Monitoring secondary outbreaks of the African armyworm in Kenya using pheromone traps for timing of Bacillus thuringiensis application

Abstract

The arrival of male moths of the African armyworm, Spodoptera exempta Walker, was monitored in Kenya using pheromone traps. Peak trap counts were obtained during March 1989, and were concentrated in three out of nine traps distributed in small farms in an area of 625 km 2 in Lambwe valley, South Nyanza. Large numbers of egg masses were located on dry stalks of last year's cereals in wild cynodon grass situated around the crop fields. Smaller numbers were found on the underside of the first emerged leaves of maize seedlings. Few egg masses were found on millet crops. Application of a Bacillus thuringiensis preparation at a concentration of only 0.2% (w/v, which is 1 10 of the ordinary concentration used) based on a new isolate obtained from a Kenyan soil sample, directed against neonate S. exempta larvae, reduced larval population by 95%.