Predators and parasitoids sharing a leafcutter ant as prey (Acromyrmex lobicornis)

ELIZALDE, L.; SUPERINA, M.

Curitiba

Congreso; XXIII Simpósio de mirmecologia; 2017

Predators and parasitoids that share the same prey can interact negatively due to intraguild predation or competition for the resource. However, they can also interact positively, e.g. by increasing prey availability for the other. Leafcutter ants are preyed by various vertebrates and invertebrates, but among the most important are armadillo (mammal). In addition, there is a group of phorid (insect) parasitoids which only use leafcutter ants as hosts for their immatures. Armadillos, phorid parasitoids and leafcutter ants overlap in much of their distribution range and constitute a good study system to research predator-parasitoid-prey trophic interactions. We quantified the effect of an armadillo, Chaetophractus villosus, and a phorid parasitoid, Myrmosicarius catharinensis, over the leafcutter ant Acromyrmex lobicornis in Patagonia (Argentina). For this, we: 1) counted the number of nests with signs of attack by armadillos, 2) collected their feces to later identify ants in them, and 3) collected ants to rear parasitoids. We found that 48% of the nests suffered armadillo attack, and the feces analysis (N=77) allowed us to determine that these mammals feed on leafcutter ants frequently. An 80% of nests had M. catharinensis of which in average 2% of the forager ants were parasitized. Then to evaluate whether these predators and parasitoids interact through their common prey, we simulated the damage caused by the armadillo in A. lobicornis nests (N=17). We collected ants to rear parasitoids to quantify parasitism prior to the damage, after one week, and a month later. As controls, we also collected ants to obtain parasitism in undamaged neighbor nests. We found that parasitism by the phorid was higher in nests after an armadillo attack compared to nests without damage. Our results show that both armadillos and parasitoids exert a strong pressure over this leafcutter ants. Additionally, armadillo predators have a beneficial effect over phorid parasitoids which targets the hosts around the nest. These results may be important for integrated biological control of these ants when they have turned into pests, and help to understand how different guilds can interact to regulate herbivore natural populations.