The hop looper, Hypena humuli Harris, is an increasingly important pest of hops in the USA, particularly in Washington State (the center of the North American hop industry), where it is the most abundant lepidopteran found on this crop. High numbers of H. humuli larvae can result in extensive defoliation and damage to developing hop cones. The studies reported here were conducted to elucidate the life history and phenology of H. humuli and to test the efficacy of the bacterial insecticide Bacillus thuringiensis Berliner as a first step toward developing an integrated control strategy for this pest. Data on adult longevity and fecundity indicate that females can live for up to 39 days and can produce more than 600 eggs, while adult flight periods, egg deposition patterns and larval development suggest that there are three generations per year. Extensive overlap between successive larval generations makes it difficult to target insecticidal treatments against the smallest stages (i.e. first and second instar larvae). Nevertheless, at least one formulation of B. thuringiensis gave commercially acceptable control, even when 22% of the population consisted of fourth or fifth instar larvae.