Induction of paternal genome loss by the paternal-sex-ratio chromosome and cytoplasmic incompatibility bacteria (Wolbachia): A comparative study of early embryonic events

Paternal genome loss (PGL) during early embryogenesis is caused by two different genetic elements in the parasitoid wasp, Nasonia vitripennis. Paternal sex ratio (PSR) is a paternally inherited supernumerary chromosome that disrupts condensation of the paternal chromosomes by the first mitotic division of fertilized eggs. Bacteria belonging to the genus Wolbachia are present in Nasonia eggs and also disrupt paternal chromosome condensation in crosses between cytoplasmically incompatible strains. Cytoplasmic incompatibility Wolbachia are widespread in insects, whereas PSR is specific to this wasp. PGL results in production of male progeny in Nasonia due to haplodiploid sex determination. The cytological events associated with PGL induced by the PSR chromosome and by Wolbachia were compared by fluorescent light microscopy using the fluorochrome Hoescht 33258. Cytological examination of eggs fertilized with PSR-bearing sperm revealed that a dense paternal chromatin mass forms prior to the first metaphase. Quantification of chromatin by epifluorescence indicates that this mass does undergo replication along with the maternal chromatin prior to the first mitotic division but does not replicate during later mitotic cycles. Contrary to previous reports using other staining methods, the paternal chromatin mass remains condensed during interphase and persists over subsequent mitotic cycles, at least until formation of the syncytial blastoderm and cellularization, at which time it remains near the center of the egg with the yolk nuclei. Wolbachia-induced PGL shows several marked differences. Most notable is that the paternal chromatin mass is more diffuse and tends to be fragmented during the first mitotic division, with portions becoming associated with the daughter nuclei. Nuclei containing portions of the paternal chromatin mass appear to be delayed in subsequent mitotic divisions relative to nuclei free of paternal chromatin. Crosses combining incompatibility with PSR were cytologically similar to Wolbachia-induced PGL, although shearing of the paternal chromatin mass was reduced. Wolbachia may, therefore, block an earlier stage of paternal chromatin processing in the fertilized eggs than does PSR. © 1995 Wiley-Liss, Inc.     

Mitochondrial DNA phylogeography of the Cotesia flavipes complex of parasitic wasps (Hymenoptera: Braconidae)

The Cotesia flavipes species complex of parasitic wasps are economically important worldwide for the biological control of lepidopteran stem borers. The complex currently comprises three species: Cotesia flavipes Cameron, C. sesamiae (Cameron) and C. chilonis (Matsumura) (Hymenoptera: Braconidae), which appear morphologically similar. Despite their economic importance, little is known about the genetic diversity and phylogeography of these parasitoids. Differences in the biology of geographic populations have generally been interpreted as genetic divergence among strains, but direct genetic evidence is lacking. In Australia, several stem borer pests in neighbouring countries have been identified as significant threats to the sugar industry. However, the status of C. flavipes in Australia is unknown. To examine the genetic variation among worldwide populations of the C. flavipes complex and investigate the status of the Australian C. flavipes-like species, partial sequence data were generated for mitochondrial gene regions, 16S rRNA and COI. Parsimony, minimum evolution and Bayesian analyses based on 21 geographic populations of the complex and four outgroups supported the monophyly of the complex and the existence of genetically divergent populations of C. flavipes and C. sesamiae. The geographically isolated Australian haplotypes formed a distinct lineage within the complex and were ~3.0% divergent from the other species. The results indicated that historical biogeographic barriers and recent biological control introductions play an important role in structuring lineages within these species. This study provides a phylogeographical context for examining adaptive evolution and host range within biologically divergent strains of the C. flavipes complex.     

