Submitted to: Entomological Society of America Miscellaneous Publications
Publication Type: Proceedings
Publication Acceptance Date: 11/1/2007
Publication Date: 12/3/2007
Publication URL: http://esa.confex.com/esa/2007/techprogram/paper_31456.htm
Citation: Jaronski, S. 2007. Mycosis Inhibits Grasshopper Necrophagy. Entomological Society of America Miscellaneous Publications. Paper No. 31456. Available: http://esa.confex.com/esa/2007/techprogram/paper_31456.htm Interpretive Summary: The report research indicates that the presence of fungal infection in a grasshopper cadaver prevents other grasshoppers from feeding on that cadaver. This inhibition greatly limits the secondary spread of a fungal pathogen in a grasshopper population, which inhibition has important bearing on the continued efficacy of a fungal agent after it is applied to rangeland.
Technical Abstract: Necrophagy is common among the Acrididae and the tettigonid, Anabrus simplex; these behaviors have been proposed as mechanisms for the horizontal transmission of Microsporida and entomopathogenic fungi. After anecdotal observations that Melanoplus sanguinipes and A. simplex did not eat cadavers that had been killed by Beauveria bassiana, I examined whether or not insects, freshly killed by B. bassiana or Metarhizium anisopliae var. acridum, would be consumed by healthy individuals. Necrophagy was examined in a series of no-choice tests with individual insects. Test insects included healthy, adult M. sanguinipes, M. differentialis, Schistocerca americana, and A. simplex. Individual insects were confined in small containers with either a mycotic or uninfected cadaver and observed periodically for the first 12 hours; after 24 hours the cadavers were scored for the degree to which they had been consumed. Very few mycotic cadavers were attacked by the healthy insects; at most only the tarsi were attacked. All four species refused to eat fungus-infected cadavers. In contrast, freeze-killed cadavers were partly or entirely consumed by most of the test insects, often within a few hours. Confinement with mycotic cadavers did not result in transmission of the fungus unless it had sporulated on the exterior of the cadaver. Mycotic cadavers were produced by topically dosing healthy individuals with conidia of B. bassiana Strain GHA or Metarhizium anisopliae var. acridum strain FI985 and incubating the treated insects at 26-28' C. until death. The fungus-killed cadavers were collected daily and used immediately. Uninfected cadavers were created by freezing healthy insects then ageing them at room temperature for about 6-12 hours.