Parasitism of the leaf‐cutting ant Atta bisphaerica by phorid flies: biology and seasonal and inter‐colonial parasitism rates

The leaf‐cutting ant Atta bisphaerica Forel (Hymenoptera: Formicidae, Attini) forages leaves from monocotyledons in natural environments and is a serious pest of pastures and sugarcane plantations in Brazil. This study investigated aspects of the interactions between A. bisphaerica and dipteran Phoridae parasitoids. The seasonal and inter‐colonial variations in parasitism rates were also investigated. Ants from four A. bisphaerica colonies were sampled, with a total of 91 554 worker ants collected and evaluated. Of these ants, 4.4% were found to have been parasitized by three phorid species: Apocephalus attophilus Borgmeier (relative parasitism rate: 40%), Myrmosicarius grandicornis Borgmeier (31%), and Eibesfeldtphora bragancai (Brown) (28%). The months with the lowest average temperatures, lowest relative humidity, and lowest rainfall (characteristics of the dry season of the region under study) corresponded to the highest parasitism rates, especially by A. attophilus. Apocephalus attophilus and E. bragancai had the highest relative parasitism rates in two of the colonies, 45 and 41%, whereas M. grandicornis was the dominant species in each of the other two colonies, corresponding to approximately 40% of total parasitism. The variation in parasitism rates observed between colonies could be explained, at least in part, by the relationship between the size of the parasitoids and the size of the host ants. Concerning the biological characteristics, A. attophilus had the shortest life cycle, the highest successful emergence rate, and produced 2.5× more parasitoids per host. These characteristics, combined with the ability to cause higher levels of mortality of parasitized worker ants when compared to the two other phorid species, indicates that A. attophilus is an efficient natural enemy of A. bisphaerica and is therefore a candidate for a biocontrol program.