The Fungous Disease Caused by Entomophthora grylli Fres., and its Effects on Grasshopper Populations in Saskatchewan in 1963

Abstract

A widespread epizootic of the fungous disease caused by Entomophthora grylliFres. occurred among grasshoppers in Saskatchewan in 1963. Camnula pellucida(Scudder), in particular, suffered high mortality and was nearly wiped out in those areas of central and east-central Saskatchewan where heavy infestations had been present. Weather was warm and humid during the outbreak with above normal rainfall in the seriously affected areas.

Field-cage studies showed that proper timing of rainfall was essential for continuation and spread of the disease. Rainfall shortly after death of the diseased grasshopper induced profuse growth of conidiophores along with intense discharge of conidia. When death occurred during hot, dry weather, no sporulation was noted and the insects rapidly dried up. The interval from infection to death of the grasshopper was about 13 days.

The fungous disease also developed in natural field populations of Melanoplus bivittatusSay, but none was noted in field cages where this grasshopper was being reared alongside of or together with C. pellucidathat were dying continuously from the disease; this suggests that different strains of E. grylliwere involved.