative estimate, as it is impossible pling continuously over an extended period, to be certain about the absolute area or volu- including night as well as daytime. Due to the me over which the trap is operating. If exter- length of operating time, often several days, nal conditions (weather, habitat structure the influence of short-term fluctuations in etc.) are similar, estimates using the same sam- weather are evened out. 'Instantaneous' sam- pling technique should be broadly comparable pling techniques, by comparison, are always across space and time. Active sampling tech- subject to the influence of time of day, weat- niques such as sweep-netting can be standar- her conditions and other short-term factors. dised by expressing samples in numbers caught Measured against this, traps left untended are per unit of effort (usually sampling time or the vulnerable to adverse weather, human vanda- number of sweeps), but can not readily be lism and damage by other animals (e.g. grazing expressed directly in terms of densities. stock). The single greatest disadvantage, however, of most trapping techniques is that The distinction between absolute and the resultant catch is strongly influenced by relative population sampling techniques is not the activity of the insects themselves. Seden- always clear cut. Relative estimates can some- tary species will be caught less frequently than times be converted to absolute densities, if a highly active ones, even if their actual popula- good correlation can be demonstrated bet- tion densities are similar. Consequently, data ween counts from the technique and those from attraction or interception traps should from another more accurate estimate of abso- not be analysed quantitatively until the relati- lute density. However, the calibration is likely onship between catch size and population to be both species- and site-specific and assu- density has been checked. This relationship mes that various extraneous environmental will undoubtedly vary between species and, for factors are kept constant. Wherever possible, any one species, between sexes, seasons or dif- attempts should be made to quantify the effi- ferent habitats. ciency of the technique being employed. This can be done by comparing the sample count In summary, in order to generate the most with the number of insects added after a com- accurate population estimate, a selection of prehensive search of the target area, perhaps different techniques should be tested simulta- by removal or fumigation of the whole plant neously and the results compared. The final or grassland turve and careful examination for choice of technique(s) to adopt will be a tra- any individuals missed by the initial sampling. de-off between accuracy and cost. Similarly, Similarly, active sampling (such as direct before proceeding with detailed studies, rese- counts or sweep netting) should be carried out archers should have a clear appreciation of the wherever possible by the same person, to avoid absolute efficiency of their chosen sampling introducing individual operator bias. If more technique(s) for the species under investiga- than one worker is involved, their relative tion and within the context of the particular 'sampling efficiencies' should be compared, habitat.

495 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Estimation of absolute population the light or by using transmitted light. A simi- density lar technique can be used for eggs laid into i) Direct counts small leaf veins, but those placed in larger veins, petioles, buds or stems can usually be Counting individuals in situ is clearly the detected only by careful dissection of the most direct method for estimating population plant. This is laborious but produces very density on plants, but is not always possible or detailed information on oviposition behaviour practicable, particularly with very active spe- (CLARIDGE & REYNOLDS 1972; THOMPSON cies. This approach is best applied to large or 1978; STILING 1980). conspicuous species, but may also be favoured when counting the earlier life-history stages or Attempts have been made to accelerate adults of the more sedentary species. WHITTA- the process of detecting eggs laid within plant KER (1965) for example was able to measure tissue using a variety of chemical techniques. the density of spittle masses of the cercopids These generally involve clearing the plant Neophilaenus lineatus and N. exclamations wit- tissue in boiling lactophenol, which also serves hin wire quadrats in grassland, whilst vertical to coagulate the egg proteins so that the out- stratification in the community of planthop- lines of the eggs become visible under magnifi- pers on the salt marsh grass Spartina patens was cation (CARLSON & HiBBS 1962). Other tech- quantified by counting directly the number of niques use hydrogen peroxide or glacial acetic individuals in five vertical strata up the stem acid for clearing the leaf tissue, followed by staining with acid fuchsin (CHATTERJEE & (DENNO 1980). RAM 1970). Such techniques, or modifica- Many continental European workers stu- tions thereof (SIMMONS et al. 1984), have now dying grassland communities have favoured a been used to detect eggs in a wide variety of direct counting technique called the 'bioceno- plant species (SlMONET &. PIENKOWSKI 1977; meter' (KONTKANEN 1950; ANDRZEJEWSKA SIMMONS et al. 1985; HEADY et al. 1985). 1965; NOVOTNY 1992). In essence, this invol- Major disadvantages are that they are time- ves delimiting a unit area of ground (typically consuming to perform and involve the use of 0.25 m2) by covering it with a cylinder or box hazardous chemicals. that has an open base and gauze-covered top, from which all insects are extracted by hand- held aspirator. Other authors refer to this ii) Suction samplers device as a 'box quadrat' (CHERRILL & BROWN Various mechanical devices have been 1990). It is designed to provide a standardized developed for the physical extraction of in- areal count, but its accuracy is reliant both on sects from vegetation, using a strong current of the box being positioned rapidly before any air generated by a motorised fan. The first device highly mobile individuals escape and on the to achieve widespread use was the DlETRlCK, observer detecting all the trapped insects. Alt- or 'D-Vac', suction sampler (DlETRlCK 1961) hough the equipment costs are negligible, (Fig. 1). Typically, it comprises a fan unit sampling using this method is very time-con- powered by a 100 cm-' two-stroke engine, suming and has largely been superseded by the connected via a flexible hose to a plastic or more automated methods dealt with below. fibreglass cylindrical inlet tube housing a mesh The egg stage within the life cycle pre- collection bag. The inlet cylinder has gauze- sents special sampling problems. In most covered apertures around the rim to allow air Auchenorrhyncha species, the eggs are too to enter near the soil when it is held over the small to be detected easily and most are inser- vegetation. The result is a powerful updraught ted directly into the plant tissue of either lea- of air through the vegetation, which sucks the ves or stems. Eggs laid within the leaf lamina insects into the collection bag. are generally placed just beneath the surface As the material does not pass through the and are therefore detectable under relatively fan, the insects are generally retained in near- low magnification as simple bulges in the leaf perfect condition. This means that Auche- epidermis. Sometimes, detection can be norrhyncha collected alive with this apparatus improved by varying the angle of incidence of can be used for subsequent experimentation.

496 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

It should be noted however that smaller and estimate of population density, samples from more delicate species may receive some dam- contrasting grassland types should be directly age. Also, parasitised Auchenorrhyncha may comparable. However, there is a limit to the suffer increased mortality and rearing parasi- vegetation height beyond which the process of toids from surviving individuals may be less positioning the inlet tube will flatten or com- Fig. 1. D-Vac suction sampler. The engine successful. press the plant material so that air is sucked and fan unit is mounted on a back- The whole unit is mounted on a backpack over, rather than through, the vegetation. pack frame (left) and connected via a long flexible hose (middle) to the worn by the operator, whose hands are left free The D-Vac, including various minor inlet cylinder which contains the to place the no::le over the vegetation and modifications of the original design (e.g. sample bag (right). empty the bag at the end of sampling without the need to take off the equipment or stop the engine. The collection no::le is placed verti- cally over the vegetation for a standard time period (at least 20 s.), after which any insects sucked into the collection bag can be emptied into a separate container, killed and stored. The greatest advantage of this technique is that it facilitates sampling of a standardized area of ground. As the cross-sectional area delimited by the inlet nozzle is generally c. 0.1 m:, it is customary1 to take ten such 'sucks' to produce a sample from lm2 of ground.

D-Vac suction sampling is often the pre- ferred method for sampling grassland and low crops when compared with other techniques such as sweep netting and various types of trap or beating tray (e.g. SlMONET et al. 1979; BUN- TIN 1988). This is because it often produces the highest density estimates and the lowest variation between samples. When measured, D-Vac extraction efficiencies have been shown to vary for different insect groups (HENDERSON Fig. 2. Two types of G-Vac & WHITTAKER 1977) and to be sensitive to a suction sampler. number of extraneous factors (HAND 1986). Right: the simplest Rather few of these studies provide data speci- design has a net collection bag inser- fically for Auchenorrhyncha. DUFFEY (1980) ted into the inlet reported Auchenorrhyncha extraction effi- tube and secured ciencies in rough grassland that varied from around the nozzle. The inlet tube has a 23% in May to 62% in August (presumably cross-sectional area coinciding with the peak nymphal and adult of 0.01m2. Left: alter- native design where stages respectively). Efficiency rose to 70% on a custom-built inlet grazed (i.e. short) grassland. HENDERSON & tube has a larger WHITTAKER (1977) also reported a sward-length cross-sectional area (0.025m2) and a flan- effect, with extraction efficiency in-creasing ge with gauze- from 32% in long grassland (20-30 cm height) covered holes that is to 76% in short grass (<5cm tall). mounted beyond the collection bag to Efficiency is severely compromised if the allow unimpeded entry of air into the vegetation is moist (although probably not as inlet tube. Both seriously as when using a sweep net) or 'lodged' samplers are powe- (flattened by wind, rain or trampling). Theo- red by 30 cm3 engines. retically, as this method provides an absolute

