Molecular quantification of spider preying on springtails in winter-spring fallow waterlogged paddy fields

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Fallow waterlogged paddy field (FWPF) is a subtropical type of winter-spring fallow rice fields. Arthropod predation is crucial for their survival during the long-duration FWPF seasons. No research has been conducted in the trophic link of arthropod predators and their prey in FWPFs. Here, we used a quantitative real-time PCR approach, both in lab and field, to detect the trophic link. DNA-based identification confirmed the results of a morphological classification in two dominant species of springtail, Homidia socia Denis and H. tiantaiensis Chen and Lin (Collembola: Entomobryidae). The fastest degradation in H. socia DNA copy numbers in spider Pirata subpiraticus (Bosenberg and Strand) (Araneida: Lycosidae) guts occurred within 8 h under lab conditions. Quantitative comparisons of preying on H. socia by H. socia DNA copy numbers indicated that Oedothorax insecticeps (Bosenberg and Strand), Erigonidium graminicolum (Sundevall) (Araneida: Linyphiidae) and P. subpiraticus were more active springtail predators than others under field conditions. There were significant differences in the DNA copy numbers of springtails in gut of P. subpiraticus among different overwintering periods that was significantly positive related to the springtail densities. This study highlights springtail importance at species level as the prey of spiders in FWPFs and illustrates the utility of our approach to quantify their trophic linkages among different spider species or postharvest seasons.