Impact ofBacillus popilliae, Rickettsiella popilliaeand entomopathogenic nematodes on a population of the scarabaeid,Cyclocephala hirta

Abstract

Larvae of the scarabaeid, Cyclocephala hirta, are major pests of turfgrass in California. A field test was conducted against third instars that included the following treatments: untreated control; chemical insecticide (bendiocarb); milky disease bacterium (Bacillus popilliae); and entomopathogenic nematodes (Steinernema feltiae and Heterorhabditis bacteriophora). There were no significant differences in population reduction among the treatments, but the larval population in all plots showed a dramatic decline. The C. hirta population had a natural occurrence of milky disease and blue disease caused by Rickettsiella popilliae. The prevalence of blue disease during the course of the study averaged < 10% but that of milky disease averaged about 20%. More significantly, the soil from all treatment plots when bioassayed for B. popilliae showed that 67–90% of the larvae became infected with this bacterium. None of the larvae became infected with the blue disease organism. We conclude that B. popilliae was occurring in epizootic proportions in our field tests and was a significant mortality factor in causing the decline of the C. hirta population.