Social behaviour in the form of parental care is widespread among insects but the evolutionary histories of these traits are poorly known due to the lack of detailed life history data and reliable phylogenies. Treehoppers (Hemiptera: Membracidae) provide some of the best studied examples of parental care in insects in which maternal care involving egg guarding occurs frequently. The Membracinae exhibit the entire range of social behaviour found in the treehoppers, ranging from asocial solitary individuals, nymphal or adult aggregations, to highly developed maternal care with parent-offspring communication. Within the subfamily, subsocial behaviour occurs in at least four of the five tribes. The Aconophorini and Hoplophorionini are uniformly subsocial, but the Membracini is a mixture of subsocial and gregarious species. The Hypsoprorini contains both solitary and gregarious species. Accessory secretions are used by many treehoppers to cover egg masses inserted into plant tissue while oviposition on plant surfaces is restricted to a few species. Presumed aposematic colouration of nymphs and teneral adults appears to be restricted to gregarious and subsocial taxa. Ant mutualism is widespread among membracine treehoppers and may play an important role in the evolutionary development of subsocial behaviour. The life history information provides a basis for comparative analyses of maternal care evolution and its correlation with ant mutualism in membracine treehoppers. The results show that there is a strong phylogenetic component to the evolution of maternal care in membracine treehoppers, and provide the first quantitative evidence of correlated evolution of maternal care and ant mutualism in treehoppers. Further research on natural history, particularly of the tropical fauna, will be necessary to better understand the evolution of social behaviour and life history in treehoppers.
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