Invasive Termite Research Articles

Connectivity and climate change drive the global distribution of highly invasive termites

Termites are amongst the most abundant and ecologically-important groups of insects in tropical forests. However, the destructive potential of some species amounts to billions of dollars in damage each year. Despite their economic and ecological impacts, only a limited number of invasive termite species have been studied using distribution modelling and no studies have taken trade, transport and demography variables into account. We used Species Distribution Models (SDMs) to investigate the potential distribution of 10 highly-invasive termites. Our study includes bioclimatic conditions, land-use patterns, elevation and connectivity predictors (i.e. urban areas, human population, accessibility to cities and private vessels), alongside different climatic and socioeconomic change scenarios. The distribution of the termite species hinges on bioclimatic and connectivity variables, highlighting the significance of these latter factors in invasive species analyses. Our models demonstrate the potential of these invasive termites to thrive in large urbanised and connected areas within tropical and subtropical regions and to a lesser extent within temperate regions. As climate changes and urbanisation intensifies, most species’ range could expand, particularly under a “fossil fuel-driven development” scenario. Furthermore, while some species may have a slightly reduced range, they could extend their presence into more urbanised and connected areas, increasing the risks and costs associated with termite damages. Our models highlight the anticipated role of growing connectivity and climate change dynamics in facilitating the widespread proliferation of invasive termites in the coming years.

Comparative analysis of adipokinetic hormones and their receptors in Blattodea reveals novel patterns of gene evolution.

Adipokinetic hormone (AKH) is a neuropeptide produced in the insect corpora cardiaca that plays an essential role in mobilising carbohydrates and lipids from the fat body to the haemolymph. AKH acts by binding to a rhodopsin-like G protein-coupled receptor (GPCR), the adipokinetic hormone receptor (AKHR). In this study, we tackle AKH ligand and receptor gene evolution as well as the evolutionary origins of AKH gene paralogues from the order Blattodea (termites and cockroaches). Phylogenetic analyses of AKH precursor sequences point to an ancient AKH gene duplication event in the common ancestor of Blaberoidea, yielding a new group of putative decapeptides. In total, 16 different AKH peptides from 90 species were obtained. Two octapeptides and seven putatively novel decapeptides are predicted for the first time. AKH receptor sequences from 18 species, spanning solitary cockroaches and subsocial wood roaches as well as lower and higher termites, were subsequently acquired using classical molecular methods and in silico approaches employing transcriptomic data. Aligned AKHR open reading frames revealed 7 highly conserved transmembrane regions, a typical arrangement for GPCRs. Phylogenetic analyses based on AKHR sequences support accepted relationships among termite, subsocial (Cryptocercus spp.) and solitary cockroach lineages to a large extent, while putative post-translational modification sites do not greatly differ between solitary and subsocial roaches and social termites. Our study provides important information not only for AKH and AKHR functional research but also for further analyses interested in their development as potential candidates for biorational pest control agents against invasive termites and cockroaches.

First outdoor records in the Old World of the invasive drywood termite, Cryptotermes brevis (Walker, 1853) (Kalotermitidae)

AbstractCryptotermes brevis (Walker, 1853) (Kalotermitidae), commonly called the West Indian drywood termite, is an important structural pest in many parts of the world. Almost all records of C. brevis come from timber or furniture inside human structures. Although originally described for Jamaica, this species appears to be native to the coastal desert area of Peru and Chile, where it commonly occurs outdoors in the dead wood of both living and dead trees in riparian habitats and irrigated agricultural areas. Here, we report outdoor records of C. brevis from an agricultural habitat at the western edge of the Sahara Desert, an area climatically similar to their native range in South America. This constitutes the first outdoor report of the invasive termite in the Old World. In Dakhla, Moroccan Sahara, we found these termites living in the dead wood of a Brazilian peppertree (Schinus terebinthifolia Raddi) and the hollow stems of giant reeds (Arundo donax L.). In North Africa, C. brevis is otherwise known only from structural timbers in northern Egypt. Whether this termite become a significant pest in North Africa remains to be seen.

