TARGETING TERMITES

Much has been said about the benefits of termite baits. Compared to barrier treatments, their performance is less affected by building design and the need to protect vulnerable termite entry points. Baiting systems also have consumer appeal, since installation and maintenance are relatively non-intrusive and only small amounts of pesticide are applied.

Despite these attributes, baiting can be a slow, time-consuming process. Several weeks or months may pass before subterranean termites initially find and begin feeding in below-ground stations. In the meantime, customers may perceive that their homes are accruing damage. In a recent homeowner survey, 92 percent of respondents believed termites ate wood quickly and could cause extensive damage to a house in a short period of time (see "Termites & Public Attitudes," PCT, February 2000, www.pctonline.com/articles/article.asp?MagID=1&ID=975&IssueID=122).

But suppose we could predict where termites are foraging below ground. This would help bait installers optimize their placements around structures and perhaps reduce the time required to suppress or eliminate infestations. The following study explores this possibility — read on and you may find the results surprising.

THE STUDY. Our study examined two related questions: First, whether subterranean termites (Reticulitermes spp.) are more likely to attack below-ground monitors in certain locations around structures; and second, can environmental cues from the landscape help bait system installers predict where termites are present? We were especially curious whether incidence of attack on monitors would be higher in areas often considered "conducive" to termite foraging.

Two different methods were used to monitor for termites in residential settings. The first used pine wood stakes installed around 24 houses in Lexington, Ky. Each house had a history of termite problems and had been treated with barrier-type organophosphate or pyrethroid termiticides in the past few years. Wooden stakes were hammered into the ground at 10-foot intervals around the outside perimeter of each home, 1 to 2 feet from the foundation wall. An average of 19.8 ± 0.7 (range: 14-27) stakes were installed per house. The stakes were examined for live termites or signs of feeding for 16 consecutive months.

Termite foraging activity was also monitored using below-ground stations of the Sentricon® Colony Elimination System. Stations were installed around 22 additional houses in central and western Kentucky by 11 different pest control firms (two houses per company), working under our direct supervision. Each house had an active termite infestation, many of which were severe. Stations provisioned with wood monitoring pieces were installed around the outside of each building, about 10 feet apart and 1 to 2 feet out from the foundation. Additional below-ground stations were installed near wood-to-ground contacts and in areas containing termites. An average of 20.5 ± 1.4 (range: 13-43) Sentricon stations were initially installed per house, exclusive of auxiliary stations subsequently added for baiting purposes. Stations were inspected monthly or quarterly for live termites from installment in 1995 until December 1999.

During installation, we characterized the location of each wooden stake or Sentricon station in terms of landscape parameters that would be apparent to bait installers. We recorded whether the monitor was located near (within 5 feet) of suspected moisture sources, such as roof down spouts, air conditioner condensate lines or flowerbeds, as well as the type of prevailing ground cover (bare soil, grass or mulch). We also rated each monitor’s level of sun exposure (shade, partial and full sun) and noted its directional aspect (N, S, E, W) relative to the structure. We recorded whether stakes or stations were located adjacent to wooden decks, dirt-filled porches and preexisting termite activity (damaged wood, mud tubes, swarms) evident within the structure.

The percentage of termite-attacked stakes and stations associated with each parameter was analyzed. In the case of Sentricon monitors, only originally installed stations were used in the analysis; auxiliary stations subsequently installed for baiting purposes were not included.

Fig.1 Termite attack on monitors was no higher near suspected sources of moisture. [Fisher's Exact Test; P=0.5 Sentricon, P=0.61 Stakes]

RESULTS
During the study, 13.7 percent of wooden stakes and 20.2 percent of original Sentricon stations installed around the 46 houses were attacked or "hit" by termites — an average of 2.7 and 4.1 hits, respectively, per structure. Although some aspects of the landscape were associated with higher rates of attack, the location of monitors was generally a poor predictor of termite presence. The incidence of attack on monitors was not significantly greater for stakes or stations located near suspected sources of moisture (down spouts, air conditioners or flower beds), compared with placements in other areas around houses (Figure 1). Termite activity was significantly associated with the type of ground cover present around monitors, but results were inconsistent. As might have been expected, a significantly higher percentage of wooden stakes (24 percent) were attacked in mulched areas, than in bare ground (11 percent) or grass (6 percent). However, around houses monitored with Sentricon, termites attacked more stations located in bare ground (24 percent) than in grass (15 percent) or mulch (12 percent). Both stakes and stations situated in full sun had significantly fewer hits than those located in areas partly or fully shaded by vegetation (Figure 2)

Fig.2Termites attacked significantly more monitors located in partial of full shade [Fisher's Exact Test, P=0.03]

No significant difference in infestation rate occurred on the north, south, east or west sides of houses monitored with Sentricon. Although a higher total percentage of hits occurred on the west side of houses monitored with wooden stakes, the difference was only significant during July and August — pretty unusual, considering that western exposures tend to be hotter and dryer. No significant influence of directional aspect occurred during cooler times of the year.

Finally, monitors installed near dirt-filled porches, wooden decks or previous termite damage had no higher incidence of attack than monitors situated in other locations — another unexpected result. SIGNIFICANCE. The subterranean environment around the foundation of a building is a complex system of soil, moisture and temperature gradients, plant roots and other factors. While it is known that termites respond to various physical and chemical "cues" in soil (Ettershank et al. 1980, Smith and Rust 1994, Forschler 1998), it may be hard for humans to discern which factor(s) around a certain structure are most influential. (Around our houses, were more termites detected in shaded areas due to temperature or moisture influences, presence of woody vegetation or a combination of factors?)

Our findings suggest that in routine, commercial practice, it will be difficult to pinpoint where termites are foraging or predict which monitoring stations are likely to be attacked. According to Sterett Robertson, Sentricon’s product development manager, installers around the country do not see much "rhyme or reason" to which stations are infested either. Nevertheless, some bait manufacturers still promote the targeted placement of stations into "critical areas of known, probable or suspected termite foraging."

As companies seek to reduce the labor associated with baiting, we fear a trend toward using fewer below-ground monitors in areas arbitrarily deemed conducive to termites. Based on our observations, this could be a mistake. Until new insight or innovation helps us pinpoint the movements of termites underground, it would seem prudent to install more, rather than fewer, stations around the structure to increase the chances of discovery and add additional stations wherever termites are found. When no termites are evident, as is often the case, baiting may not be so different than fishing without a fish finder — the more "casts" made the better.

Dr. Michael Potter is a professor and urban extension entomologist at the University of Kentucky, Dr. Eileen Eliason is an assistant professor specializing in horticultural entomology at the University of Florida and Kevin Davis is a former graduate student at the University of Kentucky.

References

Ettershank, G., J.A. Ettershank and W.G. Whitford. 1980. Location of food sources by subterranean termites. Environ. Entomol. 9: 645-648.

Forschler, B.T. 1998. Subterranean termite biology in relation to prevention and removal of structural infestation. Part II. NPCA research report on subterranean termites. National Pest Control Association, Dunn Loring, Va.

Smith, J.L. and M.K. Rust. 1994. Temperature preferences of the western subterranean termite, Reticulitermes hesperus Banks. J. Arid Environ. 28: 313-323.