Adult mortality rates in young colonies of a swarm-founding social wasp (Polybia occidentalis)

The swarm founders are unusual among the social wasps in having socialized the dispersal stage of the life cycle. Colonies are initiated by groups of workers accompanied by smaller numbers of queens. Thus, swarm founders avoid the colony size bottleneck faced by the independent founders, whose colonies start with one or a few queens. Among the advantages of swarm founding is a reduction of the risk of colony failure due to attrition of the founding adults. Stochasticity in adult mortality is less likely to lead to outright extinction of a large founding group before new workers are produced (pre-emergence period). However, it is not known how important pre-emergence mortality is as a selective force on founding and dispersal behaviour in swarm founders, since colony-wide mortality rates have never been reported for a large-colony social wasp. Sixty-eight swarms of Polybia occidentalis were censused just before colony initiation and again 24 days later. Mortality over this period averaged 0.41±0.12 of the founding swarm population. Including mortality on the day of emigration and extrapolating to day 30, when the first adult offspring eclose, the original absconding swarm would be reduced by 0.52 of its initial size. Rates of loss during the first week, while the colonies engaged in nest construction, did not differ from rates over the full 24 days. Thus, colony founding in P. occidentalis is both costly and highly variable in terms of mortality of the founding adults.     

Age polyethism and defense in a tropical social wasp (Hymenoptera: Vespidae)

Although tapping the nest in simulated vertebrate attack caused all but 1-day-old workers of Polybia occidentalis to rush from inside and cover the envelope, defense itself—attack of a target—was shown to be carried out only by workers older than about 10 days. While foraging was also performed by older workers, the frequency-age distribution of defensive behavior was skewed to a significantly younger age than was that of foraging. The plot of mean individual probability of defending as a function of age was logistic, leveling off at 0.11 by the age of about 13 days. The distribution of the probability of defending among workers 13 days of age was random, indicating that there is no specialized defender class among older workers. Workers that defended were recruited from among both nest workers and foragers. Although foragers were more likely to defend than were nonforagers, nonforagers contributed more individuals to the pool of defenders because they were more numerous.     

A test of adaptive hypotheses for rapid nest construction in a swarm-founding wasp

Most social insect species enlarge their nests gradually and in close correlation with the growing need for space for brood and/or stored food. In contrast, some species of swarm-founding eusocial wasps construct the nest rapidly to a final size in the first two to three weeks of the founding stage. We considered four hypotheses on the functions of rapid nest construction in the wasp Polybia occidentalis and directly tested two of them. The first hypothesis is that rapid construction maximizes output of the worker force when there are few other work demands; it predicts that construction rate remains high until the first eggs begin to hatch, following which it declines as increasing amounts of worker effort are allocated to the feeding of larvae. The second says that rapid nest construction minimizes the time the adults in the swarm are exposed to predation and the elements; it predicts that nest-construction rate should drop steeply after the nest is large enough to house all the adults in the swarm. We measured pulp-foraging rates for the first 12 days of the founding stage in control colonies and in colonies whose nests we manipulated to prevent housing of the swarm. The treatment and control groups did not differ in construction rate for several days following the housing event, contradicting the adult-protection hypothesis. Late in nest construction, treatment colonies were building at significantly higher rates than were control colonies. If demand for brood care were a major factor in determining construction rate, both groups would have responded to the eclosion of larvae in the same way and shown a parallel decline in construction rate, but this did not happen. Instead, the patterns of nest construction rate we observed provided indirect support for the two remaining hypotheses. The first of these is that rapid construction minimizes exposure of the brood to natural enemies and desiccation. The second is that rapid construction promotes competition among queens by providing empty cells for oviposition, thereby facilitating the selecting out of the less fecund of the multiple reproductive females. Also consistent with this hypothesis is the apparent absence of explosive nest construction in monogynous, eusocial bees. Received 13 October 2007; revised 31 March 2008; accepted 6 April 2008.     

Timing of insemination in terms of age of new reproductive females of a temperate-zone polistine wasp,Polistes snelleni (Hymenoptera: Vespidae)

Summary The present study investigated the age at which insemination takes place in Polistes snelleni, a species in which mating begins while new reproductives are still emerging from the nest. Insemination of new reproductive females began as early as 5 days of age, and most females were inseminated by 10 days of age.     

Differences in caste dimorphism among three hornet species (Hymenoptera: Vespidae): forewing size, shape and allometry

Caste shape dimorphism (CShD) has previously been studied in wasps through comparison of different body parts, originating from different imaginal discs. Using geometric morphometrics with a new protocol for measuring wings of pinned specimens from natural history collections, we tested CShD of three hornet species in an organ developed from a single imaginal disc: the forewing. Gaussian mixture models retrieved most castes and species levels, confirming that caste is an important component of wing variations in females of these hornets. Size and allometry - the influence of size on shape - contribution to wing dimorphism between castes was major, but failed to explain the entire shape dimorphism. This deviation from simple allometric scaling was not similar in the three species: in Vespa tropica, allometric directions in the shape space differed between castes, whereas in V. crabro and V. velutina, they were similar but a significant part of CShD resulted from lateral transpositions. These results clearly indicate that queens are not just enlarged workers. They also support that the different patterns of CShD may result from different developmental mechanisms. Finally, they highlight that even in a highly social group like hornets, there is still variation in caste dimorphism among species.     

