Social insects rank among the most ubiquitous and ecologically dominant terrestrial animals on Earth. Complex communication and social organization are two defining features of social insect societies and ants, in particular, have evolved extensive systems of chemical communication. In both natural and agricultural systems, including coffee agroecosystems, ants are important predators and often have strong and complex effects on pest species. In this dissertation, I explore how chemical communication plays a role in dynamics between ants and their natural enemies within these coffee agroecosystems, to gain a better understanding of both how ants utilize their own chemical communication systems and how natural enemies of ants take advantage of these systems to exploit ants.
In the first dissertation chapter, I review the literature on chemical and visual cues that one natural enemy of the ant, the phorid fly, uses to successfully parasitized its host ants. Phorid fly parasitoids that use ants as hosts often require the use of multiple cues, ranging from general to highly specific, to home in on an ideal host. Here I outline the five common steps in which phorid flies use cues: (a) host habitat location, (b) host location, (c) host acceptance, (d) host discrimination and (e) host regulation. I then discuss our current understanding of how phorid flies use each of these steps to successfully parasitize ant hosts. Finally, I examine the wide variety of strategies and cues used by a multiple species of phorid flies within three separate genera (Apocephalus, Pseudacteon, and Neodohrniphora) and discuss future directions within this field of study.
In the second dissertation chapter, I investigate the role of Azteca ant cuticular hydrocarbon cues as a short-range cue for a suite of Pseudacteon spp. phorid fly parasitoids commonly found within coffee agroecosystems. Here I describe the hierarchy of cues Pseudacteon spp. phorid flies use to successfully identify Azteca host ants. I use behavioral observations in the field to show phorid flies are attracted to two cryptic Azteca taxa, but will only attack Azteca sericeasur (Hymenoptera: Formicidae: Dolichoderinae). To test whether the phorid flies are able to distinguish between the two Azteca taxa using their cuticular hydrocarbons, I first document and compare the cuticular hydrocarbons of two cryptic Azteca taxa using gas chromatography-mass spectrometry (GC/MS). Using cuticular hydrocarbon transfer experiments with live ants from both Azteca taxa, I identify the cuticular hydrocarbons of Azteca sericeasur as a short-range host location cue used by Pseudacteon lasciniosus (Diptera: Phoridae) to locate the ants.
In the third chapter, I describe two new species of Myrmedonota (Coleoptera: Staphylinidae) that are also natural enemies of Azteca sericeasur ants. Here I record this genus of beetle in Mexico for the first time, and describe M. xipe and M. shimmerale for the first time. This chapter also documents that both Myrmedonota species will aggregate towards agitated ants, to prey on Azteca sericeasur and these species will form mating swarms, either with no apparent landmark or in the vicinity of ants.
My fourth chapter examines the role of the beetle, Myrmedonota xipe, in Azteca ant-phorid fly interactions. Here I use pheromone bioassays to show that M. xipe is attracted to a component of A. sericeasur alarm pheromone. In the field experiments, I determine that the beetles are able to locate parasitized ants as prey items but not healthy ants. In choice tests in the lab, I also show that beetles will preferentially attack parasitized ants over healthy ants. Analysis of the choice tests also indicates that the aggression in parasitized ants is so reduced that beetles are essentially able to eat these ants alive without interruption. These results suggest that, although beetles are predators of the ants, by preying primarily on ants harboring phorid fly eggs, the beetles may also provide indirect positive effects for the ant colonies as a whole.
In my final dissertation chapter I examine the variation in cuticular hydrocarbon blends of three species of arboreal twig nesting ants, Pseudomyrmex simplex, Pseudomyrmex ejectus and another Pseudomyrmex sp. (referred to as PSW-53) commonly found within the coffee agroecosystems of Southern Mexico. In this study, I examined whether variation in the ecology and social structure of these species is reflected in the variation in their cuticular hydrocarbon profiles. I tested the hypothesis that the more abundant species with higher nest densities exhibit lower cuticular hydrocarbon variation. The results showed that worker ants of abundant P. ejectus and P. simplex from the study site exhibit significantly lower variation in cuticular hydrocarbon profiles than workers of the rare ant species P. PSW-53. Our study reinforces the idea that examining cuticular hydrocarbon profiles can provide insight into the colony structure of social insects.
Overall, the results from my dissertation provide insight into the complex interactions between ants and their natural enemies, particularly shedding light on how these interactions are facilitated through the use of ant pheromones as cues and signals. The ants and their natural enemies that I focus on in my dissertation are also important players within the greater coffee agroecosystems in which they inhabit, and this body of work is thus critical for understanding how their network of interactions involving ants and their natural enemies may impact coffee pest control.
