Behavioral variation among tunnelers in the Formosan subterranean termite

Division of labor is a common feature of insect societies and has been theorized to account for much of their success. Asymmetries in the work of individuals, whose aggregate labor results in the completion of a task, can lead to the emergence of key individuals that dominate or govern the task. Coptotermes formosanus Shiraki excavate in a series of alternating workers whose efforts combine not only to elongate tunnels, but also to guide the direction of propagation. When groups of 100 termites were presented with a single tunnel, only ～ 16% of termites entered. Of those that entered, the level of excavation was not uniform, with 20.6% of termites responsible for over half of the total excavation. These termites, a small percentage of the total available workforce, act as key individuals, producing the majority of labor and possibly guiding the efforts of others. An examination of the excavation patterns of individuals shows that some individuals excavate sporadically, but at a very high rate (number of excavation events per time). By focusing their effort over a short period, these highly active individuals may influence the orientation of a tunnel and the formation of branches to a degree out of proportion to the total amount of digging they engage in.     

Molting in workers of the Formosan subterranean termite Coptotermes formosanus

The Formosan subterranean termite, Coptotermes formosanus, with its huge colonies, is a major urban pest in several southern states and Hawaii as well as in South Asia. Because of their cryptic nature (underground habitat) and very long life cycle, not much is known about molting in termite workers. In C. formosanus, the workers stop foraging and lose their gut fauna, respectively, approximately 10 and 5 days prior to ecdysis. In any given colony an average of 1.01% (range 0.6-1.8) of the workers were found to molt each day under laboratory conditions. Workers destined to molt become sluggish and their head capsules develop a mottled texture one day prior to ecdysis. Ecdysis was generally accomplished with the assistance of other workers, which also fed on the exuviae. Immediately after molting worker mandibles were light pink in color and became fully melanized approximately two days later. Gut fauna were acquired on the fourth day after molting. Flagellates were transferred as small encysted cells from other workers through proctodeal feeding. Juvenile hormone III titer ranged between 30-41 pg/mg bodyweight in all stages except in workers sampled 6 days prior to ecdysis. In these workers the titer was 80.5 pg/mg. The high juvenile hormones (JH) titer may also be involved in causing defaunation. Ecdysteroid titer increased from 2.1 pg/mg in non-molting workers to 359.5 and 332.4 pg/mg one and two days following defaunation, respectively. There was a second smaller peak two days prior to ecdysis.     

Colony breeding system influences cuticular bacterial load of Formosan subterranean termite (Isoptera: Rhinotermitidae) workers

The goal of this study was to test whether the breeding system and/or the degree of inbreeding of field colonies of the Formosan subterranean termite, Coptotermes formosanus, Shiraki (Isoptera: Rhinotermitidae) influences bacterial load on the cuticle of foraging workers. We enumerated bacterial load on the cuticle of groups of workers foraging in 20 inground monitoring stations surrounding the French Market in New Orleans, LA, and identified bacteria species using 16S rRNA gene sequencing. We used microsatellite genotyping to assign the 20 worker groups to seven simple family colonies (headed by a single pair of reproductives) and four extended family colonies (headed by multiple inbreeding reproductives) with a wide range of degrees of inbreeding. Workers from extended family colonies had a higher bacterial load than those from simple family colonies; however, bacterial load was not significantly correlated to the degree of inbreeding, possibly because of confounding factors in colony life history, such as age and/or size of colonies. Colonies with high bacterial load did not have a higher proportion of entomopathogens, and thus, bacterial load is not necessarily an indicator for disease risk. The majority of bacteria cultured from the cuticle of termites were soil bacteria with no known pathology against termites.     

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.     

Distribution of Formosan subterranean termite (Isoptera: Rhinotermitidae) in Mississippi

An extensive monitoring and survey program in Mississippi was conducted from 2000 to 2004 to investigate the distribution of the Formosan subterranean termite, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae). Seventy-two towns from 22 counties in southern Mississippi were monitored with a total of 3914 traps that catch alates during the swarming season. In addition, 259 licensed pest management professionals in Mississippi were surveyed to determine the locations of termite infestations treated. The alates of C. formosanus were recovered in 12 counties with light traps, and termite infestations were documented in an additional 13 from data collected in the termite survey. Infestations of C. formosanus have been documented in urban, urban cluster, rural, and forested areas of Mississippi. However, the distribution in mean total capture of alates for 4 yr differed significantly among the four ecological areas with the highest percentage in forested areas (31%) and the lowest percentage in urban cluster areas (17%). Most of the infestations of C. formosanus were geographically distributed along the coastal areas of southern Mississippi from Gulfport to Pascagoula. The greatest total number of alates captured in light traps was documented in Pearl River County. Mass swarming of C. formosanus occurred primarily in May or June, depending on weather conditions. The number of documented counties with the evidence of large and widely dispersed swarms of C. formosanus in different ecological areas, and the increase in total annual alate captures from 2000 to 2003, suggest that this invasive termite species is now firmly established in Mississippi.     

