Natural Enemy Communities Research Articles

Density-dependent responses of soybean aphid (Aphis glycines Matsumura) populations to generalist predators in mid to late season soybean fields

Abstract Since the arrival of the soybean aphid, Aphis glycines, to the U.S. in 2000, year to year abundances have varied substantially. Although, field studies have suggested that several resident generalist predators have the ability to suppress A. glycines populations, factors responsible for its population dynamics remain unclear. For natural enemies to regulate herbivore populations, predation rates must increase as prey population densities increase (i.e., density dependence). Experiments were conducted in 2004–2006 to assess the ability of the existing natural enemy community to exert density-dependent effects on A. glycines populations. Aphid densities were manipulated on individual plants (transplanted to the field) or in small plots to contain a range of aphid densities from low (10 per plant) to high (>1000 per plant). Populations were then monitored weekly. Caged controls were included to measure population growth in the absence of predators. In 2006, an additional treatment was included to quantify the proportion of aphids emigrating from plants. In all experiments, a strong density-dependent decline in population abundance was observed as aphid populations on plants with low initial densities ( 100 aphids per plant) decreased by as much as two orders of magnitude over a 1–2 week period. We estimate that fewer than 5% of aphids emigrated from plants when aphid densities were below 4000 per plant. This suggests that the extreme declines in aphid populations over these brief experiments were not due to aphids leaving plants, but rather, due to an aggregative response of predators to high density prey populations. Given the rapidity and degree of density-dependent population decline in three consecutive years of study, we suggest the resident community of natural enemies in Midwestern soybean may have great potential to regulate soybean aphid populations.

Are the conservation of natural enemy biodiversity and biological control compatible goals?

In conservation biological control (CBC), we attempt to reduce pest problems by increasing the abundance and diversity of the natural enemy community. However, rather than consistently strengthening herbivore suppression, studies show that the conservation of natural enemy species richness sometimes weakens, or has no affect, on biological control. Evidence is mounting that this idiosyncratic mix of positive, negative, and neutral effects of enemy diversity is caused by niche complementarity, intraguild predation, and functional redundancy, respectively. While the balance of evidence suggests that the conservation of natural enemy diversity and biological control are compatible goals, CBC practitioners cannot ignore the fact that conserving intraguild predators can sometimes disrupt biological control. Recent studies have made important progress toward identifying the traits of enemies and their prey that promote intraguild predation, functional redundancy, and niche complementarity. However, intraguild predation has received more attention than niche complementarity, and more theoretical and empirical work is needed rectify this asymmetry. We suggest that a continued focus on natural enemy functional traits, particularly those that are expressed at larger spatiotemporal scales, will increase our ability to identify the “right” kind of diversity and may ultimately improve the practice of conservation biological control.

Alfalfa Living Mulch Advances Biological Control of Soybean Aphid

Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies and experienced a delay in A. glycines establishment that resulted in lower peak populations. From our experiments, we concluded that the current natural enemy community in Iowa can delay A. glycines establishment, and an increase in aphidophagous predator abundance lowered the rate of A. glycines population growth preventing economic populations (i.e., below the current economic threshold) from occurring. Incorporation of a living mulch had an unexpected impact on A. glycines population growth, lowering the aphids' intrinsic rate of growth, thus providing a bottom-up suppression of A. glycines. We suggest future studies of living mulches or cover crops for A. glycines management should address both potential sources of suppression. Furthermore, our experience suggests that more consistent biological control of A. glycines may be possible with even partial resistance that slows but does not prevent reproduction.

Alfalfa Living Mulch Advances Biological Control of Soybean Aphid

Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies and experienced a delay in A. glycines establishment that resulted in lower peak populations. From our experiments, we concluded that the current natural enemy community in Iowa can delay A. glycines establishment, and an increase in aphidophagous predator abundance lowered the rate of A. glycines population growth preventing economic populations (i.e., below the current economic threshold) from occurring. Incorporation of a living mulch had an unexpected impact on A. glycines population growth, lowering the aphids’ intrinsic rate of growth, thus providing a bottom-up suppression of A. glycines. We suggest future studies of living mulches or cover crops for A. glycines management should address both potential sources of suppression. Furthermore, our experience suggests that more consistent biological control of A. glycines may be possible with even partial resistance that slows but does not prevent reproduction.

