Insecticide susceptibility in Coptotermes formosanus and Reticulitermes virginicus (Isoptera: Rhinotermitidae).

Lethal time to mortality responses were established for eight insecticides against workers and soldiers of the Formosan subterranean termite, Coptotermes formosanus Shiraki, and workers of Reticulitermes virginicus (Banks). There were significant differences in the tolerance ratios between workers of C. formosanus colonies to all toxicants tested except fipronil. One colony was 16 times more tolerant than another to deltamethin. C. formosanus soldiers had significant differences in tolerance ratios among colonies exposed to all toxicants except chlorpyrifos. Methoxychlor, permethrin, deltamethrin, and fipronil did not kill soldiers from two, one, one, and three colonies, respectively, within 8 h. Seventy-five percent of R. virginicus colonies were significantly less susceptible than the most susceptible colony to chlordane, methoxychlor, chlorpyrifos, cypermethrin, and fipronil, with 50% of the colonies less susceptible to permethrin and bendiocarb. In 50% of C. formosanus colonies the worker lethal time curves displayed substantial flattening in response to permethrin, and deltamethrin. Lethal time curses for C. formosanus soldiers exposed to chlordane, chlorpyrifos, permethrin, cypermethrin, deltamethrin, and bendiocarb showed substantial flattening. R. virginicus workers demonstrated substantial curve flattening when exposed to chlordane, methoxychlor, chlorpyrifos, deltamethrin, and fipronil. These findings indicate substantial intercolony and intra-colony differences in susceptibility to insecticides.     

Interspecific Interactions Between Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae) in Laboratory Bioassays

Experiments were conducted to examine competitive interactions between the Formosan subterranean termite, Coptotermes formosanus Shiraki (FST), and the eastern subterranean termite, Reticulitermes flavipes (Kollar) (EST), using groups of termites with different worker:soldier proportions. Experiments were conducted using three connected test chambers: an FST chamber, an unoccupied center chamber, and an EST chamber. When groups of FST were comprised of 20% soldiers versus 2% EST soldiers, only 8% of center chambers were occupied exclusively by EST. When groups of FST were comprised of 10% soldiers versus 1% EST soldiers, 44% of center chambers were occupied exclusively by EST. When the only food source was located in the center chamber, 60% of center chambers were occupied by both species. FST did not completely displace EST in any of these experiments.     

Response variability of juvenile hormone and juvenile hormone analogs in workers of the Formosan subterranean termite (Coptotermes formosanus Shiraki)

Juvenile hormone (JH) or juvenile hormone analog (JHA) can induce soldier formation in termites. However, different studies have yielded inconsistent results on the effects of JHA on soldier production in Coptotermes formosanus Shiraki. Using filter paper as the testing substrate, the effects of JH III, pyriproxyfen and methoprene on the intact filter paper left, worker mortality and presoldier formation were tested on six colonies. Our results showed that pyriproxyfen and methoprene were more repellent than JH III. No significant difference in toxicity was observed among methoprene, pyriproxyfen and JH III. JH III and pyriproxyfen did not cause workers to differentiate into presoldiers, but methoprene can induce formation of presoldiers. Colony response variability to methoprene was observed. The confirmation of the effects of JH/JHA on C. formosanus establishes the foundation for molecular studies of soldier differentiation in this species.     

A mathematical model for the territorial competition of the subterranean termites Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae)

The foraging territories of two subterranean termites, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), were simulated using a two-dimensional model to explore how territorial competition changes according to two variables characterizing territory formation: the total number of territories, and the blocking probability. Meanwhile, the blocking probability quantitatively describes the likelihood that a tunnel will be terminated when another tunnel is encountered. In our previous study, we introduced an interference coefficient γ to characterize territorial competition, and obtained γ as a function of the total number of territories and the blocking probability for a single termite species by model simulation. In the field, the territorial competition of more than two termite species is frequently observed. Here, we extended the γ function to be able to explain the competition between the two species by applying statistical regression to the simulation data. Further, we statistically checked the extended γ function by comparing the γ function for a single species. We also discuss another approach to mathematically derive the extended γ function, which can be easily generalized for use in cases of territorial competition involving more than two termite species.     

