Life-history and sex allocation in Trypoxylon (syn. Trypargilum) lactitarse (Hymenoptera; Crabronidae)

Hymenopterans have become a model for the study of factors that govern sex allocation. In 1983, Seger proposed a model to study Sphecidae wasps with a strong prediction that sex ratio for univoltine wasps should be 1 : 1 (female : male), and for partially bivoltine species it should be male-biased. The present study investigates if Trypoxylon lactitarse (Saussure, 1867) is a univoltine or a bivoltine species and if Seger's model prediction fits the pattern of sex ratio found in this species. The study was carried out at Parque Municipal das Araucárias, in the municipality of Guarapuava, state of Paraná, southern Brazil, from December 2001 to December 2004. Nests of T. lactitarse were obtained using trap-nests drilled longitudinally to a depth to 80 mm with 7.0, 10.0 and 13.0 mm opening diameter. They were placed in a very heterogeneous site filled with araucaria forests, swamps and grasslands. Trypoxylon lactitarse showed two alternative life histories: either they pupated immediately and emerged as adults later in the same season (direct development), or they entered diapause, overwintering and pupating the following spring (delayed development). Its annual sex ratios were not significantly different from 1 : 1, and both sex ratio of overwintering and sex ratio of direct-developing wasps were also not significantly different from 1 : 1, in all years of this study. By examining these results, it was possible to conclude that although T. lactitarse is a multivoltine species, with four generations per year and two alternative life histories, its sex ratio did not support Seger's model.     

Biology of the solitary wasp Trypoxylon (Trypargilum) agamemnon Richards 1934 (Hymenoptera: Crabronidae) in trap‐nests

Buschini, M.L.T. and Fajardo, S. 2009. Biology of the solitary wasp Trypoxylon (Trypargilum) agamemnon Richards 1934 (Hymenoptera: Crabronidae) in trap‐nests. —Acta Zoologica (Stockholm) 91 : 426–432. Some Trypoxylon species build their nests in preexisting tubular cavities like hollow stems and beetle borings in branches. Study of the biology of these insects is relatively easy because the females of these wasps nest with enormous success in trap‐nests. The aim of this study was to investigate the abundance, seasonality and life‐history of Trypoxylon agamemnon. For capture of these insects, trap‐nests were installed in the Parque Municipal das Araucárias in araucaria forest, grassland and swamp, from December, 2001 to December, 2005. Two hundred and ninety seven nests were obtained. They were constructed more often during the summer (from December to April). The nests were built only in araucaria forest and consisted of a linear series of cells, divided by mud partitions, whose number varied from 1 to 7. Normally they have only one vestibular cell. The inner cells had been provisioned, usually with spiders of Anyphaenidae family. Sex‐ratio was strongly female biased. Its main natural enemies included Chrysididae, Ichneumonidae and Tachinidae.     

Gene variation and genetic differentiation among populations of the solitary mud dauber wasp Trypoxylon (Trypargilum) albitarse Fabricius 1804 (Hymenoptera, Crabronidae)

Trypoxylon is a genus of solitary crabronid wasps whose populationgenetics is poorly known. The purpose of the present study was to investigate thegenetic variation and differentiation among five populations of Trypoxylonalbitarse, a species widely distributed throughout the Neotropics, withrecords from Panama to northern Argentina. Eight species-specific microsatellite lociwere used for genotyping 96 adult wasps (one female per nest) sampled at five sitesin Brazil. The analysis of allelic richness and private alleles indicated highgenetic diversity in the populations sampled. Pairwise comparisons using theF_st and D_est indices revealed significant differentiation for all, but one pair ofpopulations. F_st, D_est, AMOVA and assignment test values pointed to inter-population differentiation.Additionally, the analysis of population structure using Bayesian and PCA methodscharacterized two alternative genetic groups. The Mantel test indicated nocorrelation between genetic and geographic distances. Despite evidence ofconsiderable dispersal capacity for T. albitarse, the data indicatelow to moderate population structuring in this species.     

