Factors affecting mate choice in the subterranean termite Reticulitermes chinensis (Isoptera: Rhinotermitidae)

Termites are a group of eusocial insects. Mate choice is the most important step which affects the subsequent new colony foundation and development in termites. This study investigated the effects of the four factors on mate choice in the subterranean termite Reticulitermes chinensis Snyder, including colony origin, entry time, physical damage of antennae, and fresh body weights of male dealates. The results showed that the pairing number of dealates from the different colonies was significantly higher than that from the same colonies. The male dealates with early entry time achieved a significantly higher pairing number than the male dealates with late entry time. The male dealates with complete antennae achieved a the significantly higher pairing number than the male dealates lacking the six terminal segments of antennae. Moreover, the heavier male dealates achieved a significantly higher pairing number than the lighter male dealates. However, there were no significant differences in the pairing time for all the experimental treatments. These results suggested that the male dealates, which are heterogenous, healthy, heavy, and more familiar with the environment in R. chinensis, have the obvious advantages in the mate choice. This rule of mate choice is helpful for termites to avoid inbreeding and to maintain the genetic diversity of offspring, which is very important for the environmental adaptability and development of termite colonies.     

Variation in queen size across a behavioral transition zone in the ant Messor pergandei

Summary. Ant colonies should be selected to optimally allocate resources to individual reproductive offspring so as to balance production costs with offspring fitness gains. Different modes of colony founding have different size-dependent fitness functions, and should thus lead to different optimal queen sizes. We tested whether a behavioral transition from solitary colony founding (haplometrosis) to group colony founding (pleometrosis) across the range of the ant Messor pergandei was associated with a difference in queen size or condition. Both winged gynes and founding queens were significantly smaller and lighter at pleometrotic than at haplometrotic sites, with an abrupt shift in these characters across the 8.5 km-wide behavioral transition zone. Both the mutualistic advantages of grouping and among-queen competition within associations are likely to be important in selecting for smaller queen size in pleometrotic populations.Received 16 January 2004; revised 13 August 2004; accepted 16 August 2004.     

The frequency of multi‐queen colonies increases with altitude in a Nearctic ant

1. Most ants in boreal and alpine habitats are facultatively polygynous, i.e. their colonies may contain one or several queens. It was investigated how the proportion of polygynous colonies varies along an elevation gradient from 60 to 2700 m in the Nearctic ant Temnothorax rugatulus (Emery). 2. Across all populations, the proportion of polygynous colonies was positively correlated with altitude. The correlation was considerably stronger when only populations in the narrow area of the Chiricahua Mts, Arizona, were compared. 3. The dominance of polygynous colonies at high altitudes may be associated with selection against solitary colony founding by young queens. In areas with short summers and long winters, hibernation mortality of solitarily founding queens may select for alternative reproductive tactics, such as polygyny and colony founding by budding. 4. Colony founding tactics need to be taken into account to more fully understand altitudinal and latitudinal patterns of ant faunas.     

Queen phenotype and behaviour during cooperative colony founding in Polyrhachis moesta

Summary. Founding queens of the arboreal ant Polyrhachis moesta aggregate independently of kinship and cooperate in caring for their brood. In field studies, the number of queens in a founding nest varied from 1 to 8. The number of queens in the nests with multiple queens decreased significantly with time after the nuptial flight, resulting in monogynous or oligogynous nests. Single- and multiple-founding queens did not differ in characteristics representing nutritional states or body size immediately after the nuptial flight. Wet body weight decreased as days passed, whereas head width of founding queens who overwintered successfully were relatively larger. In laboratory studies, founding queens performed liquid food exchanges more frequently with queens from other founding nests or immature colonies than with those from the same nests. Queens in founding nests and immature colonies were observed to show no aggression against non-nestmate queens, whereas queens in established colonies showed aggressive behaviours against non-nestmates. This indicates that founding queens change drastically in their aggression levels before and after colony establishment. Multiple-founding queens started laying eggs earlier than single-founding queens under laboratory conditions. Higher brood productivity and lower brood mortality were observed in multiple-queen nests. These potential advantages in multiple-queen founding may support the cooperative association among unrelated founding queens.Received 1 December 2003; revised 25 March and 20 May 2004; accepted 3 June 2004.     

