RESEARCH PROGRAM
Goals
The goal of our program is to provide a scientific basis for ongoing biocontrol efforts to establish a suite of phorid fly species and pathogens for fire ant biological control. The effectiveness of such biocontrol is expected to depend on the suite of introduced phorid species, coupled with other parasitoids and pathogens acting synergistically and having greatest impacts during periods of environmental stress.
A key feature of our efforts to achieve a lasting solution to the imported fire ant problem is to develop a fundamental understanding of the population and community ecology of native and imported fire ants, their parasitoid flies and pathogens, while simultaneously applying our findings to biological control efforts.
We seek to understand why ant species of the genus Solenopsis can vary so dramatically in native and introduced ranges in terms of degree of ecological dominance and thus, their status as ecological and economic pests. Our research to date has identified flies of the genus Pseudacteon (family Phoridae), specialized fire ant parasitoids, as species-specific biological agents whose co-occurrences with host populations of fire ants and their pathogens appears to keep hosts in check and below pest status. Other parasitoids and pathogens are also being considered for biocontrol by our team and other research groups such as USDA.
Research Program
1) Behavioral and community ecology of Solenopsis ants and Pseudacteon flies.
Experimental field studies in Texas and Argentina have been designed to explain precisely how and to what extent Pseudacteon phorid flies reduce the competitive advantage of host fire ants. We wish to explain why native fire ants (S. geminata) and imported fire ants (S. invicta) can each be either a pest or "just another ant" depending on circumstances of geography and ecology.
2) Comparative analyses of Pseudacteon phorid fly ecology and their interactions with fire ants.
Comparative studies of over 20 phorid species from Argentina and Brazil will determine to what extent the ecological and behavioral differences among fly species correlate with relative differences in their ability to reduce the competitive advantage of S. invicta over other ants. We are studying the manner in which these 20+ fly species differ in their detection and use of their hosts.
3) Laboratory analysis of Pseudacteon host specificity.
Our initial studies of attack behavior in the laboratory determined that the degree of host specificity by egg-laying phorid females varies among species. A few South American phorid species show interest in S. invicta, but with low attack rates and low development of flies arising from these attacks.
4) Field and laboratory studies of Pseudacteon life histories.
Research on the life cycles of Pseudacteon phorids in nature are needed to understand how they survive harsh seasons, how long they live in nature and how they disperse.
5) Development of methods for mass production of Pseudacteon species for field release.
Laboratory rearing of Pseudacteon phorids will be critical in the initial phases of employing them in fire ant biocontrol, since spreading them artificially, will be preferable to waiting for the slow process of natural dispersal to work. At the moment we are unsure about many key aspects of life cycle that are necessary to understand before large-scale production facilities can be possible. Life history details are a prerequisite for all aspects of the work. For example, knowing what adult flies eat in the wild will improve survivorship during transport and laboratory experiments. Knowing where flies pupate in the field will suggest ways to duplicate necessary conditions in the laboratory. To date only two species of ant parasitoid phorids have been successfully cultured. Our lab allocates considerable effort to development of rearing methods for other S. invicta-specialized phorids which effectively suppress fire ant foraging in South America.
6) Field releases of South American phorids in Texas.
Initial experimental releases of introduced phorids will be focused on areas where our continuing basic studies of native ant vs. imported fire ant interactions provide population data for the baseline against which change will be measured. Since native ants constitute the force that phorids help amplify against S. invicta, boundaries where in-holdings of native ants meet the "sea of S. invicta" should be the most effective places to initiate, as well as document, phorid-driven biological control. Therefore, our basic studies at such sites will lay the ground work for applying phorids to biocontrol of the imported fire ant, and for monitoring its progress.
7) Development of criteria for choosing the most effective Pseudacteon species for fire ant biocontrol in Texas.
Comparative studies of different phorids are used to fine-tune the release details to maximize biocontrol potential. Preliminary data indicate that some phorids will have a greater impact than others in disrupting fire ant activity, and that likewise, particular combinations of phorid species may be more effective than single species (most sites we study in South America and Texas have 2-4 common Pseudacteon species attacking fire ants). Additional considerations include similarities in climates between source areas and release areas. Basic ecological studies in Argentina are significant because of its Texas-like winter conditions.
8) Tracking the dispersal dynamics of introduced Pseudacteon species.
The release of Pseudacteon phorids provides an important opportunity to study the dispersal of species as would occur when an invasive species becomes established. We have found that introduced populations of phorids go through a local growth period of about one year followed by a major expansion of up to 70km per year with the wind. However their spread against the wind is limited to less than 10km per year.
9) Understanding the mechanisms involved with newly assembled communities of phorid flies.
Most often, ecologists are only able to guess at the possible mechanisms that govern the relative abundances of each species in a community. But as we add more species to the local pools of phorids at different sites in Texas, we are able to monitor how the species interact and set up experiments to understand the mechanisms that allow certain species to dominate while others become scarce.
10) Evaluating the impacts of introduced flies on the invasive fire ants.
While several studies show a decrease in resource acquisition by fire ants in the presence of phorid flies, the ultimate impact of phorid flies on fire ant populations has yet to be demonstrated in the field. We have initiated several studies including setting up baseline surveys of ant communities and fire ant densities to monitor long term changes that may take well over 10 years to show such effects. Meanwhile, other studies will look at changes within fire ant colonies that may occur if flies reduce resources reaching the colonies.
11) Evaluating the impacts and interactions between phorid flies and fire ant pathogens.
We are studying whether phorid flies may be involved with transmitting pathogens such as microsporidia and other fungi between fire ant colonies. If this is confirmed, then the role of phorid flies becomes even more important as a biocontrol tool.
OVERVIEW OF RESEARCH TACTICS
As indicated above, our strategy has been to pursue all key parts of the problem simultaneously rather than to work on narrow pieces in linear fashion. This "parallel processing" approach depends heavily on involving a talented group of ecologists and entomologists who can effectively attack their respective parts of the project, and coordinate with others in integration of findings to effect biocontrol of fire ants.
