Carabid populations in field beans and their effect on the population dynamics of Sitona lineatus (L.)

The abundance and diversity of potential carabid predators of Sitona lineatus (L.) in field beans were monitored between 1980 and 1983. The absolute abundance of the large predatory species was determined in mark-recapture experiments and a radio-labelling technique was used to estimate the level of predation in the field. Using previously published population data for S. lineatus, the importance of predation in the population dynamics of the weevil was estimated. The mortality of weevil larvae due to predation varied from 0.6%– 10.5% while that of adult weevils varied from 2.6%– 23.8%. It appeared that carabids played a significant role in the population dynamics of S. lineatus and, in years when abundant, could reduce the population of larvae and overwintering adults by more than 30%.     

Investigations of the host feeding preferences ofSitona weevils found commonly on white clover (Trifolium repens) in the UK

A series of laboratory and field studies were done to evaluate a range of leguminous plant species for their feeding potential by adult weevils of the genusSitona Germar. (Coleoptera: Curculionidae). Three species ofSitona, S. lineatus L.,S. flavescens Marsh. andS. hispidulus F. all of which are found commonly on white clover (Trifolium repens L.) in the UK were offered a range of 11 legume species,T. repens (white clover, cv. Olwen),T. pratense L. (red clover, cv. Marcom),T. fragiferum L. (strawberry clover, cv. Palestine),T. hybridum L. (hybrid clover, cv. Tetra),T. incarnatum L (crimson clover),T. dubium Sibth. (lesser yellow trefoil),Lotus corniculatus L. (birdsfoot-trefoil, cv. Leo),L. uliginosus Schkuhr. (large birdsfoot-trefoil),Melilotus alba Desr. (white melilot),Medicago sativa L. (lucerne, cv. Europe) andM. lupulina L. (black medick) in two laboratory experiments. The weevils were offered a choice of these legumes in one experiment whilst in the other they did not have a choice of food material. These legumes were also sown in the field and a number of measurements of damage, together with counts ofSitona spp., were made. In the laboratoryS. lineatus andS. hispidulus favoured some of the legumes to a greater or lesser extent than white clover.S. flavescens was more restricted in its feeding than the other two weevil species. In the field studyS. lineatus invaded the experimental area quickly and tended to favourMedicago spp. andMelilotus spp. Later in the yearS. flavescens dominated the sitona fauna on the experiment, with the exception of aggregations ofS. lineatus onM. sativa andM. alba. In a separate screen of 5 varieties of white clover (cvs Donna, Menna, Kersey, Olwen and Grasslands Huia), cv. Olwen appeared to be the most susceptible to sitona attack.     

Sitona weevils (Coleoptera: Curculionidae) as agents for rapid transfer of nitrogen from white clover (Trifolium repens L.) to perennial ryegrass (Lolium perenne L.)

The effects of root feeding by larvae of Sitona hispidulus (F.) (a common weevil pest of white clover) on the rate of transfer of nitrogen between plants of white clover (Trifolium repens L.) and perennial ryegrass (Lolium perenne L.) were investigated using a nutrient slant board technique. Clover plants, labelled with ¹⁵N were grown adjacent to ryegrass plants and were either infested with Sitona larvae or not infested. Ryegrass plants associated with the infested clover plants had a significantly higher dry matter yield and nitrogen content (75% and 74% respectively) than the uninvested plants, after 33 days exposure to insect herbivory. It was concluded that root feeding insects could play an important role in the cycling of nitrogen in grass/clover swards.     

Chemical stimulation of the virulence of entomopathogenic fungi

The effect of magnesium and manganese ions on the virulence of Beauveria bassiana, Metarhizium anisopliae, Paecilomyces farinosus, and Paecilomyces fumosoroseus entomopathogenic fungi was tested. The virulence of entomopathogenic fungi to Sitona lineatus (L) weevil, pupae and larvae, was increased by tested metal ions. Mg ions increased the virulence of B. bassiana against S. linatus (L) weevils 100%. The fungi exhibited various sensitivity to these metal ions.     