Colony pollen reserves affect body size,sperm production and sexual development in males of the stingless bee <Emphasis Type="Italic">Melipona beecheii</Emphasis>

The production of male sexual offspring by social insect colonies is often strongly seasonal or resource-dependent. In stingless bees, males are produced in smaller numbers under conditions of low colony food reserves; whether such males are negatively affected in traits related to reproductive success is not known. We compared body size, sperm production and sexual maturity in Melipona beecheii males reared with experimentally supplemented or reduced pollen reserves, but with otherwise equal numbers of workers and equal quantities of honey reserves. We also studied the same traits in males collected from non-manipulated colonies with pollen reserves intermediate between the supplemented or reduced groups but with more workers and honey reserves. Males reared under experimentally reduced pollen reserves had significantly smaller bodies and lower sperm counts compared to those reared in colonies with experimentally supplemented pollen reserves. There was also a significantly positive relationship between the number of sperm and body size in males across all colony treatments. The maximum number of sperm in seminal vesicles was recorded 2 days later in males from colonies with reduced pollen compared to males from colonies with supplementary pollen. Males from non-manipulated colonies were intermediate in size, sperm count and speed of maturation. Our study documents for the first time the existence of large size variation in males of stingless bees that is related with the amount of pollen reserves in their natal colony. We conclude that a colony’s pollen reserves have a major impact on male body size, sperm production and speed of sexual maturity in this stingless bee, which may be the case in other social insects. Stingless bees are a good model system to study the balance between colony-level selection and individual-level selection on male sexually selected traits such as body size.     

A shift in colony founding behaviour in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2

Summary. A shift in colony founding behaviour from single queen (haplometrosis) to multiple queens (pleometrosis) was observed locally in the obligate plant-ant Crematogaster (Decacrema) morphospecies 2, which is associated with Macaranga trees in Borneo. In addition, about a quarter of all mature colonies (27 of 95 trees examined) were found to be multiple queen colonies. They arose either directly from pleometrotic founding colonies or secondarily by adoption of additional queens. Using microsatellite markers, we showed that queens in colonies founded through pleometrosis are unrelated and each queen participates in producing worker offspring, albeit with significant skew in a third of the colonies. In mature polygynous colonies, all resident queens contributed to the production of workers and sexual offspring. Relatedness of queens in mature polygynous colonies was not significantly higher than in foundress associations. We hypothesize that increased nest site limitation in this specific interaction trigger the observed shift in colony founding behaviour. Crematogaster msp. 2 inhabits the light demanding pioneer plant species Macaranga pearsonii that is typical for early successional stages of secondary forests. Thus suitable host-plants for colonisation are abundant for only a short time in highly disturbed sites and become increasingly sparse when secondary forest matures.Received 6 September 2004; revised 29 November; accepted 10 December 2004.     

Variable worker behaviour in the weakly eusocial sweat bee, <Emphasis Type="Italic">Halictus sexcinctus</Emphasis> Fabricius

Summary Studies of eusocial halictines suggest that workers have many reproductive options, including sterile altruism in the maternal nest, combined helping and personal reproduction, and diapause and spring nest founding. How and when workers exercise these various options influences the strength of colony social organization. Halictus sexcinctus exhibits highly polymorphic social behaviour, with solitary colonies in central Europe and both eusocial and communal colonies in southern Greece. Indirect evidence suggests that some worker-brood females are actually gynes. A distinctly bimodal size distribution among foundresses in 1998, the lower size peak being close to the modal body size of workers from 1997, suggests that large worker-brood females overwinter and return to the aggregation as eusocial foundresses. Other first-brood females remain in the maternal nest as workers, although few can be classified as classical, sterile altruists. Only 17% of older, healthy workers are sterile (i.e. had ovarian development scores 0.1), whereas about 83% are reproductive, exhibiting at least one 1/4-developed oocyte. About 57% of older workers have at least one fully or 3/4 developed oocyte, signifying that they are ready or almost ready to lay. Sterile workers exhibit greater total wear (combined mandibular and wing wear) scores than reproductive workers, suggesting that they are older, have higher activity rates, or both.     