Male mating performance and cytoplasmic incompatibility in a wPip Wolbachia trans‐infected line of Aedes albopictus (Stegomyia albopicta)

Wolbachia pipientis Hertig (Rickettsiales: Rickettsiaceae) is a maternally inherited endosymbiont of a large number of insects and other arthropods that induces various effects on host reproductive biology. Among these, cytoplasmic incompatibility (CI) is a form of sterility induced in eggs produced by mating between infected males and females uninfected or infected by an incompatible Wolbachia strain. This phenomenon has been proposed as a potential way to produce functionally sterile males to be used in genetic control programmes. In this paper, we report on experiments carried out to evaluate the mating performances of males of an Aedes albopictus (Stegomyia albopicta) (Diptera: Culicidae) line (ARwP), harbouring a new Wolbachia infection [the wPip strain from Culex pipiens Linnaeus (Diptera: Culicidae)], in comparison with naturally infected males (SR line). ARwP males did not differ from SR males with regard to insemination capacity. Mating competitiveness did not differ significantly between lines in either laboratory or greenhouse conditions. Moreover, crosses with SR females were characterized by a 100% CI regardless of ARwP male age. All of these findings suggest that ARwP males may represent a very efficient tool for control programmes against Ae. albopictus based on the release of functionally sterile males.     

高温冲击对沃尔巴克氏体(Wolbachia)诱导孤雌产雌的丽蚜小蜂(Encarsia formosa)生殖和发育的影响

研究了持续高温(31℃恒温)和高适温交替(白天31℃/夜间25℃变温)条件对感染沃尔巴克氏体(Wolbachia)的丽蚜小蜂生殖和发育的影响.结果发现在持续高温条件下,丽蚜小蜂的生殖力和羽化率降低、寿命缩短、后代雄性比例增加,丽蚜小蜂从F1代开始产生雄性后代,且雄性比例在45%以上,F2代雄性比例达到最高值,表明高温冲击会对丽蚜小蜂的控害潜能产生不利的影响,因此在丽蚜小蜂的商业生产和田间应用中要注意环境温度,避免因高温带来的损失.在31℃恒温条件下连续培养3代或6代再转入25℃培养,丽蚜小蜂雄性后代比例和沃尔巴克氏体在丽蚜小蜂雌性群体中的感染率都能够很快恢复到高温处理前的水平.说明沃尔巴克氏体对环境变化有一个自动调节和适应的过程.变温条件下丽蚜小蜂从F2代开始产生雄性后代,但雄性后代比例较低(13%),表明短期高温冲击对丽蚜小蜂的生殖方式影响不大,但是短期高温冲击如果持续作用就会产生积累效应,影响丽蚜小蜂的后代性别.     

二斑叶螨两种群中Wolbachia诱导的胞质不亲和作用的影响因子比较研究

Wolbachia诱导胞质不亲和（cytoplasmic incompatibility, CI）是对寄主的生殖调控中最常见的一种方式,在不同种群中CI表达的差异较大。以二斑叶螨Tetranychus urticae辽宁兴城（LN）和江苏徐州（JS）两个地理种群为实验材料,经筛选获得100%感染Wolbachia和不感染Wolbachia的品系,通过杂交实验和实时定量PCR的方法研究寄主遗传背景、雄螨日龄、温度以及雄螨体内Wolbachia菌量等因子对我国二斑叶螨体内Wolbachia诱导CI能力的影响。结果表明：1,3,5和7日龄的雄螨诱导的CI的强度没有差异,表明雄螨日龄对我国二斑叶螨体内Wolbachia诱导CI的能力没有影响。二斑叶螨分别放在20℃的低温、 25℃的适温和30℃的高温条件下饲养时,Wolbachia诱导CI的能力也没有任何变化,表明温度对我国二斑叶螨体内Wolbachia诱导CI的能力也没有影响。江苏徐州种群所感染Wolbachia菌量显著高于辽宁兴城种群,并且这两个种群感染Wolbachia菌量都随着雄螨日龄的增大而显著增加,表明Wolbachia菌量对我国二斑叶螨体内Wolbachia诱导CI的能力没有影响;江苏徐州种群内Wolbachia不能诱导CI可能是Wolbachia株系与寄主的遗传背景共同作用的结果。研究结果为进一步了解Wolbachia的生殖调控机理提供了重要依据。     

Biology of Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae): A facultative Hyperparasitoid of stem borers

