Life-History Traits and Parasitism Rates of Four Phorid Species (Diptera: Phoridae), Parasitoids of Atta vollenweideri (Hymenoptera: Formicidae) in Argentina

Abstract

Leaf-cutting ants in the genus Atta F. (Formicidae, Attini) are among the most important pest arthropods in Central and South America, consuming more vegetation than any other animal group. Among the organisms attacking ants in nature, flies of the family Phoridae have been proposed as the most promising biocontrol agents for pest ants. Four phorid species, Apocephalus setitarsus Brown, Myrmosicarius brandaoi Disney, Myrmosicarius gonzalezae Disney, and Eibesfeldtphora trilobata Disney, were reared from ants collected at Atta vollenweideri Forel nests and off foraging trails in Santa Fe province in Argentina. E. trilobata attacked larger ants and had bigger adults than the other species, also exhibiting the longest developmental time. Correlations between size of hosts and size of adults, as well as between size of adults and developmental times, could be established only in some cases. No differences were found between the sizes of the hosts from which males and females emerged. The natural percentage of parasitism varied throughout the seasons and seemed to be influenced by the extreme drought affecting the study site. We discuss why all four species would be suitable candidates for integrating an assemblage of biocontrol agents against A. vollenweideri.

Phorid Flies Parasitizing Leaf-Cutting Ants: Their Occurrence, Parasitism Rates, Biology and the First Account of Multiparasitism

“…The larva of A. vicosae, using a still unknown method, then migrated to the thorax to feed on the contents of the prothorax. Larva of M. grandicornis consumes the head content of the ant host; the pupa is found at the bottom of the capsule, under the "tentorium" (Tonhasca et al, 2001 Guillade & Folgarait, 2011). Oviposition by M. grandicornis is directed always at the right side of the host's head because of an asymmetry of the ovipositor (Tonhasca et al, 2001).…”

Leaf-Cutter Ant Parasitoids: Current Knowledge

“…Their developmental times are the longest recorded to date, even considering that developmental periods of phorids that attack Acromyrmex ants are longer than those coming from Atta. Furthermore, considering that these flies attack small ants [20], these lengthy developments are even more surprising as, in general, phorids attacking smaller ants develop faster than those attacking larger ones [25,44,45]. Probably, the ants involved in this task, such as carrying refuses plus working on them, are constantly dealing with infectious pathogens and may well be considered disposable ants from the colony point of view (either for being old or having a bad health) and, in turn, poor hosts from a phorid nutritional perspective.…”

“…Natural parasitism from the same nests of Atta vary through time [25,32], and these rates may reflect changes in health status of each colony or physiological tolerances of phorids to different weather conditions. For comparable data, percentages of natural parasitism in Atta are greater than in Acromyrmex in Argentina.…”

“…For example, for At. vollenweideri sampled at the same sampling site, maximum values range from 4% to 35% at different years [25,32].…”

“…The parasitoid decision, about which host is good or not, should involve not only quality but also host size or amount of available food. In general, the larger the host selected, the bigger the resulting adult phorid [9,25]. Host size is related to the amount of food available for the internal larvae to feed and be able to pupariate.…”