Seasonal Abundance of Liriomyza sativae (Diptera: Agromyzidae) and its Parasitoids on Vegetables in Southern Vietnam

Native to the North America, Liriomyza sativae (Blanchard) (Diptera: Agromyzidae) is widespread worldwide but mostly occurs in the temperature regions including South East Asian countries (Spencer, 1973; Murphy and LaSalle, 1999). Recently, L. sativae has been also recorded from China (Zhao and Kang, 2000) and Japan (Iwasaki et al., 2000). In Japan, L. sativae was found for the first time in 1999 in Kyoto and Yamaguchi Prefectures (Iwasaki et al., 2000). This species has quickly spread and become a serious pest of vegetable and ornamental crops in the fields and greenhouses. This rapid spread was mainly caused by transportation of plant materials for greenhouses and plastic tunnels. In northern areas beyond latitude 34 N in China, L. sativae can not overwinter in the outdoors (Zhao and Kang, 2000). In Vietnam, L. sativae is an economically important pest of a wide variety of vegetable and ornamental crops in the open fields (Andersen et al., 2002; Tran et al., 2005a, b). Recent outbreaks of the leafminer were treated by a wide range of conventional insecticides, but control was unsatisfactory (Johansen et al., 2003; Tran and Takagi, 2005). Frequent applications of these broad spectrum insecticides can adversely affect parasitoid abundance in the vegetable agro–ecosystems (Saito et al., 1996; Johansen et al., 2003), can promote the development of pesticide resistance within fly populations (Keil et al., 1985, Johansen et al., 2003; Hofsvang et al., 2005) and frequently lead to an increase in leafminer density (Oatman and Kennedy, 1976; Murphy and LaSalle, 1999). Agromyzid leafminers are known to have rich natural enemy communities. Eighteen species of hymenopteran parasitoids have been recovered from Liriomyza leafminers in central and southern Vietnam. Among them, Neochrysocharis beasleyi Fisher & LaSalle, Neochrysocharis okazakii Kamijo, Neochrysocharis formosa (Westwood) and Asecodes delucchii (Boucek) (Hymenoptera: Eulophidae) are numerically dominant species (Tran et al., 2006). They have played a very important role in leafminer suppression in natural ecosystems and cultivated areas with reduced insecticide use (Johnson et al., 1980; Murphy and LaSalle, 1999). The objectives of this study were to survey damage caused by L. sativae in two important vegetable–growing areas of the Ho Chi Minh City, southern Vietnam, and to monitor the seasonal abundance of the leafminer and its parasitoids. In this paper, the seasonal occurrence of L. sativae in Vietnam and Japan was also discussed. Seasonal Abundance of Liriomyza sativae (Diptera: Agromyzidae) and its Parasitoids on Vegetables in Southern Vietnam

The influence of organic transition systems on beneficial ground-dwelling arthropods and predation of insects and weed seeds

AbstractThe influence of farm management practices on ground-dwelling natural enemy communities and predation of insects and weed seeds was investigated over the first 2 years of the transition from conventional to organic production. Three transition strategies were selected that differed in their management and input intensities, and were characteristic of pasture/ley systems (low intensity), cash grain systems (intermediate intensity), and vegetable production (high intensity). Beneficial arthropods (insectivores and granivores) were monitored using pitfall (arthropod activity) and quadrat (arthropod density) samples. The frequency of predation on restrained larvae ofGalleria mellonellaand the species observed feeding were recorded. Weekly removal rates of weed seeds representative of abundant species at our site were monitored over a 3-week period during fall. Management intensity affected the activity and abundance of biological control agents. In year two of the transition, biological control agent densities were higher in the low-intensity treatment than in the other two treatments, but activity of insectivores and granivores was reduced in this treatment relative to the higher intensity systems. The patterns in the abundances of biological control agents may be explained by habitat stability within the different cropping systems. Quadrat samples were strongly correlated with the insectivory index, although pitfall samples were not. Insectivory rates were highest (>80% ofG. mellonellalarvae) in the low-intensity treatment. Predation patterns over a 17-h period differed substantially among the management treatments, indicating behaviorally distinct insectivore communities. Seed removal was also highest in the low-intensity treatment. We conclude that low-intensity cropping systems are most favorable to the abundance and function of beneficial ground-dwelling arthropod communities (insectivores and granivores) during the transition process.

