Valuation of efficacy and nonrepellency of indoxacarb and fipronil-treated soil at various concentrations and thicknesses against two subterranean termites (Isoptera: Rhinotermitidae)

The efficacy and nonrepellency of indoxacarb (150 SC, 150 g [AI]/liter) and fipronil (Termidor SC, 9.1% [Al]) against field-collected eastern subterranean termite, Reticulitermes flavipes (Kollar), and the Formosan subterranean termite, Coptotermes formosanus Shiraki, were evaluated for mortality and penetration into treated soil in laboratory glass tube bioassays. Both insecticides were tested at five concentrations (0, 1, 10, 50, and 100 ppm) and two thicknesses (20 and 50 mm) of treated soil. Indoxacarb caused significantly greater mortality than controls at all treatment thicknesses of > or = 10 ppm, but not at 1 ppm. Concentration and treatment thickness of indoxacarb significantly affected termite mortality. Eastern subterranean termites were significantly more susceptible to indoxacarb than Formosan subterranean termites, but there were no intercolony differences in either species. Termites completely penetrated through all treatment thickness of indoxacarb-treated soil at all concentrations, except one of the six Formosan subterranean termite replicates of 50 mm at 50 ppm, when all termites were killed before tunneling through the treated soil. Fipronil resulted in significantly faster and greater termite mortality than indoxacarb at corresponding concentrations. Concentration and treatment thickness of fipronil also significantly affected termite mortality. There was no intercolony difference in susceptibility to either insecticide in either termite. Both termite species completely penetrated 20-mm treatments of all tested fipronil concentrations, as well as 50-mm soil treated with fipronil at < or = 10 ppm. At 50 and 100 ppm fipronil, termites tunneled only a mean of 87 +/- 0.21 and 47 +/- 0.18% deep into 50-mm treated soil, respectively, before death. Both insecticides demonstrated a delayed mode of activity and nonrepellency against the two termite species.     

Transferof chlorfenapyr among workers of Reticulitermnes flavipes (Isoptera: Rhinotermitidae) in the laboratory

The potential for transfer of chlorfenapyr among subterranean termites was investigated using a donor-recipient (5:95 ratio) experiment. In one experiment, workers of Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) were exposed to treated sand at 0, 50, 100, 250, and 500 ppm chlorfenapyr (wt [AI]/wt sand). Exposed workers were allowed to interact with untreated nestmates for 14 d, after which mortality was assessed. The three colonies responded differently to the treatments in this experiment. For two colonies, donor exposure rates of 500 ppm (as well as 250 ppm for colony B) chlorfenapyr resulted in significantly greater recipient mortality than controls. For colony C, donor chlorfenapyr exposure did not significantly influence recipient mortality. In a second experiment examining donor mortality over time, donor termites exposed to all test concentrations of chlorfenapyr (except for 0 ppm) suffered 100% mortality within 5 d. Analysis of donor termite body washes using gas chromatography indicated a linear uptake of chlorfenapyr by termites over the concentration range studied. Thus, for this concentration range, no upper limit (saturation plateau) of termite uptake for chlorfenapyr was reached.     

Laboratory evaluation of bistrifluron, a benzoylphenylurea compound, as a bait toxicant against Coptotermes formosanus (Isoptera: Rhinotermitidae)

Bistrifluron, a benzoylphenylurea compound, was evaluated with regard to its efficacy against workers of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) by using three laboratory tests. In the no-choice feeding test, the mortality of bistrifluron-treated worker termites was significantly higher than that of termites exposed to the same concentrations of hexaflumuron (e.g., 6 wk at 500 ppm, 4 wk at 5,000 ppm, and 2 wk at 50,000 ppm) and untreated controls. Bistrifluron showed higher dose dependence and a faster speed of action than hexaflumuron. Both bistrifluron and hexaflumuron had feeding-deterrent effects at 5,000 ppm in the two-choice feeding test, although the mortality of worker termites exposed to bistrifluron or hexaflumuron at 5,000 ppm was not significantly different from untreated controls. In the allogrooming inhibition test, to examine effects of bistrifluron on allogrooming behavior of termites, termite movement was affected at 1 wk before termites died when exposed to 5,000 ppm bistrifluron. These results indicate bistrifluron is effective as a bait toxicant at 5,000 ppm; however, bistrifluron may cause some feeding repellency at > or = 5,000 ppm.     