Overwintering conditions affect cold hardiness,survival, and post-overwintering fitness of the pea leaf weevil

Overwintering conditions affect the physiological state of ectotherms, and therefore, their cold hardiness and survival. A measure of the lethal and sublethal impacts of overwintering conditions on pest populations is crucial to predict population dynamics and to manage pests the following spring. The impact of winter conditions can be most intense for invasive insects undergoing range expansion. Insect herbivores can display plastic host use behaviours that depend on their body condition following winter. The pea leaf weevil, Sitona lineatus L. (Coleoptera: Curculionidae), is an invasive pest of field peas, Pisum sativum L., and faba bean, Vicia faba L. (Fabaceae). Pea leaf weevil has expanded its range in North America to include the Prairie Provinces of Canada. This study investigated the effects of temperature and microhabitat on overwintering survival and cold hardiness of pea leaf weevil in its expanded range. Further, we investigated the sublethal effect of overwintering temperature and duration on post-overwintering survival, feeding, and oviposition of pea leaf weevil. We also investigated the role of juvenile hormone in modulating body condition of overwintering weevils. The overwintering survival of pea leaf weevil adults increased with soil temperature and varied with region and microhabitat. More weevils survived winters when positioned near tree shelterbelts compared to open alfalfa fields. The supercooling point of pea leaf weevil varied throughout its expanding range but did not differ for weevils held in the two microhabitats. The average threshold lethal temperature of pea leaf weevil at all three sites was −9.4 °C. Weevils that overwintered for a longer duration and at a higher temperature subsequently fed more on faba bean foliage and laid more eggs compared to those which overwintered for a shorter duration at a lower temperature. Our findings highlight that warm winters would increase overwintering survival and post-overwintering fitness, facilitating further pea leaf weevil invasion northward in the Prairie Provinces of Canada.     

Transmission of broad bean stain virus and Echtes Ackerbohnenmosaik-Virus to field beans (Viciajaba) by weevils

Sitona lineatus and Apion vorax were the two most common species of weevil on field beans (Vicia faba minor) at Rothamsted between 1970 and 1974. In glasshouse tests, A. vorax was a much more efficient vector than 5. lineatus of broad bean stain virus (BBSV) and Echtes Ackerbohnenmosaik-Virus (EAMV), and both species transmitted EAMV more often than BBSV. Five other species of Apion transmitted the viruses infrequently or not at all. S. lineatus adults transmitted no more often after 8–16 days on infected plants than after 1–2 days. Some A. vorax adults transmitted EAMV, but not BBSV, after feeding on infected leaves for a few minutes. After 4 days on infected plants, A. vorax sometimes remained infective for the following 8 days. No A. vorax collected from woodland plants in spring was infective with BBSV or EAMV, but 4% from bean crops containing seed-borne infection carried BBSV and 17% carried EAMV. BBSV and EAMV were recovered from triturated weevils, but not from weevil haemolymph. Possibly the viruses are transmitted as contaminants of the mouthparts or by regurgitation during feeding, but A. vorax was observed to regurgitate only when anaesthetized. BBSV and EAMV were not transmitted by aphids (Aphis fabae and Acyrthosiphon pisum), nor by pollen beetles {Meligethes spp.). Field observations suggest that infected seed is the main source of BBSV and EAMV in spring-sown crops, and that crops grown from virus-free seed, and isolated from infected crops by 250–500 m, remain free of infection for most of the season.     

Identification of potential natural enemies of the pea leaf weevil,Sitona lineatus L. in western Canada

