BIONOMICS OF MICROPLITIS MEDIATOR (HYM: BRACONIDAE) PARASITIZING PSEUDALETIA SEPARATA (LEP: NOCTUIDAE)*

Abstract This paper deals with the bionomics of Microplitis mediator parasitizing Pseudaletia separata. There were some stings (ca. 3. 1%) in which female wasps oviposited more than one eggs and about 4. 6% stings that there was no egg laid into a host. A negative correlation existed between the host age and percentage of parasitization. When the host suffered more stings by the parasitoid wasps, the percentage of parasitization was higher. But there was no correlation between the parasitoid sex ratio and the host age or the frequency of stings by the parasitoids. The host age is not the major factor affecting the offspring sex ratio of the parasitoid. Some putative sex determinant factors in the parasitoid are discussed and the 2nd instar of the host is recommended as a suitable host age in which parasitization could be performed for the purpose of the parasitoid mass culture.     

Toxic and behavioral effects of selected insecticides on theHeliothis parasitoidMicroplitis croceipes

Toxic and behavior-modifying actions of several formulated insecticides were determined forMicroplitis croceipes (Cresson), a braconid parasitoid ofHeliothis spp. Exposure of adult parasitoids to cotton plants sprayed at recommended field rates with a pyrethroid/formamidine mixture (fenvalerate/chlordimeform) resulted in significantly higher mortality rates (10.4 to 22.6 percent) than in controls. Exposure to the carbamate thiodicarb resulted in similar rates of mortality. Only methomyl, a type of carbamate different from thiodicarb, caused mortality significantly higher than all other treatments, ranging to about 70%. Flight activity was measured by attraction to cotton in a laboratory wind tunnel bioassay. Females sprayed directly with a fenvalerate/chlordimeform mixture had significantly decreased flight activity up to 20 h post-treatment. Alternatively, attraction to cotton sprayed with either the fenvalerate/chlordimeform mixture or with methomyl to unsprayed females was significantly decreased, compared to plants sprayed with water only. These results suggest that the actions of insecticides, other than those of direct toxicity, may be important on beneficial parasitoids. Behaviors, such as flight activity and foraging, may be altered by even relatively non-toxic insecticides, thus potentially modifying the effectiveness of natural enemies. This article reports the results of research only. Mention of a proprietary product does not constitute endorsement or a recommendation for its use by the U.S. Department of Agriculture.     

斜纹夜蛾取食四种植物对马尼拉侧沟茧蜂发育和繁殖的影响

研究斜纹夜蛾Spodoptera litura幼虫取食4种植物后对马尼拉侧沟茧蜂Microplitis manilae生长发育和繁殖的影响,为利用该蜂开展斜纹夜蛾的生物防治提供理论依据。在人工气候箱内(26℃±1℃、RH 65%±5%、L∶D=12∶12)研究了斜纹夜蛾取食豇豆Vigna unguiculata、芋艿Colocasia esculenta、烟草Nicotiana tabacum和芥蓝Brassica alboglabra 4种植物对马尼拉侧沟茧蜂的生长发育和繁殖的影响。结果表明:马尼拉侧沟茧蜂寄生取食豇豆的夜蛾幼虫,其幼虫期最短,化蛹率、羽化率和累计存活率最高,性比最低,寿命最长;寄生取食烟草的夜蛾幼虫,其幼虫期最长,化蛹率、羽化率和累计存活率最低,蛹重最轻,蛹期最长;从取食芥蓝的斜纹夜蛾幼虫体内育出的雌蜂产卵量最高,但成蜂寿命最短;斜纹夜蛾取食4种植物对雌蜂个体大小无显著影响,但取食烟草的夜蛾幼虫体内育出的雄蜂个体最小。马尼拉侧沟茧蜂寄生取食不同植物的斜纹夜蛾幼虫,马尼拉侧沟茧蜂的发育和繁殖存在显著差异。     

Developmental status of endo-developmental stages of Microplitis rufiventris kok. in Spodoptera littoralis (boisd.) larvae topically treated by juvenile hormones I and II

The juvenile hormones I and II (JHI and JHII) were topically applied at concentrations of 1 or 5 μg to Spodoptera littoralis larvae containing newly deposited eggs of Microplitis rufiventris. The study demonstrated that both hormones do influence several aspects of the development of the parasitoid after treatment of its host larvae. Of these effects: (1) significant lengthening of periods of eggs and larvae, (2) moulting failure of parasitic larvae, (3) moulting the parasitic larvae into supernumerary instar, (4) arrest of postembryonic development in the first larval instar, (5) reduction in the emergence rate of parasitoid larvae, and (6) influence on embryogenesis. The application of JHI was more effective in disrupting the endo-development of the parasitoid than JHII. In all tests, control hosts produced significantly (P < 0.01) more parasitoids than treated ones. Off-target effects on natural enemies may seriously limit the use of JHs, especially in integrated control programmes.     

