Mode of inheritance of field-evolved resistance to pirimiphos-methyl in Sitophilus oryzae (Linnaeus) (Coleoptera: Curculionidae)

Abstract

Sitophilus oryzae is an economic pest of stored grain worldwide with the ability to transmit mycotoxigenic fungi in the infested commodities. Recently this pest has shown field-evolved resistance to pirimiphos-methyl in Pakistan. Understanding mode of inheritance of insecticide resistance is of prime importance in order to implement a successful resistance management program. Here, we studied the mode of inheritance of resistance to pirimiphos-methyl in two field-evolved resistant strains (LR-SO and HR-SO) of S. oryzae. LR-SO and HR-SO strains exhibited 31.05 and 219.18 fold resistance to pirimiphos-methyl compared with an insecticide susceptible reference strain (Lab-SO). Reciprocal progenies revealed an indistinguishable difference in their response (LC50s) to pirimiphos-methyl pointing out the absence of maternal effects or sex-linkage and autosomal inheritance pattern. The degree of dominance values for all the reciprocal and pooled progenies ranged from −0.47 to −0.78 suggesting that resistance to pirimiphos-methyl was expressed as an incompletely recessive trait. Chi-square and log-dose probit line analyses of self-bred and backcross progenies exhibited significant variation between the expected and observed mortality, which suggest that resistance was governed by more than one gene. In conclusion, field-evolved resistance to pirimiphos-methyl in S. oryzae was autosomal, incompletely recessive, and multigenic. Our results provide basic information about the nature of resistance to pirimiphos-methyl that will be helpful to formulate successful management strategies for controlling S. oryzae and to alleviate the allied threats to environment and human health.