Host choice and fitness correlates for conopid flies parasitising bumblebees

Two parasitoid flies,Physocephala rufipes andSicus ferrugineus (Diptera, Conopidae), and their hosts,Bombus spp., coexist at various locations in northwestern Switzerland. A detailed field study showed that both conopid species use the hostB. pascuorum to a similar degree, while the hostB. terr-luc (a pooled category ofB. terrestris andB. lucorum) is more frequently parasitised than expected byS. ferrugineus. The hostB. lapidarius in turn is exclusively used byP. rufipes. Furthermore, hosts ofB. terr-luc andB. pascuorum parasitised byS. ferrugineus were larger than hosts parasitised byP. rufipes, or than those not parasitised. The findings suggest thatS. ferrugineus selects larger hosts and may displaceP. rufipes. Pupal weight, a predictor of adult body size and parasitoid fecundity, is positively correlated with host size and larger pupae are more likely to emerge, while host species had no effect on the probability of emergence in either conopid species. Host species affected pupal weight inS. ferrugineus, but not inP. rufipes, althoughP. rufipes grew larger in hosts of a given size. Daughters emerged from larger pupae than males, but this did not correlate with larger host sizes. These observations add to the scarce knowledge of dipteran parasitoids.     

Parasitic flies (Conopidae, Diptera) may be important stress factors for the ergonomics of their bumblebee hosts

Bumblebees harbour a wide range of parasitic organisms that attack all stages of their life cycles (reviews in Postner, 1951; Pouvreau, 1973, 1974; Alford, 1975; Kistner, 1982). Among them, conopid flies (Conopidae, Diptera) are particularly interesting because they attack foraging bumblebees which are handling flowers, or even on the wing (Frison, 1926; Cumber, 1949; Postner, 1951; Howell, 1967; Askew, 1971). A single egg is attached to (Frison, 1926; Plath, 1934; Cumber, 1949) or inserted into (DeMeijre, 1904; Howell, 1967) the host's abdomen, where the larva hatches and feeds on haemolymph and internal organs. Within 6–10 days the larva passes through three recognizable stages (Pouvreau, 1974) before the fly pupates in situ within the abdomen. The host bee dies shortly before the parasite pupates (Postner, 1951; Smith, 1966) and the parasite overwinters in its puparium; the adult fly then emerges in early summer (Frison, 1926; Townsend, 1935; Cumber, 1949; Postner, 1951). Conopid flies as parasites of bumblebees are known from all major habitats where the hosts occur (e.g. Kröber, 1939; Smith, 1966). However, the effect of parasitism on distribution and abundance of bumblebees is not known. In this preliminary note we have estimated degrees of infestation and concomitant reduction of life span in affected workers. The results are compared with literature reports on infestation levels in Europe.     

Diet breadth,coexistence and rarity in bumblebees

Factors that determine the relative abundance of bumblebee species remain poorly understood, rendering management of rare and declining species difficult. Studies of bumblebee communities in the Americas suggest that there are strong competitive interactions between species with similar length tongues, and that this competition determines the relative abundance of species. In contrast, in Europe it is common to observe several short-tongued species coexisting with little or no evidence for competition shaping community structure. In this study we examine patterns of abundance and distribution in one of the most diverse bumblebee communities in Europe, found in the mountains of southern Poland. We quantify forage use when collecting nectar and pollen for 23 bumblebee species, and examine patterns of co-occurrence and niche overlap to determine whether there is evidence for inter-specific competition. We also test whether rarity can be explained by diet breadth. Up to 16 species were found coexisting within single sites, with species richness peaking in mountain pasture at ~1,000 m altitude. Results concur with previous studies indicating that the majority of pollen collected by bumblebees is from Fabaceae, but that some bee species (e.g. B. ruderatus) are much more heavily dependent on Fabaceae than others (e.g. B. lucorum). Those species that forage primarily on Fabaceae tended to have long tongues. In common with studies in the UK, diet breadth was correlated with abundance: rarer species tended to visit fewer flower species, after correcting for differences in sample size. No evidence was found for similarity in tongue length or dietary overlap influencing the likelihood of co-occurrence of species. However, the most abundant species (which co-occurred at most sites) occupied distinct dietary niche space. While species with tongues of similar length tended, overall, to have higher dietary niche overlap, among the group of abundant short-tongued species that commonly co-occurred there was marked dietary differentiation which may explain their coexistence.     

