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.     

Aphid dispersal flight disseminates fungal pathogens and parasitoids as natural control agents of aphids

Abstract.  1. Dispersal flight, a well-known strategy for aphids to locate suitable plants, was studied for its possible role in disseminating fungal pathogens and parasitoids as natural control agents of aphids by air captures in Hangzhou, China during 2001–2005. Up to 3183 migratory alates of green peach aphid Myzus persicae were captured from air using a yellow-plus-plant trap on the top platform of a six-storey building in an urbanised area, and individually reared in a laboratory for ≥ 7 days.
2. Among the captured alates, 28.9% survived on average for 2.5 days and then died from mycoses attributed to 10 species of obligate or non-obligate aphid pathogens. These were predominated by Pandora neoaphidis , which was causative of 80% of the mycosed alates. Another 4.4% survived for an average of 3.7 days, followed by mummification of Aphidius gifuensis (52.9%) and Diaeretella rapae (47.1%).
3. Numerous progeny colonies individually initiated by infected, parasitised, or healthy alates were monitored daily for 12 days, and fitted well to a logistic equation depicting the potential of their post-flight colonisation and fecundity. Both infected and parasitised alates from air were highly capable of initiating progeny colonies independently, although their potential fecundity was greatly reduced compared with that of healthy counterparts.
4. Our results confirmed that both obligate and non-obligate pathogens can be widespread with aphid dispersal flight, and demonstrated that parasitoids also took advantage of the host flight for their dispersal. This study provides new insights into aphid dispersal biology.     

Experimental simulation of transmission of an obligate aphid pathogen with aphid flight dispersal

The wide dispersal of Entomophthorales-caused mycoses that usually regulate aphid populations is most likely to be associated with the flight of infected alates. This hypothesis was examined via simulated flight and postflight colonization of Myzus periscae alates exposed to spore showers of Pandora neoaphidis, a common obligate aphid pathogen prevalent world wide. A total number of 407 alates were showered in different batches, then individually flown in a computer-monitoring flight mill system and reared on cabbage leaves for 14-day free reproduction and contagious infection within progeny colonies at 20-23 degrees C. On average, 80.6% of them flew 2.6 km in 1-5 h, survived 3.2 days, produced 5.3 nymphs, and transmitted their infection to progeny successfully. However, 9.8% of the flown alates left no progeny although they survived at least 1 day prior to mycosis while the rest were not mycosed, producing significantly more nymphs during the first week. The flight distances of the infected (0.01-10.2 km) or uninfected alates (0.1-8.3 km) were exponentially correlated to the flight time (r( 2) >or= 0.98). When grouped by the flight ranges of <1.0, 1.0-3.0, 3.0-5.0 and >5.0 km, the number of live aphids and the proportion of mycosed individuals per progeny colony over colonization days fit well to a complex logistic model (r( 2) = 0.984) and modified Gompertz model (r( 2) = 0.978) respectively. Both models included flight distance, postflight survival time, premycosis fecundity and primary infection rate as independent variables to affect the developmental rates. The results highlight the significant role of infected alates in the wide dispersal of P. neoaphidis-caused mycoses among aphids.     

Sitobion avenae alatae infected by Pandora neoaphidis: their flight ability, post-flight colonization, and mycosis transmission to progeny colonies

