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.     

我国新疆和湖南棉铃虫种群的遗传学研究

采自湖南衡阳(HY)和新疆哈密(HM)的棉铃虫Helicoverpa armigera(Hubner)种群被室内杂交和回交,杂交F₁代和回交F₂代雌成虫的产卵量、卵孵化率和产卵时间等繁殖力参数均无明显的变化。在22℃下,HM、HY、HM♀×HY♂、HY♀×HM♂和(HY♀×HM♂)×HY♂后代蛹滞育的临界光周期分别为13h 35 min,11 h,11 h 45 min,11 h 43min和11 h9min。在一15℃下,HM、HY、HM♀×HY♂、HY♀×HM♂、HY♀×(HY♀×HM♂)♂和(HY♀×HM♂)♀×HM♂后代滞育蛹的致死中时间(LT”)分别是159.7h、34.27h、100.65 h、116.75h、90.78h和135.58h,亲本F₁代显性度D(HM♀×HY♂)和D(HY♀XHM♂)分别为0.3998和0.5926。遗传分析表明棉铃虫滞育蛹的抗寒性由多个不完全显性的基因控制。     

Wolbachia do not live by reproductive manipulation alone: infection polymorphism in Drosophila suzukii and D. subpulchrella

Drosophila suzukii recently invaded North America and Europe. Populations in Hawaii, California, New York and Nova Scotia are polymorphic for Wolbachia, typically with <20% infection frequency. The Wolbachia in D. suzukii, denoted wSuz, is closely related to wRi, the variant prevalent in continental populations of D. simulans. wSuz is also nearly identical to Wolbachia found in D. subpulchrella, plausibly D. suzukii's sister species. This suggests vertical Wolbachia transmission through cladogenesis (‘cladogenic transmission’). The widespread occurrence of 7–20% infection frequencies indicates a stable polymorphism. wSuz is imperfectly maternally transmitted, with wild infected females producing on average 5–10% uninfected progeny. As expected from its low frequency, wSuz produces no cytoplasmic incompatibility (CI), that is, no increased embryo mortality when infected males mate with uninfected females, and no appreciable sex‐ratio distortion. The persistence of wSuz despite imperfect maternal transmission suggests positive fitness effects. Assuming a balance between selection and imperfect transmission, we expect a fitness advantage on the order of 20%. Unexpectedly, Wolbachia‐infected females produce fewer progeny than do uninfected females. We do not yet understand the maintenance of wSuz in D. suzukii. The absence of detectable CI in D. suzukii and D. subpulchrella makes it unlikely that CI‐based mechanisms could be used to control this species without transinfection using novel Wolbachia. Contrary to their reputation as horizontally transmitted reproductive parasites, many Wolbachia infections are acquired through introgression or cladogenesis and many cause no appreciable reproductive manipulation. Such infections, likely to be mutualistic, may be central to understanding the pervasiveness of Wolbachia among arthropods.     

High incidences and similar patterns of Wolbachia infection in fig wasp communities from three different continents

Abstract Wolbachia are endosymbiotic bacteria that infect numerous arthropod species. Previous studies in Panama and Australia revealed that the majority of fig wasp species harbor Wolbachia infections, but that similar patterns of incidence have evolved independently with different wasp species and Wolbachia strains on the two continents. We found Wolbachia infections in 25/47 species (53%) of fig wasp associated with 25 species of Chinese figs. Phylogenetic analyses of Wolbachia wsp sequences indicated that very similar strains are not obviously found in either closely related or ecologically linked fig wasps species. The extremely high prevalence of Wolbachia in fig wasps (over 50% of species infected) is not constrained by geographical origin and is a recurrent theme of fig wasp/Wolbachia interactions.     

