Submitted to: Journal of Insect Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2013
Publication Date: 11/5/2013
Citation: Jaronski, S. 2013. Mycosis inhibits cannibalism by Melanoplus sanguinipes, M. differentialis, Schistocerca americana, and Anabrus simplex. Journal of Insect Science. 13(122):1-9.
Interpretive Summary: Many grasshopper species, and also the Mormon cricket, are noted for being cannibals, attacking and feeding upon injured or dead siblings. This cannibalism has been invoked to not only promote transmission of peroral pathogens, such as viruses and Microsporida, but also insect pathogenic fungi, such as Metarhizium acridum, developed for locust control in Africa and Australia. In the case of the latter organisms this phenomenon could lead a transient mycoinsecticide to become a persistent classical biocontrol agent – a potentially undesirable event. The experiments reported here demonstrate that starved grasshoppers and Mormon crickets are generally averse to feed on kin killed by either of two insect pathogenic fungi, and that fungal transmission is very minor or nonexistent even with prolonged confinement of healthy with fungus-killed cadaver.
Technical Abstract: Cannibalism is common among the Acrididae and the Mormon cricket, Anabrus simplex, a tettigonid. 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 the insect pathogenic fungus Beauveria bassiana, I examined whether or not insects, freshly killed by B. bassiana or Metarhizium acridum, would be consumed by healthy individuals. Cannibalism was examined in a series of no-choice tests with individual insects. Test insects included healthy, adults of the four species. Individual, starved grasshoppers or Mormon crickets were confined in small cages with either a fungus-killed (but unsporulated) or uninfected cadaver. The insects were then observed periodically for the first 4 hours; after 24 hours the cadavers were scored for the degree to which they had been consumed. Very few mycotic cadavers were fed upon by the healthy insects; at most only the tarsi were eaten. All four species generally 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. Transmission of infection through contact in these tests was 0-18.9%, depending upon the fungus and insect species and, in all cases, was lower than the prevalence of cannibalism.