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

Termite baiting-how it changed the landscape of the pest management industry and termite research in Southeast Asia

The management of subterranean termite pests remains a major challenge in Southeast Asia, where these pests cause significant structural and economic damage. Termite baiting has emerged as an effective option to conventional soil termiticides, offering a safer pest management approach with reduced chemical input into the environment. In this paper, we review the history of termite research in Southeast Asia, highlighting the turning points of termite research, from agriculture and plantations to buildings and structures, and the transformative impact of termite baiting on the pest management industry in the region over the last 25 yr. We also discuss the outcome of a survey of pest management professionals on their baiting practices, bait performance, and reinfestation rates. All bait products eliminated termite colonies. There were significant differences in terms of the baiting period to colony elimination, with Xterm outperforming Sentricon, Exterra, and Exterminex. Above-ground (AG) baiting was preferred over in-ground (IG) baiting due to construction constraints and low IG station interception rates. While bait effectively controlled Coptotermes spp., challenges persist in managing fungus-growing termites such as Macrotermes gilvus Hagen. Reinfestation occurred in < 10% of baited premises.

Toxicity and horizontal transfer of chitin synthesis inhibitors in the western drywood termite (Blattodea: Kalotermitidae)

Three chitin synthesis inhibitors (CSIs), bistrifluron, chlorfluazuron, and noviflumuron, were evaluated for their toxicity and horizontal transfer against the western drywood termite, Incisitermes minor (Hagen), when used to treat wood. In a no-choice bioassay, bistrifluron provided significantly faster kill than chlorfluazuron or noviflumuron treatments at 0.1 and 0.5% (wt/wt) rates over a 60-d period, providing 99% mortality. In a choice bioassay using 0.1% rate, bistrifluron provided a significantly faster kill than chlorfluazuron or noviflumuron treatments over a 60-d period, resulting in 96% mortality. In a transfer bioassay, a group of bistrifluron-fed termites, donors (D), was placed with a group of unexposed nestmates, recipients (R). Based on the visual marking, the food material of the donor termites was readily transferred to the recipients within 24 to 48 h. Overall, survival curves were similar between 1:19 (5% donor) and 10:10 (50% donor) D:R ratios, resulting in 100% mortality by day 90. This result indicated that lethal doses of bistrifluron were retained and effectively transferred, even from limited numbers of termites that originally ingested the compound. Implications for drywood termite management and future development are discussed.

The potential of 20-hydroxyecdysone to accelerate termite baiting programs

While chitin synthesis inhibitor baits are environmentally friendly and sustainable measures to control subterranean termites compared to conventional termiticides, the lengthy time required to eliminate a termite colony is perceived as a drawback for both homeowners and pest control industry. Recent efforts have focused on overcoming such problem by accelerating the baiting process. To accelerate termite colony elimination, 20-hydroxyecdysone was proposed as a potential active ingredient due to its similar mode of action observed in chitin synthesis inhibitors. Termites ingesting 20-hydroxyecdysone displayed hyperecdysonism, and mortality occurred much faster than with chitin synthesis inhibitor-ingesting termites. However, trial with 20-hydroxyecdysone alone and 20-hydroxyecdysone mixed with noviflumuron baits with intact colonies of Coptotermes formosanus Shiraki failed to accelerate the colony elimination time due to the feeding cessation. To bypass this issue, lower concentrations of 20-hydroxyecdysone may be necessary and sequential feeding of chitin synthesis inhibitors and 20-hydroxyecdysone have been proposed. In this review, a few more potential approaches were summarized which can be used to accelerate termite baiting program.

