Prevention of Colony Foundation by Cryptotermes brevis and Remedial Control of Drywood Termites (Isoptera: Kalotermitidae) with Selected Chemical Treatments

Abstract

A wooden trap-block bioassay, tested over 2 flight seasons, was found to be a suitable colonization platform for Cryptotermes brevis (Walker) dealates. A crevice designed into trap blocks Was the preferred locus for nuptial chamber construction by dealates. Lone heterosexual pairs were found in 52%of chambers containing live termites. Of colonies containing brood, 80%were headed by lone heterosexual pairs. The broods in 4- or 6-mo-old C. brevis colonies were small, with ≤3 eggs, larvae, or a combination. In 1995, a choice test of disodium octaborate tetrahydrate (DOT) solution, chromium copper arsenate (CCA), and water-treated (control) trap blocks was exposed to swarming C. brevis . Four months after swarming ceased, live dealates and brood were recovered from nuptial chambers in control blocks, but not from DOT or CCA-treated blocks. These results indicated that DOT and CCA-treated wood surfaces were unpreferred substrates for colony foundation by C. brevis , but that these deposits were not toxic to dealates as demonstrated by their survival in neighboring control blocks. In 1996, no-choice tests were conducted using trap blocks partially treated with DOT solution or water (control). Live dealates, heterosexual dealate pairs, and brood were detected in all control treatments at 6 mo. The mean number of nuptial chambers and live termites was not significantly different among the control treatments. The number of nuptial chambers in all DOT treatments, however, was significantly lower compared with control blocks and no live termites were found in any DOT-treated blocks. These results demonstrate that partial DOT deposits deterred C. brevis dealates from colonizing blocks. Choice tests also were conducted in 1996. A silica gel-pyrethrin dust, spinosad suspension concentrate (SC), and DOT dust were applied to trap block tops and tested against control blocks. Significantly fewer nuptial chambers and live termites were found in silica gel-treated blocks compared with neighboring controls. Although the number of nuptial chambers was reduced significantly in spinosad-treated blocks compared with control blocks, there was no significant difference in the number of live termites. No live termites were detected in either DOT-dusted trap blocks or in adjacent control blocks, implying that dealates searching for colonization sites were intoxicated by DOT dust and unable to colonize neighboring control blocks. In remedial control tests, mature colonies of C.brevis and Incisitermes snyderi (Light) in naturally infested wood were exposed to single-point gallery injections of spinosad SC or surface applications of aqueous DOT. Infested wood members were bisected, and the resultant halves differentially treated with chemical or water. Member halves were destructively censused at 28-33 d and 97-109 d after treatment with spinosad and DOT, respectively. Spinosad-treated halves yielded 92-100% mortality in 8 of 9 wood members containing either I. snyderi or C. brevis infestations. Surface applications of DOT caused partial and sporadic mortality. Mortality ranged from 1 to 88% for I.snyderi and was significantly greater overall compared with water-injected halves, whereas mortality in C. brevis infestations treated with DOT ranged from 0 to 35%.Mortality in water-treated half members ranged from 0 to 9%.Results of remedial control tests demonstrate the advantages of intragallery applications over surface-only treatments for drywood termite infestations.