Termite Mortality Research Articles

Evaluation of Six Techniques for Control of the Western Drywood Termite (Isoptera: Kalotermitidae) in Structures

Chemical and nonchemical methods for control of western drywood termites, Incisitermes minor (Hagen), were evaluated under conditions that simulated infestations in structures. The efficacy of excessive heat or cold, electrocution, microwaves, and 2 fumigants was evaluated. Termite mortality in artificially infested boards was 100% at 3 d after treatment for both fumigant gases. Heating the whole-structure or spot-applications using microwaves resulted in 96 and 90% mortality, respectively, 3 d after treatment. Mortality levels 4 wk after treatment increased to 98% for heat and 92% for microwaves. Spot-applications of liquid nitrogen at 381.8 kg/m3 achieved 100% mortality 3 d after treatment. However, for 122.7 and 57.3 kg/m3, mortality levels 4 wk after treatment were 99 and 87%, respectively. Mortality by spot-applications of electricity was 44% 3 d after treatment in the 1st test. Four weeks after treatment drywood termite mortality increased to 81%. In a 2nd electrocution test, using spot application techniques infrequently used in structures, mortality levels increased to 93% at 3 d and 99% at 4 wk after treatment. The distribution of termite survivors within the test building and test boards varied for some treatment techniques. For naturally infested boards, both fumigants exceeded 99% mortality. Use of heat and microwaves resulted in 100 and 99% mortality levels, respectively, 4 wk after treatment. Applications of liquid nitrogen resulted in mortality ≥99.8% at 381.8 and 122.7 kg/m3; however, mortality for 57.3 kg/m3 was significantly lower (74%). Mortality levels from electrocution were 89 and 95% 4 wk after treatment, respectively, in the 2 tests. Damage to test boards and the test building did occur. Six test boards were scorched during microwave treatment, 80% of test boards were damaged during electrocution, and visible signs of damage to the test building were noted for whole-structure heating. This study provides information for evaluation of the relative efficacy of fumigation and nonchernical alternatives for the control of drywood termite infestations in structures.

Disodium Octaborate Tetrahydrate Treatments to Slash Pine for Protection Against Formosan Subterranean Termite and Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

Minimum retentions of disodium octaborate tetrahydrate (DOT) needed in slash pine, Pinus elliottii Engelm. variety elliottii, wood to provide maximum protection against 2 species of subterranean termites were determined in choice and no-choice laboratory tests. Efficacy criteria for DOT were ≥90% termite mortality and ≤5% loss in weight of treated wooden blocks. For termites fed only DOT-treated wood, 0.10 and 0.30% boric acid equivalent (BAE, percentage of boric acid based on dry weight of wood, assuming all boron is present as boric acid) protected wood from the eastern subterranean termite, Reticulitermes flavipes (Kollar), and Formosan subterranean termite, Coptotermes formosanus Shiraki, respectively. When termites had a choice between treated or nontreated wooden blocks, 0.30% BAE protected wood from R. flavipes, but the highest retention tested, 0.54% BAE, was not effective against C. formosanus. In a nonleaching field study where wooden blocks were not in contact with soil or exposed to rain, a BAE of 0.30% protected the wood from naturally occurring Reticulitermes sp. for 18 mo. In wooden structures under constant pressure from subterranean termites, concentrations >0.54% BAE may be required to protect wood, especially against C. formosanus.

Mortality of Eastern Subterranean Termites (Isoptera: Rhinotermitidae) Exposed to Four Soils Treated with Termiticides

Termite survivorship was affected by soil type and termiticide tested in constant-exposure bioassay. Four soil types were tested at the same percentage soil moisture (15% wt:wt). Soil pH values were between 5.4 and 5.5 with organic matter contents ranging from <0.07 to 3.75%. Soils tested included a sand, sandy loam, sandy clay loam, and sandy clay. Six termiticide formulations were tested including chlorpyrifos (Dursban TC), fenvalerate (Tribute), cypermethrin (Prevail FT, Demon 2 EC), and permethrin (Dragnet FT, Torpedo). Estimated lethal concentrations for all termiticides were at least 7 times lower in sand compared with sandy loam or sandy clay loam soils. However, soil type alone could not be used to predict termite mortality with the termiticides tested.

