Entomology
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Item Effects of diet quality on performance and nutrient regulation in an omnivorous katydid(Blackwell, 2011) Pearson, Rachel; Behmer, Spencer; Gruner, Daniel; Denno, Robert1. Omnivores by definition eat both plants and animals. However, little is known about how diet macronutrient content affects omnivore performance, or the extent to which they can regulate macronutrient intake. We assessed these questions using the salt marsh katydid, Conocephalus spartinae Fox (Tettigoniidae). 2. In our first experiment we used artificial diets with different protein–carbohydrate ratios to assess the effects of diet quality on survival, growth, and lipid accumulation. We found that diets with a high protein–carbohydrate ratio negatively affected Conocephalus survival. Among surviving individuals growth was not significantly different across the treatments, but lipid content decreased significantly as the protein–carbohydrate ratio of diets increased. 3. In a second experiment we explored the ability of Conocephalus to regulate their protein–carbohydrate intake. Results revealed that Conocephalus did not feed randomly when presented with two nutritionally complementary foods. A detailed analysis of their protein–carbohydrate intake revealed selection for a protein-biased diet, but a lack of tight regulate of protein–carbohydrate intake. 4. We discuss how key macronutrients can limit omnivores, and how nutritional flexibility may enable omnivores to persist in nutritionally heterogeneous environments.Item Potential for entomopathogenic nematodes in biological control: a meta-analytical synthesis and insights from trophic cascade theory(2008) Denno, Robert; Gruner, Daniel; Kaplan, IanEntomopathogenic nematodes (EPN) are ubiquitous and generalized consumers of insects in soil food webs, occurring widely in and agricultural ecosystems on all continents. Augmentative releases of EPN have been used to enhance biological control of pests in agroecosystems. Pest managers strive to achieve a trophic cascade whereby natural-enemy effects permeate down through the food web to suppress host herbivores and increase crop production. Although trophic cascades have been studied in diverse aboveground arthropod-based systems, they are infrequently investigated in soil systems. Moreover, no overall quantitative assessment of the effectiveness of EPN in suppressing hosts with cascading benefits to plants has been made. Toward synthesizing the available but limited information on EPN and their ability to suppress prey and affect plant yield, we surveyed the literature and performed a meta-analysis of 35 published studies. Our analysis found that effect sizes for arthropod hosts as a result of EPN addition were consistently negative and indirect effects on plants were consistently positive. Results held across several different host metrics (abundance, fecundity and survival) and across several measures of plant performance (biomass, growth, yield and survival). Moreover, the relationship between plant and host effect size was strikingly and significantly negative. That is, the positive impact on plant responses generally increased as the negative effect of EPN on hosts intensified, providing strong support for the mechanism of trophic cascades. We also review the ways in which EPN might interact antagonistically with each other and other predators and pathogens to adversely affect host suppression and dampen trophic cascades. We conclude that the food web implications of multiple-enemy interactions involving EPN are poorly studied, but, as management techniques that promote the long-term persistence of EPN are improved, antagonistic interactions are more likely to arise. We hope that the likely occurrence of antagonistic interactions in soil food webs should stimulate researchers to conduct field experiments explicitly designed to examine multiple-enemy interactions involving EPN and their cascading effects to hosts and plants.