Toxicity, uptake, and transfer efficiency of fipronil in western subterranean termite (Isoptera: Rhinotermitidae)

The potential horizontal transfer ofnonrepellent termiticides has become an important paradigm to control termites in recent years. In this study, 14C-radiolabeled fipronil was used in a series of laboratory experiments to demonstrate the extent and ability of termites to transfer lethal amounts of fipronil to unexposed nestmates. Fipronil is an active and nonrepellent termiticide against western subterranean termites, Reticulitermes hesperus Banks, on sand at relevant doses. It exhibited delayed toxicity with the lowest LD50 approximately 0.2 ng/termite expressed between day 4 and 7. Both continuous and brief exposures to fipronil-treated sand seriously impaired the termite's ability to move and respond to a dodecatrienol trail, limiting potential horizontal transfer. In tunneling studies, fipronil prevented termite tunneling at concentrations as low as 0.5 ppm and was nonrepellent even at 500 ppm. Greater than 90% mortality was recorded by day 7 with concentrations ranging from 0.5 to 500 ppm. There was a linear relationship between the time of exposure and uptake of [14C]fipronil when termites were continuously exposed to 0.5, 1.0, and 5.0 ppm for 24 h. However, uptake discontinued when the termites were immobilized. Maximum transfer of fipronil from donors to recipients occurred within the first 24 h. Fipronil was transferred by body contact and trophallaxis did not play a major role in horizontal transfer. In successive transfer studies, there was not enough fipronil on recipients for them to serve as secondary donors and kill other termites. In a linear arena study, there was an inverse relationship between the amount offipronil on dead termites and their distance from the treated zone. Maximum mortality was observed within 1.5 m from the treated zone. Results in our laboratory studies suggest that horizontal transfer was not a major factor contributing to the efficacy of fipronil in the field.     

Penetration of the eastern subterranean termite into soil treated at various thicknesses and concentrations of Dursban TC and Premise 75

The ability of eastern subterranean termites, Reticulitermes flavipes (Kollar), to penetrate various concentrations and treatment thicknesses ranging from 1.0 to 50.0 mm of Dursban TC and Premise 75 was evaluated in a laboratory bioassay. Termites penetrated only a few millimeters into 500 ppm Dursban TC-treated soil at all thicknesses. As concentration decreased, termite penetration into Dursban TC-treated soil increased with termites generally penetrating completely through 5.0- and 0.5-ppm treatments. Termites penetrated at least 30% into 10-, 25-, and 50-mm thicknesses of 100 ppm Premise 75. Termites generally completely penetrated all concentrations < or = 100 ppm and thicknesses < or = 5 mm. At 7 d, termite mortality was 100% at all treatment thicknesses of Dursban TC at 500 and 50 ppm. At 5.0 and 0.5 ppm Dursban TC, termite mortality ranged from approximately 45 to 98% across all treatment thicknesses. At 100- and 10-ppm concentrations of Premise 75-treated soil, termites suffered > or = 75% mortality. Premise 75 at 1.0 and 0.1 ppm generally killed < or = 50% of the assayed termites at all treatment thicknesses.     

Toxicity, repellency, and transfer of chlorfenapyr against western subterranean termites (Isoptera: Rhinotermitidae)