Nesting biology of Trypoxylon (Trypargilum) lactitarse Saussure (Hymenoptera, Crabronidae) in trap-nests in Southern Brazil.

This study was carried in the Parque Municipal das Araucárias in the municipality of Guarapuava, state of Paraná, Southern Brazil. Three hundred and sixty five nests of T. lactitarse were obtained using trap-nests of 0.7, 1.0, and 1.3 cm in diameter. All of them had similar architecture, regardless of the diameter of the trap-nest. Completed nests consisted of a linear series of brood cells whose average number per nest was of 3.3, 4.0 and 3.6 for the nests with 0.7 cm, 1.0 cm and 1.3 cm in diameter, respectively. They were constructed more often during the summer. T. lactitarse had two types of life cycles: direct development (without diapause), and delayed development (with diapause during winter). Natural enemies included Chrysididae, Sarcophagidae, Dolichopodidae and Ichneumonidae. Out of 1,353 identified spider prey, 1,313 belonged to the Araneidae family.     

Nesting biology of four species of Trypoxylon (Trypargilum) (Hymenoptera: Crabronidae) in Chaco Serrano woodland, Central Argentina

Trypoxylon (Trypargilum) (Crabronidae) wasps are solitary spider predators that can build their nests in artificial trap-nests, which enables study of their nesting architecture and biology. Twenty traps (each containing 15-30 internodes of cane) were placed in each of nine sites of Chaco Serrano Woodland in Central Argentina (Córdoba) in October 2005, and were recovered in June 2006. We obtained 91 nests of four species of Trypoxylon (Trypargilum). In the laboratory, each Trypoxylon nest was sectioned longitudinally to study its architecture. The number of brood cells was counted, and the occurrence and length of vestibular and intercalary cells and the pre-closing plug space were recorded. We measured the diameter of the cane entrance, total length of the nest, length of each brood cell, maximum thickness of mud partitions and closing plug thickness. We also recorded the cell contents: the wasps, their natural enemies and the prey spiders. Mortality was assessed and the sex ratio calculated for each species. Finally, the nests were examined to help clarify the function of the vestibular cell. The nest architecture was similar in the four species, with linear brood cells located one after the other separated by mud partitions, as in other species of the subgenus Trypargilum. Forty-eight percent of the nests had vestibular cells, but only two had intercalary cells. The thickness of the mud partitions and the length of the brood cells differed among species and were related to the size of the emerged wasp. The diameter of the nest entrance was directly related to the average length of the fore-tibia. Sex ratios of all species did not deviate from 0.5. Mortality due to parasitoids (Eulophidae; Melittobia sp.) was similar among species, while the mortality due to cuckoo wasps (Chrysididae) in T. lactitarse was higher than in the other species. The presence of vestibular cells was not related either to the mortality due to natural enemies or to the orientation of the trap in the field. Spiders in the family Araneidae were the most frequently collected prey.     

中国切方头泥蜂属一新种记述(膜翅目:方头泥蜂科)

记述中国广西方头泥蜂科Crabronidae切方头泥蜂属Ectemnius 1新种:漫黄切方头泥蜂Ectemnius anomalifulvus, sp. nov..模式标本保存于云南农业大学昆虫标本室.     

中国方头泥蜂科一新记录属附记一新种(膜翅目)

记述方头泥蜂科Crabronidae中国1新记录属:阳完眼泥蜂属Solierella Spinola,1851,并记述了1新种:金足阳完眼泥蜂Solierella cerinusipedalis,sp.nov.。模式标本保存在云南农业大学昆虫标本室。     

Disentangling sex allocation in a viviparous reptile with temperature‐dependent sex determination: a multifactorial approach

Females are predicted to alter sex allocation when ecological, physiological and behavioural variables have different consequences on the fitness of male and female offspring. Traditionally, tests of sex allocation have examined single causative factors, often ignoring possible interactions between multiple factors. Here, we used a multifactorial approach to examine sex allocation in the viviparous skink, Niveoscincus ocellatus. We integrated a 16‐year observational field study with a manipulative laboratory experiment to explore whether the effects of the maternal thermal environment interact with the resources available to females for reproduction to affect sex allocation decisions. We found strong effects of temperature on sex allocation in the field, with females born in warm conditions and males in cold conditions; however, this was not replicated in the laboratory. In contrast, we found no effect of female resource availability on sex allocation, either independently, or in interaction with temperature. These results corresponded with an overall lack of an effect of resource availability on any of the life history traits that we predicted would mediate the benefits of differential sex allocation in this system, suggesting that selection for sex allocation in response to resource availability may be relatively weak. Combined, these results suggest that temperature may be the predominant factor driving sex allocation in this system.     

