Distinct chemical blends produced by different reproductive castes in the subterranean termite Reticulitermes flavipes

The production of royal pheromones by reproductives (queens and kings) enables social insect colonies to allocate individuals into reproductive and non-reproductive roles. In many termite species, nestmates can develop into neotenics when the primary king or queen dies, which then inhibit the production of additional reproductives. This suggests that primary reproductives and neotenics produce royal pheromones. The cuticular hydrocarbon heneicosane was identified as a royal pheromone in Reticulitermes flavipes neotenics. Here, we investigated the presence of this and other cuticular hydrocarbons in primary reproductives and neotenics of this species, and the ontogeny of their production in primary reproductives. Our results revealed that heneicosane was produced by most neotenics, raising the question of whether reproductive status may trigger its production. Neotenics produced six additional cuticular hydrocarbons absent from workers and nymphs. Remarkably, heneicosane and four of these compounds were absent in primary reproductives, and the other two compounds were present in lower quantities. Neotenics therefore have a distinct 'royal' blend from primary reproductives, and potentially over-signal their reproductive status. Our results suggest that primary reproductives and neotenics may face different social pressures. Future studies of these pressures should provide a more complete understanding of the mechanisms underlying social regulation in termites.

Seasonal Activity, Spatial Distribution, and Physiological Limits of Subterranean Termites (Reticulitermes Species) in an East Texas Forest

One of the major goals of ecology is to understand how co-habiting species partition limited resources. In the eastern U.S., at least three species of Reticulitermes subterranean termites often occur in sympatry; however, little is known about how these species divide food resources. In this study, we characterized the foraging activity of Reticulitermes flavipes (Kollar), R. hageni Banks, and R. virginicus (Banks) across seasons to assess the impact of environmental conditions on resource partitioning. A field site consisting of two grids of wooden monitors was sampled monthly for 28 months. Foraging activity in all three species was correlated with the interaction of temperature and moisture. This correlation was influenced by temperature and moisture approximately equally in R. flavipes, whereas temperature contributed more to the correlation in R. hageni, and moisture contributed more in R. virginicus. These differences caused each species to preferentially forage during specific environmental conditions: R. flavipes continued foraging after high moisture events, R. hageni increased foraging under higher soil moisture, and R. virginicus increased foraging under lower soil temperatures. We attempted to explain these patterns by the species' physiological limits; however, we found no differences in upper lethal limit, desiccation, or submersion limits across species. These results add to the overall understanding of resource partitioning by emphasizing the ability of multiple species to utilize the same resource under different environmental conditions and raise questions regarding the physiological and/or behavioral mechanisms involved.

Ergatoid reproductives in the Neotropical termite Nasutitermes aquilinus (Holmgren) (Blattaria: Isoptera: Termitidae): developmental origin, fecundity, and genetics

Termite colonies are usually headed by primary reproductives, which establish nests during the swarming season. However, secondary reproductives may develop in some species and become supplementary or replacement breeders, extending colony lifespan. Here we investigate the developmental origin, fecundity and genetic characterization of ergatoid reproductives in the Neotropical termite Nasutitermes aquilinus (Holmgren), using morphometrical and histological techniques, five microsatellite loci and the COI mitochondrial DNA. Twelve measurements performed on 208 apterous individuals of N. aquilinus revealed 10 groups, including ergatoid females, which developed from major workers through two successive molts, and were characterized by the presence of imaginal features such as eyes and wing buds. The differentiation of these features was correlated to physogastric development in these ergatoids. Histology revealed oocytes in all maturation stages in worker-derived reproductives of N. aquilinus, presence of nonflagellate spermatozoa inside the spermatheca, and royal fat body. Thus, ergatoid reproductives were reproductively functional. According to the genotypes of 221 individuals from 11 nests, and mitochondrial haplotypes of 43 ergatoids, 73% of the colonies were simple families, whereas 27% were extended families. Despite the occurrence of related reproductives, low inbreeding rates were detected within and among colonies. Such values could be explained given that sib mating itself cannot result in a higher inbreeding rate but depend on several factors discussed in detail. This is the first study to investigate the genetic structure of termite colonies influenced by the development of ergatoids, and further investigations are encouraged to understand the influence of these reproductives on colony lifespan.

