A key feature of our efforts to achieve a lasting solution to the imported fire ant problem is to quickly develop a fundamental understanding of the population and community biology of native and imported fire ants, while simultaneously applying our findings to biological control efforts. The first goal of this work is to understand why ant species of the genus Solenopsis can vary so dramatically from place to place in terms of degree of ecological dominance and thus, 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-occurences with host populations of fire ant appears to keep host in check and below pest status. Both the phorid fly biocontrol research and research on species-specific biopesticides for fire ants are based at Brackenridge Field Laboratory.
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Important basic research initiatives underway include:
1) behavioral and community ecology of Solenopsis ants.
Experimental field studies currently underway in Texas and Brazil are 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 in Texas, native fire ants (S. geminata) and imported fire ants (S. invicta) can each be a pest or "just another ant" depending on circumstances of geography and ecology. Key studies in Texas will be focused 1) in the zone around small inholdings of native fire ant populations in regions dominated by the invader (e.g., Central Texas) and 2) around isolated outbreaks of the invading species beyond its continuous range (e.g., coastal South Texas).
2) comparative analysis of Pseudacteon ecology and attack behavior.
Comparative studies of some 15 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. Preliminary observations indicate that phorid females differ rather dramatically in how and where they pursue their victim. Accordingly, ant responses depend on which phorid species is (are) present.
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 females varies among species. Not all South American Pseudacteon are as host-specific as are Texas native Pseudacteon (which attack only S. geminata-group fire ants). Some Brazilian species tested attack S. geminata as readily as normal host, S. invicta, and were not proposed for release.
4) field and laboratory studies of Pseudacteon life history.
Research on life cycle of Pseudacteon phorids in nature are needed to understand how they survive harsh seasons, how newly emerging adults avoid attack by ants, whether adults feed, and how long they live in nature.
RESULTS OF THESE BASIC INVESTIGATIONS WILL BE SEAMLESSLY INTEGRATED (I.E.; SAME PEOPLE, SAME LOCATIONS, AND IN A CONTINUOUS PERIOD OF TIME) WITH PARALLEL RESEARCH DIRECTED TOWARD THE GOAL OF FIRE ANT BIOLOGICAL CONTROL.
Major applied research initiatives that emerge from the above four areas of basic studies include:
1) 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 x 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 inholdings 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.
2) development of criteria for choosing the most effective Pseudacteon species for fire ant biocontrol in Texas.
Comparative studies of different phorids will be applied to fine-tuning 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 Brazil 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.
3) increasing the pool of Pseudacteon species which can be included under the Environmental Assessment for release which we obtained from APHIS in May,1995.
Permission to release particular South American phorids in Texas depends in large part upon laboratory experiments that document degree of host specificity. It is important to extend the list of species available for field trials in Texas as explained above. This is an important application of our host preference studies (currently we have APHIS permission to release four Brazilian Pseudacteon species in Texas based on past host specificity studies).
4) 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.
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, coordinate with others in integration of findings to effect biocontrol of fire ants. The ultimate goal is to initiate fire ant biological control in Central and South Texas by the year 2000.
SUMMARY OF RESEARCH PERSONNEL ON PHORID PROJECT AND DESCRIPTION OF ACTIVITIES
Bibliography of BFL-based fire ant research
Funding Sources (*currently active)
Additional Collaborators and Colleagues
Former Employees at the BFL Fire Ant Lab
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