Bal K. Gautam

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.

Effect of Soil Type and Exposure Duration on Mortality and Transfer of Chlorantraniliprole and Fipronil on Formosan Subterranean Termites (Isoptera: Rhinotermitidae)

ABSTRACT The uptake and potential transfer of chlorantraniliprole and fipronil by the Formosan subterranean termite, Coptotermes formosanus Shiraki, was investigated in the laboratory by using donor-recipient model bioassays. Two different types of substrates, sandy loam soil (18.6% organic matter) and sand (0.19% organic matter), were used to evaluate how these treated substrates impact the direct mortality and transfer efficiency of the two nonrepellent termiticides tested at different concentrations. Chlorantraniliprole exhibited a more delayed mortality on termites than fipronil in sand. In soil, chlorantraniliprole did not cause higher mortality to either donor or recipient termite at any of the tested concentrations during a 21-d test period when compared with controls. Compared with the controls, a greater number of donors died in the soil treated with fipronil at 14 h postinteraction, and higher death of recipients occurred at 21 d but only in the 60-ppm concentration tested. Our data showed that chlorantraniliprole performed best in substrate with low organic matter against C. formosanus.

Wood Consumption by Formosan Subterranean Termites (Isoptera: Rhinotermitidae) as Affected by Wood Moisture Content and Temperature

ABSTRACT Understanding foraging behaviors and food preferences of termite colonies is critical to optimizing control strategies. The relationship between the moisture content (MC) of wood blocks and the feeding preference of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) at three ambient temperatures (19, 28, and 35°C) was investigated with multiple-choice as well as no-choice feeding bioassays. In multiple-choice tests, when four wood blocks with initial MC as dry (0–3%), low MC (22–24%), medium MC (70–90%), and high MC (125–150%) were exposed to workers and soldiers, the highest consumption was found in the high MC wood blocks at all three temperatures, although high MC wood consumption at 19°C was significantly lower than that at 28 or 35°C The preference for high MC wood blocks was detectable within the first few hours and continued for the duration of the test. In no-choice tests, the highest wood consumption also was obtained on the high MC wood blocks at all three temperatures. However, in no-choice tests, significant mortality was observed with termites exposed to dry or low MC wood blocks. Termite mortality was found to be higher with higher ambient temperature. Sustained feeding was not observed on wood blocks with ≤24% MC. When wood moisture is low, no free water exists in the cell cavities, which perhaps influenced feeding choices. Temperature played a vital and complementary role for wood consumption at all moisture levels.

Toxicity and Horizontal Transfer of 0.5% Fipronil Dust Against Formosan Subterranean Termites

ABSTRACT The toxicity and horizontal transfer of a new formulation of fipronil, 0.5% fipronil dust, was tested against Coptotermes formosanus Shiraki in the laboratory. The formulation was applied in three different ways: 1) Directly applied to termites (donors) and mixed with untreated termites (recipients) at three ratios, viz., 50 donors: 50 recipients, 20 donors: 80 recipients and 10 donors: 90 recipients. 2) Applied onto the surface of 3 mm thick sand or soil substrate in a petri dish and then topped with another 3 mm thick sand or soil layer whereupon termites were released. 3) Applied to the inner surface of a tube (either 5 cm or 15 cm long) that connected two foraging dishes, one containing dry sand and the other moist sand plus a wood block and termites were released into the dry sand dish. All donors and >93% of the recipients were dead by 42 h after treatment in the direct treatment experiment. Significant mortalities of both donors and recipients were observed at 5 h after treatment at all donor: recipient ratios. During this period, the mortality of the recipients (but not donors) at 10: 90 was significantly lower than those at the other two ratios. All termites were dead at 65 h after exposure (HAE) on the sand treatment and at 190 HAE on soil treatment. More than 96% mortality was observed at 40 HAE on the sand treatment as compared with only 6% mortality on soil treatment during the same time period. In the tube treatment experiment, >97% mortality was observed at 90 h after release for both tube lengths as compared with <3% mortality in controls. About half of the termites were dead by 15 h after release regardless of the tube length. Our results showed that 0.5% fipronil dust is nonrepellent and readily transferred from treated to nontreated termites.

Relative Humidity Preference and Survival of Starved Formosan Subterranean Termites (Isoptera: Rhinotermitidae) at Various Temperature and Relative Humidity Conditions

ABSTRACT Foraging groups of Formosan subterranean termites, Coptotermes formosanus Shiraki were tested for their relative humidity (RH) preference in a humidity gradient arena in the laboratory at a constant temperature of 26°G Five RH levels (9%, 33%, 53%, 75%, and 98%) were maintained in the test arena comprising of a series of closed containers by using dry silica gel, saturated salt solutions, or distilled water alone. Termites gradually aggregated to the highest RH chamber in the arena. After 1h, a significantly greater percentage of termites (≈46%) aggregated to the highest RH chamber (98%) than to the lower RH chambers (≤75%). After 12 h, > 97% of the termites aggregated to the 98% RH chamber. In survival tests, where termites were exposed to 15 combinatorial treatments of five RH levels (9%, 33%, 53%, 75%, and 98%) and three temperatures (20°C, 28°C, and 36°C) for a week, the survival was significantly influenced by RH, temperature, and their interaction. A significantly higher mortality was observed on termites exposed to ≤75% RH chambers than to 98% RH chamber at the three temperatures and significantly lower survival was found at 36°C than at 28°C or 20°C. The combination of temperature and RH plays an important role in the survival of C. formosanus.

