Wolbachia modifies thermal preference in Drosophila melanogaster

Environmental variation can have profound and direct effects on fitness, fecundity, and host–symbiont interactions. Replication rates of microbes within arthropod hosts, for example, are correlated with incubation temperature but less is known about the influence of host–symbiont dynamics on environmental preference. Hence, we conducted thermal preference (T_p) assays and tested if infection status and genetic variation in endosymbiont bacterium Wolbachia affected temperature choice of Drosophila melanogaster. We demonstrate that isogenic flies infected with Wolbachia preferred lower temperatures compared with uninfected Drosophila. Moreover, T_p varied with respect to three investigated Wolbachia variants (wMel, wMelCS, and wMelPop). While uninfected individuals preferred 24.4°C, we found significant shifts of −1.2°C in wMel- and −4°C in flies infected either with wMelCS or wMelPop. We, therefore, postulate that Wolbachia-associated T_p variation within a host species might represent a behavioural accommodation to host–symbiont interactions and trigger behavioural self-medication and bacterial titre regulation by the host.     

Wolbachia effects on thermal preference of natural Drosophila melanogaster are influenced by host genetic background,Wolbachia type,and bacterial titer

Temperature plays a fundamental role in the fitness of all organisms. In particular, it strongly affects metabolism and reproduction in ectotherms that have limited physiological capabilities to regulate their body temperature. The influence of temperature variation on the physiology and behaviour of ectotherms is well studied but we still know little about the influence of symbiotic interactions on thermal preference (T_p) of the host. A growing number of studies focusing on the Wolbachia-Drosophila host-symbiont system found that Wolbachia can influence T_p in Drosophila laboratory strains. Here, we investigated the effect of Wolbachia on T_p in wild-type D. melanogaster flies recently collected from nature. Consistent with previous data, we found reduced T_p compared to an uninfected control in one of two fly strains infected with the wMelCS Wolbachia type. Additionally, we, for the first time, found that Wolbachia titer variation influences the thermal preference of the host fly. These data indicate that the interaction of Wolbachia and Drosophila resulting in behavioural variation is strongly influenced by the genetic background of the host and symbiont. More studies are needed to better understand the evolutionary significance of T_p variation influenced by Wolbachia in natural Drosophila populations.     

Elimination of Wolbachia from Urolepis rufipes (Hymenoptera: Pteromalidae) with Heat and Antibiotic Treatments: Implications for Host Reproduction

Molecular analyses using ftsZ and wsp primers identified infections of type-A Wolbachia bacteria in populations of Urolepis rufipes (Ashmead) (Hymenoptera: Pteromalidae), a potential biocontrol agent for pest flies (Diptera: Muscidae) in livestock confinements. Incidence of infections ranged from 10 to 45% for three field populations and 100% in a laboratory colony. Provision of adult wasps with sugar water containing 50 μg mL^–1 tetracycline hydrochloride, or continuous rearing at 34±0.5°C eliminated Wolbachia from experimental populations after four and six generations, respectively. Results were similar for experimental crosses between infected parents, between uninfected parents, and between infected female and uninfected male parents. Embryonic mortality was less than 5% for the F₁ generation, which had an adult sex ratio of 2♀:1♂. In contrast, experimental crosses between uninfected female and infected male parents were associated with an embryonic mortality of about 20% and produced 37% fewer F₁ adults. However, because of an F₁ sex ratio of almost 0♀:1♂,?this latter cross produced an overall higher number of F₁ males. These combined results reflect elements of both male development (MD) type cytoplasmic incompatibility (CI) and female mortality (FM) type CI Wolbachia. MD type CI Wolbachia in incompatible crosses causes haploidization of fertilized (i.e., female) eggs. The resultant haploid eggs develop into males so that more males are produced in incompatible versus compatible crosses. FM type CI produces fewer offspring and a male-biased F₁ generation caused by enhanced mortality of female embryos. We speculate that the fate of fertilized eggs - haploidization versus mortality - may reflect differences in bacterial densities.     