Sitona lineatus L., the pea leaf weevil, is an invasive pest of Pisum sativum L. (field pea) that has recently become established in Alberta, Canada. Adults consume seedling foliage and larvae feed on Rhizobium root nodules thereby reducing nitrogen fixation; both life stages can reduce yield. Eggs and adults are vulnerable to predators and parasitoids. In 2009, a series of experiments was undertaken to identify potential indigenous natural enemies of S. lineatus in southern Alberta. In three test arenas, eggs were exposed to starved ground beetles in no‐choice tests for 48 h. Egg debris was observed when eggs were exposed to Bembidion quadrimaculatum L., Microlestes linearis (LeConte), Bembidion rupicola (Kirby), Bembidion timidum (LeConte), Poecilus scitulus LeConte, and staphylinid beetles. Of the two most abundant carabid species, the smaller B. quadrimaculatum consistently removed significantly more eggs (94.6%) than the larger Pterostichus melanarius (17.4%). Similar results were observed in Petri dish and egg card tests. No egg debris was observed in tests with Pt. melanarius. Presence of the larger beetle, Pt. melanarius, resulted in a lower rate of egg removal by the smaller B. quadrimaculatum relative to the rates observed for B. quadrimaculatum alone. Intraguild predation of B. quadrimaculatum by Pt. melanarius was observed in 47% of tests. These results suggest that B. quadrimaculatum is a potential predator of S. lineatus eggs in field pea agroecosystems and should be considered for use in conservation biological control and integrated pest management programs.     

Spring dispersal ofSitona lineatus: The use of aggregation pheromone traps for monitoring

The spring dispersal ofSitona lineatus L. (Coleoptera; Curculionidae) was investigated on a Danish farm.S. lineatus dispersed by flight in the early spring on sunny, calm days with temperatures above ca. 15°C. Two thirds of the population ofS. lineatus dispersed from perennial leguminous crops (clover and lucerne) in the first period of flight activity. The next dispersal did not occur until one month later despite several intermediate flight activity periods. The first period of dispersal occurred before the germination of the spring sown summer host crop,Vicia faba L. The field bean crop was infested in three later invasions during a period of more than three weeks. The aggregation pheromone, 4-methyl-3,5-heptanedione, had a significant effect on captures of both males and females in cone traps placed on the ground. There was no effect of the pheromone on captures in yellow sticky traps placed 1.5 m above ground. The pheromone effect is discussed in relation to behavioural observations. Both types of traps may be used in a survey system for monitoring spring dispersal ofS. lineatus and optimal timing of insecticide spraying. However, the pheromone cone traps were highly specific whereas all kinds of flying insects were caught in the yellow sticky traps, thus making the latter traps less suitable for monitoring.     

Causes of different feeding rates of pea leaf weevil Sitona lineatus on three pea cultivars

The causes of different feeding rate in female pea leaf weevil (Sitona lineatus L.) were investigated with three cultivars, namely Gorkovskij, Lancet and Neuga. A negative correlation between leaf thickness and feeding rate was demonstrated, but by using artificial diet saturated with leaf sap, some effects were shown to be of a chemical nature.The effect of some compounds, the concentrations of which differed in the experimental cultivars, was verified by feeding tests. A strong inhibition of feeding was induced by the amino acid tyrosine. Among tested sugars saccharose was the most effective for stimulation of feeding.

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zusammenfassung In Freilandversuchen wurden drei Erbsensorten mit unterschiedlicher Frassintensität durch Sitona lineatus ausgewählt, die stark befallene Gorkovskij, die intermediäre Lancet und die wenig befallene Neuga. Die Ursachen der Befallsunterschiede wurden dann im Laboratorium mit weiblichen Käfern untersucht. Blattscheibentests mit frischen Blättern der drei Sorten bestätigten die Feldversuche. Versuche mit künstlichen Substraten, welche mit Blattsaft gesättigt waren, deuteten auf einen Einfluss physikalischer Faktoren, also des anatomischen Baus der Blätter, hin. Zwischen Frassstärke und Blattdicke ergab sich eine negative Korrelation.Bei den Tests mit künstlichen Substraten wurde der Einfluss der biochemischen Zusammensetzung des Blattsafts nachgewiesen. Aufgrund der Pflanzensaftanalyse wurden dann einige Stoffe in ihrer Wirkung auf den Käferfrass geprüft. Die stärkste Frasshemmung bewirkte bei den Aminosäuren Tyrosin, die stärkste Stimulation bei den Zuckern Saccharose.

