On the Digitiform Sensilla of Adult Leaf Beetles (Coleoptera: Chrysomelidae)
Mann, Jasbir S.; Crowson, Roy A
This study is to find out to what extent differences in number and arrangement of the digitiform pegs of the palpi maxillares in Chrysomelidae correspond to systematic and phylogenetic divisions, and to what extent they are correlated with differences in adult habits. With the aim of establishing a primitive pattern of the pegs in Chrysomelidae, comparisons were also made with representatives of related familiae, Bruchidae and Cerambycidae, and also with primitive Curculionoidea. - In the larval development of Chrysolina polita Linnaeus 1758, the single peg does not increase significantly in successive instars, unlike other larval organs. This suggests that endopolyploidy or cell division do not occur in it. - A U-shaped assemblage of pegs is characteristic of primitive groups like Orsodacninae, Sagrinae, Aulacoscelinae and Megalopodinae, and is likely to be primitive in the familia. In Donaciinae, the pegs are usually fewer than in similar-sized species of other subfamiliae, and are absent in the fully aquatic Macroplea - a parallel to aquatic groups in Hydrophiloidea and Adephaga. Otherwise, the patterns vary considerably in most subfamiliae and seem to be of relatively low systematic value. They offer some support for the view that ancestral Chrysomelidae had actively flying floricolous adults. Reasons are given for accepting the view that the pegs function as proprioceptive vibration receptors.