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.     

Ecdysone agonist halofenozide affects corpora allata and reproductive physiology of the Formosan subterranean termite,Coptotermes formosanus

Following a short swarming flight, winged adults of the Formosan subterranean termite, Coptotermes formosanus lose their wings and form tandem pairs. These dealates or primary reproductives then form incipient colonies. Topical application of 5 microg of the non-steroidal ecdysone agonist RH-0345 (halofenozide) in 0.1 microl DMSO to the primary reproductives during the 2000 season resulted in significant reduction in the number of eggs laid. There was however complete recovery of the treated females. Apparently the non-treated partner removed the treatment chemical while grooming indicating oral activity. In 2001 both topical application as well as feeding methods were tried. Significant effects were observed only in the topical treatment group, perhaps because of inconsistency in feeding. In this group, total progeny, the number of ovarioles in ovaries and the size of the female's corpora allata (CA) were all significantly reduced. Ultrastructure of the CA of treated females showed extensive vacuolation near the surface of the gland. The experiment was repeated in 2002 using both topical application and an improved oral feeding method. Whereas there was apparent recovery in the topically treated group after 90 days, the oral treatment was more persistent in its effect perhaps due to a higher amount of halofenozide consumed during feeding.     

台湾乳白蚁行为多型的研究

本文对台湾乳白蚁的打洞挖掘行为、取水行为、修饰行为和交哺行为进行了比较详细的定量分析,探讨了年龄和品级对台湾乳白蚁群体中行为多型的影响。实验结果表明大（老）龄工蚁承担了台湾乳白蚁群体内大多数的任务,对台湾乳白蚁群体的维持具有重要意义。另外品级也是影响台湾乳白蚁群体内劳动分化的一个重要因素。在营养交哺方面,若蚁尚不具备完好的取食行为,是群体中营养交哺的受益者,而兵蚁在台湾乳白蚁群体中占据着较重要的地位,享受着营养物质优先供应的特殊权利。     

Group size effect on worker juvenile hormone titers and soldier differentiation in Formosan subterranean termite

In a finite environment, population growth can lead to crowding, increased densities and stress. Termites live in highly organized societies and densities can increase astronomically as colonies grow. However, little is known about juvenile hormone (JH) changes in these insects as numbers increase, despite the fact that JH is a critical caste regulator in this insect. Using Formosan subterranean termites as a model, we evaluated minimum group size requirements for soldier differentiation and the effect of density (50, 100, 500, and 1000 individuals/experimental unit) on worker JH titers either with or without initial soldiers being present. The minimum group size investigation indicated that groups initiated with 5 workers were insufficient for soldier differentiation. Soldiers were produced in groups initiated with 10 or more workers. As density increased from 50 to 1000 individuals per experimental unit, worker JH levels were elevated. Presence of soldiers lessened the effect of density on rising worker JH titers, indicating that soldiers have the ability to down-regulate worker JH. The study provides direct evidence of a population density effect on JH in eusocial insects and sheds light on understanding of the regulatory mechanisms associated with termite soldier caste differentiation.     

Musty odor of entomopathogens enhances disease-prevention behaviors in the termite Coptotermes formosanus

Termites often eliminate pathogens directly through mutual grooming, and are thereby prevent infections from entomopathogenic fungi. Our previous study confirmed that the antennae of Coptotermesformosanus sensitively responded to the musty odor of entomopathogenic fungi. However, it is unclear if this odor has any effect on termite behavior. The purpose of this study was to clarify the effects of fungal odor on termite behavior, especially on conidia removal. The musty odor was prepared as an aqueous solution by immersing conidia in distilled water. When untreated termites were mixed with fungal-odor-treated termites at a ratio of 4:1, mutual grooming and attack of treated termites were frequently observed. This indicated that the fungal odor triggered these behavioral responses. While some components of the fungal odor were found in all of the entomopathogenic fungi tested, the odor profiles differed among the isolates.     

