Intra- and Inter-colonial Agonistic Behavior in the Termite, Microcerotermes fuscotibialis Sjostedt (Isoptera: Termitidae: Termitinae)

Pairing termite workers from cultures obtained from same colony of Microcerotermes fuscotibialis Sjostedt did not result in agonistic behavior or mortality of the paired individuals. Termite pairings from different colonies located at different distances resulted in serious encounters and aggressive behavior leading to significant mortality of the individuals. Subtle agonistic behavior was observed when colony mates were reunited after months of separation, but this did not result in any significant mortality. These results confirmed observations of non-overlap of foraging trails of these termites in the field which averts possible encounters and conflict. Therefore these termites are able to recognize their colony mates irrespective of period of separation, a factor for colony affiliation, kinship and recognition.     

Agonistic behavior correlated with hydrocarbon phenotypes in dampwood termites,Zootermopsis (Isoptera: Termopsidae)

The dampwood termite genus ZootermopsisEmerson contains three recognized species with four distinct and consistent hydrocarbon phenotypes. Agonistic behaviors among nonreproductive insects from colonies of the same and different hydrocarbon phenotypes were observed in the laboratory. Various combinations of soldier versus nymphs, pseudergate versus pseudergate, and soldier versus soldier encounters were used in experimental trials. Soldiers or pseudergates seldom attack individuals of the same hydrocarbon phenotype. Z. angusticollis(Hagen) (phenotype II) is typically aggressive toward phenotype III of Z. nevadensis(Hagen) but not always aggressive against phenotype I of Z. nevadensis.The variation in response is dependent on which castes are placed in the bioassay arena: soldier versus soldier bouts result in consistent aggression, while pseudergate versus pseudergate or soldier versus nymphs contacts do not. Both pseudergates and soldiers of Z. laticeps(Banks) (phenotype IV) respond agonistically toward the other three phenotypes: Z. angusticollis (II) and Z. nevadensis(I and III). Although hydrocarbon phenotypes I and III, both Z. nevadensis,are morphologically indistinguishable, agonistic behavioral responses between phenotype I and phenotype III are not equivalent to I versus I or III versus III behavioral responses. The I versus III engagements, regardless of the castes involved, display a greater proportion of avoidance and aggressive responses than I or III intraphenotype encounters. We interpret the lack of avoidance or aggressive behavior within each of the two phenotypes of Z. nevadensisand the significant avoidance and aggressive behavior between phenotypes as definite evidence of discrimination between disparate hydrocarbon phenotypes. These agonistic bioassays along with data on distinct hydrocarbon patterns and geographic distributions serve as the basis for creating two subspecies of Z. nevadensis: Z. n. nevadensis(Hagen) and Z. n. nuttingiHaverty and Thorne, ssp. nov.     

Association between caste and genotype in the termite Mastotermes darwiniensis Froggatt (Isoptera: Mastotermitidae)

Abstract Termite workers and soldiers differ markedly in their morphology and behaviour. We sought evidence for genetic influences on caste determination in the giant northern termite, Mastotermes darwiniensis , by investigating if workers and soldiers from the same colony differed genetically. The genotypes of 795 termites from 11 distinct colonies were assayed at six polymorphic microsatellite loci. We found that the multilocus genotypes of workers and soldiers from 8 of the 11 colonies did not differ significantly. Thus, the majority of the data provided no evidence for a genetic association with caste in workers and soldiers of M. darwiniensis . However, the genotype frequencies of workers and soldiers from three colonies differed, suggesting that genotype is occasionally associated with caste in this species. The genetic differentiation of castes within these colonies could reflect differences in the propensities of termites with distinct genotypes to develop into particular castes and provide a selective advantage to colonies headed by multiple reproductives.     