Epizootics caused by the obligate Entomophthorales pathogen Pandora neoaphidis may result from more than one possible means of fungal dissemination among host aphids, but we hypothesize that wide dispersal of the fungus is most likely to be associated with the flight behavior of migratory alates. We tested this hypothesis in a simulation experiment by assessing the flight capability of Sitobion avenae alates infected with P. neoaphidis and the potential of their post-flight survival, colonization, and mycosis transmission to progeny. A total of 281 alates were inoculated with P. neoaphidis, individually flown for up to 5h and 9km in a computer-monitored flight mill system and then reared for 10 days on wheat seedlings. The infected alates were capable of surviving on average for 2.9 days (range 1-7 days) and leaving 4.6 nymphs prior to deaths. Transmission of fungal infection within progeny colonies occurred after the mother alates died from P. neoaphidis mycosis. The level of contagious infection among the nymphs reached up to 16.8% within 7 days but varied with the survival time of the infected mother alates after flight. Based on stepwise polynomial regression analysis, progeny colony size was highly correlated with the interactions of flight time with both post-flight survival time and the number of nymphs left per alate before death (r2 = 0.997). Progeny mortality on day 5 after colonization was inversely correlated with post-flight survival time (r2 = 0.949) whereas infection on day 7 was correlated with flight distance and an interaction of post-flight survival time with fecundity of the infected alates (r2 = 0.970). Progeny mortality observed on day 10 was merely correlated to mortality observed on day 5 (r2 = 0.946). These results indicate a successful transmission of alate-borne P. neoaphidis to progeny colonies and further support our hypothesis on the means of primary dispersal of aphid epizootics by migratory alates in a geographically wide range.     

Effect of parasitism on flight behavior of the soybean aphid, Aphis glycines

Many aphid species possess wingless (apterous) and winged (alate) stages, both of which can harbor parasitoids at various developmental stages. Alates can either be parasitized directly or can bear parasitoids eggs or larvae resulting from prior parasitism of alatoid nymphs. Winged aphids bearing parasitoid eggs or young larvae eventually still engage in long-distance flights, thereby facilitating parasitoid dispersal. This may have a number of important implications for biological control of aphids by parasitoids. In this study, we determined the effect of parasitism by Aphelinus varipes (Hymenoptera: Aphelinidae) on wing development and flight of the soybean aphid, Aphis glycines (Hemiptera: Aphididae). We also quantified the influence of aphid flight distance on subsequent A. varipes development. Parasitism by A. varipes was allowed at different A. glycines developmental stages (i.e., alatoid 3rd and 4th-instar nymphs, alates) and subsequent aphid flight was measured using a computer-monitored flight mill. Only 35% of aphids parasitized as L3 alatoid nymphs produced normal winged adults compared to 100% of L4 alatoids. Flight performance of aphids parasitized as 4th-instar alatoid nymphs 24 or 48 h prior to testing was similar to that of un-parasitized alates of identical age, but declined sharply for alates that had been parasitized as 4th-instar alatoid nymphs 72 and 96 h prior to testing. Flight performance of aphids parasitized as alate adults for 24 h was not significantly different from un-parasitized alates of comparable ages. Flight distance did not affect parasitoid larval or pupal development times, or the percent mummification of parasitized aphids. Our results have implications for natural biological control of A. glycines in Asia and classical biological control of the soybean aphid in North America.     

Chemical communication in termites: syn-4,6-dimethylundecan-1-ol as trail-following pheromone, syn-4,6-dimethylundecanal and (5E)-2,6,10-trimethylundeca-5,9-dienal as the respective male and female sex pheromones in Hodotermopsis sjoestedti (Isoptera, Archotermopsidae)

The trail-following pheromone and sex pheromones were investigated in the Indomalayan termite Hodotermopsis sjoestedti belonging to the new family Archotermopsidae.Gas chromatography coupled to mass spectrometry (GC–MS) after solid phase microextraction (SPME) of the sternal gland secretion of pseudergates and trail-following bioassays demonstrated that the trail-following pheromone of H. sjoestedti was syn-4,6-dimethylundecan-1-ol, a new chemical structure for termite pheromones. GC–MS after SPME of the sternal gland secretion of alates also allowed the identification of sex-specific compounds. In female alates, the major sex-specific compound was identified as (5E)-2,6,10-trimethylundeca-5,9-dienal, a compound previously identified as the female sex pheromone of the termite Zootermopsis nevadensis. In male alates, the major sex-specific compound was identified as syn-4,6-dimethylundecanal, a homolog of syn-4,6-dimethyldodecanal, which has previously been confirmed as the male sex pheromone of Z. nevadensis. The presence of sex-specific compounds in alates of H. sjoestedti strongly suggests for this termite the presence of sex-specific pairing pheromones which were only known until now in Z. nevadensis. Our results showed therefore a close chemical relationship between the pheromones of the taxa Hodotermopsis and Zootermopsis and, in contrast, a clear difference with the taxa Stolotermes and Porotermes, which is in total agreement with the recent creation of the families Archotermopsidae and Stolotermitidae as a substitute for the former family Termopsidae.     