Chlorfenapyr is a slow-acting insecticide against western subterranean termite, Reticulitermes hesperus Banks, when applied to sand. The LD50 at day 7 for workers is 29.98 ng per termite and considerably higher than that of chlorpyrifos (14.01), cypermethrin (3.21), and fipronil (0.16). Brief exposures to sand treated with chlorfenapyr resulted in dose-dependent mortality over a broad range of concentrations. Brief 1-h exposures to > or =75 ppm provided >88% kill of termites at day 7. Chlorfenapyr deposits did not repel termites, even at 300 ppm. Termites tunneled from 0.1 to 1.8 cm into sand treated with 10- to 300-ppm chlorfenapyr deposits, resulting in > or =70% mortality. Within 1 h after being exposed to 50 ppm chlorfenapyr, approximately 17% of the termites exhibited impaired responses to synthetic trail pheromone. By 4 h, nearly 60% of the workers were not able to follow a 10 fg/cm pheromone trail. There was a direct linear relationship of the uptake of [14C]chlorfenapyr as concentration and duration of exposure increased. The percentage of chlorfenapyr transferred to recipients varied from 13.3 to 38.4%. Donors exposed for 1 h transferred a greater percentage of chlorfenapyr than did donors exposed for 4 h. A 1-h exposure on 100-ppm deposits provided sufficient uptake to kill 100% of the donors and sufficient transfer to kill 96% of the recipients. There was not enough transfer for recipients to serve as secondary donors and kill other termites. Horizontal transfer is limited to contact with the original donor and by the decreased mobility of workers within 4-8 h after exposure to treated sand. The effectiveness of chlorfenapyr barrier treatments is primarily due to its nonrepellency and delayed toxicity.     

Effects of sublethal exposure to imidacloprid on subsequent behavior of subterranean termite Reticulitermes virginicus (Isoptera: Rhinotermitidae)

Experiments were conducted to determine whether subterranean termites, Reticuliternes virginicus (Banks), previously exposed to sublethal doses of imidacloprid (Premise), and allowed to recover for 1 wk, demonstrated behavioral aversion to a subsequent exposure. Worker termites experiencing a previous sublethal but debilitating exposure to imidacloprid-treated sand (either 10 or 100 ppm for 4 h) showed no apparent aversion to a second encounter with imidacloprid-treated sand under conditions of this experiment. If these laboratory results hold in the field and termites traveling through a zone of soil treated with imidacloprid are impaired but subsequently recover, they will be just as likely as their naive nestmates to reenter the treated area if their travels take them through the nonrepellent application a second time. Our results also indicate that a sublethal exposure to imidacloprid can affect termite tunneling behavior. Many worker termites that received an initial 4-h exposure to 100 ppm imidacloprid-treated sand died, but those that survived tunneled significantly less than did their naive nestmates, as did some termites exposed to 10 ppm imidacloprid.     

Toxicity, repellency, and effects of acetamiprid on western subterranean termite (Isoptera: Rhinotermitidae)

The insecticidial and biological activity of the cyano-substituted neonicotinoid acetamiprid was determined against the western subterranean termite, Reticulitermes hesperus Banks (Isoptera: Rhinotermitidae). Acetamiprid was very active against termites in topical applications, with an LD50 = 0.02 ng per termite. Even though acetamiprid was extremely toxic in topical applications, deposits > or =50 ppm on sand were required to consistently provide >90% kill of termites within 7 d after a 1-h exposure. Termites were quickly affected by brief exposures to sand treated with 1 ppm acetamiprid and within 1 h, their locomotion was dramatically impaired. Acetamiprid was transferred from donors to recipients only when donors were held on deposits > or =50 ppm for 1 h. Deposits even as low as 1 ppm were repellent and termites failed to tunnel into treated sand, and there was no significant mortality. Exposure to acetamiprid impaired locomotion of termites as did other slow-acting neonicotinoids, such as imidacloprid. Acetamiprid was repellent at all concentrations tested, acting like type I pyrethroid treatments in soil. A new subcategory of type III soil termiticides is proposed that incorporates the sublethal and delayed effects observed in neonicotinoid insecticides, and repellency at certain concentrations.     

