David F. Williams

Impact of Thelohania solenopsae (Microsporidia: Thelohaniidae) on Polygyne Colonies of Red Imported Fire Ants (Hymenoptera: Formicidae)

Abstract Three studies were conducted to assess the effects of the entomopathogen Thelohania solenopsae on polygynous, red imported fire ant, Solenopsis invicta Buren, colonies. A total of 57 of 122 queens (46.7%) from nine, field-collected, polygyne, S. invicta colonies, was infected with T. solenopsae. Infection rate of queens for each colony ranged from 25 to 75%. Laboratory colonies of polygyne S. invicta, with three to 12 queens, were inoculated and infected with T. solenopsae. Brood levels in all infected colonies declined to 0 after 26–52 wk. Brood did not reappear in any of the colonies after 3–11 wk, even though in two of the eight infected colonies, five fertile queens that were uninfected were recovered. Thus, polygyne, S. invicta colonies infected with T. solenopsae, which were confined and isolated under laboratory conditions, did not recover. Field plots that contained polygynous S. invicta colonies, which were infected with T. solenopsae, were monitored over a 2-yr period. Infection rates increased during the study and reached a maximum of 93%. Fire ant nest density and colony sizes fluctuated over time, with maximum reduction of 63% per plot. In general, fire ant reductions were attributed to smaller colony sizes. T. solenopsae infections in polygynous S. invicta can result in a slow colony decline and death. Under field conditions, the prolonged colony death may mask the impact of T. solenopsae by allowing for concurrent reinfestations.

Detection of Thelohania solenopsae (Microsporidia: Thelohaniidae) in Solenopsis invicta (Hymenoptera: Formicidae) by multiplex PCR

Oligonucleotide primer pairs were designed to unique areas of the small subunit (16S) rRNA gene of Thelohania solenopsae and a region of the Gp-9 gene of Solenopsis invicta. Multiplex PCR resulted in sensitive and specific detection of T. solenopsae infection of S. invicta. The T. solenopsae-specific primer pair only amplified DNA from T. solenopsae and T. solenopsae-infected S. invicta. This primer pair did not produce any amplification products from DNA preparations from uninfected S. invicta, seven additional species of microsporidia (including Vairimorpha invictae), or Mattesia spp. The Gp-9-specific primers recognized and amplified DNA from Solenopsis xyloni, Solenopsis richteri, Solenopsis geminata, the invicta/richteri hybrid, and monogyne and polygyne S. invicta, but not from T. solenopsae, and, as such, served as a positive control verifying successful DNA preparation. Multiplex PCR detected T. solenopsae in worker fire ants infected with as few as 5000 spores. Furthermore, multiplex PCR detected T. solenopsae in all developmental stages of S. invicta. However, detection could be made more sensitive by using only the T. solenopsae-specific primer pair; ants infected with as few as 10 spores were able to be discerned. Multiplex PCR detection of T. solenopsae offers the advantages of a positive control, a single PCR amplification, detection of all developmental stages, and increased sensitivity and specificity compared with microscopy.

Yellow-head disease caused by a newly discovered Mattesia sp. in populations of the red imported fire ant, Solenopsis invicta

Recent surveys conducted in Florida, USA to determine the presence of Thelohania solenopsae revealed a new protozoan in S. invicta populations. The pathogen was first observed in workers collected from southwest Alachua Co., Florida. Large workers and female alates exhibited atypical yellow-orange colouration in the head and sometimes in the thorax, hence the designation yellow-head disease. The abdomen of the infected ants is normally as dark as those of older ants. Examination of the body contents of the ants showed many spindle-shaped, paired oocysts in the cuticle in all body regions and inside different body parts including the head and appendages. Further morphological examination of the oocysts identified the pathogen as belonging to the genus Mattesia. Notes on the distribution and pathogenesis of the protozoa are presented.

Field host range of the fire ant pathogens Thelohania solenopsae (Microsporida: Thelohaniidae) and Vairimorpha invictae (Microsporida: Burenellidae) in South America

