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Abstract Biocontrol agents are critical for pest management in sustainable agriculture. Generalist arthropod predators may hold a great potential as biocontrol agents because they are ubiquitous and consume pests in agroecosystems. However, their diet composition over the entire crop season has rarely been quantified, which hinders our ability to assess their biocontrol potential in real field conditions that foster temporal dynamics of pest and alternative prey populations. To fill this knowledge gap, we surveyed arthropod communities over crop stages in organic and conventional rice farms (n = 7 each) and used stable isotope analysis (δ13C and δ15N) to quantify the diet composition of generalist arthropod predators over time. We aimed to (1) examine the resource partitioning (trophic niches) in these predators, (2) quantify these predators’ diet composition from potential prey sources (rice herbivores, tourist herbivores, and detritivores), and (3) investigate the effects of farm type (organic/conventional) and crop stage (tillering/flowering/ripening stage) on pest (rice herbivore) consumption by the predators. The results show that generalist predators in both organic and conventional farms shifted trophic niches over the crop season and consumed a higher percentage of rice herbivores at late than at early crop stages (e.g., 90–93% at ripening vs. 34–55% at tillering), suggesting an increasing biocontrol value over time regardless of farm type. Surprisingly, generalist predators consumed higher proportions of rice herbivores in conventional than organic farms at tillering and flowering stages, highlighting their underappreciated potential as biocontrol agents in conventional farms. These results demonstrate that although generalist arthropod predators do consume non‐pest alternative prey, they have a high biocontrol potential (per capita pest consumption) in both organic and conventional rice farms. We encourage modern agriculture to develop techniques to support robust populations of these predators and the ecosystem services that they provide.

Biocontrol agents are critical for pest management in sustainable agriculture. Generalist arthropod predators may hold a great potential as biocontrol agents because they are ubiquitous and consume pests in agroecosystems. However, their diet composition over the entire crop season has rarely been quantified, which hinders our ability to assess their biocontrol potential in real field conditions that foster temporal dynamics of pest and alternative prey populations. To fill this knowledge gap, we surveyed arthropod communities over crop stages in organic and conventional rice farms (n = 7 each) and used stable isotope analysis (δ13C and δ15N) to quantify the diet composition of generalist arthropod predators over time. We aimed to (1) examine the resource partitioning (trophic niches) in these predators, (2) quantify these predators' diet composition from potential prey sources (rice herbivores, tourist herbivores, and detritivores), and (3) investigate the effects of farm type (organic/conventional) and crop stage (tillering/flowering/ripening stage) on pest (rice herbivore) consumption by the predators. The results show that generalist predators in both organic and conventional farms shifted trophic niches over the crop season and consumed a higher percentage of rice herbivores at late than at early crop stages (e.g., 90–93% at ripening vs. 34–55% at tillering), suggesting an increasing biocontrol value over time regardless of farm type. Surprisingly, generalist predators consumed higher proportions of rice herbivores in conventional than organic farms at tillering and flowering stages, highlighting their underappreciated potential as biocontrol agents in conventional farms. These results demonstrate that although generalist arthropod predators do consume non‐pest alternative prey, they have a high biocontrol potential (per capita pest consumption) in both organic and conventional rice farms. We encourage modern agriculture to develop techniques to support robust populations of these predators and the ecosystem services that they provide. [ABSTRACT FROM AUTHOR]

Emergent aquatic insects can be major conduits of resources moving from freshwater to adjacent terrestrial ecosystems. These allochthonous resources can influence the structure and function of adjacent ecosystems, yet their effect on arthropod consumer populations remains largely unknown. In this study, we investigated how flying adult midges influence terrestrial arthropod food webs in subarctic grasslands by blocking midge inputs over four years in 2 × 2‐m plots near the shore of Lake Mývatn, Iceland, where midge abundances are naturally high. We examined responses of terrestrial arthropods by measuring their densities, community composition, and stable isotopes (δ13C) in midge‐exclusion and open (control) plots. Cage treatments significantly reduced midge deposition into exclusion plots (99% reduction) relative to control plots but were designed to allow ground‐active arthropods to move freely among plots. Predator densities (e.g., spiders and harvestmen) were on average 30% lower in exclusion plots relative to control plots, while no other trophic guild (detritivores, omnivores, or herbivores) showed a response to midge exclusion. As a result, blocking midges shifted arthropod communities toward a composition dominated by springtails, mites, and aphids relative to large predators such as wolf spiders and harvestmen. All trophic guilds (detritivores, omnivores, and predators), except for herbivores, were more depleted in δ13C in midge‐exclusion plots, indicating an increased reliance on terrestrial (i.e., plant‐based) resources when midge inputs were blocked. Arthropod predators were the only guild that had both a depleted δ13C and a negative density response to midge exclusion. Apart from predators, these results indicate a weak association between resource type (aquatic vs. terrestrial) and density responses across most arthropod guilds in this grassland system. Overall, our findings suggest that aquatic insect subsidies have significant effects on terrestrial arthropod communities, but predators appear most responsive to insect allochthony in subarctic grasslands. [ABSTRACT FROM AUTHOR]

Ecosystem engineers have important effects on abundance and diversity of organisms and are vital for conservation efforts. Some large mammalian grazers are engineers because their grazing activity radically changes plant community structure, an effect which then cascades to other consumers. Many large grazers also behaviorally modify the physical environment. American bison (Bison bison) are known for their wallowing, a behavior that creates distinct areas of high disturbance with modified biological and physical characteristics, but how this behavior affects other consumers is poorly understood. In this study, we investigated arthropod abundance and diversity patterns in active and abandoned wallows compared to those in surrounding tallgrass prairie. We found that active wallows contained lower arthropod abundance and diversity compared to surrounding prairie. Herbivorous arthropods were particularly affected and only about 50% as abundant in wallows, while carnivores and detritivores were affected similarly, but to a lesser degree. In contrast, abandoned wallows had higher arthropod abundance seasonally and higher species richness in several feeding groups. Because of arthropod differences in active and abandoned wallows compared to adjacent prairie, it appears that the impact of wallowing is dependent on time since occurrence, with long‐term effects creating patches of higher arthropod abundance and richness. These patches are likely important, at least seasonally, for other consumers higher on the food web. Together with publications documenting positive effects of bison grazing on arthropod abundance and diversity, our results indicate that wallowing effects are potentially additive. These results suggest that physical changes caused by bison behavior are important for maintaining arthropod biodiversity of tallgrass prairies, and bison may therefore be valuable conservation tools. Bison have been proposed as important candidates for rewilding portions of North America, and our results suggest that they could indeed be valuable toward this end. [ABSTRACT FROM AUTHOR]