Effect of Two Ant Species (Hymenoptera: Formicidae) on the Foraging and Survival of the Formosan Subterranean Termite (Isoptera: Rbinotermitidae)

We examined the effect of 2 ant species, the bigheaded ant, Pheidole megacephala (F.), and Ochetellus glaber (Mayr),on the Formosan subterranean termite, Coptotermes formosanus Shiraki. We also examined how differences in the proportion of termite soldiers affected the susceptibility of C. formosanus to predation by P. megacephala . In sand-filled containers, C. formosanus was more vulnerable to predation by P. megacephala than by O. glaber . However, the presence of ants of either species caused substantial mortality of termite soldiers P. megacephala was much more invasive of termite galleries than O. glaber . Termites exposed to P. megacephala suffered greater mortality compared with controls, regardless of worker to soldier ratio. However, there was no difference in termite mortality among replicates with different worker to soldier ratios. In the absence of sand, both ant species caused 100% mortality of termites after 1 wk of exposure.

Subterranean Termite Behavioral Reaction to Water and Survival of Inundation: Implications for Field Populations

Laboratory tests involving termite response to rising water levels demonstrated that subterranean termites (Reticulitermes spp.) do not try to escape being submerged. Studies in which termites were completely submerged in water provided LT50s of 19.6 h for eastern subterranean termites,Reticulitermes flavipes (Kollar), 13.9 h for R. virginicus (Banks), and 11.1 h for, Formosan subterranean termites, Coptotermes formosanus Shiraki. These data suggest that subterranean termites, in the field, escape drowning not by seeking higher ground but by entering a state of quiescence when confronted with excessive amounts of water in their subterranean habitat. Under normal rainfall conditions, water should move through the soil profile within several hours. If this does not occur, then high termite mortality could result. In the summer of 1992, we characterized the foraging populations of 5 subterranean termite colonies using the triple mark–recapture technique. These colonies averaged 99,000 (range, 157,000–14,000) foraging termites per colony. In the spring 1993, these same colonies were recharacterized and their populations averaged 21,000 (range, 53,000–1000) foraging termites per colony. This represents a 77% reduction in the average foraging populations for these colonies. In this article we provide empirical evidence that these population reductions were a result of heavy rainfall in west–central Georgia during the winter of 1992–1993.

Toxicity and Repellency of Semiochemicals Extracted from a Dolichoderine Ant (Hymenoptera: Formicidae) to the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

The anal gland secretions of ants in the subfamily Dolichoderinae contain terpenoids that are known to have insecticidal properties. The repellency and toxicity of whole-body extracts and chemical fractions of such extracts from the dolichoderine ant ochetellus glaber (Mayr) to Coptotermes formosanus Shiraki (Isoptera : Rhinotermitidae) were examined. Extract-treated sand caused significant termite mortality in a direct-exposure assay. Termites were also repelled by extract-treated sand and the chemical repellency lasted for at least one month in treated sand. The principal repellent components of O. glaber secretions were determined to be cis,trans-and trans,cis-isomers of dolichodial in a 3 :1 ratio.

Carbon dioxide as a potential fumigant for termite control

AbstractFormosan subterranean termites, Coptotermes formosanus Shiraki, were exposed to ⩾ 95% or 50% carbon dioxide atmospheres for intervals of 24‐120 h at 26(±3)°C. A 24‐h exposure to ⩾ 95% carbon dioxide caused significant termite mortality, but 60 h were required for complete mortality. Exposure to 50% carbon dioxide for 60 h resulted in approximately 70% termite mortality, while complete mortality was recorded after 120 h. When termites were sealed in wooden blocks (90 × 90 × 152 mm), 72‐96 h exposure to ⩾ 95% carbon dioxide was necessary for complete control. A limited study with Cryptotermes brevis (Walker) suggested that this drywood termite is also susceptible to carbon dioxide fumigation, although slightly longer exposures may be required than with C. formosanus. Carbon dioxide‐modified atmospheres are a viable alternative to conventional fumigants for vault fumigation of termite‐infested materials, and may also be applicable to larger‐scale fumigations to control structural pests.