Recent Detection of Multiple Populations of the Tropical Bed Bug (Hemiptera: Cimicidae) Exhibiting kdr-Associated Mutations in Hawaii

In recent years, bed bugs have experienced a remarkable resurgence on a near global scale. While reports have primarily focused on the common bed bug, Cimex lectularius (L.), which has resurged largely in temperate regions, in tropical regions the tropical bed bug, Cimex hemipterus (F.) (Hemiptera: Cimicidae), has reemerged as well. Recent reports of C. hemipterus introductions to subtropical and temperate regions, outside of the species natural distribution, suggest the potential for establishment and further spread. Establishment may be aided by insecticide resistance mechanisms, such as the presence of knockdown resistance (kdr)-associated mutations, which potentially confer resistance to pyrethroid, pyrethrin, and organochloride insecticides. Here, we present the first report of the detection and likely establishment of C. hemipterus in Honolulu, Hawaii, from samples collected in 2009 and 2019. Furthermore, through partial sequencing of the voltage-gated sodium channel, we report the presence of kdr-associated mutations in all samples. These findings have implications for the implementation of control strategies aimed at eradicating infestations.

Genetic Diversity of Culicoides stellifer (Diptera: Ceratopogonidae) in the Southeastern United States Compared With Sequences From Ontario, Canada

Much of the bluetongue (BT) and epizootic hemorrhagic disease (EHD) research in North America focuses on white-tail deer and Culicoides sonorensis (Wirth & Jones) (Diptera: Ceratopogonidae), though several other biting midge species have been suggested as vectors. Culicoides stellifer (Coquillett) has been associated with hosts susceptible to hemorrhagic disease (HD), and more recently, specimens from Florida have tested positive for EHD and BT viral RNA. If C. stellifer is acting as a vector, this could have an impact on the distribution of HD in North America. To determine if gene flow is occurring across the range of C. stellifer within the southeast United States, a mitochondrial haplotype analysis was performed using the COI gene. Our haplotype network showed no population structure in C. stellifer from Florida, Texas, and South Carolina, as the overall genetic divergence between these sites was equal to the genetic divergence within each. We also compared these haplotypes to published sequences of C. stellifer collected in Ontario, Canada. Surprisingly, the genetic diversity of the flies from Ontario was two times greater than what was observed between the southeast U.S. collection sites. This considerable divergence could be evidence of a cryptic species. A better understanding of the connectivity between C. stellifer populations across all of North America will give insight into the distribution of HD. Our results show that gene flow is occurring between sites in the southeastern United States and potentially throughout the eastern distribution of the species.

Increased genetic diversity from colony merging in termites does not improve survival against a fungal pathogen

In some species of social insects the increased genetic diversity from having multiple breeders in a colony has been shown to improve pathogen resistance. Termite species typically found colonies from single mated pairs and therefore may lack the flexibility to buffer pathogen pressure with increased genetic diversity by varying the initial number of reproductives. However, they can later increase group diversity through colony merging, resulting in a genetically diverse, yet cohesive, workforce. In this study, we investigate whether the increased group diversity from colony fusion benefits social immunity in the subterranean termite Reticulitermes flavipes. We confirm previous findings that colonies of R. flavipes will readily merge and we show that workers will equally groom nestmates and non-nestmates after merging. Despite this, the survival of these merged colonies was not improved after exposure to a fungal pathogen, but instead leveled to that of the more susceptible or the more resistant colony. Our study brings little support to the hypothesis that colony fusion may improve immunity through an increase of genetic diversity in R. flavipes. Instead, we find that following exposure to a lethal pathogen, one colony is heavily influential to the entire group's survival after merging.

