Short Distance Cues Used by the Adult Parasitoid <Emphasis Type="Italic">Microctonus hyperodae</Emphasis> Loan (Hymenoptera: Braconidae,Euphorinae) for Host Selection of a Novel Host <Emphasis Type="Italic">Listronotus oregonensis</Emphasis> (Coleoptera: Curculionidae)

Insect parasitoids use host kairomone to detect their hosts. However, in parasitoid species that attack adult hosts, the mobility of adult insect may mean that the host can move away for kairomone sources. The effect of Listronotus oregonensis LeConte (Coleoptera: Curculionidae) adult sex, feces and movement on host selection behavior by Microctonus’’ hyperodae Loan (Hymenoptera: Braconidae; Euphorinae) females was evaluated in the laboratory. We hypothesized that, in addition of using host kairomones, parasitoids of adult stage should use host movement for host selection. The sex of L. oregonensis did not affect the host selection behavior of M. hyperodae. However, host feces decreased the number of weevil antennations done by M. hyperodae. Microctonus hyperodae stopped less frequently near immobile L. oregonensis than near walking ones and these latter were frequently pursued by M. hyperodae. Host movement was the stimulus that elicited oviposition by M. hyperodae. The adaptive implications of these results are discussed.     

Odor specificity testing in the assessment of efficacy and non-target risk for Trichogramma ostriniae (Hymenoptera: Trichogrammatidae)

Trichogramma ostriniae Pang and Chen (Hymenoptera: Trichogrammatidae) is an indigenous egg parasitoid of Ostrinia furnacalis Guenée (Lepidoptera: Crambidae) in China. We evaluated T. ostriniae's responses in olfactometer and wind tunnel assays to various host and plant odors that are likely to impact the efficacy and non-target risk of utilizing T. ostriniae as an augmentative biocontrol agent against Ostrinia nubilalis Hübner in the USA. In a Y-olfactometer, female T. ostriniae exhibited innate positive responses to the egg mass volatiles, scale volatiles, and synthetic sex pheromones of O. nubilalis. When exposed to O. nubilalis pheromone while walking on a platform in a wind tunnel, the wasps manifested significant changes in patch exploration behavior, including delayed dispersal from the platform and slowed walking. The wasps did not respond innately to the synthetic pheromone of a non-target species, Spodoptera frugiperda J. E. Smith (Lepidoptera: Noctuidae), however. Exposing wasps to S. frugiperda pheromone together with eggs of a factitious rearing host prior to testing also did not alter the wasps’ lack of response to the pheromone, indicating that associative learning of the novel odor did not occur. Lastly, wasps showed no innate responses to leaf volatiles from corn (Zea mays L.) and pepper (Capsicum annuum L.), two crops attacked by O. nubilalis. We conclude that T. ostriniae is likely to be highly efficient at finding O. nubilalis eggs in the field through the exploitation of host chemical cues. Further, T. ostriniae's response to moth pheromone appears to be relatively host-specific, since the wasps responded to the pheromone of a congener to their natural host, but not to the pheromone of a more distantly related non-target species. This type of odor-specificity could be an important mechanism for reducing the risk of T. ostriniae attack on non-target species.     

Relationships between parasitoid host range and host defence: a comparative study of egg encapsulation in two related parasitoid species

Abstract. Parasitoid host range may proceed from traits affecting host suitability, traits affecting parasitoid foraging behaviour, or both. We tested the hypothesis that encapsulation can be used as a reliable indicator of parasitoid host range in two closely related larval endoparasitoids of Lepidoptera. Cotesia glomerata (L.) (Hymenoptera: Braconidae) is gregarious and a generalist on several species of Pieridae, whereas C. rubecula (Marshall) is solitary and specific to Pieris rapae (L.). We determined the effects of host species ( Pieris brassicae (L.), P. napi (L.) and P. rapae ) (Lepidoptera: Pieridae) and host developmental stage (early first, second and third instar) on encapsulation of parasitoid eggs. Host species and parasitoid species, as well as the resulting interaction between these two factors had significant effects on encapsulation of Cotesia eggs. Encapsulation in Pieris hosts was much lower for C. glomerata (<34%, except for second and third instar of P. rapae ) than for C. rubecula (>32%), even when the latter was parasitizing P. rapae. Encapsulation increased with the age of the larvae, although the only significant difference was for C. glomerata. Overall, P. rapae showed a stronger encapsulation reaction than P. brassicae and P. napi. Encapsulation levels of C. glomerata corresponded well to patterns of female host species and host age preference for oviposition and parasitoid larval performance. In contrast, percentages of encapsulation of C. rubecula were not consistent with host preference and host suitability. We argue that encapsulation alone is unlikely to provide a sufficient explanation for C. glomerata and C. rubecula host range.     