Suppression of Population Growth of the Soybean Aphid, <I>Aphis glycines</I> Matsumura, by Predators: The Identification of a Key Predator and the Effects of Prey Dispersion, Predator Abundance, and Temperature

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has recently invaded North America from Asia and has become a major pest in soybean. Using field surveys and cage exclusion techniques, we identified the effect of natural enemies and abiotic factors on the growth of soybean aphid populations in 2004 and 2005. The soybean aphid population was significantly limited by natural enemies in the field. Generalist predators dominated the natural enemy community. One species, Orius insidiosus Say (Hemiptera: Anthocoridae) represented 85–90% of predators found. There was a significant negative relationship between aphid population growth and O. insidiosus abundance. For other predators, there were no relationships between abundance and aphid population growth. The spatial distribution of aphids among plants affected the impact of O. insidiosus on aphid population growth. When aphids were distributed in a clumped manner, increases in O. insidiosus numbers resulted in lower aphid growth rates. For randomly distributed aphids, there was no effect of O. insidiosus abundance on aphid population growth. Finally, we found no relationship between aphid population growth and degree-day accumulations. The potential of O. insidiosus to suppress soybean aphid population growth at low aphid numbers and the importance of the predator to soybean aphid integrated pest management are discussed.

Population dynamics of Spodoptera frugiperda Smith (Lepidoptera: Noctuidae) and associated arthropod natural enemies in Honduran subsistence maize

We investigated relationships between the population dynamics of the pest insect, the fall armyworm Spodoptera frugiperda (Smith) and associated natural enemies within small-scale maize fields in the Honduran highlands. In general, pest infestation levels remained below regionally defined economic thresholds. A broad complex of arthropod predators, parasitoids and entomopathogens was recorded from field plots. Low levels (1–11%) of parasitism of Spodoptera frugiperda were recorded, with the braconid Aleiodes laphygmae (Viereck) and the ichneumonid Campoletis sonorensis (Cameron) the most commonly observed parasitoids. Incidence of entomopathogens and parasitic nematodes was low, affecting only 3.8% of collected fall armyworm larvae. The most abundant predator was the earwig Doru taeniatum (Dorhn), which reached maximum densities of 2.3 individuals per plant. Frequently observed predators belonged to the order Aranea and insect families Formicidae, Carabidae and Pentatomidae. The ant community was dominated by the fire ant Solenopsis geminata (F.). Natural enemy abundance and diversity differed considerably between fields, as did their associations with fall armyworm infestation. High abundance of spiders during early maize developmental stages was associated with lowered pest levels. High abundance of ground beetles and earwigs was associated with lowered pest population levels throughout the maize vegetative cycle. Time-lagged relationships were found between pest population dynamics and the abundance of vespid wasps and ants. Spodoptera frugiperda infestation levels were lower at higher altitudes. When correcting for altitudinal effects, many associations between predator abundance and fall armyworm dynamics remained valid. Our study shows that the interaction between altitude, the natural enemy community and fall armyworm population dynamics in maize fields needs to be taken into consideration for the development of IPM in this crop. We suggest that conservation biological control programs can take advantage of the impact of predators and provide management recommendations tailored to the region's subsistence farming sector.

