Molecular phylogeny and host plant use of Thymogethes pollen beetles (Coleoptera) on Lamiaceae

The 24 members of the Euro-Asiatic genus Thymogethes are highly specialized pollen beetles associated as larvae with flowers of Lamiaceae Nepetoideae. All members of the genus were analyzed in within the framework of an integrative taxonomy approach, which was aimed to reconstruct the phylogenetic relationships, as well as the possible pattern of evolution of their larval-host-plant association. Evidence from multiple molecular markers [COI; 16S; H3], combined with an estimation of divergence times using an average rate of 0.0177 substitutions/site/My among branches, placed the origin of the genus at a minimum of 9-10 Mya. This date of origin approximates the known evolution of the host-plants in Euro-Mediterranean areas. Evidence from combined molecular and cladistic morphological analyses, resulted in suitable agreement with the previously established morphology-based systematics of the genus, although members of the exilis species-group were split into three clades. The only disagreement between results of this new combined phylogeny and previous classification is in the exclusion of “Thymogethes” grenieri. This species is herein positioned outside the genus, based on molecular evidence. Our analysis depicts several Thymogethes species differentiating in the last few Mys, specifically those included in the T. lugubris species-group. Combined evidence from DNA, morphology, and ancestral state parsimony reconstruction of larval-host-plant associations, suggests that subtribe Menthinae likely represents the ancestral host-plants, with a series of independent host shifts during the radiation of the clade, in association first with Menthinae, and subsequently with Lavandulinae and Nepetinae. Steno-oligophagy is the most frequent (86%) condition, while strictly monophagous species are less numerous (14%).