The impact of Operation Full Stop, New Orleans, Louisiana on suppressing Formosan subterranean termite (Coptotermes formosanus) colonies: 10 years later

The Formosan subterranean termite management initiative dubbed "Operation Full Stop", sought to protect structures within New Orleans' historic French Quarter. This program, lasting from 1998 to 2012, was able to decrease the overall population of Formosan subterranean termites in the area but did not eliminate all detectable colonies. Since Operation Full Stop ended in 2012, there has been a significant decrease in the number of alates observed in the French Quarter during reproductive flight season. Pedigree analysis was conducted on alates trapped during major swarm events in 2021. It was determined that an average of 7.25 (SD = 2.95) distinct colonies per glue trap were contributing to these swarm events. A bait-use survey was also conducted in the French Quarter, in which all accessible properties were checked to determine whether termite bait products were still in use within the French Quarter. We determined that approximately half (51.00%) of the structures in the French Quarter still currently have bait products installed around their perimeter. The interception of durable baits by neighboring termite colonies may be the reason why there has not been an increase in alate numbers since Operation Full Stop ended.

Subterranean termites (Coptotermes formosanus [Blattodea: Rhinotermitidae]) colonies can readily intercept commercial inground bait stations placed at label-prescribed distance

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is both an economically impactful pest and a successful invader. One method of subterranean termite control is baiting. According to the label, baits are installed surrounding the structure at a uniform interval distance of ≈3 m. However, homeowners and pest control professionals are often concerned that termites may bypass bait stations and have access to the structure. To address this concern, we experimentally duplicated field conditions using a large planar arena (3.6 m × 1.1 m) to study the optimal distribution of bait stations based on colony-wide foraging activity. We installed 2 bait stations 3 m apart as per label instructions and introduced C. formosanus colonies to allow them to explore the arena by tunneling through the sand. In this real-scale arena, all termite colonies intercepted a bait station in an average of 21 (± 8 SD) days. We assumed that termites could find bait faster if there were more bait stations by overlaying additional hypothetical baits closer than per label instruction, but the improvement was incremental, requiring 4 times more stations (0.45 m interval) to obtain a significant difference. We also revealed the characteristic behavior after intercepting bait stations, termites created a burst of tunnels that radiated from the bait station. These branching tunnels averaged 16 cm in length, suggesting immediate interceptions of additional auxiliary stations placed within 16 cm of an active station. These findings contribute to our understanding on how subterranean termites intercept inground bait stations.

How do termite baits work? implication of subterranean termite colony demography on the successful implementation of baits

In 1995, the launch of the first commercial chitin synthesis inhibitor (CSI) bait led to the transformation of the subterranean termite control industry around the world. Their slow mode of action, which relies on both their ability to be transferred among nestmates and termite molting biology, has made them cost-effective solutions for subterranean termite colony elimination while minimizing the introduction of pesticides into the soil toward an environmentally sustainable strategy. However, despite successful commercial implementations, the acceptance of their use varies within the pest control industry around the world. Notably, the nuanced complexity of how CSI baits lead to colony elimination upon feeding by termite foragers has, in part, remained elusive for the past 3 decades, allowing for long-lasting misconceptions to persist. A recent series of studies has since provided complementary elements of understanding how CSI baits utilize termites' inherent colony demography, behavior, and physiology to trigger colony elimination after a characteristic succession of events within the colony collapse process. I here provide a synthetic overview of subterranean termite colony characteristics when exposed to CSI baits using Coptotermes (Wasmann) (Blattodea: Heterotermitidae) as a primary model system. The changes in colony demography through the colony collapse reflect how the mode of action of CSI baits makes them a prime solution for sustainable subterranean termite pest management. Following decades of innovation, ongoing interactions among termite researchers, bait product manufacturers, and pest management providers must continue to bring solutions to existing and emerging termite pest problems around the world.

