Donald P. Jouvenaz

Transmission and infectivity of spores of Burenella dimorpha (Microsporida: Burenellidae)

Abstract Burenella dimorpha infects the tropical fire ant, Solenopsis geminata , producing two morphologically distinct types of spores. A binucleate, nonpansporoblast membrane-bounded (NPMB) spore develops in and destroys the hypodermis, rupturing the cuticle in the pupal stage. A uninucleate, pansporoblast membrane-bounded (PMB) spore develops in the fat body. Adult ants cannibalize ruptured pupae but do not ingest spores. Instead, the spores and particulate foods are diverted to the infrabuccal cavity, formed into an infrabuccal pellet, and fed to fourth-instar larvae only. This larval instar is the only stage in the life cycle of S. geminata that is vulnerable to infection. NPMB spores are infective, but PMB spores do not extrude their polar filaments in the larval gut and are expelled in the meconium upon pupation.

First Observation of Polygyny in Fire Ants,Solenopsis SPP., in South America

Polygyny, the coexistence of two or more egg-laying queens in a single colony of a social insect, occurs in several subfamilies of ants (Wilson 1971). The species of Solenopsis, however, were considered to be monogynous until Banks et al. (1973), and Glancey et al. (1973) observed polygyny in Solenopsis geminata (F.) and Solenopsis invicta Buren, respectively. Subsequently, Summerlin (1976) found a single polygynous colony of Solenopsis xyloni McCook. The existence of a spectrum from monogyny to extreme polygyny in the North American S. invicta population was substantiated by Fletcher et al. (1980). Populations of polygynous S. invicta are now known from Florida, Georgia, Mississippi, Louisiana, Texas (Lofgren and Williams 1984), Alabama, Arkansas, and Oklahoma (Banks and Wojcik unpublished). These populations are spreading, and in some cases are proving to be more difficult to control with pesticides than monogynous populations (Glancey et al. 1987). They are also characterized by increased densities of both ants and mounds (Lofgren and Williams 1984). Thus, polygyny in fire ants is currently a subject of interest and concern. We have not encountered polygynous colonies in our extensive surveys for biological control agents for fire ants in the states of Mato Grosso and Mato Grosso do Sul, Brazil, the presumed homeland of S. invicta (Wojcik 1986). Recently, however, we extended our surveys to Argentina, where we collected colonies of polygynous Solenopsis richteri Forel and Solenopsis quinquecuspis Forel. We were alerted to the possibility that we had encountered polygynous fire ants by the enormous biomass of brood in a colony of S. richteri, which has been separated from the soil by flotation (Banks et al. I98 1). This colony yielded 16 non-physogastric, dealate

Steinernematid nematode drenches for control of fire ants, Solenopsis invicta, in Florida.

Recent developments in low-cost, large-scale production of entomogenous nematodes of the genera Steinernema and Heterorhabditis (Bedding 1984) have facilitated largescale field testing against various soil-infesting insect pests (Kaya 1985, Poinar 1986), with good potential for commercial control in some applications. Early research by Poole (1976) and Quattlebaum (1980) showed promise that entomogenous nematodes have potential for controlling fire ants, Solenopsis spp. Furthemore, these nematodes have the ability to invade adult insects, and thus potential to kill fire ant queens. Agents which only kill worker ants do not effectively eliminate colonies, although they may temporarily reduce their size. A variety of entomopathogens, including viruses, bacteria, fungi, protozoa, and other species of nematodes have been evaluated for fire ant control. These organisms, with the possible exception of a fungus (Beauveria sp.) isolated from fire ants in Brazil (Stimac et al. 1987), produced little or no mortality in laboratory and/or field tests. Jouvenaz (in press) recently reviewed these evaluations and discussed the special problems attending the development of biological formicides. We selected a strain of Steinernemafeltiae produced by Biosys Inc. (Palo Alto, CA) for field evaluation after screening several strains of Steinernema and Heterorhabditis spp. in the laboratory. In the laboratory tests, groups of ants composed of queens (from a polygynous colony), about 25-30 workers, and a small quantity of brood were placed in 16 x 125 mm glass culture tubes containing 25 mm of slightly moistened sandy soil. The tubes were capped with plastic tops which allowed gas exchange and were maintained at 290 C. After two or three days of acclimation, one ml of deionized water without nematodes or containing 5,000 or 50,000 nematodes was added to each tube, and survival of queens was scored daily for four days. Ten replicates (a total of 50 queens) were used for each nematode concentration and for the control. After 96 h, the strain we selected had produced queen mortalities of 40% and 58% in 5,000 and 50,000 nematode dosaged, respectively. Mortality of workers and brood, although not quantitatively determined, was estimated to be at least 80%. Mortality of queens, workers or brood was not observed in the control group. In separate tests we observed that colonies of ants vacated soil treated with high concentrations of nematodes. The first of the two field evaluations reported here was conducted in October and November, 1987, at Site No. 1 in southeast Gainesville, Alachua Co., Florida. This site was a utiities right-of-way measuring about 365 x 23-30 m, with sandy soil and surrounded by trees. The site had been mowed regularly prior to the test, but was not mowed during the test period. The second test was conducted during June and July, 1988, at Site No. 2, 4 mi north of LaCrosse, Alachua Co., Florida. This site was an approximately rectangular plot 1.4 ha in size on a sod farm and was also bordered by trees. On both plots, the grass varied from 10-30 cm high, and was not mowed during the test period.