Manipulating plant resources to enhance beneficial arthropods in agricultural landscapes

Annual crop fields typically are simple habitats dominated by a few plant species where pesticides play a major role in managing weed and insect infestations. Recently, there has been significant interest in the potential to reduce reliance on pesticides by manipulating plant species and communities to benefit natural enemies of insects and weeds. Such efforts aim to enhance natural enemy impact by providing appropriate food, shelter, and hosts, and efforts typically are accomplished by manipulation of plant species, populations, or communities. Habitat management is generally viewed as an important factor in maintaining stable insect and natural enemy populations in agricultural systems and may have a similar function in increasing weed seed predation. Crop and noncrop habitats provide resources to natural enemies either directly through floral nectar and pollen, indirectly by increased host or prey availability, or through emergent properties of the habitat such as by moderating the microclimate. These critical resources for natural enemies can be provided in agricultural ecosystems at several scales: within fields, at field margins, or as a component of the larger landscape. Because individual natural enemy species may require quite specific resources at different times and spatial scales, not all attempts to manipulate habitat diversity are equally effective. We review the role of plant resources, including weeds, in supporting natural enemy communities and provide case studies of how varying plant diversity at different spatial scales can influence the effectiveness of biological control in agricultural landscapes.

Long-Term Assessment of the Effects of TransgenicBtCotton on the Function of the Natural Enemy Community

Field studies to assess effects of transgenic crops on nontarget organisms primarily have focused on nontarget abundance and diversity, whereas few have examined effects on nontarget community function. A 5-yr field study in Arizona assessed whether transgenic cotton producing the Cry1Ac toxin of Bacillus thuringiensis (Bt) had an effect on the natural enemy community’s impact on three key pests. Predator:prey ratios for Bemisia tabaci (Gennadius) and Lygus hesperus Knight were similar in unsprayed Bt and non-Bt cotton. Insecticide applications in positive control plots inconsistently altered ratios for B. tabaci. Predation indices based on the known feeding activity of selected predators showed that potential predator impact was unaltered by Bt cotton but was consistently depressed with insecticide applications. Sentinel eggs and pupae of Pectinophora gossypiella (Saunders) experienced the same rates of predation in both unsprayed Bt and non-Bt cotton. Cohort-based life tables for B. tabaci showed that rates of sucking predation, parasitism, and dislodgement (chewing predation in part) were unchanged by Bt cotton. Underlying experimental designs were sufficient to consistently detect changes of <20% in predator:prey ratios and predation indices and changes of <10% in rates of P. gossypiella and B. tabaci mortality with >80% power ( = 0.05). These long-term studies showed essentially no effects of Bt cotton on natural enemy function in Arizona cotton and further showed that minor reductions in density of several predator taxa in Bt cotton observed in a companion study may have little ecological meaning relative to natural enemy impact on key pests in the system.

Long-Term Assessment of the Effects of Transgenic &lt;I&gt;Bt&lt;/I&gt; Cotton on the Function of the Natural Enemy Community

Abstract Field studies to assess effects of transgenic crops on nontarget organisms primarily have focused on nontarget abundance and diversity, whereas few have examined effects on nontarget community function. A 5-yr field study in Arizona assessed whether transgenic cotton producing the Cry1Ac toxin of Bacillus thuringiensis (Bt) had an effect on the natural enemy community’s impact on three key pests. Predator:prey ratios for Bemisia tabaci (Gennadius) and Lygus hesperus Knight were similar in unsprayed Bt and non-Bt cotton. Insecticide applications in positive control plots inconsistently altered ratios for B. tabaci. Predation indices based on the known feeding activity of selected predators showed that potential predator impact was unaltered by Bt cotton but was consistently depressed with insecticide applications. Sentinel eggs and pupae of Pectinophora gossypiella (Saunders) experienced the same rates of predation in both unsprayed Bt and non-Bt cotton. Cohort-based life tables for B. tabaci show...

