Male soldier caste larvae are non-aggressive in the polyembryonic wasp Copidosoma floridanum

Polyembryonic wasps are the only parasitoids in which sociality has evolved. Theory implicates both competition and sex ratio manipulation in the evolution of a sterile soldier caste. However, investment in soldiers by males and females is predicted to differ depending upon how offspring are allocated to hosts and the mating system. Here, we compared male and female soldiers in the polyembryonic wasp Copidosoma floridanum. We found that male and female soldiers are morphologically identical. Unlike females, however, male soldiers were non-aggressive towards all competitors. We discuss these results in relation to theory and polyembryonic wasp biology.     

Phenotypically plastic traits regulate caste formation and soldier function in polyembryonic wasps

Polyembryonic encyrtid wasps are parasitoids that have evolved a clonal form of embryogenesis and a caste system where some progeny become reproducing wasps whereas others develop into a sterile soldier caste. Theory based on the biology of Copidosoma floridanum predicts that the primary role of soldier larvae is to mediate conflict over sex ratio, which also favours female‐biased soldier production. Other data, however, suggest that female‐biased soldier production reflects a developmental constraint. Here, we assessed whether female‐biased soldier function by polyembryonic wasps reflects sex‐specific adaptation or constraint by conducting comparative studies with Copidosoma bakeri, a species that produces clutch sizes similar to C. floridanum yet rarely produces broods associated with sex ratio conflict. Our results indicate that the oviposition behaviour of adults, development of progeny and function of soldier larvae differ greatly between C. bakeri and C. floridanum. These findings indicate that caste formation and soldier function in polyembryonic encyrtid wasps are regulated by phenotypically plastic traits. Our results further suggest that the primary function of the soldier caste in some species is defence of host resources from competitors whereas in others it is the resolution of sex ratio conflict.     

Higher aggression towards closer relatives by soldier larvae in a polyembryonic wasp

In the polyembryonic wasp Copidosoma floridanum, females commonly lay one male and one female egg in a lepidopteran host. Both sexes proliferate clonally within the growing host larva. Distinct larval castes develop from each wasp egg, the majority being ‘reproductives’ plus some ‘soldiers’ which sacrifice reproduction and attack competitors. Maturing mixed sex broods are usually female biased, as expected when intra-brood mating is common. Pre-mating dispersal followed by outbreeding is expected to increase sexual conflict over brood sex ratios and result in greater soldier attack rates. Owing to sexually asymmetric relatedness, intra-brood conflicts are expected to be resolved primarily via female soldier attack. We observed soldier behaviour in vitro to test whether lower intra-brood relatedness (siblings from either within-strain or between-strain crosses were presented) increased inter-sexual aggression by female as well as male soldiers. As found in prior studies, females were more aggressive than males but, contrary to expectations and previous empirical observations, soldiers of both sexes showed more aggression towards more closely related embryos. We speculate that lower intra-brood relatedness indicates maternal outbreeding and may suggest a rarity of mating opportunities for reproductives maturing from the current brood, which may enhance the value of opposite sex brood-mates, or that higher aggression towards relatives may be a side-effect of mechanisms to discriminate heterospecific competitors.     

Evolution of eusociality and the soldier caste in termites: a validation of the intrinsic benefit hypothesis

In termites the evolution of reproductive altruism is not based on a particularly high relatedness between nestmates. For the evolution and maintenance of the ancestral sterile soldier caste, the benefits generated by the soldiers' presence must compensate the loss of the soldiers' reproductive potential. To study the impact of soldiers on colony's fitness, we manipulated the proportion of soldiers to nonsoldiers in colonies of the dry-wood termite Cryptotermes secundus.'Soldier-less' colonies were obtained by removing soldiers and inhibiting their development with an extract of soldier heads. The colonies were set up for 1 year in experimental nests in the field. 'Soldier-less' colonies produced fewer soldiers. The reduction of soldiers neither affected colony survival nor helper growth, but fewer dispersing sexuals were produced in 'soldier-less' than in control colonies. This confirms what was only supposed so far, that in termites soldiers are maintained for their intrinsic benefit to cost ratio.     

