Data from: Generalist predators function as pest specialists: Examining diet composition of spiders and ladybeetles across rice crop stages

Biocontrol, the use of natural enemies to manage pests, has a long history
in agriculture.  It has gained renewed interest because of its
importance in sustainable agriculture.  To solve a long-standing
puzzle in biocontrol—how well the ubiquitous generalist arthropod
predators (GAPs) function as biocontrol agents—this study aimed to 1)
quantify the diet composition of GAPs (spiders and ladybeetles) at
different crop stages using stable isotope analysis, 2) examine the
consistency of GAPs in pest consumption over years, and 3) investigate how
abiotic and biotic factors (farm type, crop stage, surrounding vegetation,
and relative prey abundance) affect pest consumption by GAPs.
Specifically, we sampled arthropod prey and GAPs in seven pairs of
sub-tropical organic and conventional rice farms over crop stages
(seedling, tillering, flowering, and ripening) in three consecutive
years.  Among our sweep-net samples, 352 arthropod predator and
828 prey isotope samples were analyzed to infer predator-prey
interactions. Our results show the following:  a) The proportion
of rice pests in GAPs’ diets in both organic and conventional rice farms
increased over the crop season, from 21-47% at the tillering stage to
80-97% at the ripening stage, across the three study years.  The
high percentage of pest consumption at late crop stages (flowering and
ripening) suggests that GAPs can function as specialists in pest
management during the critical period of crop production. 
Regarding individual predator groups, spiders and lady beetles exhibited
distinct dietary patterns over crop stages.  b) The high pest
consumption by GAPs at late crop stages was similar across years despite
variable climatic conditions and prey availability, suggesting a
consistency in GAP feeding habits and biocontrol value.  c) The
proportion of rice pests in GAPs’ diets varied with farm type and crop
stage (e.g., higher in conventional farms and during flowering/ripening
stages). Synthesis and applications: By quantifying the diet composition
of GAPs over crop stages, farm types, and years, this study reveals that
generalist predators have the potential to produce a stable, predictable
top-down effect on pests in rice agroecosystems.  Therefore,
promoting the field densities of ubiquitous generalist predators will
likely enhance pest management and support sustainable agriculture.