Condition-dependent sex allocation in a lek-breeding wader,the ruff (Philomachus pugnax)

Sex allocation theory predicts that females should bias the production of offspring towards the sex that will maximize maternal fitness. Here we demonstrate evidence for nonrandom sex allocation by female ruffs (Philomachus pugnax), at both the individual and population level in relation to female condition. At the population level, female condition varies significantly across 3 years and is mirrored by population sex ratio, such that in years when females are in poor condition the population offspring sex ratio is female-biased, while in years when females are in better condition there was little or no bias. In the year when females were in overall poor condition, females in better condition produced more daughters. The same relationship is also revealed by comparing the sex ratios of individual females breeding in two consecutive years in different condition. As the condition of an individual female improves (across years) she tends to produce more female offspring. Although we have shown that, as in other birds, female condition is an important determinant of sex allocation, our results also suggest that such nonrandom allocation does not occur in every year, being particularly strong in a year when females, on average, are in poorer condition. We suggest that our results are consistent with the idea that skewing the sex ratio is likely to carry a cost to females and that it is adaptive only when the fitness differential between sons and daughters is sufficient to outweigh probable costs.     

Size‐dependent sex allocation in a simultaneous hermaphrodite parasite

Most models of sex allocation distinguish between sequential and simultaneous hermaphrodites, although an intermediate sexual pattern, size‐dependent sex allocation, is widespread in plants. Here we investigated sex allocation in a simultaneous hermaphrodite animal, the tapeworm Schistocephalus solidus, in which adult size is highly variable. Sex allocation was determined using stereological techniques, which allow measuring somatic and reproductive tissues in a common currency, namely volume. We investigated the relationships between individual volume and allocation to different reproductive tissues using an allometric model. One measure of female allocation, yolk gland volume, increased more than proportionally with individual volume. This is in contrast to the measure of male allocation, testis volume, which showed a strong tendency to increase less than proportionally with individual volume. Together these patterns led to sex allocation being strongly related to individual volume, with large individuals being more biased towards female allocation. We discuss these findings in the light of current ideas about size‐dependent sex allocation in, primarily, plants and try to extend them to simultaneous hermaphrodite animals.     

Sex‐allocation conflict and sexual selection throughout the lifespan of eusocial colonies

Models of sex‐allocation conflict are central to evolutionary biology but have mostly assumed static decisions, where resource allocation strategies are constant over colony lifespan. Here, we develop a model to study how the evolution of dynamic resource allocation strategies is affected by the queen‐worker conflict in annual eusocial insects. We demonstrate that the time of dispersal of sexuals affects the sex‐allocation ratio through sexual selection on males. Furthermore, our model provides three predictions that depart from established results of classic static allocation models. First, we find that the queen wins the sex‐allocation conflict, while the workers determine the maximum colony size and colony productivity. Second, male‐biased sex allocation and protandry evolve if sexuals disperse directly after eclosion. Third, when workers are more related to new queens, then the proportional investment into queens is expected to be lower, which results from the interacting effect of sexual selection (selecting for protandry) and sex‐allocation conflict (selecting for earlier switch to producing sexuals). Overall, we find that colony ontogeny crucially affects the outcome of sex‐allocation conflict because of the evolution of distinct colony growth phases, which decouples how queens and workers affect allocation decisions and can result in asymmetric control.     

