Sex-related differences in the susceptibility of Periplaneta americana and Capnodis tenebrionis to the entomopathogenic nematode Steinernema carpocapsae

Entomopathogenic nematodes have a broad range of insect hosts, but efficacy varies depending on many factors including insect species and life stage of the host. In this study we examined the susceptibility of males and females of two insect species, the American cockroach Periplaneta americana and the flatheaded rootborer Capnodis tenebrionis to Steinernema carpocapsae by exposing adults to different concentrations. A separate study examined the routes of entry used by nematodes into males and females. Males of both species were more susceptible than females, with greater than 97% infection when a concentration of 50 IJs/cm2 was applied, whereas mortalities lower than 58% were achieved against females 14 days post-infection. Infective juveniles were detected in similar number on the surface of both sexes, but when compared among internal regions the number of nematodes was significantly higher in gonads and ducts of males than of females for P. americana (5.49 in males; 0.02 in females) and C. tenebrionis (6.88 in males; 0.00 in females).

Highlights► Steinernema carpocapsae caused higher mortality of males than females of Periplaneta americana and Capnodis tenebrionis. ► There were more nematodes found in the genitalia of the males than in the females of both species. ► The genital aperture of males was an easier portal of entry than the ovipositor of females.