Ovipositional discrimination by Microplitis rufiventris females between healthy and granulosis virus-infected Spodoptera littoralis larvae

Ovipositional choice tests by Microplitis rufiventris females (Hym., Braconidae) between granulosis virus‐infected (GVI) and non‐infected (NI) Spodoptera littoralis larvae (Lep., Noctuidae), were assessed using discriminatory methods for re‐isolating the NI and virus‐infected hosts after removing the female parasitoid. When M. rufiventris females were given a choice between NI and GVI S. littoralis hosts, the adult females exhibited marked preference (P < 0.01) for the NI (i.e. higher quality) hosts. In this case, M. rufiventris females and S. littoralis GV (SlGV) did not significantly compete for the same type of host larvae and are, generally, compatible. However, when the choice was given between two low qualities of S. littoralis hosts, i.e. virus‐free previously parasitized hosts and viral‐infected hosts a significant preference (P < 0.01) of the parasitoid females for the GVI larvae was observed. In this case, the parasitoid would be at a disadvantage when competing with GV for the same host. However, the parasitoid could be used as an additional tool for the dissemination of biocontrol viruses within different pest populations, i.e. hosts other than S. littoralis. Importantly, the results showed different strategies of parasitoid female in egg‐laying management. When M. rufiventris female was given a choice between healthy and SlGVI hosts, the female deposited more eggs than when she was given a choice between two low qualities of host larvae. The results of the study may have implications in pest management strategies using M. rufiventris and SlGV against S. littoralis larvae.     

Learning and the role of host-specific volatiles during in-flight host-finding in the specialist parasitoid Microplitis croceipes

Abstract The effect of antennal contact with host-related stimuli on the subsequent flight response to host-specific volatiles was examined in the specialist parasitoid, Microplitis croceipes (Cresson) (Hymenoptera: Braconidae). In a choice test between two species of caterpillars feeding on cowpea, free-flying female M.croceipes lacking prior contact with host cues landed more often on sources of odour from its host, Heliothis tea (Boddie), than from non-host Spodoptera frugiperda (Smith). After female parasitoids contacted host cues with their antennae, more landings on sources containing hosts were observed only when caterpillars used in the pre-flight treatment and in the odour sources fed on the same plant species. The degree to which host-experienced wasps landed more often on hosts as compared with non-hosts varied with host-instar and plant species. The role of learning in host finding in specialist parasitoids is discussed.     

侧沟茧蜂属二新种记述(膜翅目,茧蜂科)

记述了采自福建武夷山、浙江(龙王山、百山祖)、湖北神农架、山东崂山和黑龙江镜泊湖等地的侧沟茧蜂属Microplitis Foerster 2新种。两色侧沟茧蜂Microplitis bicol-oratus sp．nov．(♀)和长径侧沟茧蜂Microplitis longiradiusis sp．nov．(♀)。两色侧沟茧蜂Microplitis bicoloratus与M．obscuripennis Xu and He相似,但以下特征与之区别：1)前后单眼间距与单眼直径等长(后者小于单眼直径);2)中胸盾片具一宽而深的中纵沟,且内具小脊(后者无中纵沟);3)后翅后小脉直(后者明显弯向翅基);4)翅半透明,淡烟褐色,前翅翅痣下方具一暗色斑(后者翅不透明,一致暗烟褐色);5)后足胫节中部具1黄白色环(后者为一致黑色)。采自福建、浙江、湖北和山东。长径侧沟茧蜂Microplitis longiradiusis与M．marshalli Kokujev相似,但以下特征与之区别：1)后单眼间距与单复眼间距等长(后者短于单复眼间距);2)腹部第2～3背板红黄色(后者黑色);3)后足基节红黄色(后者黑色);4)前翅r脉短于2-SR脉(后者与2-SR脉等长);5)前翅1-R1脉特别短,约与翅痣等长(后者明显长于翅痣长)。采自黑龙江。本文附中国侧沟茧蜂属种类检索表。模式标本均保存在浙江大学植保系寄生蜂标本室。     

侧沟茧蜂属二新种记述 （膜翅目：茧蜂科，小腹茧蜂亚科）

 记述采自辽宁、宁夏、新疆、浙江和贵州的侧沟茧蜂属Microplitis Foerster 二新种：宽背侧沟茧蜂M. amplitergius sp.nov.和内弯侧沟茧蜂M. incurvata s p.nov.。模式标本保存在浙江大学植物保护系昆虫标本室。