Suppressing tawny crazy ant (Nylanderia fulva) by RNAi technology

The tawny crazy ant (Nylanderia fulva) is a new invasive pest in the United States. At present, its management mainly relies on the use of synthetic insecticides, which are generally ineffective at producing lasting control of the pest, necessitating alternative environmentally friendly measures. In this study, we evaluated the feasibility of gene silencing to control this ant species. Six housekeeping genes encoding actin (NfActin), coatomer subunit β (NfCOPβ), arginine kinase (NfArgK), and V-type proton ATPase subunits A (NfvATPaseA), B (NfvATPaseB) and E (NfvATPaseE) were cloned. Phylogenetic analysis revealed high sequence similarity to homologs from other ant species, particularly the Florida carpenter ant (Camponotus floridanus). To silence these genes, vector L4440 was used to generate six specific RNAi constructs for bacterial expression. Heat-inactivated, dsRNA-expressing Escherichia coli were incorporated into artificial diet. Worker ants exhibited reduced endogenous gene expression after feeding on such diet for 9 d. However, only ingestion of dsRNAs of NfCOPβ (a gene involved in protein trafficking) and NfArgK (a cellular energy reserve regulatory gene in invertebrates) caused modest but significantly higher ant mortality than the control. These results suggest that bacterially expressed dsRNA can be orally delivered to ant cells as a mean to target its vulnerabilities. Improved efficacy is necessary for the RNAi-based approach to be useful in tawny crazy ant management.

The underdog invader: Breeding system and colony genetic structure of the dark rover ant (Brachymyrmex patagonicus Mayr)

Ants are among the most successful species at invading new environments. Their success undeniably comes from their various modes of reproduction and colony breeding structures, which influence their dispersal ability, reproductive potential, and foraging strategies. Almost all invasive ant species studied so far form supercolonies, a dense network of interconnected nests comprising numerous queens, without aggression toward non-nestmates. This strategy results in invasive colonies that are able to grow extremely fast and large while avoiding intraspecific competition, allowing them to monopolize environmental resources and outcompete native species. Here, we developed and used 10 microsatellite markers to investigate the population structure and breeding system of the dark rover ant Brachymyrmex patagonicus Mayr in its introduced range. We determined whether this species exhibits a supercolonial structure by assessing whether different nests belonged to the same genetic colony. We inferred its dispersal ability by investigating isolation by distance and estimated the numbers of queens per colonies and mating per queen through parent-offspring inferences. We found that most of the colonies of B. patagonicus were comprised of a single nest, headed by a single queen. Each nest was distinct from one another, without isolation by distance, which suggests strong dispersal ability through nuptial flights. These features are commonly observed in noninvasive and native ant species, but they are surprising for a successful invasive ant, as they strongly differ from other invasive ants. Overall, we discuss how this seemingly unfavorable strategy for an invasive ant might favor the invasive success of the dark rover ant in the United States.

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.

Queen and king recognition in the subterranean termite, Reticulitermes flavipes: Evidence for royal recognition pheromones

Royal recognition is a central feature of insect societies, allowing them to maintain the reproductive division of labor and regulate colony demography. Queen recognition has been broadly demonstrated and queen recognition pheromones have been identified in social hymenopterans, and in one termite species. Here we describe behaviors that are elicited in workers and soldiers by neotenic queens and kings of the subterranean termite, Reticulitermes flavipes, and demonstrate the chemical basis for the behavior. Workers and soldiers readily perform a lateral or longitudinal shaking behavior upon antennal contact with queens and kings. When royal cuticular chemicals are transferred to live workers or inert glass dummies, they elicit antennation and shaking in a dose-dependent manner. The striking response to reproductives and their cuticular extracts suggests that royal-specific cuticular compounds act as recognition pheromones and that shaking behavior is a clear and measurable queen and king recognition response in this termite species.