Effect of juvenile hormone on the embryogenesis of a polyembryonic wasp,copidosoma floridanum,in vitro

Summary Single two-cell-stage embryos of a polyembryonic waspCopidosoma floridanum cultured in 20 μl droplets of culture medium developed to morulae at the same developmental rate as those in host eggs, but the subsequent development into polymorulae was inferior. This inferior development was markedly improved by addition of juvenile hormone (I, II, or III) or its analogues to the culture medium in a concentration-dependent manner.     

A case for a free-running circannual rhythm in soldier developmental time of Formosan subterranean termites

The success of all insect societies relies on their ability to maintain optimal levels of different castes. Here we report on an apparent free-running circannual rhythm that optimizes the developmental time of the soldier caste of Coptotermes formosanus Shiraki. Over a 3 year period, bioassays were conducted each month (except June) with groups of 100 termite workers in a 28°C incubator in total darkness. The number of days needed for C. formosanus soldiers to develop varied depending on the time of the year (month). In March, just prior to the major swarming exodus for alates (April to June), 9 days were required before a worker molted to a presoldier. Longer times were required for such a molt in all other months, with an increasing trend from April to December (from 13 to 30 days) and a decreasing trend from January to February (from 25 to 12 days). Colony origin or the length of time that termites were kept in the laboratory under constant conditions (26 – 28°C, 70 – 80% RH) before testing (7 days – 1 year) did not affect this rhythm. This is the first demonstrated evidence of a free-running circannual rhythm in a social insect. Received 23 July 2007; revised 9 and 21 August 2007; accepted 23 August 2007.     

Interspecific competition between the polyembryonic wasp Copidosoma floridanum and the gregarious endoparasitoid Glyptapanteles pallipes

We examined interspecific competition between the egg-larval polyembryonic parasitoid Copidosoma floridanum (Hymenoptera: Encyrtidae) and the gregarious larval endoparasitoid Glyptapanteles pallipes (Hymenoptera: Braconidae). Approximately 72% of multiparasitized Acanthoplusia agnata (Lepidoptera: Noctuidae) produced C. floridanum adults, 14% produced G. pallipes adults, and 14% died without producing any parasitoids. Development was delayed and the rate of weight gain was reduced in multiparasitized hosts that produced C. floridanum compared with singly-parasitized hosts. In contrast, only weight was reduced in multiparasitized hosts that produced G. pallipes adults. Compared with single parasitism, the brood size of wasps emerging from multiparasitized hosts was reduced in both species. The percentage of hosts containing precocious larvae of C. floridanum, which are considered to be soldiers, did not increase in response to parasitization by G. pallipes. However, developmental cessation and death of G. pallipes eggs and larvae may be closely related to the number of coexisting precocious larvae.     

Entomophthora lampyridarum,a fungal pathogen of the soldier beetle,Chauliognathus pennsylvanicus

In 1974 and 1979 in Clemson, South Carolina, adults of the common soldier beetle, Chauliognathus pennsylvanicus, were found to be infected by the fungal pathogen, Entomophthora lampyridarum. After infected beetles died they remained attached by their mandibles to foliage and flowers. The wings of infected beetles remained open, allowing conidiophores to develop on the upper surface of the abdomen. Primary conidia were elongate and measured 36.5 × 17.1 μm. Two types of secondary spores were formed: Type I spores were similar in form to primary conidia, but were somewhat smaller; Type II spores were formed at the apex of slender stalks and measured 37.7 × 15.3 μm. Resting spores were spherical, hyaline, and 22.3 μm in diameter.     

