Morphology of the unique structures of adult female lac insects (Hemiptera: Coccoidea: Kerriidae)

The brachia, brachial plates, canellae, dorsal spine and post-oral lobes of adult female lac insects are described based on observations under SEM of Austrotachardia acaclae (Maskell), Austrotachardia sp. ex Cassinia, Kerria lacca (Kerr) and Paratachardina decorella (Maskell), and under light microscope of these and a few other species of lac insects. These structures, like the anal tubercle, are considered unique to the family Kerriidae. The canellae, brachia and brachial plates together may be considered homologous to the anterior stigmatic area, groove, cleft and other associated structures of Coccidae and related lecanoid scale insects. These structures collectively assist the mesothoracic spiracle in its function of gas exchange. The dorsal spine has possible secretory function while the post-oral lobes probably serve as anchor during vertical movement and balance. The dorsal spine and post-oral lobes appear to be autapomorphic features of lac insects. On the other hand, like the anal tubercle and its associated structures and the vestigial anal cleft, the brachia, brachial plates and canellae are probably homologous to morphological features found in Coccidae and other lecanoid scale insects. These homologies suggest common ancestry and possible sister-group relationship between the Kerrlidae and Coccidae or another closely related family. The details of these morphological structures as revealed by SEM not only provide new insights into homology or phylogenetic relationships but also facilitate interpretation of these characters under the light microscope.