We studied the field host specificity of the microsporidia Thelohania solenopsae and Vairimorpha invictae and their prevalence in the imported fire ants, Solenopsis invicta and S. richteri. Terrestrial ants were sampled by using bait traps and/or nest sampling at preselected sites in Argentina and Brazil. The sampling included the genera Solenopsis, Pheidole, Camponotus, Crematogaster, Linepithema, Brachymyrmex, Paratrechina, Dorymyrmex, and Wasmannia. The samples were examined under a phase-contrast microscope for the presence of microsporidian infections. The bait trap sampling revealed that: (1) T. solenopsae infected only S. richteri, S. invicta, and Solenopsis sp. at 6–67% of the sites and in 1.5–29% of the traps; (2) V. invictae infected only S. invicta at 6% of the sites and in 3% of the samples. The nest sampling revealed that: (1) T. solenopsae infected S. invicta, S. richteri, and S. macdonaghi, at 41–67% of the sites and in 11–58% of the colonies; (2) V. invictae infected the same species at 15–50% of the sites and in 2–26% of the colonies. We detected T. solenopsae and V. invictae in equal percentages of S. invicta sites (41%); however, the percentage of colonies infected with V. invictae was 20% and with T. solenopsae only 11%. At S. richteri sites, in contrast, T. solenopsae occurred at 46% of the sites and 15% of the colonies and V. invictae occurred at only 15% of the sites and 2% of the colonies. In S. macdonaghi, T. solenopsae was detected at 67% of the sites and 58% of the colonies, and V. invictae was detected at 50% of the sites and 26% of the colonies. This is the first report of V. invictae infecting S. macdonaghi. The proportion of S. richteri and S. invicta infected with T. solenopsae was similar. In contrast, the proportion of S. invicta infected with V. invictae was higher than S. richteri. We conclude that the microsporidia, T. solenopsae and V. invictae, show a very high specificity for Solenopsis ants in the field. It appears that T. solenopsae infects S. invicta and S. richteri equally but V. invictae may be more adapted to infect S. invicta. Published by Elsevier Science (USA).

Thelohania solenopsae (Microsporidia: Thelohaniidae) Infection in Reproductives of Red Imported Fire Ants (Hymenoptera: Formicidae) and Its Implication for Intercolony Transmission

Abstract The natural mechanism of intercolony transmission of Thelohania solenopsae, a pathogen of red imported fire ants, Solenopsis invicta, is unknown. However, T. solenopsae can be transmitted by introducing infected brood into an uninfected colony. We hypothesized that the transfer of brood among colonies during intercolony competition may be a mechanism for the horizontal transmission of T. solenopsae. Male and female reproductive caste alates, collected during the initiation of mating flights from infected colonies, had T. solenopsae infection rates of 93 and 75%, respectively. In addition, 47 field-collected, newly mated queens that were reared in the laboratory established T. solenopsae-infected colonies that contained egg, larvae, pupae, and adults. Because T. solenopsae is transovarially transmitted, this indicated that infected founding queens generated infected colonies. A life span of ≤52 wk was documented for 81% of the infected queens and 59% for uninfected queens. To determine whether imported fire ant colonies can become infected with T. solenopsae via colony raiding, seven pairs of S. invicta colonies consisting of large, uninfected and small, infected colonies were given access to each other in the laboratory. T. solenopsae infection was detected in four of seven of the large colonies. In the four large, infected colonies, brood levels declined an average of 64% after 22 wk in contrast to a 116% increase in the controls. Thus, there was evidence that incipient, T. solenopsae-infected colonies could provide a source of inocula for the horizontal transmission of T. solenopsae through the transfer of brood during colony raiding.

Symposium on Imported Fire Ants: The Development of Toxic Baits for the Control of the Imported Fire Ant

The red imported fire ant (RIFA), Solenopsis invicta Buren, and the black imported fire ant, Solenopsis richteri Forel were introduced into the United States at Mobile, Alabama, about 40 to 60 years ago. This paper will be limited to the RIFA. The ants spread rapidly from this initial port of entry and now infest all or parts of 9 states and Puerto Rico. Eventually the mound building and stinging habits of the ants caused farmers in infested areas to demand relief and in 1957 the U.S. Congress voted to establish a Federal-State Cooperative Imported Fire Ant Program (Lofgren et al. 1975). A summary of the important events related to the introduction and control of imported fire ants is shown in Table 1. Chemical control of the imported fire ants has involved 3 methods; (1) residual

Seasonal studies of an isolated red imported fire ant (Hymenoptera: Formicidae) population in Eastern Tennessee.

Abstract Seasonal studies on a 1,200-ha isolated infestation of Solenopsis invicta Buren located in McMinn County, TN, were initiated in 1993 and continued through 1997. Winter survivability was evaluated and compared with a southern Mississippi site. The impact of S. invicta on local myrmecofauna was compared with a Tennessee non-infested site. Data collected over four winters indicate that consecutive days at a low ambient air maximum temperature is more indicative of S. invicta winter survivability than minimum temperature. After significant S. invicta mortality the first winter (1993–1994), we did not find significant differences in ant species diversity between the S. invicta infested Tennessee site and a similar, but non-infested site, 32 km away. Species commonly collected in the S. invicta infested site included Forelius pruinosus Roger, an unnamed Forelius sp., Paratrechina terricola (Buckley) and Pheidole vinelandica Forel.