A loop-mediated isothermal amplification (LAMP) assay for the detection of Cryptotermes brevis West Indian drywood termite (Blattodea: Kalotermitidae)

Cryptotermes brevis is one of the most destructive invasive termites in the subtropics and tropics and is a common biosecurity intercept at the Australian border. Drywood termite species are cryptic and difficult to identify morphologically in situations when soldiers or imagos are unavailable. We developed a novel DNA based loop-mediated isothermal amplification (LAMP) assay to detect C. brevis and differentiate it from other drywood termites. Validated voucher specimens of 30 different drywood termite species were obtained from several insect collections from which DNA was extracted and amplified. The amplicons containing partial mitochondrial 16S rRNA were sequenced and a DNA database was created from which C. brevis LAMP primers were developed, optimized, and tested. The assay was assessed against a range of target and non-target species and found to be specific, successfully amplifying the target specimens of C. brevis in under 30 min. Amplification success was variable against C. brevis faecal pellets due to minute, unmeasurable or degraded DNA. This LAMP test is a new tool for the rapid detection of C. brevis that will enable faster and less destructive management of drywood termite infestations.

Potential Invasive Termites in India and Importance of Integrative Taxonomy

Termites are ubiquitously abundant in the tropics and subtropics. Globally 28 species are considered invasive among the 2937 species in nine families known. Among the invasive species, most are considered nuisance organisms to humans in urban areas, and a few have invaded natural forests. Generally, the invasive termites share three qualities: (i) they eat wood, (ii) make nests in wood, and (iii) they quickly generate secondary reproductives. These qualities are the most common in the Kalotermitidae and Rhinotermitidae (Blattodea: Isoptera), which enhance their opportunities for producing viable and reproductively capable individuals. Species of the Termitidae cannot produce secondary reproductives, and this is attributed as a reason for their lack of invasiveness. The 28 species recognized as strongly invasive have the potential to widen their geographical range from their present distribution locations. According to available data, 10 out of the 17 recognized invasive species have expanded their area of occurrence since 1969. Among the 28, three are known in India, although their exact distribution data in the Indian subcontinent, the damage they inflict, and consequent economic loss are yet to be worked out in detail. Climate change, intensifying urbanization, and globalization, acting either individually or in combination, are likely to exacerbate ecological and economic effects. Strict quarantine measures and appropriate treatment of every wood material imported are imperative. Efforts have been made to list the potential invasive termites in India based on imported-wood material. Approximately 70 species reported in the GenBank database for about 300 species known from India, emphasizing a dire need for accurate morphological and molecular determinations. Gene sequences of some of the Indian termite species submitted are incorrectly identified, as their presence and distribution in India is doubtful. Therefore, in this article, I discuss the importance of the combined and efficient use of morphological and molecular taxonomy in determining termites in India.

Ethyl Formate-Based Quarantine Treatment for Exotic Ants and Termites in Imported Rubber Plants and Stone Products

Exotic ants and termites, including Solenopsis invicta, are frequent hitchhikers intercepted from miscellaneous nonfood commodities. In particular, S. invicta has been intercepted in Korea in imported nursery plants, stone, and lumber products, which increases the potential for establishment of this destructive invasive pest in Korea. In this study, we conducted commercial-scale fumigation trials to evaluate ethyl formate (EF) as a potential alternative of methyl bromide using two species of imported rubber plants and pieces of marble as representative good and workers of Reticulitermes speratus as an EF-resistant surrogate for S. invicta. An EF treatment at 35 g/m3 for 4 h at >15 °C, the dose required for LCt99% (lethal concentration × time product required for 99% mortality of R. speratus), resulted in the complete control of R. speratus workers tested with rubber plants (Ficus benghalensis and F. retusa) and marble, 9% (w/v) and 60% (v/v) loading ratios, respectively. EF treatment did not adversely affect the leaf chlorophyll content, leaf color, and overall health of rubber plants or the visual appearance of the marble. Our results suggest that EF fumigation is a potential alternative to methyl bromide for the disinfestation of hitchhiking invasive termites and ants, including S. invicta, on imported rubber plants and stone products.