Population‐specific effect of Wolbachia on the cost of fungal infection in spider mites

Many studies have revealed the ability of the endosymbiotic bacterium Wolbachia to protect its arthropod hosts against diverse pathogens. However, as Wolbachia may also increase the susceptibility of its host to infection, predicting the outcome of a particular Wolbachia‐host–pathogen interaction remains elusive. Yet, understanding such interactions and their eco‐evolutionary consequences is crucial for disease and pest control strategies. Moreover, how natural Wolbachia infections affect artificially introduced pathogens for biocontrol has never been studied. Tetranychus urticae spider mites are herbivorous crop pests, causing severe damage on numerous economically important crops. Due to the rapid evolution of pesticide resistance, biological control strategies using entomopathogenic fungi are being developed. However, although spider mites are infected with various Wolbachia strains worldwide, whether this endosymbiont protects them from fungi is as yet unknown. Here, we compared the survival of two populations, treated with antibiotics or naturally harboring different Wolbachia strains, after exposure to the fungal biocontrol agents Metarhizium brunneum and Beauveria bassiana. To control for potential effects of the bacterial community of spider mites, we also compared the susceptibility of two populations naturally uninfected by Wolbachia, treated with antibiotics or not. In one population, Wolbachia‐infected mites had a better survival than uninfected ones in absence of fungi but not in their presence, whereas in the other population Wolbachia increased the mortality induced by B. bassiana. In one naturally Wolbachia‐uninfected population, the antibiotic treatment increased the susceptibility of spider mites to M. brunneum, but it had no effect in the other treatments. These results suggest that natural Wolbachia infections may not hamper and may even improve the success of biological control using entomopathogenic fungi. However, they also draw caution on the generalization of such effects, given the complexity of within‐host–pathogens interaction and the potential eco‐evolutionary consequences of the use of biocontrol agents for Wolbachia‐host associations.     

Melanic mutation causes a fitness decline in bean beetles infected by Wolbachia

Wolbachia cannot live outside a host, which is thought to be the reason for host‐Wolbachia coevolution toward benign parasitism, especially because the fitness of Wolbachia is traded against its host's fitness. Insect melanism has been reported to have a positive effect on pathogen resistance, but melanic mutants of Callosobruchus analis (Fabricius) and Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae) are infected with Wolbachia. Callosobruchus chinensis is infected with CI‐inducing Wolbachia, and melanic mutants exhibit fitness decline. Interestingly, this decline is not observed in C. analis melanic mutants that are infected with CI‐free Wolbachia. Our research question is whether the infection of CI‐inducing Wolbachia causes fitness decline of melanic hosts in C. analis. We examined fecundity, fertility, and longevity of C. analis melanic mutants and compared them between uninfected and infected hosts with CI‐inducing Wolbachia. Infected melanic mutants of C. analis exhibited fitness decline leading to reduced hatch rates even when parental combinations were compatible. Wolbachia can invade a host population by causing CI to decrease the fraction of uninfected hosts, but melanic mutant hosts decrease the number of infected hosts through fitness decline. Nevertheless, the melanism in hosts is not able to stop Wolbachia invasion in C. analis.     

The culture ofEntomophthora muscae (C) Fres. in carrot flies (Psila rosae F.) and the effect of temperature on the pathology of the fungus

A method for maintaining anin vivo culture ofEntomophthora muscae (C) Fres. on its original host, adult carrot flies (Psila rosae F.), is described. The lethal time for adult carrot flies was greatly influenced by temperature, both for infected and for uninfected flies. In the range 8.2°C–20.2°C the LT₅₀ for infected flies was about 5.4 times shorter than the estimated average life-span for uninfected flies. The discharge of primary spores was also strongly dependent on temperature. The total number of primary spores discharged per fly at 100% RH and in darkness ranged between 1.2×10⁴ and 9.6×10⁴ with a mean of 5.1×10⁴.      

