Developmental studies of transgenic maize expressing Cry1Ab on the African stem borer, <i>Busseola fusca</i> ; effects on midgut cellular structure

Abstract BACKGROUND: Busseola fusca is a major pest of maize in Africa but unfortunately is difficult to control using chemical insecticides. Insect‐resistant transgenic crops may provide an alternative viable strategy to control this pest. RESULTS: Recombinant Cry1Ab (1%) reduced larval weight by 60% over the trial period, while larval weight in the control group increased by 25%; no effects on mortality were observed. Insect survival, developmental rate and pupal and adult weight were significantly reduced ( P < 0.05) on maize expressing Cry1Ab (MON810) compared with the non‐transformed parental line. These differences were more pronounced with second‐instar larvae than with third‐instar larvae. Leaf area consumed by Bacillus thuringiensis ( Bt )‐fed larvae was significantly lower (0.5 cm 2 larva −1 day −1 ) compared with the area consumed by control‐fed insects (3.3 cm 2 larva −1 day −1 ). EM studies revealed that consumption of Bt maize deleteriously affected gut integrity. Effects were observed in columnar cells of the midgut epithelium, with the cytoplasm becoming highly vacuolated; the microvilli were disorganised, the mitochondria were abnormal and there was an increase in the number of lysosomal bodies. The rough endoplasmic reticulum had also become dilated. CONCLUSION: This study confirms the potential for Bt maize, when used as part of an IPM programme, for control of B. fusca . Copyright © 2011 Society of Chemical Industry