Thermal tolerance of an invasive drywood termite, Cryptotermes brevis (Blattodea: Kalotermitidae)

West Indian drywood termites (Cryptotermes brevis, Blattodea: Kalotermitidae) are an important invasive termite in many countries including Australia where they are spreading across two eastern states. Fumigation is often used to eliminate infestations, but it is costly, has negative environmental effects and does not prevent reinfestation. Heat treatment has been suggested as an alternative. Many insect pest mitigation strategies recommend 30 min exposure at 56 °C, but this may be difficult to achieve in structural applications. The potential for heating at lower temperatures was explored to determine the effect on termite survival and gut fauna. Exposure to 40 °C up to an hour did not kill the termites; however, 1-h exposure at 45 °C was lethal. Exposure for little as 3 min at 50 °C or 2 min at 55 °C was lethal. Protozoa levels were lower in termites that survived shorter exposures, but there appeared to be some recovery over time. The results suggest that short term exposures to 50 or 55 °C could be used to eliminate infestations, creating an opportunity for localized spot heating as a mitigation measure.

Predicting ecological impacts of invasive termites.

There are 28 invasive termite species, most belong to two families, the Kalotermitidae (esp. Cryptotermes spp.) and Rhinotermitidae (esp. Coptotermes spp.). Six invasive termite species are known to have spread into natural habitats, but little direct research has been conducted into their ecological impacts. Predictions based on indirect research (natural durability of commercial wood species) suggest fast-growing, pioneer tree species with low density wood, perhaps notably legumes, are most vulnerable to invasive termites, but even slow growing climax tree species may succumb. Cryptotermes will likely have less ecological impact, due to small colonies attacking dead branch stubs in the canopy. Coptotermes will likely have greater impact, due to large colony sizes and nesting in living trees, which they hollow out and can kill. There are no studies of invasive termites on native termites, other wood-eating insects, or predators, such as ants, showing considerable scope for future research.

Geography, opportunity and bridgeheads facilitate termite invasions to the United States

With the ever-increasing rate of globalization, port of entry data can be an important source of information for the introduction and spread of invasive species on a worldwide scale. Using a comprehensive dataset spanning records from 1923 to 2017, termite interceptions at US ports of entry were analyzed. We identified 906 non-native interceptions originating from outside the US, including four families, 32 genera and 75 different termite species. Non-native termites originated from 88 different countries and were intercepted in 29 different states. There was a strong regional bias, with termite-rich areas closest to the US—Central America, South America and the Caribbean—the greatest exporters of termite species to the US. Among the 75 non-native termites intercepted, 12 had already become established outside of their native range, with eight appearing to utilize bridgeheads to expand their global distribution. Additionally, the establishment probability of a species was positively influenced by the number of interceptions, as three of the most common non-native species intercepted at ports of entry are currently established within the US—Nasutitermes corniger, Cryptotermes brevis and Coptotermes formosanus. Our results reveal important insights into the global dispersal of invasive termites and contribute further evidence towards the importance of trade, increased propagule pressure and the bridgehead effect as drivers of global invasion rates.

Research on termites in urban areas: approaches and gaps

Termites comprise a large group of organisms in urban areas, and this leads us to believe that there is a comprehensive literature on the subject, sufficient for conducting a systematic review of the last years. Consequently, the aim of this study was a descriptive analysis of publications that addressed the issue of termites in urban areas between the years 1945 and 2018. For the systematic review, a literature search was initiated using the ISI Web of Science (WoS), SCOPUS (Elsevier) and SCIELO databases. In total, 180 relevant studies in the field concerning urban termites were published, out of which most (58.33%) investigated about the invasive termites, followed by studies that addressed the issue of control of pest termites (28.33%) and ecology and biodiversity (13.33%). The most studied species on the invasive termites’ category was Coptotermes formosanus, which was present in 22.78% of the publications. Studies on urban termites that highlighted the importance of the control of pest termites in urban areas began in 1983. Most of them were focussed on tests with chemical products. The most tested chemical probe in different termite species was hexaflumuron. Coptotermes formosanus was the most tested, followed by Reticulitermes flavipes. The publication of studies that focus on the ecology and biodiversity of urban termites began after 1958; they compared the diversity of termites in other locations within urban areas and is distributed in a small number of papers. Some gaps in studies that may serve as suggestions for future studies and, consequently, bring new contributions and advances in the scientific knowledge of urban termites were identified and discussed.

Genetic Analysis of Invasive Conehead Termites (Blattodea: Termitidae) Reveals a Single Origin for Two Populations in Florida.