黑水虻幼虫和预蛹的饲料价值研究进展

黑水虻Hermetia illucens L.是一种全世界广泛分布的资源昆虫,幼虫在自然界以动物粪便、腐烂的有机物,如腐肉、腐烂的水果、蔬菜和植物性垃圾为食,能够被用于畜禽粪便的无害化处理。黑水虻幼虫在将粪便转化成昆虫生物量的同时,减少了粪便的污染。利用畜禽粪便饲养的黑水虻幼虫干重达到42%～43%,其中粗蛋白含量占干重的42%～44%,脂肪含量占干重的31%～35%,灰份占干重的11%～15%,钙质占干重的4.8%～5.1%,磷占干重的0.60%～0.63%。使用粪便饲养的幼虫和预蛹,含有丰富的必需氨基酸和矿物质,是家禽、家畜和鱼类养殖的良好饲料来源。文章综述利用不同动物粪便饲养的黑水虻幼虫和预蛹的饲料价值及其幼虫和预蛹用于鸡、猪和鱼类饲料添加剂的研究进展。     

Morphology and gonad development of normal soldiers and reproductive soldiers of the termite Zootermopsis nevadensis nevadensis (Isoptera, Archotermopsidae)

Reproductive or neotenic soldiers of the Archotermopsid Zootermopsis nevadensisnevadensis (Hagen) are compared to sterile soldiers and primary male reproductives. Several head capsule morphometrics correlate significantly with gonad size across all forms and both sexes of soldiers. The easily observed field character of ratio of mandible length to labrum length is a consistent and reliable feature of head capsule external morphology for predicting gonad development and reproductive potential of soldier forms regardless of age, sex, or live weight.     

Fitness consequences of ovicide in a parasitoid wasp

Ovicide, superparasitism and host rejection are alternative reproductive tactics facing female parasitoid wasps encountering an already-parasitized host. Superparasitism is simply the addition of an egg or a clutch of eggs by the secondary parasitoid, but under ovicide the primary clutch is removed or destroyed. Host rejection occurs if the wasp leaves without laying a clutch. The ectoparasitoid Laelius pedatus (Say) (Hymenoptera: Bethylidae) performs ovicide in this situation. Clutch manipulation experiments show that secondary clutches suffer high mortality in competition with primary clutches, which increases with increasing time delay between clutches. Primary clutches however suffer little in competition with secondary clutches, even if there is minimal time delay between clutches. These data suggest that the offspring of ovicidal females are substantially fitter than the offspring of superparasitizing females. Handling time and clutch size do not differ significantly between first (sole) parasitoids and second (ovicidal) parasitoids. The same is true for offspring survival and development time. However, offspring of second females are slightly smaller. This suggests that parasitized and unparasitized hosts are resources of similar quality when ovicide is performed. These data strongly support the predictions of evolutionary models of ovicide. They may also give some insight into the taxonomic distribution of ovicide in parasitoids.     

Sperm mobility determines the outcome of sperm competition in the domestic fowl

The aim of this study was to establish whether the mobility of sperm of the domestic fowl, as measured by an in vitro assay, predicted the outcome of sperm competition. Thirteen pairs of New Hampshire roosters, comprising one male categorized as having high-mobility sperm and the other as having average-mobility sperm, were used. Each male provided 25 x 10(6) sperm, which were mixed and artificially inseminated into between four and seven New Hampshire hens, each of which produced 2-11 offspring. The experiment was conducted twice, such that the same pair of males inseminated the same females. Paternity was assigned by using microsatellite markers. There was a clear effect of sperm-mobility phenotype on the outcome of sperm competition: in all 13 pairs the high-mobility male fathered the majority of offspring (75.3% overall; p < 0.0001). The proportion of offspring fathered by the high-mobility male within pairs varied significantly between male pairs (p < 0.0005). This effect was associated with the difference in sperm-mobility scores between males within pairs; there was a significant positive relationship between the proportion of offspring fathered by the high-mobility male and the ratio of mobility scores between males (p < 0.05). In addition, compared with their success predicted from the non-competitive situation, in the competitive situation high-mobility males were disproportionately successful in fertilizing eggs compared with average-mobility males. This may occur because female sperm storage is limited in some way and a greater proportion of high-mobility sperm gain access to the female's sperm storage tubules. There was no evidence that female effects accounted for any of the variation in paternity.     