     

Presence and possible assimilation of Rhizobium leguminosarum in the gut of pea leaf weevil, Sitona lineatus, larvae

The presence and possible assimilation of Rhizobium leguminosarum in the gut of the pea leaf weevil (Sitona lineatus (L.)) larvae was investigated with a fluorescent antibody technique and electron microscopy. The fluorescent antibody technique proved that many R. leguminosarum bacteroids were present in the gut of 14-day old larvae which had been feeding within pea (Pisum sativum L.) root nodules. Examination of larval midgut thin sections with transmission electron microscopy also revealed many R. leguminosarum bacteroids as a constituent of the gut contents. Intact bacteroids were more prevalent in the anterior and middle portions of the midgut while bacteroids with disrupted cell walls were observed more often in the posterior portions of the midgut. Of the hindgut sections examined, none showed the presence of intact bacteroids. These results provide strong evidence that R. leguminosarum bacteroids are digested, absorbed and possibly assimilated by pea leaf weevil larvae.

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Résumé Des anticorps fluorescents et la microscopie électronique ont été utilisès pour déceler la présence et une possible assimilation de Rhizobium leguminosarum dans le tube digestif des larves de Sitona lineatus L. La technique des anticorps fluorescents prouve que de nombreux bactéroïdes de R. leguminosarum sont dans le t.d. de larves agées de 14 jours qui se sont alimentées sur des nodules racinaires de Pisum sativum L. L'examen de coupes fines de l'intestin moyen en microscopie électronique a révélé de nombreux bactéroïdes R. leguminosarum comme constituants du contenu du t.d. Des bactéroïdes intacts sont plus fréquents dans les portions antérieures et moyennes du t.d. moyen, tandis que des bactéroïdes avec des parois cellulaires brisées sont observés plus souvent dans les parties postérieures du t.d. moyen. Aucune section du t.d. postérieur examinée ne contenait de bactéroïde intact. Ces résultats fournissent des arguments solides sur la digestion, l'absorption, et peut être l'assimilation, des bactéroïdes R. leguminosarum par les larves de S. lineatus L.

     

Interaction between Sitona lepidus and red clover lines selected for formononetin content

Adult clover root weevil Sitona lepidus show a feeding preference for white clover Trifolium repens over red clover Trifolium pratense. The effects on S. lepidus of three red clover T. pratense lines, selected for high, medium, or low levels of the isoflavone formononetin in foliage, were compared in three experiments using white clover as a control. In a no‐choice slant board experiment, weevil larval weights were greater for larvae feeding on white clover roots than those feeding on roots of the red clovers. The effect of larval root herbivory on plant growth was similar for all four clovers. Following root herbivory, a large increase in root and shoot formononetin levels was observed in the high‐formononetin selection of red clover but little change in the low‐formononetin red clover. In a no‐choice experiment with sexually mature female adult weevils feeding on foliage of the four clovers, all the red clovers had increased weevil mortality. Female weevils eating the high‐formononetin red clover laid fewer eggs than weevils eating white clover. The red clover diet caused a large accumulation of abdominal fat and/or oil in the weevils, whereas weevils feeding on white clover did not accumulate fat/oil. When sexually immature adult weevils were given a choice of foliage from all four clovers, white clover was eaten preferentially, and the low‐formononetin red clover was preferred to the high‐formononetin red clover. The results suggest that formononetin and associated metabolites in red clover may act as chemical defences against adult S. lepidus and that distribution in forage legumes can be manipulated by plant breeding to improve root health.     

Pea leaf weevil herbivory on pea seedlings: effects on growth response and yield

Field experiments were conducted to determine growth and yield responses ofPisum sativum L. to defoliation by adultSitona lineatus (L.). Seedlings grown under conventional (moldboard plowed) and conservation (chisel plowed) tillage treatments were infested for a 1-week period with 0, 1 and 8 weevils per plant at two times: at 75% field emergence and 1 week later. After the early infestation, defoliation for the control, low and high weevil densities was about 0,15 and 50%, respectively, while defoliation after the late infestation was about 0, 10 and 35%. An undercompensatory growth response was observed in one experiment after seedlings were subjected to moderate levels of early defoliation. Exact compensation was observed in two experiments after early infestations of low and highSitona densities.Sitona defoliation reduced the number of pods per plant and pod length in two experiments. However, seed biomass was never significantly reduced. Averaged over all experiments, reduction in seed biomass due to highSitona densities was 10 and 5% for early and late infestations, respectively. Tillage treatments did not affectPisum compensatory growth response, although yield components were sometimes greater in conservation tillage than in conventional tillage, possibly due to slightly greater soil moisture in the conservation tillage plots.     