The influence of parthenogenesis-inducing Wolbachia on the oviposition behaviour and sex-specific developmental requirements of autoparasitoid wasps

Parthenogenesis-inducing (PI) Wolbachia are bacteria that cause incipient male eggs of parasitoid wasps to develop as females. These microbes may invade populations and lead to fixation of parthenogenesis. In this study, the consequences of fixation of PI Wolbachia on evolution of behaviour and development were addressed in three species of whitefly parasitoids in the genus Encarsia. Most sexual Encarsia are obligate autoparasitoids. In these haplodiploid wasps, fertilized, female-producing eggs are laid in whitefly or scale insect nymphs, while unfertilized, male-producing eggs are laid in immature parasitoids within the homopteran integument. The oviposition behaviour and progeny developmental requirements of unmated females of a sexual autoparasitoid species were compared with two species that were fixed for PI Wolbachia. All species were treated with antibiotics, effectively ‘curing’ the asexual species of Wolbachia infection. As expected, unmated females of the sexual species, E. pergandiella, laid few eggs in whiteflies relative to immature parasitoids, and males emerged exclusively from parasitoids. In contrast, females of one of the parthenogenetic species, E. formosa, laid few eggs in parasitoids relative to whiteflies, and male progeny emerged exclusively from whiteflies. Females of the second parthenogenetic species, E. hispida, were intermediate in their oviposition behaviour. Females laid eggs in both wasps and whiteflies. However, all of the males except one emerged from the whiteflies. The results suggest that the association of autoparasitoids and PI Wolbachia may result in dramatic evolutionary change of both host selection behaviour and developmental requirements of the infected wasps.     

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.     

褐飞虱翊型分化遗传规律的研究

以褐飞虱Nilaparvata lugens (Stal)长翅型(macroptery,简称M)、短翅型(brachyptery,简称B)的遗传纯系为实验材料,进行亲本、稻株生育期、虫口密度三因子交互实验。结果表明：(1)在环境条件(指稻株生育期、虫口密度等)一致时,B♀×B♂、B♀×M♂、M♀×B♂、M♀×M♂四种亲本组合的F1代短翅型成虫百分率分别为：98%、92%、64%、29%,各亲本组合间差异极显著;(2)亲本相同时,将F1代褐飞虱初孵若虫多头词养(多于l0头/株)在黄熟期稻株上,其长翅型雌、雄成虫百分数均高于灌浆期稻株上;(3)单头饲养实验中发现,不论亲本组合、稻株生育期如何,雌虫绝大多数分化为短翅型,而雄虫则几乎全为长翅型。这表明褐飞虱的翅型分化遗传由一个受多种因子影响的调控体系决定,且调控作用与性别有关。     

共生菌Cardinium对朱砂叶螨的生殖调控作用

为了了解共生菌Cardinium对朱砂叶螨Tetranychus cinnabarinus (Boisduval)的生殖调控作用,从检测到感染Cardinium的种群中选取山西运城和甘肃兰州2个感染率较高的种群作为实验材料,对Cardinium在寄主生殖调控方面的作用进行研究。通过人工培养100%感染Cardinium的种群和100%不感染的种群,并从中挑取不同感染类型的雌雄螨单独进行杂交实验,设立感染Cardinium(♀)×感染Cardinium(♂),感染Cardinium(♀)×不感染(♂),不感染(♀)×感染Cardinium(♂),不感染(♀)×不感染(♂) 4种杂交组合。结果发现,抗生素处理后不感染的雌螨和受感染雄螨的交配表现出了单向的胞质不亲和,而且2个种群表现出了2种类型：在山西种群不亲和的组合中,CI表现为卵孵化率显著降低,多数雌螨都产生出F₁雌螨后代,但是F₁代雌螨数量相对于其他3种组合明显减少; 而在甘肃种群不亲和的组合中则表现为卵全部孵化且幼螨100%存活,但全部为雄螨后代。2个种群中Cardinium的亲缘关系非常相近,而它们却能够在不同的地理种群中表现出不同的CI表型,这提示亲缘关系非常接近的品系也可以产生不同的表型。研究结果为深入揭示Cardinium的感染机制和生殖调控作用提供重要基础。     

