Response of the Formosan Subterranean Termite to Neighboring Con-Specific Populations After Baiting With Noviflumuron

Life and Death of Termite Colonies, a Decades-Long Age Demography Perspective

A eusocial insect colony represents a complex biological entity that must ensure degrees of perennity once it reaches maturity (production of dispersing imagoes over many successive years) to optimize its reproductive success. It is known that a subterranean termite colony invests differentially in different castes over time and adjusts colony functions depending on colony internal and external conditions over many years of activity. However, the current study demonstrates that Coptotermes formosanus Shiraki field mature colonies go through dramatic demographic changes and breeding structure shifts, even many years after they have reached reproductive success. By analyzing the changes in age demography of C. formosanus colonies from four field sites, we here provide a new perspective on how a colony may function over decades, which reveals that each colony demographic trajectory is unique. In a way, throughout its life, a termite colony displays its own “demographic individuality” that drives its growth, its foraging ability, its competitiveness, its age demography, its senescence and ultimately its death. This study is therefore a narrated story of the life -and death- of different C. formosanus field colonies over decades of observation.

Subterranean Termite (Coptotermes gestroi (Blattodea: Rhinotermitidae)) Colony Elimination Through Exposure to a Novaluron CSI Bait Formulation in Laboratory

The development of baits for subterranean termite control over the past 25 yr has provided cost-effective alternatives to liquid termiticide treatments. Current bait products use one of the few available benzoylurea chitin synthesis inhibitors (CSIs) labeled for subterranean termites. These insecticides are used because of their nonrepellency, their slow-acting mode of action, and their dose-independent lethal time. Although many studies have provided ample evidence of the efficacy of CSI baits for subterranean termite colony elimination, most have focused on hexaflumuron and noviflumuron. However, bait products using alternative CSIs have not received the same level of scrutiny, limiting the amount of evidence proving their efficacy. One such compound is novaluron, the active ingredient currently used in the Trelona ATBS-Advance Termite Baiting System bait product. The current study independently tested the efficacy of this commercially available bait formulation against whole colonies of Coptotermes gestroi (Wamann) (~63,910 workers) in the laboratory, using an extended experimental setup to simulate a 15-m foraging distance from the central part of the nest to the bait, while having access to alternative food sources. Treated colonies progressively ceased to feed on wood items within 45 d after being provided access to the novaluron bait formulation, with a subsequent progressive collapse of the population, leading to colony elimination by 91 d. This study therefore confirms the efficacy of novaluron baits against subterranean termites, and currently remains one of the few CSIs that can be applied for the successful control of Coptotermes infestations.

Colony Suppression and Possible Colony Elimination of the Subterranean Termites Coptotermes formosanus and Reticulitermes speratus by Discontinuous Soil Treatment Using a Diluent of Fipronil Suspension Concentrate

Simple Summary

Termites play an important role in maintaining ecosystems, but they are also pests, exerting major economic impacts. Among the over 3000 known termite species, Coptotermes species and Reticulitermes species are the most common pest species. As one of the primary methods for controlling these subterranean termites, liquid termiticide is applied to the soil under and next to the building foundation to create a continuous chemical barrier. Nonrepellent slow-acting liquid termiticides, such as fipronil and imidacloprid, are used as the active ingredients in termite soil treatments. In the present study, to minimize the use of insecticides, a discontinuous soil treatment using fipronil was applied against subterranean termites, namely Coptotermes formosanus and Reticulitermes speratus, instead of the traditional continuous chemical barrier of termiticides. C. formosanus and R. speratus colonies were subjected to discontinuous soil treatments with fipronil and were strongly affected by the treatment at the colony level, resulting in colony suppression and possible colony elimination. Termite activity in the treated colony of C. formosanus was not found for more than two years, while that of R. speratus was not detected for three years.

