Control of Herpomyces spp. (Ascomycetes: Laboulbeniales) infection in the wood cockroach, Parcoblatta lata (Dictyoptera: Blattodea: Blattellidae), with benomyl.

The Laboulbeniales are a group of obligate parasitic ascomycete fungi that grow on the cuticle of arthropods. Most of the over 2000 species have been described from adult Coleoptera and Diptera, but the genus Herpomyces is found exclusively on cockroaches (Guthrie and Tindall, 1968; Richards and Smith, 1956; Roth and Willis, 1960). The haustoria of Herpomyces penetrate the cuticle of the cockroach, entering the underlying cells and causing a dermatitis with characteristic histopathology; however, there is no evidence of pathogenicity (Richards and Smith, 1956). Nymphs and adults of wood cockroaches, Parcoblatta lata (Brunner), developed a severe Herpomyces spp. infection in our laboratory colony. The thalli were visible with the naked eye and grew in large numbers on the antennae, palpi, and cerci and in lower numbers on the legs, head, pronotum, thorax, and abdomen. The fungus did not cause high mortality, but many individuals had broken antennae, palpi, and cerci and some exhibited unusual color patches on their cuticle. Heavily infected individuals moved slowly and became moribund indicating, in contrast to the study of Richards and Smith (1956), a pathogenic effect of Herpomyces spp. on the cockroach colony. The aim of this study was to test the efficacy of the fungicide benomyl [methyl 1-(butylcarbamoyl)benzimidazol-2yl-carbamate] as a treatment against Herpomyces spp. infecting P. lata. We chose this chemical because it exhibits relatively low toxicity to mammals (EPA class IV—practically nontoxic), it is in widespread use in agriculture, and it has been reported to be effective against microbial infections (microsporidia) in insects (Brooks et al., 1978). We tested the antifungal properties of several concentrations of benomyl in different formulations, as well as the toxicity of benomyl to healthy cockroaches. Nymphs were reared in clear-plastic containers with an egg carton shelter. Drinking water was supplied in glass tubes with a cotton stopper; diet consisted of dog chow (Purina Dog Chow Nutritional Excellence Formula, Purina Mills, St. Louis, Missouri) provided ad libitum. The rearing room was maintained at 27 1 C