Sporulation of Metarhizium anisopliae and Beauveria bassiana on Coptotermes formosanus and in vitro

The sporulation of 22 total isolates of Metarhizium anisopliae and Beauveria bassiana was quantified on cadavers of the Formosan subterranean termite, Coptotermes formosanus. Conidial production increased significantly over 11 days post-death. Effects of isolates of M. anisopliae and B. bassiana on in vivo sporulation were significant. Although the overall effects of fungal species on in vivo sporulation were not significant, the interactions between fungal species and certain times post-death were significant, indicating different sporulation patterns between the two fungal species. B. bassiana isolates could be categorized into a group with high total sporulation (day 11) and low quick sporulation (on days 2 and 3), while M. anisopliae isolates fell into another group with high quick sporulation and low total sporulation. This could give M. anisopliae an advantage over B. bassiana in termite microbial control due to termite defensive social behaviors. Conidial production was significantly higher in vitro than in vivo. In vitro and in vivo sporulation differed by as much as 89x and 232x among the selected isolates of B. bassiana and M. anisopliae, respectively. Correlation between in vivo and in vitro conidial production was positive and significant. This may allow preliminary in vitro screening of a large number of isolates for high in vivo sporulation.     

Defense mechanism of the termite, Coptotermes formosanus Shiraki, to entomopathogenic fungi

Termites, Coptotermes formosanus Shiraki, reared individually, were highly susceptible to entomopathogenic fungi, Paecilomyces fumosoroseus and Beauveria brongniartii and Metarhizium anisopliae, while termites reared in groups were highly resistant. Quantitative assays with an epifluoresent microscope revealed a significant difference in the number of conidia attachments among three entomopathogenic fungi. The conidia of B. brongniartii and P. fumosoroseus bound to termite cuticles more effectively than M. anisopliae conidia. Our results also suggested that self-grooming behavior is less effective, but mutual grooming is very effective in the removal of conidia from cuticles of their nestmates. Statistical analysis of removal rates indicated that conidia of P. fumosoroseus and B. brongniartii were removed more rapidly than M. anisopliae conidia from termite cuticles.     

Behavioral changes in the termite, Coptotermes formosanus (Isoptera), inoculated with six fungal isolates

The studies of pathogen-prevention behaviors of termites have focused on hygiene behavior directed only against highly virulent pathogens. Therefore, we compared behavioral changes in the subterranean termite Coptotermes formosanus following contact with entomopathogenic fungi with different levels of virulence. The fungal virulence was inferred from the daily mortality and the LD₅₀ value in previous data. When untreated termites were allowed to contact their fungus-inoculated nestmates, mutual grooming was frequent during 30 min after inoculation. The inoculated termites were often attacked and eaten by their uninoculated nestmates, and then buried after death. Notably, there was no influence of fungal virulence on these pathogen-prevention behaviors. However, the fungal isolates and genera affected not only the frequency of the behaviors but also the horizontal transmission pattern, the number of dead individuals and the survival period before the first death following infection.     

Minimizing moving distance in deposition behavior of the subterranean termite

Subterranean termite nests are located underground and termites forage out by constructing tunnels to reach food resources, and tunneling behavior is critical in order to maximize the foraging efficiency. Excavation, transportation, and deposition behavior are involved in the tunneling, and termites have to move back and forth to do this. Although there are three sequential behaviors, excavation has been the focus of most previous studies. In this study, we investigated the deposition behavior of the Formosan subterranean termite, Coptotermes formosanus Shiraki, in experimental arenas having different widths (2, 3, and 4 mm), and characterized the function of deposited particles. We also simulated moving distance of the termites in different functions. Our results showed that total amounts of deposited particles were significantly higher in broad (4 mm width) than narrow (2 mm) tunnels and most deposited particles were observed near the tip of the tunnel regardless of tunnel widths. In addition, we found that deposited particles followed a quadratic decrease function, and simulation results showed that moving distance of termites in this function was the shortest. The quadratic decrease function of deposited particles in both experiment and simulation suggested that short moving distance in the decrease quadratic function is a strategy to minimize moving distance during the deposition behavior.     