Death zone minimizes the impact of fipronil-treated soils on subterranean termite colonies by negating transfer effects

The use of nonrepellent liquid termiticides against subterranean termites has long relied on the assumption that foraging termites in soils could transfer toxicants to nestmates to achieve population control. However, their dose-dependent lethal time can lead to rapid termite mortality in proximity of the treatment, triggering secondary repellency. The current study characterizes the dynamic nature of the "death zone," i.e., the area adjacent to soil termiticides that termites would avoid owing the accumulation of cadavers. Using whole subterranean termite laboratory colonies of Coptotermes gestroi (Wasmann) with 3 × 15 m foraging distances, fipronil was implemented at 1.5 m, 7.5 m, or 12.5 m away from colony central nests, emulating a corrective action against an termite structural infestation. For treatments at 7.5 m and 12.5 m, the death zone stabilized at an average of ~2.56 m away from the treatment after 40 d post-treatment, and colonies suffered as little as 1.5% mortality by 200 d post-treatment. Colonies located 1.5 m away from the treatment minimized the death zone to ~1.1 m and suffered as little as 23.5% mortality. Mortality only occurred within the first few days of treatment from initial exposure, as the rapid emergence of the death zone negated further transfer effects among nestmates over time. In some cases, foraging termites were trapped within the infested structure. While technically nonrepellent, fipronil becomes functionally repellent from the rapid mortality onset near the treatment. Even if diligently implemented to successfully protect structures, surrounding termite colonies are minimally impacted by fipronil soil treatments.

Feeding cessation after feeding on 20-hydroxyecdysone in the Formosan subterranean termite

BACKGROUND

To control subterranean termite pests, chitin synthesis inhibitor (CSI) baits have been widely applied. Despite CSI baits having low impacts on the environment, they require a lengthy time period to eliminate colonies. 20-hydroxyecdysone (20E) was proposed to speed up the baiting process as it showed faster mortality than CSI baits. However, the efficacy of 20E has previously not been tested at the colony level prior to applying in the field.

RESULTS

We compared the effect of 20E, 20E + noviflumuron, noviflumuron and untreated control using colonies of Coptotermes formosanus. Our result revealed that both 20E and 20E + noviflumuron did not accelerate colony elimination and termite activity remained relatively stable during the observation periods. To determine the limited effects of 20E, we further investigated feeding duration and consumption amount of 20E with different concentrations (control, 100 and 1000 ppm) for 10 days. Termites ceased feeding after 1 day in 100 and 1000 ppm treatment and 100% mortality was observed within 10 days in 1000 ppm 20E, while mortality in the 100 ppm 20E treated group was much lower than that in the 1000 ppm group. Furthermore, no termites molted in the control and termites died from hyperecdysonism in 1000 ppm 20E treatment, whereas about 20% of termites molted in 100 ppm 20E.

CONCLUSION

This study demonstrated that 20E may not be suitable as a sole active ingredient to accelerate elimination of a subterranean termite colony, while CSI baits and lower concentrations of 20E may reduce the lengthy time period in colony elimination. © 2023 Society of Chemical Industry.

Elimination of structural and tree infestations of the Asian subterranean termite, Coptotermes gestroi (Wasmann) (Blattodea: Rhinotermitidae) with noviflumuron baits in above-ground stations

The traditional stake survey and in-ground (IG) monitoring stations have been ineffective in aggregating the Asian subterranean termite, Coptotermes gestroi (Wasmann) in southeastern Florida. In this study, we used both IG and above-ground (AG) Sentricon stations to monitor and bait C. gestroi, and as expected, none of the 83 IG stations was intercepted. Despite this, AG bait stations with 0.5% noviflumuron were successfully used to eliminate C. gestroi colonies. From 2 field experiments, the mean colony elimination time (±SD) using AG baits were 6.4 ± 3.8 wk (n = 4) and 8.0 ± 2.1 wk (n = 12), respectively. Such results were compatible with baiting studies against field colonies of C. gestroi elsewhere, that is, 4-9 wk. The successful rates in monitoring and baiting of C. gestroi with IG stations in other regions also varied, which may be due to the variabilities in tunnel geometry of this species in different environments. In areas with established C. gestroi populations, routine inspection for signs of activity in structures and surrounding trees can be a critical component for pest control providers for early detection of infestation and colony elimination with AG bait stations.