497 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

THORNHILL 1978), has remained the standard and suction power generated by these machi- equipment for quantitative sampling from a nes compared to the original D-Vac. The por- variety of crops and grassland habitats for tability of these new machines make them ide- many years. It does, however, suffer from a al for more general collecting, especially of number of severe disadvantages, not least of those species which reside close to the ground which are cost, weight and a poor reputation or in otherwise inaccessible places (WILSON et for mechanical reliability. In recent years, al. 1993). It is also a useful technique for various workers have developed smaller hand- collecting from very tall plants that are not held suction samplers, by modifying 'suck-or- easily swept (e.g. the reed Phragmites australis) blow' machines sold for collecting garden refu- or in damp or flooded situations where a sweep se (SUMMERS et al. 1984; HOLTKAMP & net bag would soon become saturated and THOMPSON 1985; DE BARRO 1991; WILSON et al. unworkable. 1993; ARNOLD 1994; MCLEOD et al. 1994, The inlet nozzle of any suction sampler 1995; SAMU & SÄROSPATAKI 1995; STEWART has to be placed quickly onto the ground in 6k WRIGHT 1995). BELL & WHEATER (2001) order to avoid invertebrates from outside the 1 refer to these types of machine as 'G-Vacs . delineated area being sucked into the sample. The various models available are generally SAMU et al. (1997) compared samples of spi- similar in design and operation, in that power ders taken from an alfalfa crop by a hand-held 3 is provided by a 30 cm petrol-driven engine suction apparatus from within enclosed areas which sucks air through a smaller (usually c.12 (each approximately 0.5m2) with samples cm. diameter) inlet tube. The only modificati- representing the same area of ground but on of the gardening equipment that is needed taken from a series of unenclosed sampling to convert it to an insect suction sampler is to points. Although the species compositions attach a fine net bag to the inside of the inlet and abundance rankings were similar for the nozzle to retain the insect material collected two sampling methods, the catches based on (Fig. 2) (STEWART & WRIGHT (1995) provide unenclosed sampling points were substantially more detailed instructions). larger than those where the sampling area was The inlet nozzle cross-sectional area of enclosed. They therefore suggest that the these more compact machines is rather too action of placing the inlet tube nozzle onto small (-0.01 m2) for each 'suck' to be regarded the ground draws in extra individuals from as a single sample. However, sampling from a outside the target area and that such an 'edge larger area can be standardized by delimiting a effect' may produce inflated estimates of popu- fixed area of ground with an open-ended cylin- lation density. der (e.g. 36 cm diameter, to be comparable to The suction power of most conventional the D-Vac collection nozzle) placed over the samplers is severely reduced when the air flow vegetation. The nozzle of the G-Vac suction is impeded; this may happen when the inlet sampler can then be inserted into the cylinder nozzle is placed over the ground surface or and passed repeatedly across the vegetation for when a large amount of debris builds up in the a set time interval to collect any insects trap- collection bag. The Vortis sampler is designed ped inside. to circumvent these problems, firstly by intro- In the only detailed study of the efficacy of ducing air into the system from higher up the this equipment for sampling Auchenorrhyn- inlet tube, and secondly by dispensing with cha, STEWART & WRIGHT (1995) showed that any sort of collection bag (ARNOLD 1994). catches of most species using a G-Vac sampler Instead, insects are sucked up the inlet tube were comparable with those taken from an into an enlarged chamber designed to create a equivalent area of ground by D-Vac. Some spe- vortex of circulating air, from which centrifu- cies known to inhabit the layer closest to the gal forces propel the insects into a detachable ground were sampled in greater numbers with collection vessel mounted on one side (Fig. 3). the G-Vac, although this effect was better Whilst the mechanical principles behind this demonstrated in certain epigeal species of device represent an improvement on the Coleoptera and Araneae. This observation design of previous suction samplers, its use in reflects the considerably greater air velocity practice is prone to a new set of problems. The

498 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at insects have much further to travel before rea- easily removed and killed (see MOORE et al. ching the collection vessel, including passing (1993) for full details). Both adult and nym- through a set of fixed metal vanes that induce phal Auchenorrhyncha self-sorted very rapid- the vortex of air; risk of damage to specimens ly in this apparatus, nearly 100% of individu- is therefore increased. Similarly, there is an als separating within 4-8 hours. BuNTIN enhanced danger of specimens adhering to the (1988) achieved 94% recovery of leafhoppers interior walls of the suction tube or chamber if using a laboratory-based device that was simi- either become coated in moisture. The only lar in principle, funnelling the insects straight published data on sampling efficiency suggest into an ethanol-filled vial. that Homoptera are sampled substantially bet- Fig. 3. ter by the conventional D-Vac (ARNOLD Vortis suction sampler. Suction is pro- 1994). The absolute efficiency of the appa- vided by a 30 cm3 engine (top). Air is ratus for this or any other insect group remains sucked into the inlet tube through a gauze cone (bottom), drawn through to be tested. a set of radiating internal vanes that Any type of suction sampler will remove generate a vortex and then into an some quantities of dead plant material, soil expansion chamber (middle). Insects that are circulated by the vortex in particles and other debris (more powerful the expansion chamber are propelled machines will collect more). Sorting dead in- by centrifugal forces into an escape sects from this waste material is probably the tube mounted on the side (middle most time-consuming part of this sampling left) and drop down into a detachable collection vessel below. method. Consequently, several workers have attempted to develop techniques whereby, before being killed, the insects' phototactic responses are exploited to segregate them from the unwanted material. DlETRlCK et al.'s (1959) original method was to transfer the material collected by D-Vac into a Berlese funnel to sort the animals into tubes of alco- hol. WALOFF (1980) reported using a 'sorting frame' to separate Auchenorrhyncha from debris collected by D-Vac sampling. This com- prised a wooden-framed muslin funnel with a clear plastic window at one end. The frame was placed in front of a light source and the whole sample was emptied into the funnel. Emergent insects were attracted to the light and moved towards the plastic window, from which they could be removed by hand-aspira- tor. MOORE et al. (1993) have attempted to take this principle a stage further towards automation, by developing a field-based method that can be employed immediately after collection of the sample. Using the prin- ciple employed in the traditional capture of lobsters (Crustacea: Nephropidae), they con- structed a 'light-sorter' device from joined sec- tions of plastic soft drink bottles that were painted matt black or left clear. The suction sample debris was placed in the dark section of the sorter and the insects were left to move of Fig. 4. their own accord away from the debris and Sorting the catch from a suction sampler. Most suction samples contain substantial amounts of plant and soil debris. The debris (left) is examined carefully and all insects into the light section, where they could be are removed with fine forceps (top). The catch can then be sorted into species (right).

499 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Where such automatic sorting devices are ning). They found that trap efficiency was not available or the insect sample has already generally unaffected by wind, temperature or been killed, catches have to be separated from crop height but was significantly reduced at the associated plant and soil debris by hand. lower sunlight levels. However, SlMONET et al. Finding small insects in larger amounts of (1979) found that this method was considera- debris can be extremely time-consuming and bly less efficient for sampling E. fabae adults the process is also subject to a number of bia- than either suction or sweep net techniques. ses connected with the skill of the sorter, the BUNTIN (1988) came to a similar conclusion amount, nature and condition of the dead for extracting cicadellid adults from bermuda- plant material and the relative crypsis of the grass, Cynodon dactylon, and found that the insect species. The most efficient technique is technique did not recover any nymphs. In the to spread the entire sample evenly onto a clean cooler climate of central Finland, TÖRMÄLÄ light background, such as a white plastic tray. (1982) reported this method to be very ineffi- Individual specimens can then be picked out cient for sampling the grassland Auchenorr- from the debris using fine forceps (Fig. 4). hyncha community, comparing unfavourably Sorting effort can be standardised by imposing with sweep netting, suction sampling and a fixed time limit for processing each sample. even pitfall trapping in terms of the numbers Where either the number of insects or the amounts of debris are excessive, it may be of individuals and species caught. pragmatic to process only a sub-set of the material in each sample. This can be done by iv) Marking techniques evenly spreading each sample over the sorting Mark-release-recapture techniques have tray and separating off a fixed fraction for been used to estimate population sizes of a detailed sorting. wide variety of mobile animals including in- sects (SOUTHWOOD 1978). At their simplest, iii) Emergence traps these involve catching, marking and releasing Emergence traps make use of the positive a number of individuals within a population, phototactic response of many mobile insects. followed by re-sampling after a period to allow Individual trap designs vary but all consist of for re-mixing. The ratio of marked to unmar- an open-ended opaque box or cylinder, with ked individuals in the second sample should an aperture at the top providing the only sour- be the same as that in the population as a ce of light. Insects moving up the chamber whole; this fact allows a simple estimation of towards the light are funnelled into a collec- the total population size. The technique tion vessel. Samples are standardized because makes a number of critically important the trap base covers a fixed area of ground. assumptions, including (i) random selection of The apparatus is placed rapidly over the vege- individuals for marking (e.g. across sexes, phe- tation and sealed at the soil surface to prevent notypes and age classes), (ii) fully random insects escaping. CHERRY et al. (1977) suspen- mixing of marked individuals with unmarked ded the trap from the end of a long pole which ones after release, (iii) a marking technique was used to lower the trap over the vegetation that is persistent but does not affect survival or at a distance from the operator; this was inten- subsequent behaviour of individuals, and (iv) ded to reduce disturbance of the resident a population which is closed (i.e. no birth, Auchenorrhyncha by the operator. The alter- immigration, death or emigration) within the native is to position the trap early in the mor- period of study. These assumptions are rarely ning when the insects are likely to be least fully met and their violation can produce active and then leave it in place for several serious biases in the resultant population esti- hours (TÖRMÄLÄ 1982) or days (CLEMENTS mates. The comparative ease and accuracy of 1979). CHERRY et al.(1977) found that this other methods of population estimation have method recovered more than 80% of potato meant that this technique has not been widely leafhoppers E. fabae from alfalfa (absolute used by workers studying Auchenorrhyncha. densities being calculated after fumigation of However, various marking techniques the trap to retrieve any individuals remai- have been employed in studies of local disper-