Tracking larval insect movement within soil using high resolution X-ray microtomography

Abstract.  1. In contrast to above-ground insects, comparatively little is known about the behaviour of subterranean insects, due largely to the difficulty of studying them in situ .
2. The movement of newly hatched (neonate) clover root weevil ( Sitona lepidus L. Coleoptera: Curculinidae) larvae was studied non-invasively using recently developed high resolution X-ray microtomography.
3. The movement and final position of S. lepidus larvae in the soil was reliably established using X-ray microtomography, when compared with larval positions that were determined by destructively sectioning the soil column.
4. Newly hatched S. lepidus larvae were seen to attack the root rhizobial nodules of their host plant, white clover ( Trifolium repens L.). Sitona lepidus larvae travelled between 9 and 27 mm in 9 h at a mean speed of 1.8 mm h⁻¹.
5. Sitona lepidus larvae did not move through the soil in a linear manner, but changed trajectory in both the lateral and vertical planes.     

Feeding preferences of the weevils Sitona gressorius and Sitona griseus on different lupin genotypes and the role of alkaloids

The weevils Sitona gressorius and Sitona griseus are specialist herbivores on lupins in Europe. The adult weevils feed on the leaves, and the larvae on the root nodules of the plants. This causes severe damage to lupin crops. In the present study, the feeding preferences of lupin weevil adults on different lupin genotypes were examined with respect to a possible effect of lupin alkaloids on host selection. A total of 12 genotypes from the species Lupinus albus, L. angustifolius, L. luteus, and L. nanus were grown in a field experiment and the feeding damage on the leaves caused by naturally occurring lupin weevil adults was estimated. Additionally, a feeding choice test with S. gressorius adults was performed to examine feeding preferences under laboratory conditions. A gas chromatographic analysis provided information on the alkaloid content and profiles in the leaves of the tested lupin genotypes. In the field experiment, significant differences in the extent of the feeding damage within the 12 lupin genotypes were observed. The dual-choice feeding bioassay did not show discrimination of lupin species, but two L. angustifolius genotypes were significantly less affected than the standard L. luteus “Bornal”. The alkaloid analysis revealed large contrasts in alkaloid concentrations and profiles in the leaves of the tested genotypes. Correlation analysis with the results from the field and laboratory did not indicate a significant influence of the total foliar alkaloid content on the extent of weevil feeding.     

Genome mapping of white clover (<Emphasis Type="Italic">Trifolium repens</Emphasis> L.) and comparative analysis within the Trifolieae using cross-species SSR markers

Allotetraploid white clover (Trifolium repens L.), a cool-season perennial legume used extensively as forage for livestock, is an important target for marker-assisted breeding. A genetic linkage map of white clover was constructed using simple sequence repeat (SSR) markers based on sequences from several Trifolieae species, including white clover, red clover (T. pratense L.), Medicago truncatula (Gaertn.) and soybean (Glycine max L.). An F₁ population consisting of 179 individuals, from a cross between two highly heterozygous genotypes, GA43 and Southern Regional Virus Resistant, was used for genetic mapping. A total of 1,571 SSR markers were screened for amplification and polymorphism using DNA from two parents and 14 F₁s of the mapping population. The map consists of 415 loci amplified from 343 SSR primer pairs, including 83 from white clover, 181 from red clover, 77 from M. truncatula, and two from soybean. Linkage groups for all eight homoeologous chromosome pairs of allotetraploid white clover were detected. Map length was estimated at 1,877 cM with 87% genome coverage. Map density was approximately 5 cM per locus. Segregation distortion was detected in six segments of the genome (homoeologous groups A1, A2, B1, B2, C1, and D1). A comparison of map locations of markers originating from white clover, red clover, and alfalfa (M. sativa L.) revealed putative macro-colinearity between the three Trifolieae species. This map can be used to link quantitative trait loci with SSR markers, and accelerate the improvement of white clover by marker-assisted selection and breeding. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Insect invasions of agroecosystems in the western Canadian prairies: case histories,patterns, and implications for ecosystem function

