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Potential Biological Control Agents for the Red Imported

Bastiaan M. Drees and Allen E. Knutson Department of Entomology, A&M University, College Station, Texas

The , Solenopsis invicta release in the U.S., the natural enemy is reared in Buren (: Formicidae), arrived in the large numbers and released at multiple locations , with few parasites or pathogens during several years. The goal of importation that attack this pest in its native home of South biological control is to establish permanent and America (Wojcik 1998). Lack of natural enemies effective populations of the natural enemy. is believed to be one factor that has allowed the Establishment of the natural enemy at effective red imported fire ant to spread and dominate the levels eliminates the need for further mass-rearing landscape Porter 1998). Fire ant densities are five and release, which is expensive. times greater in the U.S. than in , Some imported natural enemies may be where this pest is attacked by many different effective but fail to establish permanent natural enemies. Biological control, the use of populations. Other natural enemies may be already natural enemies to suppress pest populations, present in the U.S. but occur in numbers too small offers an opportunity to re-establish these natural to provide effective control. In these cases, it may enemies with the introduced pest(s) or augment be possible to mass-rear the enemy and these natural enemies in the U.S. and reduce the periodically release it to increase the level of impact of the red imported fire ant. Biological biological control. This activity is termed control is one area funded for expanded research augmentation biological control. under the Texas Fire Ant Research and This approach requires rearing procedures that Management Plan (see Brochure, “”Red maintain the genetic characteristics necessary for Imported Fire Ant Highlights 1997-2003). the natural enemy to be effective when released in the field. Some natural enemies, especially How Is Biological Control pathogens, may be formulated and applied much like an insecticide. Accomplished? Biological control can be pursued through the introduction and establishment of new natural How Does Biological Control Work? enemies or by mass-rearing and periodically Pathogens, predators, and parasites can impact releasing new or existing natural enemies. The fire ant populations directly by killing or first approach is termed importation biological indirectly by making them less competitive with control. native ants. Native fire ants compete with red The first step is to search for promising natural imported fire ants for food. Also, native ants feed enemies in the ant’s native home. Only natural on fire ant queens and can eliminate colonies enemies that attack the red imported fire ant, and while they are still small. Currently, most of our not ants native to the U.S., are considered for native ant species cannot compete effectively with importation and release. This is important fire ants and are soon overwhelmed. If imported because native ant species compete with natural enemies reduce the fire ant’s ability to imported fire ants for food. Native ants also forage for food, reproduce, or disperse, then native attack and kill young fire ant queens as the ant species may gain a competitive edge and queens begin to establish colonies in new suppress fire ant densities. territories. A combination of several natural enemies The importation of exotic natural enemies must will likely be necessary to shift the balance in be approved by the U.S. Department of favor of native ants. Establishing new enemies and Agriculture- and Plant Health Inspection developing methods for augmenting natural Service. Once approved for importation and enemies of the red imported fire ant require long-

Fire Ant Plan Fact Sheet #009 fireant/fapfs009.2002rev June 2002 revision term commitments to research and development. Phorid flies. Phorid flies ( species) Even then, natural enemies alone are not are small flies that parasitize fire ants. The adult expected to control fire ants. Rather, biological flies are about 1/16 inch long and fly rapidly. control will be one part of an integrated pest They hover above disturbed mounds or along management program that will likely include foraging trails waiting for an opportunity to swoop selective insecticides, cultural practices, and down and deposit an egg on a fire ant worker. other control methods (see Brochure, “Areawide Once on the ant, the egg quickly hatches into a suppression of fire ants”, USDA-ARS). tiny maggot, which bores into the fire ant. The maggot feeds inside the ant for about three weeks Natural Enemies of the before the parasitized ant dies. During the final stage of attack, the maggot consumes all of the

