Abstract: The effects on host hemocytes with the microinjection with venom from an endoparasitoid, Pteromalus puparum (Hymenoptera: Pteromalidae) into its host pupae of Pieris rapae (Lepidoptera: Pieridae) in vivo were bioassayed. The results indicated that the venom at the dose of 0.5 venom reservoir equivalent (VRE) per host pupa was enough to significantly reduce the spreading and viability of host plasmatocytes and granular cells as well as the capability of host hemocytes to encapsulate Sephadex A-50 beads at 4 h and 24 h after injection. The same physiological effects were performed by the venom at the dose ranging from 0.002 to 0.02 VRE/μL as P. rapae hemocytes were incubated with the venom of this parasitoid in vivo. The concentrations of the venom to inhibit 90% plasmatocytes and granular cells of P. rapae were 0.00076 VRE/μL and 0.00804 VRE/μL, respectively. The medium concentrations of the venom to inhibit encapsulation capacity of P. rapae hemocytes in vivo and in vitro were 0.0425 VRE/pupa and 0.00007 VRE/μL, respectively. Thus, it is clear that P. puparum venom has the physiological function of markedly inhibiting the spreading and encapsulation capacity of its host hemocytes and resulting in the death of its host hemocytes. In contrast, the venom from Nasonia vitripennis (Hymenoptera: Pteromalidae), an ectoparasitoid that does not parasitize P. rapae in nature, did not appear to have any effect on P. rapae hemocytes either in vivo or in vitro under the same conditions as that of the experiments with P. puparum venom. These findings suggest that the physiological effect of the venom from a defined species against insect target hemocytes has its host specificity.

Key words: Pteromalus puparum, Nasonia vitripennis, venom, Pieris rapae, hemocyte, spreading, viability, encapsulation