ABILITY OF EUPELMUS-ORIENTALIS ECTOPARASITOID LARVAE TO DEVELOP ON AN UNPARALYSED HOST IN THE ABSENCE OF FEMALE STINGING BEHAVIOR

The reproductive behaviour exhibited by the females of the solitary ectoparasitoid Eupelmus orientalis on Callosobruchus maculatus host larvae is characterized by the fact that almost all the egg depositions are associated with a stinging behaviour, even though the eggs are laid externally on the hosts, The venomous sting induces permanent paralysis and developmental arrest in the host larvae, The poison gland was shown to be the only source of venom material in the females of this species, Injections of diluted venom into C. maculatus larvae were found to be sufficient to induce these alterations in the host's physiology for concentrations of 0.2 and 0.1 wasp equivalent per host. In order to study the influence of this stinging behaviour on the successful parasitization of a host, E. orientalis eggs were transferred onto C. maculatus larvae that had not been previously stung by an E. orientalis female. The comparison of their development with that of eggs placed on stung hosts revealed that the secretions injected by an ovipositing female only contributed to a reduction in egg mortality, and did not seem to have any further influence either on the survival of the developing parasitoids once they had hatched, or on their mean developmental time. This result can be attributed to the effects that E. orientalis Ist instar larvae had on their hosts, First instars proved able to paralyse C. maculatus hosts through a biting behaviour, in which the injection of secretions from the salivary glands is likely to be implicated, Newly hatched larvae, biting host larvae for just a few minutes, were able to induce a delayed paralysis and a developmental arrest in the majority of the bitten hosts. This indicates that the larval secretions involved can be presumed to be very powerful and efficient. In contrast, later larval stages of E. orientalis were subjected to high mortality rates when confronted with non-stung hosts. This higher mortality could possibly be due to behavioural changes rather than to any difference in the physiological abilities of the parasitoid larvae.