Sexual conflict and reproductive isolation in flies

Sexual conflict is predicted to generate more rapid reproductive isolation between larger populations. While there is some empirical support for this, the data are inconsistent and, additionally, there has been criticism of some of the evidence. Here we reanalyse two experimental-evolution datasets using an isolation index widely applied in the speciation literature. We find evidence for reproductive isolation through sexual conflict in Sepsis cynipsea, but not in Drosophila melanogaster, and this occurred to a greater degree in larger populations, which is consistent with previous findings.     

Genetic variation in a host-parasite association: potential for coevolution and frequency-dependent selection

Abstract.— Models of host‐parasite coevolution assume the presence of genetic variation for host resistance and parasite infectivity, as well as genotype‐specific interactions. We used the freshwater crustacean Daphnia magna and its bacterial microparasite Pasteuria ramosa to study genetic variation for host susceptibility and parasite infectivity within each of two populations. We sought to answer the following questions: Do host clones differ in their susceptibility to parasite isolates? Do parasite isolates differ in their ability to infect different host clones? Are there host clone‐parasite isolate interactions? The analysis revealed considerable variation in both host resistance and parasite infectivity. There were significant host clone‐parasite isolate interactions, such that there was no single host clone that was superior to all other clones in the resistance to every parasite isolate. Likewise, there was no parasite isolate that was superior to all other isolates in infectivity to every host clone. This form of host clone‐parasite isolate interaction indicates the potential for coevolution based on frequency‐dependent selection. Infection success of original host clone‐parasite isolate combinations (i.e., those combinations that were isolated together) was significantly higher than infection success of novel host clone‐parasite isolate combinations (i.e., those combinations that were created in the laboratory). This finding is consistent with the idea that parasites track specific host genotypes under natural conditions. In addition, correspondence analysis revealed that some host clones, although distinguishable with neutral genetic markers, were susceptible to the same set of parasite isolates and thus probably shared resistance genes.     

Mate sampling and the sexual conflict over mating in seaweed flies

The order in which females encounter, or sample, males in apopulation may have important consequences for mate choice,with the information gathered about males influencing boththe preference function and degree of choosiness of females.Sexual selection may be affected as a result. Sampling of particularsubsets of males may be a crucial component of individual variation in mate preferences within populations. However, the sequencein which males are sampled may also be important in specieswithout traditional, active mate choice, such as when sexualselection involves sexual conflict over mating. This wouldoccur if the likelihood of a female mating with a male of acertain phenotype changes as a result of previous encounters.We examined the effects of encountering males differing inbody size, a sexually selected phenotype, in the seaweed flyCoelopa frigida. Sexual selection occurs in this species asa result of a sexual conflict over mating. We show that theoutcome of the sexual conflict is independent of the orderin which males are encountered by female seaweed flies, withthe overall mating advantage to large males being unaffected.In addition, we explored female preference functions and evaluatethe heterogeneity in female willingness to mate. We suggestthat consideration of mate sampling theory is valuable whenexamining mate choice in species in which sexual selectionis driven by sexual conflict.     

New technologies to study helminth development and host-parasite interactions

How parasites develop and survive, and how they stimulate or modulate host immune responses are important in understanding disease pathology and for the design of new control strategies. Microarray analysis and bulk RNA sequencing have provided a wealth of data on gene expression as parasites develop through different life-cycle stages and on host cell responses to infection. These techniques have enabled gene expression in the whole organism or host tissue to be detailed, but do not take account of the heterogeneity between cells of different types or developmental stages, nor the spatial organisation of these cells. Single-cell RNA-seq (scRNA-seq) adds a new dimension to studying parasite biology and host immunity by enabling gene profiling at the individual cell level. Here we review the application of scRNA-seq to establish gene expression cell atlases for multicellular helminths and to explore the expansion and molecular profile of individual host cell types involved in parasite immunity and tissue repair. Studying host-parasite interactions in vivo is challenging and we conclude this review by briefly discussing the applications of organoids (stem-cell derived mini-tissues) to examine host-parasite interactions at the local level, and as a potential system to study parasite development in vitro. Organoid technology and its applications have developed rapidly, and the elegant studies performed to date support the use of organoids as an alternative in vitro system for research on helminth parasites.     

Shared traits make flies and bees effective pollinators of oilseed rape (Brassica napus L.)