Heritable differences in the response of the braconid waspMicroplitis croceipes to volatile allelochemicals

The heritable nature of differential responses by Microplitis croceipes(Cresson) (Hymenoptera: Braconidae) to airborne allelochemicals was investigated. Four isofemale lines were tested for three generations in a flight tunnel. Flight response was found to be strongly dependent on the familial origin, with two highly responsive lines being clearly differentiated from two less responsive ones. Each isofemale line could also be recognized by typical behaviors that suggested that M. croceipesfemales may inherit independent characters of sensory acuity to plant and to host chemicals and of learning ability.     

Differential attraction of parasitoids in relation to specificity of kairomones from herbivores and their by‐products

Infochemicals are used by foraging parasitoids in the host selection process from habitat preference until host recognition. Kairomones from the herbivore host plays a vital role in the attraction of parasitoids, particularly in the micro‐habitat. Parasitoids are specifically attracted to their respective herbivore species even when different herbivores are present on the same plant. Chemicals emitted from different stages of host (eggs, larvae, pupae, adult), host by‐products (e.g., frass, exuviae, mandibular gland secretions, defense secretions etc.), or intra‐specific infochemicals (pheromones) can be main signals for the parasitoids. Parasitoids can differentiate between host and non‐host, between different hosts and host stages by perceiving specific volatile and contact kairomones from the host itself, host along with its by‐product, by‐products alone or intra‐specific infochemicals; of which frass (by‐product) and intra‐specific infochemicals are the most reported ones. Adult and larval parasitoids have been reported to be attracted to kairomones of their target stage or byproduct of their host. Pupal parasitoids have been found to utilize kairomones from the preceding host stage while egg parasitoids are known to exploit a variety of host infochemicals, for example, either from eggs themselves or other non‐target host stages, especially adults and adult‐related by‐products. The kairomonal chemicals identified so far include various groups, but mainly hydrocarbons. A high degree of host specificity and host acceptance is important for the parasitoids as any mistake may result in the loss of fitness.     

Polydnavirus of Microplitis croceipes prolongs the larval period and changes hemolymph protein content of the host,Heliothis virescens

Polydnaviruses from certain parasitoid Hymenoptera have been reported to interfere with both host immunity and host development. Heliothis virescens larvae injected with either calyx fluid or sucrose gradient-purified polydnavirus from Microplitis croceipes (McPDV) gained less weight than saline-injected larvae. The active feeding portion of the fifth stadium larva (time to reach the burrowing-digging stage) was doubled (7.0 vs. 3.4 days) when a 0.25 wasp equivalent (WE) of sucrose gradient-purified McPDV was injected into a newly ecdysed fifth stadium host. Many of the treated larvae were unable to pupate, successfully and died at a point of incomplete larval-pupal ecdysis. Pupae that did result from the treated larvae weighed significantly less than controls, even at 0.025 WE. The rate of weight gain and extent of delay of development were dose-dependent; as little as 0.1 WE extended the time of active feeding by 1.5 days and yielded only 25% adults. A 0.05 WE dose yielded 78% adults compared to 95% for controls. The total protein content of hemolymph from individuals injected with McPDV was significantly less than that of controls at any McPDV dose equal to or greater than 0.1 WE. SDS-PAGE profiles of hemolymph proteins from control and McPDV-injected larvae revealed a marked inhibition of the normal accumulation of storage proteins during the fifth stadium and a lesser reduction of serine protease inhibitor protein. Thus, McPDV-injected larvae exhibited some symptoms (less total hemolymph protein and reduced amounts of storage protein) similar to those shown by both parasitized larvae and by larvae injected with M. croceipes teratocytes. However, McPDV affected development during the active feeding stage of the larva, while teratocytes primarily impacted larvae at the time when larval-pupal transformation processes are initiated. © 1995 Wiley-Liss, Inc.     

Differential attraction of parasitoids in relation to specificity of kairomones from herbivores and their by-products

Infochemicals are used by foraging parasitoids in the host selection process from habitat preference until host recognition. Kairomones from the herbivore host plays a vital role in the attraction of parasitoids, particularly in the micro-habitat. Parasitoids are specifically attracted to their respective herbivore species even when different herbivores are present on the same plant. Chemicals emitted from different stages of host （eggs, larvae, pupae, adult）, host by-products （e.g., frass, exuviae, mandibular gland secretions, defense secretions etc.）, or intra-specific infochemicals （pheromones） can be main signals for the parasitoids. Parasitoids can differentiate between host and non-host, between different hosts and host stages by perceiving specific volatile and contact kairomones from the host itself, host along with its by-product, by-products alone or intra-specific infochemicals; of which frass （by-product） and intra-specific infochemicals are the most reported ones. Adult and larval parasitoids have been reported to be attracted to kairomones of their target stage or byproduct of their host. Pupal parasitoids have been found to utilize kairomones from the preceding host stage while egg parasitoids are known to exploit a variety of host infochemicals, for example, either from eggs themselves or other non-target host stages, especially adults and adult-related by-products. The kairomonal chemicals identified so far include various groups, but mainly hydrocarbons. A high degree of host specificity and host acceptance is important for the parasitoids as any mistake may result in the loss of fitness.     