The biology of the parasitoid Tetrastichus howardi, which was introduced from the Philippines into South Africa for the biological control of the stem borer Chilo partellus, was studied in the laboratory. On average, a T. howardi female produced 101 progeny (92% females) which developed in 4.3 hosts. The upper threshold temperature for development was around 33°C, the minimum threshold was calculated as 12.8°C and the thermal constant as 239.8 day‐degrees. With hosts, females lived 23.6 and males 16.7 days. T. howardi was found to be a facultative hyperparasitoid with a very wide host range. As a primary parasitoid, it developed in pupae of various Lepidoptera as well as Coleoptera and Hymenoptera and as a hyperparasitoid in dipteran and hymenopteran parasitoids. A linear relation was found between the number of emergent parasitoids and the volume of the host from which they emerged. Preference tests indicated that T. howardi preferred to parasitize the phytophagous insects C. partellus and Heliothis armigera, over their parasitoids Xanthopimpla stemmator and Palexorista laxa. The host selection of inexperienced T. howardi females was different from the experienced parasitoids. When given a choice, females showed preference for the host species they were allowed to parasitize previously and the host species from which they had been reared. The use of facultative hyperparasitoids in biological control in general and against stem borers in South Africa in particular is discussed.     

西安城区环境中释放花绒寄甲成虫对光肩星天牛的生物防治效果评价

光肩星天牛Anoplophora glabripennis(Motsch.)是我国西北及华北地区危害杨树、柳树等树种的主要蛀干害虫,较难防治.花绒寄甲Dastarcus helophoroides(Fairmaire)是光肩星天牛等林木蛀干害虫的重要天敌昆虫.我国近儿年来已开始广泛利用花绒寄甲对光肩星天牛进行生物防治,...     

Intra-individual coexistence of a Wolbachia strain required for host oogenesis with two strains inducing cytoplasmic incompatibility in the wasp Asobara tabida

Cytoplasmically inherited symbiotic Wolbachia bacteria are known to induce a diversity of phenotypes on their numerous arthropod hosts including cytoplasmic incompatibility, male-killing, thelytokous parthenogenesis, and feminization. In the wasp Asobara tabida (Braconidae), in which all individuals harbor three genotypic Wolbachia strains (wAtab1, wAtab2 and wAtab3), the presence of Wolbachia is required for insect oogenesis. To elucidate the phenotype of each Wolbachia strain on host reproduction, especially on oogenesis, we established lines of A. tabida harboring different combinations of these three bacterial strains. We found that wAtab3 is essential for wasp oogenesis, whereas the two other strains, wAtabl and wAtab2, seem incapable to act on this function. Furthermore, interline crosses showed that strains wAtab1 and wAtab2 induce partial (about 78%) cytoplasmic incompatibility of the female mortality type. These results support the idea that bacterial genotype is a major factor determining the phenotype induced by Wolbachia on A. tabida hosts. We discuss the implications of these findings for current hypotheses regarding the evolutionary mechanisms by which females of A. tabida have become dependent on Wolbachia for oogenesis.     

Perspectives on the development of biological control agents in Africa

Concern over the impact of chemical pesticides on human health and the environment continues to stimulate the study of alternative, biological pest control agents (BCA). In Africa, use of BCA products is just emerging, primarily in the export sector where growers are using a mixture of products from new African companies and products imported from outside Africa. In contrast, although interest in BCA for use in domestic markets has been widely supported by development funding partners for many years, few products have become available to these growers. The limited uptake of BCA in Africa suggests there may be constraints and issues working against their wider implementation. Here, we focus on non-technical constraints and issues facing microbial BCA applied inundatively, but arguments extend to a greater or lesser degree to all BCA. The challenges to wider BCA availability could be overcome by: a more coherent approach to their regulation across the continent; support for BCA development that is based on evidence of need and applicability; and political advocacy to lobby for necessary resources being made available to all stakeholders.     

