Characterizing mode of inheritance of permethrin resistance in field strains of rice weevil Sitophilus oryzae (Linnaeus) from Pakistan

Abstract

The development of insecticide resistance in stored insect pests is one of the major hurdles in the management of these pests. Sitophilus oryzae (L.) (Coleoptera: Curculionidae) is a major pest of stored grains in storage facilities worldwide, including in Pakistan. Field evolved resistance to permethrin has recently been reported in S. oryzae from Pakistan. Here we describe inheritance of resistance to permethrin in two field evolved permethrin-resistant strains (PR1-SO and PR2-SO) of S. oryzae. The PR1-SO and PR2-SO strains were 174.14 and 745.63 fold more resistant to permethrin, respectively, than the Lab-SO susceptible reference strain of S. oryzae. The F1 progenies resulting from the reciprocal crosses between Lab-SO and PR1-SO or PR2-SO yielded nonsignificant differences in their median lethal concentrations (LC_50s), which indicated the autosomal inheritance pattern behind the development of permethrin resistance. The degree of dominance of these crosses ranged from 0.01 to 0.60, which falls under the scale of incomplete dominance. The analysis of log-dose probit curves along with the chi-square method of monogenic inheritance analysis of selfbred (F₂) and six backcross progenies revealed that resistance to permethrin was controlled by more than one gene. In summary, resistance to permethrin in the PR1-SO and PR2-SO strains was autosomally inherited with incomplete dominance and governed by more than one gene. These data could support the development of a rational and effective resistance management strategy. The data predicted that permethrin resistance in S. oryzae could be managed following appropriate measures that help to dilute resistance alleles by allowing enhanced flow of susceptible alleles.