A case for a free-running circannual rhythm in soldier developmental time of Formosan subterranean termites

The success of all insect societies relies on their ability to maintain optimal levels of different castes. Here we report on an apparent free-running circannual rhythm that optimizes the developmental time of the soldier caste of Coptotermes formosanus Shiraki. Over a 3 year period, bioassays were conducted each month (except June) with groups of 100 termite workers in a 28°C incubator in total darkness. The number of days needed for C. formosanus soldiers to develop varied depending on the time of the year (month). In March, just prior to the major swarming exodus for alates (April to June), 9 days were required before a worker molted to a presoldier. Longer times were required for such a molt in all other months, with an increasing trend from April to December (from 13 to 30 days) and a decreasing trend from January to February (from 25 to 12 days). Colony origin or the length of time that termites were kept in the laboratory under constant conditions (26 – 28°C, 70 – 80% RH) before testing (7 days – 1 year) did not affect this rhythm. This is the first demonstrated evidence of a free-running circannual rhythm in a social insect. Received 23 July 2007; revised 9 and 21 August 2007; accepted 23 August 2007.     

Effect of Average Worker Size on Tunneling Behavior of Formosan Subterranean Termite Colonies

The effect of a colony's average worker size on tunneling behavior of Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae) in laboratory foraging arenas was investigated. Large groups of foragers from four colonies were added to arenas and allowed to tunnel for a period of 22 days. Various aspects of the resulting tunnel galleries were analyzed using ANOVA and regression analysis. After the exclusion of one colony due to high mortality, the only parameters shown to differ significantly were tunnel width and tunnel segmentation. Larger workers tended to construct less segmented galleries with wider tunnels. Tunnel length was positively correlated to size on the first 2 days, but the relationship reversed by day 4. Tunneling on day 1 was positively correlated to the discovery of food items. Our results indicate that a foraging group's average worker size can affect tunnel pattern and that groups composed of larger workers are better tunnelers, but groups of smaller sized workers are able to make up the difference over time. Possible explanations for size-related variation in tunneling behavior are discussed.     

Premating Behavior of Dealates of the Formosan Subterranean Termite and Evidence for the Presence of a Contact Sex Pheromone

Swarming by alates of the Formosan subterranean termite, Coptotermes formosanus Shiraki, occurs around dusk during April–June in Louisiana and adjoining states. Dispersal is the primary purpose for swarming. We studied the premating behavior, following swarming. Loss of wings, especially in females, was essential for successful formation of tandem pairs between the two sexes. No calling was observed and apparently a long-range volatile sex pheromone, reported in some other species of termites, may not be involved in mate attraction in C. formosanus. Males moving randomly use their antennae to detect a female, and, together with maxillary and labial palps, contact is maintained with her while in tandem. Previously mated males paired with virgin females showed tandem behavior. The incidence was very low when both males and females were previously mated and then paired. Males with complete ablation of antennae did not form tandem pairs. Ablation of 10 terminal antennal segments or the labial palps caused a significant increase in the time to initiate tandem behavior. Electrophysiological recordings from gustatory sensilla on both antennae and maxillary palps revealed increased neural activity in response to female abdominal tip extracts compared to activity elicited by a solvent control. Analysis of extracts of male and female abdominal tips using high-performance liquid chromatography showed a peak unique to the female extract. We discuss the presence of a nonvolatile chemical in female C. formosanus and its involvement in the specific premating behavior.     

Termite resistance of solid wood and plywood treated with quaternary ammonia compounds and common fire retardants

The ability of termites to attack solid wood and plywood treated with quaternary ammonia compounds and common fire retardants was evaluated. The plywood and solid-wood specimens treated with either monoammonium phosphate (MAP), diammonium phosphate (DAP), ammonium sulfate (AS), didecyl dimethyl ammonium chloride (DDAC), or didecyl dimethyl ammonium tetrafluoroborate (DBF) were subjected to termite resistance tests using the subterranean termites Coptotermes formosanus Shiraki under laboratory conditions. The lowest mass losses and the highest termite mortalities were obtained for the solid-wood and plywood specimens treated with DDAC and DBF. Higher termite mortalities were seen in the plywood specimens treated with the fire retardants when compared to the solid-wood specimens. The MAP, DAP, and AS treatments lowered the mass losses in both solid-wood and plywood specimens in comparison with control specimens; however, DBF and DDAC protected specimens well against termite attack at both concentration levels tested.     