High gene flow between populations of Macrotermes michaelseni (Isoptera, Termitidae)

Termite alates are thought to be poor active flyers, and this should lead to considerable genetic differentiation on small spatial scales. However, using four microsatellite loci for the termite Macrotermes michaelseni we found low values of genetic differentiation (F_ST) across a spatial scale of even more than 50 km. Genetic differentiation between populations increased with spatial distance up to 50 km. Furthermore, up to this distance, the scatter around the linear regression of genetic differentiation versus spatial distance increased with spatial distance. This suggests that across such spatial distances gene flow and genetic drift are of about equal importance, and near equilibrium. Using a regional F_ST as well as the distance between populations with non-significant F_ST-values (up to 25 km), gene flow is sufficiently high so that populations may be regarded as panmictic on spatial scales of 25 to 50 km. The apparent contradiction between dispersal distances observed in the field and estimates of gene flow from genetic markers may be due to the masses of swarming alates. Assuming a leptokurtic distribution of dispersal distances, atleast some alates are expected to travel considerable distances, most likely by passive drift. Received 25 January 2005; revised 11 April 2005; accepted 26 April 2005.     

烟蚜茧蜂随寄主有翅桃蚜迁飞而被携带扩散的模拟实验

蚜虫寄生蜂的广泛分布可能与有翅蚜的迁飞有关。为了证明这一假说, 本研究利用微小昆虫飞行磨系统, 分数十批(≤16头/批)对被烟蚜茧蜂Aphidius gifuensis Ashmead单头寄生后的有翅桃蚜Myzus persicae (Sulzer)进行模拟飞行并系统观察了飞行后有翅桃蚜的单头定殖情况。对实验观察数据按飞行时间和飞行距离进行归类, 采用单因素方差分析方法分析飞行时间和飞行距离对有翅桃蚜定殖后的存活和生殖力、烟蚜茧蜂发育等变量的影响; 采用多项式回归分析对所有变量和归类的数据进行统计和分析。结果表明: 成功飞行并定殖的有翅桃蚜有378头, 其中239头有翅桃蚜定殖后形成僵蚜。形成僵蚜的有翅桃蚜在飞行实验时平均飞行时间和飞行距离分别为2.63 h和2.16 km, 定殖后平均存活了6.11 d, 定殖第6天和第14天平均产若蚜累计数量分别为8.5头和162头。形成僵蚜和未形成僵蚜的有翅蚜的模拟飞行数据和定殖观察数据无显著差异。形成僵蚜的239头有翅桃蚜中, 最终成功育出烟蚜茧蜂205头, 僵蚜出蜂率为85.8%。雌雄性比为1∶5.2。结论认为, 专性寄生蚜虫的烟蚜茧蜂可以利用有翅蚜的迁飞而被携带扩散传播, 有翅蚜迁飞在蚜虫寄生蜂扩散中具有重要作用。     

Mechanism,induction factors,and adaptive significance of dealation in the subterranean termite <Emphasis Type="Italic">Reticulitermes speratus</Emphasis> (Isoptera,Rhinotermitidae)

Summary. We studied the dealation of a subterranean termite Reticulitermes speratus Kolbe from three different angles; mechanism, induction factors, and adaptive significance. During nuptial flight alates prevent the wings from breaking off by holding the wings in a 3-dimensional configuration. In the process of dealation, the alates hold the wings in a 2-dimensional configuration, half spread the wings in a lowered position, and bend the abdomen back toward the wings, thereby exerting high pressure at the basal sutures. This separates the wings from the body. The primary factor determining the timing of dealation appears to be isolation from other alates: It induces alates to shed their wings, whereas pairing has no effect on dealation in this species. Alates of termites are especially vulnerable to ant predation during the period between flight and colony foundation. An experiment designed to compare the risk of alates and dealates to predation by a termite-hunting ant, Brachyponera chinensis Emery, showed that dealation reduced the predation risk during the period spent running on the ground.     