Evidence for a recent horizontal transmission and spatial spread of Wolbachia from endemic Rhagoletis cerasi (Diptera: Tephritidae) to invasive Rhagoletis cingulata in Europe

The widespread occurrence of Wolbachia in arthropods and nematodes suggests that this intracellular, maternally inherited endosymbiont has the ability to cross species boundaries. However, direct evidence for such a horizontal transmission of Wolbachia in nature is scarce. Here, we compare the well‐characterized Wolbachia infection of the European cherry fruit fly, Rhagoletis cerasi, with that of the North American eastern cherry fruit fly, Rhagoletis cingulata, recently introduced to Europe. Molecular genetic analysis of Wolbachia based on multilocus sequence typing and the Wolbachia surface protein wsp showed that all R. cingulata individuals are infected with wCin2 identical to wCer2 in R. cerasi. In contrast, wCin1, a strain identical to wCer1 in R. cerasi, was present in several European populations of R. cingulata, but not in any individual from the United States. Surveys of R. cingulata from Germany and Hungary indicated that in some populations, the frequency of wCin1 increased significantly in just a few years with at least two independent horizontal transmission events. This is corroborated by the analysis of the mitochondrial cytochrome oxidase II gene that showed association of wCin1 with two distinct haplotypes in Germany, one of which is also infected with wCin1 in Hungary. In summary, our study provides strong evidence for a very recent inter‐specific Wolbachia transmission with a subsequent spatial spread in field populations.     

Wolbachia affect behavior and possibly reproductive compatibility but not thermoresistance,fecundity, and morphology in a novel transinfected host,Drosophila nigrosparsa

Wolbachia, intracellular endosymbionts, are estimated to infect about half of all arthropod species. These bacteria manipulate their hosts in various ways for their maximum benefits. The rising global temperature may accelerate species migration, and thus, horizontal transfer of Wolbachia may occur across species previously not in contact. We transinfected and then cured the alpine fly Drosophila nigrosparsa with Wolbachia strain wMel to study its effects on this species. We found low Wolbachia titer, possibly cytoplasmic incompatibility, and an increase in locomotion of both infected larvae and adults compared with cured ones. However, no change in fecundity, no impact on heat and cold tolerance, and no change in wing morphology were observed. Although Wolbachia increased locomotor activities in this species, we conclude that D. nigrosparsa may not benefit from the infection. Still, D. nigrosparsa can serve as a host for Wolbachia because vertical transmission is possible but may not be as high as in the native host of wMel, Drosophila melanogaster.     

Search Efficiency of Spalangia cameroni and Muscidifurax raptor on Musca domestica Pupae in Dairy Cattle Farms in Denmark

Indoor releases of Spalangia cameroni Perkins and Muscidifurax raptor Girauelt & Sanders (Hymenoptera: Pteromalidae) were conducted in five organic dairy cattle farms to evaluate the overall effect on parasitism and efficiency at different pupal depths of Musca domestica L. (Diptera: Muscidae). Overall, parasitism increased significantly from 5.3 to 28.8–28.7% of the exposed house fly pupae due to the release of pupal parasitoids. Spalangia cameroni was by far the most dominant species, contributing approximately 71.5–72.3% of the parasitism in the release and post-release period, whereas 20.9–24.4% could be attributed to Muscidifurax raptor. A naturally occurring ichneumonid, Phygadeuon fumator Gravenhorst (Hymenoptera: Ichneumonidae) parasitized 4.1–6.8% of the exposed fly pupae. The placement of house fly pupae at two depths of the bedding, 5–10 and 15–20 cm had no significant effect on overall parasitism whereas M. raptor attacked the house fly pupae significantly more when placed in the 5–10 cm stratum (10.0%) compared to the 15–20 cm stratum (3.2%). The two pupal depths had no significant effect on parasitism by S. cameroni and P. fumator. Albeit S. cameroni contributed significantly to overall parasitism, M. raptor had a significantly higher attack rate when first a female had located bags with sentinel pupae. Based on the above results, however, S. cameroni seems the most appropriate species for managing house flies in straw bedded dairy cattle farms in Denmark. A biological control strategy of simultaneous releases of S. cameroni and M. raptor is discussed.     