Territory size distribution of Formosan subterranean termites in urban landscape: Comparison between experimental and simulated results

The territory size distribution of Formosan subterranean termites in an urban landscape was studied by using a two-dimensional lattice model with minimized local rules on the basis of empirical data to determine the development of a territory. An urban landscape including components such as complex man-made structures, trees, and lakes was constructed on a lattice space. Each component was described by assigning values ranging from 0.0 to 1.0. These values were interpreted as transition probabilities, P_trans, which represented the spatially distributed properties of the components. The higher the P_trans values, better were the environmental conditions for territory growth. We applied this model to the termite colonies in Louis Armstrong Park in New Orleans, LA. A comparison of the model prediction and the observed territory size distribution showed very similar trends in maximum territory on a size-normalized scale. The trends emerged from two effects: first, when a founding pair was surrounded by lattice cells with low P_trans values, its growth was strongly inhibited, and second, when territories competed with each other at shared boundaries, their growth was restrained. In addition, we investigated the effect of the presence/absence of landscape components on the territory size distribution in the simulation.     

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.     

五种染色剂对台湾乳白蚁的染色效果

对于白蚁种群动态的研究可以利用多种不同颜色的染料作为标记物.为了寻找适用于台湾乳白蚁Coptotermes formosanus的标记物及其使用浓度,本文选取中性红、苏丹红Ⅳ、结晶紫、孔雀石绿以及天青Ⅱ五种染色剂作为标记物,分析测定了它们对台湾乳白蚁的染色效果.结果表明,浓度为0.2%中性红适用于估计种群数量;浓度分别为0.1%、0.2%和0.5%中性红,0.5%苏丹红,0.2%结晶紫,0.5%孔雀石绿以及0.1%天青Ⅱ均适合作为监测群体活动范围的标记物.     

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.     

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.     

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.     

Presence of nitrogen fixing Klebsiella pneumoniae in the gut of the Formosan subterranean termite (Coptotermes formosanus)

A gram-negative facultative anaerobic enteric bacterium, Klebsiella pneumoniae was isolated from the hindgut of the Formosan subterranean termite (FST). It was characterized using, fatty acid methyl ester (FAME) analysis, BIOLOG assay, sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and biochemical studies. The role of this isolate seems to be nitrogen fixation because the termite's diet is nitrogen deficient and the isolate produced significant amounts of ammonia when it was grown on nitrogen deficient medium under anaerobic condition with nitrogen gas in the headspace.     

Genetic diversity and genotypic differentiation between the sexes in swarm aggregations decrease inbreeding in the Formosan subterranean termite

The life of a colony of subterranean termites, such as Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae), has natural inbreeding and outbreeding cycles. Reproductives of mature colonies can be replaced by their offspring, which increases the degree of inbreeding in each generation. High degrees of inbreeding may lead to inbreeding depression. In this study we focused on mechanisms for inbreeding avoidance during swarming that do not require kin recognition. We investigated genetic differentiation between swarm aggregations (isolation by distance), genetic diversity within swarm aggregations (multiple colony origin) and genetic differentiation between sexes. Alates were collected from five swarm aggregations in New Orleans, La. The genetic make-up of each swarm aggregation was then described by microsatellite genotyping. Alates from the different swarm aggregations were genetically differentiated; however, no isolation by distance up to at least 1000 m was detected. The dispersal distance of alates was sufficient to guarantee mixing of an average of 13 colonies within swarm aggregations. On average, eleven percent of all possible pairs of alates in each swarm aggregation were putative full siblings. Genotypic frequencies differed significantly between males and females. This could not be explained by sex-biased dispersal. We hypothesize sex-biased investment at the colony level to account for this difference. Genetic differentiation between the sexes and dispersal distances sufficient to promote high genetic diversity within swarm aggregations each facilitate inbreeding avoidance. These observations are consistent with the results of previous studies demonstrating that the majority of simple family colonies in Louisiana populations are headed by unrelated and outbred pairs of reproductives. Received 11 August 2005; revised 5 December 2005; accepted 20 December 2005.     

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.     

Evaluation of treatment success and patterns of reinfestation of the Formosan subterranean termite (Isoptera: Rhinotermitidae)

Spread of the Formosan subterranean termite, Coptotermes fornwsanus Shiraki (Isoptera: Rhinotermitidae), is connected with the transport of infested wood, in particular, railroad ties. Therefore, efficient treatment of infestations, especially along railroads, is imperative to prevent further termite damage and spread. Evaluation of treatment success hinges on the ability to assign infestation sites to colonies and compare colony identity before and after treatment. Because colonies of the Formosan subterranean termite can be headed by a pair of reproductives (simple families) or by multiple reproductives (extended families), the question arises whether the breeding system of a colony influences treatment success and whether treatment of an area might have an impact on the breeding system. We used microsatellite genotyping to compare colony affiliation and breeding systems of Formosan termites infesting the Riverfront Railroad, New Orleans, LA, before and after treatment with 0.5% noviflumuron. Before treatment, four colonies were simple families, and 11 colonies were extended families. A year after treatment began, all treated colonies had vanished and did not reappear during this study. One colony from an untreated monitoring station moved into a nearby station after treatment. Colonies that were detected after treatment consisted of 12 simple families and six extended families; extended families found after treatment contained a higher number of reproductive neotenics than the extended families found before treatment. Extended families were more likely than simple families to move into inground stations that had been previously occupied by termite colonies.     

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.