Local mate competition and precise sex ratios in Telenomus fariai (Hymenoptera : Scelionidae), a parasitoid of triatomine eggs

Telenomus fariai is a gregarious endoparasitoid of the eggs of several spec ies of Triatominae (Hemiptera) with a high degree of sibmating: males ferti lize their sisters inside the host egg before emergence or emerge first and copulate with their sisters as these emerge. Our results show that, when l aying alone, T. fariai behaves adaptively, minimizing offspring mortality a nd conforming to the prediction of local mate competition (LMC) theory by l aying a single male, which is sufficient to fertilize all the sisters. When more than one wasp was placed with one host, sex ratios still conformed to LMC predictions but, despite the decreasing number of eggs laid per wasp, clutch size could not be completely adjusted to avoid mortality. This is no t surprising, as superparasitism is rare in the field. Offspring production was independent of the contacts between conspecifics but was affected by t he number of mothers laying on a single host egg. The sex of the progeny wa s precisely determined: a female produced one male per clutch when laying o n both unparasitized or previously parasitized hosts. On the other hand, a mother produced less daughters when superparasitizing. Under crowded condit ions, the number of eggs laid per female wasp and per host decreased as the number of mothers increased. Developmental mortality also increased with t he number of ir: fariai eggs per host, determining a maximum of approximate ly 14 emerged adults. Host resources per individual affected male and femal e adult size with similar intensity, and male adult mortality was slightly higher than that for females. These results, and previous findings, suggest that T. fariai attains Hamiltonian sex ratios by laying one male and a var iable number of females, and that the detection of chemical marks left by c onspecifics provides information on the number of foundresses sharing a pat ch.