Functional response of six indigenous trichogrammatid egg parasitoids (Hymenoptera: Trichogrammatidae) in Kenya: influence of temperature and relative humidity

Laboratory tests were conducted to evaluate the functional responses of six species/strains of native Kenyan trichogrammatids using the factitious pyralid host, Corcyra cephalonica, under different temperature and relative humidity regimes. The objective was to identify promising species/strains for controlling the noctuid Helicoverpa armigera, a serious pest of vegetables in Kenya. The six species/strains of Trichogramma and Trichogrammatoidea represented collections from low (<700 m), mid (between 700 and 1200 m) and high (>1200 m) altitude locations. They were compared for parasitisation rates at six temperatures (10, 15, 20, 25, 30 and 35 °C) and two relative humidity levels (40-50% and 70-80%), at five host egg densities (6, 12, 18, 24, and 30 per adult female). Temperature affected parasitisation rates while relative humidity did not. Trichogrammatoidea sp. nr. lutea from a high altitude location, Trichogramma sp. nr. mwanzai from a low altitude site, Trichogramma sp. nr. mwanzai from a mid-altitude location and Trichogrammatoidea. sp. nr. lutea from medium altitude showed higher parasitism across a wider temperature range compared to the other strains. There was no relationship between source (altitude, climate) and performance of the strains at the temperatures and host densities tested. The implications of these results for deploying the strains for inundative biocontrol of H. armigera in agroecosystems in Kenya are discussed.