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.     

Wood excavations of three species of subterranean termites

We compared the feeding excavations on wood blocks of three species of subterranean termites, Coptotermes formosanus Shiraki, Reticulitermes flavipes (Kollar), and R. virginicus (Banks). Feeding rate followed the order C. formosanus > R. flavipes > R. virginicus. Wood surface area (mm²) exposed per unit feeding was higher for C. formosanus and R. flavipes than for R. virginicus. This was caused by the tendency of C. formosanus and R. flavipes to make internally penetrating tunnels, thereby increasing surface area, whereas R. virginicus made trough- and bowl-like depressions on the outside of blocks, sometimes decreasing the size of blocks outwardly without a corresponding high increase in surface area typical with the tunnels of the other species. Consequently, wood surface area was sometimes reduced, rather than increased as a result of feeding by R. virginicus. Different patterns of wood excavation suggest that these termites have divergent roles in wood decay processes.

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Résumé Les organismes pionniers qui modifient le bois et le rendent acceptable par les insectes qui le perforent sont généralement des champignons du bois pourri. Cependant, une fois que les termites ou autres insectes perforant le bois ont pénétré, leurs galeries favorisent les bactéries fixatrices d'azote, permettent l'invasion d'autres organismes décomposeurs, et de ce fait régularisent la décomposition du bois (Ausmus, 1977). L'exposition de la surface à l'intérieur des perforations jouant un rôle très important dans le processus de pourrissement, il est souhaitable de pouvoir quantifier la surface des galeries dues à l'alimentation des termites. Une courbe type permettant de prédire l'aire de la surface perforée a été construite en perçant 109 morceaux de bois de trous cylindriques de différents diamètres, en calculant l'aire de la surface des morceaux de bois, en appliquant et pesant une couche de vernis pour bois au polyuréthane, et en divisant la masse de polyuréthane par l'aire de la surface. Le modèle prédictif qui en découle est: Y=0,01443×-3,51825 (P=0,0001; r=0,68), y étant la masse de polyuréthane (en g) et x la surface (en mm²) du morceau de bois. En traitant de la même façon au polyuréthane les morceaux de bois perforés par les termites, nous pourrions déduire leur surface.Une expérience a été effectuée avec 3 espèces de rhinotermitides,- Coptotermes formosanus Shiraki, Reticulitermes flavipes (Kollar) et R. virginicus (Banks). Des groupes de chaque espèce se sont alimentés pendant 11 ou 12 jours sur des morceaux de bois non contaminés par des champignons. Nous avons déterminé la survie, la consommation, la modification de la surface du morceau de bois (par utilisation du modèle prédictif) et le changement de surface par terminte.La survie est la même, mais la consommation est dans l'ordre suivant: C. formosanus > R. flavipes > R. virginicus. L'aire de la surface exposée par unité d'alimentation était plus élevée pour C. formosanus et R. flavipes que pour R. virginicus (Tab. 1). Ceci est dû à la tendance de C. formosanus et R. flavipes de creuser des galeries vers l'intérieur, tandis que R. virginicus fait des cuvettes à la surface du bois. Les attaques superficielles de R. virginicus réduisent parfois le volume du morceau de bois sans accroître proportionnellement la surface comme le font les espèces creusant des galeries. Ainsi, avec R. virginicus la surface peut être réduite au lieu d'augmenter. Des différences entre colonies s'observent avec toutes les variables (Tab. 2).Nos résultats suggèrent que C. formosanus et R. flavipes contribuent plus que R. virginicus à exposer le bois aux autres organismes décomposeurs. Cependant, ces résultats peuvent être modifiés par un conditionnement préalable du bois par des champignons.

     

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.     

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.     

