The fate of an internal parasitoid,Nemeritis canescens,in a variety of insects

• 1 The fate of Nemeritis canescens has been studied in 36 species or, counting different stages, in 51 kinds of insects, in order to discover the causes of its success or failure in each.
• 2 The parasitoid was able to develop to the adult stage in 14 of the species studied.
• 3 A defence reaction of the host, cellular encapsulation, was by far the most frequent cause of the death of canescens in species in which it could not develop.
• 4 Deposition of melanin over its mouth probably caused the death of canescens in two species; in other species the role of melanisation was subordinate to encapsulation.
• 5 Very few species, if any, were unsuitable as food; larvae of the parasitoid ingested and assimilated the blood of a wide variety of insects.
• 6 Some individuals of a few species were unsuitable as a habitat for the parasitoid larva.
• 7 The survival of canescens in suitable hosts is discussed with reference to the means by which this parasitoid resists defence reactions.
• 8 Attention is drawn to incidental results of the research: (i) a state of diapause in some hosts was transmitted to first-instar larvae of canescens and delayed their development; (ii) evidence was found that the teratocytes formed by braconid parasitoids function as a means of preventing cellular defence reactions, that they act by attrition of the host, and that they protect a larva of canescens present in the same host; (iii) observations concerning the behaviour of adult canescens in attacking some species, and the survival of supernumerary larvae after competing for the host, are mentioned.

     

Stage-dependent strategies of host invasion in the egg-larval parasitoid Chelonus inanitus

Chelonus inanitus (Braconidae) is a solitary egg-larval parasitoid which lays its eggs into eggs of Spodoptera littoralis (Noctuidae); the parasitoid larva then develops in the haemocoel of the host larva. Host embryonic development lasts approx. 3.5 days while parasitoid embryonic development lasts approx. 16 h. All stages of host eggs can be successfully parasitized, and we show here that either the parasitoid larva or the wasp assures that the larva eventually is located in the host's haemocoel. (1) When freshly laid eggs, up to almost 1-day-old, are parasitized, the parasitoid hatches while still in the yolk and enters the host either after waiting or immediately through the dorsal opening. (2) When 1-2-day-old eggs are parasitized, the host embryo has accomplished final dorsal closure and is covered by an embryonic cuticle when the parasitoid hatches; in this case the parasitoid larva bores with its moving abdominal tip into the host. (3) When 2.5-3.5-day-old eggs are parasitized, the wasp oviposits directly into the haemocoel of the host embryo; from day 2 to 2.5 the embryo is still very small and the wasps, after probing, often restrain from oviposition for a few hours.     

寄生蜂成虫在寄主搜索过程中的学习行为

综述了寄生蜂寄主搜索过程中的学习行为的概念、过程、适应性意义及影响因子。学习是寄生蜂的一种普遍特征,但学习基本上只发生在成虫期,其中联系性学习是一个主要特征。学习可产生启动和嗜好性学习二种效应,在寄生蜂搜索寄主的各个步骤中发挥重要作用,使其在复杂多变的生存环境中可高效地识别和利用各种有用信息,提高搜索效率。学习的潜力及效应可依寄生蜂和寄主的食性专化程度、寄主的发育阶段、寄生蜂自身的生理状态及环境中刺激的性质等因子而变化。对寄生蜂学习行为的了解有助于发展对其行为调控的技术,提高寄生蜂对害虫控制的效能。     

Development of a gregarious ectoparasitoid, Euplectrus separatae (Hymenoptera; Hymenoptera: Eulophidae), that parasitizes Pseudaletia separata (Lepidoptera: Noctuidae)