Various infection status and molecular evidence for horizontal transmission and recombination of Wolbachia and Cardinium among rice planthoppers and related species

Wolbachia and Cardinium are widely distributed and are considered important for their ability to disturb reproduction and affect other fitness‐related traits of their hosts. By using multilocus sequence typing (MLST), RFLP (restriction fragment length polymorphism) and 16S ribosomal DNA gene sequencing methods, we extensively surveyed Wolbachia and Cardinium infection status of four predominant rice planthoppers and one kind of leafhopper in different rice fields. The results demonstrated that Sogatella furcifera (Horváth) and Laodelphax striatellus (Fallén) were infected with the same Wolbachia strain (wStri), while Nilaparvata lugens (Stål) and its closely related species Nilaparvata muiri China were infected with two phylogeneticlly distant strains, wLug and wMui, respectively. Three new Wolbachia strains (provisionally named wMfas1, wMfas2 and wMfas3) were detected in the leafhopper Macrosteles fascifrons (Stål). Only S. furcifera was co‐infected with Cardinium, which indicated that the distribution of Cardinium in these rice planthoppers was narrower than that of Wolbachia. Unambiguous intragenic recombination events among these Wolbachia strains and incongruent phylogenetic relationships show that the connections between different Wolbachia strains and hosts were more complex than we expected. These results suggest that horizontal transmission and host associated specialization are two factors affecting Wolbachia and Cardinium infections among planthoppers and their related species.     

Impact of Wolbachia on Infection with Chikungunya and Yellow Fever Viruses in the Mosquito Vector Aedes aegypti

Incidence of disease due to dengue (DENV), chikungunya (CHIKV) and yellow fever (YFV) viruses is increasing in many parts of the world. The viruses are primarily transmitted by Aedes aegypti, a highly domesticated mosquito species that is notoriously difficult to control. When transinfected into Ae. aegypti, the intracellular bacterium Wolbachia has recently been shown to inhibit replication of DENVs, CHIKV, malaria parasites and filarial nematodes, providing a potentially powerful biocontrol strategy for human pathogens. Because the extent of pathogen reduction can be influenced by the strain of bacterium, we examined whether the wMel strain of Wolbachia influenced CHIKV and YFV infection in Ae. aegypti. Following exposure to viremic blood meals, CHIKV infection and dissemination rates were significantly reduced in mosquitoes with the wMel strain of Wolbachia compared to Wolbachia-uninfected controls. However, similar rates of infection and dissemination were observed in wMel infected and non-infected Ae. aegypti when intrathoracic inoculation was used to deliver virus. YFV infection, dissemination and replication were similar in wMel-infected and control mosquitoes following intrathoracic inoculations. In contrast, mosquitoes with the wMelPop strain of Wolbachia showed at least a 10⁴ times reduction in YFV RNA copies compared to controls. The extent of reduction in virus infection depended on Wolbachia strain, titer and strain of the virus, and mode of exposure. Although originally proposed for dengue biocontrol, our results indicate a Wolbachia-based strategy also holds considerable promise for YFV and CHIKV suppression.     

