Gregg Henderson

Evaluation of Vetiver Oil and Seven Insect-Active Essential Oils Against the Formosan Subterranean Termite

Repellency and toxicity of 8 essential oils (vetiver grass, cassia leaf, clove bud, cedarwood, Eucalyptus globules,Eucalyptus citrodora, lemongrass and geranium) were evaluated against the Formosan subterranean termite, Coptotermes formosanus Shiraki. Vetiver oil proved the most effective repellent because of its long-lasting activity. Clove bud was the most toxic, killing 100% of termites in 2 days at 50 μg/cm2. The tunneling response of termites to vetiver oil also was examined. Vetiver oil decreased termite tunneling activity at concentrations as low as 5 μg/g sand. Tunneling and paper consumption were not observed when vetiver oil concentrations were higher than 25 μg/g sand. Bioactivity of the 8 oils against termites and chemical volatility were inversely associated. Listed in decreasing order of volatility, the major constituents of the 8 oils were: eucalyptol, citronellal, citral, citronellol, cinnamaldehyde, eugenol, thujopsene, and both α- and β- vetivone. Vetiver oil is a promising novel termiticide with reduced environmental impact for use against subterranean termites.

Termites fumigate their nests with naphthalene

Termite nests provide a controlled environment and physical defence for the colonies of insects they house. Another important factor involved in colony defence may be volatile chemicals present in the nest: we have found the hydrocarbon naphthalene in extracts of the nest material produced by Formosan subterranean termites. This is the first time naphthalene has been found naturally associated with any insect species.

Nootkatone is a repellent for Formosan subterranean termite (Coptotermes formosanus).

We examined the behavior of Formosan subterranean termites toward one of the components of vetiver grass oil, the roots of which manufacture insect repellents. We found nootkatone, a sesquiterpene ketone, isolated from vetiver oil is a strong repellent and toxicant to Formosan subterranean termites. The lowest effective concentration tested was 10 μg/g substrate. This is the first report of nootkatone being a repellent to insects.

Formosan Subterranean Termite (Isoptera: Rhinotermitidae) Soldiers Regulate Juvenile Hormone Levels and Caste Differentiation in Workers

Abstract A caste structure is maintained in termite societies and juvenile hormone (JH) is generally regarded as the most important regulator in these termite colonies. Here, we demonstrate that the soldier caste regulates JH in workers of Coptotermes formosanus Shiraki. Worker termites (80–100 individuals) were placed in petri dishes with 0, 5, 10, or 20% soldiers. JH III titers of groups of these workers were monitored at 14, 28, 42, and 56 d. Any changes in soldier caste proportions also were noted at each sample date. On the first sample date, the JH levels in workers were similar among treatments with different initial soldier proportions, and no new soldiers were formed. Over the next three sample dates, the worker JH levels were higher for low initial soldier proportion treatments and vice versa. Concurrently, soldier formation increased with lower initial soldier proportions. JH titers in workers showed a positive and statistically significant relationship to soldier numbers until a certain soldier proportion was reached. These results provide evidence that soldier caste proportions regulate JH levels and thereby caste differentiation in workers. The means by which this regulatory mechanism may proceed is discussed.

Effects of virulence, sporulation, and temperature on Metarhizium anisopliae and Beauveria bassiana laboratory transmission in Coptotermes formosanus

Sporulation characteristics and virulence of Metarhizium anisopliae and Beauveria bassiana were examined in relation to laboratory transmission in Coptotermes formosanus. Fungal isolates significantly affected disease prevalence in termite populations. Sporulation of M. anisopliae played a more important role than virulence in producing epizootics within small groups of termites, but this was not the case for B. bassiana. Isolates characterized by quick sporulation (day 2 after death) did not exhibit better transmission in termites than those with high total sporulation (day 11 after death) in either fungal species. An isolate of M. anisopliae ranking highly in all three categories (virulence, quick sporulation, and total sporulation) produced better epizootics than an isolate that was inferior in all three characteristics. High temperatures (35 degrees C) significantly reduced fungal germination rates, leading to significant reduction of epizootics. M. anisopliae was better than B. bassiana in producing epizootics at 27 degrees C. Thus, fungal characteristics other than virulence should be considered for the seasonal colonization approach to termite microbial control.

Efficacy of vetiver oil and nootkatone as soil barriers against Formosan subterranean termite (Isoptera: Rhinotermitidae).

Abstract Vetiver oil and its components nootkatone and cedrene were assessed as sand treatments for their efficacy to disrupt food recruitment by Coptotermes formosanus Shiraki. Termites were required to tunnel through sand treated with vetiver oil, nootkatone, cedrene, or untreated sand to reach a food source. Results showed that sand treated with vetiver oil or nootkatone disrupted termite tunneling behavior. As a consequence, after 21 d, wood consumption and termite survival were significantly lower compared with cedrene-treated or untreated sand treatments. Sand treated with vetiver oil or nootkatone at 100 μg/g substrate were effective barriers to termites.