两种鼻白蚁之间的入侵关系

设计了5个实验以研究台湾乳白蚁(Coptotermes formosanus)和黄肢散白蚁(Reticulitermes flavipes)的种间斗争关系。所试白蚁来自阿拉巴马州。实验1将两组白蚁的兵蚁和工蚁以自然比例混合(台湾乳白蚁工蚁：兵蚁＝20：5,黄肢散白蚁工蚁：兵蚁＝24：1);实验2观察了双方同数量(各25头)工蚁的种间斗争能力;实验3观察两者同数量(各5头)兵蚁的种间斗争关系;实验4、5分别研究双方工蚁与兵蚁的斗争关系。因两种工蚁形态相似,所以在实验前用0．1％Nile blue A染过的滤纸饲喂一方白蚁24h使虫体着色以便观察。所有实验在22℃,65％RH荧光灯下进行。每个实验将两方白蚁同时放入一培养皿中,观察至一方100％受伤,然后把培养皿移到培养箱内,24小时后统计死亡率。结果表明,实验一开始,双方的工蚁和兵蚁都立即进入残酷的厮杀斗争,台湾乳白蚁兵蚁和工蚁的斗争能力都明显强于黄肢散白蚁;兵蚁的斗争行为不受工蚁的影响,工蚁的斗争能力也不受兵蚁的制约。实验中台湾乳白蚁的工蚁与黄肢散白蚁的兵蚁攻击能力相当,但黄肢散白蚁的工蚁却远弱于台湾乳白蚁的兵蚁。上述结果说明,自然界中不可能出现此两种白蚁群体的偶然性融合;外来的台湾乳白蚁很可能在其群体建立的地区占据优势[动物学报49(3)：295—302,2003]。     

Skewed soldier sex ratio in termites: testing the size-threshold hypothesis

Social insect colonies contain multiple phenotypes, i.e. castes, and this caste polyphenism is often linked to sexual dimorphism. Unlike social hymenopterans, both termite sexes are diploid and contribute to helper-type tasks within the colony. Nonetheless, a biased sex ratio is frequently observed in termites, especially in soldiers. To explain this bias in soldier sex ratio, Matsuura (Evol. Ecol. 20: 565–574, 2006) postulated the existence of a size threshold for workers molting into soldiers. Under the influence of sexual size dimorphism (SSD), such a threshold was considered to indirectly favor one sex. We conducted a literature survey of sex ratio among termite soldiers and tested this size-threshold hypothesis using data for 67 termite species from a variety of termite lineages. We demonstrated the existence of a size threshold for individuals molting into soldiers, resulting in the acquisition of soldiers of only one sex in species exhibiting strong SSD. In species exhibiting weak SSD, the size threshold skews the sex ratio of soldiers, but does not necessarily cause the loss of one sex. Finally, we observed a prevalence of single-sex soldiers in the Termitidae, regardless of SSD, suggesting that the ancestral developmental mechanisms that constrain soldier differentiation from one sex are maintained in certain extant species.     

Soldier-specific modification of the mandibular motor neurons in termites

Social insects exhibit a variety of caste-specific behavioral tendencies that constitute the basis of division of labor within the colony. In termites, the soldier caste display distinctive defense behaviors, such as aggressively attacking enemies with well-developed mandibles, while the other castes retreat into the colony without exhibiting any aggressive response. It is thus likely that some form of soldier-specific neuronal modification exists in termites. In this study, the authors compared the brain (cerebral ganglion) and the suboesophageal ganglion (SOG) of soldiers and pseudergates (workers) in the damp-wood termite, Hodotermopsis sjostedti. The size of the SOG was significantly larger in soldiers than in pseudergates, but no difference in brain size was apparent between castes. Furthermore, mandibular nerves were thicker in soldiers than in pseudergates. Retrograde staining revealed that the somata sizes of the mandibular motor neurons (MdMNs) in soldiers were more than twice as large as those of pseudergates. The enlargement of MdMNs was also observed in individuals treated with a juvenile hormone analogue (JHA), indicating that MdMNs become enlarged in response to juvenile hormone (JH) action during soldier differentiation. This enlargement is likely to have two functions: a behavioral function in which soldier termites will be able to defend more effectively through relatively faster and stronger mandibular movements, and a developmental function that associates with the development of soldier-specific mandibular muscle morphogenesis in termite head. The soldier-specific enlargement of mandibular motor neurons was observed in all examined species in five termite families that have different mechanisms of defense, suggesting that such neuronal modification was already present in the common ancestor of termites and is significant for soldier function.     

Caste-biased locomotor activities in isolated termites

Eusocial insects are characterized by a well-developed division of labour among castes. Although the successful division of labour should stem from behavioural differentiation depending on caste identity, caste-specific intrinsic behavioural characteristics might be masked by social interactions within colonies. The present study explores caste-specific intrinsic locomotive activities of termites by quantifying them in isolation. We track individual movement trajectories of the damp-wood termite Hodotermopsis sjostedti over 30 min and extract individual locomotion parameters. Multivariate statistical analyses reveal significant differences among castes: soldiers move more actively than workers and neotenic reproductives. The morphometric data of test individuals indicate that locomotor activities reflected caste identity more strongly compared with quantitative morphological variations among individuals. We find that the different locomotor activities of soldiers compared with those of neotenics and workers probably reflect their physiological differentiation. The present study provides a basis for a deeper understanding of the roles of individual locomotor activities in social behaviours.     

