Summer 1997

Termite Bate Tests
Gregg Henderson and Brian T. Forschler

Termite baits were tested and evaluated in Louisiana by LSU Agricultural Center scientists and found to show promise in the battle to reduce the destruction caused by Formosan subterranean termites, the most feared and ferocious of the subterranean termites.

Subterranean termites are the most damaging and expensive insect pests to control in the southeastern United States. A single colony may contain up to 10 million individual workers and soldiers. Cellulose, the major constituent of wood, is the most essential food of subterranean termites. In Louisiana, there are three species of subterranean termitesCsouthern subterranean, Reticulitermes virginicus; eastern subterranean, Reticulitermes flavipes; and Formosan subterranean, Coptotermes formosanus, a native of China and the most feared and ferocious of them.

The hidden lifestyle of subterranean termites makes control difficult to implement and assess. Conventional treatments use combinations of chemically treated soil barriers; spot treatments with aerosols, liquids or dusts targeting infested sites; and wood preservatives. However, these methods do not generally succeed in suppressing the colony population for long. The desired effect of these applications is to provide a long-lasting chemical repellent. Unfortunately, Formosan termites, more so than others, sometimes evade these control measures. Formosan termites are more aggressive when feeding and can cause structural damage more quickly than can native subterranean termites. Their above-ground nest-building in trees, homes, telephone poles, landscaping timbers and wood piles helps a Formosan colony conserve water and bypass the need to return to subterranean galleries for moisture.

A new control strategy in use by termite control specialists involves a tool that recently received registration in the United StatesCthe termite bait. Termite baits are intended to reduce a population of termites by directing a small amount of slow-acting toxicant to a foraging colony. The bait is composed of a food substance preferred by termites, such as corrugated cardboard, and a slow-acting, non-repellent toxicant packaged in a ready-to-install, child-resistant feeding chamber. Hexaflumuron and sulfluramid are toxicants presently registered for this use. The colony foragers store the food in their bodiesCin their crops and lower intestinesCand share it with others far away from the bait site. Thus, nest caretakers, the queen, the king and soldier termites, which cannot feed themselves, can get a dose of toxic bait. In theory, an entire colony can be eliminated by using baits.

Termite baits were tested and evaluated in Louisiana by scientists at the LSU Agricultural Center. Between 1989 and 1997, 14 different termite bait toxicants supplied by chemical companies were evaluated against Formosan subterranean termites infesting water-bound bald cypress and tupelo gum trees found in the Calcasieu River near Lake Charles and in ponds in Sam Houston Jones State Park, West Lake, La. (Figure 1). Several different concentrations of the toxicants were screened, each having two to 10 tree replicates. There were approximately 100 trees in the study, all accessible only by boat. Except for the winged forms, these termite populations are unable to escape from the host tree, providing a unique field site for the evaluation of bait efficacy. In this situation, baiting results cannot be misinterpreted if the colony simply moves to a new foraging site. Termite infestations in the trees contained about 250,000 or more individuals and were easily observable due to the extensive amount of excrement and mud deposited on the bark.

Once an infested tree was selected for baiting, a 2-centimeter hole was drilled into the heartwood approximately 50 centimeters above the water line using a generator-powered drill. If the hole exposed a termite gallery or nest, and termites emerged from the opening, it was immediately fitted with a 25-centimeter length of heavy duty polyvinyl chloride (PVC) pipe, serving as a termite access bridge. Two removable PVC bait traps (15 centimeters long by 7.5 centimeters inner diameter) fixed onto a T-joint (in most cases, but not all) were placed on the proximal end of the access bridge (Figure 2). A 50-gram roll of corrugated cardboard was placed into each bait trap. Traps were inspected every two weeks until foraging termites were recorded consuming the cardboard, after which one side of the T-joint received treated bait while the other side received a bait without toxicant. Thus, each colony had three food choices: the wood on the tree, the untreated bait and the treated bait. When one or more of the treated baits was consumed, only untreated baits were put in traps thereafter to evaluate the effect of the consumed (or sometimes not consumed) treated bait on the colony. Except for sulfluramid at 100 parts per million, which was not checked for six months, untreated cardboard consumption was usually recorded every two weeks for a minimum of three months and a maximum of 10 months, depending on the combination of toxicants under evaluation. Baits were returned to the laboratory, dried and weighed for the evaluation. Determination of elimination of a tree colony required at least three inspections showing no feeding and no termite activity at baits or anywhere on the tree.