Diversity of mud-dauber wasps (Hymenoptera: Crabronidae: Trypoxylon Latreille) in a secondary forest of Trinidad,West Indies

Over a two-year period we operated two intercept traps for flying insects near and within a well-developed secondary forest in the Arima Valley of Trinidad. These yielded 368 Trypoxylon, representing 30 species. The sample’s Shannon–Wiener diversity of H′ = 2.61 is higher than that from a comparable study of Trypoxylon on the smaller island of Tobago (15 species, H′ = 2.09) and the even smaller Little Tobago (six species, H′ = 1.41). Analysis of the samples by the Chao1 method suggests that the species numbers recorded on the two smaller islands are complete, while there is at least one additional species at the Trinidad locality. The four most abundant species in our samples show no evident bias in numbers of females between the wet and dry seasons, consistent with the hypothesis that at least these species nest throughout the year.     

Condition and reproductive investment in the western mosquitofish (Gambusia affinis): little evidence for condition‐dependent sex‐biased investment

In sexually reproducing species, resources may theoretically be distributed with bias to the production of male or female offspring in response to the condition of the mother, commonly recognized as sex allocation. Using a recently characterized sex‐specific molecular marker, we tested for maternal sex allocation (i.e. maternal primary sex ratio bias and sex‐specific offspring investment) in captive laboratory‐bred western mosquitofish (Gambusia affinis) at early stages of offspring development. We found no statistical evidence to support sex allocation in G. affinis, based on maternal condition. In addition, we found little evidence for correlations between maternal condition and investment in the condition (mass) of individual offspring (of one sex or the other), although we did find that larger mothers tended to have higher fecundity.     

Female‐biased sleeping aggregations of Amegilla florea urens (Hymenoptera: Apidae)

Although male bees and wasps aggregate in specific sites overnight, few studies have addressed the behaviors of female hymenopterans during the night. It is generally understood that they spend the night in a burrow or nest structure. We found female‐biased sleeping aggregations of Amegilla florea urens in populations on Iriomote Island. The sex ratio and number of sleeping individuals in the sex‐mixed aggregations changed daily. This species used dead branches as its main sleeping places, and the maximum number of individuals observed per place was 15. Females arrived at the aggregation place later and left it earlier in the morning than did males. Our result suggests that females used the sleeping place regularly but avoided a long stay with males. The use of the same sleeping place by the two sexes may be due to a limited number of sites suitable for sleeping in the forest.     

Offspring sex ratio and development are determined by copulation activity in Echinothrips americanus MORGAN 1913 (Thysanoptera: Thripidae)

The costs of parthenogenetic reproduction are more or less unknown in thrips. However, IPM strategies require an understanding of temporal and spatial life‐history variations and sex ratios. Hence, different circumstances with regard to mating and sperm storage, and their effects on the life history of the adults and progeny, were tested in Echinothrips americanus. Different conditions were investigated: (1) one female and one male with permanent access to each other, (2) one female and one male with limited access to each other, (3) one virgin male only, (4) one virgin female only and (5) two virgin females permanently associated. Mating or not mating has a significant effect on the longevity of females and males, and on female fecundity. As a result of tested condition (2), limited access has a positive effect on longevity of a male. On the other hand, permanent access (1) or no access to a female (3) leads to shorter longevity of a male. For a female with permanent access to a male (1), longevity and oviposition rate are reduced. In addition, test conditions of parents have a significant effect on developmental time of the offspring and their sex ratio. Compared to a female under condition (1), a female with limited access to a male (2) delivers offspring with a more male‐biased sex ratio, independent of the period of time after last male access. Concerning the time for development of the offspring, females under condition (2) and under condition (4) deliver an F1 generation with a shorter developmental time than those under condition (1). Therefore, E. americanus seems to have a feedback system, that is offspring in low male‐biased populations develop faster and generate an adapted sex ratio. Hence, the assumption of a lower infestation risk in arrhenotokous than in thelytokous parthenogenesis should be reconsidered.     