Agroecosystems in the western Canadian provinces of Alberta, Saskatchewan, and Manitoba have been invaded by several alien herbivorous insects from several orders and families. These species have caused very substantial reductions in yield and quality of the dominant crops grown in this region, including cereals (primarily wheat, Triticum aestivum L., barley, Hordeum vulgare L., and oats Avena sativa L.), oilseeds (primarily canola, Brassica napus L. and Brassica rapa L., and mustard, Sinapis alba L. and Brassica juncea (L.) Czern.), and pulses (primarily field pea, Pisum sativum L., lentil, Lens culinaris Medik., and chickpea, Cicer arietinum L.). In this study, we used literature searches to identify the major species of insect pests of field crops in western Canada and determine those species indigenous to the region versus species that have invaded from other continents. We summarize invasion patterns of the alien species, and some estimated economic costs of the invasions. We document the invasion and dispersal patterns of the cereal leaf beetle, Oulema melanopus L. (Coleoptera: Chrysomelidae), for the first time in all three provinces. We also report the co-occurrence of its exotic parasitoid, Tetrastichus julis (Walker) (Hymenoptera: Eulophidae), and implications for classical biological control. We present results of field studies describing the dispersal patterns of a second recent invader, the pea leaf weevil, Sitona lineatus L. (Coleoptera: Curculionidae). The implications of invasions in this region are discussed in terms of economic and ecological effects, and challenges posed for pest mitigation.     

Effects of undersown clover on host-plant selection by Thrips tabaci adults in leek

The suppressive effects of undersown clover on Thrips tabaci Lindeman infestation in leek is known but not the stages in thrips population dynamics that are affected by intercropping and the mechanisms involved. Colonization or settling of adult onion thrips (T. tabaci) in monocropped leek (Allium porrum L.) and in leek intercropped with strawberry clover (Trifolium fragiferum L.) was studied in two potted plant experiments. Potted leek plants with and without undersown clover were placed for a short period (2 and 5 days) in monocropped or intercropped field plots when high thrips infestation was expected. Thrips adults were counted on all leaves and in the shaft during this observation period. Thrips populations were monitored weekly in the field plots throughout the entire growing season.In both potted plant experiments, there were consistently fewer thrips adults on intercropped leek plants than on monocropped plants. The plant growth parameters – number of leaves and stem diameter – were similar in all treatments and thus did not explain differences in thrips adults. Natural enemies were absent on both leek and clover, and thus cannot explain the differences in adult thrips numbers. Furthermore, no adults of T. tabaci were found on the clover in the potted plant experiment and only very few in the field experiment. Thus it was concluded that strawberry clover was not an effective trap crop for thrips.In the second potted plant experiment, clover was removed just before the leek plants were introduced to the field, thus eliminating direct physical, visual and olfactory interference by clover. After the undersown clover was removed, the leek plants harboured only one-third of the number of thrips adults, as compared to the monocropped plants. This study supports the notion that there are subtle links between intercropping and plant quality, and indicates that host-plant quality is an underlying cause of the reduction in adult thrips numbers in leek/clover intercropping.     

Field persistence of the entomopathogenic nematode <Emphasis Type="Italic">Heterorhabditis bacteriophora</Emphasis> in different crops

