Abstract
AbstractSpiders are among the dominant invertebrate predators in agricultural systems and are significant regulators of insect pests. The precise dynamics of biocontrol of pests in the field are, however, poorly understood. This study investigates how density‐independent prey choice, taxonomy, life stage, sex, and web characteristics affect spider diet and biocontrol. We collected spiders in four genera of Linyphiidae (i.e., Bathyphantes, Erigone, Tenuiphantes, and Microlinyphia), and individuals from the Lycosidae genus Pardosa, and their proximate prey communities from barley fields in Wales, UK between April and September 2018. We analyzed the gut contents of 300 individual spiders using DNA metabarcoding. From the 300 spiders screened, 89 prey taxa were identified from 45 families, including a wide range of pests and predators. Thrips were the dominant prey, present in over a third of the spiders sampled, but a type IV functional response appears to reduce their predation at peak abundances. Spider diets significantly differed based on web characteristics, but this depended on the genus and sex of the spider and it was not the principal separating factor in the trophic niches of linyphiids and lycosids. Diets significantly differed between spider genera and life stages, reflected in different propensities for intraguild predation and pest predation. Adult spiders predated a greater diversity of other predators, and juveniles predated a greater diversity of pests. Overall, Tenuiphantes spp. and Bathyphantes spp. exhibited the greatest individual potential for biocontrol of the greatest diversity of pest genera. The greater trophic niche complementarity of Pardosa spp. and Erigone spp., however, suggests that their complementary predation of different pests might be of greater overall benefit to biocontrol. Sustainable agriculture should aim to optimize conditions throughout the cropping cycle for effective biocontrol, prioritizing provision for a diversity of spiders which predate a complementary diversity of pest species.
Highlights
As insecticides decline in use due to increased resistance, regulation and detrimental environmental effects, alternative and integrated pest management is increasingly pertinent (Fountain et al, 2007; Loetti & Bellocq, 2017; MacFadyen et al, 2009; Pekár, 2013; Whitehorn et al, 2012)
Polyphagous generalist predators such as spiders, which are abundant in arable fields (Nyffeler & Sunderland, 2003), can be effective conservation biocontrol agents of crop pests, even when they first emerge or arrive (Alderweireldt, 1994; Boreau De Roincé et al, 2013; Chapman et al, 2013; Juen et al, 2002; Korenko et al, 2010; Riechert & Lockley, 1984; Symondson et al, 2002)
280 From the 300 spiders screened, data were recovered from 244 (38 Bathyphantes, 35 281 Erigone, 26 Microlinyphia, 21 Pardosa, 124 Tenuiphantes, 105 female, 93 male (46 unsexed 282 due to immaturity), 168 adults, 76 juvenile). Across these 244 spiders, 89 different prey 283 zero-radius operational taxonomic units (ZOTUs) were identified from 45 families
Summary
As insecticides decline in use due to increased resistance, regulation and detrimental environmental effects, alternative and integrated pest management is increasingly pertinent (Fountain et al, 2007; Loetti & Bellocq, 2017; MacFadyen et al, 2009; Pekár, 2013; Whitehorn et al, 2012). Specialist predators and parasitoids offer effective biocontrol, but given their dependence on a narrow niche of host/prey taxa, pest populations can reach large sizes before these biocontrol agents intervene (Ammann et al, 2020; Jordan et al, 2020; Levie et al, 2005; K.D. Sunderland et al, 1997). Pest suppression by specialists with complementary trophic niches will have a greater quantitative effect on pest populations than generalists with overlapping niches and resultantly high competition, when those generalists are engaging in intraguild predation of other natural enemies (Finke & Snyder, 2008; Radek Michalko, Pekár, Dul’a, et al., 2019). Lack niche complementarity and are vulnerable to the loss of their prey, suggesting that a diversity of natural enemies, ranging from specialist to generalist, will produce the most robust natural suppression of pests (Jonsson et al, 2017; Radek Michalko, Pekár, Dul’a, et al, 2019)
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