One of the major aims of pollination ecology has been to understand the role and relative importance of different pollinator species in both natural and agricultural systems. This study explores how the quantity of pollen delivered in a single visit to a stigma (SVD) differs across insect species from a wide range of taxa (Orders: Hymenoptera, Diptera and Coleoptera) and assesses the morphological and behavioural traits that lead to differences in pollen delivery. We used oilseed rape (OSR) (Brassica napus L.), an economically important crop with open self-fertile flowers, as a test system. Behavioural traits and SVD were measured in the field for individuals of all frequent flower-visiting species of OSR. Individuals were collected and morphological traits were measured in the laboratory. The quantities of free pollen on different body parts of flower visitors, or ‘pollen load’, were also measured. Behavioural and morphological traits were then assessed as predictors of SVD. The individuals that delivered most pollen were (in order of greatest median number of pollen grains delivered): bumblebees (Bombus spp.), mining bees (Andrenidae) and honeybees (Apis mellifera). However, all but one family of flies tested delivered a significantly greater median number of pollen grains than the control, and most delivered more than sweat bees (Halictidae). Behavioural and morphological traits were important in determining pollen delivery, with greater body length, hairiness and visit duration all resulting in greater SVD. Pollen load was measured for a proportion of individuals and we found that for momentary flower visits, a greater quantity of pollen on the head of the flower visitor was linked to a greater SVD. This study demonstrates that, while bees are important pollinators in this system, many fly taxa are also effective at delivering pollen and this is linked to morphological and behavioural traits found in both groups.     

Coexistence of a sexual and an unisexual form stabilized by parasites

An unisexual species (either parthenogenetic or gynogenetic form) often coexists sympatrically with a closely related anisogamous sexual species, forming a unisexual complex. This is puzzling because, all else being equal, a sexual population with the two-fold cost of sex (or the cost of producing males) cannot coexist with a unisexual population. This suggests that some ecological processes are at work to make possible the coexistence of the unisexual complex. Field and laboratory studies suggest that parasitism in a gynogenetic complex of the Japanese crucian carp (Carassius auratus) may play an important role in realizing the coexistence by giving frequency-dependent benefit to sexual population. Here, we study the simple dynamics of host-parasite interactions in which non-specific immune reaction of a sexual host is more effective than that of an unisexual host. We simply assume that the infective individuals are sterile. Stable coexistence of a unisexual species with their sexual relative is possible if pathogens are virulent and if the susceptibility of the unisexual form is more than twice as high as that of the sexual form. The coexistence is more difficult, when the fertility of males is relatively low in gynogenetic complexes. This implies that the coexistence of gynogenetic complexes is more difficult than that of parthenogenetic complexes in which parthenogenesis has no constraint on males. We conclude that parasitism is a promising candidate mechanism for the coexistence of unisexual complexes.     

Identifying potential evolutionary relationships within a facultative lycaenid-ant system： Ant association, oviposition, and butterfly-ant conflict

Facultative associations are commonly encountered between ants and lycaenids, although the nature and patterns of associations are typically unclear. This study investigated a facultative symbiosis involving the lycaenid Theclinesthes albocincta （Lycaenidae）, its host plant Adriana quadripartita and Australian native ants. Ants in the genera Ochetellus and Iridomyrmex were most frequently found in association with T. albocincta larvae, although Iridomyrmex ants were found in much lower abundance than were ants in Ochetellus. The abundances of Ochetellus and Iridomyrmex were highly correlated with larval abundance, but not egg abundance. Observations and experiments recorded oviposi- tion on male inflorescences on more than 95% of occasions, but oviposition was not greater on inflorescences with ants present. Behavioral assays showed that Iridomyrmex ants were aggressive towards female butterflies on significantly more occasions than were Ochetellus ants. These findings indicate potential evolutionary relationships between T. albocincta and two genera of ants that were abundant within the habitat.     

Spatial and temporal pattern of introduced Bombus terrestris abundance in Hokkaido, Japan, and its potential impact on native bumblebees

A commercial colony of Bombus terrestris (L.) was introduced to Japan in 1992 for crop pollination in greenhouses. Since then wild colonies have developed and spread in some regions. In the present study, we measured the spatial distribution and temporal change in abundance of B. terrestris in the Chitose River Basin, Hokkaido, Japan to elucidate the relation of greenhouses to the bees distribution and to evaluate its potential effects on native bumblebees. Bumblebees were collected with window traps in windbreak forests roughly 1, 2, 4, and 6 km NNW and SSE of a large greenhouse. The peak catch of B. terrestris queens occurred in early June, suggesting that they had successfully hibernated in the field. The distributions of B. terrestris and the native B. ardens were mutually exclusive, while the native B. hypocrita appeared at all sites. Catches of B. terrestris were restricted to within 4 km of the nearest greenhouse, suggesting that the invasion was still in the initial phase in this area. The reduction in abundance of the native bumblebees in the sites of high B. terrestris abundance suggests the presence of interspecies competition between B. terrestris and the native bumblebees during the early part of the colony activity, although such reduction in B. ardens can be explained by habitat suitability.     