Transfer of entomopathogenic fungi among formosan subterranean termites and subsequent mortality

Strains of the entomopathogens Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin were screened for effectiveness against the Formosan subterranean termite, Coptotermes formosanus (Shiraki). Biological control methods are being considered to augment current integrated pest management schemes that involve chemical baits and nonrepellent termiticides. In this study Formosan subterranean termites selected from four colonies in the field were exposed in the laboratory to three strains of Beauveria bassiana and two strains of Metarhizium anisopliae . The exposed termites were then allowed to mingle with an equal number of unexposed termites from the same nest and mortality of the combined group was determined. One week after exposure, B. bassiana strains, ATCC 26037 and ATCC 90519, had caused significantly higher mortality than the two M. anisopliae strains, ESC 1 and II B and the remaining strain of B. bassiana , ATCC 90518. The LT₅₀ measurement for strains 26037 and 90519 was comparable at 1.8 and 2.0 days, respectively. Strains ESC 1 and 90518 caused 50% mortality at 6.5 and 11.0 days, respectively. Termites exposed to strain II B and the control group of termites did not reach 50% mortality during the 21 day experimental period. Exposure of termites to all fungal strains resulted in mortality in excess of that seen in the control groups of unexposed termites.     

The influence of subterranean termites on the hydrological characteristics of a Chihuahuan desert ecosystem

Summary Rainfall simulation at an average intensity of 124 mm·h^-1 was used to compare infiltration and run off on arid areas where subterranean termites had been eliminated four years prior to the initiation of the study (termite free) with adjacent areas populated by subterranean termites (termites present). Infiltration rates on termite free plots with less than 5% perennial plant cover were significantly lower 51.3±6.8 mm·h^-1 than rates on comparable termites present plots 88.4±5.6 mm·h^-1. On plots centered on Larrea tridentata shrubs, there were no differences in infiltration rates with or without termites. Plots with shrub cover had the highest infiltration rates 101±6 mm·h^-1. Highest run-off volumes were recorded from termite free <5% grass cover plots and the lowest from plots with shrubs. There were no differences in suspended sediment concentrations from termites present and termite free plots. Average bed load concentration was more than three times greater from termite free, <5% cover plots than from termites present, <5% cover plots.The reduction in infiltration, high run-off volumes and high bedloads from termite free areas without shrub cover is related to increased soil bulk density resulting from the collapse of subterranean galleries of the termites that provide avenues of bulk flow into the soil. Subterranean termites affect the hydrology of Chihuahuan desert systems by enhancing water infiltration and retention of top soil. The presence of a shrub canopy and litter layer cancels any effect of subterranean termites on hydrological parameters. Since approximately 2/3 of the area is not under shrub canopies, subterranean termites are considered to be essential for the maintenance of the soil water characteristics that support the present vegetation.     

Phagostimulatory sugars enhance uptake and horizontal transfer of hexaflumuron in the western subterranean termite (Isoptera: Rhinotermitidae)

Western subterranean termite, Reticulitermes hesperus Banks (Isoptera: Rhinotermitidae), workers fed more on paper disks treated with the carbohydrates xylose, ribose, and fructose than on untreated disks. This feeding behavior of termites for certain carbohydrates was used to demonstrate an increase in the uptake and transfer of the insect growth regulator hexaflumuron among termites. The addition of 3% xylose to paper disks significantly increased the uptake of [14C]hexaflumuron and its subsequent transfer to other termites. Similarly, there was a significant increase in mortality of termites fed on paper disks treated with [14C]hexaflumuron (0.1 and 0.5%) in combination with 3% xylose for similar time periods compared with termites feeding on [14C]hexaflumuron (0.1 and 0.5%) alone. Overall percentage of mortality of termites feeding on [14C]hexaflumuron in combination with 3% xylose during the duration of the study (25-30 d) was approximately equal to 70%.     