Behavioral Response of Two Subterranean Termites (Isoptera: Rhinotermitidae) to Vibrational Stimuli

Behavioral responses to vibrational stimuli were examined in two subterranean termite species, Coptotermes formosanus Shiraki and Reticulitermes flavipes (Kollar). Termites habituated to vibrational stimulation when in social groups, but failed to do so individually, indicating that habituation is a collective action. In assays on termite groups, both species demonstrated a similar pattern of behavioral responses to vibrational stimuli: evanescent cessation of activity and movement, followed by withdrawal from the vibration source. Groups of both species then gradually moved back toward the vibration source as a consequence of continuous exposure. However, it took a significantly shorter period for C. formosanus to return (57 s) to the test arena and to resume (80 s) normal foraging activities in the test arena compared with R. flavipes, which took 97 and 227 s, respectively, when exposed to the vibration frequency of 120 bmpm. High vibration frequency (240 bmpm) increased the time required to return (C. formosanus, 80 s; R. flavipes, 153 s) and to resume regular locomotion (C. formosanus, 186 s; R. flavipes, 263 s). Our experiments demonstrate that workers play a crucial part in adjusting groups of termites to distressful vibrations. Soldiers of R. flavipes demonstrated similar behavioral responses as workers, however, C. formosanus soldiers exhibited a transient positive response before withdrawal. An erratum to this article is available at .     

The termites of Early Eocene Cambay amber, with the earliest record of the Termitidae (Isoptera)

The fauna of termites (Isoptera) preserved in Early Eocene amber from the Cambay Basin (Gujarat, India) are described and figured. Three new genera and four new species are recognized, all of them Neoisoptera – Parastylotermes krishnai Engel & Grimaldi, sp. n. (Stylotermitidae); Prostylotermes kamboja Engel & Grimaldi, gen. et sp. n. (Stylotermitidae?); Zophotermes Engel, gen. n., with Zophotermes ashoki Engel & Singh, sp. n. (Rhinotermitidae: Prorhinotermitinae); and Nanotermes isaacae Engel & Grimaldi, gen. et sp. n. (Termitidae: Termitinae?). Together these species represent the earliest Tertiary records of the Neoisoptera and the oldest definitive record of Termitidae, a family that comprises >75% of the living species of Isoptera. Interestingly, the affinities of the Cambay amber termites are with largely Laurasian lineages, in this regard paralleling relationships seen between the fauna of bees and some flies. Diversity of Neoisoptera in Indian amber may reflect origin of the amber deposit in Dipterocarpaceae forests formed at or near the paleoequator.     

Gibberellin-induced formation of tension wood in angiosperm trees

After gibberellin had been applied to the vertical stems of four species of angiosperm trees for approximately 2 months, we observed eccentric radial growth that was due to the enhanced growth rings on the sides of stems to which gibberellin had been applied. Moreover, the application of gibberellin resulted in the formation of wood fibers in which the thickness of inner layers of cell walls was enhanced. These thickened inner layers of cell walls were unlignified or only slightly lignified. In addition, cellulose microfibrils on the innermost surface of these thickened inner layers of cell walls were oriented parallel or nearly parallel to the longitudinal axis of the fibers. Such thickened inner layers of cell walls had features similar to those of gelatinous layers in the wood fibers of tension wood, which are referred to as gelatinous fibers. Our anatomical and histochemical investigations indicate that the application of gibberellin can induce the formation of tension wood on vertical stems of angiosperm trees in the absence of gravitational stimulus.     

Influence of Guidelines and Passageways on Tunneling Behavior of Reticulitermes flavipes (Kollar) and R. virginicus (Banks) (Isoptera: Rhinotermitidae)

Tunneling behavior of laboratory-maintained cultures of Reticulitermes flavipes (Kollar) and R. virginicus (Banks) was examined to determine (1) if the termites build tunnels along preexisting wires or tunnels, and (2) whether tunnels are arranged to optimize search efficiency. Tunnel patterns were considered optimal if, for the number of tunnels present, the maximum area was explored. Termites entered either control arenas or arenas in which they encountered a wire or a pre-formed tunnel. Analyses revealed that R. flavipes and R. virginicus almost always follow pre-formed tunnels, but do not follow wires as readily. Within each species, the distributions of tunnels in treatment arenas were different from distributions in control arenas, most often when pre-formed tunnels were the treatment. Optimal tunnel arrangements in control arenas were found in 62% of R. flavipes patterns with 2 tunnels and in 43% of R. virginicus patterns with 2 tunnels. None of the 3-tunnel patterns from control arenas of R. flavipes and 29% of those of R. virginicus had optimal arrangements. Overall, the spatial arrangement of tunnels in control arenas was significantly different between R. flavipes and R. virginicus.     

