Impact of Ground-Applied Termiticides on the Above-Ground Foraging Behavior of the Formosan Subterranean Termite.

We conducted a laboratory study to determine the impact of ground-applied termiticides on the above-ground foraging behavior of Coptotermes formosanus. Two concentrations (1 and 10 ppm) each of three termiticides, viz. fipronil, imidacloprid and chlorantraniliprole, were tested. After one month post-treatment (fipronil 10 ppm was run for 12 days only and all other treatments were run for one month), fipronil had the lowest percentage of survival (3%-4%) at both concentrations. Termite survival ranged from 31% to 40% in the case of imidacloprid treatments and 10 ppm chlorantraniliprole. However, 1 ppm chlorantraniliprole did not cause significant mortality compared to the controls. Foraging on the bottom substrate was evident in all replicates for all chemicals initially. However, a portion of the foraging population avoided the ground treatment toxicants after several days of bottom foraging. Only the slower-acting non-repellents created this repellent barrier, causing avoidance behavior that was most likely due to dead termites and fungus buildup on the treated bottom substrate. Fipronil appeared more toxic and faster acting at the concentrations tested, thus limiting this repellent effect. Suggestions by the pest control industry in Louisiana that some non-repellents can create a repellent barrier stranding live termites above ground are supported by this laboratory study.

Panic escape polyethism in worker and soldier Coptotermes formosanus (Isoptera: Rhinotermitidae).

Termites were the first animal to form societies. Two hundred million years of evolution provide for a multitude of innate social behaviors that can be experimentally dissected. These fine-tuned patterns of behavior are especially interesting when observing group decision making in the panic mode. In this study, we examined behavioral patterns of termites under panic conditions to gain insight into how an escape flow self-organizes. One hundred worker and 10 soldier Coptotermes formosanus were released into agar plates. After a disturbance was created most workers followed each other and ran along the wall of dishes, thus forming a unidirectional escape flow, whereas soldiers showed a significantly higher frequency of moving to the center of the arena or on periphery of the escape flow as compared to workers. Agonistic behavior was usually observed as soldiers moved to center or periphery. This is the first report on the behavioral repertoire of termites when panicked, with details on the behavioral polymorphism of workers and soldiers during an escape.

Point of No Return From Water Loss in Coptotermes formosanus (Isoptera: Rhinotermitidae).

Describing desiccation stages based on the physical appearance of termites has not been evaluated previously. Formosan subterranean termites were studied to determine the rate of water loss, singly and in groups, in the laboratory. The stages of water loss are described based on changes in physical appearance and percent total body water loss evaluated at 2- to 8-h time intervals up to 32 h. Workers in groups lost water slower than individual worker trials. Weight loss was linear over time for worker groups and individuals, as was individual soldier only trials. Water loss in individual workers was significantly faster than in soldiers. Three physical stages of desiccation are described for living workers: (I) curling of antennae, (II) on back but with assistance able to right themselves and walk, and (III) unable to get off back; and two stages for living soldiers (II and III). Recovery was determined from termites in a second trial by transferring stage I, II, and III individuals from open, dry Petri dishes to those with moist filter paper at 4, 6, 10, 12, 14, 16, 24, 26 and 28 h. After 12 h on moist filter paper, stage I workers had a 83% recovery rate, stage II had a 33%, and stage III had a 7% recovery. Soldiers had a 56% recovery at stage II and was similar to the recovery of workers at stage III. Most termites that reached stage III were destined to die.

Water Transport by Coptotermes formosanus (Isoptera: Rhinotermitidae).

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.

Lethal and sublethal effects of lufenuron on the Formosan subterranean termite (Isoptera: Rhinotermitidae).

A laboratory study was conducted to understand the effect of low concentrations of lufenuron on termite physiology and behavior. Survivorship, running speed, body water content, food consumption, tunneling, microbial infection, and two behavioral patterns (carcass-burying behavior and particle transport behavior) were compared among Formosan subterranean termites, Coptotermes formosanus Shiraki, fed lufenuron-treated (250, 500, or 1,000 ppm) or untreated (control) filter paper. In 30-32 d, all lufenuron treatments significantly reduced survivorship, running speed, consumption, and tunneling, but had no substantial effect on body water content. In addition, termites fed the three concentrations of lufenuron became infected by opportunistic pathogens. Carcass-burying and particle transport behaviors also were inhibited by lufenuron. Potential application of lufenuron at low concentrations for the control of C. formosanus is discussed.

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.

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.

Horizontal transfer of fipronil is enhanced with increased group size in Coptotermes formosanus (Isoptera: Rhinotermitidae).

Fipronil is a widely used insecticide for termite control. Although transfer of fipronil among termite cohorts has been investigated in previous studies, no study has yet focused on the influence of termite group size (density) on horizontal transfer. In this study, the mortality of donor and recipient Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) was compared among groups of 10, 25, and 50 workers. Most donor termites were dead within 20 h. There was a significantly higher mortality of recipient termites starting at 44 h when in bigger groups. LT50 and LT90 of recipient termites decreased with increase in group size, being significantly shorter in groups of 50 termites compared with groups of 10 termites. Moreover, the variance (within-group difference) of recipient mortality and lethal time estimations was lowest in the groups of 50 termites, indicating a more uniform horizontal transfer of fipronil by termites in bigger groups. Our findings suggest that group size has an influence on fipronil transfer among C. formosanus workers and should be considered as a variable of importance.

Toxicity and horizontal transfer of 0.5% fipronil dust against Formosan subterranean termites.

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 onsoil 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.

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.

Effect of soil type and exposure duration on mortality and transfer of chlorantraniliprole and fipronil on Formosan subterranean termites (Isoptera: Rhinotermitidae).

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

Relative humidity preference and survival of starved Formosan subterranean termites (Isoptera: Rhinotermitidae) at various temperature and relative humidity conditions.

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°C. 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 1 h, 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.