Female body size, fecundity parameters and foundation of new colonies in Anelosimus jabaquara (Araneae, Theridiidae)

Summary. As in other social spider species, subadult Anelosimus jabaquara females found new colonies after solitary dispersal. Some individuals, however, usually remain and reproduce in their natal nests. To test the hypothesis that large females disperse more often than smaller ones, we compared the body size of A. jabaquara females that remained in their natal colonies with those that left to build solitary webs. We also compared clutch size, egg diameter, total egg volume and spiderling size in both conditions. Emigrating females were significantly larger and laid larger clutches. The smaller females that had not dispersed laid significantly larger eggs, although their total egg volume was lower. Spiderlings of solitary females were smaller and had a smaller range of size variation than those from colonies. We discuss the implications of these results in terms of costs and benefits of dispersion for spiders in different nutritional conditions.     

Ontogeny of worker body size distribution in bumble bee (Bombus impatiens) colonies

1. Bumble bees exhibit worker size polymorphisms; highly related workers within a colony may vary up to 10‐fold in body mass. As size variation is an important life history feature in bumble bees, the distribution of body sizes within the colony and how it fluctuates over the colony cycle were analysed. 2. Ten commercially purchased colonies of Bombus impatiens (Cresson) were reared in ad libitum conditions. The size of all workers present and newly emerging workers (callows) was recorded each week. 3. The average size of bumble bee workers did not change with colony age, but variation in body size tended to decrease over time. The average size of callows did not change with population size, but did tend to decrease with colony age. In all measures, there was considerable variation among colonies. 4. Colonies of B. impatiens usually produced workers with normally distributed body sizes throughout the colony life cycle. Unlike most polymorphic ants, there was no increase in worker body size with colony age or colony size. This provides the first, quantitative data on the ontogeny of bumble bee worker size distribution. The potential adaptive significance of this size variation is discussed.     

Independent colony founding by ergatoid queens in the ant genus Pogonomyrmex: queen foraging provides an alternative to dependent colony founding

Ant queens exhibit two primary strategies to initiate nests, independent colony founding (ICF) by solitary queens and dependent colony founding (DCF) when the queen starts a nest with a group of workers that disperse on foot from the parent nest. Numerous ant species have wingless (ergatoid) queens, and it is generally assumed that these species exhibit obligate DCF because their lack of wing musculature provides them with few resources to divert towards producing their first brood of workers. Thus, ICF by ergatoid queens is viewed as maladaptive because these queens need to take additional dangerous foraging trips to garner sufficient food to rear their first brood of workers. Contrary to this prediction, I document ICF by ergatoid queens for three species of harvester ants in the genus Pogonomyrmex (subfamily Myrmicinae), P. cunicularius cunicularius, P. cunicularius pencosensis, and P. huachucanus. Queens of P. huachucanus were obligate foragers, i.e., no minim workers could be produced without external food, and one queen of P. cunicularius pencosensis was observed foraging in the field. Abundant and/or predictable food resources likely select for the evolution of semi-claustral nest founding and ICF by these ergatoid queens. Under these conditions, foraging time would be minimized and the number and size of minim workers would be maximized. These benefits should increase founding success, which could compensate for loss of long-range dispersal. Overall, this study demonstrates that care should be taken before concluding that ant colonies employ DCF based solely on queen morphology.     