Directional selection by the subterranean termite Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) at tunnel intersections

Subterranean termites construct complicated tunnel networks for foraging below ground. Thus, they often encounter tunnel intersections during foraging activity. Directional selection by termites at intersections is likely to affect foraging efficiency because depending on their selection, the path length from food resources to the nest can vary significantly. In order to understand how termites are guided to choose the most economical path without the use of pheromones, we artificially excavated two tunnels of varying widths (W₁ and W₂; 2, 3, or 4 mm) that intersected at a 90° angle in each of nine soil‐filled arenas. We observed the directional selection of termites at intersections in arenas with combinations of W₁ (mm) and W₂ (mm) (W₁, W₂). For (W₁, W₂) = (2, 2) and (4, 4), termites statistically equally chose the three directions left, right, and straight, while for the (3, 3) arena combination, termites preferentially decided to go straight. On the other hand, for (W₁, W₂) = (2, 3) (2, 4), and (3, 4), termites advancing from narrower tunnels into intersections tended to turn right or left, while termites coming from the wider tunnel were more inclined to go straight. On the assumption that a wider tunnel is more frequently used by termites in the field, we can deduce that the wider tunnel may represent the most efficient/shortest path. Thus, this simple selection mechanism can prevent termites from deviating from the most economical path.     

Development of superfluous soldiers induced by juvenile hormone analogues in the termite,Reticulitermes lucifugus santonensis

Summary The synthetic juvenile hormone (JH): 17% alltrans+83%trans, trans, cis-methyl 10-epoxy-3,7,11-trimethyl-2,6 tridecadienoate and juvenile hormone analogues (JHA): methyl 10-chloro-3,7,11-trimethyl-2 dodecenoate and ethyl 10-epoxy-3,7,11-trimethyl-2,6-dodecadienoate administered on filter paper to small groups of the European subterranean termiteReticulitermes lucifugus santonensis Feyt. caused differentiation of larvae and pseudergates into pre-soldiers and/or pseudergate-soldier intercastes. In contrast to the proportion of one soldier to 100–300 other individuals in normal colonies, the effect of the compounds tested that showed JH activity was to induce the development of a large number of superfluous soldiers in quantities that even exceeded the number of other kinds of individuals. Such a disturbance in the caste ratio leads to increased mortality.

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Zusammenfassung Das synthetische Juvenilhormon (JH): 17% alltrans+83%trans, trans, cis-Methyl 10-epoxy-3,7,11-trimethyl-2,6 tridecadienoate und die Juvenilhormonanaloge (JHA): Methyl 10-chloro-3,7,11-trimethyl-2 dodecenoate und Ethyl 10-epoxy-3,7,11-trimethyl-2,6-dodecadienoate, die auf Filterpapier kleinen Termitengruppen der europäischen ErdtermitenartReticulitermes lucifugus santonensis Feyt. zugeführt wurden, verursachten eine Differenzierung von Larven und Pseudergaten in Vorsoldaten und/oder Interkasten Pseudergate-Soldat. Zum Unterschied vom Verhältnis ein Soldat zu 100 bis 300 anderen Individuen in normalen Kolonien erscheint unter der Einwirkung der getesteten juvenilhormonwirksamen Stoffe eine grosse Menge überzähliger Soldaten, deren Anzahl jene der übrigen Individuen sogar übersteigen kann. Die Gleichgewichtstörung zwischen den Kasten hat eine höhere Absterberate der Termiten zur Folge.

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Résumé L'hormone juvénile synthétique: 17% alltrans+83%trans, trans, cis-méthyle 10-epoxy-3,7,11-triméthyle-2,6 tridecadienoate et l'analogue de l'hormone juvénile: méthyle 10-chloro-3,7,11-triméthyle-2 dodecenoate et éthyle 10-epoxy-3,7,11-triméthyle-2,6-dodecadienoate, qui ont été administrés amenés sur papier filtre à de petits groupes de termitesReticulitermes lucifugus santonensis Feyt., ont causé une différenciation de larves et de pseudergates en présoldats et/ou intermédiaires pseudergate-soldat. A la différence du rapport de 1 soldat à 100–300 autres individus dans des colonies normales, on assiste sous l'effet de la substance testée avec effet d'hormone juvénile à l'apparition d'un grand nombre de soldats en surplus, dont le nombre peut même dépasser celui des autres individus. Le trouble de l'équilibre entre les castes conduit à un taux de mortalité supérieur des termites.