Euplectrus separatae is a gregarious ectoparasitoid that parasitizes Pseudaletia separata during its third to sixth (last) instars. The eggs of the parasitoid are fixed on the integument of the host dorsolaterally with a hard substance like a piling driven into the integument by the female wasp at the time of oviposition. The first instar of the parasitoid, which hatches three days after oviposition is nourished by ingesting the hemolymph of the host, and ecdyses to the second stadium six days after oviposition. Many hemocytes and epidermal cells were found assembled under the piling and places where a parasitoid had attached its mouth, suggesting that the host had repaired the integument destroyed by the parasitoid. Botryoidal tissue, which stained well with hematoxylin, began to develop from four days after oviposition and became gradually larger with development. Botryoidal tissue appears to function as a secretory organ for thread and a storage organ for nutrients. Seven days after oviposition, the parasitoid larvae migrate down from the dorsal surface to the ventral side of the host. Just before descending they ecdyse to the third stadium and kill the host during their migration. If all parasitoid larvae were removed artificially from the host before they migrate, the host did not die. However, removing the parasitoids after they had started to migrate did not prevent the death of the host. Transmission electron microscopic (TEM) observation of salivary glands of a parasitoid larva before migrating revealed that the salivary gland was composed of cells that were rich in rough surfaced endoplasmic reticulum (rough-ER) with many ribosomes and cells that were filled with a lot of vacuoles just before their collapse. After moving from the host body, the parasitoid larvae doubled in weight by ingesting the tissue of the host and then spun a cocoon. Almost all host tissues were consumed for growth of the parasitoid, like an idiobiont parasitoid.     

Biosteres longicaudatus: Developmental dependence on host (Anastrepha suspensa) physiology

Larvae of Anastrepha suspensa that were in the first day of the third instar were parasitized by females of the solitary endoparasitoid, Biosteres longicaudatus. At the end of the 6-hr oviposition period, larvae were ligated posterior to the ring gland so that some larvae had parasitoids anterior to the ligature while in others, the parasitoids were in the abdomen, posterior to the ligature. Ninety-two percent of the parasitoids anterior to the ligature hatched to the first through third instars. Parasitoids posterior to the ligature had a 75% egg hatch to the first instar only. No larval molts to the second or subsequent instars occurred in these parasitoids. Upon parabiosis to 3-day-old, unparasitized host pupae, the ligated larvae pupated and 97% of the first-instar parasitoids in these parabiosed larval abdomens molted to the second instar. Newly laid parasitoid eggs transplanted to 3-day-old pupal hosts had less than one-third of the egg hatch of those transplanted to first-day third-instar hosts. The data implicate the physiological state of the host (vis-a-vis pupation and associated events) as being an important factor in the development of the endoparasitoid.     

PHENOTYPIC SELECTION BY PARASITOIDS ON THE TIMING OF LIFE HISTORY IN A LEAFMINING MOTH

Direct measurements of phenotypic selection by parasitoids on quantitative traits in herbivorous insects have been rare. I analysed episodes of phenotypic selection on the timing of life-history events in a multivoltine leafmining moth, Phyllonorycter mespilella, and assessed the importance of hymenopterous parasitoids as selective influences. Phyllonorycter mespilella has two consecutive stages of larval development, the sap-feeding (SF) and tissue-feeding (TF) stages. Adult parasitoids host feed predominantly on SF larvae, and oviposit predominantly on TF larvae. Oviposition attack on TF larvae caused positive directional selection on the date of transition to the the TF stage (TF date) in the third generation of P. mespilella in one population in 1991. Overwinter mortality caused negative directional selection on TF date in the third generation in a second population in 1993. No directional or variance selection on TF date was detected in the second population in the second generation of 1993. Parasitoid females accepted SF larvae for oviposition more often in the fall generation than in summer generations in both populations. The relative frequencies of SF and TF larvae may alter the pattern of oviposition attack by parasitoids, and thus the form of phenotypic selection on TF date.     

四种对虾血细胞组成及超微结构

本文应用电镜超薄切片技术,对中国对虾,日本对虾,长毛对虾和草虾的血细胞进行超微结构的研究,根据血细胞形态,超微结构特点,特别是胞质中特征性颗粒的大小和内部结构,区分为四类：１．透明细胞,其胞质不含特征性颗粒,具有较强的吞噬能力;２．小颗粒细胞,其胞质含有高电子密度的小圆形颗粒和条纹状大颗粒,在对虾防御反应中起着关键性作用;３．大颗粒细胞,其胞质中含有高电子密度的均质大颗粒,在宿主防御反应中起着细胞     

