Comparative efficacy of Bt maize events MON810 and Bt11 against Sesamia calamistis (Lepidoptera: Noctuidae) in South Africa

Maize, expressing Cry1Ab insecticidal proteins produced by the bacterium Bacillus thuringiensis (Bt), was introduced for control of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) in South Africa in 1998. In the light of the reportedly lower toxicity of Bt maize to certain noctuid borers, the effect of Bt maize was evaluated on Sesamia calamistis (Hampson) (Lepidoptera: Noctuidae) in South Africa. The characteristic larval behaviour of S. calamistis may result in reduced exposure to Bt toxin and subsequent high levels of survival since larvae do not feed on plant whorls like other borer species, but penetrate stems directly from behind leaf sheaths. Growth and survival of larvae were determined in a greenhouse bioassay with two Bt maize hybrids (Monsanto event MON810 and Syngenta event Bt11) and their non-Bt, isoline hybrids. Potted plants were artificially infested with 1st instar larvae. Percentage larval survival and mean larval mass were recorded over time. Bt maize of both events was shown to be highly toxic to S. calamistis. No larvae survived longer than 9 days on plants of either of the Bt events. S. calamistis is stenophagous and occurs in mixed populations with other borer species, with which it shares several parasitoid species in Africa. The ecological impact of local extinction of S. calamistis caused by this highly effective transgenic event is therefore not expected to be great.