500 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at sal by leafhoppers and planthoppers. The most adequate for many studies, where the primary popular technique has been the use of fluores- interest is simply in comparing population cent powders or coloured dyes (PURCELL & levels and there is no specific requirement to SUSLOW 1982; LARSEN & WHALON 1988; know the absolute population density. This is WHITNEY & MEYER 1988; POWER 1992). A generally the case where the focus is on moni- sample of insects is confined in a vessel con- toring how populations change across years or taining a small amount of the marker. The comparing between different experimental vessel is gently agitated to ensure that all indi- treatments. Relative population estimates can viduals are covered and then the insects are be derived by active sampling using nets or released at a single point. Insects recaptured through passive sampling using various types after a period of time in traps that have been of stationary trap. positioned at known distances and directions from the release point are then checked for traces of the marker. Re-captures may need to i) Sweep netting be examined under low-power magnification A sweep net is a particularly robust type of and (for fluorescent powders) ultra-violet net used to dislodge and collect insects from light. Different colours can be used to denote vegetation. It must have a reinforced rim to different release dates and/or locations, al- withstand the impact of jarring against plants though PURCELL & SUSLOW (1982) warn that and the net bag should be constructed from a colours that are too similar may be difficult to natural fibre or synthetic cloth material that is separate in the small quantities found on similarly durable. The most efficient mode of recaptured insects. action is to pass the net repeatedly through

PADGHAM et al. (1984) and PERFECT et al. the vegetation using alternate forehand and (1985) adopted a mass-marking technique, backhand strokes whilst walking forward at a both to monitor flight activity in planthopper constant speed. At the end of this sweeping, pests of rice and to help in the interpretation any insects caught can be extracted from the of catches from other trap types. They applied bag using a portable aspirator or the entire rubidium chloride as an aqueous foliar spray to catch can be emptied straight into a collection the crop arid- then attempted to recover mar- bag or killing bottle. At the end of each ked individuals using various types of trap sweeping episode, care should be taken to (water, suction and light) situated in or adja- wrap the end of the net around the rim to pre- cent to the treated plot. All planthoppers vent the more mobile species from escaping; caught were checked for traces of rubidium for this reason, the bag length should be at using atomic absorption spectrometry. ALVER- least one and a half times the diameter of the SON et al. (1980) used a similar technique to net aperture. mark the black-faced leafhopper, Graminella The sweep net is almost certainly the most nigrifrons, a virus vector on corn. widely used method for collecting herbivorous With all these techniques, the critically insects from vegetation. Its principal advanta- important assumption is that the marking does ges are that it is simple and inexpensive to not significantly affect the insects' behaviour construct, easy and quick to use, large num- or viability. All of the aforementioned studies bers of insects can be caught and extensive have therefore had to include a careful com- areas of ground can be covered. For these rea- parison of the behaviour and survival of mar- sons, it is widely used for non-quantitative sur- ked individuals with controls. vey work, for example the rapid production of faunal inventories. A significant drawback is Estimation of relative popu- that it can not be used if the vegetation is wet, lation density flattened or very short. Also, the technique can seriously damage the vegetation if applied Absolute population estimates often too vigorously (an important consideration necessitate expensive equipment or are time- when sampling crop plants) and it is not consuming to produce. Fortunately however, appropriate if plants are too large or robust relative population estimates are perfectly (taller crop plants, bushes or trees).

501 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Sweep nets are sold and can be made in a material but have a narrower aperture through variety of forms (Fig. 5). The important varia- which insects can escape. Nets made from soft bles are the size and shape of the aperture, the natural fibre cloth or 'nylon' are generally material used for the collection bag and its favoured because the catch can be temporari- Fig. 5. length. Larger diameter nets can be used to ly contained at the end of the sweeping by fol- Sweep nets. A range of sweep nets, illustrating the potential variation in sample a gTeater volume of vegetation but ding the bag over the frame. However, a size, shape and net material. The net become excessively heavy and cumbersome to variety of stiffer synthetic mesh materials (e.g. in the centre is made with semi-rigid control once the diameter of the aperture 'tygan') have also been used to produce nets gauze netting designed to maintain that retain their open shape permanently. Alt- the open net shape permanently. exceeds about 60 cm. Smaller nets collect less hough this increases the risk of insects esca- ping through the open aperture, this can be minimised by taking advantage of the insects' natural phototaxis. If the net is held with its apex pointing in the direction of the sun and with the aperture inclined slightly downwards, the insects will tend to move upwards and towards the light and therefore become trap- ped at the closed end of the net. The aperture of the net can be held close to the user's face for close inspection of the catch and selective removal of individual insects with an aspirator.

Portable aspirators (sometimes referred to as 'pooters') are also produced in a variety of forms (Fig. 6). It is important that the barrel of the aspirator is made of transparent material so that the catch can be inspected during collecting. Glass tubing presents a safety risk under field conditions but will usually remain clear for longer, whilst plastic scratches easily and therefore reduces visibility for inspection of the catch. Multi-barrel aspirators can be used to keep catches from different sites or habitats separate. Whilst sweep netting is widely used for general collecting, there are considerable pro- blems in using it for quantitative sampling. This is because capture efficiency is affected by a number of factors, including vegetation type, weather conditions and the effect that both of these have on the behaviour of the insects. Other biases may be created by varia- tion in the speed, height and angle of the net as it hits the vegetation and its orientation in relation to the wind. Recognition of these potential biases has prompted different re- sponses: DELONG (1932) doubted whether relative population densities could be estima- Fig. 6. Selection of hand-held aspirators ('pooters'). The basic design of an aspirator can be ted with any accuracy using this technique, modified to suit the particular purpose, but should have a collection barrel that is whilst ROMNEY (1945) concluded that it was transparent to allow inspection of the catch. A multi-barrel aspirator (top) can be used justified if allowance was made for the effect of to segregate samples, for example from different sites, habitats or experimental treat- ments. important environmental variables.

