Phorid parasitoids affect foraging activity ofSolenopsis richteriunder different availability of food in Argentina

Abstract

Summary1. In Argentina, six species ofPseudacteonparasitoids (Phoridae) attackSolenopsis richteri, one of the two species of South American fire ant that are exotic pests in North America.2. The presence of thesePseudacteonspecies significantly reduces the number of ants at food resources in the field, as well as foraging activity generally.3. SomePseudacteonnot only attack ants walking on trails or at feeding sites, but also at mound entrances, inhibiting workers from leaving to forage.4. The average size of foraging ants (which prescribes their suitability as hosts) decreased in the presence of phorids.5. The number of attacking phorids was correlated positively with the number of ants walking towards the food on the trail before the attack.6.Solenopsis richteriworkers responded to manipulations of food size and presence or absence of parasitoids in a risk‐adjusting way, i.e. although more foragers were recruited to larger food items, attacking phorids reduced ant foraging activity by the same factor regardless of the size of the food offered.7. The data suggest thatS. richtericolonies juggle the needs to harvest food efficiently, reduce competition, and avoid excess risks from parasitoids in complex ways.