Comparison of Temperature-Dependent Survivorship and Wood-Consumption Rate Among Two Invasive Subterranean Termite Species (Blattodea: Rhinotermitidae: Coptotermes) and Their Hybrids

Hybrids of two destructive subterranean termites established in the field, revealing a potential for gene flow between species

Hybridization between invasive pest species may lead to significant genetic and economic impacts that require close monitoring. The two most invasive and destructive termite species worldwide, Coptotermes formosanus Shiraki and Coptotermes gestroi (Wasmann), have the potential for hybridization in the field. A three-year field survey conducted during the dispersal flight season of Coptotermes in Taiwan identified alates with atypical morphology, which were confirmed as hybrids of the two Coptotermes species using microsatellite and mitochondrial analyses. Out of 27,601 alates collected over three years, 4.4% were confirmed as hybrid alates, and some advanced hybrids (>F1 generations) were identified. The hybrid alates had a dispersal flight season that overlapped with the two parental species 13 out of 15 times. Most of the hybrid alates were females, implying that mating opportunities beyond F1 may primarily be possible through female hybrids. However, the incipient colony growth results from all potential mating combinations suggest that only backcross colonies with hybrid males could sometimes lead to brood development. The observed asymmetrical viability and fertility of hybrid alates may critically reduce the probability of advanced-hybrid colonies being established in the field.

Genomics reveals widespread hybridization across insects with ramifications for species boundaries and invasive species

As the amount of genomic data for non-model taxa grows, it is increasingly clear that gene flow across species barriers in insects is much more common than previously thought. In recent years, the decreased cost and increased accuracy of long-read sequencing has enabled the assembly of high-quality, reference genomes and chromosome maps for non-model insects. With this long-read data we can now not only compare variation across the genome among homologous genes between species, which has been the basis of phylogenetics for more than thirty years, but also tease apart evidence of ancient and recent hybridization and gene flow. The implications of hybridization for species adaptation may be more positive than previously considered, explaining its prevalence across many groups of insects. Unfortunately, due to anthropogenic actions, some pest species appear to be benefitting from hybridization and gene flow, facilitating future invasions.

Equivalent Colony Growth of Hybrids of Two Invasive Coptotermes Species Can Threaten Urban Areas

Coptotermes formosanus Shiraki and C. gestroi (Wasmann) are economically important structural pests in urban areas. Due to anthropogenic activity, both species have been introduced into the United States, with their respective invasive ranges now overlapping in Florida, and the two species have the capability to hybridize. The potential for structural damage from subterranean termite colonies primarily depends on colony size. However, long-term colony growth and wood consumption capabilities of hybrid Coptotermes colonies remain to be investigated, to determine the potential pest status of field-established hybrid colonies. In this study, we investigated long-term colony development over four years to determine if aging hybrid colonies display vigor in terms of colony growth. In addition, we compared wood consumption rate of hybrid colonies to compare their potential impact as structural pests with the two parental species. In aging colonies (four-year-old), both hybrid mating types displayed a colony growth equivalent to C. formosanus. However, the wood consumption rates of four-year-old colonies of the two parental Coptotermes species and their hybrids were similar, indicating equal damaging potential. We also found multiple secondary reproductives in hybrid colonies, even in the presence of primary reproductives, which may favor their potential establishment and spread. Although hybrid colonies or hybrid alates have yet to be detected in the field, our results suggest that such hybrid colonies would be an additional termite threat in the future if they were established in the field.

A comprehensive review on the documented characteristics of four Reticulitermes termites (Rhinotermitidae, Blattodea) of China

Termites are known as social insects worldwide. Presently in China 473 species, 44 genera and 4 families of termites have been reported. Of them, 111 Reticulitermes species are widely spread in different zones of China. The dispersion flight season of these Chinese Reticulitermes species are usually started from February to June, but in some regions different species are distributed, sharing their boundaries and having overlapping flight seasons. These reasons become important sources of hybridization between two different heterospecific populations of termites. It was confirmed that the fertilized eggs and unfertilized eggs of some Reticulitermes termites have the capacity of cleavage. While the unfertilized eggs of R. aculabialis, R. chinensis and R. labralis cleaved normally and the only R. aculabialis unfertilized eggs develop in embryos. While, the R. flaviceps and R. chinensis were observed with their abnormal embryonic development, and not hatching of eggs parthenogenetically. They were reported more threatening to Chinese resources as they propagate with parthenogenesis, hybridization and sexual reproduction. Eggshell and macrophiles of eggs play important roles in species identification and control. Although, they are severe pests and cause a wide range of damages to wooden structures and products in homes, buildings, building materials, trees, crops, and forests in China's Mainland.