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Dedicated to Prof.K. Gösswald at the occasion of his 65th birthday.     

Regulation of juvenile hormone titers by soldiers in the Formosan subterranean termite, Coptotermes formosanus

In field collections of the Formosan subterranean termite Coptotermes formosanus, soldiers averaged less than 10%. The proportion of soldiers increased to about 25% or higher when termites were kept in the laboratory, as did the juvenile hormone III (JH III) titers for both workers and soldiers. In laboratory experiments with a proportion of soldiers 25% or higher, very few new pre-soldiers were formed and the JH titer in existing soldiers remained constant. On the contrary, workers from groups containing less than 25% soldiers formed more pre-soldiers. In such cases, both workers and soldiers showed higher JH titers. Newly formed soldiers also had higher JH titers than older soldiers. It is speculated that populations containing higher soldier proportions inhibit further soldier differentiation, eventually holding the JH titers under the threshold or suppressing the activity of corpora allata resulting in lower JH titers in workers.     

Factors affecting post-flight behavior in primary reproductives of the Formosan subterranean termite, Coptotermes formosanus (Isoptera: Rhinotermitidae)

After swarming, reproductive dealates of the Formosan subterranean termite, Coptotermes formosanus, run together in tandem. The tandem running is an age-related behavioral activity in C. formosanus. This behavior was not evoked in pre-flight alates less than 6-d-old that were artificially dealated. Female age was more important than male age for evoking tandem behavior. Females and males, older than 35 days, did not exhibit this behavior. Mating status was not important for female and male dealates to form the tandem pairs. The titers of the major tergal gland component, trilinolein, did not decline significantly and remained high, not only in virgin females, but also in mated females for a period of time after swarming. On the other hand, increasing amounts of the female-specific compound trilinolein were detected in male dealates 7, 14, and 42 days after pairing. This suggests that trilinolein in the females might be transferred to the males as a nuptial gift in C. formosanus. In addition, females have structurally different lateral setae that may constitute a morphological factor involved in the tandem behavior in this species. Covering the setae with dimethyl sulfoxide prevented the tandem behavior.     

Tunnel formation by Reticulitermes flavipes and Coptotermes formosanus (Isoptera: Rhinotermitidae) in response to wood in sand.

The tunneling responses of two subterranean termite species, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar), to the presence of sound wood in laboratory arenas were studied. Branching pattern and the speed of tunnel construction between R. flavipes and C. formosanus also were compared. Patlak's residence index (rho) was generated using the length, width, speed of construction, and area of the primary tunnels built by termites. In the same allotted time, C. formosanus built wider and shorter primary tunnels, whereas R. flavipes built thinner and longer primary tunnels. The presence of wood did not affect termite tunnel formation. This lack of variation in tunnel formation parameters was evidenced by the inability of the termites to locate wood sources over distance, even as short as 2.5 mm, and by the similar tunneling behaviors in areas of the arena with or without wood. Patlak's model predicted the densities of tunnels with an error between 9 and 28%. in experiments with R. flavipes exposed to a range of 0-8,000 g of wood, and between 61 and 87% in experiments with C. formosanus. These results indicated that the residence index can provide a qualitative measure of the effect of habitat heterogeneity on the individual termite tunnels. The tunneling constructions strategy of these subterranean termites is discussed.     

Elimination and reinvasion studies with Coptotermes formosanus (Isoptera: Rhinotermitidae) in Louisiana

Three Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), colonies located inside the 12.75-ha Louis Armstrong Park, New Orleans, were selected for elimination by using the chitin synthesis inhibitor hexaflumuron. Once eliminated, each vacated foraging territory was monitored for reinvasion by neighboring C. formosanus colonies, Reticulitermnes flavipes (Kollar) (Isoptera: Rhinotermitidae) colonies, or both. Each selected colony was eliminated in approximately 3 mo by using baits containing hexaflumuron. Overall activity of each untreated colony in the park remained unchanged during the same period. New C. formosanus and R. flavipes activity was detected in two of the three vacated territories, and in both areas, within days of selected colony elimination. The third vacated territory was completely reoccupied by a new C. formosanus colony approximately 7 mo later. Mark-recapture studies and DNA fingerprinting confirmed the distinctness of the reinvaders from eliminated and neighboring colonies.     

