Response of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) to sublethal treatments with phosphine

Abstract

When Tribolium castaneum (Herbst) was exposed to repeated treatments with a sublethal dose of phosphine (LD 10), mortality increased from about 10 to 28% when insects were retreated within 24 hr of the first application, but normal tolerance was regained when the interval between treatments was lengthened to 4 days. Using tritium-labelled phosphine, uptake of the fumigant was also found to be greatest when the interval between treatments was one day. Ninety-eight percent of the absorbed phosphine was found to accumulate in the cytosol of the insects. Oxygen consumption by insects declined after one or two treatments with phosphine, and exposure of phosphine-treated insects to pure oxygen appreciably increased their mortality. Treatments with hydrogen cyanide did not increase the susceptibility of insects to phosphine, or give any indication of potentiating action. Bovine liver catalase was inhibited non-competitively by 4.5 × 10 −3 M phosphine. Catalase extracted from untreated insects was inhibited in a slow, irreversible manner by phosphine in vitro. Insects treated with phosphine also showed reduced catalase activity, and this inhibition persisted for at least 2 weeks after exposure to the fumigant.