Reduced competitive ability due to Wolbachia infection in the parasitoid wasp Trichogramma kaykai

Several hymenopteran parasitoids are infected with parthenogenesis‐inducing (PI) Wolbachia. Infected wasps produce daughters instead of sons from unfertilized eggs. Thus far, little is known about the direct effects of PI Wolbachia on their host's fitness. Here, we report reduced competitive ability due to Wolbachia infection in a minute parasitoid wasp, Trichogramma kaykai Pinto and Stouthamer (Hymenoptera: Trichogrammatidae). Immature survival of infected individuals in a host parasitized by a single infected female, laying a normal clutch of eggs, was lower than those parasitized by a single uninfected individual. When the offspring of infected and uninfected females shared the same host, the infected immatures had significantly lower survival rates than their uninfected counterparts. The survival rate of infected immatures was higher when they competed with other infected immatures from a different infected parent than in competition with uninfected immatures of conspecific wasps. Thus, the host Trichogramma can suffer a substantial reduction in fitness when it is infected with the PI Wolbachia. We discuss why such a reduction is to be expected when populations of infected and uninfected individuals co‐occur, and how the reduced competitive ability of PI Wolbachia influences the spread of the bacteria in the field.     

Vertically transmitted symbiont reduces host fitness along temperature gradient

Parasites with exclusive vertical transmission from host parent to offspring are an evolutionary puzzle. With parasite fitness entirely linked to host reproduction, any fitness cost for infected hosts risks their selective elimination. Environmental conditions likely influence parasite impact and thereby the success of purely vertical transmission strategies. We tested for temperature‐dependent virulence of Caedibacter taeniospiralis, a vertically transmitted bacterial symbiont of the protozoan Paramecium tetraurelia. We compared growth of infected and cured host populations at five temperatures (16–32 °C). Infection reduced host density at all temperatures, with a peak of ?30% at 28 °C. These patterns were largely consistent across five infected Paramecium strains. Similar to Wolbachia symbionts, C. taeniospiralis may compensate fitness costs by conferring to the host a ‘killer trait’, targeting uninfected competitors. Considerable loss of infection at 32 °C suggests that killer efficacy is not universal and that limited heat tolerance restricts the conditions for persistence of C. taeniospiralis.     

Sexual selection in an isopod with Wolbachia‐induced sex reversal: males prefer real females

A variety of genetic elements encode traits beneficial to their own transmission. Despite their ‘selfish’ behaviour, most of these elements are often found at relatively low frequencies in host populations. This is the case of intracytoplasmic Wolbachia bacteria hosted by the isopod Armadillidium vulgare that distort the host sex ratio towards females by feminizing the genetic males they infect. Here we tested the hypothesis that sexual selection against Wolbachia‐infected females could maintain a polymorphism of the infection in populations. The infected neo‐females (feminized males) have lower mating rates and received less sperm relative to uninfected females. Males exhibited an active choice: they interacted more with uninfected females and made more mating attempts. A female behavioural difference was also observed in response to male mating attempts: infected neo‐females more often exhibited behaviours that stop the mating sequence. The difference in mating rate was significant only when males could choose between the two female types. This process could maintain a polymorphism of the infection in populations. Genetic females experimentally infected with Wolbachia are not exposed to the same sexual selection pressure, so the infection alone cannot explain these differences.     

<Emphasis Type="Italic">Wolbachia</Emphasis> infection increases recapture rate of field-released <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Wolbachia pipientis is a commonly occurring endosymbiont with well-characterised effects on host reproductive biology associated with its infection of the gonads. Wolbachia infections are also widespread in somatic tissues and consequently they have the potential to play a much broader role in host biology. Recently, Wolbachia was shown to alter the locomotion of Drosophila melanogaster in response to food cues in the laboratory. To determine whether this laboratory-based phenotype might translate to real differences for insects in the field, we performed a simple mark-release-recapture experiment with Wolbachia-infected D. melanogaster in a forested habitat. We demonstrate that infected flies are recaptured at twice the rate of uninfected flies, although infection does not affect the distance traveled by those flies recaptured. The differences in recapture could be explained by infection-induced changes in physiology or behavior. If generalizable, such changes may affect the interpretation of behavioral studies for Wolbachia-infected insects and have potential implications for the dynamics of Wolbachia infections in natural populations, including situations where Wolbachia-infected insects are being released for biological control.     