Feeding preference of Coptotermes formosanus (Isoptera: Rhinotermitidae) for gamma-irradiated wood impregnated with benzoylphenylurea compounds under laboratory conditions

The feeding preference of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) for 200-kGy gamma-irradiated Cryptomeria japonica D. Don (Japanese cedar) sapwood impregnated with benzoylphenylurea compounds such as hexaflumuron and noviflumuron was examined by three laboratory tests. Although termites were not deterred from feeding on gamma-irradiated wood samples that had been impregnated with hexaflumuron or noviflumuron, termite mortality was significantly higher compared with solvent controls in the no-choice test. All live termites were transferred to paper disks immediately after the no-choice test to investigate changes in mortality with time, and this test also confirmed the effects of hexaflumuron and noviflumuron on worker termites, which showed a significant feeding preference for gamma-irradiated wood. Only the 1480 ppm noviflumuron-impregnated gamma-irradiated wood specimens showed significant differences in mortality in the two-choice test. These results suggest that gamma-irradiated C. japonica wood, which is locally abundant in Japan, may have potential as a bait substrate for benzoylphenylurea compounds.     

Landscape mulches and termite nutritional ecology: growth and survival of incipient colonies of Coptotermes formosanus (Isoptera: Rhinotermitidae)

Alate swarms are one of the major visible signs of the expansion of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), in an area. Successful establishment of an incipient colony is thought to mainly rely on available food resources and moisture. The large-scale use of tree-based mulches in landscapes may inadvertently contribute to local establishment and growth of C. formosanus colonies. This research investigated the nutritional ecology of incipient colonies of C. formosanus feeding on seven tree-based, weathered, and nonweathered landscape mulches: pine straw, pine bark, cedar wood, water oak, eucalyptus, cypress, and melaleuca. Incipient colonies of C. formosanus feeding on pine straw, either weathered or nonweathered, produced significantly more progeny over the course of 1-yr feeding than colonies feeding on the other mulches tested. Regardless of weathered or not, the incipient colonies feeding on pine straw, eucalyptus, bald cypress, and water oak mulches had significantly greater survival rates after 360 d (53-77%) than colonies feeding on the other mulches tested (0-13%), but colonies feeding on nonweathered water oak had significantly lower survival (8%) than those kept on weathered water oak (58%). Colony fitness values were significantly different between the weathering treatment groups and among the different types of mulches. With regard to colony growth characteristics, three distinct growth patterns were identified: a high number of progeny (>100) with high colony survival rate (>50%), a medium number of progeny (12-50) with high colony survival rate (>50%), and a small number of progeny (0-10) with low colony survival rate (<5%). These findings suggest that different types of mulch substrates could significantly impact the nutritional ecology of the founding pairs and the successful establishment of incipient colonies during the swarming season.     

Interspecific competition and territory defense mechanisms of Coptotermes formosanus and Coptotermes gestroi (Isoptera: Rhinotermitidae)

Coptotermes formosanus Shiraki and C. gestroi (Wasmann) are the most widely distributed species of the genus and occur sympatrically in the subtropics. Results of two bioassays in the current study showed that C. gestroi was more aggressive than C. formosanus. In the petri-dish bioassays, C. gestroi won most of the agonistic encounters over C. formosanus. In the two-dimensional foraging arena bioassays, over 73% tunnel interceptions observed in the 18 replications were caused by progressing tunnels of C. gestroi encountering the tunnels of C. formosanus. Tunnel interception of the two species resulted in minor agonistic interactions. Both species quickly buried the connected tunnel at multiple locations. Termite cadavers resulting from agonistic behavior appeared to have induced sand deposition that resulted in tunnel blockages and deterred reopening of these blockages. Sealing individual tunnels in response to encounters with other species acts to prevent further agonism and mortality, and on a broad scale, the aggregate of such blocked tunnels may come to define the borders between adjacent colonies.     

