EFFECT OF HOST DENSITY ON OFFSPRING SEX-RATIOS AND BEHAVIORAL INTERACTIONS BETWEEN FEMALES IN THE PARASITOID WASP NASONIA-VITRIPENNIS (HYMENOPTERA, PTEROMALIDAE)

Pairs of females of the parasitoid wasp Nasonia vitripennis were video taped with one or two hosts. The presence of an additional host decrea sed the number of interactions between females but had no measured eff ect on the nature of the interactions, i.e., on whether the interactio n involved physical contact or occurred while one of the females was p arasitizing a host. The number of hosts did not itself affect offsprin g sex ratios but did influence which other factors were correlated wit h sex ratio. When there was one host, the proportion of sons was more positively correlated with utilization of previously drilled holes tha n with female-female interactions, whereas when there were two hosts, the reverse was true. Parasitizing an already parasitized host appeare d to affect a female's sex ratio beyond any effects of the physical pr esence of another female: When two hosts were present, the proportion of sons was greater from hosts parasitized by both females than from h osts parasitized by only one female. The observation that parasitizati ons in previously drilled holes and female-female interactions are cor related with sex ratios is consistent with previous studies; however, that these relationships are host density dependent is a new result an d remains unexplained.