Biology and host preference of Selitrichodes neseri: A potential biological control agent of the Eucalyptus gall wasp,Leptocybe invasa

Selitrichodes neseri (Hymenoptera: Eulophidae) is a parasitoid of the invasive gall-forming wasp Leptocybe invasa (Hymenoptera: Eulophidae), which has caused serious damage to Eucalyptus plantations in many parts of the world. S. neseri is a recently discovered parasitoid considered to be a potentially important biological control agent of L. invasa. The aim of this study was to provide the first basic data on the biology of S. neseri, which is essential for its application in biological control. S. neseri was shown to be a biparental ectoparasitoid. Observation from dissected galls indicated that the parasitoid developed on late larvae, pupae and callow adults, although development did occur in a range of gall ages. Observed nominal parasitism in captivity ranged from 9.7% to 71.8%. Adult S. neseri specimens, fed with honey-water and galled Eucalyptus leaves, survived an average of 26 days at 26 °C. The average developmental time from oviposition to emergence was 19.3 days ± 0.2 days. There was no pre-oviposition period. A single female produced a maximum of thirty-nine offspring, with a maximum of ten per day. Dissection of the ovaries showed that twelve ovarioles were present. The sex ratio of S. neseri observed in this study was 1:3.43 males:females. Galls of native insects most closely related to L. invasa and to galls of similar morphology to L. invasa-induced galls, were not suitable for S. neseri oviposition. S. neseri showed considerable potential as a biological control agent of L. invasa due to its relatively short developmental time, long adult life span when supplemented with carbohydrates, ability to utilize a range of gall ages and the fact that it has a high level of host specificity.     

The converse to Bergmann's rule in bumblebees,a phylogenetic approach

Two patterns commonly emerge when animal body size is analyzed as a function of latitudinal distribution. First, body size increases with latitude, a temperature effect known as Bergmann's rule, and second, the converse to Bergmann's rule, a pattern in which body size decreases with latitude. However, other geographic patterns can emerge when the mechanisms that generate Bergmann's and the converse to Bergmann's clines operate together. Here, we use phylogenetic comparative analysis in order to control for phylogenetic inertia, and we show that bumblebees exhibit the converse to Bergmann's rule. Bumblebee taxa are distributed worldwide in temperate and tropical regions. The largest species are found in places with high water availability during the driest time of the year. Nonetheless, large body size is constrained by extreme temperatures. Bumblebees’ body size could be related to a higher extent to the size of food rewards to be harvested than to the energetic advantages of thermoregulation. Moreover, we found that the body size of eusocial and cuckoo species responded in the same way to environmental variables, suggesting that they have not diverged due to different selective pressures.     

Cryopreservation of Mexican fruit flies by vitrification: stage selection and avoidance of thermal stress

This report presents details of a vitrification methodology for the cryopreservation of embryos of the Mexican fruit fly, Anastrepha ludens. The overall summary of the data indicates that selecting the correct developmental stage for cryopreservation is the most important criterion. The key aspect in selection of the correct stage is to balance depletion of the gut yolk content against development of the embryonic cuticle. Embryogenesis was divided into four stages between 90 and 120 h after incubation at 21.7 degrees C. The classification was based on the intestinal yolk content and the initial development of mandibular-maxillary complex. Stages having low mid-gut yolk content and the appearance of mouth hooks were found to be the most suitable for cryopreservation. Embryos developing at 30 degrees C had premature cuticle formation relative to gut development and significantly lower hatching after cryopreservation. Vitrification of embryos by direct quenching in liquid nitrogen was less effective than quenching after annealing the samples in liquid nitrogen vapor. Quenched samples of vitrification solutions containing 1,2-ethanediol as the major component exhibited fractures. Fracturing occurred less frequently when the solutions were annealed and when containing polyethylene glycol. Hatching of vitrified embryos stored in liquid nitrogen for over 12 months was not statistically different from those held for only 15 min. Our protocol yielded normalized hatching rates that ranged as high as 61%. Selecting the exact stage for cryopreservation from a population of embryos obtained by collection from ovipositing females during a span of just 30 min resulted in nearly 80% of the embryos hatching into larvae.     