502 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Sweep netting samples only the middle ces of bias as possible by standardising the pro- and upper layers of the vegetation, so that spe- cedure. This should include the area covered, cies occupying the layer nearest the ground the total number of sweeps, the walking pace will tend to be under-represented in catches, and the height at which the net is drawn as shown repeatedly in comparisons of sweep through the vegetation. Additionally, it may net and pitfall trap catches (PAYNE 1981; TOR - be necessary to check for differences in captu- MALA 1982; NOVOTNY 1992; CHERRILL & re efficiency between workers and adjust the SANDERSON 1994). Reactions to disturbance resultant figures if necessary. In community of the vegetation will differ between species. studies, the relationship between sampling Highly mobile species will fly away whilst effort (in this case, the total number of more sedentary species may drop deeper into sweeps) and number of species recorded will the vegetation, in both cases causing an follow the familiar asymptotic species-area under-representation in the sweep net catch. curve, whereby new species are initially added Conversely, some Delphacidae that dwell near rapidly but the species accumulation rate to the ground respond to disturbance of the levels off after a critical sample size has been upper vegetation layers by climbing the plant exceeded. The speed with which this asym- stems (perhaps in preparation for flight). Dif- ptote is reached will depend not only on the ferences in response may also be apparent bet- species richness of the community but also on ween the sexes; DECKER et al. (1971) report the structure of the habitat. In early studies that ovipositing female potato leafhoppers comparing a wide range of different grassland (Empoasca fabae) are less easily prompted to types, KONTKANEN (1950) determined that fly than males. samples of 200 sweeps were needed to reflect Recognizing these potential sources of the full spectrum of species present. bias, various attempts have been made to esta- blish the relative efficiency of sweep netting ii) Pitfall traps in comparison with other techniques. Using emergence traps to determine absolute popu- Pitfall traps are glass, metal or plastic lation densities, CHERRY et al. (1977) found collection vessels, typically 8-10 cm in diame- Fig. 7. that sweep net catches of the potato leafhop- ter and 10cm deep, set into the soil and part Pitfall trap. A collection vessel (plastic, filled with a preserving fluid (Fig. 7). Inverte- metal or glass, approximately 8-10cm. per, Empoasca fabae, were very strongly affec- diameter) is embedded into the soil ted by weather conditions. They therefore brates that are active on the soil surface or so that the rim is at or slightly below developed a calibration for conversion of within the epigeal layer fall into the trap and the soil surface. Epigeal invertebrates are unable to escape (SOUTHWOOD 1978). The fall into the vessel which contains a sweep-net catches to areal population estima- small amount of preservation fluid. tes, that included an allowance for both wind precise design of the trap is largely unimpor- Rain-shields (in this case, an inverted speed and temperature. Although WALOFF & tant, as long as the rim of the collection vessel plant pot saucer held in place by a metal wire frame) can be used to pre- is set at or just below the soil surface. After SOLOMON (1973) used a D-Vac for their detai- vent the trap from flooding in wet led population studies, sweep net catches were setting, traps are typically left for one to two weather. occasionally substituted using a conversion factor, when suction sampling was not possible (WALOFF & THOMPSON 1980). Other workers have attempted to convert sweep net catches to absolute population densities (HEIKINHEIMO & RAATIKAINEN 1962; SIMONET et al. 1978, 1979; TÖRMÄLÄ 1982). In spite of these short- comings, sweep netting often compares very favourably with other sampling techniques (SIMONET et al. 1979; BUNTIN 1988) and has the merits both of speed and of minimal cost.

If sweep net catches are to be used for rela- tive estimates of population density, it is important to minimize as many potential sour-

503 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

weeks before the contents are removed for sie- considerable numbers of a species which had ving and examination. Various fluid preserva- not been recorded for more than 50 years in tives have been used (varying-strength solu- Britain (MORRIS & PARSONS 1992). It is clear tions of alcohol, ethylene glycol or formalde- that some of these species may have been pre- hyde, with a few drops of detergent to reduce viously overlooked because they occupy the the surface tension), some of which may have lowest layer within the vegetation which is an attractive effect although this has not been poorly sampled by other methods. fully evaluated for Auchenorrhyncha. Some A further characteristic of pitfall trap cat- workers (e.g. NOVOTNY 1992) have chosen to ches is that they tend to be dominated by male shield the trap with a flat metal or plastic specimens. This feature has been noted by sheet (slightly larger than the aperture of the several workers (LE QUESNE & MORRIS 1971, trap and suspended a few centimetres above its PAYNE 1981, A.J.A. STEWART, unpublished rim); this serves to protect the trap from rain- data). The discrepancy may be very marked: fall, deter interference from mammals and NOVOTNY (1992) recorded a sex ratio of 17:1 define more precisely the vertical zone being in Aphrodes bidnctus (SCHR.) and LE QUESNE & sampled. MORRIS (1971) found a 26:1 ratio in Aphrodes The merits of pitfall traps are that they are albifrons. It is likely that this effect results from cheap, easy to set and can produce large cat- the males being more active rather than ches containing a range of species. As with because they occupy a lower stratum within other fixed traps, they can be used to sample the vegetation. This highlights the problem of continuously over long periods of time, giving catch sizes being activity dependent, which a more realistic picture than the 'snapshot' has been recognised for some time in other provided by other 'instantaneous' sampling invertebrate groups (ADIS 1979; DEN BOER methods. Despite these advantages, the use of 1986; TOPPING & SUNDERLAND 1992). pitfall traps has never been a mainstream Nevertheless, pitfall trapping remains a useful technique for sampling grassland Auchenorr- and considerably under-exploited technique hyncha. However, recent evidence suggests for general collecting and for site inventory that it has considerable potential for sampling studies on Auchenorrhyncha. More research certain species groups. A number of studies on how pitfall trap catches relate to actual comparing this method with sweep netting or population densities would be valuable. other types of sampling (CHERRILL & SANDER- SON 1994; NOVOTNY 1992; PAYNE 1981; TÖR- MÄLÄ 1982) have been instrumental in indi- iii) Attraction and interception traps cating that grassland Auchenorrhyncha are for capturing flying insects vertically stratified within the physical struc- In addition to the simple pitfall trap, a ture of the vegetation. European genera which variety of other trap types have been used for are caught in disproportionate numbers in pit- different purposes. All operate by either fall traps and are therefore assumed to dwell attracting insects to the trap, using visual or close to the soil surface include Agattia, Aphro- olfactory cues, or by intercepting their normal des, Eurysa, Delphacodes, Macustus, Megamelo- movement patterns. In both cases, as with pit- des, Megophthalmus, Strepumus, Stroggylocepha- fall traps, the resultant catches reflect a com- lus and Ulopa. bination of abundance and activity; the rela- Pitfall traps have also been used success- tionship between catch size and true abundance fully in compiling faunal inventories for cer- will vary between species and possibly also tain habitat types where other techniques are spatially and temporally. Hence, it is unwise to not practicable. In Britain, large-scale surveys use the size of such catches for quantitative of both lowland and upland peat bogs using studies, unless their accuracy in the particular pitfall traps have revealed a number of del- situation has been verified by another phacid species which were previously thought method. However, information from such to be rare and restricted in their range (HOL- traps are useful in species inventory work and MES et al. 1993). Another survey of open, spar- in indicating seasonal phenologies (e.g. the sely-vegetated shingle habitats rediscovered initiation of dispersal or migratory behaviour).

504 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Although most often associated with sam- adhesive that is resistant to water and remains pling nocturnal Lepidoptera, light traps have sticky over long periods) are perhaps the ento- also been used to sample Auchenorrhyncha. mologist's least favoured technique, as the spe- Fig. 8. Trap efficiency varies markedly between diffe- cimens caught are difficult to extract from the Water trap. Made from a plastic plant rent climatic regions. In temperate climates, adhesive and rarely remain in good condition. pot saucer mounted on a short stake Rothamsted light traps (WILLIAMS 1948) spo- and part-filled with water. Light Nevertheless, they are widely used as an inex- radically catch a limited range of species in colours (white, yellow, orange) tend pensive technique for monitoring the distribu- to be more attractive to insects than modest numbers (A.J.A. STEWART, unpublis- tion and spread of leafhopper populations in darker shades or colours (green, brown) hed data). However, tropical environments that blend more with the background commercial crops; for example, they have induce substantially larger catches, enabling vegetation . routine monitoring for pest management (PERFECT et al. 1985), biodiversity inventory- studies (SUTTON 1983; REES 1983) and long- term studies of seasonally (WOLDA 1980). TAYLOR et al. (1982) developed an upwardly- directed light trap, incorporating a device for segregating the catch into time intervals, specifically for monitoring flight activity (especially landing and settling times) in the planthopper N. lugens. If behavioural differen- ces exhibited by the Lepidoptera are represen- tative, the attractiveness of light traps for Auchenorrhyncha is likely to vary consider- ably between species and sexes, but no work has yet been done on this aspect.