Molecular detection of Wolbachia pipientis in natural populations of sandfly vectors of Leishmania infantum in endemic areas: first detection in Lutzomyia longipalpis

A polymerase chain reaction‐based method was used to screen sandflies for infection with Wolbachia (Rickettsiales: Rickettsiaceae), an intracellular bacterial endosymbiont found in many arthropods and filarial hosts. Positive results were obtained in five of 200 field‐collected sandflies and were confirmed by sequencing. All sandflies were Lutzomyia longipalpis (Diptera: Psychodidae) captured in a region endemic for visceral leishmaniasis in Brazil. This is the first study to identify Wolbachia infection in this Lutzomyia species, which is the main vector of leishmaniasis in the study area. The low infection rate found in this study (2.5%), together with the lack of detection of Wolbachia in previous studies and the diversity found in the sequences analysed, suggests horizontal transmission to these sandflies.     

Newly invading species exploiting native host-plants: the case of the African Zaprionus indianus (Gupta) in the Brazilian Cerrado (Diptera,Drosophilidae)

The African Zaprionus indianus (Diptera, Drosophilidae) was introduced into the Neotropical Region by the end of the 1990’s, and it became abundant in several types of altered and natural environments. In the Cerrado, the second South American biome in extension, it has been found mainly in open vegetation and during the rainy season. In the current work, we showed that Z. indianus utilizes a major native fruit of the Brazilian Cerrado (Solanum lycocarpum) primarily, all over the fructification period and states of fruit’s decay, confirming the adaptative versatility of this invading fly in new environments.     

Effect of sorghum phenology on the control of Chilo partellus with Nosema marucae (microspora: Nosematidae)

An aqueous suspension of Nosema marucae spores was sprayed on foliage of sorghum plants that had been infested with neonate Chilo partellus larvae at 3, 5, 7 and 9 weeks after (plant) emergence (WAE). These periods corresponded to plants at the tillering, early booting, soft dough and late maturation phenological stages, respectively. The extent of borer infestation and plant damage was monitored until crop harvest, and compared with plants which had been similarly infested but not sprayed with the pathogen, and with plants in insect‐free control plots. When applied early, infestation with neonate borer larvae caused most damage to the plants and the greatest reduction in yield in the untreated plots. Early treatment with N. marucae spores at 3 and 5 WAE resulted in the greatest reduction in damage to plants and the highest improvement in yield of seeds. It is apparent, therefore, that for maximum crop protection the microsporidian needs to be applied when sorghum is in an early phenological stage.     

Calyx fluid proteins of two Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) biotypes in Kenya: implications to biological control of the stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae)

Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous larval endoparasitoid of Busseola fusca (Fuller) (Lepidoptera: Noctuidae) in sub-Saharan Africa. In Kenya, reports suggest that C. sesamiae occurs as two biotypes. Biotype avirulent to B. fusca gets encapsulated by haemocytes in this host and is unable to complete development. Biotype virulent to B. fusca is able to overcome immune defences. Factors present in the calyx fluid such as the PolyDNAviruses (PDV), venom and calyx fluid proteins have been implicated in the variation of C. sesamiae virulence against B. fusca. In the present study, calyx fluid proteins of the two C. sesamiae biotypes were compared using 2-D gel electrophoresis. More protein spots were observed in the virulent parasitoid calyx fluid, but some proteins were specifically observed in the avirulent parasitoid calyx fluid while others were observed in both. To study changes in proteins due to parasitism of B. fusca larvae by the two strains, SDS-PAGE gel were performed on fat body tissues and the haemolymph at three time points. Differences between the two strains were observed in both the fat body and haemolymph tissues. Parasitism-specific protein bands were detectable in fat body tissues of B. fusca larvae parasitized by the two C. sesamiae strains. These proteins were absent in unparasitized larvae. Implications for using C. sesamiae as a biocontrol agent of B. fusca in Africa are discussed.     

Survey for parasites ofSesamia calamistis (Lep.: Noctuidae) andEldana saccharina (Lep.: Pyralidae) in southwestern Nigeria