Effects of Sand Moisture Level on Food Consumption and Distribution of Formosan Subterranean Termites (Isoptera: Rhinotermitidae) with Different Soldier Proportions

Formosan subterranean termites, Coptotermes formosanus Shiraki, were tested under laboratory conditions to determine preferences among different sand moisture levels in a choice test. Foraging behavior, rate of filter paper consumption and distribution patterns of the termites were studied among 3 soldier ratios: low (4% soldier), normal (16% soldier) and high (32% soldier) and 7 sand moisture gradients (4, 8, 12, 16, 20, 24 and 28% wt/wt) in a circular 3-dimensional arena. The results showed that sand moisture had a significant effect on termite distribution and filter paper consumption, whereas soldier proportions had no effect. Treatment means comparisons indicated that there were no significant differences in termite distribution or consumption among moisture levels ranging from 4 - 24%; however, significant differences were obtained when termite distribution or consumption on these moisture levels were compared with that of the saturated sand (28% moisture). Termites also were not present in the center release chamber (which had dry sand and no food) at any observation point. Within the range of 4 - 24%, we found a very uneven distribution pattern where 70 - 80% of the total released termites aggregated in 1 of the 6 moisture chambers. Filter paper consumption generally corresponded with the aggregation sites. Importantly, among the 27 replicates no particular moisture chamber was consistently chosen for aggregation indicating that Formosan subterranean termites probably can adapt to a range of substrate moisture levels in nature provided other conditions are suitable.

Sporulation of Metarhizium anisopliae and Beauveria bassiana on Coptotermes formosanus and in vitro.

The sporulation of 22 total isolates of Metarhizium anisopliae and Beauveria bassiana was quantified on cadavers of the Formosan subterranean termite, Coptotermes formosanus. Conidial production increased significantly over 11 days post-death. Effects of isolates of M. anisopliae and B. bassiana on in vivo sporulation were significant. Although the overall effects of fungal species on in vivo sporulation were not significant, the interactions between fungal species and certain times post-death were significant, indicating different sporulation patterns between the two fungal species. B. bassiana isolates could be categorized into a group with high total sporulation (day 11) and low quick sporulation (on days 2 and 3), while M. anisopliae isolates fell into another group with high quick sporulation and low total sporulation. This could give M. anisopliae an advantage over B. bassiana in termite microbial control due to termite defensive social behaviors. Conidial production was significantly higher in vitro than in vivo. In vitro and in vivo sporulation differed by as much as 89x and 232x among the selected isolates of B. bassiana and M. anisopliae, respectively. Correlation between in vivo and in vitro conidial production was positive and significant. This may allow preliminary in vitro screening of a large number of isolates for high in vivo sporulation.

Determination of feeding preference of Formosan subterranean termite (Coptotermes formosanus Shiraki) for some amino acid additives

A choice feeding test using 21 amino acids was conducted to determine the feeding preference of Formosan subterranean termite,Coptotermes formosanus Shiraki, in the laboratory. Significantly more filter paper treated withd-aspartic acid orl-glutamic acid was consumed by Formosan subterranean termites than was control filter paper treated with water. In two-choice feeding tests, termites consumed significantly more filter paper treated withd-aspartic acid orl-aspartic acid than paper treated with water. Addingl-proline,l-lysine, orl-isoleucine to filter paper significantly increased consumption compared with control filter paper in no-choice tests. The use of amino acid additives in termite baits is briefly discussed.

Antifeedant activity and acute and residual toxicity of alkaloids from Sophora flavescens (leguminosae) against formosan subterranean termites (Isoptera: Rhinotermitidae).

Abstract Ku Shen,Sophora flavescens Aiton (Leguminosae), contains alkaloids that possess broad biological activities. This study showed that total matrines (a mixture of the alkaloids), and matrine and oxymatrine (two major alkaloids) had a strong antifeedant effect against Formosan subterranean termite,Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), at all tested concentrations (ranging from 0.01 to 5%). Total matrines and matrine also had significantly toxic effects at 5%. The estimated LD50 of total matrines and matrine was 12.3 and 8.6 μg per insect, respectively, after 24 h; 13.3 and 7.1 μg per insect after 48 h; and 10.1 and 4.8 μg per insect after 1 wk. The antifeedant and toxic properties of total matrines- and matrine-treated wood remained effective at least 12 mo after treatment under both light and dark storage conditions. These chemicals have great potential for commercial development as wood treatment agents.