Powdering of egg nests with brochosomes and related sexual dimorphism in leafhoppers (Hemiptera: Cicadellidae)

Leafhoppers from 16 New World genera currently placed in the tribes Proconiini (13) and Cicadellini (2) of the subfamily Cicadellinae, in the subfamily Phereurhininae (1), and one undescribed genus exhibit a suite of morphological specializations associated with a unique type of maternal care. The females produce a specific type of brochosomes (secretory particles manufactured in the Malpighian tubules of most leafhoppers and usually forming a non-sex-specific hydrophobic coating of the integument), which they store prior to oviposition on their forewings in the form of pellets and then apply as a powdery coating to the egg clusters placed under the epidermis of leaves or, in one genus, exposed. The function of the brochosome coating is unknown, but may include protection of eggs against parasitoids and pathogens, and facilitating gas exchange. Observations on several species from the genera Phera, Hornalodisca, Oncometopia, Quichira, Cuerna, and the undescribed genus are reported, complementing scanty existing data on this behaviour. Its taxonomic occurrence is described for the first time based on study of collections, where ready-to-oviposit females are occasionally preserved with pellets of brochosomes on their forewings. A comprehensive survey of associated female-specific structural modifications is presented based on examination of c. 80 predominantly Neotropical species. These modifications include (1) production of modified brochosomes (2) modified setation of the forewing area upon which pellets of such brochosomes are placed, and (3) elongation of the metathoracic tibial macrosetae, which transfer the brochosomes onto the egg nest. The traits are absent or rudimentary in males. The specialized brochosomes display remarkable interspecific diversity and can be used for taxonomic identification of eggs. Egg-powdering apparently has evolved as a modification of the anointing and grooming behaviours involved in making coatings of integumental brochosomes in most leafhoppers. Morphological similarity, extending to characters not related to oviposition, suggests that all genera containing 'powdering' species may form a single lineage, but this hypothesis yet needs to be tested by phylogenetic analyses. Several such genera include species displaying powdering-associated traits and species lacking these, suggesting multiple independent losses or origins of powdering. This peculiar kind of maternal care provides an interesting model for study of the evolution of novel functional complexes of traits. (C) 2004 The Linnean Society of London, Zoological Journal of the Linnean Society.