Consumption of flea beetles (Phyllotreta, Coleoptera: Chrysomelidae) by spiders in field habitats detected by molecular analysis

Abstract

AbstractFlea beetles, Phyllotreta Chevrolat (Coleoptera: Chrysomelidae) species, are often found in oilseed rape (OSR), Brassica napus Linnaeus (Brassicaceae). Among predators in the generalist predator complex present in agricultural fields, wolf spiders (Araneae: Lycosidae) are found on the ground and cobweb spiders (Araneae: Theridiidae) build webs in the foliage. We present group-specific primers developed for five flea beetle species within the genus Phyllotreta and study the incidence of predation of flea beetles by these spider groups using DNA-based gut-content analysis. Wolf spiders of the genus Pardosa Koch and the cobweb spider, Phylloneta impressa (Koch), were collected in three winter OSR fields. Flea beetle densities as well as the occurrence of predators and alternative prey were monitored. In total 19.4% of the collected Pardosa tested positive for flea beetle DNA in the polymerase chain reaction analyses, whereas 10% P. impressa were positive. Pardosa were more likely to be positive for flea beetle DNA when Pardosa activity density was low. Phylloneta impressa were more likely to be positive for flea beetle DNA if they were positive for pollen beetle DNA. Implications of these results for conservation biological control and future studies of food webs in OSR are discussed.