Toxicological, Behavioral, and Horizontal Transfer Effects of Cycloxaprid Against Formosan Subterranean Termites (Blattodea: Rhinotermitidae)

Cycloxaprid, 9-((6-chloropyrid-3-yl)methyl)-4-nitro-8-oxa-10,11-dihydroimidazo-[2,3-a]-bicyclo-[3,2,1]-oct-3-ene, is a cis-configuration neonicotinoid insecticide. In the present study, the lethal and sublethal effect of cycloxaprid against Formosan subterranean termites, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), was evaluated and compared with fipronil. Toxicity bioassays showed that cycloxaprid had slightly lower toxicity than fipronil. The minimum cycloxaprid concentration in sand and soil that causes 100% termite mortality was 100 ppm. Similar to fipronil, cycloxaprid significantly reduced wood consumption and tunneling activities of termites. In the tunneling-choice tests, termite tunneling activity measured in both length and area was significantly lower in sand treated with cycloxaprid (10 or 100 ppm) than that in untreated sand. In the aggregation-choice tests, cycloxaprid exhibited inhibition to termite aggregation starting from 100 ppm. In addition, cycloxaprid exhibited significant horizontal transfer effect at 10 ppm. In conclusion, our study showed that cycloxaprid is slightly less toxic than fipronil and more repellent to C. formosanus than fipronil. Future studies are needed to evaluate the effectiveness of cycloxaprid against subterranean termites in the field.

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.

Installation Season May Significantly Impact Time Required for Subterranean Termites to Find and Feed on In-Ground Baits

Simple Summary

Insecticide baits for use against subterranean termites have been shown to be highly effective, but the time required for termites to find and feed on baits may be a barrier to adoption in some areas. One explanation for this “time-to-attack” problem is that termite foraging near the soil surface may be limited during inhospitable periods. In California, characterized by a hot-summer Mediterranean climate, western subterranean termites have mostly been observed near the surface during the wet season, suggesting that baits installed in summer may sit uninvestigated for many months. To test this hypothesis, we established research plots in areas of known termite incidence, installing baits on four different dates over a one-year period and then recording termite activity every 60 days for two years. As expected, most foraging in these stations was observed in winter and spring. Time-to-attack for stations installed at the beginning of winter was significantly less than for stations installed at the beginning of summer (194 d vs. 296 d). These findings may help pest control operators in regions with pronounced dry periods to optimize their use of bait station systems by targeting specific installation seasons.

Abstract

Rhinotermitid termites, serious pests of wooden structures throughout the world, are commonly controlled with chitin synthesis inhibitor bait systems. Seasonal termite foraging patterns in some regions may prolong bait interception time, however, significantly decreasing colony elimination speed. We hypothesized that installing baits immediately prior to the season of highest foraging activity will minimize interception time when baiting for Reticulitermes spp. in California, a region characterized by a hot-summer Mediterranean climate. To test this theory, we installed three different bait systems on four dates corresponding to the major seasons (spring, summer, autumn, winter) at five field locations known to harbor the target species. We then recorded initial termite discovery events every 60 days for two years, considering effects of installation season, bait system, site, and distance from previously observed termite incidence on bait interception time. Observed foraging activity in bait stations was highest during late winter and spring. Baits installed during winter exhibited interception times more than 100 days shorter than those of baits installed during summer. From these findings, we conclude that colony elimination speed and perceived CSI bait utility may be increased in Mediterranean climate regions when baits are installed immediately prior to the wet season.

Effects of Menadione on Survival, Feeding, and Tunneling Activity of the Formosan Subterranean Termite

