Host stage selection and the oviposition behavior of two parasitoids of Unaspis yanonensis was studied. In Aphytis yanonensis, the drilling per visit rate was not different among any pair of host stages: 2nd instar larvae, immature and mature adults. However, the oviposition per visit rate was higher on immature adults than on 2nd instar larvae and mature adults. Oviposition time in successful oviposition was longer on mature adults than on immature adults. Low parasitic rate of mature adults by A. yanonensis in the field is not due to the parasitoid preference for immature adults but to difficulty in oviposition on mature adults. In C. fulvus, both drilling and oviposition per visit rates were not different between immature and mature adults of the host. Thus, the vulnerable stage of U. yanonensis is more restrictive to A. yanonensis than to C. fulvus. Both parasitoids can discriminate between unparasitized hosts and those that had been parasitized by themselves.
