Assessment of the Dominance Level of the R81T Target Resistance to Two Neonicotinoid Insecticides inMyzus persicae(Hemiptera: Aphididae)

Abstract

Myzus persicae (Sulzer, 1776), a major crop pest worldwide, displays insecticide resistance to most molecules. The R81T substitution on the β1 subunit of nicotinic receptors of acetylcholine (nAChR) confers target site resistance to neonicotinoids and is widespread in aphid populations colonizing peach tree orchards in Southern Europe. But the impact of this resistance in the field, as well as ways to optimize its management, depends largely on the dominance level of the R81T mutation. In this study, we measured by in vitro assays the response of R81T mutation to two neonicotinoids (imidacloprid and thiacloprid) in 23 M. persicae clones with different resistance genotypes in order to assess the dominance status of this allele. In this study, all homozygous clones for the R81T mutation (genotype 81(TT)) showed a much higher level of resistance to both active substances than other clones. The heterozygous clones 81(RT) displayed a slightly higher level of resistance than wild homozygous, though resistance phenotypes against both neonicotinoids in these two genotypes were overlapping. A great variation of resistance level was found within these two latter clones' categories. The dominance level of insecticide resistance (DLC) strongly suggested that the mutant allele 81T is semirecessive (the wild 81R allele being rather dominant) for both insecticide molecules under test. Mean DLC values were 0.316 for imidacloprid and 0.351 for thiacloprid. Cross-resistance was shown between imidacloprid and thiacloprid. This partial recessivity is valuable information to broaden the knowledge on neonicotinoid resistance, a prerequisite for devising adapted management strategies against insecticide-resistant populations of M. persicae.

Evolution of imidacloprid resistance in Myzus persicae in Greece and susceptibility data for spirotetramat

“…In a recent study all homozygous clones of persicae for the R81T mutation showed a higher level of resistance to both imidacloprid and thiacloprid than heterozygous and the wild homozygous clones. The authors reported also that the mutant allele is semi‐recessive for both insecticides tested …”

An update of the Worldwide Integrated Assessment (WIA) on systemic insecticides. Part 3: alternatives to systemic insecticides

“…In Italy, 65% of the aphids studied by Panini et al (2014) had the neonicotinoid-specific R81T mutation while a few genotypes also revealed the involvement of P450-based metabolic resistance processes (Panini et al 2014). The dominance level of insecticide resistance in this species suggests that the mutant allele 81T is semi-recessive, with the wild 81R allele being rather dominant (Mottet et al 2016). The neonicotinoid sulfoxaflor, a newly developed agonist of the nicotinic receptors (Giorio et al 2017), appears to behave in a similar way in resistant strains of the same aphid M. persicae (Cutler et al 2013), although some authors say is not affected by this mutation (Wang et al 2016b).…”

Discovery of metabolic resistance to neonicotinoids in green peach aphids (Myzus persicae) in Australia

“…Target-site resistance (conferred through the R81T mutation) has only been found in connected holocyclic populations in southern Europe, and is far less common than low-level neonicotinoid metabolic resistance. 11 Target-site resistance is semi-recessive 31 and less likely to evolve where M. persicae populations are predominantly anholocyclic (asexual), which is generally the case in Australia. 32 In the wake of the widespread high-level resistance to pyrethroids and carbamates in aphid populations, the use of neonicotinoids to control M. persicae in Australia has rapidly increased in the last 5-10 years.…”