Four bait toxicants were effective in eliminating tree-infesting Formosan termite colonies: hexaflumuron, fipronil, sulfluramid and mirex (Figures 3 and 4). All other bait formulas and bait toxicants tested were ineffective because they were repellent and not fed upon or were not toxic at the concentrations tested.

Hexaflumuron (DowElanco, Indianapolis, Ind.) baits at 1,000 parts per million required the most consumption for colony elimination. Hexaflumuron works on insects when they begin the molting process. Molting is short-circuited and tree termite colonies died after 42 to 292 days. Hexaflumuron was registered in 1995 as a toxicant in a baiting system for home use by termite specialists. The result is a safe product that can help reduce or even eliminate termite populations around a structure.

Fipronil (Rhone-Poulenc, Research Triangle Park, N.C.) acts as a stomach poison on the foraging termites and was effective at very low concentrations (from 0.1 to 10.0 parts per million) although colony elimination was not always achieved. Since fipronil is in early development stages, these results are encouraging. At this writing, fipronil is not registered for use in termite baits.

Sulfluramid (FMC Corp., Princeton, N.J.) baits act as a metabolic inhibitor (similar to stomach poisons) and showed increased consumption when the concentration of toxicant was reduced. This is a dose-dependent response. All concentrations at 100 parts per million and above were effective at eliminating colonies (Figure 4). Sulfluramid baits are also available to homeowners for controlling termite populations. Above-ground baits were registered in 1996, and in-ground baits were registered in 1997.

Mirex (Allied Chemical Co., Morristown, N.J.) baits, like sulfluramid, showed a dose response. As toxicant concentrations increased, less feeding occurred and a shorter time to elimination resulted. As in this study, mirex baits had excellent results in field studies in the 1970s against termites. But since it is an organochlorine pesticide, as is DDT, it is no longer available for use in pest control.

Infestations of Formosan termites were first identified in Louisiana simultaneously in Lake Charles and New Orleans in 1966. At that time infestations already existed in several U.S. ports, including Houston, Texas, and Charleston, S.C., suggesting Formosan termite importation occurred when infested military cargo was returned from Asian countries. Living and dead trees along the river ports were natural above-ground nesting sites for this termite species. Tree infestations presently serve as dispersal units for Formosan colony reproductives (winged termites) to infest houses, wood piles, fences, other trees, mulch, etc.

Formosan termites are a frequent invader of homes in Lake Charles and New Orleans. New Orleans was recently singled out by the National Trust for Historic Preservation as one of America=s most endangered places because of the damage to historic buildings by Formosan termites. The development and use of baits have come none too soon, though it is clear that termite baits will not work in all instances. For example, in urban settings Formosan termites have more food choices available than do colonies in the Louisiana tree study, and they can build to larger numbers. One colony in New Orleans was estimated to have a population of 70 million foragers! These differences can affect bait performance.

The LSU Agricultural Center has had a key role in evaluating and developing termite baits for implementation by termite control specialists. Baits provide an advantage over current termite control measures by targeting a colony away from the hidden location of the nest. From an environmental perspective, termite bait control technology is highly successful since it reduces the amount of toxicant needed to control a termite infestation and confines the toxic bait to a limited area. These termite bait technologies offer exciting possibilities to control the Formosan subterranean termite more effectively and safely.

Gregg Henderson, Associate Professor of Entomology, LSU Agricultural Center, Baton Rouge, La., and Brian T. Forschler, Assistant Professor of Entomology, University of Georgia Experiment Station, Griffin, Ga.

Related sites:
University of Florida Formosan termite information
Auburn University Formosan termite information

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