Analysis of Factors Affecting Termite Damage to Wooden Architectural Heritage Buildings in Korea

Many wooden architectural heritage buildings exist in Korea, and the authenticity and structural stability of these cultural assets are being affected by termites. This study aimed to identify the degree of termite damage and related factors in these buildings. The degree of termite damage to 182 nationally designated wooden architectural heritage buildings (national treasures and treasures) in Korea was quantified, and data were collected for 11 factors affecting termite damage, such as the surrounding environment and architectural features. Based on the results of a general linear model analysis, the following three factors were identified to have a significant effect on termite damage: the type of contact between the ground and wooden structural items, the number of days of termite activity, and the proportion of forests in the land surrounding the property. This study is the first attempt to statistically analyze factors affecting termite damage to wooden heritage buildings, and our results provide initial data for the preservation and management of these properties.

Hybridization and invasiveness in social insects - The good, the bad and the hybrid

Hybridization may help drive biological invasions by reducing Allee effects, increasing genetic variation, and generating novel adaptive genotypes/phenotypes. Social insects (ants, bees, wasps, and termites) are among the world's worst invasive species. In this review, we study the relationship between hybridization and invasiveness in social insects. We examine three types of hybridization based on the reproductive characteristics of first-generation hybrids. We discuss several examples of the association between hybridization and invasiveness, which are predominantly found in bees and termites. However, hybridization also occurs in several non-invasive species, and highly invasive species are not consistently associated with hybridization events, indicating that hybridization is not a main driver of invasiveness in social insects. We discuss why hybridization is not more commonly seen in invasive social insects.

Subterranean Termite (Coptotermes gestroi (Blattodea: Rhinotermitidae)) Colony Elimination Through Exposure to a Novaluron CSI Bait Formulation in Laboratory

The development of baits for subterranean termite control over the past 25 yr has provided cost-effective alternatives to liquid termiticide treatments. Current bait products use one of the few available benzoylurea chitin synthesis inhibitors (CSIs) labeled for subterranean termites. These insecticides are used because of their nonrepellency, their slow-acting mode of action, and their dose-independent lethal time. Although many studies have provided ample evidence of the efficacy of CSI baits for subterranean termite colony elimination, most have focused on hexaflumuron and noviflumuron. However, bait products using alternative CSIs have not received the same level of scrutiny, limiting the amount of evidence proving their efficacy. One such compound is novaluron, the active ingredient currently used in the Trelona ATBS-Advance Termite Baiting System bait product. The current study independently tested the efficacy of this commercially available bait formulation against whole colonies of Coptotermes gestroi (Wamann) (~63,910 workers) in the laboratory, using an extended experimental setup to simulate a 15-m foraging distance from the central part of the nest to the bait, while having access to alternative food sources. Treated colonies progressively ceased to feed on wood items within 45 d after being provided access to the novaluron bait formulation, with a subsequent progressive collapse of the population, leading to colony elimination by 91 d. This study therefore confirms the efficacy of novaluron baits against subterranean termites, and currently remains one of the few CSIs that can be applied for the successful control of Coptotermes infestations.

Altered Mobility and Accumulation of Inefficient Workers in Juvenile Hybrid Termite Colonies

Hybridization of two different species is an important mechanism to have gene flows between species. Recently, mating of two economically important invasive species of subterranean termites (Coptotermes formosanusandCoptotermes gestroi) have been observed in the field and hybrids colonies have been established in the laboratory. It was previously reported that incipient colonies (~1 year old) of hybridCoptotermesspecies contained more termites than colonies of parental species, showing hybrid vigor. In this study, colony vigor and individual termite vigor were investigated in juvenile colonies (~2 year old), using colony growth parameters and the movement activity of individual termites as proxies for the evaluation of hybrid vigor beyond the initial colony foundation. After 2 years from colony foundations, hybrid colonies showed no more hybrid vigor. In addition, movement activity of termites in hybrid colonies was significantly slower than in termites from conspecific colonies. It is suggested that a reduction in the molting rates of individuals in hybrid colonies may have a negative impact on their physiology and their movement activity. These possible changes in physiology may affect the movement of individuals, and accumulation of these inefficient termites in hybrid colonies may contribute to the loss of hybrid vigor at 2 years of age in hybrid colonies.