The attraction of flying insects to particu- lar colour spectra can be turned to advantage by using water-filled coloured bowls as traps been one of the principal methods for sam- (Fig. 8). Colours differ in their attractiveness pling leafhopper vectors of X-disease in Cali- to different insect groups; yellow and to a les- fornian cherry orchards (PURCELL & ELKING- ser extent white are generally the most attrac- TON 1980). Comparison of sticky traps with tive, but may even be repellent to some groups sweep netting and suction sampling in such (DISNEY et al. 1982). KISIMOTO (1968) showed orchards showed that each technique produ- that yellow water traps were most effective for ced a different numerical balance between the catching the common rice-feeding planthop- common species. Interestingly however, the pers. Colours that match the background sticky traps caught the most species, probably vegetation more closely, such as green and due to the continuous nature of the sampling brown, provoke the least marked responses over a long period compared to the near- (either attraction or repulsion) and therefore instantaneous sampling of the other techni- may be used to produce a less selective, al- ques. though lower, catch. Water traps have the advantage of modest cost, which means that 'Flight-interception' or 'window' traps large numbers can be used to survey distribu- operate by blocking the flight path of indivi- tion patterns over substantial areas (eg. duals moving laterally through the habitat. GYORFFY & KARSAI 1991). It would be impor- They comprise a vertical barrier of transparent Fig. 9. tant to standardise on vertical positioning, as material (glass, plastic or thin mesh) suspen- Window trap. A perspex sheet (appro- evidence from using water traps to catch other ded above a fluid-filled collection trough ximately 1x1m.) is mounted vertically insect groups suggests that height (particularly which the insects drop into after colliding on a metal frame. Flying insects are height above the upper vegetation surface) intercepted and fall down into fluid- with the barrier (Fig. 9). Paired troughs either filled collection troughs running along has a pronounced effect on catch size (USHER side of the vertical barrier allow segregation of the base of the 'window'. Separate 1990). the catch into individuals moving in each of troughs on either side of the 'win- dow' allow an assessment of numbers Sticky traps (small coloured plates covered the two opposite directions. It is customary to of insects moving in the two opposite with a proprietary banding grease or other use this feature to measure movement of flying directions.

505 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

insects across habitat boundaries (e.g. between tion flux (Nf+/ = Nf + Birth + Immigration - a crop and adjacent semi-natural habitat). Death - Emigration, where Nt = the populati- There are few examples in the Auchenorr- on density at time t) recognises the effect on hyncha literature, but GYORFFY & SzÖNYI (1989) population dynamics of individuals moving report a remarkable 41,000 individuals across into and out of the population. Because of the 118 species caught over two years with this difficulties in tracking small and highly method in a study of movement patterns bet- mobile organisms, many population studies (and the theoretical models underlying them) have ween ungrazed grassland and adjacent pasture ignored the processes of immigration and emi- and forest. SCHULTZ & MEIJER (1978) employ- gration and chosen instead to concentrate on measuring the birth and death rates. This approach makes one of two assumptions: eit- her that exchange of individuals with other populations is negligible and can therefore be ignored (unlikely to be true for highly mobile species), or that immigration and emigration are equal and therefore cancel each other out. The latter assumption, even if numerically correct, is unlikely to hold for the secondary attributes of the population (e.g. sex ratio, age distribution, genetic structure). Population studies therefore should always attempt to quantify rates of movement into and out of the population.

This problem can be tackled in several ways, each method providing data of differing value and cost. Direct measures of dispersal Fig. 10. ed these and 'strip traps' (pitfall traps placed in using mark-release-recapture techniques have Malaise trap. Vertically positioned the middle of a length of gutter sunk into the been dealt with already and have been useful sheets of black netting arranged like an open-sided tent intercept the soil) to monitor immigration into new pol- in quantifying small-scale movement within movement of insects through the ders, but found that neither caught large num- and between adjacent habitats (e.g. PuRCELL habitat. Once intercepted, insects res- bers of leafhoppers. & ELKINGTON 1980). More technologically pond phototactically and move upwards towards the white roof. The A further type of flight-interception trap, advanced methods, such as using allozytne inclined ridge of the 'tent' funnels the the Malaise trap, is constructed in the fashion variation (DEN HOLLANDER 1989) and DNA insects towards the top corner, where of an open-sided tent (MALAISE 1937). It is techniques to measure genetic differentiation an aperture leads into a collection ves- sel (top left) filled with preservation generally constructed with dark walls and a and thereby infer rates of gene flow between fluid. light roof to encourage insects to move populations, have yet to be exploited widely upwards and be funnelled into a collection in this group. bottle (Fig. 10). It is very efficient at catching RAATIKAINEN (1972) inferred rates of Diptera and Hymenoptera, but has not been dispersal of leafhoppers into oatfields in Fin- widely used by collectors of Auchenorr- land by collecting a series of samples at even- hyncha. However, OWEN (1991) reports ly-spaced distances into the crop from the captures of considerable numbers in Britain margin with an adjacent ley. The results enab- across thirty species, most of which were led him to distinguish between species that cicadellids. flew only trivial distances or not at all, which declined in density from the crop edge towards Measurement of movement the middle, and species that he classed as and dispersal migrants because their densities were more The measurement of dispersal rates and even. RAATIKAINEN & VASARAINEN (1973) movement patterns in small animals such as developed a stand-mounted net apparatus that invertebrates remains a major challenge for could rotate with the wind direction, to moni- field biologists. The basic equation of popula- tor movement of flying insects above cereal

506 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at crops. Functioning of the trap was dependent Auchenorrhyncha species. Her total sample of on a certain minimum wind velocity to keep over 4100 individuals comprised 45 species, the net elevated. Also, the lack of a collection 40 of which were captured by the suction vessel meant that insects could crawl or fly out sampler and 21 by sweep netting; the pitfall of the net unimpeded. Nevertheless, the appa- traps collected 28 species, but only one of the- ratus sampled some 12,500 individuals across se was unique to this method. The difference 57 species during seven 2-month field seasons. in conclusion between this and previous stu- The best studies have used more than one dies illustrates the point that the relative effi- technique to measure different components of ciency of any sampling method should be population flux. In an exemplary study, PER- tested in the context of the particular habitat FECT et al. (1985) employed different types of being studied prior to detailed work on com- trap to separate the different components of munity composition and structure. Unfortu- flight activity in delphacid pest populations in nately, financial and time constraints often flooded rice. They suggested that the total preclude this important preparatory work. aerial density (measured using suction traps) A further important consideration con- could be partitioned into immigrants (monito- cerns the minimum sample size required to red with green water traps) and emigrants provide a reliable estimate of species richness. (using 'net canopy traps'). Insects over-flying The number of species recorded will increase the resident population (as well as immigrants with increasing total sample size up to an into it) were sampled using upward-pointing upper asymptote, which, if reached, can be light traps. taken as a true reflection of the species rich- Long-distance mass migrations of certain ness of the community. The sample size requi- important agricultural pest species have been red to reach this asymptotic species richness monitored using radar (RlLEY et al. 1991) and level will vary between taxonomic groups. trapping from aircraft (TAYLOR & RELING STANDEN (2000) also showed that it will vary 1986). Other authors working with wing-poly- according to the sampling technique used. In morphic delphacids have used the balance her study, the combined sweep net and suction between macropters and brachypters to infer sampler technique produced a species accumu- the migratory tendency of the population lation curve that started to level off at around (reviewed in KlSIMOTO & ROSENBERG 1994). 400 individuals and approached its asymptote at around 1500 individuals. Conversely, the Choice of technique and species accumulation curve for the pitfall trap minimum sample size technique was still rising steeply at the end of the study when approximately 600 individuals A number of studies comparing the sam- had been sampled. pling efficiency of different methods such as sweep netting, suction sampling and pitfall Summary and future research trapping (CHERRILL & SANDERSON 1994; NOVOTNY 1992; PAYNE 1981; TÖRMÄLÄ 1982) Techniques for sampling populations of have shown that each technique samples a Auchenorrhyncha (or indeed any other subtly different component of the total fauna. insects) that are completely objective and The conclusion usually drawn is that, if a com- unbiased simply do not exist; all methods plete inventory of a grassland fauna is sought, carry inherent biases. Table 1 summarises sweep netting or suction sampling has to be these and other attributes of the main sam- combined with pitfall trapping, since the lat- pling techniques described in this paper. The ter technique is needed to reveal the species relative efficiency of any technique will living in the lowest vegetation stratum or very depend upon a range of factors related to the close to the ground. However, in a study of the physical environmental conditions, the struc- invertebrate fauna of a calcareous grassland in ture of the habitat and the behaviour of the north-east England, STANDEN (2000) found insects themselves. Consequently, all popula- that a combination of sweep net and suction tion or community studies should (but rarely sampling revealed nearly all the resident do) start by evaluating the efficiency of the

507 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

Table 1: Attributes of different techniques for sampling grassland Auchenorrhyncha.

