Effect of the host plant on the survivorship of parasitized Chilo partellus Swinhoe (Lepidoptera: Crambidae) larvae and performance of its larval parasitoid Cotesia flavipes Cameron (Hymenoptera: Braconidae)

The effect of wild and cultivated gramineous hosts on the survivorship and weight of parasitized Chilo partellus larvae and on the performance of its larval parasitoid Cotesia flavipes were studied under laboratory conditions, in two experiments. In Experiment A, weight of Ch. partellus larvae offered to Co. flavipes was allowed to vary with host plant species in order to assess both the effect of weight and quality of larvae, as affected by the host plant, on the performance of the parasitoid. In Experiment B, larvae of similar weight across host plant species were selected to enable to separate the effect of weight from that of quality of the larvae. In Experiment A, the mean weight of larvae that produced cocoons varied significantly with plant species. In both experiments, the percentage of larvae producing cocoons and mean progeny size were lower and larvae died faster on wild than cultivated host plants. Immature development time of Co. flavipes tended to be higher on wild than cultivated grasses. The proportion of female progeny was highest on maize and lowest on the two sorghum species, in Experiment A, whereas in Experiment B, the sex ratio was similar between the host plant species. Similarly, egg-load of Co. flavipes offspring was highest on maize and lowest on Napier grass in Experiment A, but it did not vary significantly between host plants in Experiment B. It is suggested that in the coastal region of Kenya, perennial wild sorghum species are vital for the survival of Co. flavipes during the dry season, when superior plant hosts such as cultivated sorghum and maize are scarce.