Seasonal patterns in generalist predator trophic interactions based on molecular gut-content analysis

Although generalist predators are sometimes overlooked in biological control, they can exert pressure on pest populations, particularly via early-season predation. Therefore, elucidating the seasonal feeding patterns of agriculturally dominant predators is essential. Additionally, many generalist predators supplement their diets by consuming non-prey resources. Sheet-web spiders (Araneae: Linyphiidae) intercept high amounts of corn pollen during anthesis and readily consume this high-protein food resource. To delineate trophic interactions within complex food webs, six polymerase chain reaction (PCR) primer pairs were designed to amplify target DNA from a primary pest (Western corn rootworm: WCRW), two secondary pests (corn flea beetle: CFB, Aphididae), a detritivore (Collembola), a predator (Dolichopodidae) and a non-prey food (corn). Over 2,600 linyphiids were collected and screened using molecular gut-content analysis via PCR. Additionally, prey abundance and pollen interception were monitored throughout the growing seasons at spider webs and non-web sites using sticky traps and sweep net sampling. Results indicated four distinct patterns of resource utilization: 1) spiders consumed Collembola throughout the season (~50% screening positive); 2) corn consumption spiked during anthesis (~25%), corresponding to the temporal-pulse dynamics of this resource; 3) aphid predation peaked early in the season (~10%) and rapidly declined to 0% on subsequent dates, despite availability of aphids; and 4) predation was very low (<0.5%) on WCRW, CFB and dolichopodids. This research has revealed the strength of trophic connections between web-based spiders and their prey in an agroecosystem across the growing season. The early-season predation observed on aphids, particularly colonizing alates, has significance for biological control.