Method Cost of Time Sampling Absolute (A) Ability to Skill Activity Weather Range of Taxonomic Advantages / equipment efficiency interval: or relative (R) standardize required dependence dependence habitats in bias*. Disadvantages • * instantaneous (1) estimate of * * * » which Groups (italics) or extended (E) population applicable favoure density * (italics)

Direct L i 1 A H H M H H Urge spp., Non-destructive. counts sessile spp. Allows recording of microhabitat, host-plant association, feedinq position. D-Vac H M 1 A H M L L-M L Weight. Poor reliabili- ty. Efficiency declines with increasing vege- tation height and density

G-Vac M M 1 A H M L H L-M L Time needed to sort sample from debris Emcrqence L H E A H L M M L 7 Small catches. Sweep net L M 1 R M M M H H Spp in Efficiency varies middle- between operators upper layer of veqetation Pitfall trap L H 1 R M L H L L Epiqeal spp. Low cost. Light trap M H E R M L H H M •> Mains electrical source required (some traps). Differential attractiven- ess to different spp. Water trap L H E M L H M H ? Requires regular checking S change of fluid Sticky trap L H E *~ R L L H H M ? Poor condition of specimens Flight L H E 1 R L L H H M 7 Can be used to Indicate interception direction of movement ("window") trap Malaise trap M H E R L L H H M 7 Large catches of certain qroups Mark- L L 1 H H M Weed high recapture release- rate. recapture

* H: high; M: medium; L; low. sampling technique proposed. This is especial- This review also shows that, whilst a limi- ly important when monitoring the dynamics ted range of conventional sampling methods of populations over time or when comparing has been widely used, a number of other tech- spatially separated populations. It may be pos- niques more generally associated with collec- sible to do this in near-absolute terms, for ting other insect groups may also be applicable example by expressing the catch from a stan- to the Auchenorrhyncha. These techniques dard sample as a percentage of the total num- however would need to be tested rigorously for bers recovered after any extra individuals taxonomic bias before being adopted in com- found by a thorough hand-search of the habi- munity studies and for activity-dependence if tat are included. In other cases, comparison used in population monitoring. may be possible only with another relative estimate of population density. In either case, The distribution and behaviour of the spe- the investigator should be aware of how cies and the architecture of the habitat usual- extrinsic factors such as weather conditions ly dictate which sampling technique is most affect sampling efficiency and whether both appropriate. Standard equipment or techni- sexes and both nymphal and adult stages are ques will often have to be modified to impro- affected equally. Much more research is nee- ve sampling efficiency under the particular ded on the comparative efficiency of different conditions presented by the study. Whilst par- techniques in sampling Auchenorrhyncha ticular techniques have been developed to (c.f.TöRMÄLÄ 1982). sample broad species-habitat combinations,

508 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at new studies should not adopt these uncritical- References ly. In their understandable enthusiasm to pro- gress to examining patterns and processes in ADIS J. (1979) Problems of interpreting arthropod sampling with pitfall traps. — Zoologischer Auchenorrhyncha populations, investigators Anzeiger Jena 202: 177-184. should not fail to check that the techniques ALVERSON DR., ALL J.N. & P.B. BUSH (1980) Rubidium as which they are using will provide results that a marker and simulated innoculum for the are reliable both statistically and biologically. black-faced leafhopper, Graminella nigrifrons, the primary vector of maize chlorotic dwarf virus of corn. — Environmental Entomology 9: 29-31.

Zusammenfassung ANORZEJEWSKA L. (1965) Stratification and its dynamics in meadow communities of Auchenorrhyncha Die verschiedenen Methoden, um Zika- (Homoptera). — Ekologia Polska Seria A 13: den-Zönosen in Grünland zu erfassen, werden 685-715. vorgestellt und hinsichtlich ihrer Vor- und ARNOLD A.J. (1994) Insect suction sampling without nets, bags or filters. — Crop Protection 13: Nachteile diskutiert. Wie bei den meisten 73-76. Wirbellosen, so gibt es auch für Zikaden keine BELL J.R. S C.P. WHEATER (2001) Analysis of the most einzelne Methode, um das vollständige Arten- popular techniques for sampling spiders in lar- spektrum eines Lebensraums mit hinreich- ge-scale ecological experiments in grasslands. — ender Sicherheit zu erfassen oder Populations- Newsletter of the British Arachnological Society 91: 10-12. größen und Individuendichten aller Arten BROWN V.K., JEPSON M. S C.W.D. GIBSON (1988) Insect eines Lebensraums korrekt zu ermitteln. Den- herbivory: effects on early old field succession noch können mit vertretbarem Einsatz von demonstrated by chemical exclusion methods. Zeit und Ausrüstung gute Näherungswerte — Oikos 52: 293-302. sowohl für relative als auch für absolute Popu- BUNTIN G.D. (1988) Sampling techniques, population lationsdichten ermittelt werden, wenn der dispersion, and sampling plans for leafhoppers (Homoptera: Cicadellidae) in bermudagrass. — Erfassungsmethodik (Standardisierung; Environmental Entomology 17: 872-877. Vergleichbarkeit in Raum und Zeit) entspre- CARLSON O.V. & E.T. HIBBS (1962) Direct counts of pota- chende Beachtung zuteil wird. Streifnetzfänge to leafhopper, Empoasca fabae, eggs in Sola- (Kescherfänge) sind eine kostengünstige und num leaves. — Annals of the Entomological Society of America 55: 512-515. einfache Methode, um relative Häufigkeiten zu ermitteln, haben aber den Nachteil, daß sie CHATTERJEE S.N. & R.D. RAM (1970) A technique for staining and counting leaf-hopper eggs in leaf schwer standardisierbar sind und daß damit tissue. — Science & Culture 36: 597-598. zudem die Häufigkeiten epigäischer Arten CHERRILL A.J. & V.K. BROWN (1990) The life cycle and unterschätzt wird. Die herkömmlichen distribution of the Wart-biter (Decticus verruci- „D-Vac"-Sauger wurden in jüngerer Zeit durch vorus (L) (Orthoptera: Tettigoniidae) in a chalk grassland in southern England. — Biological verschiedene kleinere und billigere umgebau- Conservation 53: 125-143. te „Laubsauger" ersetzt. Sie können gut dazu CHERRILL A.J. S R.A. SANDERSON (1994) Comparison of eingesetzt werden, um absolute Häufigkeiten sweep-net and pitfall trap samples of moorland in Grünlandökosystemen zu ermitteln und Hemiptera: evidence for vertical stratification erreichen insbesondere bei epigäischen Arten within vegetation. — The Entomologist 113: 70-81. einen höheren Erfassungsgrad als Streifnetz- CHERRY R.H., WOOD K.A. & W.G. RUESINK (1977). Emer- fänge. Die effektivste Methode zur Erfassung gence trap and sweep net sampling for adults der epigäischen Arten sind jedoch Bodenfal- of the potato leafhopper from alfalfa. — Jour- len (Barberfallen). Um ein möglichst voll- nal of Economic Entomology 70: 279-82. ständiges Zikadenartenspektrum eines Lebens- CLARIDGE M.F. & WJ. REYNOLDS (1972) Host plant speci- raums zu erhalten, sollten daher Bodenfallen ficity, oviposition behaviour and egg parasitism in some woodland leafhoppers of the genus entweder mit Streifnetzfängen oder Saugpro- Oncopsis (Hemiptera Homoptera: Cicadellidae). ben kombiniert werden. Methoden zur Erfas- — Transactions of the Royal Entomological sung fliegender Insekten und zur Abschätzung Society of London 124: 149-166. von Ausbreitungs- und Wanderverhalten wer- CLEMENTS R.O. (1979) A collapsible emergence trap for grassland insects. — Entomologist's Monthly den ebenfalls kurz diskutiert. Magazine 115: 219-224.

509 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

DECKER G.C, KOUSKOLEKAS C.A. & R.J. OYSART (1971). GYÖRFFY G. & G. SZÖNYI (1989) Movements of phyto- Some observations on fecundity and sex ratios phagous insect populations between ungrazed of the potato leafhopper. — Journal of Econo- sandy grassland and adjacent areas. — Acta Bio- mic Entomology 68: 563-564. logica Szegediensis 35: 129-155.