Stable coexistence of incompatible Wolbachia along a narrow contact zone in mosquito field populations

In arthropods, the intracellular bacteria Wolbachia often induce cytoplasmic incompatibility (CI) between sperm and egg, which causes conditional embryonic death and promotes the spatial spread of Wolbachia infections into host populations. The ability of Wolbachia to spread in natural populations through CI has attracted attention for using these bacteria in vector‐borne disease control. The dynamics of incompatible Wolbachia infections have been deeply investigated theoretically, whereas in natural populations, there are only few examples described, especially among incompatible infected hosts. Here, we have surveyed the distribution of two molecular Wolbachia strains (wPip11 and wPip31) infecting the mosquito Culex pipiens in Tunisia. We delineated a clear spatial structure of both infections, with a sharp contact zone separating their distribution areas. Crossing experiments with isofemale lines from different localities showed three crossing types: wPip11‐infected males always sterilize wPip31‐infected females; however, while most wPip31‐infected males were compatible with wPip11‐infected females, a few completely sterilize them. The wPip11 strain was thus expected to spread, but temporal dynamics over 7 years of monitoring shows the stability of the contact zone. We examined which factors may contribute to the observed stability, both theoretically and empirically. Population cage experiments, field samples and modelling did not support significant impacts of local adaptation or assortative mating on the stability of wPip infection structure. By contrast, low dispersal probability and metapopulation dynamics in the host Cx. pipiens probably play major roles. This study highlights the need of understanding CI dynamics in natural populations to design effective and sustainable Wolbachia‐based control strategies.     

Effects of Wolbachia on fitness of the Mediterranean fruit fly (Diptera: Tephritidae)

Wolbachia pipientis is a widespread endosymbiont of insects and other arthropods exerting a wide range of biological effects on their hosts. A growing number of recent studies document the influence of Wolbachia on reproduction and lifespan of insect host species. However, little is known regarding effects of Wolbachia on the demographic traits of different host populations. Moreover, whether different Wolbachia strains exert different effects on fitness components of their hosts remains largely unknown. We studied the effects of (a) the Wolbachia strain wCer2 on fitness components of two laboratory lines of the Mediterranean fruit fly, Ceratitis capitata (Diptera: Tephritidae) and (b) two different Wolbachia strains (wCer2 and wCer4) on one of the Mediterranean fruit fly lines. Wolbachia infection (wCer2) shortens the egg‐to‐adult developmental duration of both C. capitata lines, although it prolongs embryonic development. In one of the two lines, egg‐to‐adult mortality increased. Wolbachia infection shortens adult lifespan (to a different extent in males and females) and reduces female fecundity. The different Wolbachia strains differentially affect both immature mortality and developmental duration, and adult longevity and female fecundity. Our findings demonstrate both differential response of two C. capitata lines to Wolbachia infection and differential effects of two Wolbachia strains on the same Mediterranean fruit fly line. Practical and theoretical implications of our findings are discussed.     

Wolbachia infection in six species of gall wasps and their parasitoids

Wolbachia are endosymbiotic bacteria that are widely present in nematodes and arthropods and sometimes have a significant impact on the evolution, ecology, and biology of their hosts. The co-occurrence of Wolbachia within both Cynipid gall wasps and their parasitoids has rarely been studied. In this study, we report the occurrence of six species of gall wasps and 10 species of their parasitoids in central China. Wolbachia detection using the wsp gene showed that Wolbachia infected two species of gall wasps as well as their parasitoids, indicating that horizontal transmission of Wolbachia occurs between gall wasps and their parasitoids. Given that parasitoids will kill their hosts, Wolbachia may be horizontally transferred from gall wasps to their parasitoids. Using multilocus sequence typing (MLST) analysis, five new strains of Wolbachia were identified, all of which belonged to supergroup A. The strains of Wolbachia that infected gall wasps were not the same as those that infected their parasitoids. This result indicated that Wolbachia may evolve independently in parasitoids after they have been transferred from the host gall wasps.     

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.     