Red Imported Fire Ant head’s contents and transforms to the pupa stage. The following is a list of pathogens, predators The ant’s head then falls from its body as enzymes and parasites under study for potential use as produced by the parasite dissolve the connecting biological control agents. Most are in the early tissue. The adult fly emerges from the ant’s head stages of research. A few species have been about three weeks later. released in limited numbers under controlled Typically, phorid flies parasitize only 1 percent conditions. None are yet available for general to 3 percent of the native fire ants, and this alone distribution. has little impact on fire ant numbers. The flies’ Thelohania. Thelohania solenopsae is a effect on ant behavior is more important. Fire ant microscopic protozoan that infects immature and workers quickly recognize when phorid flies are adult fire ants. Diseased ants, including queens, present and either attempt to escape underground have shorter life spans, and over a period of or assume a defensive posture. The presence of several months to a year, the colony declines. only three to four flies is sufficient to disrupt ant The pathogen is apparently transmitted by activity. diseased ants moving between multiple-queen As a result, ants attacked by phorid flies spend colonies. Thelohania attacks only the exotic red less time searching for food. Other ant species, not and the and does not attacked by the phorid flies, benefit by the greater attack other ant species native to the U.S. food resource available to them. Thus, the decline In Argentina, about 20 percent of the red in food collection and increased competition from imported fire ant colonies are infected. Surveys native ants has a much greater negative impact on in the U.S. did not detect this disease organism a fire than does death of a small until 1997, when it was discovered in Florida. percentage of worker ants actually parasitized. It Since then, Thelohania has also been found in is expected that red imported fire ants in the U.S. Texas and Mississippi. Research is under way to will respond similarly to introduced phorid flies as discover ways to increase the impact of this do the red imported ants in South America. pathogen and culture it in the laboratory and the The phorid flies native to the U.S. attack only field (Williams et al. 1999). the native fire ant species, Solenopsis geminata. Beauveria. is a common There are about 15 species of Pseudacteon in fungus that attacks many species of . A Brazil and Argentina that attack the red imported strain of Beauveria that attacks the imported fire fire ant and several of these species are being ant was reported from Brazil in 1987. This evaluated for rearing and release in the U.S. It is fungus produces microscopic spores that attach expected that those phorid species that attack ants to the ant’s body, germinate, and grow inside the foraging for food will be more effective than those ant. The fungus feeds on the internal organs of fly species that attack ants only at disturbed the ant. The ant soon dies, and its body is filled mounds. Mass rearing techniques are being with a fungal growth. The fungus sometimes developed, and one exotic species was released by grows outside the dead ant, covering it with a the USDA-ARS in Florida in 1997. Researchers white, fuzzy growth. Studies have shown that at the University of Texas also have released an Beauveria applied to the is much less exotic species in Texas, effective than if the spores are applied directly to Borgmeier (Porter & Alonso 1999). Studies are the ants. The application of Beauveria to fire ant under way to determine if the released species baits is being investigated (Bextine & Thorvilson 2002).