Scientific Notes: Evaluation of the Nematode Steinernema Carpocapsae to Control Fire Ants in Nursery Stock

Recent developments in low-cost, large scale production of entomopathogenic nematodes of the genera Steinernema and Heterorhabditis (Bedding 1984) have facilitated large-scale field testing against various soil-infesting insects (Kaya 1985, Poinar 1986), with good potential for control in some applications. Early research by Poole (1976) and Quattlebaum (1980) indicated that the potential included fire ants. Citrus growers in Florida using nematodes (BioVectorg; Biosys, Inc.) for control of soil insects have reported fewer problems with fire ants (personal communications to W. R. Martin). Jouvenaz et al. (1990), however, did not achieve significant control of red imported fire ants, Solenopsis invicta Buren, in field trials of nematodes (Biosys, Inc.) conducted in Florida. Steinernematid nematodes may be moderately effective against fire ants in irrigated soil. Morris et al. (1990) reported 47% control with Steinernema carpocapsae versus 39% control with the Amdro standard at sites containing irrigated turf. This level of control is far below normal for Amdro (Williams et al. 1987; Jouvenaz et al. 1990), indicating that it may have been broadcast on wet soil (personal communication, D. F. Williams, USDA, ARS). Unmarked mounds found outside the blocks after treatment were not included in the assessment for activity; thus, control by nematodes may have been overestimated due to mound relocation. Considerable relocation of fire ant nests occurred in the tests conducted by Jouvenaz et al. (1990). Had not mound movement been taken into consideration (Poole and Quattlebaum scored all mounds uninhabited after treatment as dead), the apparent control would have been over 77% (of 44 treated mounds, 34 were inactive). We subsequently confirmed the aversion of fire ants to nematodes by controlling the movement of small laboratory colonies between containers of sandy soil with single applications of BioSafe? Lawn and Garden Insect Control (Steinernema carpocapsae; Biosys, Inc., Palo Alto, CA). The readiness with which fire ants relocated their nests in the field and vacated soil in containers to avoid nematodes prompted us to evaluate the potential of these parasites to eliminate fire ants from nursery stock. The early spread of fire ants in the southeastern United States was greatly facilitated by the shipment of infested nursery stock (Lofgren 1986). Recently these pests have been transported to Arizona and California; if they become established in the West, their range will increase substantially. Currently, federal certification of nursery stock for shipment through quarantine is based solely on incorporation of chlorpyrifos. Granular chlorpyrifos is not as effective as previously believed, drenching poses problems of worker exposure, and both treatments are expensive (personal communication, H. Collins, USDA, APHIS). The improvement of methods for control of fire ants is a critical need of the nursery industry (Regelbrugge 1991). In the present study, three sequential tests were conducted using BioSafe against fire ants nesting in nursery pots containing Pittosporum sp. shrubs. A colony of S. invicta consisting of five queens, 3,000-5,000 workers and about 1.5 g brood was introduced into each of 50 1 gal pots containing shrubs 20-35 cm in height. The ants were

Some Protozoa Infecting Fire Ants, Solenopsis Spp

The black and the red imported fire ants, Solenopsis richteri and Solenopsis invicta, are medically and agriculturally important insects that infest ca. 8 × 107 ha (2 × 108 acres) in the southeastern United States. Both species were introduced into the United States from South America at Mobile, Alabama; the black imported fire ant about 1918 and the red imported fire ant about 1940. Solenopsis riahteri is now restricted to a relatively small area in northeastern Mississippi and northwestern Alabama; S. invicta infests Florida and Louisiana, and parts of North Carolina, South Carolina, Georgia, Alabama, Mississippi, Texas, and Arkansas. The tropical fire ant, Solenopsis geminata, may also be an introduced species; however, it has been a resident of this country for so long it is generally regarded as native.

Histopathology of the tropical fire ant, Solenopsis geminata, infected with Burenella dimorpha (Microspora: Microsporida)

Abstract Pupae of the tropical and fire ant, Solenopsis geminata, infected by the microspordium Burenella dimorpha develop clear, blister-like areas in the vertex of the head and in the petiole. In sexual pupae, clearing may also develop in the dorsal thorax. The developing eyes of both worker and sexual pupae appear sunken and irregular in outline, with deranged facits. These pathognomonic signs are the result of destruction or inhibition of development of the cuticle. The clear areas results from tissue fluids seeping into the space between the denuded hypodermal tissue and the pupal sheath (old larval integrument). The fact body is progressively diminished and the brain shrinks as the disease progresses. These organs, which are covered by a layer of hypodermal tissues, decrease in mass and recede from the pupal sheath, which is kept extended by tissue fluids. The malformation of the eyes is also the results of destruction of the cuticle. The lenses, which are cuticular, are destroyed, leaving the ommatidia unanchored distally. In advanced infection, the pupae rupture and are cannibalized by adult workers. The workers do not ingest the spores into the crop, but divert them (with other particulate matter) to the infrabuccal cavity. An infrabuccal pellet is formed which is subsequently expelled and fed to fourth instar larvae only. The intracolonial dissemination of spores is thus facilitated by the destruction of the cuticle of infected pupae.