Phosphine fumigation and the ecology of the rust red flour beetle, Tribolium castaneum: the effects of phosphine resistance genes and sublethal exposure

Abstract

Post-harvest losses of stored products are fairly common despite widespread use of chemical treatments to control pests. Phosphine has been used to control insect pests of various stored products in many parts of the world for at least half a century. However, extensive use of this fumigant has contributed to the development of resistance in several species of stored-product insects globally. Expression of phosphine resistance has been linked to mutations in two autosomal genes that contribute to enzymatic changes involved in basic metabolic pathways and impose metabolic stress, which, in turn, affects energy demanding behaviours.Insecticide resistance is generally accompanied by a variety of physiological changes that may have negative influences on the organisms in the absence of the insecticide selective agent. The present investigations were undertaken to determine the effects of phosphine resistance genes on the fitness of Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) beetles, serious pests of stored products worldwide. I designed laboratory assays to examine if the phosphine resistance genes affect activities that depend on a reliable energy source, including particular aspects of the beetle's walking and flight activities. I measured walking and flight parameters of four T. castaneum genotypes: 1) a field-derived population, 2) a laboratory cultured, phosphine-susceptible reference strain, 3) a laboratory cultured, phosphine-resistant reference strain, and 4) a resistant introgressed strain that is almost identical genetically to the susceptible population. The temporal pattern of flight was identical across all populations, but resistant reference beetles took flight significantly less, walked more slowly, and located resources less successfully than did susceptible reference beetles. These results suggest an association between phosphine resistance and the reduced ability of these resistant reference individuals, and they suggest that these influences are likely to have an impact on the spread of the resistance genes spatially.I also conducted a series of experiments in a wind tunnel to determine whether intrinsic variables (mating status) and environmental variables (presence or absence of lures, type of lures) further influence the movement abilities of the phosphine resistant beetles.Significantly fewer flight initiations and less success at locating pheromone and food lures by resistant reference beetles were observed compared with those of the susceptible reference ones (although their odour preferences were similar). Pheromone and cotton seeds appeared to be stronger inducements for location of the lure compared with wheat flour. A clear iii preference for the pheromone lure was evident in unmated resistant beetles compared to mated resistant beetles. However, this pattern was not repeated with flying resistant beetles, as no significant difference was observed in flight response of mated and unmated resistant beetles towards the pheromone lure. Mating status had statistically sim...