DE BARRO P.J. (1991) A cheap lightweight efficient HAND S.C (1986) The capture efficiency of the Die- vacuum sampler. — Journal of the Australian trick vacuum insect net for aphids on grasses Entomological Society 30: 207-208. and cereals. — Annals of Applied Biology 108: DE LONG D.M. (1932) Some problems encountered in 233-241. the estimation of insect populations by the HEADY S.E., MADDEN L.V. & L.R. NAULT (1985) Ovipositi- sweeping method. — Annals of the Entomolo- on behaviour of Dalbulus leafhoppers (Homop- gical Society of America 25: 13-17. tera: Cicadellidae). — Annals of the Entomolo- DEN BOER P.J. (1986) Carabids as objects of study. — In: gical Society of America 78: 723-727. Carabid beetles; their adaptations and dynamics HEIKINHEIMO O. & M. RAATIKAINEN (1962) Comparison of (eds DEN BOER P.J., LUFF M.L., MOSSAKOWSKI D. S F. suction and netting methods in population WEBER) pp. 539-551. Stuttgart: Gustav Fischer investigations concerning the fauna of grass Verlag. leys and cereal fields, particularly in those con- DEN HOLLANDER J. (1989) Electrophoretic studies on cerning the leafhopper Calligypona pellucida planthoppers and leafhoppers of agricultural (F.) — Publ. Finn. State Agirc. Res. Board 191: 1- importance. — In: LOXDALE H.D. & J. DEN HOLLAN- 31. DER (eds), Electrophoretic studies on agricultural pests. Oxford: Clarendon Press. HENDERSON I.F. & T.M. WHITTAKER (1977) The efficiency of an insect suction sampler in grassland. — Eco- DENNO R.F. (1980) Ecotope differentiation in a guild logical Entomology 2: 57-60. of sap-feeding insects on the salt marsh grass, Spartina patens. — Ecology 61: 702-714. HILDEBRANDT J. S H. NICKEL [in press): Auchenorrhyn- cha communities as indicators of disturbance in DENNO R.F., RAUPP M.J., TALLAMY D.W. & C.F. REICHEN- DERFER (1980) Migration in heterogeneous envi- grasslands (Insecta, Hemiptera) - a case study ronments: differences in habitat selection bet- from the Elbe flood plains (Northern Germany). ween the wing-forms of the dimorphic plant- — Agriculture, Ecosystems and Environment. hopper, Prokelisia marginata (Homoptera: Del- HOLMES P.R., BOYCE D.C. & D.K. REED (1991) The Welsh phacidae). — Ecology 61: 859-867. Peatland Invertebrate Survey - Preliminary DENT D. (1991) Insect Pest Management. — Walling- Report: Methodology and study sites. — Chief ford: CAB. International. Scientist's Directorate Report No. 1125. Peter- DIETRICK E.J. (1961) An improved backpack motor fan borough: Nature Conservancy Council. for suction sampling of insect populations. — HOLTKAMP R.H. & J.I. Thompson (1985) A lightweight, Journal of Economic Entomology 53: 394-395. self-contained insect suction sampler. — Journal

DIETRICK E.J., SCHUNGER E.I. & R. VAN DEN BOSCH (1959) A of the Australian Entomological Society 24: 301- new method for sampling arthropods using a 302. suction collecting mechine and modified Berle- HURLBERT S.H. (1984) Pseudoreplication and the se funnel separator. — Journal of Economic Ent- design of ecological field experiments. — Ecolo- omology 52: 1085-1091. gical Monographs 54: 187-211.

DISNEY R.H.L., ERZINCUOGLU Y.Z., HENSHAW DJ. DE C, KISIMOTO R. (1968) Yellow pan water trap for sam- UNWIN D.M., WITHERS P. & A. WOODS (1982) Collec- pling the small brown planthopper, Laodelphax tings methods and the adequacy of attempted striatellus (FALLEN), a vector of the rice stripe faunal surveys, with reference to the Diptera. — virus. — Appl. Entomol. & Zool. 3: 37-48. Field Studies 5: 607-621. KISIMOTO R & L.J. ROSENBERG (1994) Long-distance DONDALE CD., REDNER J.H. & R.B. SEMPLE (1972) Diel migration in delphacid planthoppers. — In: DEN- activity periodicities in meadow arthropods. — Canadian Journal of Zoology 50: 1155-1163. NO R.F. & T.J. PERFECT (eds), Planthoppers: their ecology and management. New York: Chapman DUFFEY E. (1980) The efficiency of the DIETRICK vacuum & Hall. sampler (D-Vac) for invertebrate population stu- dies on different types of grassland. — Bulletin KONTKANEN P. (1950) Quantitative and seasonal stu- of Ecology 11:421-431. dies on the leafhopper fauna of the field stra- tum on open areas in North Karelia. — Annls DUTILLEUL P. (1993) Spatial heterogeneity and the Zool. Soc. Zool.-Bot. Fenn. „Vanamo" 13(8): 1- design of ecological field experiments. — Ecolo- 91. gy 74: 1646-1658.

EBERHARDT L.L. & J.M. THOMAS (1991) Designing envi- KUNO E. (1991) Sampling and analysis of insect popu- ronmental field studies. — Ecology 61: 53-73. lations. — Annual Review of Entomology 36: 285-304. GYÖRFFY G. & I. KARSAI (1991) Estimation of spatio- temporal rearrangement in a patchy habitat LARSEN K.J. & M.E. WHALON (1988) Dispersal of Para- and its application to some Auchenorrhyncha phlepsius irroratus (SAY) (Homoptera: Cicadelli- populations. — Journal of Animal Ecology 60: dae) in peach and cherry orchards. — Environ- 843-855. mental Entomology 17: 842-851.

510 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

LEGENDRE P. (1993) Spatial autocorrelation: trouble or OWEN J. (1991) The ecology of a garden: the first fif- new paradigm? — Ecology 74: 1659-1673. teen years. — Cambridge: Cambridge University Press. LEQUESNE W.J. & M.G. MORRIS (1971) Auchenorrhyn- cha from pitfall traps at Weeting Heath Natio- PAYNE K. (1981) A comparison of the catches of nal Nature Reserve. Norfolk. — Entomologist's Auchenorrhyncha (Homoptera) obtained from Monthly Magazine 107: 39-44. sweep netting and pitfall trapping. — Entomo- logist's Monthly Magazine 117: 215-223. LEWIS T. & L.R. TAYLOR (1965) Diurnal periodicity of flight by insects. — Transactions of the Royal PERFECT T.J., COOK A.G., PADGHAM D.E. & J.M. CRISOSTO- Entomological Society of London 116: 393-479. MO (1985) Interpretation of the flight activity of Nilaparvata lugens (STAL) and Sogatella furcifera LOTT D.A. & M.D. EYRE (1996) Invertebrate sampling (HORVÄTH) (Hemiptera: Delphacidae) based on methods. — In: EYRE M.D., Environmental moni- comparative trap catches and field marking toring, surveillance and conservation using with rubidium. — Bulletin of Entomological invertebrates. EMS Publications: Newcastle- Research 75: 93-106. upon-Tyne. PADGHAM D.E., COOK A.G. & D. HUTCHISON (1984) Rubi- MALAISE R. (1937) A new insect-trap. — Ent. Tidskr. dium marking of the rice pests Nilaparvata 58: 148-160. lugens (STAL) and Sogatella furcifera (HORVATH) MCLEOD A., WRATTEN S.D. & R.W.J. HARWOOD (1994) (Hemiptera: Delphacidae) for field dispersal stu- The efficiency of a new lightweight suction dies. — Bulletin of Entomological Research 74: sampler for sampling aphids and their predators 379-385. in arable land. — Annals of Applied Biology, PETER H.-U. (1981) Weitere Untersuchungen zur ein- 124: 11-17. nischung der Zikaden in den Halbtrockenrasen MCLEOD A., SOTHERTON N.W., HARWOOD R.W.J. & S.D. des Leutratais bei Jena. — Zool. Jb. Syst. 108: WRATTEN (1995) An improved suction sampling 563-588. device to collect aphids and their predators in POTVIN C. & J. TRAVIS (1993) Concluding remarks: a agroecosystems. — In: TOFT S. & W. RIEDEL (eds), drop in the ocean ... — Ecology 74: 1674-1676. Arthropod Natural Enemies in Arable Land. I. Density, spatial heterogeneity and dispersal. POWELL W., WALTON M.P. & M.A. JERVIS (1996) Popula- Aarhus University Press. tions and communities. — In: M.A. JERVIS & N.A.C. KIDD (eds.). Insect Natural Enemies: Prac- MOORE R., CLARKE R.T. & S. CREER (1993) An insect sor- tical Approaches to their Study and Evaluation. ting device to be used in conjunction with insect London: Chapman & Hall. suction samplers. — Bulletin of Entomological Research 83: 113-120. POWER A.G. (1992) Host plant dispersion, leafhopper movement and disease transmission. — Ecologi- MORRIS M.G. (1971) Differences between the inverte- cal Entomology 17: 63-68. brate faunas of grazed and ungrazed chalk grassland. IV. Abundance and diversity of PURCELL A.H. & J.S. ELKINGTON (1980) A comparison of Homoptera-Auchenorrhyncha. — Journal of sampling methods for leafhopper vectors of X- Applied Ecology 8: 37-52. disease in California cherry orchards. — Journal of Economic Entomology 73: 854-860. MORRIS M.G. (1981a) Responses of grassland inverte- brates to management by cutting. III. Adverse PURCELL A.H. & K.G. SUSLOW (1982) Dispersal beha- effects on Auchenorrhyncha. — Journal of viour of Colladonus montanus (Homoptera: Applied Ecology 18: 107-123. Cicadellidae) in cherry orchards. — Environ- mental Entomology 11: 1178-1182. MORRIS M.G. (1981b) Responses of grassland inverte- brates to management by cutting. IV. Positive RAATIKAINEN M. (1972) Dispersal of leafhoppers and responses of Auchenorrhyncha. — Journal of their enemies to oatfields. — Annales Agricul- Applied Ecology 18: 763-771. turae Fenniae 11: 146-153.