Seasonal extension of the soldier instar as a route to increased defence investment in the social aphid Pemphigus spyrothecae

Abstract.  1. The possibility that the duration of the soldier instar could be extended over the course of the galling season was examined in Pemphigus spyrothecae Passerini (Hemiptera: Aphididae). In this species, the individuals of one morph of the dimorphic first instar are non-sterile specialised defenders known as soldiers.
2. In the face of a declining birth rate, the proportion of first-instar soldiers to first-instar non-soldiers was found to increase. This provides strong evidence of extension of the soldier instar over time.
3. Instar extension provides a mechanism for post-natal investment in soldiers and allows individuals with insufficient time to mature to remain in the defensive stage so that they may continue to make an indirect contribution to their clone's reproductive success.     

Sex-ratios of the wasp Nasonia vitripennis from self-versus conspecifically-parasitized hosts: local mate competition versus host quality models

Sex ratio patterns in the parasitoid wasp Nasonia vitripennis are frequently cited in support of a major group of evolutionary sex ratio models referred to as local mate competition (LMC) models. It has been shown repeatedly that, as predicted by LMC models, females generally oviposit a greater proportion of sons in previously parasitized hosts than in unparasitized hosts. However, this sex ratio pattern is also a prediction of another group of sex ratio models, the host quality models. Here I test a prediction of LMC models that is not also a prediction of host quality models: a female should produce a greater proportion of sons when she parasitizes a host previously parasitized by a conspecific female than when she parasitizes a host previously parasitized by herself. Females made this predicted distinction between self- and conspecifically-parasitized hosts under some conditions. There was no evidence that a female recognizes a self-parasitized host when her exposure to the host is interrupted by exposure to an unparasitized host, or that a female can distinguish between hosts parasitized by sisters versus nonsisters.     

Soldier caste with morphological and reproductive division in the aphid tribe Nipponaphidini

Summary. We investigated demographic, morphological and histological aspects of Distylaphis foliorum, a gall-forming nipponaphidine aphid from Java, Indonesia, whose first instar nymphs had been reported to have enlarged forelegs and attack other insects. The gall inhabitants of D. foliorum consisted of two discrete populations; one developing normally and the other remaining at the first instar. Morphometric analysis identified two types of first instar nymphs; nymphs with relatively long forelegs and slender abdomen, and nymphs with relatively short forelegs and fat abdomen. The former nymphs were found from both young galls and mature galls, while the latter nymphs were from young galls only. Histological analysis strongly suggested a reproductive division in the first instar. In the former nymphs from mature galls, ovaries and mycetomes were degenerate and replaced by well-developed fat body cells. These results indicated that D. foliorum has a morphologically differentiated sterile soldier caste in the first instar. This study is the first report of a soldier caste with morphological and reproductive division in the aphid tribe Nipponaphidini, and suggests that highly specialized soldier castes have evolved at least four times in aphids.Received 25 June 2004; revised 24 September 2004; accepted 11 October 2004.     

Parasitic mites as part-time bodyguards of a host wasp

Some bees and wasps that host mites have peculiar pocket-like structures called acarinaria. These have long been considered as morphological adaptations to securely transfer beneficial mites into nests, and thus are thought to be the product of a mutualistic relationship. However, there has been little compelling evidence to support this hypothesis. We demonstrated that the parasitic mite Ensliniella parasitica, which uses acarinaria, increases the reproductive success of its host wasp Allodynerus delphinalis by protecting it from parasitoid wasps. Every time the parasitoid Melittobia acasta accessed a prepupal or pupal wasp host cell, adult mites attacked it, continuously clinging to it and possibly piercing the intersegmental membrane of the parasitoid with their chelicerae. Subsequent mortality of the parasitoid depended on the number of attacking mites: an average of six mites led to a 70% chance of mortality, and 10 mites led to a 100% chance of mortality. In this way, parent mites protect the food source (juvenile wasps) for themselves and ultimately for their offspring. We propose that wasps evolved acarinaria to maintain this protective guarding behaviour.     

