Phosphine resistance in Sitophilus oryzae (L.) from eastern Australia: Inheritance, fitness and prevalence

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

“…Overall, however, the current results show that weak resistance is common in eastern Australia while strong resistance is rare. These results are similar to those recently published for the rice weevil, Sitophilus oryzae (L.), in eastern Australia (Daglish et al, 2014). Populations of S. oryzae with weak resistance were common but the frequency of phenotypically resistant individuals within populations was typically low.…”

“…The finding of no evidence of a fitness cost associated with weak resistance in T. castaneum is similar to that obtained in a recently published study on T. castaneum using the population cage approach and phenotype testing of a single population derived by a susceptible  weakly resistant cross (Jagadeesan et al, 2012), although subsequent molecular screening of sub-samples from that study showed a slight increase in the frequency of the rph1 resistance allele over time (Jagadeesan et al, 2013). The finding of no apparent fitness cost is also similar to a recently published study on S. oryzae using the population cage approach and phenotype testing of replicated populations derived from a susceptible and weakly resistant cross (Daglish et al, 2014). On the basis of published population cage studies and the one reported in this paper, it appears that there is little or no cost or benefit associated with weak phosphine resistance.…”

“…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.…”

Genetic characterization of field-evolved resistance to phosphine in the rusty grain beetle, Cryptolestes ferrugineus (Laemophloeidae: Coleoptera)

“…In homozygous isolation, each of these genes confers only weak resistance, ~4-30×, however, when they occur together in one individual, they interact synergistically and provide a very high level of resistance, up to ~600× [6][7][8]. Genes rph1 and rph2 are expressed as incompletely recessive in all the three species, irrespective of the phenotypes, and are not sex linked [6][7][8][9]. This genetic information together with well-established efficacy data against R.…”

“…The possibility of an additional dominant factor contributing to phosphine resistance was also observed in R. dominica [6] in heterozygotes from a cross of Weak-R x Strong-R. However, this effect was not observed either in T. castaneum [7] or S. oryzae [8,9], indicating the existence of differences between species in background genetic factors contributing to the expression of the resistance phenotype. Similarly, higher survival of F 1 (R x S) hybrids than expected in permethrin-resistant tobacco budworm, Heliothis virescens (F.), was attributed to the presence of minor dominant factors in addition to a major recessive factor, regulating the overall expression of resistance phenotype in this pest [31].…”