The rph2 Gene Is Responsible for High Level Resistance to Phosphine in Independent Field Strains of Rhyzopertha dominica

Yosep S Mau,Gregory J Daglish,Manoj K Nayak,Paul R Ebert,Patrick J Collins,Christian Schönbach

doi:10.1371/journal.pone.0034027

Abstract

The lesser grain borer Rhyzopertha dominica (F.) is one of the most destructive insect pests of stored grain. This pest has been controlled successfully by fumigation with phosphine for the last several decades, though strong resistance to phosphine in many countries has raised concern about the long term usefulness of this control method. Previous genetic analysis of strongly resistant (SR) R. dominica from three widely geographically dispersed regions of Australia, Queensland (SRQLD), New South Wales (SRNSW) and South Australia (SRSA), revealed a resistance allele in the rph1 gene in all three strains. The present study confirms that the rph1 gene contributes to resistance in a fourth strongly resistant strain, SR2QLD, also from Queensland. The previously described rph2 gene, which interacts synergistically with rph1 gene, confers strong resistance on SRQLD and SRNSW. We now provide strong circumstantial evidence that weak alleles of rph2, together with rph1, contribute to the strong resistance phenotypes of SRSA and SR2QLD. To test the notion that rph1 and rph2 are solely responsible for the strong resistance phenotype of all resistant R. dominica, we created a strain derived by hybridising the four strongly resistant lines. Following repeated selection for survival at extreme rates of phosphine exposure, we found only slightly enhanced resistance. This suggests that a single sequence of genetic changes was responsible for the development of resistance in these insects.

Highlights

Phosphine (PH3) is the most economically viable fumigant for the control of insect pests of stored grain, making it the major method of control worldwide [1,2,3,4,5]
Previous work suggested that evolution of resistance was constrained in the order in which genetic changes could occur [19]; that two genes contributed to resistance in multiple instances and that at least one resistance gene was common to multiple highly resistant strains [20]
The rph1 gene contributes to resistance in SR2QLD The second strongly resistant strain from Queensland, SR2QLD, is distinct from SRQLD that was analysed previously [18] (Schlipalius et al 2002)

Summary

Introduction

Phosphine (PH3) is the most economically viable fumigant for the control of insect pests of stored grain, making it the major method of control worldwide [1,2,3,4,5]. Widespread high level resistance to phosphine in recent years threatens the continued use of this chemical [7]. The lesser grain borer Rhyzopertha dominica (F.) is one of the most destructive pests of stored grains and high levels of phosphine resistance have been reported from several countries, such as Bangladesh [8], Brazil [9,10], India [11,12], China [13,14], and the Philippines [15]. Emergence of strongly phosphine resistant strains of R. dominica was recently reported in New South Wales [17] and in South Australia (Wallbank, personal communication)

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Conclusion