Brain organization mirrors caste differences,colony founding and nest architecture in paper wasps (Hymenoptera: Vespidae)

The cognitive challenges that social animals face depend on species differences in social organization and may affect mosaic brain evolution. We asked whether the relative size of functionally distinct brain regions corresponds to species differences in social behaviour among paper wasps (Hymenoptera: Vespidae). We measured the volumes of targeted brain regions in eight species of paper wasps. We found species variation in functionally distinct brain regions, which was especially strong in queens. Queens from species with open-comb nests had larger central processing regions dedicated to vision (mushroom body (MB) calyx collars) than those with enclosed nests. Queens from advanced eusocial species (swarm founders), who rely on pheromones in several contexts, had larger antennal lobes than primitively eusocial independent founders. Queens from species with morphologically distinct castes had augmented central processing regions dedicated to antennal input (MB lips) relative to caste monomorphic species. Intraspecific caste differences also varied with mode of colony founding. Independent-founding queens had larger MB collars than their workers. Conversely, workers in swarm-founding species with decentralized colony regulation had larger MB calyx collars and optic lobes than their queens. Our results suggest that brain organization is affected by evolutionary transitions in social interactions and is related to the environmental stimuli group members face.     

短刺刺腿食蚜蝇生物学特性的初步研究

1991-1993年,在福州郊区调查,短刺刺腿食蚜蝇Ischiodon scutelloris为该地区优势种,一年发生6-7代,有越夏年份发生6代,无越夏年份发生7代。主要以蛹在土壤中越冬和越夏,世代历期随温度高低而异,平均气温为16.6℃时,世代历期长达45.3天;平均气温28.2℃时,为21.1天。幼虫期平均捕蚜量可达278.5头,三龄幼虫食量最大,占幼虫期总食量的80%以上,食蚜蝇姬蜂是造成本区秋季短刺刺腿食蚜蝇种群数量下降的主要原因。     

Reproductive conflicts in polyandrous and polygynous ant Formica sanguinea

The occurrence of multiple reproductives within an ant colony changes the balance between indirect fitness benefits and reproductive competition. We test whether the number of matings by an ant queen (polyandry) correlates negatively with the number of reproductive queens in the colony (polygyny), whether the patrilines and matrilines differ in their contribution to the sexual and worker progeny and whether there is an overall reproductive skew. For these aims, we genotyped both worker and sexual offspring from colonies of the ant Formica sanguinea in three populations. Most colonies were monogynous, but eight (11%) were polygynous with closely related queens. Most queens in the monogynous colonies (86%) had mated with multiple males. The effective paternity was lower than the actual number of mates, and the paternity skew was significant. Furthermore, in some monogynous colonies, the patrilines were differently represented in the worker pupae and sexual pupae produced at the same time. Likewise, the matrilines in polygynous colonies were differently present in worker pupae and male offspring. The effective number of matings by a queen was significantly lower in polygynous colonies (mean m_e = 1.68) than in monogynous colonies (means 2.06–2.61). The results give support to the hypotheses that polyandry and polygyny are alternative breeding strategies and that reproductive competition can lead to different representation of patrilines and matrilines among the sexual and worker broods.     

Worker Age, Ovary Development, and Temporal Polyethism in the Swarm-Founding Wasp Polybia occidentalis (Hymenoptera: Vespidae)

I measured oocyte sizes of Polybia occidentalis workers to assess whether ovary development corresponded with adult age or with individual variation in behavior. Workers exhibited temporal polyethism by first working inside the nest, then performing on-nest tasks, and later foraging and defending the nest. Individuals varied in their ages at first performance of each of these sets of behavioral acts. Ovary development corresponded strongly with adult age. Workers' ovaries declined quickly after an initial phase of partial development. The period of ovary decline overlapped with the age range at which most workers began performing tasks on the exterior nest surface. However, after accounting for age effects, individual behavioral differences (rate of temporal polyethism and performance of foraging and defense tasks) did not correspond with ovary development. These data suggest that ovary development had little or no effect on variation in task performance by P. occidentalis workers on the nest surface.     

Effect of a foreign male's age on acceptance into a conspecific colony in a Neotropical wasp

We conducted field experiments to examine whether young males of different age cohorts were accepted from alien colonies in the swarm‐founding wasp Polybia paulista. We showed, as for young females in other social wasp species, that newly emerged males were frequently accepted from alien colonies. Our study suggests that young males of P. paulista acquire colony‐specific chemical odors shortly after emergence.     

盾负泥虫对鸭跖草的专食性

盾负泥虫Lema scutellaris (Kraatz.)1年发生1代, 以成虫滞育。用与鸭跖草Commelina communis L. 同科及近缘科,属的植物对其食性进行测定,结果是食性单一,只取食鸭跖草。盾负泥虫的发生期与鸭跖草的苗期同步,幼虫的喜食与鸭跖草的多分枝特性相吻合。取食营养位与粘液细胞在鸭跖草植株上的分布及细胞的含糖量关系密切。