Effects of antibiotics on hydrogen production and gut symbionts in the Formosan subterranean termite Coptotermes formosanus (Isoptera: Rhinotermitidae)

Abstract Symbiotic microorganisms that inhabit the gut of Coptotermes formosanus enable this termite to degrade lignocelluloses and further produce hydrogen as an important intermediate to be recycled in its hindgut or as a byproduct to be emitted to the atmosphere. Both symbiotic protists and prokaryotes in the guts of termites demonstrated some different roles with respect to hydrogen production. In this study, the effects of two antibiotics, ampicillin and tetracycline, on hydrogen emission and the gut symbionts of C. formosanus were investigated. Hydrogen emission from termite guts was significantly enhanced when termites fed on wood diets treated with either ampicillin or tetracycline. The greatest H₂ emission rates, 2 519 ± 74 and 2 080 ± 377 nmol/h/g body weight, were recorded with the treatments of ampicillin and tetracycline, respectively, which showed 6–7 times more H₂ production than that of controls. Antibiotic‐treated diets negatively affected the prokaryotic communities and reduced their abundances, particularly on those ectosymbionts inhabiting the gut walls or in the gut fluid of C. formosanus, such as spirochetes. However, no significant reductions in the counts of gut cellulolytic protists, Pseudotrichonympha grassii and Holomastigotoids hartmanni, were recorded; and with a further observation by confocal laser scanning microscopy, the endosymbionts inhabiting P. grassii generally survived the antibiotic treatments. These results suggest that some prokaryotes may serve as the main hydrogen consumers, while P. grassii, together with its endosymbionts, may function as the main contributors for hydrogen production in the hindgut of C. formosanus.     

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.     

Morphology,fine structure,and functional aspects of the labial gland reservoirs of the subterranean termite Reticulitermes santonensis de Feytaud (Isoptera: Rhinotermitidae)

The morphology and fine structure of the labial gland reservoirs in the subterranean termite Reticulitermes santonensis (Isoptera: Rhinotermitidae) was studied by light and transmission electron microscopy. The reservoir wall consists of a single epithelial cell layer and a cuticular intima. The reservoir ducts are formed by a flat epithelial matrix with cuticular ridges lining the duct lumen. Measurements of the ionic concentrations of reservoir fluids and haemolymph show that the osmolality of reservoir fluid ranges from 7 to 28 mosmol kg⁻¹; the haemolymph osmotic pressure was 201 ± 31 mosmol kg⁻. The reservoir lumen is effectively separated from the haemolymph compartment; a net water flow through the reservoir wall could not be induced in physiological experiments. Moreover, typical epithelial structures associated with a fluid transport against an osmotic gradient are lacking. Thus, our fine structural and physiological data support the view that a water transfer from the haemolymph through the reservoir wall into the reservoir lumen does not occur.     

Responses of Coptotermes formosanus and Reticulitermes flavipes (Isoptera: Rhinotermitidae) to three types of wood rot fungi cultured on different substrates

This study examined the responses of two termite species, the Formosan subterranean termite, Coptotermes formosanus Shiraki, and the eastern subterranean termite, Reticulitermes flavipes (Kollar), to three types of wood decay fungi: a brown rot fungus, Gloeophyllum trabeum (Persoon: Fries) Murrill; a white rot fungus, Phanerochaete chrysosporium Burdsall; and a litter rot fungus, Marasmiellus troyanus (Murrill) Singer. We also examined the responses of termites to these three types of fungi grown on different substrates. For all three fungal species, both termite species showed a strong preference for fungus-infected sawdust over uninfected sawdust. In choice tests, both termite species preferred sawdust infected with either M. troyanus or P. chrysosporium over G. trabeum. However, termites did not show any preference for fungus-infected potato dextrose agar over uninfected potato dextrose agar. Tunneling activity of C. formosanus was greater in sand treated with methanol extracts of fungus-infected sawdust than in sand treated with extracts of uninfected sawdust. Because chemicals in the fungal extracts caused termites to tunnel further into treated sand than untreated sand, these chemicals could potentially be used to direct termite foraging toward bait stations in the field.