Exposed Neophasia terlooii (Lepidoptera: Pieridae) Eggs are Resistant to Desiccation During Quiescence

Terrestrial insects face the risk of desiccation owing to their small size and high surface area to volume ratios. Insect eggs adhered to exposed substrates are especially prone to extremes in temperature and available moisture. The potential of butterfly egg clusters to withstand desiccation in saturated and unsaturated atmospheres was investigated in this study. Butterflies in the genus Neophasia (Lepidoptera: Pieridae) lay their eggs along live pine needles and they must survive long intervals without available liquid water while overwintering. After 2 d in a desiccating environment, groups of Neophasia terlooii Behr eggs were exposed to several different humidified chambers for 8 d at 5°C. Group masses were monitored over time and the change in mass was compared to the pre-desiccation mass. Changes in mass were minimal, ranging from a 3% increase in the saturated chamber (100% RH) to a 2% decrease in the driest chamber (<10% RH). Ambient humidity was recorded from among the pine needles of a live tree branch in the natural habitat for 2 wk at the start of the overwintering period. Daytime relative humidity among the pine needles dropped as low as 14.5% but rose as high as 92% at night. In the absence of precipitation, N. terlooii eggs can remain within 2% of their starting weight for 10 d at a constant RH of <10% at 5°C. The mechanism for avoiding desiccation and the physical properties of the egg coating are discussed in the context of life in an arid environment.

The Complete Protist Symbiont Communities of Coptotermes formosanus and Coptotermes gestroi: Morphological and Molecular Characterization of Five New Species

Coptotermes formosanus Shiraki and Coptotermes gestroi (Wasmann) (Blattoidea: Rhinotermitidae) are invasive subterranean termite pest species with a major global economic impact. However, the descriptions of the mutualistic protist communities harbored in their respective hindguts remain fragmentary. The C. formosanus hindgut has long been considered to harbor three protist species, Pseudotrichonympha grassii (Trichonymphida), Holomastigotoides hartmanni, and Cononympha (Spirotrichonympha) leidyi (Spirotrichonymphida), but molecular data have suggested that the diversity may be higher. Meanwhile, the C. gestroi community remains undescribed except for Pseudotrichonympha leei. To complete the characterization of these communities, hindguts of workers from both termite species were investigated using single-cell PCR, microscopy, cell counts, and 18S rRNA amplicon sequencing. The two hosts were found to harbor intriguingly parallel protist communities, each consisting of one Pseudotrichonympha species, two Holomastigotoides species, and two Cononympha species. All protist species were unique to their respective hosts, which last shared a common ancestor ~18 MYA. The relative abundances of protist species in each hindgut differed remarkably between cell count data and 18S rRNA profiles, calling for caution in interpreting species abundances from amplicon data. This study will enable future research in C. formosanus and C. gestroi hybrids, which provide a unique opportunity to study protist community inheritance, compatibility, and potential contribution to hybrid vigor.

Courtship Behavior Confusion in Two Subterranean Termite Species that Evolved in Allopatry (Blattodea, Rhinotermitidae, Coptotermes)

Congeneric species that live in sympatry may have evolved various mechanisms that maintain reproductive isolation among species. However, with the spread of invasive organisms owing to increased global human activity, some species that evolved in allopatry can now be found outside their native range and may have the opportunity to interact, in the absence of mechanisms for reproductive isolation. In South Florida, where the Asian subterranean termite, Coptotermes gestroi (Wamann), and the Formosan subterranean termite, Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae) are invasive, the two species can engage in heterospecific mating behavior as their distribution range and their dispersal flight season both overlap. Termites rely on semiochemicals for many of their activities, including finding a mate after a dispersal flight. In this study, we showed that females of both species produce (3Z,6Z,8E)-dodeca-3,6,8-trien-1-ol (DTE) from their tergal glands as a shared sex pheromone. We suggest that both species primarily rely on an inundative dispersal flight strategy to find a mate, and that DTE is used as a short distance pheromone or contact pheromone to initiate and maintain the tandem between males and females. The preference of C. gestroi males for C. formosanus females during tandem resulted from the relatively high amount of DTE produced by tergal glands of C. formosanus females, when compared with those of C. gestroi females. This results in confusion of mating in the field during simultaneous dispersal flights, with a potential for hybridization. Such observations imply that no prezygotic barriers emerged while the two species evolved in allopatry for ~18 Ma.