Long-Term Assessment of the Effects of Transgenic &lt;I&gt;Bt&lt;/I&gt; Cotton on the Abundance of Nontarget Arthropod Natural Enemies

Abstract A 6-yr field study assessed the long-term impact of Bt cotton producing the Cry1Ac δ-endotoxin on 22 taxa of foliar-dwelling arthropod natural enemies in Arizona. No chronic, long-term effects of Bt cotton were observed over multiple generations of nontarget taxa. Zero-2 taxa declined significantly in unsprayed Bt compared with non-Bt cotton each year. In contrast, positive control studies showed that insecticide applications for caterpillars and other pests in both non-Bt and Bt cotton had much greater negative effects on 10 taxa. Multivariate principal response curves supported the findings of univariate analyses for the entire natural enemy community, showing no effect of Bt cotton but large and long-lasting negative effects from the use of insecticides. Multi-year analyses provided greater statistical power and indicated significant reductions that averaged 19% in five arthropod predator taxa in unsprayed Bt compared with non-Bt cotton. Most of these reductions were likely associated with red...

Monoclonal antibodies reveal the potential of the tetragnathid spider Pachygnatha degeeri (Araneae: Tetragnathidae) as an aphid predator

The drive towards a more sustainable and integrated approach to pest management has engendered a renewed interest in conservation biological control, the role of natural enemy communities and their interactions with prey. Monoclonal antibodies have provided significant advances in enhancing our knowledge of trophic interactions and can be employed to help quantify predation on target species. The tetragnathid spider Pachygnatha degeeri Sundevall was collected from fields of winter wheat in the UK and assayed by ELISA for aphid proteins. It was demonstrated that this spider did not simply consume greater quantities of aphids because it was bigger. In addition, P. degeeri contained significantly greater concentrations of aphid in their guts than other spiders, showing that aphids comprised a greater proportion of their diet. Although P. degeeri constituted only 6% of the spider population numerically, females and males respectively contained 16% and 37% of total aphid proteins within all spiders screened, significantly more than their density would predict. These spiders also preyed upon aphids at a disproportionately high rate in June, during the aphid establishment phase, theoretically the best time for limiting growth in the aphid population. Although less abundant than other generalist predators, the capability of these hunting spiders to consume large numbers of aphids highlights them as a more significant component of the predator complex than had previously been realized. Limitation of aphid numbers early in the year by generalist predators provides more time for the specialist aphid predators and parasitoids to move in.

Intraguild predation of Orius tristicolor by Geocoris spp. and the paradox of irruptive spider mite dynamics in California cotton

Abstract It is paradoxical when a community of several natural enemies fails to control a pest population when it can be shown experimentally that single members of the natural enemy community are effective control agents when tested individually. This is the case for spider mites, Tetranychus spp., in California cotton. Spider mites exhibit irruptive population dynamics despite that fact that experiments have shown that there are at least four predators ( Galendromus occidentalis , Frankliniella occidentalis , Orius tristicolor , and Geocoris spp.) that, when tested singly, can suppress mite populations. One possible explanation for the paradox is intraguild predation, wherein one predator consumes another. Here, I evaluate the hypothesis that intraguild predation is a strong interaction among spider mite predators. I report manipulative field experiments, focal observations of freely foraging predators in the field, and population survey data that suggest that the minute pirate bug O. tristicolor , is subject to strong predation by other members of the predator community, and in particular by Geocoris spp. These results, combined with the results of prior work, suggest that pervasive intraguild predation among spider mite predators may explain the pest status of Tetranychus spp. in cotton.