Age,tissue, genotype and virus infection regulate Wolbachia levels in Drosophila

The bacterial symbiont Wolbachia can protect insects against viral pathogens, and the varying levels of antiviral protection are correlated with the endosymbiont load within the insects. To understand why Wolbachia strains differ in their antiviral effects, we investigated the factors controlling Wolbachia density in five closely related strains in their natural Drosophila hosts. We found that Wolbachia density varied greatly across different tissues and between flies of different ages, and these effects depended on the host–symbiont association. Some endosymbionts maintained largely stable densities as flies aged while others increased, and these effects in turn depended on the tissue being examined. Measuring Wolbachia rRNA levels in response to viral infection, we found that viral infection itself also altered Wolbachia levels, with Flock House virus causing substantial reductions in symbiont loads late in the infection. This effect, however, was virus‐specific as Drosophila C virus had little impact on Wolbachia in all of the five host systems. Because viruses have strong tissue tropisms and antiviral protection is thought to be cell‐autonomous, these effects are likely to affect the virus‐blocking phenomenon. However, we were unable to find any evidence of a correlation between Wolbachia and viral titres within the same tissues. We conclude that Wolbachia levels within flies are regulated in a complex host–symbiont–virus‐dependent manner and this trinity is likely to influence the antiviral effects of Wolbachia.     

Development of a new attract‐and‐kill technology for Oriental fruit moth control using insecticide‐impregnated fabric

Various physiological effects of Wolbachia infection have been reported in invertebrates, but the impact of this infection on behavior and the consequences of these behavioral modifications on fitness have rarely been studied. Here, we investigate the effect of Wolbachia infection on the estimation of host nutritive resource quality in a parasitoid wasp. We compare decision‐making in uninfected and Wolbachia‐infected strains of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) on patches containing either fresh or old host eggs. For both strains, fresh eggs were better hosts than older eggs, but the difference was smaller for the infected strain than for the uninfected strain. Oviposition behavior of uninfected wasps followed the predictions of optimal foraging theory. They behaved differently toward high‐ vs. low‐quality hosts, with more hosts visited and more ovipositions, fewer high‐quality hosts used for feeding or superparasitism, and a sex ratio that was more biased toward females in patches containing high‐quality hosts than in patches containing low‐quality ones. Uninfected wasps also displayed shorter acceptance and rejection times in high‐quality hosts than in hosts of lower quality. In contrast, infected wasps were less efficient in evaluating the nutritive quality of the host (fresh vs. old eggs) and had a reduced ability to discriminate between unparasitized and parasitized hosts. Furthermore, they needed more energy and therefore engaged in host feeding more often. This study highlights possible decision‐making manipulation by Wolbachia, and we discuss its consequences for Wolbachia fitness.     

Combined effects of elevated CO2 concentration and Wolbachia on Hylyphantes graminicola (Araneae: Linyphiidae)