Costs and benefits of joint colony founding in Australian Acacia thrips

Facultative joint colony founding by social insects (pleometrosis) provides an outstanding opportunity to analyze the costs and benefits of sociality. Pleometrosis has been documented for a range of social insects, but most studies on the adaptive benefits of this behavior are restricted to the Hymenoptera. In this study, we provide the first analysis of costs and benefits associated with pleometrosis for Australian Dunatothrips, which form domiciles by glueing together phyllodes (leaves) of their Acacia host plant. In Dunatothrips aneurae, the distribution of foundress numbers per nest indicated that females formed associations non-randomly. Furthermore, average group size was independent of both the number of foundresses on the host plant and the number of mature colonies, suggesting that this behavior was not simply a response to limited availability of nesting sites. Although per capita reproduction declined with increasing group size, we also identified two benefits of pleometrosis: (1) individual foundresses in groups had higher survival than solitary foundresses during the brood development period, and (2) larger colony sizes resulting from pleometrosis provided a benefit later in colony development, because a higher proportion of D. aneurae adults survived invasions by the kleptoparasite Xaniothrips mulga when colony size was larger. These results demonstrate that the reproductive costs of pleometrosis are at least partially counterbalanced by survival benefits. Received 4 April 2006; revised 9 September 2006; accepted 20 September 2006.     

The period of sexual maturation and the age at mating in Iridomyrmex humilis, an ant with intranidal mating

The process of sexual maturation was studied in the ant Iridomyrmex humilis. Spermatogenesis starts during the pupal stage and sperm is transferred to the seminal vesicles during the first four days after emergence. The testes start to degenerate early in the pupal stage and totally shrivel up during the first days after emergence. Males therefore have a fixed amount of sperm. Both males and females reach sexual maturity only 2–3 days after emergence; some of them mate as early as the first day after emergence. Overall, it appears that the length of time needed to reach sexual maturity in ants is highly correlated with the mode of colony founding. The maturation period is much longer in those species in which young queens initiate colonies without the help of workers (independent founding) than in those where young queens need the help of workers (dependent founding). This is probably associated with the fact that independent founding queens require large amounts of energy reserves in order to found colonies; these energy reserves are accumulated after emergence. In contrast, dependent founding queens do not accumulate as many energy reserves and are therefore sexually receptive at a younger age.     

A trade-off between number and size within the first workers of the ant Camponotus japonicus

In social insects, the limited amount of resources during the claustral founding predicts a trade-off between the number and size of the first-generation of workers. Here, we demonstrate this predicted trade-off in founding colonies of the ant Camponotus japonicus. Worker size was found to correlate negatively with the number of first workers produced when the amount of investment was controlled. Both size and number of the first generation of workers increased when a queen invested more resources. We also examined how a queen adjusts the size and number of the first workers depending on her condition.     

Rates of brood development in a social wasp: effects of colony size and parasite infection

Summary Colonies of eusocial insect species are most vulnerable during the founding stage. Many species have evolved means to minimize the length of the founding, or pre-emergence, stage by accelerating the rate of development of the first worker offspring. Other things being equal, the sooner a colony can begin producing workers, the less the risk of colony failure, the steeper the growth curve of the colony during the ergonomic stage, and the larger the colony will be at reproductive maturity. Swarm-founding species, whose founding units consist of hundreds or thousands of workers, may face less selection pressure to minimize the duration of the founding stage than independent-founding species. However, swarm size varies within species, and small swarms face greater risk of extinction during the founding stage than large swarms. This consideration predicts that within a species, small swarms should have shorter founding stages than large swarms, likely by rearing a small group of precocious brood. On the other hand, evidence that large social groups organize colony labor more efficiently, gather resources more predictably, and homeostatically maintain physical conditions inside the nest within narrower ranges, predicts that larger groups should rear all brood more rapidly and therefore have shorter founding stages. To test whether small or large swarms have shorter founding stages in colonies of Polybia occidentalis, a Neotropical swarm-founding wasp, we measured brood development rates in colonies collected after 28 days of development, just short of the minimum egg-to-adult development time. We found that as size increased across colonies, pre-emergence times decreased, mean age of pupae in the nest increased, and median age of the brood (larvae + pupae) increased. That is, brood developed significantly faster in large colonies than in small ones. Using these same measures, we also found that infection by a gregarine parasite increased brood development time, independently of colony size.Received 10 April 2003; revised 29 October 2003; accepted 21 November 2003.     

