Natural enemies are one of the main mortality factors in bees and wasps attacking either immature stages or adults of their hosts. Dipterans of the genus Physocephala (Diptera: Conopidae) are parasitoids that attack adult bees during their field activities, and the parasitoid larvae develop inside the host abdomen. However, little is known about the biology of these natural enemies and their interactions with their solitary bee hosts. This study is aimed at analyzing attacks by conopid flies in one of their hosts, the solitary bee species Centris analis (Apidae: Centridini), and the consequences in the nesting behavior of this bee species. Higher incidences of parasitism occurred during the hot/wet season, and seven fly species attacking C. analis were identified. Of the fifty-six females observed during their nesting activities, seven of them were parasitized. These females showed alterations in their nesting behavior, depositing extra oil on the plug of finished nests and building plugs in empty cavities. The behavioral changes observed in these females began during larval stage L1 of the parasitoid. In the last stages of parasitoid development (L3 PUP and pupa), the bees ceased their flight activities and entered cavities at the nesting site, remaining there until death.
Keywords: Centris analis; Endoparasitism; Exploitation competition; Nesting biology; Physocephala.