The Formosan subterranean termite, Coptotermes formosanus Shiraki, is a highly destructive pest and a cosmopolitan invasive species. Sustainable termite management methods have been improving with the search for novel insecticides that are effective, safe, and cost efficient. Menadione, also known as vitamin K₃, is a synthetic analogue and biosynthetic precursor of vitamin K with low mammalian toxicity. Menadione has shown insecticidal activity in several insects, presumably due to interference with mitochondrial oxidative phosphorylation. However, little is known about its effectiveness against termites. In this study, we evaluated the toxicity and repellency of menadione in C. formosanus. Our results showed that menadione affected the survival and feeding activity of termites both in filter paper and substrate (sand) treatments, and menadione influenced termite tunneling activity in treated sand. In a no-choice assay, ≥90% mortality after seven days and minimal or no food consumption were recorded when sand was treated with menadione at 6 to 600 ppm. In a two-choice assay with a combination of treated and untreated sand, termites were deterred by menadione at 6 to 600 ppm and exhibited low mortality (≤30%) over seven days, while tunneling activity was prevented with 60 to 600 ppm of menadione treatment. Overall, our study demonstrated dose-dependent toxicity and repellency of menadione in C. formosanus. The potential use of menadione as an alternative termite control agent is discussed.

Queen Egg Laying and Egg Hatching Abilities are Hindered in Subterranean Termite Colonies When Exposed to a Chitin Synthesis Inhibitor Bait Formulation

Subterranean termite control methods using chitin synthesis inhibitors (CSIs) aim at eliminating colonies that feed upon a bait formulation. Several benzoylurea active ingredient formulations are currently commercially available as alternative termite management strategies to liquid termiticides. Individual workers need to molt on a regular basis and CSIs interfere with such molting process, allowing sufficient time for the acquisition of a colony-wide lethal dose prior to widespread mortality. As workers progressively die, the colony eventually collapses, leaving only soldiers and primary reproductives that starve to death. One common observation is that young workers often die early owing to their relatively short molting cycle. However, the absence of brood in dying colonies raises questions about the potential fate of eggs laid by the queen. This study aims to determine if CSI baits also terminate the ability of a colony to produce a new cohort of workers by disabling the ongoing brood development. Incipient termite colonies were used to test the impact of noviflumuron on the queen's ability to lay eggs and on the eggs' ability to hatch. Our results showed that queens in colonies exposed to CSI not only initially laid less eggs than the control queens, but eggs also did not develop and were progressively cannibalized, eventually leading to colony establishment failure. This result implies that queens of mature colonies exposed to CSI would lose the ability to lay viable eggs as the colony collapses, leading to an absence of worker replacement, aiding in colony elimination.

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.

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.

Inferring Termite Colony Size Using Wood Consumption in Subterranean Termites (Blattodea: Rhinotermitidae) in Laboratory-Rearing Conditions

Termite colony size can influence its foraging activity, reproductive maturity, and, for pest species, potential for structural damage. Estimating colony size of subterranean termite species in field conditions has been challenging owing to their extensive foraging territory and their cryptic nesting habit and has primarily relied on mark-recapture methods. With laboratory-reared colonies in individual containers, determining colony size can be achieved by processing all termites from the nest material, which can be labor intensive and partially destructive. However, with the recent rise in the need of large laboratory colonies for use in colony-wide experimental protocols, there was an imperative to develop a procedure to estimate initial colony sizes without imposing a major stress on colonies before an experiment. In this study, the average daily wood consumption of whole colonies was used to infer the colony size of two Coptotermes, Wasmann (Blattodea: Rhinotermitidae) species and their hybrids in laboratory-rearing conditions. Correlations between the daily wood consumption and several demographic variables within colonies were established. Linear models varied across all species mating types with R2 values greater than 0.8 for all demographic variables. For colonies from all mating combinations, Pearson's correlation coefficient values were greater than 0.94 between their daily wood consumption and both the number of workers and total number of termites, and greater than 0.91 between daily wood consumption and colony mass. Therefore, in colonies with fixed laboratory conditions, their average daily wood consumption determination, which is nondestructive on colonies, can be used to infer colony size of subterranean termites.