In 2001, Nasutitermes corniger (Motschulsky), common name conehead termite, were discovered near a marina in Dania Beach, FL, where the invasive species was probably transported from its native range in Central and South America or the Caribbean. In January 2016, an infestation was found in Pompano Beach, Florida, approximately 21 km north of the Dania Beach population. This study compares variants in seven microsatellite loci across specimens from 11 nests in Dania Beach and 8 nests in Pompano Beach. Results are consistent with all N. corniger in both locations being descendants of a single introduced colony, spreading within Broward County, FL through human transport of infested materials. No more than four alleles were found at any of the seven microsatellite loci analyzed, inferring that a single Queen and King, or multiple sibling reproductives descended from a monogamous pair, headed the colony that arrived in Florida. The potential economic and environmental impacts of this invasive termite are enormous due to its broad diet, including agricultural crops and orchards, native and ornamental plants, natural landscapes, and structures. Conspicuous tunnels and aboveground nests are the key aspects of N. corniger biology that render colonies vulnerable to discovery and control. The now proven ability of N. corniger to establish breeding populations in the United States, to cause extensive property and landscape destruction, and to spread by human transport underscores the need for continued aggressive efforts toward eradication of known infestations as well as quick operational actions the next time invasive N. corniger are discovered.

Coptotermes gestroi(Wasmann) (Blattodea [Isoptera]: Rhinotermitidae), a Threat to the Southeastern Florida Urban Tree Canopy

In addition to being a structural pest, the Asian subterranean termite, Coptotermes gestroi (Wasmann) (Blattodea [Isoptera]: Rhinotermitidae), appears to be a serious pest of the native urban tree canopy of southeastern Florida. Asian subterranean termite colonies have the ability to cause feeding damage to a wide range of trees comprising the urban canopy, some potentially to a lethal level. Slash pine, Pinus elliottii Engelm. (Pinaceae), appears to be particularly susceptible to C. gestroi feeding damage, as the termites feed primarily on the outer layers of the wood, immediately beneath the bark, wounding live tissues and ultimately girdling the tree. In comparison, hardwood trees such as live oak, Quercus virginiana Mill. (Fagaceae), sustain damage to the heartwood at the center of the tree, resulting in a central cavity, but leaving the live tissue intact. Our results suggest that C. gestroi has the potential to kill pine trees within the local urban canopy, which may irreversibly alter the urban forest composition. In addition, many large trees in our survey have been consumed partially by mature C. gestroi colonies, potentially compromising their structural integrity. Some large oak trees that were extensively hollowed out by C. gestroi collapsed in 2017 during hurricane Irma. We discuss different potential approaches for protecting susceptible trees, as a comprehensive IPM strategy is needed for this invasive termite pest species, especially in the complex and extensive urban forest of southeastern Florida.

Potential spread of the invasive North American termite, Reticulitermes flavipes, and the impact of climate warming

Reticulitermes flavipes is an invasive termite from North America that is found in several European countries, including France from north to south. It feeds on several timber species and can cause major damage when it infests lumber. Termites are urban pests: they are often found in and around towns and their expansion is closely linked to human activity. Although, by law, termite infestations must be reported and treated, R. flavipes continues to spread. To better identify areas that may soon be colonized, it is crucial to understand the mechanisms underlying the termite’s spread at a fine spatial scale. However, the complexity of the species’ dispersal dynamics (i.e., via swarming, budding, or human-mediated transport of infested material) and social organization render this process difficult. The goal of our study was to determine R. flavipes’ potential to expand its current range within a region of France: Centre-Val de Loire. We focused on one administrative department within the region—Indre and Loire—where infestations are common and data on termite presence date back to the 1980s. We developed a spatiotemporal model to study the growth and dispersal of termite colonies within favorable habitat. Habitat favorability was defined based on the density of urbanization and annual mean minimum temperature. First, we modeled temporal population dynamics, using biological parameters describing the transitions between life stages/castes within colonies; we could thus estimate alates production. Then, using this information, we modeled termite dispersal within favorable habitat, and determined the termite’s potential spread. We validated the results by comparing the model’s output with actual data on the termite’s range expansion between 1985 (when the termite was first observed in the region) and 2013. Finally, the model was used to predict the termite’s future spread given climate warming for the period from 2013 to 2030. The results show that an increase in temperature should increase the amount of favorable habitat and, as a consequence, termites could continue to spread within this region. In addition to continuing current control efforts, it will be necessary to enact preventative strategies in newly favorable habitat. In these areas, monitoring efforts should therefore be intensified, as they might be able to slow down the termite’s spread and limit its impact.