The increasing concentration of carbon dioxide in atmosphere is not only a major cause of global warming, but it also adversely affects the ecological diversity of invertebrates. This study was conducted to evaluate the effect of elevated CO₂ concentration (ambient, 400 ppm and high, 800 ppm) and Wolbachia (Wolbachia‐infected, W⁺ and Wolbachia‐uninfected, W^?) on Hylyphantes graminicola. The total survival rate, developmental duration, carapace width and length, body weight, sex ratio, net reproductive rate, nutrition content, and enzyme activity in H. graminicola were examined under four treatments: W^? 400 ppm, W^? 800 ppm, W⁺ 400 ppm, and W⁺ 800 ppm. Results showed that Wolbachia‐infected spiders had significantly decreased the total developmental duration. Different instars showed variations up to some extent, but no obvious effect was found under elevated CO₂ concentration. Total survival rate, sex ratio, and net reproductive rate were not affected by elevated CO₂ concentration or Wolbachia infection. The carapace width of Wolbachia‐uninfected spiders decreased significantly under elevated CO₂ concentration, while the width, length and weight were not significantly affected in Wolbachia‐infected spiders reared at ambient CO₂ concentration. The levels of protein, specific activities of peroxidase, and amylase were significantly increased under elevated CO₂ concentration or Wolbachia‐infected spiders, while the total amino content was only increased in Wolbachia‐infected spiders. Thus, our current finding suggested that elevated CO₂ concentration and Wolbachia enhance nutrient contents and enzyme activity of H. graminicola and decrease development duration hence explore the interactive effects of factors which were responsible for reproduction regulation, but it also gives a theoretical direction for spider's protection in such a dynamic environment. Increased activities of enzymes and nutrients caused by Wolbachia infection aids for better survival of H. graminicola under stress.     

Wolbachia‐induced expression of kenny gene in testes affects male fertility in Drosophila melanogaster

Wolbachia are Gram‐negative endosymbionts that are known to cause embryonic lethality when infected male insects mate with uninfected females or with females carrying a different strain of Wolbachia, a situation characterized as cytoplasmic incompatibility (CI). However, the mechanism of CI is not yet fully understood, although recent studies on Drosophila melanogaster have achieved great progress. Here, we found that Wolbachia infection caused changes in the expressions of several immunity‐related genes, including significant upregulation of kenny (key), in the testes of D. melanogaster. Overexpression of key in fly testes led to a significant decrease in egg hatch rates when these flies mate with wild‐type females. Wolbachia‐infected females could rescue this embryonic lethality. Furthermore, in key overexpressing testes terminal deoxynucleotidyl transferase‐mediated dUTP‐biotin nick‐end labeling signal was significantly stronger than in the control testes, and the level of reactive oxygen species was significantly increased. Overexpression of key also resulted in alterations of some other immunity‐related gene expressions, including the downregulation of Zn72D. Knockdown of Zn72D in fly testes also led to a significant decrease in egg hatch rates. These results suggest that Wolbachia might induce the defect in male host fertility by immunity‐related pathways and thus cause an oxidative damage and cell death in male testes.     

Population genetics of Wolbachia‐infected,parthenogenetic and uninfected,sexual populations of Tetrastichus coeruleus (Hymenoptera: Eulophidae)

Wolbachia are endosymbiotic bacteria known to manipulate the reproduction of their hosts. These manipulations are expected to have consequences on the population genetics of the host, such as heterozygosity levels, genetic diversity and gene flow. The parasitoid wasp Tetrastichus coeruleus has populations that are infected with parthenogenesis‐inducing Wolbachia and populations that are not infected. We studied the population genetics of T. coeruleus between and within Wolbachia‐infected and uninfected populations, using nuclear microsatellites and mitochondrial DNA. We expected reduced genetic diversity in both DNA types in infected populations. However, migration and gene flow could introduce new DNA variants into populations. We therefore paid special attention to individuals with unexpected (genetic) characteristics. Based on nuclear and mitochondrial DNA, two genetic clusters were evident: a thelytokous cluster containing all Wolbachia‐infected, parthenogenetic populations and an arrhenotokous cluster containing all uninfected, sexual populations. Nuclear and mitochondrial DNA did not exhibit concordant patterns of variation, although there was reduced genetic diversity in infected populations for both DNA types. Within the thelytokous cluster, there was nuclear DNA variation, but no mitochondrial DNA variation. This nuclear DNA variation may be explained by occasional sex between infected females and males, by horizontal transmission of Wolbachia, and/or by novel mutations. Several females from thelytokous populations were uninfected and/or heterozygous for microsatellite loci. These unexpected characteristics may be explained by migration, by inefficient transmission of Wolbachia, by horizontal transmission of Wolbachia, and/or by novel mutations. However, migration has not prevented the build‐up of considerable genetic differentiation between thelytokous and arrhenotokous populations.     

