Distribution across Italy of chs-1 alleles associated to Diflubenzuron resistance in Culex pipiens

In Italy, control interventions against mosquito larvae rely heavily on treatments of rain catch basins by Diflubenzuron (DFB), an insect- growth regulator targeting the chitin-synthase (chs-1). Strong resistance to DFB in Culex pipiens populations and high frequencies of mutations at position 1043 of the chs-1 gene, known to be associated with DFB resistance, are reported in populations from Emilia- Romagna region. The aim of the present study was to assess the circulation of alleles 1043L/M in Cx. pipiens populations from 6 Italian regions, with a focus on Veneto region, where data on the effectiveness of surveillance activities were available. Overall, 1,030 specimens were analyzed using an AS-PCR approach for the presence of mutations I1043L/M. Allele 1043L was found across Italy (Trentino 19%-36%; Veneto 0%-91%; Piemonte 11%; Liguria 28%; Lazio 0%-8%; Puglia 5%). Highest frequencies (up to >90%) were observed in the Venetian lagoon where also allele 1043M, absent elsewhere, was detected. The widespread presence of I1043L mutation in Italy suggests spreading of resistance mechanisms, whose impact on effectiveness of catch basin treatments needs to be evaluated.