Parasitoid-mediated transmission of an iridescent virus

We examined the interaction between an invertebrate iridescent virus (IIV) isolated from Spodoptera frugiperda (J.E. Smith) and the solitary ichneumonid endoparasitoid Eiphosoma vitticolle Cresson. In choice tests, parasitoids examined and stung significantly more virus infected than healthy larvae, apparently due to a lack of defense reaction in virus infected hosts. Parasitoid-mediated virus transmission was observed in 100% of the female parasitoids that stung a virus infected host in the laboratory. Each female parasitoid transmitted the virus to an average (+/-SE) of 3.7+/-0.3 larvae immediately after stinging an infected larva. Caged field experiments supported this result; virus transmission to healthy larvae only occurred in cages containing infected hosts (as inoculum) and parasitoids (as vectors). The virus was highly detrimental to parasitoid development because of premature host death and lethal infection of the developing endoparasitoid. Female parasitoids that emerged from virus infected hosts did not transmit the virus to healthy hosts. We suggest that the polyphagous habits of many noctuid parasitoids combined with the catholic host range of most IIVs may represent a mechanism for the transmission of IIVs between different host species in the field.     

The life history and larval morphology of Aperilampus (Hymenoptera: Chalcidoidea: Philomidinae), with a discussion of the phylogenetic affinities of the Philomidinae

Abstract. The host association and larval morphology of Aperilampus (Hymenoptera: Chalcidoidea: Philomidinae) are documented for the first time based on specimens collected during the excavation of ground-nesting bee nests in South Africa. Aperilampus varians Strand is a primary parasite of the pupa of Halictus (Seladonia) africanus Friese (Hymenoptera: Halictidae). The first and final-instar larvae are described and illustrated, and notes are provided on the behaviour of the first-instar larva. The first-instar larva is a planidium and synapomorphies are documented between the first-instar larva of Aperilampus and the planidia of Chrysolampinae, Perilampidae and Eucharitidae.     

Experimental studies on parasitization byApanteles Glomeratus V. Relationships between growth rate of parasitoid and host age at the time of oviposition

The growth and development ofApanteles glomeratus L. eggs and larvae in the host larva (Pieris rapae crucivora Boisduval) was investigated by calculating their volume. WhenA. glomeratus eggs increase 90 fold in volume after being laid, larvae hatch from them. The larvae grow exponentially and the growth rate of the parasitoid is dependent on the host stage. Being laid in the 1st instar host, the parasitoids grow more slowly than those laid in 2nd–4th instar host. A pupal host stage prevents the parasitoids’ development. When larvae exceed the threshold size of 5.0×10⁸ μ³, they enter the 2nd instar. A few days after they attain the maximum size of 3.3×10⁹ μ³, they moult and egress from the host body.     

团角锤天蛾的生物学特性

团角锤天蛾Gurelca hyas(Walker)危害园林植物——银边六月雪(Serissa foetida cv.Aureovaiegata),以幼虫取食寄主叶片和嫩梢。该虫在湖南省衡阳地区1年发生3代,以老熟幼虫在寄主附近土壤中筑土室化蛹并以蛹在土室中越冬。翌年8月上旬越冬代成虫开始羽化。幼虫5龄,多数幼虫在发育过程中会出现体色变化。第1代、第2代和第3代幼虫分别于8月中旬、9月中旬和10月中旬孵化,各代幼虫均能对寄主造成严重为害。     

Resistance of Apanteles eggs to the haemocytic encapsulation by their habitual host, Pieris

The calyx fluid in the lateral oviduct of a gregarious parasitoid, Apanteles glomeratus contained ellipsoid particles of ca. 130 × 200 nm. These calyx fluid particles did not appear to be embedded in a fibrous outer layer on the surface of eggs in the lateral oviduct. They were not observed on the surfaces of the eggs 3 to 4 hr after being deposited into the host haemocoele. Oviposition experiments indicated that the occurrence of haemocytic defence reactions of the late 2nd instar larvae of the Pieris rapae crucivora against 1 st instar larvae of the parasitoid increased with a decreasing number of the parasitoid eggs introduced into a host, and that more than 5 to 9 parasitoid eggs were needed for suppressing the ability of the host to encapsulate its parasitoid larvae immediately after hatching. When eggs with calyx fluid obtained from egg reservoir were injected into the host, they were found to be encapsulated 1 to 2 days after the injection. They could not start their embryonic development. When calyx fluid-free 3-hr-old eggs were injected in a number of more than 5 eggs into a 5th instar larva of Pieris, 58% of 31 eggs injected had normally hatched without evoking encapsulation reactions by the host. Both electron microscopic observations of parasitoid eggs in the host haemocoele and the experimental results suggested that calyx fluid or calyx fluid particles of the parasitoid might not be involved in the encapsulation-inhibiting activity of the parasitoid eggs. Rather it was anticipated that a substance (or substances) might be secreted by the parasitoid eggs into the haemocoele of the host, which suppressed defence reactions of the host.     