Potential Hybridization between Two Invasive Termite Species, Coptotermes formosanus and C. gestroi (Isoptera: Rhinotermitidae), and Its Biological and Economic Implications.

The Asian subterranean termite, Coptotermes gestroi, is a tropical species but has increasingly been collected from the subtropics in recent years, making it sympatric to the Formosan subterranean termite, C. formosanus in at least three areas, Taiwan, Hawaii, and Florida. Simultaneous flights by these two species were observed since 2013 in South Florida, during which interspecies tandems were observed. Laboratory mating of C. formosanus and C. gestroi alates produced hybrid incipient colonies of larger population size. Studies are underway to examine the presence in the field of hybrid colonies in sympatric areas of Taiwan and Florida. Other biological characteristics of C. formosanus × C. gestroi hybrids being studied include temperature tolerance and preference, colony growth rate, wood-consumption rate, and reproductive fertility. This current research aims to determine the potential establishment of a hybrid termite population in south Florida and Taiwan. It investigates the risk of introgressive hybridization in field populations, with an emphasis on its potential ecological, evolutionary, and economic consequences.

Invasive termites in a changing climate: A global perspective.

Termites are ubiquitous insects in tropical, subtropical, and warm temperate regions and play an important role in ecosystems. Several termite species are also significant economic pests, mainly in urban areas where they attack human‐made structures, but also in natural forest habitats. Worldwide, approximately 28 termite species are considered invasive and have spread beyond their native ranges, often with significant economic consequences. We used predictive climate modeling to provide the first global risk assessment for 13 of the world's most invasive termites. We modeled the future distribution of 13 of the most serious invasive termite species, using two different Representative Concentration Pathways (RCPs), RCP 4.5 and RCP 8.5, and two projection years (2050 and 2070). Our results show that all but one termite species are expected to significantly increase in their global distribution, irrespective of the climatic scenario and year. The range shifts by species (shift vectors) revealed a complex pattern of distributional changes across latitudes rather than simple poleward expansion. Mapping of potential invasion hotspots in 2050 under the RCP 4.5 scenario revealed that the most suitable areas are located in the tropics. Substantial parts of all continents had suitable environmental conditions for more than four species simultaneously. Mapping of changes in the number of species revealed that areas that lose many species (e.g., parts of South America) are those that were previously very species‐rich, contrary to regions such as Europe that were overall not among the most important invasion hotspots, but that showed a great increase in the number of potential invaders. The substantial economic and ecological damage caused by invasive termites is likely to increase in response to climate change, increased urbanization, and accelerating economic globalization, acting singly or interactively.

Potential economic costs of invasive structural pests: conehead termites, Nasutitermes corniger, in Florida

Increased trade and human mobility result in sizable benefits to society, but are often accompanied by negative consequences, such as increased introduction of invasive pests to different landscapes and seascapes. In this paper, we couple an existing model of the biological spread of Nasutitermes corniger, an invasive neotropical termite recently introduced to Florida, with information on the costs to treat and repair affected structures, and use this coupled model to simulate the potential short-term costs of establishment of this structural pest. We construct empirical distributions of control and repair costs, using surveys of the pest control industry and homeowners, and use them to simulate treatment and damage costs through a re-sampling procedure. Our results suggest that the net present value of potential costs from an unchecked N. corniger invasion in Florida range between $6.9 and $9.9 million over the next 10 years.

Stochastic spread models: A comparison between an individual-based and a lattice-based model for assessing the expansion of invasive termites over a landscape

Spatially-explicit simulation models can help state and local regulatory agencies to predict both the rate and direction of the spread of an invasive species from a set of surveyed locations. Such models can be used to develop successful early detection, quarantine, or eradication plans based on the predicted areas of infestation. Individual-based models (IBMs) are often used to replicate the dynamics of complex systems and are both able to incorporate individual differences and local interactions among organisms, as well as spatial details. In this work, we introduce a new stochastic lattice-based model for simulating the spread of invasive termites over a landscape and compare it to a recently published stochastic individual-based approach, based on the same ecological parameters, with the goal of improving its computational efficiency. The two modeling frameworks were tested over a homogeneous landscape with randomly located sources of infestation. Further, the setting of a case-study of an invasive termite, Nasutitermes corniger (Motschulsky), was used to simulate the spread of the species in Dania Beach, Florida, U.S.A., and the results of the proposed model were compared with an earlier application of the IBM over the same area. The results show that the extent of the infested areas predicted by the new lattice-based model is similar, thus comparable, to the individual-based model while improving the computation time significantly. The simulation presented in this work could be used by the regulatory authorities to draw one or more areas of intervention instead of wasting resources by randomly surveying unknown perimeters.

