Variation in tolerance of seven species of stored product Coleoptera to methyl bromide and phosphine in strains from twenty-nine countries

Abstract

The toxicities at 25°C and 70% RH of methyl bromide at about 4 mg/litre and phosphine at about 0·24 mg/litre were determined for large populations, including all developmental stages, of a number of strains of seven species of stored product beetles from 29 countries for a range of exposure periods. The species tested were Oryzaephilus surmamensis (L.), Rhyzopertha dominica (F.), Sitophilus granarius (L.), S. oryzae (L.), S. zeamais Motsch., Tribolium castaneum (Hbst.) and T. confusum Duv. With both fumigants, some individuals of certain strains of S. oryzae and T. castaneum survived a concentration × time product twice that sufficient to kill every individual of other strains of these species, and this was also true for R. dominica with methyl bromide and T. confusum with phosphine. With methyl bromide, some individuals of six species survived the longest exposure used. For the two species of Tribolium, this was 48 h, and for the three of Sitophilus and R. dominica it was 32 h. With phosphine, individuals in many strains of S. granarius, S. oryzae and S. zeamais survived for 8 days. In several of the species, there was some correlation between the tolerances of immature stages and of adults for both fumigants. Many strains were tolerant to both fumigants.