Complex interactions between a plant pathogen and insect parasitoid via the shared vector-host: consequences for host plant infection

Plant viruses modify the development of their aphid vectors by inducing physiological changes in the shared host plant. The performance of hymenopterous parasitoids exploiting these aphids can also be modified by the presence of the plant pathogen. We used laboratory and glasshouse microcosms containing beans (Vicia faba) as the host plant to examine the interactions between a plant virus (pea enation mosaic virus; PEMV) and a hymenopterous parasitoid (Aphidius ervi) that share the aphid vector/host Acyrthosiphon pisum. Neither PEMV-infection of V. faba, nor the carriage of PEMV virions by A. pisum, affected the growth or morphology of the aphid, or the oviposition behaviour and development of A. ervi. The presence of developing Aphidius ervi larvae within Acyrthosiphon pisum did not affect the ability of the aphids to transmit PEMV. However, by reducing their longevity, parasitism ultimately decreased the time viruliferous aphids were able to inoculate plants. In terms of virus dispersal, parasitized aphids exhibited more movement around experimental arenas than unparasitized controls, causing a slight increase in the proportion of beans infected with PEMV. Exposure to adult Aphidius ervi caused Acyrthosiphon pisum to rapidly drop off bean plants and disperse to new hosts, resulting in considerably higher plant infection rates (70%) than that seen in control arenas (25%). The results of this investigation demonstrate that when parasitoids are added to a plant-pathogen-vector system, benefits to the host plant due to reduced herbivore infestation must be balanced against the consequences of parasitoid-induced aphid dispersal and a subsequent increase in the level of plant infection.     

Parasitoid Encapsulation as a Defense Mechanism in the Coccoidea (Homoptera) and Its Importance in Biological Control

Encapsulation is a common defense mechanism exerted by a host insect in response to invasion by a metazoan parasitoid or other foreign organisms. In the process of encapsulation, the host forms a capsule around the parasitoid egg or larva, which is usually composed of host blood cells and the pigment melanin. The capsule may kill the parasitoid and thus prevent successful parasitism. Encapsulation may adversely affect the degree of biological control effected by parasitoids as it may either prevent the establishment of exotic parasitoids in new regions or reduce parasitoid efficacy. A high incidence of encapsulation may also cause difficulties in mass rearing of parasitoids. In the Coccoidea (Homoptera), parasitoid encapsulation has so far been recorded in three families: Coccidae (soft scale insects), Diaspididae (armored scale insects), and Pseudococcidae (mealybugs). Important factors that affect the frequency of parasitoid encapsulation in the Coccoidea include: Host and parasitoid species, the host's physiological age and physiological condition, the host origin (or strain), superparasitism, the rearing and/or ambient temperature, and the host plant. The effects of these factors on the incidence of parasitoid encapsulation in the Coccidae, Diaspididae, and Pseudococcidae are described.     

The response of Hyssopus pallidus to hosts previously parasitised by Ascogaster quadridentata: heterospecific discrimination and host quality