Fire Ant Plan Fact Sheet #009 fireant/fapfs009.2002rev June 2002 revision survive. Additional releases are planned as flies Orasema. Species of Orasema (Eucharididae) become available. are tiny wasps that parasitize immature fire ants. Parasitic ant. Solenopsis daguerri is an Female Orasema wasps lay large numbers of eggs unusual ant species that takes control of the fire on plant leaves and buds. The eggs hatch into tiny ant colony by parasitizing the fire ant queen or flattened larvae called planidia. The planidia lie in queens. The parasitic ant enters the fire ant wait and attach to passing ants. Once in the ant colony and is not killed because it produces the colony, the planidia leave the worker ant and same pheromone (chemical signals) that fire ants attach to ant larvae. When the ant larva pupates, use to recognize their fellow nest mates. The the planidia consumes the ant pupa. Typically, parasitic ant seeks out a fire ant queen, crawls on only a small percent of the fire ants are killed by top of her, and grasps her tightly with its legs and Orasema. Several species of Orasema parasitize jaws. A fire ant queen can become “yoked” by the imported fire ant in South America, and two or three parasitic ants. Each parasite several other species of Orasema occur in the U.S. produces queen pheromones that allow it to Research is under way to learn more about these masquerade as a fire ant queen. Thus deceived, ant parasites and to develop mass-rearing the worker fire ants proceed to feed the parasite techniques. and tend the eggs it produces. The fire ant queen, Nematodes and mites. Certain nematodes left untended by the workers, gradually stops (Steinernema carpocapsae and Heterorhabditis laying eggs and starves to death. Fire ant species) also attack and parasitize red imported workers rear the parasitic ant eggs and soon the fire ants, and other insects (see FAPFS012). Ants fire ant colony becomes a colony of parasitic in treated colonies often leave the nesting site or ants. Emerging parasitic ants, which are all mound and move to a new location (Drees et al. queens (no worker ants are needed) leave the 1992). However, field evaluations of colony in search of new fire ant colonies to commercially available species/strains of these parasitize. In South America, the parasitic ant is parasites currently being marketed for fire ant present in about 1 percent to 4 percent of the fire control have not yet been conducted to ant colonies. The parasitic ant is currently in demonstrate their effectiveness. quarantine in the U.S. Researchers are The straw itch mite, Pymotes tritici, is a native developing methods to rear sufficient numbers of external parasitic mite of insects that does not the parasite for eventual release in the U.S. normally attack fire ants. However, when applied Strepsiptera. Strepsiptera are minute insects in large numbers to fire ant colonies under that parasitize other insects. One species, laboratory conditions, straw itch mites will feed Caenocholax fenyesi, attacks the red imported on immature ants. Published field research fire ant in the U.S. Like other Strepsiptera, C. evaluating commercially available straw itch mites fenyesi has a complex and unusual life cycle. applied as directed to fire ant colonies have The female parasitizes a species of bush cricket, reported insignificant levels of control (Thorvilson Hapithus agitator. Once the immature parasite et al. 1987). Moreover, the straw itch mite is has consumed the cricket, she develops into the widely regarded as a pest and, as its name implies, adult stage. However, the adult female never can cause skin irritation in humans. leaves the dead cricket. Rather, she produces The Pymotes mite and parasitic nematodes have thousands of eggs that hatch into larvae called been available for sale as individual mound triungulins. The tiny, flattened triungulins leave treatments. Their high cost may prohibit large- the female and search for new hosts. While scale use. Also, their effects, if any, are generally female triungulins must find another bush limited to the treated ant colonies and are not cricket, male triungulins develop in fire ant expected to persist in the environment or spread adults. Once a male triungulin attaches to a from colony to colony. However, additional passing fire ant, it burrows into the ant to feed research may improve strains and delivery and develop. Parasitized fire ants typically climb methods of the nematodes and mites to make them to a high perch where they soon die. The adult effective biological control agents. male Strepsiptera then emerges from the dead fire ant. Only about 1 percent to 2 percent of the fire ants in a colony are parasitized by C. fenyesi in Texas.

