Behavioral mechanisms of parasitic wasps for searching concealed insect hosts

Wood borers are important forest insect pests and difficult to be controlled owing to their concealed behavior. However, parasitic wasps can effectively ascertain and parasitize wood borers as well as other concealed pests by using special searching, finding and attacking mechanisms, which have been developed during the course of long-term coevolution with their hosts. The present paper summarizes the behavioral mechanisms of parasitic wasps involved in searching and locating their concealed hosts. Parasitic wasps can accurately find the location of their hidden hosts and then parasitize them, usually by using olfactory semiochemicals from hosts (lavare and adults), host frass and symbiotic microorganisms in host galleries; visual signals from color contrast of plant surface; contact stimuli from characters of host physical defense; substrate vibrations produced by host feeding and movement; infrared radiation from host activities and metabolizability. Some parasitic wasps may integrate the information of several stimuli from different sources to enhance the reliability and accuracy of host locations. In addition, the potentials for utilizing the host location signals of parasitoids in biological control are discussed.     

Delayed inhibition of host development by the nonparalyzing venoms of parasitic wasps

The nonparalyzing venoms of two unrelated parasitic wasps, Eulophus larvarum and Clinocentrus gracilipes, in separate ways cause delayed yet well-defined arrests in their hosts' development, apparently by disrupting events normally under endocrine control. The venom of E. larvarum (for which species host acceptance and oviposition behavior is described) prevents apolysis in its host after a depressed feeding period. The venom employed by C. gracilipes switches the host to a pharate pupal stage irrespective of its larval instar.     

Sex allocation of parasitic wasps: local mate competition,dispersal before mating and host quality variation

We constructed a sex allocation model for parasitic wasps to explain the wide variation in their sex ratio, considering the effects of local mate competition, partial dispersal of progeny before mating, and heterogeneity in host quality among patches. We conducted an experiment to compare with the predictions of our model. We considered the following situations. First, the hosts are distributed in discrete patches: a number of female wasps visit and oviposit in each patch. Second, all the progeny do not mate within the natal patch; some of them disperse to take part in population-wide random mating. We calculated ES sex ratios in cases where there are two kinds of patches: good ones and poor ones. We examined the dependency of ES sex ratios on several parameters, i.e., 1) the probability that a daughter mates in her natal patch, 2) the ratio of the female fitness of the good patch to that of the poor patch, 3) the proportion of poor patches, and 4) the number of foundresses in a patch. The result of our experiment showed the same tendency as the calculation in case where the LMC effect is high in each patch. We briefly discuss a possible selection pressure for dispersal of progeny, with special reference to the mating structure of parasitic wasps.     

生物因子对寄生蜂滞育的影响

在影响寄生蜂滞育的生物因子中,寄主及亲代是主要影响因子。寄主可以从种类、类型、生理状态及丰富度等方面影响寄生蜂的滞育:寄生不同种类的寄主,寄生蜂的滞育反应、滞育进度、滞育比例以及光周期反应表现等均有不同;寄主类型的影响在蚜茧蜂类群中表现最为突出,不同寄主类型能对蚜茧蜂的滞育诱导产生不同影响;此外,寄主生理状态和寄主丰富度也是影响寄生蜂滞育的重要因子。亲代对寄生蜂滞育的影响则通过其所经历的环境条件以及自身因素等方面来表现:亲代经历的光周期和温度等能显著影响子代的滞育,甚至起完全决定作用;在亲代自身因素的影响中,亲代虫龄差异是主要因素。本文同时对寄生蜂滞育的研究及应用前景也一并作了展望。     

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.     

水稻大螟越冬幼虫寄生蜂种类调查与主要寄生蜂越冬动态分析

大螟Sesamia inferens(Walker)是水稻上一种重要的钻蛀性害虫,其寄主范围广,近年来为害加重。由于长期以来对大螟的防治采取兼治策略,大螟已经对多种农药产生了抗性。因此,掌握水稻大螟生物防治资源有重要的应用意义。本研究报道了江苏扬州地区水稻大螟越冬幼虫体内仅有两种寄生蜂,分别是中华茧蜂Amyosoma chinensis和螟黄足盘绒茧蜂Cotesia flavipes,其中螟黄足盘绒茧蜂是优势种群。通过近三年的系统调查发现：在自然界中螟黄足盘绒茧蜂在大螟越冬幼虫体内的寄生率呈现动态变化,最高寄生率达33.33%,并且不同年份之间有差异。螟黄足盘绒茧蜂最短出茧时间仅为5.0 d,最长不超过14.0 d。除了12月份至次年1月份采集的螟黄足盘绒茧蜂外,其它时间点采集到的螟黄足盘绒茧蜂的羽化率高达75%以上。该研究结果为利用螟黄足盘绒茧蜂防治大螟提供了研究基础。     