1. Two basic tenets of competition among parasitoids, that taxonomically distinct parasitoids are unable to discriminate against hosts that have previously been attacked by a competitor and that previous parasitism reduces the quality of a host, were tested by monitoring the oviposition response of Hyssopus pallidus, a gregarious ectoparasitoid, to healthy codling moth larvae and codling moth larvae that had previously been parasitised by a solitary endoparasitoid, Ascogaster quadridentata. 2. Hyssopus pallidus accepted both categories of host larva for oviposition when its competitor was constrained as a first‐instar larva by the diapause development of its host, but discriminated against previously parasitised host larvae when its competitor was present as a larger larva in a non‐diapausing host. 3. Hyssopus pallidus distinguished between the two categories of host larva by allocating twice as many eggs to host larvae previously parasitised by A. quadridentata, a response that was not influenced by previous oviposition experience. 4. The larger clutch sizes allocated to previously parasitised host larvae produced twice as many female progeny, each of a typical size, such that the total biomass was twice that produced from the smaller clutches laid on healthy host larvae. Possible confounding influences of host age and diapause are discounted. 5. These results demonstrate that interspecific discrimination does occur in H. pallidus and that host quality can be improved through previous parasitism by an endoparasitoid. Although interspecific discrimination appears rare among insect parasitoids, it may have been overlooked among ectoparasitoids and requires examination of the fitness consequences of interspecific interactions to clarify its adaptive significance.     

Response of an aphid parasitoid, Aphelinus asychis to its host, plant, host-plant complex, and to malathion

Aphelinus asychis (Walker) can be valuable as a biocontrol agent of the aphid, Schizaphis graminum (Rondani), a major pest on grain crops in the United States. This study reports the wind tunnel, and olfactometric responses of this parasitoid to the host (aphid), plant (sorghum), and host-plant complex (aphid-infested sorghum). In addition, the parasitoids' response to malathion-treated plants is also presented. The goal of the present study was to test the hypothesis that volatiles associated with the host attract natural enemies, as reported in cases of many hymenopterous parasitoids, and also to learn about the effects of insecticides on these parasitoids. In wind tunnel studies, these parasitoids moved upwind in the direction of the host-infested plant. There was no direct flight observed, however, these parasitoids were observed to hop and jump, and sometimes walk to their host. In the olfactometer experiments, we found that A. asychis is attracted to host-plant complex. The parasitoids' response to malathion in the olfactometer suggested that a malathion formulation when applied to plants can lure these beneficials, thus providing new insight into the ongoing task of integrating chemical and biological control of insect pests.     

The evolutionary pattern of host use in the Bombyliidae (Diptera): a diverse family of parasitoid flies

The larval host associations and mode of parasitism of Bombyliidae (bee flies) are summarized and analysed within an evolutionary framework. We discuss difficulties in extracting information from the (almost 1000) host records, noting that most observations are made by chance, often imprecise, and distributed unevenly across bombyliid taxa. These caveats aside, the vast majority of Bombyliidae are ectoparasitoid; endoparasitoids are known in only three tribes belonging to two distandy related subfamilies, the Toxophorinae (Gerontini and Systropodini) and Anthracinae (Villini). The recorded host range of Bombyliidae spans seven insect Orders and the Araneae; almost half of all records are from bees and wasps (Hymenoptera). No Bombyliidae have evolved structures to inject eggs directly into the host as is the case in many hymenopterous parasitoids. Bombyliid larvae usually exhibit hyper-metamorphosis, and contact their host while it is in the larval stage. Bee fly larvae consume the host when it is in a quiescent stage such as the mature larva, prepupa or pupa. Records of hyperparasitism by Bombyliidae are uncommon, most occurring in genera of the Anthracinae. All bombyliids recorded as hyperparasitoids do not appear to have evolved in any close association with the primary host, and are best termed pseudohyperparasitoids. Both facultative and obligate pseudohyperparasitism has been recorded. Bombyliidae are difficult to place in the koinobiont/idiobiont classification used most extensively in Hymenoptera but they share most features of koinobionts. Provision-directed cleptoparasitism has been recorded in one genus. We propose an evolutionary scenario progressing from an ancestral substrate-zone free-living predator to ectoparasitoid, a broadening of host range to include the consumption of orthopteran egg pods, and the independent development of endoparasitism in two lineages. The suggestion that host range narrows as the intimacy of encounter between female parasitoid and host increases is supported in the Bombyliidae. Amongst the basal subfamilies which are parasitoids, host range is narrowest in the Toxophorinae. In the more derived subfamilies host range is generally broad, and is dictated by ecological context rather than host phylogeny. Bombyliidae violate the prediction of increased species richness in parasitic groups, and the broad host range of most bee flies is a possible explanation.     

