Studies of the potential Non-target effects of Bacillus Thuringiensis Cryiab toxin on two Stemborer Parasitoids, Cotesia Flavipes Cameron, Xanthopimpla Stemmator Thunberg, and the Butterfly Acraea Eponina Cramer

Abstract

A risk assessment on parasitoid and butterfly species was carried out as a precaution for the introduction of Bacillus thuringiensis (Bt) maize in Kenya. MON810 Bt maize variety, which expresses CrylAb toxin was considered as the model for the experiments. The studies investigated whether sub lethal concentrations of toxin that are ingested by stemborers are harmful to parasitoids; and whether densities of Bt maize pollen deposited on host plants are harmful to caterpillars. Experiments were conducted using purified CrylAb toxin and two stemborer parasitoids Cotesia jlavipes Cameron (Braconidae) and Xanthopimpla stemmator Thunberg (Ichneumonidae). The butterfly Acraea eponina Cramer (Acraeidae) was also studied. Neonates of the stemborer Chilo partellus (Swinhoe) (Crambidae) were fed on artificial diet with purified toxin at O.005/-lg/mland O.Ol/-lg/ml.Controls included normal diet and a diet with phosphate buffered saline (PBS). Larvae at the age of 22- and 25- days were parasitized by C. jlavipes. Three days old pupae were parasitized by X stemmator. Host suitability and fitness parameters-w~ere~recorded. The effects of Bt toxin on C. jlavipes included reduction in host quality, small brood sizes, longer development time and higher immature mortality, oviposition of fewer eggs, smaller egg loads, short life span, and small adult size. The toxin affected X stemmator by increasing mortality of parasitized hosts. Non-Bt maize was planted on plots while Waltheria indica L., a host plant for Acraea eponina, were planted in plastic pots. The host plants were arranged at different distances in four directions of maize plots during anthesis. Densities of maize pollen deposited on the host plant leaves were estimated using a O.25cm2 wire quadrat. The

maximum density encountered was 492 grains / em2, These densities were converted to Bt toxin concentrations basing on Cry lAb levels in MON8IO variety. Two toxin concentrations that corresponded to 246 and 492 grains / cm2 were prepared. The toxins were fed to A. eponina 2nd and 4th instar larvae on leaf discs and mortality of was recorded. The toxin caused high mortality of the larvae. The results indicate that introduction of Bt maize would harm parasitoids and butterfly larvae. An ecological imbalance may result as a consequence of these effects. More research should therefore be carried out using the actual transgenic plants prior to any introduction of Bt maize in Kenya.