Molecular tracking of arthropod predator-prey interactions in Mediterranean lettuce crops

- The main pests in Mediterranean lettuce crops are N. ribisnigri and F. occidentalis. Collembolla is the main non-pest prey.
- Predation of both pests and Collembolla within the studied generalist predators is confirmed by molecular methods.
- Hoverflies were the most polyphagous, preying on both pests as well as on Collembola
- Orius fed mainly on F. occidentalis, spiders on Collembola and ladybugs on N. ribisnigri.
- Predator communities differed with the season, providing groundwork information for conservation biological control programs.

The feeding habits of the generalist arthropod predators in agroecosystems are often difficult to determine, as they are small, mobile and live among the vegetation or in the soil. DNA-based gut-content analysis is a powerful tool that enables the study of arthropod predator-prey interactions. Predation on two of the main pests of Mediterranean lettuce crops, the lettuce aphid, Nasonovia ribisnigri, and the western flower thrips, Frankliniella occidentalis, as well as on Collembola, the most abundant non-pest prey, was studied. Generalist arthropods, like hoverflies, anthocorids (Orius spp.), coccinellids and spiders were collected in lettuce plots in two seasons (spring and summer) and analysed by conventional PCR using N. ribisnigri, F. occidentalis and Collembola-specific primers. Our results showed that in spring the main pest was N. ribisnigri, which was consumed by hoverfly larvae and coccinellids. In summer, the main pest was F. occidentalis, which was mainly predated by Orius spp. followed by hoverfly larvae. Spiders, which fed mainly on Collembola, did not seem to contribute to control of either target pest. This study offers a deeper knowledge of the trophic relationships present in Mediterranean lettuce crops, laying the groundwork for implementing biological control programmes based on the conservation of natural enemies.