黑胸散白蚁补充型生殖蚁的产生及发育的观察

根据翅和翅芽的有无、长短,把分离群体中培养出的黑胸敌散蚁Reticulitermes chinensis Suyder补充生殖蚁命名为翅鳞型、长翅年型、短翅芽型、微翅芽型和无翅型补充生殖蚁.在工蚁、兵蚁、若蚁组成的群体中,分化较复杂,能培养出多种类型的补充生殖蚁,而在工蚁和兵蚁组成的群体中多数只培养出无翅型补充生殖蚁,少数远能培养出微翅型补充生殖蚁.短翅型、微翅型、无翅型补充生殖蚁需要经历一个后熟期才能产卵.此外,还对分离群体产生补充生殖蚁的频率、数量及初期产卵能力进行了观察.     

尖唇散白蚁工蚁、兵蚁和繁殖蚁精子发生的比较研究

为探讨白蚁非生殖品级和生殖品级生殖细胞发育差异,采用组织学染色技术对尖唇散白蚁Reticulitermes aculabialis Tsaiet Hwang繁殖蚁、工蚁和兵蚁的精巢发育以及精子发生进行了显微观察和比较研究。结果发现3个品级间精巢发育的程度差异很大,三者精巢切面面积相对大小之比为:繁殖蚁∶工蚁=1.7∶1;繁殖蚁∶兵蚁=29.3∶1;工蚁∶兵蚁=17.1∶1。繁殖蚁和工蚁精巢管内有精子的形成,工蚁和繁殖蚁精子的发生都经历了精原细胞、初级精母细胞、次级精母细胞、精细胞和精子时期,但工蚁有大量次级精母细胞呈细胞凋亡状态。兵蚁生殖细胞发育仅有精原细胞、初级精母细胞、次级精母细胞,没有精细胞和精子产生。工蚁的生殖细胞显著小于同一时期繁殖蚁的生殖细胞,兵蚁的各时期生殖细胞均极显著小于繁殖蚁同一时期的生殖细胞。研究表明各品级之间生殖功能分化与生殖细胞发育有直接关系,工蚁有转化为补充繁殖蚁和兵蚁的能力;而兵蚁由于精巢极度退化不能产生精细胞和精子,因此是非生殖品级分化的终极形式,不具有转化成补充繁殖蚁或其它品级的能力。     

Endocrine control of cuticular hydrocarbon profiles during worker-to-soldier differentiation in the termite Reticulitermes flavipes

The social organization of termites, unlike that of other social insects, is characterized by a highly plastic caste system. With the exception of the alates, all other individuals in a colony remain at an immature stage of development. Workers in particular remain developmentally flexible; they can switch castes to become soldiers or neotenics. Juvenile hormone (JH) is known to play a key role in turning workers into soldiers. In this study, we analyzed differences in cuticular hydrocarbon (CHC) profiles among castes, paying particular attention to the transition of workers to soldiers, in the subterranean termite species Reticulitermes flavipes. CHCs have a fundamental function in social insects as they serve as cues in inter- and intraspecific recognition. We showed that (1) the CHC profiles of the different castes (workers, soldiers, nymphs and neotenics) are different and (2) when workers were experimentally exposed to a JH analog and thus induced to become soldiers, their CHC profiles were modified before and after the worker-presoldier molt and before and after the presoldier-soldier molt.     

尖唇散白蚁兵蚁和工蚁卵巢和卵子形态特征的比较

兵蚁和工蚁是白蚁中的非生殖品级,兵蚁是由工蚁分化产生。为了探讨兵蚁品级性腺不育的原因以及兵蚁和工蚁性腺发育的差异,采用组织学染色观察与测量方法对尖唇散白蚁Reticulitermes aculabialis Tsai et Hwang的兵蚁和工蚁的卵子发生各阶段进行比较和分析。结果显示:两者性腺发育大小呈极显著性差异(P<0.01),兵蚁与工蚁卵巢横切面面积之比约为1∶7;兵蚁的卵子发生与工蚁相比,仅有卵母细胞的分化期,没有生长期;兵蚁的卵母细胞比工蚁的小,两者的分化期卵母细胞体积之比约为1∶16。该结果表明工蚁向兵蚁转化过程中性腺进一步退化,兵蚁性腺极度退化使其丧失了成为补充繁殖蚁的可能性。该研究结果为兵蚁不能生殖提供组织学上的证据,同时又揭示了兵蚁和工蚁在潜在生殖能力差异方面的组织学基础。     

