Milky Diseases of European Chafer Larvae

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Abstract
The susceptibility of larvae of Amphimallon maialis to the milky disease organisms Bacillus popilliae and lentimorbus was demonstrated. Spore injection and ingestion tests indicated that the regular type A strain of popilliae is as pathogenic to European chafer larvae as it is to larvae of the Japnaese beetle, Popillia japonica. The regular type B strain of lentimorbus exhibited low pathogenecity to chafer larvae by both methods of infection. Type B Amphimallon and the type A strains were highly pathogenic by both methods, producing 95 to 100% infection 2 weeks after being injected with a million spores per larvae and incubated at 80[degree]F. Rate of infection was directly related to incubation temp. with disease starting in 6 weeks at 60[degree]F, in 2 weeks at 70[degree], and in 1 week at 80 and 90*. Spore ingestion tests were performed by incubating larvae in soil inoculated with 0.25, 0.5, 1, and 2 billion spores per kilogram of soil with type B Amphimallon. regular type A, and type A anxia strains. There was no difference in incidence of disease among the strains nor was there any correlation between incidence of disease and concentration of spores with 31 to 70% of the larvae becoming infected after 4 weeks incubation at 75 to 80[degree] F. Diseased larvae have been recovered from 15 of the 17 plots where milky disease spores have been distributed since 1945. Three other areas were discovered where milky disease has occurred naturally and infected larvae were recovered consistently. The tentatively named type B Amphimallon strain was the causal organism in 2 of these areas where 80 and 95% of the larvae were found diseased in early June 1951. Larvae infected with a type A strain were found in the 3rd area. Disease incidence was high in a plot treated with type A and type A anxia strain of popilliae in 1945. When all factors are considered, there is promise of obtaining economic control of European chafer larvae through the use of milky disease.

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