The gene Cry1Ab derived from the entomopathogenic bacterium Bacillus thuringiensis is currently deployed commercially for control of Pyralid stem borers of maize in the USA. In this study various events of the Bt-gene were evaluated in maize inbred lines and hybrids for leaf feeding resistance to the local stem borers Busseola fusca and Chilo partellus, using artificially infested plants under greenhouse and field conditions. The event MON810 proved superior to all other events tested. C. partellus was more susceptible than B. fusca to the same events. Significant maternal effects were observed. Efficacy was not negatively affected by variations in the time of infestation. Hybrids did not respond equally to transformation with the same event, which was attributed to differences in adaptation to adverse environmental conditions.

Evaluation of Bt.-Transgenic maize for resistance to the stem borers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) in South Africa

The comparative influence of Busseola fusca (Fuller) and Chilo partellus (Swinhoe), both as separate and mixed populations, on growth and yield of grain sorghum was investigated in a field experiment, using an artificial infestation in cages. C. partellus was more injurious than B. fusca as indicated by whorl damage, stalk injury and yield loss. In the case of mixed populations, dispersion of larvae and damage were independent of B. fusca numbers. A regression equation, Logit Y = 0.24 + 2.06 logit x, relating visible plant damage to yield loss was determined. Control strategies in the case of mixed stem borer populations should be directed against C. partellus.

Comparative injuriousness of Busseola fusca (Lepidoptera: Noctuidae) and Chilo partellus (Lepidoptera: Pyralidae) on grain sorghum

During the 1998/99 season considerable stem damage was caused by B. fusca in commercial plantings of Bt-maize, without leaf feeding damage during the vegetative stages of plant development. This indicated that larvae may survive on some less toxic plant part subsequent to the vegetative stages. In this study a laboratory bioassay was conducted, using forced feeding of larvae on various parts of Bt-maize. In a field trial larval survival and plant damage were recorded following artificial infestation of Bt- plants one week before, and one and three weeks after tasseling. It appears that there is a window of approximately 14 days immediately preceding tasseling, in which relatively late infestations may result in increased larval survival, due to the availability of silks as a primary food source to neonate larvae. The Bt-protein concentration in silks appears to be low enough to allow survival of some larvae until completion of the first two instars, after which the ear tips and husk leaves serve as import...

Larval mortality and injury patterns of the African stalk borer, Busseola fusca (Fuller) on various plant parts of Bt-transgenic maize

Maize plants were subjected to controlled infestations of Busseola fusca (Fuller). Variations in inter- and intra- row spacing had a pronounced influence on the damage caused by the pest. Both the rates of dispersal and the survival of the larvae were enhanced by increased plant population, with a concomitant increase in the number of damaged plants. High yielding, longer growing season maize cultivars suffered more severe yield losses under identical circumstances of infestation than shorter season cultivars of moderate yield potential.

Plant population and cultivar effects on yield losses caused by the maize stalk borer, Busseola fusca (Lepidoptera: Noctuidae)

The use of Bt maize could directly or indirectly affect non-target organisms. Assessment of the impacts of Bt crops is hampered by the lack of even the most basic checklist of the species present in most systems. In South Africa the maize agroecosystem is of particular interest because of the large area planted with Bt maize (Event MON810) for the control of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) populations. The aims of this study were to determine the diversity of Lepidoptera species that feed on or are closely associated with maize, and to assess the possible effects of Bt maize on the incidence of Lepidoptera damage under field conditions. Field surveys were conducted at 24 sites during the 2004/2005 and 2005/2006 cropping seasons. Fifteen species of Lepidoptera were recorded on maize. Six of these species were recorded to feed on Bt maize. Limited information is available on host plants and biology of some of these species. The...

Diversity and comparative phenology of Lepidoptera on Bt and non-Bt maize in South Africa

Maize plants were artificially infested with egg batches of Busseola fusca at different times after crop emergence. Regression equations of yield loss on percentage plants with eggs varied over different seasons, which was attributed to hybrid differences and variation in climate.

J.H. Van Rensburg

Papers

Response of maize to levels and times of infestation by Busseola fusca (Fuller) (Lepidoptera: Noctuidae)