Morphometry of the sexual forms of Acromyrmex subterraneus brunneus Forel, 1911 (Hym., Formicidae) in queenright and queenless laboratory colonies

Abstract:  A morphometric study was performed on the sexual forms of Acromyrmex subterraneus brunneus in colonies kept under laboratory conditions. The males studied were obtained from queenright and queenless colonies, i.e. they were produced by either the queen or the workers. Cluster analysis revealed a wide distribution in the size of the sexual forms produced in queenless colonies compared with queenright colonies, and that some of the worker-produced males were significantly smaller than those produced in queenright colonies. However, we found no indication that the males produced in queenless colonies are unable to mate, as smaller and larger males had identical genitalia that varied only in size, and therefore probably represent an alternative route of reproduction in this species.     

Termite colony ontogeny: a long-term assessment of reproductive lifespan, caste ratios and colony size in Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Thirty Reticulitermes flavipes (Kollar) colonies established by alates collected from two separate field sites were raised in the laboratory for eight years. Twenty-one of the colonies were founded by alates from one field source and nine from another, providing demographic data from two unrelated parental lineages. Colony totals ranged from 3620 to 11641 individuals, with no significant difference in size between lineages. Soldier caste proportion of the colony total and mean wet weights for workers, soldiers and kings were significantly different between the two lineages. This suggests that at least a portion of the variability observed in caste ratios and body size may be heritable. One founding reproductive had died in five of the colonies (17%); none lost both parents. The queenless colonies contained exclusively female replacement reproductives (neotenics); the kingless colony contained a female-skewed mixture of male and female neotenics. All the nests that lost a founding parent contained significantly more pre-alate nymphs than the nests with both a king and a queen. Comparisons with published reports of ontogenetic patterns in other termites and social insects are discussed.     

Three queen morphs with alternative nest-founding behaviors in the ant, Temnothorax longispinosus

In many ant species, multiple modes of founding new colonies occur in the same population. These modes include dependent founding, independent founding by haplometrosis (single queen), and independent founding by pleometrosis (multiple queens). In several cases, a dimorphism in queen size has been found, such that each morph specializes in a particular nest-founding behavior. I investigated queen size in the ant Temnothorax longispinosus in several southern Wisconsin populations and found three distinct queen morphs: small queens with very low fat content and short wings, large queens with low fat and long wings, and large queens with high fat and very long wings. Several traits associated with founding behavior correlated with these queen sizes. Small queens were produced in lower numbers, were more common in polygynous nests, and returned to the nest in higher proportions than both large queen morphs. The size ranges and fat levels of each queen morph were similar to those of other species that specialize in either haplometrosis (very large, high fat), pleometrosis (large, low fat), or dependent founding (small and low fat). However, there was extensive overlap in several of the founding behaviors, suggesting that the morphs in these populations have some flexibility in founding behavior. The queen morphs in these populations of T. longispinosus may resemble early stages in the evolution of more specialized dispersal polymorphisms found in other ant species. Received 11 January 2006; revised 15 September 2006; accepted 18 September 2006.     