黑水虻幼虫肠道和体表产酶细菌的分离和鉴定

从野外收集和室内饲养的黑水虻Hermetia illucens L.幼虫体表和肠道分离出同时具蛋白质和有机磷分解能力的细菌10株,其中编号为T2、T4、T6、T7和T8的菌株分离自体表,编号为S14、S15、S16、S19和S20的菌株分离自肠道。克隆细菌的16S rDNA和DNA促旋酶B亚基编码基因gyrB对10株细菌进行了鉴定。通过16S rDNA序列确定10株菌为芽孢杆菌属,根据gyrB基因以及BLAST结果构建系统发育树,将10株细菌鉴定为枯草芽孢杆菌。然后将10株菌的gyrB基因以B.subtilis subsp.subtilisstr.168和模式菌株B.subtilis subsp.subtilis BCRC10255相应基因序列为参照构建系统发育树,分析10株菌在种的水平上的亲缘关系,发现10株菌存在亲缘关系差异,没有重复菌株。     

Transplantation of a polyembryonic wasp embryo: a technique for transferring endoparasitic embryo into the host egg

Concealed development of many animal embryos prevents examination of development and limits the application of embryo manipulation techniques aimed at understanding developmental processes. In embryos developing in utero, such as in mammals, it is necessary to dissect embryos from the mother and, upon manipulative intervention, to implant them back into the recipient. Parasitic wasps present a promising system for understanding the evolution of early developmental processes. In basal ectoparasitic species that lay eggs on the surface of the host, it is possible to adapt embryo manipulation techniques developed in Drosophila. However, their derived endoparasitic relatives, which exhibit various modifications of developmental programs, undergo concealed development within the host body. For example, the parasitic polyembryonic wasp Copidosoma floridanum oviposits an egg into the egg of the host moth Trichoplusia ni. The host larva emerges and the parasite undergoes development within the host body, preventing embryo manipulation as a means of examining developmental regulation. Here we present a protocol for embryo transfer that allows the transplantation of C. floridanum egg into the host egg. This approach opens a new avenue in the application of various embryo manipulation techniques aimed at understanding the evolution of embryogenesis in endoparasitic Hymenoptera. In addition, this approach has potential for the development of other tools in C. floridanum, such as transgenesis and reverse genetics, which can also be extended to other endoparasitic species.     

Oviposition behavior and progeny allocation of the polyembryonic waspCopidosoma floridanum (Hymenoptera: Encyrtidae)

Oviposition behavior was used to determine the primary clutch size and sex ratio of the polyembryonic wasp Copidosoma floridanumAshmead (Hymenoptera: Encyrtidae) parasitizing Pseudoplusia includens(Walker) (Lepidoptera: Noctuidae). The laying of a female egg was associated with a pause in abdominal contractions during oviposition, while the laying of a male egg was associated with uninterrupted abdominal contractions. Although unmated females produced only male broods, they also displayed male and female egg oviposition movements. Wasps always laid a primary clutch of one or two eggs. For mated females if only one egg was laid, the emerging secondary clutch was all male or female, but if two eggs were laid a mixed brood of males and females was almost always produced. The secondary clutch of single sex broods was usually between 1000 and 1200 individuals, but the secondary clutch of mixed broods averaged 1143 females and 49 males. Thus, the primary sex ratio for mixed broods was 0.5 (frequency males), but the secondary sex ratio was 0.042. Manipulation of the sequence of male and female egg oviposition or of the primary clutch did not produce major alterations in the secondary clutch size or sex ratio.