Secondary pollen carryover by ants in a natural population of Scleranthus perennis (Caryophyllaceae)

Summary Secondary pollen carryover is defined as the process whereby a pollinator receives previously deposited pollen grains when visiting a flower and transfers them into a new (secondary) carryover sequence. The secondary pollen carryover in a system of ants, Formica rufibarbis, visiting Scleranthus perennis (Caryophyllaceae) was studied using fluorescent dyes as pollen analogues. The mean secondary carryover was found to be 1.2 flowers compared with 4.5 flowers for the primary carryover. The number of dye grains deposited per flower visited is lower and the frequency of zero deposition is higher in the secondary carryover sequence than in the primary.     

Pollen carbohydrates and water content during development, presentation, and dispersal: a short review

Summary. Pollen accumulates starch reserves during development and the final stage of ripening. Before the anther opens, starch is totally or partially converted to pectins, glucose, fructose, sucrose, and to some unknown polysaccharides. Pollen is exposed to dispersing agents in an arrested developmental state which differs according to pollen water content. Pollen is classified as partially dehydrated or partially hydrated. The final water content may be reached before or after anther opening. Especially during exposure and dispersal, partially dehydrated pollen may interconvert soluble and insoluble reserves, modifying internal turgor pressure and hindering water loss or gain. Partially hydrated pollen is commonly devoid of mechanisms to conserve viability in time but has the advantage of quickly emitting pollen tubes on reaching the stigma. Correspondence and reprints: Department of Environmental Sciences, Siena University, 4 Via P.A. Mattioli, 53100 Siena, Italy.     

Effect of temperature on woodwasp (Sirex noctilio F.) development and parasitism by the entomopathogenic nematode,Deladenus siricidicola

The woodwasp, Sirex noctilio, is a significant global pest of exotic pine plantations in the Southern Hemisphere and now threatens native pine forests in North America. Management in Australia relies on biocontrol using the nematode, Deladenus (= Beddingia) siricidicola (Bedding), which infects and sterilises females who then further disperse the nematode. This pest is spreading into warmer regions in Australia and South America and coupled with the threat of global climate change, there is uncertainty as to how increasing temperatures will affect the biocontrol program. S. noctilio within nematode-inoculated wood were reared at four temperatures (24, 25.3, 26.6 and 28 °C) to investigate the effects of elevated temperatures on wasp development (emergence time, sex ratio and size), development of eggs (number, size, and maturation) and infection by the nematode. At 24 °C, which reflects current field temperature, S. noctilio were bigger in size and all the eggs were normal and all were infected with nematodes. Modest rises in temperature reflecting climate change scenarios resulted in smaller sized S. noctilio, disrupted egg development and maturation, and lowered the nematode sterilisation rate in females. Reduced S. noctilio female body size and egg infection will likely compromise biocontrol by D. siricidicola in its current distribution, but disrupted egg development may act directly on the pest, limiting dispersal of S. noctilio into subtropical pine plantations and adaptation to climate change.     

Paxiximyia sulmatogrossensis,a new genus and species of Tachinidae (Diptera) reared from Urucumania borellii () (Phasmatodea: Pseudophasmatidae) collected in the state of Mato Grosso do Sul,Brazil

A new genus and species of Tachinidae (Diptera), Paxiximyia sulmatogrossensisn. gen. and n. sp., and its puparium are described. It was reared from the walking stick, Urucumania borellii (Giglio-Tos, 1897), collected in Aquidauana, Mato Grosso do Sul, Brazil.     

Pollen transfer by hummingbirds and bumblebees, and the divergence of pollination modes in Penstemon

We compared pollen removal and deposition by hummingbirds and bumblebees visiting bird-syndrome Penstemon barbatus and bee-syndrome P. strictus flowers. One model for evolutionary shifts from bee pollination to bird pollination has assumed that, mostly due to grooming, pollen on bee bodies quickly becomes unavailable for transfer to stigmas, whereas pollen on hummingbirds has greater carryover. Comparing bumblebees and hummingbirds seeking nectar in P. strictus, we confirmed that bees had a steeper pollen carryover curve than birds but, surprisingly, bees and birds removed similar amounts of pollen and had similar per-visit pollen transfer efficiencies. Comparing P. barbatus and P. strictus visited by hummingbirds, the bird-syndrome flowers had more pollen removed, more pollen deposited, and a higher transfer efficiency than the bee-syndrome flowers. In addition, P. barbatus flowers have evolved such that their anthers and stigmas would not easily come into contact with bumblebees if they were to forage on them. We discuss the role that differences in pollination efficiency between bees and hummingbirds may have played in the repeated evolution of hummingbird pollination in Penstemon.