Aphid individual performance may not predict population responses to elevated CO2 or O3

AbstractChanges in atmospheric composition affect plant quality and herbivore performance. We used the Aspen Free Air CO2 Enrichment (FACE) facility to investigate the impacts of elevated carbon dioxide (CO2) and ozone (O3) on the performance of the aphid Cepegillettea betulaefoliae Granovsky feeding on paper birch (Betula papyrifera Marsh.). In Year 1, we simultaneously measured individual performance and population growth rates, and in Year 2 we surveyed natural aphid, predator and parasitoid populations throughout the growing season. Aphid growth and development (relative growth rate (RGR), development time, adult weight, embryo number and the birth weight of newborn nymphs) were unaffected by CO2 and O3. Aphid fecundity decreased on trees grown at elevated CO2, O3 and CO2+O3. Neither nymphal performance nor adult size were reliable indicators of future fecundity at elevated CO2 and/or O3. Aphid populations protected from natural enemies were unaffected by elevated CO2, but increased significantly at elevated O3. Individual fecundity in elevated CO2 and O3 atmospheres did not predict population growth rates, probably because of changes in the strength of intraspecific competition or the ability of the aphids to induce nutrient sinks. Natural aphid, predator and parasitoids populations (Year 2) showed few significant responses to CO2 and O3, although CO2 and O3 did affect the timing of aphid and natural enemy peak abundance. Elevated CO2 and O3 affected aphid and natural enemy populations independently: no CO2× O3 interactions were observed. We conclude that: (1) aphid individual performance did not predict population responses to CO2 and O3 and (2) elevated CO2 and O3 atmospheres are unlikely to affect C. betulaefoliae populations in the presence of natural enemy communities.

Species Composition and Distribution of Hessian Fly (Diptera: Cecidomyiidae) Parasitoids in Northern Idaho

Economically damaging infestations of Hessian fly, Mayetiola destructor Say (Diptera: Cecidomyiidae) have been reported in northern Idaho and damage from the pest has been increasing in this region for the last 12 years. Despite the seriousness of this pest, there is no published information on the natural enemy community associated with Hessian fly in northern Idaho. Studies were conducted in 1998 and 1999 to determine the abundance, distribution, and species composition of Hessian fly parasitoids in northern Idaho. Surveys of commercial wheat fields were conducted in eight counties, and samplings were done in spring wheat trials established near Lewiston, Bonners Ferry, Genesee and Greencreek. Seven species of hymenopterous parasitoids of Hessian fly are reported from Idaho for the first time. Parasitoids were collected from flies in all eight counties. Of the species found, Platygaster hiemalis (Forbes) (Platygastridae) was the most numerous, and Homoporus destructor Say (Pteromalidae) and Pediobius epigonus Walker (Eulophidae) the most widespread. Trichomalopsis subapterus Riley, T. americanus Gahan (Pteromalidae), Eupelmus allynii French and E. vesicularis (Retzius) (Eupelmidae) were encountered in lower numbers and only in one or two counties.

Predation of green peach aphids by generalist predators in the presence of alternative, Colorado potato beetle egg prey

Abstract In Washington State two insect herbivores commonly co-occur on potato (Solanum tuberosum L.), the green peach aphid (“GPA,” Myzus persicae Sulzer) and the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). Locally, generalist predators dominate the community of natural enemies in potato fields. The presence of multiple prey species might distract generalists from feeding on any single target pest. In the laboratory, we examined whether consumption rates of several predator species on focal (GPA) prey was reduced in the presence of alternative (CPB egg) prey. In initial measurements of predation rates we found that two predator species, Nabis spp. and Geocoris spp. bugs, had the highest consumption rates on aphids, potato beetle eggs and small potato beetle larvae. So, we focused on Nabis spp. and Geocoris spp. in later experiments. In Petri dish arenas Nabis ate significantly more GPA per capita than did Geocoris; both predators exhibited weakly suppressed aphid consumption rates when CPB eggs were also present. However, in experiments in larger greenhouse microcosms including potato plants, this weak disruptive effect of CPB eggs disappeared. Geocoris ate nearly identical numbers of aphids across a 4-fold range of CPB egg density. Nabis, in contrast, ate significantly more aphids when 40 CPB eggs were included in microcosms, compared to microcosms with no alternative prey present. Thus, we would not expect any strong disruption of M. persicae control by Nabis spp. or Geocoris spp. when L. decemlineata eggs are also present in the field.