Susceptibility of neem to attack by the Formosan subterranean termite, Coptotermes formosanus Shir. (Isopt., Rhinotermitidae)

AbstractThe neem tree, Azadirachta indica, is a source of natural compounds with potent insecticidal, feeding deterrent and insect growth regulator activity. However, little information is available on the effects of these natural products on termites. We assessed the effects of mulches made from ground neem branches and roots on survival of the Formosan subterranean termite, Coptotermes formosanus, and compared termite feeding and survival on neem wood and bark to that on susceptible Pseudotsuga menziesii wood. Termite survival was fairly low in both P. menziesii heartwood and neem mulches over the 14 day test period, and did not differ significantly among those treatments. However, termites exposed to either P. menziesii wood, neem wood, or neem bark for 4 weeks fed significantly less on neem wood and bark. Feeding on neem bark caused significant termite mortality (56.4%) in comparison to that induced by feeding on neem wood (27.1%) or P. menziesii wood (12.5%). Thus, although neem is not entirely resistant to termite attack, the antifeedant properties of its wood and bark and the toxicity of neem bark support the use of neem trees for arboriculture in areas where termites are a problem.

Potential use of pathogenic fungi in baits to control the Formosan subterranean termite (Isopt., Rhinotermitidae)

AbstractA laboratory choice test was developed to assess the efficacy and acceptability of sporulating strains of Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metsch.) Sorokin to foraging Formosan subterranean termites, Coptotermes formosanus Shiraki. Filter paper disks were saturated with agar media and inoculated with either B. bassiana strain 787 or 3041, or M. anisopliae strain 346, 472 or 2162. Filter papers containing eight‐day‐old cultures were rolled into cylinders with the sporulating culture on the inside of the cylinder, and placed in one of two plastic jars, connected by a glass tube. Termites were placed in the other jar (refugia), and allowed to forage throughout both jars. This apparatus simulates the use of a fungal bait for subterranean termite control in the field. Termites did not avoid contact with the fungal baits, and fed upon the agar‐treated filter papers. Exposure to M. anisopliae strains 346 and 2162 resulted in rapid termite mortality while exposure to the B. bassiana strains caused slower, but escalating, mortality. Efficacy of the fungi was not affected by the degree of sterility of the termite tunnelling medium. Living cultures of entomopathogenic fungi hold promise for further development as baits for subterranean termite control.

Persistence of Organochlorine Insecticides for Formosan Subterranean Termite (Isoptera: Rhinotermitidae) Control in Hawaii

In a long-term field test, five organochlorine soil insecticides were applied at two concentrations to crushed coral, Catano sandy loam, or Waimanalo silty clay. The treated soils were weathered in exposed field plots in Waimanalo on the island of Oahu, Hawaii, and tested periodically for efficacy against the Formosan subterranean termite, Coptotermes formosanus Shiraki. We report the toxicity of aldrin, chlordane, DDT, dieldrin, and heptachlor to C. formosanus 17, 20, 24, 28, and 33 yr after treatment. The degree of penetration of the treated soils by C. formosanus was also measured in laboratory bioassays. After 28 yr, termites tunneled significantly less in soils treated with 0.5% aldrin (in coral and clay), 0.3% dieldrin (in clay), 1.0% heptachlor (in sandy loam), and 2.0% DDT (in coral). None of the insecticides prevented termite penetration 33 yr after application. At label-recommended concentrations, all pesticides except DDT (8.0%) caused high termite mortality up to 28 yr after application. Only 0.5% aldrin, 0.3% dieldrin, and 1.0% heptachlor caused significant mortality after 33 yr. Results of this study should be of value in estimating the risks of temlite reinfestation of structures in the tropics and Pacific islands where organochlorine insecticides have been used.