Diversity of Termite Breeding Systems

Termites are social insects that live in colonies headed by reproductive castes. The breeding system is defined by the number of reproductive individuals in a colony and the castes to which they belong. There is tremendous variation in the breeding system of termites both within and among species. The current state of our understanding of termite breeding systems is reviewed. Most termite colonies are founded by a primary (alate-derived) king and queen who mate and produce the other colony members. In some species, colonies continue throughout their life span as simple families headed by the original king and queen. In others, the primary king and queen are replaced by numerous neotenic (nymph- or worker-derived) reproductives, or less commonly primary reproductives, that are descendants of the original founding pair leading to inbreeding in the colony. In still others, colonies can have multiple unrelated reproductives due to either founding the colonies as groups or through colony fusion. More recently, parthenogenetic reproduction has shown to be important in some termite species and may be widespread. A major challenge in termite biology is to understand the ecological and evolutionary factors driving the variation in termite breeding systems.

Supercolonial structure of invasive populations of the tawny crazy ant Nylanderia fulva in the US

BACKGROUND

Social insects are among the most serious invasive pests in the world, particularly successful at monopolizing environmental resources to outcompete native species and achieve ecological dominance. The invasive success of some social insects is enhanced by their unicolonial structure, under which the presence of numerous queens and the lack of aggression against non-nestmates allow high worker densities, colony growth, and survival while eliminating intra-specific competition. In this study, we investigated the population genetics, colony structure and levels of aggression in the tawny crazy ant, Nylanderia fulva, which was recently introduced into the United States from South America.

RESULTS

We found that this species experienced a genetic bottleneck during its invasion lowering its genetic diversity by 60%. Our results show that the introduction of N. fulva is associated with a shift in colony structure. This species exhibits a multicolonial organization in its native range, with colonies clearly separated from one another, whereas it displays a unicolonial system with no clear boundaries among nests in its invasive range. We uncovered an absence of genetic differentiation among populations across the entire invasive range, and a lack of aggressive behaviors towards conspecifics from different nests, even ones separated by several hundreds of kilometers.

CONCLUSIONS

Overall, these results suggest that across its entire invasive range in the U.S.A., this species forms a single supercolony spreading more than 2000 km. In each invasive nest, we found several, up to hundreds, of reproductive queens, each being mated with a single male. The many reproductive queens per nests, together with the free movement of individuals between nests, leads to a relatedness coefficient among nestmate workers close to zero in introduced populations, calling into question the stability of this unicolonial system in which indirect fitness benefits to workers is apparently absent.

Inbreeding tolerance as a pre-adapted trait for invasion success in the invasive ant Brachyponera chinensis

Identifying traits that facilitate species introductions and successful invasions of ecosystems represents a key issue in ecology. Following their establishment into new environments, many non-native species exhibit phenotypic plasticity with post-introduction changes in behaviour, morphology or life history traits that allow them to overcome the presumed loss of genetic diversity resulting in inbreeding and reduced adaptive potential. Here, we present a unique strategy in the invasive ant Brachyponera chinensis (Emery), in which inbreeding tolerance is a pre-adapted trait for invasion success, allowing this ant to cope with genetic depletion following a genetic bottleneck. We report for the first time that inbreeding is not a consequence of the founder effect following introduction, but it is due to mating between sister queens and their brothers that pre-exists in native populations which may have helped it circumvent the cost of invasion. We show that a genetic bottleneck does not affect the genetic diversity or the level of heterozygosity within colonies and suggest that generations of sib-mating in native populations may have reduced inbreeding depression through purifying selection of deleterious alleles. This work highlights how a unique life history may pre-adapt some species for biological invasions.

Genetic diversity and colony structure of Tapinoma melanocephalum on the islands and mainland of South China

AIM

Tapinoma melanocephalum is listed as one of the most important invasive pest species in China. Information regarding the patterns of invasion and effects of geographic isolation on the population genetics of this species is largely lacking.

LOCATION

South China.