Comparative Study of the Labial Gland Secretion in Termites (Isoptera)

Labial glands are present in all castes and developmental stages of all termite species. In workers, their secretion contains a food-marking pheromone and digestive enzymes, while soldier secretion plays a defensive role. However, these functions were studied only in a limited set of species, and do not allow drawing general conclusions. Hence, we have investigated the chemical composition of the labial gland extracts from soldiers and workers in 15 termite species belonging to 6 families using an integrative approach based on proteomic and small-molecule profiling. We confirmed the presence of hydroquinone and cellulase in the labial glands of workers, and we identified new toxic compounds in soldiers and workers of several species. Our results highlight the dual role of labial gland secretion, i.e. the defensive role in soldiers and workers of several termite species, and the digestive function in workers.     

八种白蚁的兵蚁和工蚁消化道形态比较研究(等翅目)

为探讨白蚁消化道形态品级差异及其系统学意义,对4个科8种白蚁兵蚁和工蚁的消化道进行比较形态学研究.结果表明:低等白蚁的兵蚁和(拟)工蚁形态较为相似,高等白蚁的兵蚁与工蚁局部特征存在明显差异.由低等到高等兵蚁和工蚁消化道各部分差异呈增多趋势.前、中、后肠占消化道的百分比在山林原白蚁Hodotermopsis sjoest...     

Differences in cellulose digestive systems among castes in two termite lineages

Abstract.  Termites (Isoptera) are eusocial insects and express polyphenism. Soldiers have specialized morphology for colony defense, but their feeding activity is dependent on other colony members. To determine differences in cellulose degradation between soldier and worker termites, enzymatic activity and cellulase gene expression, as well digestive tract histology, are examined in two phylogenetically distant species. In Hodotermopsis sjostesti (family Termopsidae) , endo-β-1,4-glucanase activity is identified in the salivary glands, whereas β-glucosidase activity is identified in salivary glands and hindgut. The relative expression levels of endo-β-1,4-glucanase genes in soldiers are significantly lower than in workers. Thin sections of salivary gland of workers and soldiers are different in H. sjostedti . In Nasutitermes takasagoensis (family Termitidae), the endo-β-1,4-glucanase activity is restricted to the midgut in four tested castes (i.e. three types of workers and soldier). Examination of activity per termite reveals the highest activity in minor workers and the lowest activity in major workers and soldiers. The β-glucosidase activity is also concentrated on the midgut in all four castes. The relative expression level of the endo-β-1,4-glucanase gene does not correspond with its activity in the midgut. In thin sections prepared from N. takasagoensis , the folds and pulvillus in the gizzards, and cuticle structure of soldiers are less developed compared with the other three worker castes. The differences in digestive system among termite castes in terms of caste development in each species are discussed.     

X‐ray computed tomography reveals that intraspecific competition promotes soldier differentiation in a one‐piece nesting termite

Investment in soldier production in eusocial lineages involves a trade‐off between maintenance costs and defense benefits. Termites are eusocial insects that live in colonies organized into three castes: primary reproductives, soldiers, and workers or pseudergates. Neotermes chilensis (Blanchard) (Isoptera: Kalotermitidae) is a one‐piece nesting termite that nests and forages in a single piece of wood. Two scenarios may be of importance in a defense context of one‐piece nesting termites: during swarms, when colonies may be invaded by winged termites (alates) in search of a place to found a new colony, and when colonies of conspecifics are present within the same substrate. It was hypothesized that the ratio of soldiers to non‐soldiers would be higher at the onset of the swarming period and in substrates bearing more than one termite colony. A method based on X‐ray computed tomography (CT) was developed to study gallery connectivity in colonies of N. chilensis and caste composition within colonies. Computed tomography allowed the digital reconstruction of the galleries within the substrate, even when they belonged to different colonies, and was effective in distinguishing termites from substrate, and soldiers from reproductives and pseudergates. Using CT, the ratio of soldiers to non‐soldiers was shown to be highest in colonies within multicolonial scapes (i.e., neighboring colonies were present in the same substrate) during the swarming season, thus supporting our initial hypotheses. These results constitute a unique example of induced defenses arising from intraspecific interactions in termites.     