Field surveys were conducted during 1990–92 to document the relative abundance of different species of parasites of the lepidopterous stem borersSesamia calamistis Hampson andEldana saccharina Walker in maize fields in southwestern Nigeria. Species of parasitoids detected on both stem borers included the larvalpupal parasitoidsSturmiopsis parasitica Curran (Diptera: Tachinidae) andBrachymeria feae Masi (Hymenoptera: Chalcididae), and the larval parasitoidDolichogenidea polaszeki Walker (Hymenoptera: Braconidae). The braconidCotesia sesamiae (Cameron) was found attackingS. calamistis. The hyperparasitoidExoristobia dipterae (Risbec) (Hymenoptera: Encyrtidae) was detected on a pupa ofS. parasitica. Parasitic nematodes belonging toMermis sp. and/orHexamermis sp. were found infesting larvae of both stem borers. Overall, larval/pupal parasitization levels at Ibadan were low and ranged from 4.2 to 22.8% forS. calamistis and 1.2 to 13% forE. saccharina. Of the parasites found,S. parasitica was the most common, followed by nematodes. Four hymenopteran egg parasitoids were found attackingS. calamistis: Telenomus busseolae Gahan,T. isis Polaszek (Scelionidae),Lathromeris ovicida Risbec, andTrichogrammatoidea eldanae Viggiani (Trichogrammatidae). Egg parasitization ranged from 13.4 to 41.5%. The only egg parasitoid detected onE. saccharina wasTelenomus applanatus Bin and Johnson, which inflicted only 5% parasitization.     

Laboratory studies on the biology and host range of Dichrorampha odorata (Lepidoptera: Tortricidae), a biological control agent for Chromolaena odorata (Asteraceae)

Dichrorampha odorata (Lepidoptera: Tortricidae) is a moth from Jamaica whose larvae bore into, and kill, the shoot tips of the invasive alien plant, Chromolaena odorata (L.) King and Robinson (Asteraceae). This study reports aspects of the biology of D. odorata, and also determined the host specificity (larval and adult no-choice trials) of the moth. Adults were short lived (ranging from 2 to 7 days), with females laying a mean of 15.4 eggs. Eggs took 9 days to hatch, larvae 20–23 days to develop and the pupal stage lasted 11–12 days, giving an overall lifecycle period of 41–45 days. Larval no-choice tests using 34 asteraceous test species indicated that only C. odorata could sustain complete development of D. odorata to adulthood, although there was slight initial boring 14 test species (plus chromolaena). Results from the adult nochoice trials, in which seven test-plant species were exposed to D. odorata, were consistent with those from larval trials, with larval damage, pupae and adults of D. odorata recorded from only C. odorata. This confirmed that only C. odorata is a suitable host for D. odorata in South Africa. Permission has subsequently been granted for the release of D. odorata in South Africa, thus making it the first shoot-tip attacking agent to be released against C. odorata. It is hoped that in the field, high levels of damage by the moth will reduce the height and therefore competitiveness of C. odorata, thereby contributing to the success of biological control of this plant.     

A simulation model of biological control of social wasps (Vespinae) using mermithid nematodes

Abstract

The nematode (Pheromermis spp.) is a potential biocontrol agent for wasps (Vespula spp.) in countries where invasive populations of wasps cause serious economic, social, and conservation problems. Using a simulation model previously developed for hornets, which belong to a genus with a similar biology to Vespula, we investigated the possibility of using nematodes as a biological control agent. The model wasp colony was exposed to different simulated levels of nematode infection during colony development, and the final number of wasp sexuals produced recorded. The model predicted that early and high levels of wasp infection had the greatest effect on reducing sexual production. However, even colonies with high (80%) levels of infection were still able to produce some sexuals, indicating that wasp colonies are resilient to infections. The model identified several key areas needing further research, including the effects of nematodes on the behaviour and physiology of wasps, of lengthening the infective period, and of increasing infection levels in both the wasps and intermediate transport hosts.     

First record of a specialist folivore of Chromolaena odorata (Asteraceae) in Togo,and indices of its range expansion in Nigeria: implications for biological control

Pareuchaetes pseudoinsulata is reported for the first time in Togo and widespread in south-western Nigeria, albeit in low densities and difficult to detect. Country-wide surveys are warranted in both countries, with the intention of renewing efforts in the biological control of Chromolaena odorata in western Africa, where the socio-ecological impact of the weed is significant.     