METHODS

To address this problem, we genotyped 39 colonies (two colonies were collapsed due to genetic similarity) using microsatellite markers and mitochondrial DNA sequencing to compare colony genetic structure of T. melanocephalum on the mainland and islands of South China.

RESULTS

An analysis of the colony genotypes showed that the genetic diversity of the mainland population was slightly higher than that of the island populations but not significantly so. However, the observed heterozygosity on Shangchuan Island (SCD) was significantly lower than that of the other colonies. We also found six haplotypes in 111 mitochondrial DNA COI sequences. The relatedness (r) value between colonies of SCD was 0.410, higher than that of the other populations. The genetic clusters among colonies were not related to geographic locations and exhibited admixture likely due to frequent human-mediated dispersal associated with trade between the mainland population and the islands. Pairwise FSTs between populations showed differentiation among mainland populations, while SCD displayed high levels of divergence (FST > 0.15) from most mainland populations. There was no significant isolation by distance among colonies. Most populations showed signs of a bottleneck effect.

MAIN CONCLUSIONS

Our study suggests that there was no significant difference in the genetic diversity among the islands and the mainland; however, the lower genetic diversity, the higher degree of genetic divergence from other colonies, and the higher relatedness among nestmates made the SCD population stand out from all the others.

Identification of a queen and king recognition pheromone in the subterranean termite Reticulitermes flavipes

Chemical communication is fundamental to success in social insect colonies. Species-, colony-, and caste-specific blends of cuticular hydrocarbons (CHCs) and other chemicals have been well documented as pheromones, mediating important behavioral and physiological aspects of social insects. More specifically, royal pheromones used by queens (and kings in termites) enable workers to recognize and care for these vital individuals and maintain the reproductive division of labor. In termites, however, no royal-recognition pheromones have been identified to date. In the current study, solvent extracts of the subterranean termite Reticulitermes flavipes were analyzed to assess differences in cuticular compounds among castes. We identified a royal-specific hydrocarbon-heneicosane-and several previously unreported and highly royal enriched long-chain alkanes. When applied to glass dummies, heneicosane elicited worker behavioral responses identical to those elicited by live termite queens, including increased vibratory shaking and antennation. Further, the behavioral effects of heneicosane were amplified when presented with nestmate termite workers' cuticular extracts, underscoring the importance of chemical context in termite royal recognition. Thus, heneicosane is a royal-recognition pheromone that is active in both queens and kings of R. flavipes The use of heneicosane as a queen and king recognition pheromone by termites suggests that CHCs evolved as royal pheromones ∼150 million years ago, ∼50 million years before their first use as queen-recognition pheromones in social Hymenoptera. We therefore infer that termites and social Hymenoptera convergently evolved the use of these ubiquitous compounds in royal recognition.

A Genomic Imprinting Model of Termite Caste Determination: Not Genetic but Epigenetic Inheritance Influences Offspring Caste Fate

Eusocial insects exhibit the most striking example of phenotypic plasticity. There has been a long controversy over the factors determining caste development of individuals in social insects. Here we demonstrate that parental phenotypes influence the social status of offspring not through genetic inheritance but through genomic imprinting in termites. Our extensive field survey and genetic analysis of the termite Reticulitermes speratus show that its breeding system is inconsistent with a genetic caste determination model. We therefore developed a genomic imprinting model, in which queen- and king-specific epigenetic marks antagonistically influence sexual development of offspring. The model accounts for all known empirical data on caste differentiation of R. speratus and other related species. By conducting colony-founding experiments and additively incorporating relevant socio-environmental factors into our genomic imprinting model, we show the relative importance of genomic imprinting and environmental factors in caste determination. The idea of epigenetic inheritance of sexual phenotypes solves the puzzle of why parthenogenetically produced daughters carrying only maternal chromosomes exclusively develop into queens and why parental phenotypes (nymph- or worker-derived reproductives) strongly influence caste differentiation of offspring. According to our model, the worker caste is seen as a "neuter" caste whose sexual development is suppressed due to counterbalanced maternal and paternal imprinting and opens new avenues for understanding the evolution of caste systems in social insects.

