Seasonality of parasitism of phorid flies (Diptera: Phoridae) in the leafcutter ant Atta sexdens Linnaeus (Hymenoptera: Formicidae) in an Atlantic Forest area

There is a lack of information regarding the variations in parasitism rates of parasitoid phorids for more than one year, whether they follow a pattern of distribution, and whether climatic factors affect the parasitism rates. We observed the parasitism rates caused by parasitoids of Atta sexdens and analysed whether there is seasonality in the occurrence of parasitism and studied the effects of climatic factors on parasitism rates. Atta sexdens foragers were collected during 24 months from an area in the Atlantic Forest and the parasitism rate was calculated. Path analysis was used to identify and quantify the direct and indirect effects between parasitism rates and climatic factors. The mean parasitism rate was 5.8%, with Apocephalus attophilus accounting for 4.2%, Eibesfeldtphora spp. 1.4% and Myrmosicarius grandicornis 0.2%. Parasitism of A. attophilus and Eibesfeldtphora spp. increased as temperature decreased. The effect of relative humidity was significant and negative on Eibesfeldtphora spp. and M. grandicornis, whereas the effect of rainfall was significant and positive on M. grandicornis. We conclude that there is a seasonal pattern in the occurrence of parasitism by A. attophilus and that temperature is the main climatic variable associated with the fluctuation of parasitism, where the peaks occur in winter, followed by spring and autumn, and the lowest rates were in the summer.