Effects of colony size on larval performance in a processionary moth

1. Some lepidopteran species have larvae that live gregariously, especially in early instars. Colony‐living species may benefit from improved protection from predators, thermoregulation, and feeding facilitation, for example. 2. While many studies have compared solitary and gregarious life styles, few data exist as to the relationship between size of the larval colony and larval performance in gregarious species. The present study was aimed at understanding the importance of colony size for growth and survival of the northern pine processionary moth (Thaumetopoea pinivora) larvae. 3. Field studies, comparing three different sizes of colonies of T. pinivora larvae, showed that individuals in larger colonies had a higher survival rate compared with those living in smaller colonies and also a faster growth rate. 4. The higher survival rate of large colonies was attributed to improved protection from predacious arthropods. 5. In early spring, the young larvae bask in the sun to increase their body temperature. In field experiments the thermal gain was higher in large colonies, and individuals in such colonies also grew faster. As growth rate was not affected by colony size when the ability to bask was experimentally removed in a laboratory experiment, the higher growth rate of the larger colonies was probably due to improved thermoregulation rather than feeding facilitation. 6. The size of larval colonies of gregarious insects depends on natural mortality events as well as on female oviposition strategy. Our results show that decreasing colony size can lead to a reduction in growth rate and survival. It is therefore important to understand whether or not small colonies will benefit equally from the gregarious behaviour.     

Does the mode of transmission between hosts affect the host choice strategies of parasites? Implications from a field study on bat fly and wing mite infestation of Bechstein's bats

In a two-year field study, we analyzed the distribution of two hematophagous ectoparasites, the bat fly Basilia nana and the wing mite Spinturnix bechsteini , within and among 14 female colonies and among 26 solitary male Bechstein's bats Myotis bechsteinii . Our goal was to investigate whether differences in the transmission mode of the parasites, which result from differences in their life cycle, affect their distribution between host colonies and among host individuals within colonies. Bat flies deposit puparia in bat roosts, allowing for the transmission of hatched flies via successively shared roosts, independent of body contact between hosts or of hosts occupying a roost at the same time. In contrast, wing mites stay on the bat's body and are transmitted exclusively by contact of bats that roost together. As expected in cases of higher inter-colony transmissibility, bat flies were more prevalent among the demographically isolated Bechstein's bat colonies and among solitary male bats, as compared to wing mites. Moreover, the prevalence and density of wing mites, but not of bat flies, was positively correlated with colony size, as expected in cases of low inter-colony transmissibility. Within colonies, bat flies showed higher abundance on host individuals in good body condition, which are likely to have high nutritional status and strong immunity. Wing mites showed higher abundance on hosts in medium body condition and on reproductive females and juveniles, which are likely to have relatively weak immunity. We suggest that the observed infestation patterns within host colonies reflect different host choice strategies of bat flies and wing mites, which may result from differences in their inter-colony transmissibility. Our data also indicate that infestation with wing mites, but not with bat flies, might be a cost of sociality in Bechstein's bats.     

The worldwide expansion of the Argentine ant

Aim The aim of this study was to determine the number of successful establishments of the invasive Argentine ant outside native range and to see whether introduced supercolonies have resulted from single or multiple introductions. We also compared the genetic diversity of native versus introduced supercolonies to assess the size of the propagules (i.e. the number of founding individuals) at the origin of the introduced supercolonies. Location Global. Methods We used mitochondrial DNA (mtDNA) markers and microsatellite loci to study 39 supercolonies of the Argentine ant Linepithema humile covering both the native (n = 25) and introduced range (n = 14). Results Data from three mitochondrial genes and 13 nuclear microsatellites suggest that the introduced supercolonies studied originated from at least seven founding events out of the native area in Argentina (primary introductions). The distribution of mtDNA haplotypes also suggests that supercolonies in the introduced range each derive from a single source supercolony and that one of these source supercolonies has been particularly successful, being the basis of many introduced populations spread across the world. Comparison of the genetic diversity of supercolonies based on the five most diverse loci also revealed that native and introduced supercolonies have greatly overlapping ranges of diversity, although the genetic diversity is on average less in introduced than in native supercolonies. Main conclusions Both primary introductions (from the native range) and secondary introductions (from sites with established invasive supercolonies) were important in the global expansion of the Argentine ant. In combination with the similar social organization of colonies in the native and introduced range, this indicates that invasiveness did not evolve recently as a unique and historically contingent event (e.g. reduction of genetic diversity) in this species. Rather, native L. humile supercolonies have characteristics that make them pre‐adapted to invade new – and in particular disturbed – habitats when given the opportunity. These results have important implications with regard to possible strategies to be used to control invasive ants.