Inferring Termite Colony Size Using Wood Consumption in Subterranean Termites (Blattodea: Rhinotermitidae) in Laboratory-Rearing Conditions

Termite colony size can influence its foraging activity, reproductive maturity, and, for pest species, potential for structural damage. Estimating colony size of subterranean termite species in field conditions has been challenging owing to their extensive foraging territory and their cryptic nesting habit and has primarily relied on mark-recapture methods. With laboratory-reared colonies in individual containers, determining colony size can be achieved by processing all termites from the nest material, which can be labor intensive and partially destructive. However, with the recent rise in the need of large laboratory colonies for use in colony-wide experimental protocols, there was an imperative to develop a procedure to estimate initial colony sizes without imposing a major stress on colonies before an experiment. In this study, the average daily wood consumption of whole colonies was used to infer the colony size of two Coptotermes, Wasmann (Blattodea: Rhinotermitidae) species and their hybrids in laboratory-rearing conditions. Correlations between the daily wood consumption and several demographic variables within colonies were established. Linear models varied across all species mating types with R2 values greater than 0.8 for all demographic variables. For colonies from all mating combinations, Pearson's correlation coefficient values were greater than 0.94 between their daily wood consumption and both the number of workers and total number of termites, and greater than 0.91 between daily wood consumption and colony mass. Therefore, in colonies with fixed laboratory conditions, their average daily wood consumption determination, which is nondestructive on colonies, can be used to infer colony size of subterranean termites.

Temperature Preference of Two Invasive Subterranean Termite Species and Their Hybrids (Blattodea: Rhinotermitidae: Coptotermes)

Temperature preference of two invasive subterranean termites, Coptotermes gestroi (Wasmann) and Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), and their hybrids were determined in a horizontal thermal gradient. The activity of workers of four mating combinations: ♀C. gestroi × ♂C. gestroi (C. gestroi), ♀C. formosanus × ♂C. formosanus (C. formosanus), ♀C. gestroi × ♂C. formosanus (Hybrid G), and ♀C. formosanus × ♂C. gestroi (Hybrid F), when placed on the temperature gradients were videotaped and analyzed to determine the mean temperature preference values (mTPV). The temperature ranges for active termites were 21.9-39.5°C for C. gestroi, 11.1-39.5°C for C. formosanus, 25.3-38.2°C for Hybrid G, and 24.9-39.3°C for Hybrid F. There was no significant difference in the mTPV of C. gestroi and both hybrid mating combinations. The mTPV of both Hybrid G and Hybrid F was significantly higher than the parental species C. formosanus. Our results indicate that hybrid populations of C. formosanus and C. gestroi might be more active in tropical than temperate regions, and if established in temperate regions, they will be more active in summer months when the mean temperature exceeds 25°C.

A Reproductives Excluder for Subterranean Termites in Laboratory Experiments

As a social insect, termites have different castes and division of labor in a colony. Investigating the social behavior of subterranean termites is a challenge due to the cryptic nature and large colony size. Planar arenas are commonly used to study these termites under laboratory conditions, and have provided several advantages. However, there is no means to designate areas such as a royal chamber or central nest from foraging sites because reproductives can move freely across arenas. In this study, we examined the minimum passing size of different castes of Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae), in order to develop a reproductive excluder and correlated minimum passing size with head widths and heights. We found that workers and soldiers of C. formosanus were able to pass through a gap greater than or equal to 0.7 mm. Our results showed that there are significant differences in the head width and height based on castes and head height was more critical than head width to determine passing size. We further confirmed feasibilities of the reproductive excluders using incipient colonies of C. formosanus. Confining reproductives using the excluder in laboratory experiments will provide more chances to study the royal chamber and central nest independently of foraging sites.