To investigate nematode establishment and persistence, dauer juveniles (DJs) of Heterorhabditis bacteriophora were applied at 50 cm^-2 in different crops in June and July with conventional spraying equipment and 420 l water ha^-1. Application hardly had any effects on survival and infectivity. The number of DJs reaching the soil was assessed and the establishment and persistence recorded by baiting soil samples with larvae of the wax moth Galleria mellonella. The better the plant canopy was developed the fewer DJs reached the soil during application. Whereas in pasture 77% and in potatoes 78% of the applied nematodes reached the soil, in wheat and peas little less than 50%, in oil-seed rape only 5% and in lupine 6% were recorded. Between 50 and 60% of the soil samples contained H. bacteriophora a month after application with the exception of wheat (>90%) and potatoes (<5%) indicating that the number of nematodes reaching the soil during application had no influence on their establishment in the soil. Probably DJs can survive in the plant canopy and reach the soil later after application. The percentage of nematode-positive soil samples dropped considerably after tillage. In potatoes no nematodes were recovered after two months, which probably was also due to the intensive movement of the soil. Although nematodes are susceptible to freezing, temperatures below 0°C during the winter did not extinguish the H. bacteriophora population. In field crops EPN usually persisted not much longer than one year. The longest persistence of H. bacteriophora was detected 23 months after release in beans followed in rotation by wheat with red clover as cover crop. In this field larvae of the pea weevil Sitona lineatus (Coleoptera: Curculionidae) were detected in soil samples and found infected with the released nematode population. In the laboratory the field soils were tested for persistence of H. bacteriophora at 8°C and a half-life of 24.8 days was recorded in the absence of host insects and plants. Thus long-term persistence in the field was a result of recycling in host insects, which could not be detected in other crops than beans and clover. As H. bacteriophora seems to be restricted in its host potential, this species disappears after release once the host population is not available anymore.     

Sampling to determine density of arthropods in intensively grazed grasslands

Arthropod population field studies undertaken to understand the impacts and population dynamics of the target organism rely on sampling methods that provide accurate measurements of population density. Unsuitable methods may underestimate or provide widely variable measures of population density. The suitability of three vacuum sampling methods: a domestic vacuum cleaner, Vortis™, and blower-vac (G-vac), plus heat extraction of turves were compared for sampling common species in an intensively grazed irrigated dairy pasture. Each method used a different approach to sampling with the number of samples per method based on protocols that had been used in grasslands. Overall, for adults of the weevil Listronotus bonariensis, no method provided a consistently high mean density, while for adults of the weevil Sitona obsoletus, the vacuum cleaner and turf heat extraction methods gave generally higher mean densities. For predatory beetles and lacewings, heat extraction was the most effective for density measurements, while for ladybirds and spiders, the Vortis™ provided the best estimate of mean density. Increasing pasture dry matter (kg Dm/ha) generally had a significant negative effect on S. obsoletus density but not for L. bonariensis. While no method was consistently superior than another, the vacuum cleaner and heat extraction methods generally provided higher mean densities. The G-vac generally produced the lowest density estimates, but the sampling protocol meant a larger collection area per unit effort and therefore the probability of detection was higher compared with the three other methods. In conclusion, the study showed that the optimal sampling method depends on the taxa targeted, and more than one method may be required to measure density and diversity of species in both natural and modified grasslands.     

Influence of flowering cover crops on Anagrus parasitoids (Hymenoptera: Mymaridae) and Erythroneura leafhoppers (Homoptera: Cicadellidae) in New York vineyards

Abstract 1 We tested the hypothesis that providing nectar‐producing cover crops will enhance the biological control of grape leafhoppers (Erythroneura spp.) by Anagrus wasps in commercial vineyards in New York, U.S.A. 2 We established three cover crops between vine rows in a commercial vineyard: buckwheat (Fagopyrum esculentum (Moench)), clover (Trifolium repens L.) and mowed sod (Dactylis glomerata L.). 3 There was no effect of cover crop on adult Anagrus in 1996, whereas in 1997 adults were more abundant within edge vines with buckwheat compared to vines with clover or sod; adults were more abundant at the vineyard edge, especially early in the season. 4 Parasitism of ‘sentinel’ leafhopper eggs was higher on vines with buckwheat compared to parasitism on vines with clover or sod in 1996; a similar, non‐significant trend, was observed in 1997. 5 Neither the abundance nor the distribution of leafhoppers was influenced by cover crops, although in 1997 there was a trend toward greater numbers of nymphs on edge vines with buckwheat. 6 In a cage experiment, parasitism by Anagrus of leafhopper eggs on grapes was greater when adults had access to flowering buckwheat rather than buckwheat without flowers. 7 In a laboratory study, longevity of female Anagrus was increased when provided with honey or sugar water compared to water only or nothing. 8 Our results suggest that parasitism of grape leafhoppers by Anagrus may be enhanced by providing floral resources within vineyards in New York, although it is unclear whether this will produce meaningful reductions in pest abundance.