Wide dispersal of aphid-pathogenic Entomophthorales among aphids relies upon migratory alates

Entomophthoralean mycoses are of general importance in the natural control of aphids, but mechanisms involved in their dissemination are poorly understood. Despite several possible means of fungal survival, the dispersal of the mycoses in aphids has never been related to the flight of their migratory alates that are able to locate suitable host plants. In this study, aphid-pathogenic fungi proved to be widely disseminated among various aphids by their alates through migratory flight based on the following findings. First, up to 36.6% of the 7139 migratory alates (including nine species of vegetable or cereal aphids) trapped from air > 30 m above the ground in three provinces of China were found bearing eight species of fungal pathogens. Of those, six were aphid-specific Entomophthorales dominated in individual cases by Pandora neoaphidis, which occurs globally but has no resting spores discovered to date. Secondly, infected alates were confirmed to be able to fly for hours, to initiate colonies on plants after flight and to transmit fungal infection to their offspring in a laboratory experiment, in which 238 Sitobion avenae alates were individually flown in a computer-monitoring flight mill system after exposure to a spore shower of P. neoaphidis and then allowed to colonize host plants.     

Longevity, fecundity, change in degree of gravidity and lipid content with adult age, and lipid utilisation during tethered flight of alates of the corn leaf aphid, Rhopalosiphum maidis

The longevity, daily fecundity, degree of gravidity and lipid content of alates of varied ages, and lipid utilisation during sustained tethered flight of the corn leaf aphid, Rhopalosiphum maidis, were studied. Alates had a mean longevity of 9.7 days and a mean fecundity of 14.9 nymphs. A significant increase in the lipid content of alates before emerging as adults was observed. Newly emerged and half-day-old alates had more lipid reserve and embryos than 1-, 2-, 4-, 8-, and 16-day-old specimens. The lipid content of alates decreased significantly with age. The alates' degree of gravidity and lipid content had a low but significant correlation. Half- to 1-day-old alates flew readily and could fly for much longer durations than 2- and 4-day-old. Eight-day-old alates were not capable of flight. R. maidis utilised lipid during prolonged tethered flight. Our data suggest that there is a threshold point when alates cease utilising stored lipid as the energy source and start utilising non-lipid sources as flight fuel energy.     

A strain of the fungus Metarhizium anisopliae for controlling subterranean termites

Alates of the Formosan subterranean termite, Coptotermes formosanus Shiraki, collected after swarming in 2002 died within 48 h, and the cadavers were visibly infected with a fungus. Fungi were picked from the cadavers, transferred to media, and ultimately isolated to purity. The individual fungal cultures were then used to infect Formosan subterranean termite workers. A single fungal isolate, C4-B, taxonomically identified as Metarhizium anisopliae (Metschnikoff), was found to cause rapid mortality of Formosan subterranean termite alates. This is the first report of a biological control agent for termite alates. In initial experiments, C4-B was more lethal to both alates and workers compared with M. anisopliae strain ESC 1, previously marketed as the termite biocontrol agent BioBlast. Dose-response assays in which Formosan subterranean termite alates were exposed to a known concentration of C4-B spores revealed that 10(6) spores/microl killed 100% of the alates in 3 d, both 10(5) and 10(4) spores/microl in 6 d, 10(3) spores/microl in 9 d, and 10(0) spores/microl in 12 d. Assays with workers demonstrated that 10(6) and 10(5) spores/microl killed 100% of the workers in 6 d. In an experiment to test the transfer of inoculum from infected workers to uninfected nestmates, 62.8% of the workers died in 21 d when only 20% of the workers had been inoculated. Mortality of alates caused by C4-B was tested at two field sites by dispersing fungal spores on grassy lawns and collecting alates from the treated areas. Alates thus infected showed 100% mortality by day 5, whereas only 64.8% of untreated control alates from the same collection area were dead on that day.     