Novel use of aliphatic n-methyl ketones as a fumigant and alternative to methyl bromide for insect control

BACKGROUND

Fumigants like phosphine, methyl bromide and sulfuryl fluoride are highly effective for the control of structural, storage and agricultural arthropod pests. Unfortunately, many of these synthetic compounds are highly toxic to people, many pests have developed resistance to these compounds and methyl bromide, the 'gold standard' for fumigants, was de-registered because of its contribution to depletion of the stratospheric ozone layer. Alternative fumigant chemistry is needed.

RESULTS

Several plant species produce n-aliphatic methyl ketones to prevent plant herbivory. To examine the use of methyl ketones as a fumigant, structure-mortality studies were conducted using the red imported fire ant, Solenopsis invicta Buren, as a model. A new easy-to-use, inexpensive and disposable bioassay system was developed for this study. The LC₅₀ values for heptanone, octanone, nonanone and undecanone were 4.27, 5.11, 5.26 and 8.21 µg/cm³ of ambient air, respectively. Although heptanone, octanone and nonanone were more effective than undecanone, subsequent research was conducted with 2-undecanone because this compound already has US Environmental Protection Agency (EPA) registration as a biopesticide. In dose-response field studies, 12.4 mL of undecanone injected into mounds was the lowest application rate that produced no ant activity in the mound with no re-establishment of ants. Reagent grade undecanone was more cost-effective than methyl bromide for fire ants, adult German cockroaches and tobacco budworm eggs, but slightly more expensive for adult flour beetles.

CONCLUSION

The naturally occurring methyl ketone undecanone has the potential to be an alternative to current fumigants for a variety of pest applications. © 2017 Society of Chemical Industry.

Radiocarbon analysis reveals expanded diet breadth associates with the invasion of a predatory ant

Invasions are ecologically destructive and can threaten biodiversity. Trophic flexibility has been proposed as a mechanism facilitating invasion, with more flexible species better able to invade. The termite hunting needle ant Brachyponera chinensis was introduced from East Asia to the United States where it disrupts native ecosystems. We show that B. chinensis has expanded dietary breadth without shifting trophic position in its introduced range. Transect sampling of ants and termites revealed a negative correlation between the abundance of B. chinensis and the abundance of other ants in introduced populations, but this pattern was not as strong in the native range. Both termite and B. chinensis abundance were higher in the introduced range than in native range. Radiocarbon (¹⁴C) analysis revealed that B. chinensis has significantly younger 'diet age', the time lag between carbon fixation by photosynthesis and its use by the consumer, in the introduced range than in the native range, while stable isotope analyses showed no change. These results suggest that in the introduced range B. chinensis remains a termite predator but also feeds on other consumer invertebrates with younger diet ages such as herbivorous insects. Radiocarbon analysis allowed us to elucidate cryptic dietary change associated with invasion success.

Efficacy of Chlorantraniliprole in Controlling Structural Infestations of the Eastern Subterranean Termite in the USA

Subterranean termites are the most economically important structural pests in the USA, and the eastern subterranean termite, Reticulitermes flavipes (Kollar) (Dictyoptera: Rhinotermitidae) is the most widely distributed species. Soil treatment with a liquid termiticide is a widely used method for controlling subterranean termites in structures. We assessed the efficacy of a nonrepellent termiticide, Altriset^® (active ingredient: chlorantraniliprole), in controlling structural infestations of R. flavipes in Texas, North Carolina, and Ohio and determined the post-treatment fate of termite colonies in and around the structures. In all three states, microsatellite markers indicated that only one R. flavipes colony was infesting each structure. A single chlorantraniliprole treatment provided effective structural protection as there was no further evidence of termite activity in and on the majority of structures from approximately 1 month to 2 years post-treatment when the study concluded. Additionally, the treatment appeared to either severely reduce the infesting colony’s footprint at monitors in the landscape or eliminate colony members from these monitors. A supplemental spot-treatment was conducted at one house each in Texas and North Carolina at 5 and 6 months post-treatment, respectively; no termites were observed thereafter in these structures and associated landscaping. The number of colonies found exclusively in the landscape (not attacking the structure) varied among the states, with the largest number of colonies in Texas (0–4) and North Carolina (0–5) as compared to 0–1 in Ohio, the most northern state.