Increased male sex ratio among brachypterous progeny in Melittobia femorata, a sib-mating parasitoid wasp (Hymenoptera: Eulophidae)

Abstract Melittobia are gregarious ectoparasitoid wasps that primarily attack various solitary bees and wasps. Characterized by high levels of inbreeding and an extremely female-biased sex ratio, these wasps appear to satisfy Hamilton's criteria for local mate competition. However, previous studies of sex ratio have failed to take into account an important aspect of Melittobia life history, namely that every clutch represents the combined reproductive output of the initial foundress female plus as many as 37 non-disperser short-winged daughters. Melittobia femorata Dahms is unique among the 13 species of Melittobia in that adults emerge as two temporally distinct clutches. While the overall sex ratio of the combined progeny from both clutches (0.025 ± 0.01) is typical for that for other Melittobia species (between 0.02 - 0.04 for single foundress cultures of the five other species included in this study), the sex ratio for the brachypterous first clutch of M. femorata from field-parasitized hosts averaged about 10 times greater (0.303 ± 0.10). Laboratory experiments with single foundress M. femorata cultures on the same host species ( Trypoxylon politum Say) maintained at 25°C or 30°C produced smaller first clutch sizes compared to the field-infested hosts. While the number of brachypterous first clutch daughters was similar, significantly reduced first clutch sex ratios relative to field-parasitized hosts (0.07 - 0.10) were due to significantly fewer males being produced. Possible reasons for these differences and the elevated first clutch sex ratio in this species are discussed.     

Symbiotic streptomycetes in antennal glands of the South American digger wasp genus Trachypus (Hymenoptera,Crabronidae)

Several insect taxa have evolved symbioses with actinobacteria that protect the host or its nutritional resources against pathogens. Digger wasps of the genus Philanthus (‘beewolves’; Hymenoptera, Crabronidae) cultivate ‘Candidatus Streptomyces philanthi’ (Ca. S. philanthi) in specialized antennal glands and transfer them to subterranean brood cells, where the symbionts provide protection for the beewolf larva against pathogens by producing a cocktail of antibiotic substances. The present study investigates the occurrence of antennal symbionts in two species of the genus Trachypus, which is the closest relative to Philanthus. Cross sections of the antennae from females of both Trachypus denticollis and Trachypus boharti reveal bacteria‐containing gland reservoirs that are morphologically very similar to those found in Philanthus spp. Polymerase chain reaction‐based screens with specific primers, sequencing of the partial 16S rRNA gene, and fluorescence in situ hybridization confirm the presence of close relatives of ‘Ca. S. philanthi’ in T. denticollis and T. boharti. However, 16S rRNA sequence divergence between Trachypus spp. and Philanthus spp. symbionts is much higher for T. boharti than for T. denticollis, suggesting that horizontal transmission and/or de novo uptake of symbionts from the environment occurs occasionally. The results obtained indicate that the protective symbiosis with antennal actinobacteria is older and more widespread than previously recognized and occurs in at least two genera of digger wasps that comprise approximately 170 species.     

Colony structure, provisioning and sex allocation in the sweat bee Halictus ligatus (Hymenoptera: Halictidae)

Population and colony-level sex allocation and nest productivity in the eusocial sweat bee Halictus ligatus Say were studied by excavating nests during one season. The emphasis was on measuring the provision masses, which differ in size and shape depending on the sex of the egg to be laid on them (male-producing provision masses are smaller and more or less round, whereas gyne-producing provision masses are larger and 'loaf-shaped). The primary aim of this study was to test theoretical predictions about female-bias of the sex ratio in the summer brood, both on the population level and on the colony level.
The overall sex ratio of the summer brood was moderately biased towards gynes. A significant positive correlation between the overall size of provision masses (as an estimate for the degree of female bias of the nest sex ratio) and the number of eusocial workers was found. This relationship further improved in partial analyses in which the provision mass weights were adjusted for sampling date, removing the effect of protandry. Foundress size, however, had no effect on the second brood provision masses and neither was there an effect of worker number on the size of gynes and males separately. In the first brood only the size of the foundress had a consistently positive effect on the size of the provision masses and on the size of the emerging daughter workers.
The observed increase of female bias in the nest sex ratio with increasing numbers of eusocial worker bees conforms to optimization predictions following from kin-selection theory.