Resistance of the termite, <Emphasis Type="Italic">Coptotermes formosanus</Emphasis> Shiraki to <Emphasis Type="Italic">Metarhizium anisopliae</Emphasis> due to grooming

Termites, Coptotermes formosanus, reared individually, were highly susceptible to the entomopathogenic fungus, Metarhizium anisopliae, while termites reared in␣groups were highly resistant. When reared in groups, the termites treated with M.␣anisopliae conidia on the body surface were groomed by their nestmates and more than 80% of the conidia were removed from the cuticle within 3 h. However, there was not a significant reduction in the numbers of conidia on the body surfaces of termites reared individually. For the termites maintained in groups, conidia were found in foreguts, midguts and hindguts, but very few conidia were detected in the guts of termites reared individually. Conidia in the alimentary tracts did not germinate, but some of were alive. As a result, it seems that the removal of foreign bodies, such as fungal conidia, from the␣cuticle is one function of termite mutual grooming behavior and that conidia removed from the cuticle are eliminated through alimentary tracts. This study indicates that mutual grooming behavior is very effective in protecting these termites from M.␣anisopliae infection.     

Interference competition in desert subterranean termites

We examined interspecific aggression between two subterranean termite species, Heterotermes aureus (Snyder) (Rhinotermitidae) and Gnathamitermes perplexus (Banks) (Termitidae). In laboratory tests with worker termites, neither species was the inherently superior fighter, but rather the outcome of interspecific encounters depended on the number of conspecifics. We then investigated patterns of resource use by these species during a 13-month period in the Sonoran Desert. Baits consisted of toilet-paper rolls, which have been shown to be a mutually acceptable food source. Analyses of foraging activity demonstrated that the two species did not forage independently of each other. Not only were the two species negatively associated spatially, but extended periods of temporal segregation were observed. G. perplexus took significantly longer to return to sites that it had simultaneously occupied with H. aureus than to sites that G. perplexus had occupied alone. The pattern of co-occurrence of these two species is consistent with the hypothesis that interspecific interference competition affects their spatial and temporal distribution.     

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.     

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.

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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.

     

Hoarding behaviors of two wood mouse species: Different preference for acorns of two Fagaceae species

Two species of wood mouse, Apodemus argenteus and A. speciosus, were observed consuming and hoarding acorns of Quercus serrata and Castanopsis cuspidata. When each species of acorn was supplied individually, both species of mice used each species of acorn for eating and hoarding. When both species of acorn were supplied, A. argenteus consumed or hoarded only C. cuspidata, whereas A. speciosus tended to eat C. cuspidata acorns at the feeding site, and disperse or hoard Q. serrata acorns. Apodemus speciosus is unlikely to disperse C. cuspidata acorns (their utilization was biased towards consumption) when Q. serrata acorns are also available. Apodemus argenteus will make almost no contribution to the dispersal of Q. serrata when the two acorn species coexist.     

The distribution,abundance, and the effects of fire on mound building termites (Trinervitermes and Cubitermes spp., Isoptera: Termitidae) in northern guinea savanna West Africa

Summary Termite mound densities in typical guinea savanna, Detarium, and grassland (boval) habitats in northern guinea savanna were determined by random quadratting of 2–3 sites in each habitat (100, 10x10 m quadrats per habitat). Dominant species in guinea savanna were T. geminatus (46 mounds ha^-1) and T. oeconomus (21 mounds ha^-1), in Detarium T. geminatus (59 mounds ha^-1) and C. curtatus (45 mounds ha^-1) and in boval C. curtatus (72 mounds ha^-1) and T. geminatus (22 mounds ha^-1). Only C. curtatus densities and total densities differed significantly between sites within habitats, but all species differed significantly in abundance between habitats. The composition of each community was related to general environment but no particular environmental variable was shown to be a major determinant of termite distribution. Evidence for the limitation of termite populations was obtained from indirect evidence of competition between colonies in Detarium, and by experimental manipulation of fire regimes in the typical guinea savanna habitat. Harvester termites increased four-five fold over two years in fire-protected plots as a result of increased food supplies. Total termite densities in the fire-protected community equilibrated to the new population density (100 mounds ha^-1) after only two-three years.