BIOCHEMICAL PHENOTYPIC AND GENETIC STUDIES OF TWO INTRODUCED FIRE ANTS AND THEIR HYBRID (HYMENOPTERA: FORMICIDAE)

Two introduced fire ants, Solenopsis invicta and S. richteri, and their hybrid were studied using phenotypic markers from gas chromatographic analysis of hydrocarbons and venom alkaloids, as well as genetic markers from enzyme electrophoresis. Both methods show that extensive gene introgression is occurring over a distance of at least 120 km at the contact zone between the two forms in eastern Mississippi. Genetic analyses suggest that the hybrid population does not depart dramatically from panmixia. Also, recombinant genotypes predominate in the hybrid zone, indicating that F₁ hybrids are viable. Allele frequency clines through the hybrid zone are apparent for four polymorphic loci. Data sets generated by the chromatographic and electrophoretic methods are highly concordant in that they differentiate completely between the two forms and agree in designating colonies from the contact zone as hybrid or parental in a high proportion (90%) of cases. The two methods can serve as complementary tools for studying closely related but genetically distinct populations in this, and perhaps other, groups of insects.

Restricted Gene Flow among Lineages of Thrips tabaci Supports Genetic Divergence Among Cryptic Species Groups

Knowledge of the relative influence of population- versus species-level genetic variation is important to understand patterns of phenotypic variation and ecological relationships that exist among and within morphologically indistinguishable cryptic species and subspecies. In the case of cryptic species groups that are pests, such knowledge is also essential for devising effective population management strategies. The globally important crop pest Thrips tabaci is a taxonomically difficult group of putatively cryptic species. This study examines population genetic structure of T. tabaci and reproductive isolation among lineages of this species complex using microsatellite markers and mitochondrial COI sequences. Overall, genetic structure supports T. tabaci as a cryptic species complex, although limited interbreeding occurs between different clonal groups from the same lineage as well as between individuals from different lineages. These results also provide evidence that thelytoky and arrhenotoky are not fixed phenotypes among members of different T. tabaci lineages that have been generally associated with either reproductive mode. Possible biological and ecological factors contributing to these observations are discussed.

Subterranean termite phylogeography reveals multiple postglacial colonization events in southwestern Europe

A long‐standing goal of evolutionary biology is to understand how paleoclimatic and geological events shape the geographical distribution and genetic structure within and among species. Using a diverse set of markers (cuticular hydrocarbons, mitochondrial and nuclear gene sequences, microsatellite loci), we studied Reticulitermes grassei and R. banyulensis, two closely related termite species in southwestern Europe. We sought to clarify the current genetic structure of populations that formed following postglacial dispersal from refugia in southern Spain and characterize the gene flow between the two lineages over the last several million years. Each marker type separately provided a fragmented picture of the evolutionary history at different timescales. Chemical analyses of cuticular hydrocarbons and phylogenetic analyses of mitochondrial and nuclear genes showed clear separation between the species, suggesting they diverged following vicariance events in the Late Miocene. However, the presence of intermediate chemical profiles and mtDNA introgression in some Spanish colonies suggests ongoing gene flow. The current genetic structure of Iberian populations is consistent with alternating isolation and dispersal events during Quaternary glacial periods. Analyses of population genetic structure revealed postglacial colonization routes from southern Spain to France, where populations underwent strong genetic bottlenecks after traversing the Pyrenees resulting in parapatric speciation.