Resistenze “target-site” in popolazioni italiane dell’afide verde del pesco (Myzus persicae)

[Autom. eng. transl.] Introduction Over the years, the green peach aphid has developed several mechanisms of insecticide resistance, as evidenced by the numerous reports of lack of efficacy of treatments (Whalon et al., 2008). In Italy, the high level of resistance to many classes of insecticides such as phosphoric esters, carbamates and pyrethroids has been documented for a long time (Mazzoni and Cravedi, 2002; Cravedi et al., 2009). Since 2010, even for neonicotinoids, which still represent one of the main tools for the fight against this insect, serious resistance problems have been highlighted in Spain, France and Italy (Slater et al., 2012; Panini et al., 2013). The present study updates the knowledge on the diffusion of mutations linked to target-site resistance to neonicotinoids, pyrethroids and carbamates in the Italian populations of M. persicae. Results The survey was conducted on 75 populations of M. persicae collected in 2012 (n = 50) and in 2013 (n = 25) in various Italian areas, both from peach (n = 69), and from some secondary hosts ( pepper: n = 3; eggplant: n = 2; tobacco: n = 1). The presence of point-related mutations linked to resistance has been highlighted with molecular techniques such as PASA-PCR (specific allele PCR) and pyrosequencing. Their percentage frequency was variable according to the type of mutation, the geographical area of origin and the host of collection of the studied populations. Mutations L1014 (kdr) and M918T (s-kdr), responsible for resistance to pyrethroids, are present with percentages close to 100% in all populations. In the s-kdr locus, a different mutation (M918L), recently described in literature, whose effects on pyrethroid resistance are being further characterized, has also been found in about 22% of the populations. The R81T mutation linked to resistance to neonicotinoids and able to confer, depending on the genotypic combinations, resistance factors of over 100 times, was found, in 2012, in about 65% of the analyzed aphids. The percentage was slightly reduced in the 2013 samples, reaching around 45%. For the first time the presence of this mutation has also been discovered in living aphids on herbaceous hosts, contrary to what has been observed by other authors (Slater et al., 2012). The S431F mutation in the acetylcholinesterase gene, linked to dimethylcarbamate resistance, was found in 25% of the analyzed aphids. The percentage of individuals with the simultaneous presence of multiple mutations is particularly high. Final considerations The data collected describe a worrying situation that will require continuous attention to maintain the effectiveness of the insecticide treatments performed against M. persicae. The results of the analyzes conducted in the two-year period 2012-2013 describe a substantial constancy over time in the resistance to dimethylcarbamates: the percentage of presence of the S431F mutation is in fact the same as that reported in a similar survey conducted in previous years (Criniti et al., 2008). In contrast, pyrethroid resistance has become widespread and is now present, even in different genotypic combinations of kdr and s-kdr, in almost all populations of M. persicae collected in Italy. The application of any insecticide of the pyrethroid class can therefore be completely ineffective against the infestations of this aphid. Finally, resistance to neonicotinoids, documented for the first time in 2010, quickly reached worrying rates. Although a slight decline in the percentage of carrier individuals was observed between 2012 and 2013, the number of reports of non-effective treatment with this class of products is still high. The risk of its greater diffusion is consistent, above all in the herbaceous crops for which the ne