Clifford S. Lofgren

Isolation of the trail recruitment pheromone ofSolenopsis invicta.

TheSolenopsis invicta trail pheromone is synthesized by the Dufours gland and is released through the sting apparatus. The recruitment subcategory of theS. invicta trail pheromone was shown to be composed of a mixture of the orientation pheromone, (Z,E)-α-farnesene and an unidentified homosesquiterpene consisting of three rings and one double bond (C-1). C-1 is present in worker Dufours glands at only 75 pg per worker equivalent. This is the first report that demonstrates that different exocrine products from the same gland control different subcategories of behavior related to mass recruitment.

Symposium: New Technologies for the Taxonomic Identification of Arthropods: Use of Chemical Characters in Defining Populations of Fire Ants, Solenopsis Saevissima Complex, (Hymenoptera: Formicidae)

The fire ants, Solenopsis invicta and S. richteri, were accidentally imported into the United States in the first half of this century from South America. In their adopted habitat the imported fire ants have thrived causing considerable medical and agricultural problems in the nine widely infested states of the south and southeast. The red imported fire ant, S. invicta was considered the dominant ant in the infested areas, having displaced the black imported fire ant, S. richteri, into a small enclave in northeastern Mississippi. However, a large reproductively viable S. invicta/S. richteri hybrid population was recently discovered across northern Alabama and into Mississippi and Georia by chemical analysis. This paper reports on the use of three species-specific chemical characters (venom alkaloids, cuticular hydrocarbons, and trail pheromones) to define S. invicta, S. richteri, and hybrid populations in the United States. In addition, these characters have been applied to fire ant taxonomy in South America. We also discuss fire ant population dynamics in the United States and its implications on several models of hybridization. These results have important consequences regarding the species status of the two imported fire ants and the taxonomy of fire ant populations in South America.

Student Symposium: Alternatives to Chemical Control of Insects: Adoption of Newly-Mated Queens: A Mechanism for Proliferation and Perpetuation of Polygynous Red Imported Fire Ants, Solenopsis Invicta Buren

The polygynous form of the red imported fire ant, Solenopsis invicta Buren was first reported from Mississippi in 1973; however, the source of the numerous fertile queens in polygynous colonies has remained an enigma. In 1987, 400 queens from a mating flight were marked with a durable paint and released in an area heavily populated with the polygynous form. None were recaptured after one week, but 9 months later, 4 clearly-marked queens were found in a nest 65 meters from their release point. This finding clearly points to adoption. About 5 weeks later, 37 of 107 fertile queens collected from 37 polygynous nests, were found to have partially histolyzed wing muscles and undeveloped ovaries. Mating flights had occurred a few days prior to the queen collections, thus it was apparent that these queens were newly adopted. This observation was verified following a second mating flight one week later. The results of our 3 studies clearly indicate that polygynous S. invicta can proliferate and perpetuate their colonies by queen adoption.

Major hydrocarbons of the post-pharyngeal glands of mated queens of the red imported fire antSolenopsis invicta

Thin layer and column chromatographic analyses showed that hydrocarbons were the major lipoidal components of post-pharyngeal glands of mated queens of the red imported fire ant,Solenopsis invicta. Gas liquid chromatographic analyses on an OV-17 column showed four major hydrocarbons which have been identified and confirmed by synthesis and comparative mass spectral analyses as 13-methylheptacosane, 13,15-dimethylheptacosane, 3-methylheptacosane, and 3,9-dimethylheptacosane. When microgram quantitites of the natural alkanes on filter paper were placed in colonies of ants, the ants clustered on the paper about the sample and proceeded to masticate the paper in the area containing the alkanes.

The orientation inducer pheromone of the fire ant Solenopsis invicta

Abstract Foraging ants recruit nestmate workers to food sources by a variety of mechanisms. We report that one behavioural subcategory of the recruitment pheromone complex of Solenopsis invicta Buren involves orientation induction. The orientation inducer pheromone exerts its effects by changing the physiological state of the recipient rather than by releasing a measurable behaviour. Some ant species use a physical ‘waggle’ behaviour to motivate (change physiological state) nestmate workers to follow their chemical trail. The orientation inducer pheromone can be interpreted as a chemical analogue of the physical ‘waggle’ inducing effects. This behaviour is not elicited by the recruitment pheromone components responsible for orientation and/or attraction. Each of these behavioural categories is mediated by a different blend of chemicals from the Dufours gland. Activity‐concentration thresholds indicate that the attraction and inducer part of the recruitment pheromone require about 250 times more worker equivalents for a response than the orientation pheromone. Therefore, the recruitment sub‐categories are differentially activated by the amount of Dufours gland material released.

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.

Tissue specificity and systematics of a Nosema in some species of Aedes, Anopheles, and Cules

Abstract Studies of the host-parasite relationships of a Nosema in four species of mosquitoes showed that the primary sites of infection were: (1) Anopheles quadrimaculatus —accessory glands, brain, fat body, gut, Malpighian tubules, muscle, nerve ganglia, rectum, ventral diverticula, and the ventriculus; (2) Culex quinquefasciatus —fat body, gut, and Malpighian tubules; (3) Culex salinarius —fat body, gut, Malpighian tubules, and muscle; and (4) Aedes aegypti —brain and nerve ganglia. The variation in susceptibility of tissues in host species is interesting and illustrates the danger of differentiating Microsporidia solely on the basis of the sites of the infection in hosts. Since anopheline mosquitoes appear to be the primary hosts, the parasite might be useful in control programs for anopheline mosquitoes and/or the interruption of development of plasmodia in the female mosquito. The taxonomic placement is also discussed.

Biochemical and behavioral evidence foe hybridization between fire ants,Solenopsis invicta andSolenopsis richteri (Hymenoptera: Formicidae)

Behavioral and biochemical evidence is presented for hybridization between the fire ants,Solenopsis richteri andS. invicta. The response of the two species to extracts of their trail pheromones presented as a point source is clearly species-specific; however, hybrid workers responded to parental Dufours gland extracts and parental workers responded to Dufours gland extracts of the hybrid. The behavioral evidence for hybridization was confirmed by gas Chromatograph comparison of the Dufours gland extracts of the three fire ant forms, which showed a pattern for the hybrid that was intermediate to the two parental species.

Synthesis of homofarnesenes: trail pheromone components of the fire ant, Solenopsis invicta

Abstract The synthesis of tour isomeric homofarnesenes, 3,4,7,11-tetramethyl-1, 3,6,10-dodecatetraenes, is reported. The major synthetic step was the indirect formation of a tetra-substituted double bond through the acid catalyzed oxidative rearrangement of an appropriate vinyl carbinol. Two of these compounds, the Z,E- and E,E- isomers were identical to two naturally occuring homofarnesene components of the trail pheromone of the fire ant, Solenopsis invicta .

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.