Oral Toxicity of Barium Metaborate to the Eastern Subterranean Termite (Isoptera: Rhinotermitidae)

The oral toxicity of barium metaborate monohydrate (Busan 11-Ml) to Reticulitermes flavipes (Kollar) was evaluated in no-choice assays by feeding termite workers for 15 and 30 days on filter papers treated with concentrations of 500–40,000 ppm (weight/weight). In the 15 day assay, 30,000 ppm resulted in 92 ± 17% termite mortality and a concomitant 86% reduction in paper consumption. Feeding for 30 days on 1,500 ppm resulted in 100% mortality. Reduced paper consumption was associated with termite mortality, and feeding on low concentrations did not differ from that on control papers. Concentrations ≥ 20,000 ppm provided protection from termite feeding, while concentrations ≤ 5,000 ppm may be applicable in developing baits for subterranean termite control.

Damage to crops bymicrotermes najdensis(isoptera, macrotermitinae) in irrigated semi‐desert areas of the red sea coast. 2. cotton in the Tokar delta region of Sudan

Abstract Microtermes najdensis is a major pest of cotton in the Tokar Delta of Sudan, where it causes damage by penetrating and hollowing the roots and entering the stems. Attack usually occurs late in the growing season. The efficacy of aldrin and less persistent insecticides was evaluated in a series of trials in different areas of the delta from 1982 to 1986. Plant mortality and yields varied widely among sites and years. Application of aldrin gave up to 132% increase in yield in some trials but in others no differences were detected. Treatment of seed with aldrin was more cost‐effective than a planting‐hole treatment. Residue levels (aldrin, dieldrin) were low in soil, cotton (seed, fibre and foliage), well water, and crops planted in plots treated with aldrin in previous seasons. Termite attack in trials of other insecticides was very low, and the efficacy of these could not be evaluated. There was no clear relationship between termite foraging activity and either plant mortality or yield.

Concentration-Time Relationship for Fumigant Efficacy of Sulfuryl Fluoride Against the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

The Formosan subterranean termite, Coptotermes formosanus, was exposed to sulfuryl fluoride over a range of six accumulated concentrations (10-60 mg h/liter) and 12 exposure times (1-96 h), to determine the concentration-time relationship on termite mortality. Time threshold in sulfuryl fluoride fumigation was<1h. The results demonstrated that C0.93t = k was a satisfactory model to describe the response relationship in fumigant efficacy of sulfuryl fluoride against this termite. Because the toxicity index (n = 0.93) approximates to 1, the assumption that the exposure time is equally important to concentration is functionally valid.

Allelochemical resistance of bald cypress,Taxodium distichum, heartwood to the subterranean termite,Coptotermes formosanus

The heartwood of bald cypress,Taxodium distichum (L.) Rich., resisted feeding attack by the Formosan subterranean termite,Coptotermes formosanus Shiraki. Hexane-extracted heartwood, however, was consumed at > 12 times the amount of sound heartwood eaten. A bioassay usingT. distichum sapwood as a feeding substrate was employed to assess the antitermitic activity of successive hexane, acetone, and methanol extracts of heartwood shavings and isolates derived from the active hexane extract. Two fractions, eluted from the crude hexane extract by liquid chromatography, significantly reduced termite feeding compared to the parent extract, while a third fraction was less active than the original hexane extract. Each fraction contained one major component. All three components were structurally related diterpenes. The two most active heartwood constituents were identified by GC-MS and NMR as ferruginol and manool, while the third and least active, but most prevalent, compound in heartwood was identified as nezukol. Results of bioassays suggest that these allelochemicals act principally as feeding deterrents with accompanying termite mortality due to starvation.

Characterization of Slow-acting Insecticides for the Remedial Control of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

We describe a method to examine time trends in mortality of the Formosan subterranean termite, Coptotermes formosanus Shiraki, exposed to insecticides. Slow-acting toxicants required a longer time to kill termites at low concentrations than at high concentrations. The level of mortality and the speed of death were dependent on concentration. With acute toxicants, the time required to kill termites was similar at high or low concentrations, while the mortality levels were concentration-dependent. This speed of death at various concentrations of an insecticide can be quantified for comparison purposes using the proposed effective lethal time 90% (ELT90), defined as the amount of time required for an insecticide to kill 90% of the treated individuals within a maximum 14-day span. Slow-acting toxicants were characterized by ELT90 values that spanned a broad range of time, while acute toxicants exhibited a narrow range of ELT90 values.

