Sex ratio and mating behaviour of Anisandrus dispar (Fabricius) (Coleoptera: Curculionidae: Scolytinae) in hybrid chestnut orchards

Abstract Anisandrus dispar is an economically important ambrosia beetle associated with damage in hybrid chestnut orchards in southern Italy. This study investigated the haplotype diversity, infestation patterns, seasonal emergence, sex ratio, and mating behaviour of A. dispar populations in three hybrid chestnut orchards in Calabria. Branches were sampled monthly (April–June) and during winter. Ten females were used for cytochrome c oxidase subunit I barcoding and haplotype analyses. Gallery traits, emergence patterns, sex ratios, and mating behaviour of overwintering males were assessed under laboratory conditions. Molecular analyses revealed six European haplotypes with none shared among orchards or invasive. A total of 708 adults emerged from rearing cages, 111 adults were recovered by branch dissection, 97 adults emerged from winter-collected branches, and 64 were identified through winter dissections. Adult emergence from reared branches was recorded from May to mid-December, with the highest numbers observed in early June, and showed a pronounced female bias, with male-to-female ratios of 0.23:1 in emergence cages and 0.37:1 in dissected woody tissues. This skewed sex ratio persisted in branches collected during winter, while gallery spacing decreased as branch diameter increased. The number of exit holes, averaging 3.31 per branch, was positively correlated with branch diameter. Overwintering males successfully copulated under laboratory conditions. The high infestation levels and associated tree mortality indicate that A. dispar is well established in these orchards and may require host-specific monitoring and management in chestnut agroecosystems.