Abstract
Benomyl or MBC phosphate incorporated into the meridic diet of eastern spruce budworm, Choristoneura fumiferana (Clem.), reduces the incidence of infection of adults by the microsporidian Nosema fumiferanae (Thom.). Some reduction in microsporidian levels is produced by 25 ppm benomyl; higher concentrations are more effective but even 250 ppm failed to reduce the incidence of microsporidia below 29% in a heavily infected stock. At benomyl concentrations of 75 ppm and above, budworm growth and fertility were reduced. The most notable effect of benomyl was the reduction of fertile matings and of percentage eclosion of eggs. Males were more sensitive to benomyl than females.