Comparison of two populations of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) as candidates for biological control of the invasive weed Schinus terebinthifolia (Sapindales: Anacardiaceae)

Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae) (hereafter Schinus), is one of the worst invasive species in Florida and Hawaii. The thrips Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae) is being considered as a potential biological control agent of Schinus. Two populations of this thrips were collected in the weed's native range; one from central-east Brazil (Ouro Preto thrips) and a second from north-east Brazil (Salvador thrips). Temperature requirements, adult fecundity and impact on different plant haplotypes by P. ichini were examined in the laboratory. Complete development of thrips from both populations occurred at temperatures ranging from 20 to 30°C. Two approaches were used to model the predicted distributions of the thrips populations in the USA: the physiological model (NAPPFAST) based on cold tolerance and the ecological niche model based on climatic variables (MaxEnt). The physiological model predicted that both populations of P. ichini may establish in similar areas of the USA, overlapping with the distribution of Schinus. However, the niche model predicted that only the Ouro Preto thrips could establish in the USA. The difference in model predictions suggests an apparent preadaptation of the Salvador thrips to lower temperatures than those experienced at the locations they were collected in Brazil. The Ouro Preto thrips had similar fecundity on two Florida Schinus haplotypes, whereas lower fecundity on haplotype A was found for the Salvador thrips. Based on these results, the Ouro Preto population may be better adapted to the climatic conditions and plant haplotypes found in Florida. Moreover, greenhouse studies indicated that Schinus growth was greatly reduced by thrips feeding, which may result in lower weed reproduction and densities in the field.     

中国部分地区柑桔木虱体内感染Wolbachia的检测及其系统发育分析

Wolbachia是一种广泛分布于节肢动物体内的共生细菌, 该共生菌经寄主卵的细胞质传播并参与多种寄主生殖活动调控, 对节肢动物的物种进化有着重要意义并可能应用于害虫的生物防治。本研究以柑桔黄龙病（Huanglongbing, HLB）的主要传播媒介——柑桔木虱Diaphorina citri为研究对象, 通过Wolbachia的16S rDNA、 细胞分裂基因（ftsZ）、 表面蛋白基因（wsp）的特异引物对来自于中国广西北海、 广西柳州、 广东深圳、 广东阳春、 福建福州5个地区的柑桔木虱进行PCR扩增, 并对扩增产物进行克隆测序, 与GenBank中相关序列进行比对分析, 建立了柑桔木虱共生Wolbachia的系统发育树。结果显示上述5个地区的柑桔木虱均存在Wolbachia感染, 通过Wolbachia的16S rDNA, ftsZ基因和wsp基因DNA序列的系统发育分析表明, 5个地区的柑桔木虱体内的Wolbachia均属于B组; 基于wsp基因的系统发育分析进一步表明5个地区的亚洲柑桔木虱体内的Wolbachia属于B组的Con亚组, 且不同地区柑桔木虱体内的Wolbachia的16S rDNA, ftsZ基因和wsp基因序列差异不明显。研究结果为认识柑桔黄龙病传播媒介昆虫的进化及其综合防治提供了重要的参考依据。     

Natural biological control of green scale (Hemiptera: Coccidae): a field life-table study

Understanding how the biotic and abiotic factors influence pest-population dynamics is important to implement sound pest management strategies in biological control and integrated pest management (IPM) programmes. Coccus viridis (Green) is an important indirect pest of coffee plants, but very little has been done to understand the factors that contribute most for its biological control in the field. In the present study, we examined the critical life stage and the key factors associated with the mortality of C. viridis in coffee plantations in Brazil by conducting field-based life table studies. Predators, parasitoids, fungi, infested leaf abscission and rainfall were collectively responsible for a total C. viridis mortality of 96.08%. Predation by coccinellids was the key factor governing the mortality of C. viridis. The parasitism of early instars by parasitoids was the second most important factor contributing to C. viridis mortality. Unlike the parasitoids, the fungus Lecanicillium lecanii caused mortality of scales in more advanced life stages. The abscission of infested leaves from the trees, and rainfall also contributed to the mortality of C. viridis. The nymph stage was considered the critical stage for mortality of C. viridis in the field. The results suggest that predators (Coccinellidae) are the most important factors controlling C. viridis, and thus should be the target of conservation measures in coffee plantations infested with this pest.