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.     

Arolia in termites (Isoptera): functional significance and evolutionary loss

Summary. Termite workers from all families examined had no arolia (=adhesive pads) on their tarsi and are unable to climb smooth vertical surfaces such as glass or polypropylene plastic. This contrasts with ants where both workers and alates of most species possess arolia and are able to climb these surfaces. Arolia were present in alates of the majority of species investigated from three of the four most basal termite families (Mastotermitidae, Termopsidae and Kalotermitidae), though absent from the basal family Hodotermitidae that contains only three genera. Alates in the two kalotermitid species tested readily climbed glass walls. The complete evolutionary loss of arolia from alates in the specious two most apical termite families (Rhinotermitidae and Termitidae) suggests paedomorphosis. Very smooth surfaces probably cannot be used to completely prevent entry of rhinotermitid termites into buildings because these termites can eventually build galleries of feces and soil over these surfaces. However, an experiment with Coptotermes formosanus showed that a smoother surface significantly slows down the rate of gallery building.Received 12 February 2004; revised 17 June 2004; accepted 29 June 2004.     

Flight energetics and dispersal capability of the fire ant, Solenopsis invicta Buren

Experiments were conducted to estimate the flight capabilities of fire ant (Solenopsis invicta Buren) alates. These experiments were designed to: (1) quantify energetic expenditure during fixed flight; (2) characterize metabolic substrates of male and female alates; (3) estimate flight speed of male and female alates; and (4) quantify wingbeat frequency and water loss of females during flight. Flying males (in closed-system respirometry) increased metabolic rate approximately 38.4-fold over resting rate. Females increased metabolic rate approximately 51-fold (closed-system respirometry) and 48-fold (flow-through respirometry) over resting rate. Female alates had a mean respiratory quotient (RQ) of 0.999, indicating reliance on carbohydrates. The mean RQ of males was significantly lower (0.867). The flight speed of females on a circular flight mill averaged approximately 0.7 m s(-1), and increased with temperature but decreased with increasing body mass. The flight speed of males was 43% greater (approximately 1.0 m s(-1)) and increased linearly with temperature and increasing body mass. Female alates lost an average of 1.8 mg water h(-1) during flight. A simple energetics model, combined with previous work on the nutrient content of S. invicta and patterns of CO(2) release observed in this study, indicate that the flight capability of S. invicta female alates is limited to <5 km in the absence of wind.     

Impact of orphaning on field colonies of Southeast Asian Macrotermes gilvus (Hagen) and M. carbonarius (Hagen) (Termitidae, Macrotermitinae)

Field colonies of Macrotermes gilvus (Hagen) and M. carbonarius (Hagen) were experimentally orphaned to examine their potential for producing replacement reproductives. Orphaned colonies were investigated only once for caste composition at selected time intervals at 3, 6, 9 or 12 months after orphaning. Of the 38 orphaned colonies of M. gilvus, 15 colonies (39.5%) re-established. In M. carbonarius, three colonies out of 20 (15%) re-established. Re-established colonies were headed by adultoids which were morphologically indistinguishable from primary reproductives. In naturally orphaned colonies of M. gilvus, we often found multiple adultoids with normal pigmentation but torn wings, i.e. the colonies retained alates as replacement reproductives. The number of reproductives probably declines over time. It may take alates of M. gilvus 6 months to develop into functional adultoids, and up to 12 months for alates of M. carbonarius. Our results also demonstrate that the presence of sexual castes (nymphs or alates) at the time of orphaning does not necessarily guarantee the success of colonies in re-establishing themselves as breeding colonies. We also found a high prevalence of occupation of the mounds by other termite species, after the death of M. gilvus (18.4%) or M. carbonarius (30.0%) colonies, probably using them as foraging sites.     

