Gene interactions constrain the course of evolution of phosphine resistance in the lesser grain borer, Rhyzopertha dominica

Abstract

Phosphine, a widely used fumigant for the protection of stored grain from insect pests, kills organisms indirectly by inducing oxidative stress. High levels of heritable resistance to phosphine in the insect pest of stored grain, Rhyzopertha dominica have been detected in Asia, Australia and South America. In order to understand the evolution of phosphine resistance and to isolate the responsible genes, we have undertaken genetic linkage analysis of fully sensitive (QRD14), moderately resistant (QRD369) and highly resistant (QRD569) strains of R. dominica collected in Australia. We previously determined that two loci, rph1 and rph2, confer high-level resistance on strain QRD569, which was collected in 1997. We have now confirmed that rph1 is responsible for the moderate resistance of strain QRD369, which was collected in 1990, and is shared with a highly resistant strain from the same geographical region, QRD569. In contrast, rph2 by itself confers only very weak resistance, either as a heterozygote or as a homozygote and was not discovered in the field until weak resistance (probably due to rph1) had become ubiquitous. Thus, high-level resistance against phosphine has evolved via stepwise acquisition of resistance alleles, first at rph1 and thereafter at rph2. The semi-dominance of rph2 together with the synergistic interaction between rph1 and rph2 would have led to rapid selection for homozygosity. A lack of visible fitness cost associated with alleles at either locus suggests that the resistance phenotype will persist in the field.

Genetics of phosphine resistance in the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

“…However, this study was limited to the responses of the susceptible, resistant strains and non-reciprocal F 1 hybrids between the susceptible and resistant strains. Genetic mechanism of phosphine resistance in S. oryzae is very similar to that previously reported for other stored grain pests: R. dominica (Ansell et al, 1990, Schlipalius et al, 2002, Schlipalius et al, 2008, Mau et al, 2012b, Mau et al, 2012a, T. castaneum (Bengston et al, 1999, Jagadeesan et al, 2012 and Cryptolestes ferrugineus .…”

“…Phosphine resistance has been found to be conferred by two genes that act in synergy in both R. dominica , Schlipalius et al, 2002, Schlipalius et al, 2008, Mau et al, 2012a, Mau et al, 2012b and T. castaneum , Jagadeesan et al, 2013.…”

“…dominica , Schlipalius et al, 2008 (Pimentel et al, 2007, Sousa et al, 2009). These studies indicated that a higher level of resistance to phosphine was accompanied by lower rates of development and respiration.…”

“…Each gene on its own causes only weak resistance, about 50x and 12.5x in synergistic interaction between the two genes results in resistance of 250x and 431x in the respective species (Schlipalius et al, 2002, Jagadeesan et al, 2012. The identity of rph1/tc_rph1 has until now remained unknown, although candidates for this gene have been isolated on chromosome 6 of R. dominica and on chromosome 8 of T. castaneum (Schlipalius et al, 2008, Jagadeesan et al, 2013. However, determined that the rph2/tc-rph2 gene encodes the metabolic enzyme dihydrolipoamide dehydrogenase (DLD) in both species.…”

Prevalence and potential fitness cost of weak phosphine resistance in Tribolium castaneum (Herbst) in eastern Australia

“…Therefore, knowing if there are fitness costs associated with phosphine resistance could help in resistance management. Fitness has been investigated in a range of insect pests of stored grain using different experimental approaches (Pimentel et al, 2007;Schlipalius et al, 2008;Sousa et al, 2009;Pimentel et al, 2011;Jagadeesan et al, 2012Jagadeesan et al, , 2013Daglish et al, 2014). Some studies have used the population cage approach in which susceptible and resistant strains are hybridized and the resulting populations are reared in the absence of phosphine selection.…”