Fire Ant Plan Fact Sheet #009 fireant/fapfs009.2002rev June 2002 revision Some Potential and Natural # Mites. Pyemotes ventricosus (Acarina: Enemies of Red Imported Fire Ants Pyemotidae). Common in the U.S. These mites are not normally found attacking fire ants but will feed on fire ants if applied in Pathogens large numbers. # Thelohania solenopsae (Protozoa: Predators Microspora: Thelohaniidae). Produces large cysts in adult ants; found in adult and # Several different kinds of insects live in fire immature ants. ant colonies and feed on immature ants. These include species of beetles (Scarabaeidae, # Vairimorpha invictae (Protozoa: Microspora: Histeridae and Chrysomelidae), true bugs Burenellidae). Does not produce cysts; found (Hemiptera: Lygaeidae) and silverfish in adult and immature ants. (Thysanura). None of these are being considered at this time as biological control # geminata (Protozoa: Neogregarinida: agents. Lipotrophidae). Spores found in immature fire ants, and infected individuals die in the pupal stage. Literature cited: # Beauveria bassiana (Fungi: Deutero- mycotina). A strain of this common fungus Bextine, B. R. and H. G. Thorvilson. 2002. grows internally in adult fire ants and causes Monitoring Solenopsis invicta (Hymenoptera: their death. Formicidae) foraging with peanut oil-baited, UV-reflective Beauveria alginate pellets. Parasites Southwestern Entomologist 27(1):31-36. Drees, B. M., R. W. Miller, S. B. Vinson & R. # Parasitic fly. Pseudacteon and Apodicrania Georgis. 1992. Susceptibility and behavioral spp. (Diptera: ). Larvae are internal response of red imported fire ant parasites, but few (1 percent to 3 percent) of (Hymenoptera: Formicidae) to selected the ants are parasitized. Egg-laying attempts entomogenous nematodes (Rhabditida: by adult flies prevent daytime ant foraging Steinernematidae & Heterorhabditidae). J. behavior, providing time for native ants to Econ. Entomol. 85(2):365-370. forage. Porter, S. D. 1998. Biology and behaviour of Pseudacteon decapitating flies (Diptera: # Parasitic ant. Solenopsis daguerri. Phoridae) that parasitize Solenopsis fire ants (Hymenoptera: Formicidae). Workerless, (Hymenoptera: Formicidae). Florida Entomol. obligate parasitic ant. 81(3):292-308. Porter, S. D. and L. E. Alonso. 1999. Host # Strepsiptera. Tiny parasites of fire specificity of fire ant decapitating flies ants. (Diptera: Phoridae) in laboratory oviposition trials. J. Econ. Entomol. 92(1):110-114. # Parasitic wasp. Orasema spp. (Hymenoptera. Thorvilson, H. G., S. A. Philips, Jr., A. A. ). Females lay eggs on plant Sorenson & M. R. Trostle. 1987. The straw tissue. After eggs hatch, the planidia (first itch mite, Pyemotes tritici (Acari: stage larvae) are phoretic on worker ants. In Pyemotidae), as a biological control agent or the nest, planidia feed externally on ant red imported fire ants, Solenopsis invicta pupae, and adult ants fail to emerge. (Hymenoptera: Formicidae). The Florida Entomol. 70 (1): 440-444. # Nematodes. Tetradonema solenopsis Williams, D. F., D. H. Oi, and G. J. Knue. 1999. (Nematoda: Mermithoidea: Infection of red imported fire ant Tetradonematidae). Commercially available (Hymenoptera: Formicidae) colonies with the species include Steinernema caropcapsae entomopathogen Thelohania solenopsae and Heterorhabditis heliothidis.

Fire Ant Plan Fact Sheet #009 fireant/fapfs009.2002rev June 2002 revision (Microsporidia: Thelohaniidae). J. Econ. For more information regarding fire ant Entomol. 92: 830-836. management, see Extension publications B-6043, Wojcik, D. P. 1998. Survey of biological control Managing Red Imported Fire Ants in Urban agents in Brazil - a final report, with Areas; B-6076, Managing Red Imported Fire Ants comments on preliminary research in in Agriculture; B-6099, Broadcast Baits for Fire Argentina. in Proceedings of the 1998 Ant Control; or L-5070 The Texas Two-Step Imported Fire Ant Conference, Athens, GA, Method Do-It-Yourself Fire Ant Control for pp. 50-61. Homes and Neighborhoods. Also visit our web site at http://fireant.tamu.edu.

The information given herein is for educational Acknowledgment purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by This fact sheet was originally written and Texas Cooperative Extension or the Texas Agricultural released in May 1998. The authors are grateful to Experiment Station is implied. Dr. Sanford Porter, Dr. Harlan Thorvilson, and Dr. S. Bradleigh Vinson for their review of Educational programs conducted by Texas Cooperative earlier drafts of this fact sheet. Extension serve people of all ages regardless of socioeconomic level, race, color, sex, religion, disability or national origin.

Fire Ant Plan Fact Sheet #009 fireant/fapfs009.2002rev June 2002 revision