Natural Occurrence and Laboratory Studies of the Fire Ant Pathogen Vairimorpha invictae (Microsporida: Burenellidae) in Argentina

Abstract We surveyed 154 sites in north-central Argentina and sampled 2,528 fire ant colonies for the presence and intracolonial prevalence of the microsporidium, Vairimorpha invictae Jouvenaz & Ellis, in the red imported fire ant, Solenopsis invicta Buren. The concentrations of meiospores and binucleate spores were quantified in workers and sexuals; and the occurrence and intracolonial prevalence of dual infections with Thelohania solenopsae Knell, Allen & Hazard were studied. To study the effect of V. invictae in infected colonies of S. invicta, we compared the proportion of infected living workers to the proportion of infected dead workers, and compared the survival of uninfected and infected workers. V. invictae occurred at 13% of the sites and 2.3% of the colonies. At times, the disease reached epizootic levels in certain areas. We found vegetative stages in 4.8–52.3% of eggs, larvae, pupae, and queens, meiospores in 4–56.3% of pupae and mature stages, and binucleate spores in 9.5–63% of all life stages, except eggs. Evidence for transovarial transmission is provided. The percentage of sexual males infected was significantly higher than that of sexual females (44.9 versus 15.9%, respectively). Dual infections (V. invictae + T. solenopsae) occurred in 0.24% of the colonies. V. invictae was present in 9.3% of living workers and in 56.7% of dead workers. Mortality rates of workers from Vairimorpha-infected colonies were higher than those of workers from uninfected colonies. Survival times of infected workers were 18.8–31.7% less than those of uninfected workers. The studies reported here contribute to the evaluation of V. invictae for use as a classical biological control agent against the red imported fire ant in the United States.

Pseudacteon Obtusus (Diptera: Phoridae) Attacking Solenopsis Invicta (Hymenoptera: Formicidae) in Brazil

Although parasitism of ants (Hymenoptera: Formicidae) by phorid flies (Diptera: Phoridae) has been reported by a number of investigators, their behavior is still poorly understood (Pergande, 1901; Wasmann, 1918; Borgmeier, 1925, 1931, 1963, 1969; Donisthorpe, 1927; Steyskal, 1944). Recently Williams et al. (1973), Williams and Whitcomb (1974) and Williams (1980) reported on two genera of phorids, Pseudacteon and Apodicrania, that attack fire ants in South America. They noted that Apodicrania larvae were endoparasites of fire ant larvae (Solenopsis invicta) while sixteen species of the genus Pseudacteon seem to parasitize workers of the Solenopsis saevissima complex. Although attacks by Pseudacteon on fire ants have been observed, evidence of actual parasitism (i.e. oviposition by the parasite) is lacking. Here, we report field observations of Pseudacteon attack on foraging S. invicta workers and document parasite oviposition on a host ant. Our observations indicate that the parasite preferentially attacks major workers of the host species. Possible reasons for this caste-bias are discussed. Data were collected on April 18 (16:00-16:30), April 19 (11:00-15:30) and on April 24 (15:00-17:00), 1985 in Caceres, Mato Grosso, Brazil during studies of ant species competing for baits. At this time the phorid flies, Pseudacteon obtusus Borgmeier were observed hovering over workers of the fire ant Solenopsis invicta Buren as they fed at bait stations or moved along the foraging trails. Between one and four P. obtusus were observed during any one observation period. Only a few attempts (n3) were made by phorids to attack minor workers, and in these cases two of the minor workers escaped by crawling under debris, leaves or grass, while the

Biological control of fire ants: an update on new techniques

OBJECTIVE To review the present understanding of biological control methods for imported fire ants (IFAs). DATA SOURCES We searched MEDLINE, Biological Abstracts, and the US Department of Agriculture Formis Ant Literature database. STUDY SELECTION All articles published in the last 10 years on biological control of fire ants were selected. RESULTS The decapitating flies Pseudacteon tricuspis, Pseudacteon curvatus, and Pseudacteon litoralis have been successfully released in the United States. The continued releases of multiple species of decapitating flies will expand the area of impact, applying greater pressure on IFA populations throughout the southern United States. The microsporidium Thelohania solenopsae causes the slow demise of a fire ant colony. The advantages of T. solenopsae as a biological control agent include debilitation of queens, specificity for IFAs, self-sustaining infections, and lower relative tolerance to chemical pesticides. Solenopsis daguerrei has also been shown to have detrimental effects on IFA colony growth, the number of sexual reproductives produced, and the number of host queens in multiple queen colonies; however, this parasite is difficult to rear in the laboratory and to introduce into IFA colonies. CONCLUSIONS It is unlikely that IFAs can be completely eradicated from the United States. However, technology using chemicals and/or natural control agents could eventually maintain populations at low levels if an integrated approach is used for control.