Controlling insecticide resistant clones of the aphid, Myzus persicae, using the entomopathogenic fungus Akanthomyces muscarius: fitness cost of resistance under pathogen challenge

Abstract

BACKGROUND Biological control is a cornerstone of integrated pest management and could also play a key role in managing the evolution of insecticide resistance. Ecological theory predicts that the fitness cost of insecticide resistance can be increased under exposure to invertebrate natural enemies or pathogens, and can therefore increase the value of integrating biological control into pest management. In this study of the peach potato aphid, Myzus persicae, we aimed to identify whether insecticide resistance affected fitness and vulnerability of different aphid clones to the entomopathogenic fungus Akanthomyces muscarius. RESULTS Insecticide resistant clones were found to be slightly less susceptible to the pathogen than susceptible clones. However, this pattern could also be explained by the influence of length of laboratory culture, which was longer in susceptible clones and was positively correlated with susceptibility to fungi. Furthermore, resistance status did not affect aphid development time or intrinsic rate of increase of aphids. Finally, in a cage trial the application of fungus did not increase the competitive fitness of insecticide resistant clone ‘O’. CONCLUSION We found no fitness cost in reproductive rate or pathogen susceptibility associated with chemical resistance in M. persicae. In contrast, some susceptible clones, particularly those subject to decades of laboratory rearing, showed enhanced susceptibility to a fungal pathogen, but not reduced reproductive fitness, an observation consistent with down‐regulation of costly immune functions in culture. Overall, fungal pathogen control is compatible with insecticides and should not increase the selection pressure for resistance of M. persicae to chemical insecticides.

Fungicides have transgenerational effects on Rhopalosiphum padi but not their endosymbionts

“…[7][8][9][10][11] To mitigate the risk of R. padi evolving further resistance, a diverse suite of R. padi management approaches is required to ensure farmers rely less on commonly used insecticides and reduce selection for resistance. 12,13 As in other aphid species, R. padi fitness (i.e., survival and reproduction) and pest ecology (e.g., the variety of plants they attack) depend upon the endosymbionts they harbor. 14,15 Endosymbionts are heritable bacteria or fungi that are hosted within aphids and many other taxonomic groups (e.g., flies, thrips, lepidoptera, mites, mollusks), which can dramatically modify several host phenotypes.…”

“…In turn, R. padi populations, as in the case of many pest species, have encountered intense selection that has favored the rapid evolution of resistance to insecticides 7–11 . To mitigate the risk of R. padi evolving further resistance, a diverse suite of R. padi management approaches is required to ensure farmers rely less on commonly used insecticides and reduce selection for resistance 12,13 …”

Evidence of enhanced reproductive performance and lack‐of‐fitness costs among soybean aphids, Aphis glycines, with varying levels of pyrethroid resistance

“…This may not be surprising given that fitness varies across different unrelated genetic backgrounds, 86–88 or lines with other mechanisms or vgsc mutations conferring pyrethroid resistance 89 . Likewise, no clear association of reduced reproductive performance and insecticide resistance were shown among clones of M. persicae 90‐92 . Regardless, our data indicate a significant reproductive advantage of one isofemale line carrying heterozygous super ‐ kdr M918I + L1014F genotype (Table 3), observed in pre‐oviposition period and increased overall fecundity.…”

“…[90][91][92] Regardless, our data indicate a significant reproductive advantage of one isofemale line carrying heterozygous super-kdr M918I + L1014F genotype (Table 3), observed in pre-oviposition period and increased overall fecundity. Likewise, a significant higher reproductive performance was observed in insecticide-resistant M. persicae 90 and Sitobion avenae. 93 Although our results suggest that mutations in the vgsc genes of A. glycines did not confer a fitness cost, limitations within this study prevented us from reaching this conclusion.…”

Malathion-resistant Tribolium castaneum has enhanced response to oxidative stress, immunity, and fitness

“…Further work is needed to extend the implications to other strains of T. castaneum and of course other species with stable rersistance, but there has been some support from mosquitoes with another parasite type (McCarroll and Hemingway, 2002). In Myzus persicae with multiple resistance mechanisms there was no fitness cost in reproduction or susceptibility to a pathogen (Erdos et al, 2021). Thus, the pathogen control method would be compatible with insecticides, but would not be so in our case with resistant T. castaneum and P. whitei.…”