Localized treatments using commercial dust and liquid formulations of fipronil against Coptotermes formosanus (Isoptera: Rhinotermitidae) in the laboratory

Use of proper application methods and formulations of termiticides are important to reduce their negative impact to the environment. In this study, we conducted laboratory experiments to determine the effect of localized treatments with commercial dust and liquid formulations of fipronil against Formosan subterranean termites, Coptotermes formosanus Shiraki. The test arena consisted of a specially designed 16‐chambered structure with a center chamber connected to 5 foraging chambers that themselves were connected to 10 additional foraging chambers. One peripheral chamber received a liquid or dust treatment and termites were released in the center chamber. Results showed that >91% of the termites were dead within the 9‐d test period despite the localized treatment of only 1 foraging chamber. Termites that were still alive after 9 d were transferred to an untreated dish and held for 10 more days. The majority of those termites were dead and the rest were moribund on day 19. Regardless of the specific dish treated, both formulations of fipronil were found to be highly efficacious. Termites did not exhibit repellency to either formulation. Our results suggest that localized (or spot) treatment with either commercially available dust or liquid formulations of fipronil can be a viable option for control of a termite infestation where complete soil drenching is not desirable.

Lufenuron Suppresses the Resistance of Formosan Subterranean Termites (Isoptera: Rhinotermitidae) to Entomopathogenic Bacteria

ABSTBACT Pesticides can negatively affect insect immunity. Although studies show that Formosan subterranean termites, Coptotermes formosanus Shiraki, are resistant to microbial infections, the effects of pesticides on disease resistance is not well studied. In this study, C. formosanus previously fed lufenuron was exposed to each of the three entomopathogenic bacteria, Pseudomonas aeruginosa (Schroeter) Migula, Serratia marcescens Bizio, and Bacillus thuringiensis Berliner subsp. israelensis. We found that termite mortality was significantly higher and synergistic in the combination of lufenuron and P. aeruginosa compared with treatment of lufenuron or P. aeruginosa alone. Other bacteria and lufenuron combinations were not quite as effective. Interestingly, only in treatments without lufenuron did termites show carcass-burying behavior. The results indicate that lufenuron, a chitin synthesis inhibitor, can suppress Formosan subterranean termite resistance to P. aeruginosa. Possible suppression mechanisms are discussed.

Effects of m-Tyrosine on Feeding and Survival of Formosan Subterranean Termites (Isoptera: Rhinotermitidae)

Abstract Amino acids are important to all animal life. Termites rely mainly on microorganisms to retrieve these nitrogen sources from their food. One naturally occurring amino acid, m-tyrosine, has been reported to be toxic to bacteria and weeds. Its direct effects on termite survival are unknown however. Both no-choice and choice bioassays using five different doses of m-tyrosine were conducted to determine the feeding response and survival of Formosan subterranean termites, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), in the laboratory. In no-choice tests, although all doses of m-tyrosine tested reduced filter paper consumption, only the highest dose tested (0.05 M) had significantly lower consumption compared with the control. This dose also caused significantly high termite mortality. In a five-choice bioassay, all doses of m-tyrosine tested reduced filter paper consumption significantly compared with the control. No mortality was observed in the choice tests, and very little feeding of filter paper treated with m-tyrosine occurred. From these experiments, we conclude that m-tyrosine is toxic to Formosan subterranean termites and acts as a feeding deterrent, and therefore, may be a promising wood preservative.

Water Transport by Coptotermes formosanus (Isoptera: Rhinotermitidae)

ABSTRACT Subterranean termites are extremely vulnerable to desiccation, and high moisture makes their habitat and food favorable for survival and colony growth. Although there is a general perception that termites can manipulate moisture, documentation is surprisingly scanty with regard to how termites transport water and the factors that impact it. There has been no study of water transfer by Coptotermes formosanus Shiraki, a notoriously invasive termite in the southern United States. We conducted a study to determine if C. formosanus transfers water. Bioassays using arenas with a dry food source connected to a moist substrate by either a short tube (10 cm) or a long tube (100 cm) were conducted. Three moistened substrate types were tested to see how they impacted water transfer. In addition, workers and soldiers sampled from a moist sand substrate were dissected to determine water sac volumes for possible transfer of water to wood. The results indicated that some water transfer is achieved by the evacuation of water sacs. However, moist soil was also moved to increase humidity. When termites had use of moist silty clay, wood moisture gain increased significantly in both 10 and 100 cm tubes. As tube distance increased, moisture to the more distant food source decreased. Workers had the largest water sacs, though soldiers appear to contribute in water transfer via water sacs as well. Water transfer and its implications are discussed.

Laboratory Study of the Influence of Substrate Type and Temperature on the Exploratory Tunneling by Formosan Subterranean Termite.

Using two-dimensional foraging arenas, laboratory tests were conducted to investigate the effect of soil type, soil moisture level and ambient temperature on the exploratory tunneling by Coptotermes formosanus Shiraki. In choice arenas consisting of two substrate types having two moisture levels each, and conducted at a constant temperature of 22 °C, a significantly greater proportion of termites aggregated in sand than in sandy loam. Similarly, the length of excavated tunnels was also increased in sand. In a given substrate, termite aggregation or tunnel length did not differ between 5% and 15% moisture levels. In no-choice tests, where three different substrates (sand, sandy loam and silt loam) were tested at two temperatures (22 °C and 28 °C), excavations were significantly greater in sand than either sandy loam or silt loam at 22 °C. Fewer primary tunnels were constructed in sandy loam than in sand and fewer branched tunnels than either in sand or silt loam. No significant difference in either tunnel length or number of primary or branched tunnels was found between these two temperatures.