Comparison of Laboratory Methods for Estimating Wood Consumption Rates by Coptotermes formosanus (Isoptera: Rhinotermitidae)

Three methods of calculating wood consumption rates (milligrams of wood per gram of termite per day) by laboratory groups of the termite, Coptotermes formosanus Shiraki, were compared. Rates calculated from 6- and 8-week data confirmed that a model which assumed no termite mortality during the feeding trial significantly underestimated wood consumption. A second model which assumed a linear increase in mortality during the trial gave consumption rates for 42-day tests which did not differ significantly from those derived from a third model based upon actual mortality records. This suggests that consumption rates can be predicted accurately in 42-day experiments with a model that assumes mortality increases linearly. Wood consumption rates calculated at 8 weeks were lower than those at 6 weeks, indicating that feeding rates were declining. This occurred even though little or no mortality was observed beyond day 28. It is proposed that feeding trials be carried out only while wood consumption (milligrams of wood per gram of termite) remains constant. In 6-week trials, C. formosanus consumed 55.04 mg/g per day when termite biomass was based on a linear-mortality model. This was more than 16% greater than consumption at 8 weeks based on termite weight calculated with a no-mortality model (46.56 mg/g per day).

Is β-Phenylnitroethane the Active Principle of Dennettia Oil?

β-Phenylnitroethane (1-nitro-2-phenylethane) was synthesized from l-bromo-2-phenylethane and sodium nitrite and evaluated for its toxicity against four species of insects. Acetone deposits containing up to 32 µg/cm2 of 1-nitro-2-phenylethane produced no mortality within 96 h in adult Blattella germanica (L.) males and nymphal Periplaneta americana (L.). No toxicity was observed up to 7 days after topical application of the nitro compound at a dosage of 40 µg/g insect to the pennultimate sternite of B. germanica . Nymphs of Incisitermes minor (Hagen), exposed to 0.5 mg/cm2 deposits of the compound in a closed system, were killed within 48 h; however, in an open system, the termite mortality was ca. 40% after 1 day with no additional mortality for 4 weeks. When the nitro compound was evaluated against 2nd- and 4th-instar Culex quinquefasciatus Say, no substantial mortality was observed at the 1 and 10 ppm concentrations. The treatment of adult C. quinquefasciatus with the nitro compound produced 0, 5, 2, and 12% mortalities at 1.6, 7.8, 16.0, and 78 µg/cm2 surface area, respectively.

Alteration of the gut microbiota and its effect on nitrogen metabolism in termites

When the spirochaetes in the gut of Nasutitermes exitiosus were killed with oxygen, the glutamate dehydrogenase activity of whole termite extracts declined by some 75%. Starvation, which caused a similar termite mortality rate to oxygen treatment, did not greatly affect this enzyme. Treatment of N. exitiosus with tetracycline to kill all the gut flora led to glutamate dehydrogenase activity falling to zero. Treatment of Coptotermes lacteus with oxygen to kill gut protozoa and spirochaetes resulted in the activity of glutamate dehydrogenase remaining low, whereas in starved and normal termites the activity of the enzyme increased about seven-fold. A similar result was observed when tetracycline was used to kill the gut flora and fauna. Aspartate aminotransferase and alanine aminotransferase activities (which appear to be of termite origin) were little affected by these treatments. The glutamate dehydrogenase was NAD +-dependent and was not found in the bacteria (excluding spirochaetes) colonising the hindgut. In all experiments there was a slight increase in the uric acid content of the termites in both control and treated insects. The free amino acid content of both species of termites was increased (about 50%) when they were starved, but was little affected when the gut flora and/or fauna were killed. Thus the gut flora and fauna do not appear to be involved in amino acid metabolism. When C. lacteus was kept under argon-oxygen mixtures for seven weeks the total nitrogen, enzyme activities and uric acid content were similar to those of termites kept under nitrogen-oxygen mixtures. These results indicate that in the short term termites do not need to fix nitrogen and also that nitrogen is well conserved.