Spatial patterns in pupal mortality in urban palm caterpillars

Abstract

Mortality factors were determined in over 20000 pupal skins of Brassolis sophorae and Opsiphanes invirae, collected from 55 sites in the urban area of Campinas, São Paulo, southeast Brazil. Almost 50% of B. sophorae pupae and 30% of O. invirae pupae were killed by various identifiable factors, which may have an appreciable influence in determining adult population size. Mortality was related to type of attachment site, distance from the center of the city, area occupied by buildings and houses, vegetation cover, and other urban variables. Exposed pupation sites such as outside walls had a lower frequency of successful eclosions than darker or more sheltered sites, such as offset skirting boards, garages, or mailboxes, which act as partial refuges against parasitoids. Mortality levels were higher in regions of the city with high vegetation cover. Vegetation cover and distance from the city center were the best predictors of parasitism level of B. sophorae by the chalcidid wasp Spilochalcis morleyi. The viability of S. morleyi (data from parasitized B. sophorae) did not differ significantly among different regions of the city. These data do not support an exclusive model of “escape from parasites” (or other natural enemies) for explaining the abundance of urban butterflies.