Effect of phosphine resistance genes on developmental stages of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae)

Phosphine gas (PH3) has been used world-wide for more than four decades as an ideal fumigant for disinfestations of stored grains and other commodities. Continuous use of phosphine for controlling insect pests of stored grain and application of inadequate dose concentrations has led to the development of insects resistant to this fumigant. One major pest species in particular has developed high-level resistance against phosphine, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae). Infested grains are likely to contain eggs, larvae and pupae and there is little information on how the resistance phenotype is expressed in these stages. The present study determined the degree of dominance of resistance phenotype in different developmental stages of R. dominica. The effect of genes responsible for phosphine resistance was observed on the developmental stages of R. dominica for strong resistant (QRD 569), sensitive (QRD 14) and reciprocal F1 strains. Resistance was constitutively expressed in all the developmental stages in the homozygous resistant strain. During the egg stage a maternally inherited resistance factor was observed, although this effect was transient and incompletely recessive in later stages. Among all the stages, egg and pupal stages were the most tolerant. Resistance was incompletely recessive in one, two and three weeks old larvae while it was completely recessive in egg and pupal stage, respectively. The resistance factor of QRD 569 eggs is ~151.9 times, one week old larvae is ~ 69.8 times, two weeks old larvae is ~ 91.28 times, three weeks old larvae is ~ 66.05 times and pupal stage is ~ 103.16 times that of the sensitive reference strain adults (QRD14).