POSSIBLE FUTURE CHEMICAL ALTERNATIVES
Hexaflumuron is a benzoylurea compound which is active as a chitin synthesis inhibitor.
Consistent with other members of this class of insect growth regulators, hexaflumuron has very low acute toxicity (oral LD50 greater than 5000 mg/kg in rats). It is not teratogenic, carcinogenic or mutagenic, and does not induce delayed neurotoxicity in hens. However, in a range of repeat-dose studies in mice, rats and dogs, it produced significant increases in methaemoglobin levels, with a resultant increase in haematopoiesis in some cases.
DowElanco are developing this compound as part of a system to detect termites, eliminate colonies and provide protection against re-infestation. The method involves placing small 'stations' (approx. 6 inches in diameter and flush with the ground, resembling a lawn sprinkler) in the ground around the house (30 for a typical house). Initially, pieces of wood are placed in the stations and if there are signs of termite activity, then hexaflumuron is applied in baits in the same stations
Studies by CSIRO in Australia have unambiguously demonstrated the elimination of field colonies of Coptotermes acinaciformis and Nasutitermes exitiosus after foragers fed on bait matrix treated with hexaflumuron.
One drawback to the widespread introduction of this system would be the need to monitor 30 or more stations on a reasonably regular basis.
A System for Elimination of
Subterranean Termite Colonies
Nan-Yao Su and Rudolf H. Scheffrahn
University of Florida, Ft. Lauderdale Research and Education Center
3205 College Avenue
Ft. Lauderdale, FL 33314
Of the approximately $1.5 billion spent annually for termite control in the U.S., subterranean termites account for an 80% share. Triple mark-recapture programs using dye markers such as Sudan Red revealed that a single subterranean termite colony may contain millions of foragers and may forage a distance of up to 300 ft (Su and Scheffrahn 1988, Grace et al. 1989, Su et al. 1993).
A large subterranean termite colony, therefore, may inhabit large areas of soil beneath an infested home, Conventional soil termiticides have been used for the last four decades to provide a chemical barrier for the exclusion of soil-borne termites from a structure. Typically, 100 - 200 gal. of liquid termiticide (8 - 17 lb. active ingredient @ 1% concentration) are applied in the soil beneath and surrounding an infested home (NPCA 1985). The vast proportion of subterranean termites, however, are not affected by such soil termiticide treatment. These termites often find their way back into the structure, causing costly re-treatment (Su and Scheffrahn 1988).
Population studies for field colonies of subterranean termites indicated that wooden stakes placed near a large colony of these cryptic insects are eventually attacked by termites. Slow-acting and non-repellent toxicants may be incorporated into such food sources to affect the vast population of the subterranean termite colony (Su et al.1982) . Through an extensive laboratory screening program (Su and Scheffrahn 1993), we discovered that a chitin synthesis inhibitor, hexaflumuron, interfered with the molting process of both the Formosan subterranean termite, Coptotermes formosanus, and the eastern subterranean termite, Reticulitermes flavipes . A baiting procedure that incorporated a matrix containing hexaflumuron was evaluated against field colonies of the Formosan and eastern subterranean termites (Su 1994a). Wooden stakes were first driven into soil to detect the presence of termites. Bait tubes were placed in the soil where termites were detected. The results demonstrated that approximately 4 - 1,500 mg (less than 1/20 oz.) of hexaflumuron was needed for 90 - 100% reduction of field populations containing 0.5 - 2.8 million eastern subterranean termites per colony , and 1.0 - 2.4 million Formosan subterranean termites per colony . Elimination of colony populations created a zone of termite-free soil surrounding a home for several years (Su 1994b).
Following the success of the initial field trials, a prototype monitoring/baiting station was designed for commercial application Figure 6 . The station containing the monitoring device is first installed in soil surrounding a home. When termites are found in the station, the monitoring device is replaced with a tube containing bait laced with a minute amount of hexaflumuron . Termites collected from the monitoring device are dislodged into an empty space on the top of the tube, called the "recruiter's chamber."
Termites placed in the recruiter's chamber have to feed their way out of the bait to reunite with nestmates . Left behind in the bait are their species- and colony-specific odors . One of such chemicals is the trail-following pheromone excreted from the sternal gland , which guides nestmates to the bait. This self-recruitment procedure enhances bait uptake by termites (Su 1994a). Hexaflumuron kills insects only when they molt every 1 - 2 months. During this period, the bait is thoroughly distributed throughout the colony populations. DowElanco (Indianapolis, IN), who invented and owns the proprietary rights to hexaflumuron. Field trials using the system typically require less than one gram (0.04 oz.) of hexaflumuron to eliminate field populations of several million termites (Su et al. 1995)
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NPCA (National Pest Control Association). 1985. Approved reference procedures for subterranean termite control. NPCA Inc., Dunn Loring, VA.
Su, N.-Y. 1994a. Field evaluation of a hexaflumuron bait or population suppression of subterranean termites (Isoptera: Rhinotermitidae). J. Econ. Entomol. 87: 389-397.
Su, N.-Y. 1994b. The termite bait age dawns. Pest Control 62: 36-38.
Su, N.-Y. and R. H. Scheffrahn. 1988. Foraging population and territory of the Formosan subterranean termite (Isoptera: Rhinotermitidae) in an urban environment. Sociobiology 14: 353-359.
Su, N.-Y. and R. H. Scheffrahn. 1993. Laboratory evaluation of two chitin synthesis inhibitors, hexaflumuron and diflubenzuron, as bait toxicants against Formosan and eastern subterranean termites (Isoptera: Rhinotermitidae). J. Econ. Entomol. 86: 1453-1457.
Su, N.-Y., M. Tamashiro, J. R. Yates and M. I. Haverty. 1982. Effects of behavior on the evaluation of insecticides for prevention of or remedial control of the Formosan subterranean termite. J. Econ. Entomol. 75: 188-193.
Su, N.-Y., P. M. Ban and R. H. Scheffrahn. 1993. Foraging populations and territories of the eastern subterranean termite (Isoptera: Rhinotermitidae) in southeastern Florida. Environ. Entomol. 22: 1113-1117.
Su, N.-Y., E. M. Thoms, P. M. Ban and R. H. Scheffrahn. 1995. A monitoring/baiting station to detect and eliminate foraging populations of subterranean termites (Isoptera: Rhinotermitidae) near structures. J. Econ. Entomol. 88: 932-936.