Tuesday, December 11, 2007

Mycosis inhibits grasshopper necrophagy

Stefan Jaronski, stefan.jaronski@ars.usda.gov, Agricultural Research Service, USDA, USDA ARS NPARL, 1500 N. Central Ave, Sidney, MT

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.

Species 1: Orthoptera Acrididae Melanoplus sanguinipes (migratory grasshopper)
Species 2: Orthoptera Acrididae Schistocerca americana (American grasshopper)
Species 3: Orthoptera Tettigoniidae Anabrus simplex (Mormon cricket)