Effects of parasitoids on a mycophagous drosophilid community in northern Japan and an evaluation of the disproportionate parasitism hypothesis

In a host–parasitoid system comprising mycophagous drosophilids and their parasitoids, the drosophilid and parasitoid species assemblages, host use, and the prevalence of parasitism were assessed, and the “disproportionate parasitism hypothesis” was examined with consideration given to yearly variations. The mycophagous drosophilids, their fungal food resources and parasitoids were studied by carrying out an intensive census throughout the activity seasons of 4 years (2000–2003) in Hokkaido, northern Japan. Five hymenopterous parasitoid species, four braconids and one eucoilid, were found. Parasitoids of mycophagous drosophilids are reported for the first time from Asia. Most parasitism (99.2%) was by braconids, in contrast to the dominance of eucoilids in Europe. Parasitism was restricted to the summer, and the rate was high from early July to early August every year. There was considerable yearly variation in the composition of abundant fungus, drosophilid and parasitoid species, especially between 2000 and 2001. The alternation of dominant host species was coupled with the alternation of dominant parasitoid species that differed in host use. Despite the yearly variation in the system, the most dominant host species suffered disproportionately heavy parasitism by the correspondingly dominant parasitoid species every year. The parasitism rate was positively correlated with the relative host abundance. This thus indicates that the disproportionate parasitism mechanism may operate, via which species coexistence is promoted by a higher rate of parasitism of the dominant species.     

Larval development of two parasitic flies (Conopidae) in the common host Bombus pascuorum

Abstract.

• 1 Whenever parasitism by more than one female occurs, larvae of parasitoids not only have to resist host defence but also face competition with other (unrelated) larvae. Competition is particularly important in solitary parasitoids where only one larva is able to complete its development. Such a situation is found in Conopidae (Diptera) parasitizing adult bumble bees where larvae of two species of conopid flies, Sicus ferrugineus L. and Physocephala rufipes F. often compete within the common host Bombus pascuorum Scopoli. This study analysed the larval development of the two species and asks how competition among larvae may be regulated.
• 2 Parasitized workers of B.pascuorum were caught in the field and kept according to different experimental schedules in the laboratory. This provided stage-structured data for the temporal course of development of the parasitic larvae. For the analysis, a simulation model was constructed that estimated the duration of all parasitic stages (Manly, 1990, first method). In both species the egg stage was found to be approximately 2 days, first instar 3 days, second instar 4 days, and third instar 3 days. The total development time is an estimated 10.8 days from oviposition in S.ferrugineus and 11.4 days in P.rufipes. S.ferrugineus develops faster in the beginning, probably because of its larger egg size, whereas P.rufipes pupates at larger size. First-instar larvae of both species possess strong, pointed mandibles.
• 3 The success of conopid larvae seems only marginally affected by host defence, for a single larva per host almost always completes development. Under competition, however, mortality rate increases substantially, and most larvae die in their first instar. Moreover, they show signs of melanization. The estimates for developmental times and the patterns found in this study suggest that conopid larvae seem capable of physical attacks, particularly during the first instar, when elimination of competitors is most common, and that S.ferrugineus has a time advantage because of its faster early development. Because most studies have previously been carried out with hymenopteran parasitoids, this study provides new information about the other large group of parasitoid insects, the Diptera, and demonstrates convergent patterns.

     

Braconiden als Schmarotzer von Staphyliniden

Summary The endoparasitic branconidsCentistes lucidator Nees andBlacus ruficornis Nees were reared fromTachyporus-species, common staphylinids of cultivated fields in Central Europe.Centistes occured inTachyporus hypnorum, obtusus, solutus andchrysomelinus, while only oneBlacus was found inT. obtusus. In the relatively cool and humid summer 1963 in the surroundings of Kiel (Germany) the rate of parasitism ofTachyporus-species byCentistes was about 3 to 8% (table 1). — During oviposition ofCentistes the host does not show any reaction. The immature stages develop in the haemocoele of the beetle. The final-instar larva emerges from the host beetle and spins a cocoon beside of it. The beetle dies while the parasite larva is emerging from it. The first-instar larva is described and illustrated. Both species hibernate as first-instar larvae in the beetles, which have an obligatory diapause and become adults in the next summer.