Arthropod Predators of &lt;I&gt;Galerucella calmariensis&lt;/I&gt; L. (Coleoptera: Chrysomelidae): An Assessment of Biotic Interference

Galerucella calmariensis L. is a leaf-feeding beetle introduced into North America for biological control of purple loosestrife, Lythrumsalicaria L. It is well known that existing natural enemy communities can reduce herbivore establishment andlimit their impacts as weedbiocontrol agents. Although such biotic interference can often initially be avoided through inundative releases or use of exclusion cages, successful biological control of L. salicaria will ultimately rest on natural coloni- zation of new host patches. The objectives of this study were: 1) identify potential arthropod predators in Michigan wetlands; 2) test predator propensity to attack G. calmariensis; and3) assess importance of biotic interference by simulating G. calmariensis colonization in wetlandhabitats. Fieldsurveys showedthat Coleomegilla maculata De Geer, Coccinella septempunctata L., and Harmonia axyridis L. (Coleoptera: Coccinellidae) were most abundant potential predators of G. calmariensis, followedby Pterostichus melanarius Illiger (Coleoptera: Carabidae) and Podisus maculiventris Say (Hemiptera: Pentatomidae). In laboratory tests, 24-h attack rates on eggs andlarvae rangedfrom 10 to 100%, with C. maculata and Forficula auricularia L. consuming the greatest number of G. calmariensis. Increasingly realistic laboratory trials d emonstratedthat several pred ators effectively locatedandconsumed immature stages of G. calmariensis under more complex conditions. In the Þeld study, predator abund ance andattack rates were low, ranging from 0.63 to 1.63 egg masses consumed(10 Ð27%). Survival of individuals to the adult stage in caged (53Ð90%) versus open treatments (24 Ð 42%) revealed a signiÞcant effect of predation. However, even the lowest survival rate observed is probably adequate to ensure effective colonization. We conclude that predation can signiÞcantly reduce G. calmariensis population increase in the Þeld , but is unlikely to prevent establishment andspreadund er the conditions studied.

Soybean Aphid Predators and Their Use in Integrated Pest Management

The discovery of the soybean aphid, Aphis glycines Matsumura, in U.S. soybean production systems in 2000 has provided a unique opportunity to study the interaction of a new invader with existing natural enemy communities. One research thrust has been examining the role of predators in soybean aphid dynamics in the Midwest. We discuss the roles of predatory arthropods in field crops and set forth a conceptual model that we have followed to identify key predators in the soybean aphid system. We identify Orius insidiosus (Say) and Harmonia axyridis (Pallas) as potentially key predators and show our findings on their phenology in soybean fields and their impact on soybean aphid population dynamics. Finally, we discuss how this information can be used in integrated pest management programs for soybean aphid and point to gaps in our knowledge where future studies are needed.

151 Skin irritation — evaluation of mechanisms: Description of an IL-1α threshold

Linyphiid spiders, as part of the community of natural enemies that frequent agroecosystems, can exert significant pressure on prey populations. Many aspects of linyphiid feeding ecology remain understudied, including temporal and seasonal patterns of prey utilization. To quantify the diversity, quantity, and spatial pattern of availability over diel and seasonal gradients, we monitored prey in an alfalfa crop, using web-site specific sticky traps. Although there were no differences in total number of prey between the day and night, significantly more Collembola were intercepted nocturnally rather than diurnally. Conversely, Diptera and Aphididae were significantly more abundant diurnally. Overall there were more prey at web-sites than in the general crop environment, indicating that spiders were selectively constructing webs where prey was relatively more abundant. However, spiders still may have experienced a high degree of prey limitation because the abundance of Collembola, an important detrital prey, was low over much of the season and below levels calculated as being required to sustain growth and reproductive output in linyphiid spiders. In conclusion, our data suggests that linyphiid spiders, in order to avoid food limitation, may benefit by foraging throughout the diel cycle, consuming herbivorous prey in addition to their core diet of detrital prey. This link between above and below ground food webs indicates the importance of understanding the trophic interactions between epigean spiders and their prey if they are to be integrated into future biological control programs.