Optimum host age and stage for development of Anisopteromalus calandrae (Hymenoptera : Pteromalidae) reared on the rice weevil (Coleoptera : Curculionidae) in wheat

Suitability of different ages of the rice weevil Sitophilus oryzae (L.) in wheat for the development of the parasitoid wasp Anisopteromalus calandrae (Howard) was examined. Infested wheat kernels were isolated using x-ray tec hniques. Groups of five infested kernels of wheat were exposed to individua l A. calandrae females 16-18, 18-20, or 20-22 days following rice weevil ov iposition, and kernels were dissected at 2-day intervals during the next 4- 14 days. The oldest of these 3 rice weevil age groups was predominantly ten eral pupae, and there was a significant difference in the tunnel widths bet ween the younger 2 larval age groups. In this no-choice test, older rice we evils were paralyzed and parasitized more often than younger ones. All A. c alandrae paralyzed and parasitized at least some hosts, suggesting that var iation in behavior among females was not the primary factor in the differen ce between the rate at which these three age groups were parasitized. Some previous studies have found that A. calandrae parasitized larvae more often than pupae. These observations suggest that the most frequently parasitize d stage in a continuous population at low density is not necessarily the op timum stage for supporting parasitoid production in high density infestatio ns.