中国陡胸茧蜂属(膜翅目,茧蜂科,小腹茧蜂亚科)两新种记述

简述了小腹茧蜂亚科陡胸茧蜂属的研究历史、现状和形态特征,描述了该属2新种:贵州陡胸茧蜂Snellenius guizhouensis sp.nov.和宽颊陡胸茧蜂Snellenius latigenus sp.nov,并与其近似种做了比较.两新种均采自贵州省,模式标本存放于贵州师范大学地理与生物科学学院.     

The role of plant chemical cues in determining host preference in the generalist aphid parasitoid Aphidius colemani

The host preference behaviour of the generalist aphid parasitoid Aphidius colemaniwas investigated using a Y-tube olfactometer. Female A. colemanishowed a preference for the host-plant complex on which they had been reared, even though the same aphid host was involved, demonstrating a host plant preference. This preference was not evident when the parasitoids were dissected from their mummies prior to adult emergence. Host plant preference exhibited during host selection appeared to be induced by chemical cues encountered on the mummy case at the time of emergence, but preferences could be changed by subsequent foraging experiences. It is concluded that plant chemical cues play a major role in determining initial preferences through a process of emergence conditioning but that learning processes, involving cues encountered during oviposition in or contact with the host, can modify these initial preferences.     

Evaluation of Fopius arisanus as a biological control agent for the olive fruit fly in California

1 The egg‐prepupal parasitoid Fopius arisanus (Hymenoptera: Braconidae) was evaluated in quarantine facilities as a potential biological control agent for the olive fruit fly Bactrocera oleae (Diptera: Tephritidae) in California, U.S.A. 2 Nontarget testing of two weed biological control agents confirmed that F. arisanus will not attack Tephritidae that feed in inflorescences or galls. It may, however, pose risks to native Tephritidae that feed in fruit. 3 Females preferentially oviposited in eggs, although first‐instar B. oleae were also attacked. Low lifetime reproductive potential and high rates of direct mortality inflicted on host eggs indicate that rearing on B. oleae may prove difficult. 4 In multiparasitized B. oleae, F. arisanus prevailed in competition against two species of larval–pupal parasitoids, Diachasmimorpha kraussii and Psyttalia concolor (both Hymenoptera: Braconidae). 5 The broad host‐range of F. arisanus with respect to fruit‐feeding Tephritidae may preclude its introduction to California, as may its low fecundity and its intrinsic competitive superiority over larva l–pupal parasitoids, which include specialists on B. oleae that are currently being introduced to California. High rates of direct mortality, however, point to potential uses in augmentative biological control. Whether or not F. arisanus is released in California, its biology as a parasitoid of B. oleae has been little studied to date and the results herein may be applied in other regions worldwide where B. oleae is a problem.     

Parasitoids select plants more heavily infested with their caterpillar hosts: a new approach to aid interpretation of plant headspace volatiles

Plants produce volatile organic compounds (VOCs) in response to herbivore attack, and these VOCs can be used by parasitoids of the herbivore as host location cues. We investigated the behavioural responses of the parasitoid Cotesia vestalis to VOCs from a plant-herbivore complex consisting of cabbage plants (Brassica oleracea) and the parasitoids host caterpillar, Plutella xylostella. A Y-tube olfactometer was used to compare the parasitoids' responses to VOCs produced as a result of different levels of attack by the caterpillar and equivalent levels of mechanical damage. Headspace VOC production by these plant treatments was examined using gas chromatography-mass spectrometry. Cotesia vestalis were able to exploit quantitative and qualitative differences in volatile emissions, from the plant-herbivore complex, produced as a result of different numbers of herbivores feeding. Cotesia vestalis showed a preference for plants with more herbivores and herbivore damage, but did not distinguish between different levels of mechanical damage. Volatile profiles of plants with different levels of herbivores/herbivore damage could also be separated by canonical discriminant analyses. Analyses revealed a number of compounds whose emission increased significantly with herbivore load, and these VOCs may be particularly good indicators of herbivore number, as the parasitoid processes cues from its external environment.