Residual Effects of Termiticides on Mortality of Formosan Subterranean Termite (Isoptera: Rhinotermitidae) on Substrates Subjected to Flooding

Concerns on efficacies of termiticides used for soil treatment to prevent Formosan subterranean termite (Coptotermes formosanus Shiraki) infestations have prompted pest control companies to suggest that retreatments are necessary after flooding of homes. Therefore, to address concerns about the efficacy of termiticides after flooding, we designed a flooding simulation experiment in the laboratory. We used four formulated termiticides containing fipronil, imidacloprid, chlorantraniliprole, or bifenthrin as active ingredients (a.i.) and two colonies of field-collected C. formosanus for this study. Evaluations of each chemical at concentrations of 1, 10, and 25 ppm in both sand and soil were conducted in the laboratory by comparing termite mortalities in no-choice bioassays after exposure to flooded (for 1 wk) and unflooded substrates. Toxicity from bifenthrin and fipronil were not affected by flooding regardless of substrate type except at the lowest concentration tested. Toxicity from chlorantraniliprole was lower in flooded sand at 1 ppm but otherwise similar among flooding treatments. In flooded soil, toxicity from chlorantraniliprole was low at 1 ppm, but unexpectedly high in flooded conditions at 10 and 25 ppm. For all concentrations of imidacloprid-treated sand, mortality of C. formosanus was reduced after a flood. However, like chlorantraniliprole, 10 and 25 ppm of imidacloprid-treated soil in flooded conditions resulted in an increased toxicity on C. formosanus. Our study supports the idea that chemicals with a higher water solubility like imidacloprid may require a home to be retreated with less water-soluble termiticides or baits after a flood.

A Reproductives Excluder for Subterranean Termites in Laboratory Experiments

As a social insect, termites have different castes and division of labor in a colony. Investigating the social behavior of subterranean termites is a challenge due to the cryptic nature and large colony size. Planar arenas are commonly used to study these termites under laboratory conditions, and have provided several advantages. However, there is no means to designate areas such as a royal chamber or central nest from foraging sites because reproductives can move freely across arenas. In this study, we examined the minimum passing size of different castes of Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), in order to develop a reproductive excluder and correlated minimum passing size with head widths and heights. We found that workers and soldiers of C. formosanus were able to pass through a gap greater than or equal to 0.7 mm. Our results showed that there are significant differences in the head width and height based on castes and head height was more critical than head width to determine passing size. We further confirmed feasibilities of the reproductive excluders using incipient colonies of C. formosanus. Confining reproductives using the excluder in laboratory experiments will provide more chances to study the royal chamber and central nest independently of foraging sites.

2018 Highlights of Urban Entomology

The field of urban entomology is primarily associated with the study of ants, bed bugs, cockroaches, termites, and other occasional invader pests that are found within or near human-made structures. A wide array of peer-reviewed studies were published in 2018. The topics of these articles ranged from genomes and basic biology of urban insects to various applied aspects of pest management. Key findings of these papers are presented and discussed from the perspective of the contributions they make to the discipline of urban entomology. Additionally, potential future research opportunities that are evident from these publications have been outlined.

Evaluation of baiting fipronil-loaded silica nanocapsules against termite colonies in fields

Various pesticide nanocarriers have been developed. However, their pest-control applications remain limited in laboratories. Herein, we developed silica nanocapsules encapsulating fipronil (SNC) and their engineered form, poly(ethyleneimine)-coated SNC (SNC-PEI), based on recombinant catalytic modular protein D4S2 and used them against termite colonies Coptotermes lacteus in fields. To achieve this, an integrated biomolecular bioprocess was developed to produce D4S2 for manufacturing SNC containing fipronil with high encapsulation efficiency of approximately 97% at benign reaction conditions and at scales sufficient for the field applications. PEI coating was achieved via electrostatic interactions to yield SNC-PEI with a slower release of fipronil than SNC without coating. As a proof-of-concept, bait toxicants containing varied fipronil concentrations were formulated and exposed to nine termite mounds, aiming to prolong fipronil release hence allowing sufficient time for termites to relocate the baits into and distribute throughout the colony, and to eliminate that colony. Some baits were relocated into the mounds, but colonies were not eliminated due to several reasons. We caution others interested in producing bait toxicants to be aware of the multilevel resistance mechanisms of the Coptotermes spp. "superorganism".

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.