Parasitoids of the poorly known Neotropical myrmicine ant Pheidole susannae
Résumé
Natural-enemy diversity effects on host population dynamics are not well understood. Enhanced host control is observed in diverse systems with different natural-enemy groups complementing one another temporally, but this is not always the case. Here we report on the co-occurrence of dipteran and hymenopteran parasitoids on a coastal population of Pheidole susannaeForel (Formicidae: Myrmicinae) in southern Quintana Roo, Mexico. This Neotropical, opportunistic cavity nesting ant occurs in various habitats including conserved seasonal dry forest and mature lowland rainforest patches, and is also present in highly disturbed areas (city parks, hospitals). Pheidole susannaeis frequently reported as a dominant species along its geographical range, yet the specieshas been poorly studied. Whole colonies or parts of colonies nesting in the soil under stones or inside decomposing coconut shells were collected. Colonies are monogynous with about 400 workers and 800 immatures on average. Larvae and pupae were found parasitized by Orasema evansi(Hymenoptera: Eucharitidae), a long known but only recently described wasp species, while adult workers were observed being attacked by female flies of the Apocephalus grandipalpis-group species (Diptera: Phoridae) in the rainy season, during a nest emigration after disturbance. Colony-level distress was obvious when flies were present and threatening. Parasitism rate by Orasemarepresented up to 12.5% of available brood. Though parasitism rate by phorids could not be evaluated, these dipteran parasitoids can also have significant ecological implications for both the host species and other interacting parasitoids, affecting host foraging patterns spatially and temporally as well as changing dominance hierarchies in ant communities,but also disturbing transport during emigrations including that of parasitized hosts. Though eucharitids may suffer a net reduction in fitness via interference competition from phorids during host nest relocation, the effect of both natural enemies on thehost population appears at least partially complementary.