When subterranean termites challenge the rules of fungal epizootics

Over the past 50 years, repeated attempts have been made to develop biological control technologies for use against economically important species of subterranean termites, focusing primarily on the use of the entomopathogenic fungus Metarhizium anisopliae. However, no successful field implementation of biological control has been reported. Most previous work has been conducted under the assumption that environmental conditions within termite nests would favor the growth and dispersion of entomopathogenic agents, resulting in an epizootic. Epizootics rely on the ability of the pathogenic microorganism to self-replicate and disperse among the host population. However, our study shows that due to multilevel disease resistance mechanisms, the incidence of an epizootic within a group of termites is unlikely. By exposing groups of 50 termites in planar arenas containing sand particles treated with a range of densities of an entomopathogenic fungus, we were able to quantify behavioral patterns as a function of the death ratios resulting from the fungal exposure. The inability of the fungal pathogen M. anisopliae to complete its life cycle within a Coptotermes formosanus (Isoptera: Rhinotermitidae) group was mainly the result of cannibalism and the burial behavior of the nest mates, even when termite mortality reached up to 75%. Because a subterranean termite colony, as a superorganism, can prevent epizootics of M. anisopliae, the traditional concepts of epizootiology may not apply to this social insect when exposed to fungal pathogens, or other pathogen for which termites have evolved behavioral and physiological means of disrupting their life cycle.     

Behavioral responses of two subterranean termite species (Isoptera: Rhinotermitidae) to instant freezing or chilling temperatures

The behavioral responses to instant freezing or chilling temperatures and survivorship of the Formosan subterranean termite, Coptotermes formosanus Shiraki, and the Eastern subterranean termite, Reticulitermes flavipes (Kollar), were studied using a novel experimental design that closely simulated subterranean termites' natural in-ground environment. Both termite species responded to changes in temperature by exhibiting a downward mass movement from the cold to warmer area of constant temperature. However, the degrees of response were specific to the species and temperature regimen. Approximately 88 and 96% of R. flavipes escaped from instant 0 degrees C and chilling regimens (from 24 to 0 degrees C at a rate of 1 degrees C/h or 1 degrees C/12 h), respectively, compared with approximately 77 and 91% of C. formosanus. No significant difference was detected between the two cooling regimens in either termite species. Controls resulted in a relatively even distribution within test tubes in both termite species. The small portion of the termites that did not escape endured a cold coma at a 24-h 0 degrees C and had low mortality of 2.2 and <1% in R. flavipes and <5.2 and <3% in C. formosanus at instant and chilling regimens, respectively. This result may have implications for understanding group intelligence and decision making evolved by subterranean termites to survive temporary freezing cold.     

Time trends in mortality for thiamethoxam and fipronil against Formosan subterranean termites and eastern subterranean termites (Isoptera: Rhinotermitidae)

Time trends in mortality for the Formosan subterranean termite, Coptotermes formosanus Shiraki, and eastern subterranean termite, Reticulitermes flavipes (Kollar), were determined for thiamethoxam and fipronil. Filter paper treated with 50 ppm thiamethoxam led to >80% mortality in 2-4 d for R. flavipes, whereas 5 ppm thiamethoxam resulted in >80% mortality in 2-3 d for C. formosanus. Filter paper treated with 1 ppm fipronil resulted in >80% mortality in 5 d for R. flavipes and 9 d for C. formosanus, indicating that thiamethoxam is faster acting than fipronil. As concentration decreases for slow-acting termiticides, the time required for adverse effects to be fully expressed increases.     

Toxic effects of 2-deoxy-D-galactose on Coptotermes formosanus (Isoptera: Rhinotermitidae) and symbionts

In the interest of developing interventions to infestations by Formosan subterranean termites, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), several rare sugars were tested for effects on the termites and symbionts. Among these, the D-galactose analog, 2-deoxy-D-galactose (2deoxyGal) showed promise as a potential control chemical. At a test concentration of 2deoxyGal (320.4 microg/mm3) in water applied to 5-cm filter paper, in bioassays with 20 termite workers, we found that worker termite mortality was significantly affected over a 2-wk period. Subsequent dose-mortality feeding studies confirmed these findings. In addition, consumption of the sugar-treated filter paper by termites caused a significant decrease in hindgut protozoan populations. 2deoxyGal caused dose-dependent termite mortality, taking on average 1 wk to begin killing workers, indicating that it may have promise as a delayed action toxin, which, if added to baits, could allow time after bait discovery for an entire colony to be affected.     