Wolbachia prevalence patterns: horizontal transmission,recombination, and multiple infections in chestnut gall wasp-parasitoid communities

The Oriental chestnut gall wasp, Dryocosmus kuriphilus Yasumatsu (Hymenoptera: Cynipidae), is a global invasive pest that causes serious damage to almost all chestnut species belonging to the Castanea genus (Fagaceae). Dryocosmus zhuili Liu et Zhu is a recently described sibling species of D. kuriphilus, which induces galls on Castanea henryi (Skan) Rehd. et Wils. There are many indigenous parasitoid species in China which play an important role in the natural regulation of their population dynamics. Wolbachia is a maternally inherited α-proteobacterium widely found in arthropods. This study screened for the presence of Wolbachia in the two chestnut gall wasps and in six parasitoid species from 12 populations, to investigate the prevalence patterns of Wolbachia in the chestnut gall wasp-parasitoid communities. We found that D. zhuili and four parasitoid species were infected with Wolbachia; among them, all individuals of the two populations of Megastigmus sp. had multiple Wolbachia infections. By using multilocus sequence types to characterize bacterial strains, three new sequence types were identified. The Wolbachia strains infecting D. zhuili (ST-507), Torymus sinensis Kamijo (ST-508), and Sycophila variegata (Curtis) (ST-508) belonged to supergroup A, whereas the Wolbachia strain infecting Megastigmus nipponicus Kamijo (ST-503) belonged to supergroup B. Our results also suggested that horizontal transmission of Wolbachia occurs between chestnut gall wasps and their parasitoids. Moreover, multiple Wolbachia infections of Megastigmus sp. may be due to gene recombination and horizontal transmission.     

Decrease of memory retention in a parasitic wasp: an effect of host manipulation by Wolbachia?

Several factors, such as cold exposure, aging, the number of experiences and viral infection, have been shown to affect learning ability in different organisms. Wolbachia has been found worldwide as an arthropod parasite/mutualist symbiont in a wide range of species, including insects. Differing effects have been identified on physiology and behavior by Wolbachia. However, the effect of Wolbachia infection on the learning ability of their host had never previously been studied. The current study carried out to compare learning ability and memory duration in 2 strains of the parasitoid Trichogramma brassicae: 1 uninfected and 1 infected by Wolbachia. Both strains were able to associate the novel odors with the reward of an oviposition into a host egg. However, the percentage of females that responded to the experimental design and displayed an ability to learn in these conditions was higher in the uninfected strain. Memory duration was longer in uninfected wasps (23.8 and 21.4 h after conditioning with peppermint and lemon, respectively) than in infected wasps (18.9 and 16.2 h after conditioning with peppermint and lemon, respectively). Memory retention increased in response to the number of conditioning sessions in both strains, but memory retention was always shorter in the infected wasps than in the uninfected ones. Wolbachia infection may select for reduced memory retention because shorter memory induces infected wasps to disperse in new environments and avoid competition with uninfected wasps by forgetting cues related to previously visited environments, thus increasing transmission of Wolbachia in new environments.     

Laboratory studies on the biology ofSpalangia nigra [Hym.: Pteromalidae]

At 21 °C,Spalangia nigra Latreille (Hymenoptera: Pteromalidae) averaged 29.3 days between exposure and emergence of 1^st progeny from host house flies,Musca domestica L. (Diptera: Muscidae). At 27 °C, the average developmental time to 1^st emergence was reduced to 26.6 days, and a majority of adult wasps emerged from host house fly puparia between 29 and 40 days postoviposition. The sex ratio of progeny ranged from 1.4 to 1.8 female-to-male, but all progeny of virgin females were male. Male wasps lived from 6.8–15 and females 11–17.8 days at 27 °C; honey as a food source increased longevity. No significant differences in parasitism byS. nigra were associated with host house fly pupal densities ranging from 1 to 200 pupae per female-male pair of wasps, but average percent parasitism decreased at host densities greater than 50. House fly pupae exposed to parasitism at ages ranging from 4 to 96 h did not differ in subsequent production of adult flies.S. nigra did not demonstrate preference for house flies or stable flies,Stomoxys calcitrans (L.) (Diptera: Muscidae) as hosts. The results of these studies indicate thatS. nigra may contribute significantly to previously unexplained mortality of house flies and stable flies.