Host-size-dependent feeding behaviour and progeny sex ratio of Anisopteromalus calandrae (Hym., Pteromalidae)

Host-size related feeding and oviposition behaviour, and allocation of prog eny sex by Anisopteromalus calandrae calandrae (Howard) were tested on Sito philus oryzae L. The parasitoid showed a host-size-dependent partition of f eeding and oviposition behaviour, preferring small hosts for feeding, but l arge hosts for oviposition. Neither the mutual interference nor the host de nsity showed any effect on the behaviour of the parasitoid. Allocation of p rogeny sex by the female parasitoid appeared to be based more likely on abs olute than on relative host size encountered. A model for the progeny sex r atio was constructed based on: (1) ovipositional preference of the parasito id on large hosts; (2) feeding preferentially on small hosts; and (3) host- size-related regulation of progeny sex ratio. The progeny sex ratio of the parasitoid predicted by the model was in close agreement with the observed value.