Predation and immunocompetence: Grasshoppers increase Mormon cricket resistance to a fungal pathogen

Authors: Srygley, Robert; Branson, David

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2026
Publication Date: 5/7/2026
Citation: Srygley, R.B., Branson, D.H. 2026. Predation and immunocompetence: Grasshoppers increase Mormon cricket resistance to a fungal pathogen. Ecological Entomology. https://doi.org/10.1111/een.70097.
DOI: https://doi.org/10.1111/een.70097

Interpretive Summary: In nature, Mormon crickets and grasshoppers frequently occur in the same locations and eat the same plants, yet little is known about their interactions. Previously, we have shown that eating grasshoppers provides a protein boost to Mormon crickets. Here we ask whether the protein boost obtained when provisioned with grasshoppers conferred a survival advantage when Mormon crickets were infected with the pathogenic fungus Beauveria bassiana. In addition, given a survival advantage was supported, we predicted that the predator would eat more grasshoppers when infected with the fungus. We caged Mormon cricket nymphs in one of four combinations of 10 or 20 Mormon crickets and 0 or 45 grasshoppers per square meter. A few weeks later, we topically applied either B. bassiana or the oil carrier without fungus to the Mormon crickets as a control and housed them individually outdoors. Those reared with 45 grasshoppers were provisioned with 5 grasshoppers, whereas those lacking grasshoppers got none. Although more fungal-treated Mormon crickets died than the controls over 23 days, mortality was substantially lower than expected from lab trials. Hence, although B. bassiana proved to be an effective pathogen of Mormon crickets, it grew slowly in the cool montane environment. Maintenance of the fungal-treated individuals at 28°C for an additional 8 days in the lab demonstrated that the insects were tolerating the infection and those provisioned with grasshoppers survived longer than those without this protein-rich food source. Although Mormon crickets did not consume more grasshoppers than controls when infected, we conclude that nutrients from grasshoppers were integrated into Mormon cricket immunity to a natural fungal control agent. Hence managers should consider both the daily ambient temperature cycle and the abundance of grasshoppers and other prey when determining the efficacy of applying the microbial control agent Beauveria bassiana to Mormon crickets.

Technical Abstract: Typically herbivorous insects cope with immunity challenges by altering the amount of macronutrients (protein or carbohydrates) or plant secondary compounds they consume. Omnivores can shift more broadly than herbivores to ingest animals in addition to plants with consequences for the food web that have been little explored. To fill this gap, we hypothesized that Mormon crickets would obtain a protein boost when provisioned with grasshoppers conferring a survival advantage when infected with the pathogenic fungus Beauveria bassiana. Consequently, we predicted that they would eat more grasshoppers when infected with the fungus than uninfected controls. We caged Mormon cricket nymphs in one of four combinations of 10 or 20 Mormon crickets and 0 or 45 grasshoppers per square meter. A few weeks later, we topically applied either B. bassiana or the oil carrier without fungus to the Mormon crickets and housed them individually outdoors. Those reared with 45 grasshoppers were provisioned with 5 grasshoppers, whereas those lacking grasshoppers got none. After 5-8 days, we drew hemolymph to measure total phenoloxidase (PO) and hemolymph protein. Cages were checked daily for mortality for 23 days. Significantly more fungal-treated Mormon crickets died than the controls, but mortality was lower than expected from lab trials. Hence, B. bassiana proved to be an effective pathogen of Mormon crickets, although it grew slowly in the cool montane environment. Provisioning grasshoppers increased the circulating protein and total PO, but did not significantly affect mortality. Maintenance of the fungal-treated individuals at 28°C for an additional 8 days in the lab demonstrated that the insects were tolerating the infection and those provisioned with grasshoppers survived longer than those without this protein-rich food source. Although Mormon crickets did not consume more grasshoppers to ward off the infection, we conclude that prey abundance affected immunocompetence of a predator with nutrients from grasshoppers integrated into Mormon cricket immunity to a natural fungal control agent.