Selection for resistance to phosphine or methyl bromide in Tribolium castaneum (Coleoptera: Tenebrionidae)

Abstract

AbstractThe build-up of resistance to phosphine and methyl bromide in the developmental stages of Tribolium castaneum (Herbst) after six selections in successive generations was investigated in the laboratory at 25 ± 1°C. Responses of the life stages of the fumigant-selected insects were compared with those of untreated controls with a 24 h exposure and mortality was assessed after 14 days. Phosphine induced the development of resistance irrespective of the life stage chosen for selection. The onset of phosphine resistance was noted after the first selection but the levels of resistance attained in the different stages varied depending on the stage tested, and in each case the degree of expression was different in the four stages of T. castaneum. After selection, phosphine resistance was highest in the pupae followed by eggs, adults and larvae. Resistance to methyl bromide in the methyl bromide treated insects increased only slightly (less than × 2.0). Adults derived from egg, larva, pupa and adult-selected methyl bromide lines showed cross-resistance to phosphine (× 1.8 to 11.5 at LD95), while cross-resistance of adults to methyl bromide was noted only in adult-selected phosphine-resistant insects (× 1.5 at LD95).