Cuticular hydrocarbons in a termite: phenotypes and a neighbour–stranger effect

Abstract The composition of cuticular hydrocarbons of different colonies of the fungus-growing termite Macrotermes falciger shows considerable intercolonial variation. Ordination, as well as cluster analyses, separate profiles into three distinct chemical phenotypes. Behavioural tests with major workers reveal no alarm behaviour or mortality in pairings of workers from the same colony but a full range from no alarm to overt aggression, with associated death, when individuals were paired from different colonies. The level of mortality increases with differences in the composition of cuticular hydrocarbons between colonies. However, no mortality occurs in pairings of individuals from neighbouring colonies belonging to different phenotypes. The data thus provide evidence for a 'neighbour–stranger' effect (so-called 'dear-enemy' phenomenon) in termites.     

Alarm Reaction of European Reticulitermes Termites to Soldier Head Capsule Volatiles (Isoptera, Rhinotermitidae)

The alarm behavior of worker and soldier castes of four European subterranean termite species of the genus Reticulitermes (R. santonensis, R. lucifugus, R. grassei, R. banyulensis) is described. In petri dish bioassays we presented filter papers with squashed soldier heads as an odor source to trigger a alarm reaction. Untreated filter papers were used as controls. The behavioral patterns were alike for all four species. In the control situation (no alarm), only occasional workers and few soldiers were seen walking in the petri dish. When the odor source was presented, a general state of alertness was observed, showing as higher activity and presence, zigzag running, antennation of nestmates, jittering and jerking, mandible snapping, head-banging, and attraction to the odor source. Workers were attracted within a few seconds (6.9–13.4 s); soldiers followed much later (18.5–64.6 s). Both workers and soldiers inspected the odor source only briefly (workers for 8.7–12.8 s, soldiers for 10.0–19.5 s), with the exception of R. santonensis, where soldiers stayed an average of 209.8 s. The number of individuals, of 50 workers and 3 soldiers, near the odor source averaged 6.0–9.2 workers and 1.2–2.3 soldiers. The presence of workers is crucial: without workers, a significant alarm reaction in soldiers could not be induced. The roles of soldier and worker castes of Reticulitermes species within alarm communication and the origin and nature of possible alarm signals are discussed.     

Asexual queen succession in the subterranean termite Reticulitermes virginicus

Termite colonies are founded by a pair of primary reproductives. In many species, including subterranean termites (family Rhinotermitidae), the primary king and queen can be succeeded by neotenic reproductives that are produced from workers or nymphs within the colony. It is generally believed that these neotenics inbreed within the colony, sometimes for many generations. Here, we show that primary queens of the North American subterranean termite, Reticulitermes virginicus, are replaced by numerous parthenogenetically produced female neotenics. We collected functional female neotenics from five colonies of R. virginicus in North Carolina and Texas, USA. Genetic analysis at eight microsatellite loci showed that 91-100% of the neotenics present within a colony were homozygous at all loci, indicating that they were produced through automictic parthenogenesis with terminal fusion. In contrast, workers, soldiers and alates were almost exclusively sexually produced by mating between the female neotenics and a single king. This is the second termite species shown to undergo asexual queen succession, a system first described in the Japanese species, Reticulitermes speratus. Thus, the conditional use of sexual and asexual reproduction to produce members of different castes may be widespread within Reticulitermes and possibly other subterranean termites.     

Tradeoffs in the Evolution of Caste and Body Size in the Hyperdiverse Ant Genus Pheidole

The efficient investment of resources is often the route to ecological success, and the adaptability of resource investment may play a critical role in promoting biodiversity. The ants of the “hyperdiverse” genus Pheidole produce two discrete sterile castes, soldiers and minor workers. Within Pheidole, there is tremendous interspecific variation in proportion of soldiers. The causes and correlates of caste ratio variation among species of Pheidole remain enigmatic. Here we test whether a body size threshold model accounts for interspecific variation in caste ratio in Pheidole, such that species with larger body sizes produce relatively fewer soldiers within their colonies. We evaluated the caste ratio of 26 species of Pheidole and found that the body size of workers accounts for interspecific variation in the production of soldiers as we predicted. Twelve species sampled from one forest in Costa Rica yielded the same relationship as found in previously published data from many localities. We conclude that production of soldiers in the most species-rich group of ants is regulated by a body size threshold mechanism, and that the great variation in body size and caste ratio in Pheidole plays a role in niche divergence in this rapidly evolving taxon.