The origins and radiation of Australian Coptotermes termites: From rainforest to desert dwellers

The termite genus Coptotermes (Rhinotermitidae) is found in Asia, Africa, Central/South America and Australia, with greatest diversity in Asia. Some Coptotermes species are amongst the world’s most damaging invasive termites, but the genus is also significant for containing the most sophisticated mound-building termites outside the family Termitidae. These mound-building Coptotermes occur only in Australia. Despite its economic and evolutionary significance, the biogeographic history of the genus has not been well investigated, nor has the evolution of the Australian mound-building species. We present here the first phylogeny of the Australian Coptotermes to include representatives from all described species. We combined our new data with previously generated data to estimate the first phylogeny to include representatives from all continents where the genus is found. We also present the first estimation of divergence dates during the evolution of the genus. We found the Australian Coptotermes to be monophyletic and most closely related to the Asian Coptotermes, with considerable genetic diversity in some Australian taxa possibly representing undescribed species. The Australian mound-building species did not form a monophyletic clade. Our ancestral state reconstruction analysis indicated that the ancestral Australian Coptotermes was likely to have been a tree nester, and that mound-building behaviour has arisen multiple times. The Australian Coptotermes were found to have diversified ∼13million years ago, which plausibly matches with the narrowing of the Arafura Sea allowing Asian taxa to cross into Australia. The first diverging Coptotermes group was found to be African, casting doubt on the previously raised hypothesis that the genus has an Asian origin.

Water Transport byCoptotermes formosanus(Isoptera: Rhinotermitidae)

Subterranean termites are extremely vulnerable to desiccation, and high moisture makes their habitat and food favorable for survival and colony growth. Although there is a general perception that termites can manipulate moisture, documentation is surprisingly scanty with regard to how termites transport water and the factors that impact it. There has been no study of water transfer by Coptotermes formosanus Shiraki, a notoriously invasive termite in the southern United States. We conducted a study to determine if C. formosanus transfers water. Bioassays using arenas with a dry food source connected to a moist substrate by either a short tube (10 cm) or a long tube (100 cm) were conducted. Three moistened substrate types were tested to see how they impacted water transfer. In addition, workers and soldiers sampled from a moist sand substrate were dissected to determine water sac volumes for possible transfer of water to wood. The results indicated that some water transfer is achieved by the evacuation of water sacs. However, moist soil was also moved to increase humidity. When termites had use of moist silty clay, wood moisture gain increased significantly in both 10 and 100 cm tubes. As tube distance increased, moisture to the more distant food source decreased. Workers had the largest water sacs, though soldiers appear to contribute in water transfer via water sacs as well. Water transfer and its implications are discussed.

Predicting the geographical distribution of two invasive termite species from occurrence data.

Predicting the potential habitat of species under both current and future climate change scenarios is crucial for monitoring invasive species and understanding a species' response to different environmental conditions. Frequently, the only data available on a species is the location of its occurrence (presence-only data). Using occurrence records only, two models were used to predict the geographical distribution of two destructive invasive termite species, Coptotermes gestroi (Wasmann) and Coptotermes formosanus Shiraki. The first model uses a Bayesian linear logistic regression approach adjusted for presence-only data while the second one is the widely used maximum entropy approach (Maxent). Results show that the predicted distributions of both C. gestroi and C. formosanus are strongly linked to urban development. The impact of future scenarios such as climate warming and population growth on the biotic distribution of both termite species was also assessed. Future climate warming seems to affect their projected probability of presence to a lesser extent than population growth. The Bayesian logistic approach outperformed Maxent consistently in all models according to evaluation criteria such as model sensitivity and ecological realism. The importance of further studies for an explicit treatment of residual spatial autocorrelation and a more comprehensive comparison between both statistical approaches is suggested.