MORRIS M.G. (2000) The effects of structure and its RAATIKAINEN M. & A. VASARAINEN (1973) Early- and dynamics on the ecology and conservation of high-summer flight periods of leafhoppers. — arthropods in British grasslands. — Biological Annales Agriculturae Fenniae 12: 77-94. Conservation 95: 129-142. REES C.J.C. (1983) Microclimate and the flying Hemip- MORRIS M.G. & R. PLANT (1983) Responses of grassland tera fauna of a primary lowland rainforest in invertebrates to management by cutting. V. Sulwesi. — In: SUTTON S.L. & T.C. WHFTMORE, Tropi- Changes in Hemiptera following cessation of cal Rainforest: ecology and management, pp. management. — Journal of Applied Ecology 20: 121-136. 157-177. RILEY J.R., CHENG X.N., ZHANG X.X., REYNOLDS D.R., Xu MORRIS R.K. & M.S. PARSONS (1992) A survey of inver- G.M., SMITH A.D., CHENG J.Y., BAO A.D. & B.P. ZHAI tebrate communities on the shingle of Dungen- (1991) The long-distance migration of Nilapar- ess. Rye Harbour and Orford Ness. — JNCC vata lugnes (STAL) (Delphacidae) in China: radar Report 77. Peterborough: Joint Nature Conser- observations of mass return flight in the vation Committee. autumn. — Ecological Entomology 16: 471-489.

NOVOTNY V. (1992) Vertical distribution of leafhop- ROMNEY V.E. (1945) The effect of physical factors pers (Hemiptera, Auchenorrhyncha) within a upon catch of the beet leafhopper {Eutettix meadow community. — Acta Entomol. Bohe- tenellus (BAK.)) by a cylinder and two sweep net moslov. 89: 13-20. methods. — Ecology 26: 135-147.

511 © Biologiezentrum Linz/Austria; download unter www.biologiezentrum.at

SAMU F. & M. SAROSPATAKI (1995) Design and use of a SOUTHWOOD T.R.E. (1978) Ecological Methods. 2nd hand-hold suction sampler, and its comparison edn. — London: Chapman & Hall. with sweep net and pitfall trap sampling. — SUTTON S.L. (1983) The spatial distribution of flying Folia Entomologica Hungarica Rovartani Köz- insects in tropical rainforest. — In: SUTTON S.L. & lemenyek 56: 195-203. T.CWHJTMORE. Tropical Rainforest: ecology and SAMU F., NEMETH J. & B. Kiss (1997) Assessment of the management, pp. 77-91. efficiency of a hand-held suction device for sam- TAYLOR J., PADGHAM D.E. & T.J. PERFECT (1982) A light- pling spiders: improved density estimation or trap with upwardly directed illumination and oversampling? — Annals of Applied Biology temporal segregation of the catch. — Bulletin 130: 371-378. of Entomological Research 72: 669-673. SANDERSON R.A., RUSHTON S.P., CHERRILL A.J. & J.P. BYRNE TAYLOR R.A.J. S D. REUNG (1986) Preferred wind direc- (1995) Soil, vegetation and space: an analysis of tion of long-distance leafhopper (Empoasca their effects on the invertebrate communities of fabae) migrants and its relevance to the return a moorland in north-east England. — Journal of migration of small insects. — Journal of Animal Applied Ecology 32: 506-518. Ecology 55: 1103-1114.

SCHAEFER M. (1973) Untersuchungen über Habitatbin- THOMPSON P. (1978) The oviposition sites of five leaf- dung und ökologische Isolation der Zikaden hopper species (Horn. Auchenorrhyncha) on einer Küstenlandschaft (Homoptera: Auchenor- Holcus mollis and H. lanatus. — Ecological Ento- hyncha). — Arch. Naturschutz u. Landschafts- mology 3: 231-240. forsch 13: 329-352. THORNHILL E.W. (1978) A motorised insect sampler. — SCHULZ CA. & J. MEIJER (1978) Migration of leafhop- Pest Articles and News Summaries 24: 205-207. pers (Homoptera: Auchenorrhyncha) into a new TOPPING C.J. 8 K.D. SUNDERLAND (1992) Limitations to polder. — Holarctic Ecology 1: 73-78. the use of pitfall traps in ecological studies SIMMONS A.M., PASS B.C. & K.V. YEARGAN (1984) Influ- exemplified by a study of spiders in a field of ence of selected legumes on egg production, winter wheat. — Journal of Applied Ecology 29: adult survival, and ovipositional preference by 485-491. the potato leafhopper. — Journal of Agricultu- TÖRMÄLÄ T. (1982) Evaluation of five methods of sam- ral Entomology 1: 311-317. pling field layer arthropods, particularly the SIMMONS A.M., GODFREY L.D. & K.V. YEARGAN (1985) leafhopper community, in grassland. — Annales Ovipositional sites of the potato leafhopper Entomologici Fenniae 48: 1-16. (Homoptera: Cicadellidae) on vegetative stage USHER M.B. (1990) Assessment of conservation soybean plants. — Environmental Entomology values: the use of water traps to assess the 14: 165-169. arthropod communities of heather moorland. SIMONET D.E. & R.L. PIENKOWSKI (1977) Sampling and — Biological Conservation 53: 191-198. distribution of potato leafhopper eggs in alfal- WALOFF N. (1980) Studies on grassland leaf hoppers fa stems. — Annals of the Entomological Society (Auchenorrhyncha, Homoptera) and their natu- of America 70: 933-966. ral enemies. — Advances in Ecological Research SIMONET D.E., PIENKOWSKI R.L, MARTINEZ D.G. & R.D. 11:81-215. BLAKESLEE (1978) Laboratory and field evaluation WALOFF N. & M.G. SOLOMON (1973) Leaf hoppers of sampling techniques for the nymphal stages (Auchenorrhyncha: Homoptera) of acidic grass- of the potato leafhopper on alfalfa. — Journal land.— Journal of Applied Ecology 10: 189-212. of Economic Entomology 71: 840-842. WALOFF N. & P. THOMPSON (1980) Census data and ana- SIMONET D.E., PIENKOWSKI R.L., MARTINEZ D.G. & R.D. lyses of populations of some leafhoppers BLAKESLEE (1979) Evaluation of sampling techni- (Auchenorrhyncha, Homoptera) of acidic grass- ques and development of a sampling program land. — Journal of Animal Ecology 49: 395-416. for potato leafhopper adults on alfalfa. — Envi- ronmental Entomology 8: 397-399. WHITNEY S.P. & J.R. MEYER (1988) Movement between wild and cultivated blueberry by two species of nd SOUTHWOOD T.R.E. (1978) Ecological Methods. 2 edi- sharpnosed leafhoppers (Homoptera: Cicadelli- tion. — London: Chapman & Hall. dae) in North Carolina. — Journal of Entomolo- STANDEN V. (2000) The adequacy of collecting techni- gical Science 23: 88-95. ques for estimating species richness of grassland WHITTAKER J.B. (1965) The biology of Neophilaenus invertebrates. — Journal of Applied Ecology 37: lineatus (L.) and W. exclamationis (THUNBERG) 884-893. (Homoptera: Cercopidae) on Pennine moor- STEWART A.J.A. & A.F. WRIGHT (1995) A new inexpensi- land. — Proceedings of the Royal Entomological ve suction apparatus for sampling arthropods in Society of London, Series A 40: 51-60. Address of the author: grassland. — Ecological Entomology 20: 98-102. WILLIAMS C.B. (1948) The Rothamsted light trap. — STILING P.D. (1980) Host plant specificity, oviposition Proceedings of the Royal Entomological Society of London 23: 80-85. behaviour and egg parasitism in some leafhop- Dr. Alan J.A. STEWART pers of the genus Eupteryx (Hemiptera: Cicadel- WILSON S.W., SMITH J.L & A.H. PURCELL (1993) An inex- School of Biological Sciences, lidae). — Ecological Entomology 5: 79-85. pensive vacuum collector for insect sampling. — Entomological News 104: 203-208. University of Sussex, Falmer, SUMMERS C.G., GARRETT R.E. & F.G. ZALOM (1984) New Brighton, Sussex, BN1 9QG, UK. suction device for sampling arthropod popula- WOLDA H. (1980) Seasonally of tropical insects. I. tions. — Journal of Economic Entomology 77: Leafhoppers (Homoptera) in Las Cumbres, Pana- e-mail: [email protected] 817-823. ma. — Journal of Animal Ecology 49: 277-290.

512