Screening for development of resistance by the spotted stem borer, Chilo Partellus Swinhoe (Lepidoptera: Pyralidae) to Bt-maize delta-endotoxins

Abstract

Stem borers are one of the major limiting factors to maize (Zea mays L.) production in the world. In Kenya the damage caused by stem borers leads to 13.5% yield loss estimated to be 400,000 MT of maize annually. The spotted stem borer Chilo partellus, Swinhoe is one of the major species of stem borers in Kenya. Bt-maize has been proved to reduce losses due to stem borer damage. Development of insect resistance among stem borers is one of the concerns of using Bt-maize. A study was conducted at the KARI Biosafety Greenhouse level 11, to determine the development of stemborer resistance to two Bt cry proteins for over four generation cycles of selection. The cry proteins were cry1Ab and cry1Ba expressed from Bt-maize event 223 carrying Bt cry1Ab gene and event 10 carrying Bt cry1Ba gene. Three hundred neonates of C. partellus were infested into maize leaves and allowed to feed for 24 hours. The surviving larvae were reared in artificial diet up to adult stage. The performance of each protein was assessed over time by estimation of the number of surviving larvae over each generation. The results showed significantly fewer surviving larvae from the Bt-maize events compared to the non-transgenic CML 216 control. The means were70.4 for CML216, 13.3 and 7.4 for Event 10 and 223 respectively. There were highly significant differences between the control and the two Bt-maize events. The two Bt-maize events were statistically not different in controlling the pest over the studied generations, indicating that there was no development of resistance to cry proteins in the tested C.partellus colony.