An order-specific monoclonal antibody to Diptera reveals the impact of alternative prey on spider feeding behavior in a complex food web

Generalist predators have the capacity to restrict pest population growth, especially early in the season before densities increase. However, their polyphagous feeding habits sometimes translate into reduced pest consumption when they target alternative prey. An order-specific monoclonal antibody was developed to examine the strength of trophic connections between Diptera, a major category of non-pest prey, and linyphiid spiders in alfalfa. We report the development and characterization of a monoclonal antibody with order-level specificity to Diptera. This antibody elicited strong absorbance to 22 Diptera from 13 families, no false-positive reactivity to non-dipteran invertebrates, and antigen detection periods following prey consumption that were comparable between spiders. Over 900 field-collected females of the linyphiid spiders Erigone autumnalis and Bathyphantes pallidus were screened for Diptera antigen. Significantly more B. pallidus screened positive for Diptera (40%) compared to E. autumnalis (16%), indicating differential reliance on these prey. In parallel with the collection of spiders for gut-content analysis, prey availability was estimated at web sites. The two spiders exhibited different feeding responses to prey availability. Consumption of Diptera by B. pallidus was strongly correlated with Diptera abundance whilst the availability of other potential prey did not influence predation rates. Conversely, E. autumnalis did not prey upon Diptera in proportion to availability, but increased Collembola activity-density reduced dipteran consumption. Integration of molecular gut-content analysis with precise sampling of prey demonstrated how two closely related linyphiid spiders exhibit different feeding responses to the availability of prey under natural field conditions. Elucidating the feeding preferences of natural enemies is critical to effective incorporation of biological control by generalist predators in the management of agricultural pests.     

Temporal distribution of Chaetocnema pulicaria (Coleoptera: Chrysomelidae) populations in Iowa

In 1999 and 2000, yellow sticky cards and sweep net samples were used to document the occurrence of an overwintering adult generation of Chaetocnema pulicaria Melsheimer, corn flea beetle, followed by two distinct populations peaks during the growing season in Iowa Emergence of the overwintering adult generation started in mid-April and continued until early June in both years, with populations as high as 45 +/- 7.9 per 10 sweeps. Periods that ranged from 14 to 32 d were observed in 1999 and 2000 when C. pulicaria was not found following the overwintering generation. The first summer peak of C pulicaria was observed between the end of June into the middle of July, with the highest observed peak at 16.70 +/- 1.42 C. pulicaria per 10 sweeps in cornfields. The second summer peak of C pulicaria was observed between the middle into early September, with populations as high as 27.80 +/- 2.76 C. pulicaria per 10 sweeps. During the growing season, more C. pulicaria were caught on yellow sticky cards originating from soybean borders than from grass borders. There were significantly greater numbers of C. pulicaria on yellow sticky cards located in grass borders adjacent to cornfields at the end of the growing season, compared with yellow sticky cards located within cornfields, indicating the movement of C. pulicaria from the cornfield back into the grass borders at the end of the growing season. In 2000, from August to the end of the corn growing season, significantly more C. pulicaria were found in grass borders than in the cornfields. Based on this new quantitative information, planting time could be altered to avoid the emergence of the overwintering generation of C. pulicaria. In addition, knowledge concerning the seasonalities of the first and second population peaks of C pulicaria during the corn growing season could be used to recommend optimal timing for foliar-applied insecticide applications. This new knowledge concerning the seasonal dynamics of C pulicaria will help to improve management recommendations for Stewart's disease of corn, caused by the bacterium Pantoea stewartii, and that is vectored by C pulicaria.     

Tracking the role of alternative prey in soybean aphid predation by Orius insidiosus: a molecular approach

The soybean aphid, Aphis glycines (Hemiptera: Aphididae), is a pest of soybeans in Asia, and in recent years has caused extensive damage to soybeans in North America. Within these agroecosystems, generalist predators form an important component of the assemblage of natural enemies, and can exert significant pressure on prey populations. These food webs are complex and molecular gut-content analyses offer nondisruptive approaches for examining trophic linkages in the field. We describe the development of a molecular detection system to examine the feeding behaviour of Orius insidiosus (Hemiptera: Anthocoridae) upon soybean aphids, an alternative prey item, Neohydatothrips variabilis (Thysanoptera: Thripidae), and an intraguild prey species, Harmonia axyridis (Coleoptera: Coccinellidae). Specific primer pairs were designed to target prey and were used to examine key trophic connections within this soybean food web. In total, 32% of O. insidiosus were found to have preyed upon A. glycines, but disproportionately high consumption occurred early in the season, when aphid densities were low. The intensity of early season predation indicates that O. insidiosus are important biological control agents of A. glycines, although data suggest that N. variabilis constitute a significant proportion of the diet of these generalist predators. No Orius were found to contain DNA of H. axyridis, suggesting intraguild predation upon these important late-season predators during 2005 was low. In their entirety, these results implicate O. insidiosus as a valuable natural enemy of A. glycines in this soybean agroecosystem.