The transmission and effects of Wolbachia bacteria in parasitoids

Wolbachia bacteria are obligatory intracellular parasites of arthropods and have been detected in about 70 species of parasitic wasps and three parasitoid flies. Wolbachia are transmitted cytoplasmically (maternally) and modify host reproduction in different ways to enhance their own transmission: parthenogenesis induction (PI), cytoplasmic incompatibility (CI), or feminization (F) of genetic males. Only PI and CI are known in parasitoids. PI-Wolbachia cause thelytoky in otherwise arrhenotokous parasitoids by generating diploid (rather than haploid) unfertilized wasp eggs. CI-Wolbachia cause incompatibility of crosses between infected males and uninfected females because the paternally derived chromosomes fail to decondense and are destroyed after syngamy. More complex situations arise when hosts harbor multiple infections, which can lead to bidirectional incompatibility and may be involved in parasitoid speciation. The relative fitness of infected and uninfected hosts is important to the population dynamics of Wolbachia, and more data are needed. Evolutionary conflict should be common between host genes, Wolbachia genes, and other "selfish" genetic elements. Wolbachia-specific PCR primers are now available for several genes with different rates of evolution. These primers will permit rapid screening in future studies of spatial and temporal patterns of single and multiple infection. Molecular phylogenies show that CI- and PI-Wolbachia do not form discrete clades. In combination with experimental transfection data, this result suggests that host reproductive alterations depend on the interaction between attributes of both Wolbachia and host. Moreover, Wolbachia isolates from closely related hosts do not usually cluster together, and phylogenies suggest that Wolbachia may have radiated after their arthropod hosts. Both results support considerable horizontal transmission of Wolbachia between host species over evolutionary time. Natural horizontal transmisson between parasitoids and their hosts, or with entomoparasitic nematodes or ectoparasitic mites, remains a tantalizing but equivocal possibility. Received: November 27, 1998 / Accepted: January 15, 1999     

Diurnal variation in repeated sprint performance cannot be offset when rectal and muscle temperatures are at optimal levels (38.5°C)

The present study investigated whether increasing morning rectal temperatures (T_rec) to evening levels, or increasing morning and evening T_rec to an “optimal” level (38.5°C), resulting in increased muscle temperatures (T_m), would offset diurnal variation in repeated sprint (RS) performance in a causal manner. Twelve trained males underwent five sessions [age (mean ± SD) 21.0 ± 2.3 years, maximal oxygen consumption (V?O₂max) 60.0 ± 4.4 mL.kg^–1 min^–1, height 1.79 ± 0.06 m, body mass 78.2 ± 11.8 kg]. These included control morning (M, 07:30 h) and evening (E, 17:30 h) sessions (5-min warm-up), and three further sessions consisting of a warm-up morning trial (M_E, in 39–40°C water) until T_rec reached evening levels; two “optimal” trials in the morning and evening (M_38.5 and E_38.5, in 39–40°C water) respectively, until T_rec reached 38.5°C. All sessions included 3 × 3-s task-specific warm-up sprints, thereafter 10 × 3-s RS with 30-s recoveries were performed a non-motorised treadmill. T_rec and T_m measurements were taken at the start of the protocol and following the warm-up periods. Values for T_rec and T_m at rest were higher in the evening compared to morning values (0.48°C and 0.69°C, p < 0.0005). RS performance was lower (7.8–8.3%) in the M for distance covered (DC; p = 0.002), average power (AP; p = 0.029) and average velocity (AV; p = 0.002). Increasing T_rec in the morning to evening values or optimal values (38.5°C) did not increase RS performance to evening levels (p = 1.000). However, increasing T_rec in the evening to “optimal” level through a passive warm-up significantly reduced DC (p = 0.008), AP (p < 0.0005) and AV (p = 0.007) to values found in the M condition (6.0–6.9%). Diurnal variation in T_rec and T_m is not wholly accountable for time-of-day oscillations in RS performance on a non-motorised treadmill; the exact mechanism(s) for a causal link between central temperature and human performance are still unclear and require more research.     