Abstract

We assessed the efficacy of a discontinuous soil treatment using a diluent of fipronil suspension concentrate in controlling colonies of Coptotermes formosanus and Reticulitermes speratus. In-ground monitoring stations were installed at Isogi Park and Kindai University, and individual termites inhabiting the stations were collected for four or six years to determine the numbers and locations of colonies present in test areas before and after the discontinuous soil treatment. Microsatellite genotyping indicated that two C. formosanus and two R. speratus colonies in the test area at Isogi Park and five R. speratus colonies in the test area at Kindai University were active and that their territories fluctuated every year. One of the two C. formosanus colonies at Isogi Park and one of the five R. speratus colonies at Kindai University were subjected to discontinuous soil treatments with fipronil and were strongly affected by the treatment at the colony level, resulting in the suppression and possible elimination of colonies. Termite activity of the fipronil-treated colony of C. formosanus was detected within one week after the discontinuous soil treatment and was not found for more than two years (28 months), while termite activity of the fipronil-treated colony of R. speratus was detected within four days and three weeks after the discontinuous soil treatment and was not detected thereafter for three years. Fipronil residue analysis showed that workers of C. formosanus moved at least 28 m and that workers of R. speratus moved 6 m from the treated soil locations for up to three weeks.

Concentration-Dependent Feeding Deterrence to 20-Hydroxyecdysone for Three Subterranean Termite Species (Blattodea: Rhinotermitidae)

Simple Summary

Subterranean termite colonies can be eliminated using baiting systems. However, for a given bait to be effective, the active ingredient must be lethal at concentrations that are also palatable to termites. The insect molting hormone, 20-hydroxyecdysone (20E), has potential for use in termite baits, but its palatability to termites has not been examined. The purpose of this study was to determine what concentrations of 20E, if any, cause termite workers to feed less readily. To test this, paper disks were treated with various concentrations of 20E. Groups of 1000 termites of three different species; the Formosan, the Asian and the Eastern subterranean termite; were placed in arenas. The termites had the option of following a path to feed on either a paper disk containing the 20E, or an untreated disk, and the amount of paper consumed was then compared. The results showed that the Asian subterranean termite had the least tolerance for the 20E, the Formosan subterranean termite had a reduced tolerance, and the presence of the 20E had no impact on the Eastern subterranean termite.

Abstract

Effective active ingredients in toxicant bait formulations must be non-deterrent to insect feeding behavior at lethal concentrations. This study evaluated feeding deterrence for Coptotermes formosanus Shiraki, C. gestroi (Wasmann), and Reticulitermes flavipes (Kollar) when provided access to cellulose impregnated with various concentrations of the insect molting hormone, 20-hydroxyecdysone (20E). Termites were exposed to 20E concentrations of 200, 500, 1000 and 2000 ppm and to noviflumuron at 5000 ppm in a 24 h choice-test, and the mass of substrate consumption from treated and untreated media pads was compared for each treatment. 20E feeding deterrence was detected at 500, 1000 and 2000 ppm for C. gestroi, and at 2000 ppm for C. formosanus. No significant differences in consumption of treated and untreated substrate was detected at any concentration for R. flavipes. Potential methods for reducing deterrence are discussed.

Effect of Polyacrylamide/Attapulgite Composite on Foraging Behaviors of Formosan Subterranean Termites (Blattodea: Rhinotermitidae)

Moisture conditions of food and soil are essential for the survival and foraging activities of subterranean termites. Polyacrylamide/attapulgite composite is a water-retaining agent that has been applied to increase moisture of agricultural soils. We hypothesize that polyacrylamide/attapulgite composite may increase the moisture of bait matrixes and soil surrounding baiting containers and therefore attract termites and increase their foraging activities. In the present study, aggregation and feeding preferences, survivorship, body water percentage, and wood consumption of Formosan subterranean termites, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), were investigated when responding to polyacrylamide/attapulgite composite that was buried within soil (substrate) or filled in the void volume of baiting containers. Two-choice tests showed that termites consumed significantly more wood when polyacrylamide/attapulgite composite was buried within dry soil (27%-moisture) than the controls (no polyacrylamide/attapulgite composite was provided). However, polyacrylamide/attapulgite composite buried within wet soil (54%-moisture) did not significantly affect foraging behaviors of termites. Multiple-choice tests showed no aggregation or feeding preference of termites in the baiting containers filled with polyacrylamide/attapulgite composite compared with the soil-filled or unfilled ones, whenever the substrate was dry or wet. No-choice tests showed that the presence of polyacrylamide/attapulgite composite (buried within soil or filled in baiting containers) significantly increased wood consumption and body water percentage of termites as well as wood moisture under dry-substrate conditions. Our studies suggest that burying polyacrylamide/attapulgite composite within dry soil may enhance foraging activities of termites, but filling the bait stations with polyacrylamide/attapulgite composite may not effectively attract termites.

