| Summary: | Bt maize expressing Cry1Ab was approved for release in South Africa for control of
Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe)
(Lepidoptera: Crambidae) in 1998. During 2012, a stacked Bt maize event,
expressing Cry2Ab2 + Cry1A.105, was also approved for control of these
abovementioned pests. The aim of this study was to determine the effects of two Bt
maize events expressing Cry1Ab (MON810 and Bt11) and a Bt maize event
expressing Cry2Ab2 + Cry1A.105 (MON89034) on selected lepidopteran non-target
pest species and certain lepidopteran stem borer species in South Africa. Results
from previous studies and this study will provide information regarding efficacy of Bt
maize against pests which have not been evaluated yet. Insects with significance in
maize agro-ecosystems in South Africa as well as the rest of Africa, were prioritised
and laboratory bioassays were conducted to evaluate the effect of Bt maize against
these selected target and non-target pest species. Studies were conducted on three
stem borers C. partellus, Eldana saccharina and Sesamia calamistis and three nontarget
lepidopteran pest species Agrotis segetum, Helicoverpa armigera and
Spodoptera exempta. Results showed that MON810 maize was not effective against
A. segetum larvae feeding on maize seedlings. Differential levels of survival were
observed between two A. segetum populations on MON89034 with a population from
Polokwane showing survival on the stacked maize event. No S. exempta 1st instar
larvae survived on MON810 and MON89034 but 3rd instar larvae survived on
MON810 maize. Helicoverpa armigera larvae survived on ears of MON810 maize
plants but not on events MON89034 or Bt 11. Results further indicated that C.
partellus larvae were highly susceptible to these three Bt maize events. Larval
survival of S. calamistis was recorded for larvae feeding on MON810 and Bt11 maize
ears but not on MON89034 maize ears. Bt maize during the vegetative growth
stages therefore effectively controlled C. partellus, S. calamistis and E. saccharina
but the latter two species was not effectively controlled when feeding on ear tissue.
This study provides important information on the effects of Bt maize on the most
important non-target pest species of maize in sub-Saharan Africa. === MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
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