Meeting Abstract
Mormon crickets Anabrus simplex are well known for their carnivory, which effectively drives their migration in a well-organized common direction when densities are sufficiently high. Carnivorous behavior derives from a lack of protein in their diet, with those lacking protein also having less phenoloxidase (PO) available to combat foreign invaders and lower immunity to fungal pathogens. In addition to feeding on plants, Mormon crickets predate invertebrates, and we hypothesize that invertebrate prey availability determines the amount of protein in their diet. Because Mormon crickets commonly occur with grasshoppers that feed on the same plants, we investigated interactions between grasshoppers and Mormon crickets. If Mormon crickets are principally predatory on grasshoppers then grasshopper abundance could influence Mormon cricket immunity due to the role that protein availability has on circulating PO. In a field setting, we varied densities of Mormon crickets (0, 10, or 20 per cage) and grasshoppers Melanoplus borealis (0, 15, 30, or 45) in 68 1-m2 cages and measured survivorship. In addition, we measured dietary preferences and PO activity of Mormon crickets. We also measured Mormon cricket consumption of grasshoppers in a laboratory setting. In the field, both grasshopper and Mormon cricket survivorship declined with Mormon cricket density. Mormon cricket predation on grasshoppers and cannibalism were frequently observed. As predicted, diet preference shifted from protein to carbohydrates as grasshopper density increased, and PO activity also increased with grasshopper availability. Grasshoppers can be an important source of dietary protein for Mormon crickets, with grasshopper availability affecting Mormon cricket immunity to disease.