Changes in endogenous cellulase gene expression levels and reproductive characteristics of primary and secondary reproductives with colony development of the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

The unique feature of eusociality is reproductive division of labor. At the termite colony initiation stage, there are only reproductives plus larvae and eggs that need to be cared for. As workers increase in number with colony development, reproductives are thought to be relieved of the cost of brood care and able to resume reproduction. This transition of responsibility for the care of offspring from parents to their offspring has been considered as a crucial step in the evolution of termite eusociality (trophic shift model). Here, we studied the endogenous cellulase gene expression levels and reproductive characteristics of alates and primary reproductives at 30, 50, 100, and 400 days after colony foundation in the termite Reticulitermes speratus. As a result, when the numbers of workers reached about 100 (400 days), wood digestion abilities of alates and primary reproductives decreased significantly while ovaries and testis were well developed. Moreover, wood digestion abilities of female secondary reproductives with well-developed ovaries, collected in the field colony, were lower than those of any stages of primary queens. These results were consistent with the trophic shift model, and suggested the importance of switch from parental care to alloparental care for reproductive division of labor and evolution of termite eusociality.     

Potential spread of the invasive North American termite, <Emphasis Type="Italic">Reticulitermes flavipes</Emphasis>, 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.     

A novel hypothesis for the origin of the sexual division of labor in termites: which sex should be soldiers?

Sexual specialization and skewed sex ratios of the altruistic castes, especially soldiers, are common in many termite taxa. However, no theoretical or empirical studies have explained the origin of the sexual division of labor in termites. In most termite species, female alates are larger than male alates, and mature queens are much larger than kings, with females under consistent selection for high fertility. Therefore, females usually have the potential to be larger than males. Here, I present a novel preadaptation hypothesis that potential sexual differences in the suitability for the caste give rise to the sexual division of labor, and I provide the first evidence in support of this hypothesis in termites. Defense in Reticulitermes is typically performed by soldiers via mandibular and phragmotic defense in which soldiers with pluglike heads block openings, thus preventing enemies from invading the nest. Phragmotic defense requires that soldiers have heads wide enough to plug nest openings. Therefore, a size threshold for workers that develop into soldiers is a likely adaptation for effective defense. I show that sexual size dimorphism (SSD) and a size threshold for soldiers promote skewed sex ratios. A female-biased soldier sex ratio was observed in species with SSD, whereas there was no bias in soldier sex ratio in species without SSD. Thus, SSD and soldier sex ratio data from several Reticulitermes species support the preadaptation hypothesis.     

Dispersal flight and colony development in the fungus-growing termites <Emphasis Type="Italic">Pseudacanthotermes spiniger</Emphasis> and <Emphasis Type="Italic">P. militaris</Emphasis>

Pseudacanthotermes spiniger and P. militaris are two African fungus-growing termites (Termitidae, Macrotermitinae) which may become pests in disturbed agrosystems where they often live in sympatry. To study their development and their reproductive strategies, colonies of both species were reared in the laboratory for 20 and 17 years, respectively, after their foundation from reproductive pairs. The first steps of development were in great part similar in both species, although P. spiniger favoured the defence during the juvenile period, while P. militaris tended to favour a rapid development. While P. spiniger colonies did not produce alates until year 7 of colony life, P. militaris colonies were able to produce a fertile progeny 4 years after their foundation. In contrast, major soldiers were more rapidly differentiated in the incipient colonies of P. spiniger. Dispersal flights occurred every year for 10 years in P. spiniger. In P. militaris, dispersal flights did not occur regularly although alates appeared yearly. The annual number of alates produced by P. spiniger increased with the colony age to reach a maximum of 25,000 individuals and global production of alates was estimated at ca. 150,000 individuals in the life of a colony. The longevity of P. spiniger and P. militaris colonies was around 20 years. These species were shown to be reproductively isolated by multiple pre-mating mechanisms. While chronological differences in dispersal flights contribute to reproductive isolation of the two species, the non-viability of experimental hybrid colonies also indicates the involvement of post-mating mechanisms of isolation.