Dual origin of gut proteases in Formosan subterranean termites (Coptotermes formosanus Shiraki) (Isoptera: Rhinotermitidae)

Cellulose digestion in lower termites, mediated by carbohydrases originating from both termite and endosymbionts, is well characterized. In contrast, limited information exists on gut proteases of lower termites, their origins and roles in termite nutrition. The objective of this study was to characterize gut proteases of the Formosan subterranean termite (Coptotermes formosanus Shiraki) (Isoptera: Rhinotermitidae). The protease activity of extracts from gut tissues (fore-, mid- and hindgut) and protozoa isolated from hindguts of termite workers was quantified using hide powder azure as a substrate and further characterized by zymography with gelatin SDS-PAGE. Midgut extracts showed the highest protease activity followed by the protozoa extracts. High level of protease activity was also detected in protozoa culture supernatants after 24 h incubation. Incubation of gut and protozoa extracts with class-specific protease inhibitors revealed that most of the proteases were serine proteases. All proteolytic bands identified after gelatin SDS-PAGE were also inhibited by serine protease inhibitors. Finally, incubation with chromogenic substrates indicated that extracts from fore- and hindgut tissues possessed proteases with almost exclusively trypsin-like activity while both midgut and protozoa extracts possessed proteases with trypsin-like and subtilisin/chymotrypsin-like activities. However, protozoa proteases were distinct from midgut proteases (with different molecular mass). Our results suggest that the Formosan subterranean termite not only produces endogenous proteases in its gut tissues, but also possesses proteases originating from its protozoan symbionts.     

Differential susceptibility of subterranean termite castes to entomopathogenic nematodes

We examined the attachment and infectivity of two entomopathogenic nematode species, Steinernema carpocapsae and Heterorhabditis indica, on soldiers and workers in two subterranean termite species, Coptotermes formosanus and C. vastator. In attachment tests with S. carpocapsae, more nematodes attached to soldiers of C. formosanus and C. vastator in the absence of workers compared to soldiers that were in the presence of workers. In tests with soldiers alone, workers alone, and mixture of equal numbers of workers and soldiers, soldiers in the mixed groups had lower mortality than soldiers alone after 1 and 4 days for both termite species. Exposure of small groups of either termite species to S. carpocapsae resulted in higher mortality of soldiers after 1 and 4 days post exposure. Mortality in soldiers alone exposed to H. indica was not significant compared to mortality in mixed groups at 1 day exposure, but was significant after 4 days. In concentration-mortality tests, a significant two-way interaction existed between nematode concentration and termite caste for C. formosanus exposed to S. carpocapsae for 1 and 4 days. A significant effect of nematode concentration was found for C. vastator exposed to H. indica for 1 day. This termite species had lower mortality when exposed to H. indica after 1 and 4 days compared to C. formosanus. At 4 days post exposure to H. indica, the effects of nematode concentration and termite caste were significant. Steinernema carpocapsae caused higher mortality than H. indica, but mortality of workers was higher when exposed to H. indica. Soldiers of both species experienced rapid mortality when exposed to S. carpocapsae, whereas soldiers of C. vastator experienced lower mortality when exposed to H. indica. Thus, our results show that when soldiers alone or workers alone are exposed to the nematodes, there is a differential susceptibility of soldiers and workers to nematode infection with soldiers being more susceptible than workers. In a mixed group of soldiers and workers or workers alone, it appears that grooming behavior of the workers serves as a mechanism to reduce nematode infection of soldiers and workers. The reason for this differential response to nematode infection is that soldiers do not exhibit grooming behavior.     

Suppression of termite feeding and symbiotic protozoans by the dye, Sudan Red 7 B

Laboratory groups of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), were fed for 14 days on wood shavings soaked in acetone solutions of 0%, 0.5% or 1% concentrations of the dye, Sudan Red 7B or on shavings not soaked in acetone (0% non-acetone, NA). Termites feeding on dyed wood became visibly stained red. Groups of dyed or non-dyed termites were then placed in containers and allowed to feed on non-dyed wood for 21 days. Dyed termites had lower numbers of symbiotic protozoans, lower feeding rates, and lower survivorship than did non-dyed termites. Survivorship was significantly lower in the 1% concentration than in the 0.5% concentration. Covariate analyses suggested that Sudan Red acts both directly and indirectly (via suppression of gut fauna) to reduce vigor in termites. Because there is variable survival response to this dye by different populations of C. formosanus, we recommend preliminary tests of dye toxicity before using it extensively in experiments.