扬州地区水稻二化螟寄生蜂种类及主要寄生蜂发生动态

本文报道了江苏扬州地区水稻二化螟Chilo suppressalis(Walker)寄生蜂主要有10种,即中华钝唇姬蜂Eriborus sinicus(Holmgren)、二化螟盘绒茧蜂Cotesia chilonis(Munakata)、稻螟小腹茧蜂Microgaster russata Haliday、螟甲腹茧蜂Chelonus munakatae Munakata、中华茧蜂Amyosoma chinensis(Szepligeti)、螟黄足盘绒茧蜂Cotesia flavipes(Cameron)、夹色姬蜂Auberteterus alternecoloratus(Cushman)、桑蟥聚瘤姬蜂Iseropus(Gregopimpla)kuwanae(Viereck)、螟蛉瘤姬蜂Itoplectis naranyae(Ashmead)以及二化螟盘绒茧蜂的重寄生蜂绒茧灿金小蜂Trichomalopsis apanteloctena(Crawford)。田间系统调查表明:扬州地区7-9月水稻二化螟寄生蜂的主要种类为二化螟盘绒茧蜂、中华钝唇姬蜂、螟甲腹茧蜂、稻螟小腹茧蜂、螟蛉瘤姬蜂、桑蟥聚瘤姬蜂,但这些寄生蜂对一代水稻二化螟幼虫的寄生率较低,对二代水稻二化螟幼虫的寄生率高。水稻二化螟越冬期的系统调查表明:扬州地区二化螟越冬幼虫的寄生蜂主要有3种,即二化螟盘绒茧蜂、中华钝唇姬蜂和稻螟小腹茧蜂,其中二化螟盘绒茧蜂和中华钝唇姬蜂是寄生水稻二化螟越冬幼虫的优势种。水稻二化螟越冬幼虫的寄生率调查表明,扬州地区水稻二化螟越冬幼虫的寄生率在不同年份间有一定的波动,但一般都在15%以上,有的甚至高达89.88%,因此寄生蜂对二化螟越冬幼虫具有很好的控制作用,能有效压低来年水稻二化螟的田间越冬基数。此外,3种寄生蜂出茧时间在1月和2月之间达到最长,分别达到19.79 d、17.26 d和27.00 d,该结果表明,在扬州地区这3种寄生蜂可能都存在滞育现象。     

寄生蜂采集与田间调查取样技术

寄生蜂是一类十分重要的害虫天敌,在自然控制害虫数量方面发挥着巨大作用。针对寄生蜂种类繁多、寄主类型复杂、寄生方式多样等情况,发展了寄生蜂的采集和田间调查技术,并对不同采集方法的效果、不同寄主类型的调查细节进行了探讨。     

Behavioral responses of the parasitoid Melittobia digitata to volatiles emitted by its natural and laboratory hosts

Responses of macropterous females of the ectoparasitoid Melittobia digitata Dahms (Hymenoptera: Eulophidae) to direct and indirect cues emitted by its natural hosts as well as laboratory hosts were investigated using a Y‐tube olfactometer. To locate the nest of mud dauber wasps, Trypoxylon politum Say (Hymenoptera: Crabronidae), and one of their inquilines, Anthrax spec., parasitoids exploit volatiles from the freshly built nest mud and the empty cocoon constructed by the wasps, as well as their meconium. However, the parasitoids did not respond to odors emitted by older nest mud or by the host stages that are attacked (T. politum prepupae and Anthrax spec. larvae). Melittobia digitata was not attracted to direct volatiles released by the dipteran hosts Anastrepha ludens Loew (Diptera: Tephritidae) (a natural host) and Sarcophaga bullata (Parker) (Diptera: Sarcophagidae) (a laboratory host). Based on our results, we suggest that M. digitata adopts a ‘sit and wait’ strategy to locate mud dauber wasps, relying mainly on indirect host‐related cues: females search for nests that are under construction and once found, they wait inside the cell until the host completes its cocoon and releases meconium, an indicator that is associated with host suitability. No attraction was found to dipteran hosts, suggesting that parasitization of these hosts may be incidental, due to the broad host plasticity of Melittobia wasps.