Natural history and population dynamics of the subsocial tortoise beetle Omaspides (Paromaspides) brunneosignata Boheman 1854 (Coleoptera: Chrysomelidae: Cassidinae)

Abstract

Herbivorous insects have their density limited by biotic and abiotic factors, which influence their survival. For subsocial tortoise beetles (Chrysomelidae: Cassidinae) little is known about natural history and what factors affect their densities, although they are promising models for ecological and evolutionary studies. We described (1) the biology, behaviour and natural enemies of Omaspides (P.) brunneosignata Boheman 1854 (Cassidinae: Mesomphaliini); (2) its population density, and (3) the possible correlation between its density and climatic factors (temperature and precipitation) and host plant, Ipomoea syringifolia Meisn. 1869 (Convolvulaceae). The study was conducted in the Floresta Nacional de Passa Quatro, Minas Gerais, Brazil, from: October/2010 to May/2011, to investigate the species life cycle and the population dynamics, correlating the density to the climatic variables and from October/2016 to January/2018, when population dynamics was monitored again, and the density was correlated to the climatic variables and phenology of the host plant. Parental care was observed only by the female of O. (P.) brunneosignata, which cares for the offspring for approximately 48 days, the total duration of immature development. Maternal care was fundamental in the egg stage, because in the absence of the female, all the egg masses were predated, mainly by ants. Immatures were predated and/or parasitised by Hymenoptera (ants, wasps) and Coccinellidae beetles. Omaspides (P.) brunneosignata is a bivoltine species, being abundant during the hot and rainy months and not being observed in the dry and cold season, a similar pattern to that of other cassidines of mountainous tropical areas in Brazil. The density did not correlate with the climatic variables or with the leaf density of the host plant. Other factors are discussed as possible causes for the population fluctuation of the species.