---

Résumé Le colorant rouge Soudan 7B (BASF, Wyandotte Corp.) soluble dans l'huile, est un marqueur efficace des termites pour les études dans la nature. Quand les termites consomment des matériaux marqués par ce colorant, ils deviennent nettement colorés en rouge. Bien que certains travaux indiquent que le rouge Soudan n'augmente pas considérablement la mortalité, il n'y a aucune donnée concernant l'effet du colorant sur l'alimentation des termites.Un groupe de Coptotermes formosanus récolté au lac Charles en Louisiane, a été alimenté pendant 14 jours sur copeaux de Pinus sp. colorés avec des solutions 0, 0.5% et 1% (en poids) de rouge Soudan 7B dans l'acétone, ou sur copeaux non colorés et sans acétone (NA). Les groupes de termites colorés ou non sont alors placés dans des récipients pour s'alimenter sur bois non coloré pendant 21 jours. Des différences significatives ont été observées (t. 1): les termites colorés avaient moins de protozoaires symbiontes, consommaient moins de bois et vivaient moins long-temps que les termites sans colorant (t. 2). La survie a été plus faible avec la concentration 1% qu'avec 0.5%. Le nombre de protozoaires était plus faible avec une solution acétonique sans rouge Soudan qu'avec du bois sans acétone, ce qui suggère que l'effet négatif du rouge Soudan sur les protozoaires a pu être augmenté par l'extraction d'une substance favorisant les protozoaires contenue dans les copeaux de pin.La chute de la prise de nourriture a été accompagnée d'une chute parallèle de l'effectif de protozoaires. En réexaminant les résultats de Lai et al. (1983), nous constatons qu'eux aussi avaient observé une réduction de l'effectif de protozoaires de C. formosanus sous l'effet du rouge Soudan. Dans notre étude, nous trouvons que 49,6% de l'effet réducteur du colorant sur la nutrition est expliqué par l'effet simultané sur les protozoaires. Nos résultats sur la survie confirment dans l'ensemble ceux de Su et al. (1983 a) sur C. formosanus de Louisiane. Cependant, C. formosanus de Hawaï (Lai et al., 1983) et de Floride (Su et al., 1988) avaient des taux de survie bien plus élevés. C. formosanus présente nettement des réactions variables au rouge Soudan. Dans notre travail, 64,1% de l'effet du colorant sur la survie a été expliqué par des modifications chez les protozoaires. Ainsi, il semble que le rouge Soudan agisse directement sur l'alimentation et la survie de C. formosanus, et indirectement par la suppression de sa faune intestinale.Bien que nos résultats montrent les effets délétères du rouge Soudan 7B sur C. formosanus, il reste le meilleur colorant pour les termitologistes. par suite de la variabilité de son effet sur la survie, nous conseillons des tests de toxicité avant son utilisation intensive dans des expériences.

     

Aquaporin water channel in the salivary glands of the Formosan subterranean termite Coptotermes formosanus is predominant in workers and absent in soldiers

Termite society is unique because the worker caste fetches and carries free water, utilizing it as a solvent for nest construction and gallery building and to maintain wetness for their nestmates. Such water management in a social organization relies largely upon the function of the workers in the colony, as well as on the individuals controlling the location and movement of water inside their bodies. The movement of water via aquaporins (AQPs; water channels) into and out of cells is a key feature of the numerous physiological functions related to whole‐insect water balance. In the present study, the homologue of the water‐specific Drosophila AQP [Drosophila integral protein (DRIP)] is characterized in workers of the Formosan subterranean termite Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), a highly active wood decomposer. Immunoblot analysis of DRIP‐type AQP using an antibody from the silkworm Bombyx mori reveals that the Coptotermes DRIP (formerly cloned as ‘CfAQP1’) with a molecular mass of approximately 25.7 kDa is expressed predominantly in the salivary (labial) gland of the workers. The Coptotermes DRIP is present at the basal plasma membrane of the parietal cells, as demonstrated by immunocytochemistry. By contrast, there is no DRIP detected within the salivary glands of soldier termites, and neither caste expresses DRIP in their labial gland reservoir (water sac), a tissue that is suggested to have a function as a water sink. The AQP present in the salivary glands is of physiological importance with respect to salivation, aiding in the secretion of cellulolytic enzymes for wood ingestion by the workers of the subterranean termite.     