Comparative Impact of Chitin Synthesis Inhibitor Baits and Non-repellent Liquid Termiticides on Subterranean Termite Colonies Over Foraging Distances: Colony Elimination Versus Localized Termite Exclusion

This study evaluated the impact of a non-repellent liquid termiticide (fipronil) and a chitin synthesis inhibitor (CSI) termite bait (noviflumuron) on whole colonies of Coptotermes gestroi (Wasmann) (Blattodea: Isoptera: Rhinotermitidae) in laboratory conditions, over a 12-m foraging distance. The protocol simulated the implementation of remedial treatment of an infested structure, where the colony has multiple access routes, and where only a portion of the population was directly exposed to the treatment. Within 2 wk after the implementation of fipronil, all termites within 1.5 m away from the treatment died. The accumulation of cadavers near the treated area resulted in secondary repellency and the colonies avoided the treated area for the remaining 10 wk of the experiment, using alternative foraging galleries. At the end of the 12 wk, colonies exposed to fipronil did not have any difference in population size compared with control colonies. Comparatively, colonies exposed to noviflumuron had no change in foraging activity for the first ≈40 d, but then termites progressively ceased their activity throughout their foraging territory. By 12 wk, noviflumuron-exposed colonies were near-elimination, with only a few workers, soldiers remaining, and all colonies were eliminated by 95 d. This study shows that subterranean termite colonies with access to CSI baits are inevitably eliminated, regardless of the position of the bait, while colonies exposed to fipronil are only locally excluded from the area near the treatment, but may maintain their foraging activity in untreated areas, and retain their potential risk for structural damage in the long term.

Molting site fidelity accounts for colony elimination of the Formosan subterranean termites (Isoptera: Rhinotermitidae) by chitin synthesis inhibitor baits

Site fidelity by molting termites in Formosan subterranean termite, Coptotermes formosanus Shiraki colonies is a new addition to our understanding of lower termites’ behavior and biology. Our previous studies indicated that workers moved to the central nest to molt in the presence of eggs and reproductives. The current study showed that noviflumuron-affected workers also return to the central nest and died in the vicinity of reproductives and eggs. The aversion to the dead and decaying workers caused reproductives and brood to leave the original central nest site in a colony and refuge at newer sites every few days in response to newly dead workers near them. Because mortality was an event observed only in workers undergoing molting under the effect of noviflumuron- a CSI, the death of molting individuals was observed only around reproductives and brood. This study reveals a previously undiscovered behavior of molting termites and the mechanics behind a successful arsenal; noviflumuron baits used against subterranean termites.

Subterranean Termites Feeding on CSI Baits for a Short Duration Still Results in Colony Elimination

Termite baits using chitin synthesis inhibitors can protect structures from subterranean termite damage by eliminating colonies. One of the potential shortcomings of baits is that termites may have to feed extensively on a bait station for the colony to be eliminated. If disturbances occur during this critical feeding time, termites may abandon the site, which could prevent colony elimination. We exposed whole laboratory colonies of Coptotermes gestroi (Wasmann) containing an average of 59,000 termites to 0.5% noviflumuron baits, from 1 to 10 d, to simulate a temporary access to the bait as a result of disturbances. Our results show that colonies which fed for a single day and consumed as little as 1.1 g of bait matrix (=5.5 mg noviflumuron) were eliminated within 90 d. This study indicates that only a fraction of the bait matrix is necessary for elimination of large laboratory colonies, and that hypothetical disturbance reducing the access to a bait station would likely have little impact on the effect of the bait. Within 1 d, colonies had already acquired a lethal dose, which is shared by trophallaxis to all individuals of the colony, and colonies inevitably died despite short exposure to noviflumuron. It is estimated that if a field mature colony of 1 million individuals consumes more than 18.6 g of bait (=93 mg noviflumuron) in a relatively short period, it would already have acquired a colony-wide lethal dose and reached a point of no-return for colony elimination.