Resistance of insecticide-treated foam board insulation against the eastern subterranean termite and the Formosan subterranean termite (Isoptera: Rhinotermitidae)

Three foam board types, one untreated control, one containing 2,000 ppm disodium octaborate tetrahydrate (DOT), and one containing 1,000 ppm deltamethrin, were exposed to field populations of the eastern subterranean termite, Reticulitermes flavipes (Kollar), and the Formosan subterranean termite, Coptotermes formosanus Shiraki. There was no significant difference in termite damage between foam boards treated with 2,000 ppm DOT and the untreated control. Form boards containing 1,000 ppm deltamethrin were not damaged by R. flavipes, whereas only minor damage occurred after exposure to C. formosanus.     

Effect of imidacloprid soil treatments on occurrence of Formosan subterranean termites (Isoptera: Rhinotermitidae) in independent monitors

Periodic sampling of 30 independent monitors, initially active with the Formosan subterranean termite, Coptotermes formosanus Shiraki, was conducted to evaluate the effects of soil treated with imidacloprid on nearby termite activity. Monitors were located adjacent (1-3 m) to the buildings. Soil around and under the buildings was treated with 0.05% imidacloprid. None of the termites collected showed latent mortality attributed to imidacloprid intoxication. Imidacloprid soil treatments did not measurably reduce C. formosanus populations adjacent to the treatments. Imidacloprid does not seem to fit the liquid-bait model.     

Population density, species abundance, and breeding structure of subterranean termite colonies in and around infested houses in central North Carolina

Pressure from subterranean termites is known to vary geographically across the United States, but there are few quantitative studies concerning the threat of structural infestation for any geographic region. We assessed the number and locations of termite colonies present on 20 infested residential properties in central North Carolina, where subterranean termite pressure is considered to be heavy. This was achieved by using microsatellite markers to determine colony identity of termites collected over 6-14 mo from mud tubes in structures, below-ground monitors, and wood debris in the yard. In total, we identified 188 distinct colonies and determined their breeding structures. Reticulitermes flavipes (Kollar) was by far the most common species, accounting for nearly 90% of all colonies; the remaining colonies belonged to Reticulitermes hageni Banks and Reticulitermes virginicus (Banks). In four cases, there were two colonies infesting a structure simultaneously; in all other cases only a single colony was detected in the structure. Colony densities were high, averaging 62 colonies per ha (25 per acre) with a maximum of 185 colonies per ha (75 colonies per acre). Foraging ranges of R. flavipes and R. hageni colonies were generally small (<30 linear m), and most colonies were headed by a single pair of monogamous reproductives with nearly all the remaining colonies headed by relatively few inbreeding descendants of the original monogamous pair. These results provide the most detailed picture to date of the number, distribution, and colony characteristics of subterranean termite colonies located in and around residential structures.     

Field Evaluations of Subterranean Termite Preference for Sap-Stain Inoculated Wood

Few studies have focused on interactions between subterranean termites and the ophiostomatoid fungal associates of pine bark beetles or root feeding weevils. Field stake tests were employed at four locations throughout Mississippi to determine the feeding preference of subterranean termites for blue-stained, unstained, and partially decayed southern pine sapwood stakes. This study also utilized wood decayed by Gloeophyllum trabeum, a fungus previously shown to elicit a positive subterranean termite feeding response, as a positive control. Stakes inoculated with G. trabeum received significantly more attacks than all other treatments after 16 weeks. Of the stakes attacked by subterranean termites, stakes inoculated with Ophiostoma minus were degraded faster than any other treatment. Subterranean termite preference for stakes treated with either of two Leptographium spp. and the untreated negative controls did not differ; however, each was fed upon less than all other treatments. The feeding rate on stakes inoculated with O. ips and G. trabeum being fed upon by subterranean termites was not significantly different. These results represent the first evidence of wood containing non-structurally degrading fungi (O. ips and O. minus) eliciting a feeding preference from subterranean termites greater than that of decayed wood. The implications of these results are particularly relevant to pine forest ecology, nutrient cycling, subterranean termite control, and the utilization of blue-stained southern pine building products in the southeastern U.S.     

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