Effects of virulence,sporulation, and temperature on Metarhizium anisopliae and Beauveria bassiana laboratory transmission in Coptotermes formosanus

Sporulation characteristics and virulence of Metarhizium anisopliae and Beauveria bassiana were examined in relation to laboratory transmission in Coptotermes formosanus. Fungal isolates significantly affected disease prevalence in termite populations. Sporulation of M. anisopliae played a more important role than virulence in producing epizootics within small groups of termites, but this was not the case for B. bassiana. Isolates characterized by quick sporulation (day 2 after death) did not exhibit better transmission in termites than those with high total sporulation (day 11 after death) in either fungal species. An isolate of M. anisopliae ranking highly in all three categories (virulence, quick sporulation, and total sporulation) produced better epizootics than an isolate that was inferior in all three characteristics. High temperatures (35 degrees C) significantly reduced fungal germination rates, leading to significant reduction of epizootics. M. anisopliae was better than B. bassiana in producing epizootics at 27 degrees C. Thus, fungal characteristics other than virulence should be considered for the seasonal colonization approach to termite microbial control.     

Formosan subterranean termite swarming behavior and alate sex-ratio (Isoptera: Rhinotermitidae)

Summary The Formosan subterranean termite (Coptotermes formosanus Shiraki) was first sighted in the cities of New Orleans and Lake Charles, Louisiana, in 1966. Its distribution in the historic French Quarter of New Orleans 23 years later (1989) and in 1991 and 1992 is reported here using counts of alates from light-traps. Light-trappings revealed a Quarter-wide distribution of the termite.C. formosanus shows an extended pause in flight behavior in the middle of the two-month flight season that is predictable and independent of weather. A colony-level mechanism, namely, developmental inhibition of nymphs by alates, may regulate this intermission in flight. The sex-ratio of light-trapped alates varies over time, but is generally female-biased, especially at the height of the flight season.     

Bioassay design and length of time in the laboratory affect intercolonial interactions of the Formosan subterranean termite (Isoptera, Rhinotermitidae)

This study examined the effect of diet, experimental design, and length of time in the laboratory on intercolonial agonism among Formosan subterranean termite, Coptotermes formosanus Shiraki, colonies. In pairings of 12 C. formosanus Shiraki colonies collected in an urban forest, there was no significant reduction in survival of termites in 30 out of 59 colony pairs compared to colony controls, but there was <50% survival in 18 colony pairs and <10% survival in six colony pairs. There was no correlation between the level of aggressive behavior and the laboratory diet of the termites. Effect of bioassay design and length of time in the laboratory was evaluated in three colony pairs where tests were first conducted on the day of field collection, then colony pairs were retested every 7 days. Aggressive behavior decreased over time in both bioassays, but it tended to decrease more rapidly in the Petri dish tests. The rapid loss of agonism in groups of termites kept in the laboratory demonstrates that changes in environmental factors affect intercolonial agonism. This article presents the results of research only. Mention of a commercial or proprietary product does not constitute endorsement or recommendation by the USDA.     

Effect of natural products on gut microbes in Formosan subterranean termite,Coptotermes formosanus

The ability of three natural products (neem extract, capsaicin, and gleditschia) to reduce the number of Formosan subterranean termite (FST) hindgut microbes was investigated. FSTs were placed in Petri dishes containing a food source soaked in one of these extracts/compounds. The numbers of three flagellated protozoan species that inhabit the FST hindgut (Pseudotrichonympha grassii, Spirotrichonympha leidyi and Holomastigotoides hartmanni) and spirochaetes were counted over a defined period and analysed for changes in abundance. The results indicated that the neem extract was capable of reducing the population of P. grassii and spirochaetes. Exposure to this extract resulted in significant FST mortality. However, gleditschia extract and capsaicin did not reduce the FST gut microbial population at the concentrations used in this study.