Wolbachia in wasps parasitic on filth flies with emphasis on Spalangia cameroni

The house fly, Musca domestica L., and the stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), are cosmopolitan pests parasitized by a guild of more than two dozen species of wasps. Several species of these wasps have been commercialized as biocontrol agents or are being studied for this purpose. Wolbachia bacteria are known to infect at least some of these wasps and are of interest because infections can dramatically affect insect reproduction. A survey in this parasitoid–fly system detected Wolbachia in 15 of 21 species of wasps and in three of nine species of flies parasitized by these wasps. Phylogenetic analyses using wsp gene sequences identified single isolate infections in most cases. Infections of two and four isolates were detected in Nasonia vitripennis (Walker) and Spalangia cameroni Perkins (Hymenoptera: Pteromalidae), respectively. Laboratory experiments showed infections in S. cameroni to cause an incomplete form of female‐mortality (FM) type cytoplasmic incompatibility (CI). Crosses between uninfected female and infected male partners (♀×♂^w) produced fewer progeny, which had a strong male‐biased sex ratio. Crosses between ♀×♂, ♀^w×♂^w, and ♀^w×♂ produced more progeny, which had a female‐biased sex ratio. Developmental times of progeny were increased when the paternal parent was infected with Wolbachia, regardless of whether the maternal parent was infected or whether offspring developed from fertilized eggs. This result may reflect the action of Wolbachia on components of the seminal fluid that then affect the development of offspring from inseminated females. It is hoped that future studies of Wolbachia in this guild will facilitate the rearing and application of these wasps as biocontrol agents of house fly and stable fly.     

Rapid spread of male‐killing Wolbachia in the butterfly Hypolimnas bolina

Reproductive parasites such as Wolbachia can spread through uninfected host populations by increasing the relative fitness of the infected maternal lineage. However, empirical estimates of how fast this process occurs are limited. Here we use nucleotide sequences of male‐killing Wolbachia bacteria and co‐inherited mitochondria to address this issue in the island butterfly Hypolimnas bolina. We show that infected specimens scattered throughout the species range harbour the same Wolbachia and mitochondrial DNA as inferred from 6337 bp of the bacterial genome and 2985 bp of the mitochondrial genome, suggesting this strain of Wolbachia has spread across the South Pacific Islands at most 3000 years ago, and probably much more recently.     

Variation in Antiviral Protection Mediated by Different Wolbachia Strains in Drosophila simulans

Drosophila C virus (DCV) is a natural pathogen of Drosophila and a useful model for studying antiviral defences. The Drosophila host is also commonly infected with the widespread endosymbiotic bacteria Wolbachia pipientis. When DCV coinfects Wolbachia-infected D. melanogaster, virus particles accumulate more slowly and virus induced mortality is substantially delayed. Considering that Wolbachia is estimated to infect up to two-thirds of all insect species, the observed protective effects of Wolbachia may extend to a range of both beneficial and pest insects, including insects that vector important viral diseases of humans, animals and plants. Currently, Wolbachia-mediated antiviral protection has only been described from a limited number of very closely related strains that infect D. melanogaster. We used D. simulans and its naturally occurring Wolbachia infections to test the generality of the Wolbachia-mediated antiviral protection. We generated paired D. simulans lines either uninfected or infected with five different Wolbachia strains. Each paired fly line was challenged with DCV and Flock House virus. Significant antiviral protection was seen for some but not all of the Wolbachia strain-fly line combinations tested. In some cases, protection from virus-induced mortality was associated with a delay in virus accumulation, but some Wolbachia-infected flies were tolerant to high titres of DCV. The Wolbachia strains that did protect occurred at comparatively high density within the flies and were most closely related to the D. melanogaster Wolbachia strain wMel. These results indicate that Wolbachia-mediated antiviral protection is not ubiquitous, a finding that is important for understanding the distribution of Wolbachia and virus in natural insect populations.