Specificity of chemical cues used by a specialist egg parasitoid during host location

Plant synomones and host kairomones are known to guide the egg parasitoid Oomyzus gallerucae to its specific host, the elm leaf beetle Xanthogaleruca luteola (= Pyrrhalta) (Muller) feeding upon elm leaves (Ulmus spp.). In this study, we investigated whether the activities of these plant synomones and kairomones are specific for the plant and herbivore species, respectively. Olfactometer and contact bioassays were used. In habitat location, O. gallerucae (Fonscolombe) is known to use synomones from Ulmus minor (Miller) that are induced by egg depositions of X. luteola. The attractiveness of such induced volatiles was shown to be specific both for the Ulmus species and the herbivore species depositing eggs. Neither leaves of U. glabra Hudson (= U. montana) carrying eggs of X. luteola nor leaves of U. minor (= U. campestris = U. procera) carrying eggs of the chrysomelid species Galeruca tanaceti L. emitted attractive synomones. O. gallerucae is also known to be attracted by volatile kairomones from faeces of X. luteola feeding on U. minor and to show prolonged antennal drumming when contacting substrates contaminated with these faeces. The kairomonal activity of the faeces was proved to be independent of the Ulmus species, since also faeces from elm leaf beetles feeding upon U. glabra emitted attractive volatiles. However, the faecal kairomones were specific for the herbivorous species, since faeces from a lepidopteran larva (Opisthograptis luteolata L.) feeding upon elm hardly elicited any antennal drumming in O. gallerucae. The egg parasitoid studied is known to recognize host eggs of X. luteola by contact kairomones extractable from the egg shell. O. gallerucae clearly differentiated between host eggs and eggs of another closely related chrysomelid species, Galerucella lineola L., as was shown by comparing duration of antennal drumming on host eggs and eggs of G. lineola.     

Response of the elm leaf beetle to host plants induced by oviposition and feeding: the infestation rate matters

We investigated by olfactometry and feeding‐ and oviposition‐choice‐tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism.     

Smelling the tree and the forest: elm background odours affect egg parasitoid orientation to herbivore induced terpenoids

Parasitic insects use herbivore induced plant volatiles as signals for host location. However, their responses to these volatiles in the background of natural habitat odours need further evaluation for developing successful biological control strategies. Field elms (Ulmus minor Miller (Ulmaceae)) release a blend of volatiles in response to oviposition of the elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), a major urban and forest pest in the USA and Australia. This induced blend attracts the beneficial egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae). Our olfactory assays showed that an odorous background of non-attractive host plant volatiles from feeding damaged elms or (Z)-3-hexenyl acetate masks the attractive effect of the host-induced (E)-β-caryophyllene to O. gallerucae. Quantitative GC–MS analyses revealed decreased concentrations of (Z)-3-hexenyl acetate accompanied by highly increased concentrations of sesquiterpenes in oviposition and feeding treated elms compared to undamaged elms. This finding hints to how the parasitoid might distinguish between different odorous backgrounds. It is corroborated by the outcome of our field study in natural elm stands, where the egg parasitoid parasitized more host egg masses due to an artificially induced blend of elm terpenoids.     

Functional response of Tetrastichus gallerucae (Hym: Eulophidae) to different densities of the elm leaf beetle eggs,Xanthogaleruca luteola (Col: Chrysomelidae)

The elm leaf beetle is often considered as much of an indoor nuisance as a garden pest since large numbers of adults migrate into homes seeking a protected place to overwinter. Outdoors, both adults and larvae feed on the emerging leaves of virtually all species of elm trees, leaving skeleton zed foliage in their wake. Repeated severe infestations can markedly weaken a host tree, making it susceptible to other insects and diseases. The elm leaf beetle does not transmit the well-known Dutch elm disease, which is carried by another insect than elm bark beetle. The functional response of Tetrastichus gallerucae bees, that is the most important natural enemy of egg elm beetle Xanthogallerucae luteola, has been detected in Kerman province. The experiment was carried out in the growth room under conditions of 25 ± 1°C, 60 ± 5 RH and 16L:8D. Every female bee was exposed for 24 hours at densities of 2, 4, 6, 8, 10, 12, 16, 20, 30 and 40 eggs of elm leaf beetle. Every density had 10 repetitions. The results showed that T. gallerucae has the second type of functional response. The searching efficiency and the handling time of T. gallerucae was 2.63 and 0.114 on the eggs of elm leaf beetle and 2.193 and 0.112 on the eggs of hostess with diluted honey.     

RearingTetrastichus gallerucae [hymenoptera: Eulophidae] for biological control of the ELM leaf beetleXanthogaleruca luteola

Tetrastichus gallerucae (Fonscolombe) was collected in southern France in 1985 and is being reared at the Division of Biological Control in Albany, Ca for use against the elm leaf beetle (ELB),Xanthogaleruca luteola (Müller) in northern California. This egg parasitoid can be reared easily by keeping the beetle eggs on a moist substrate to prevent desiccation and by inhibiting the growth of mold with air currents. A laboratory colony of ELB adults provides a constant supply of fresh eggs for the parasitoids. In 1985 and 1986 over 80,000T. gallerucae were released at 17 sites.      

Study on some biological characteristics of Tetrastichus gallerucae (Hym. Eulophidae), important parasitoid of Elm leaf beetle eggs in Kerman,Iran

In this study, a number of biologic characteristics of Tetrastichus gallerucae, the most important natural enemy of Xanthogaleruca luteola (Col.: Chrysomellidae), were studied. Experiments were carried out in growth room with a temperature of 25°C±1°C, relative humidity of 60%±5% and light period of 16L:8D. The results demonstrated the following outcomes: without food and host egg, the longevity of male and female bees was respectively, 1.23 and 1.35 days. On the host egg, their longevities were 3.85 and 6.02 days, respectively. On rarefied honey their longevities were 14.04 and 24.74 days, respectively and on the host eggs together with rarefied honey, their longevities were 13.4 and 34.72 days, respectively. The average growth period times in the egg of elm leaf beetle of male and female bees were 12.97 and 12.63 days, respectively. The percentage of female bees decreases as the longevity of the insects increases. These bees lay eggs in the 1–9-day-old eggs of elm leaf beetle but 1-day-old eggs of the host are preferred by T. gallerucae.     

Chemical signals mediating interactions betweenGaleruca tanaceti L. (Coleoptera, Chrysomelidae) and its egg parasitoidOomyzus galerucivorus (Hedqvits) (Hymenoptera, Eulophidae)

Chemical signals mediating interactions betweenGaleruca tanaceti and its egg parasitoidOomyzus galerucivorus (Hymenoptera, Eulophidae) were studied. Neither odor of gravid females ofG. tanaceti nor volatiles of their feces were attractive to the parasitoid. However, the presence of the beetles’ feces on a substrate arrested the parasitoid and elicited frequent antennal drumming. Thus, feces may contain a kairomone important for host finding. Odors of damaged and undamaged host plants had no effect on the parasitoids.O. galerucivorus did not detect its host eggs at close range but encountered them by chance. Neither the structure nor the dark color of the egg surface play a key role in host recognition, but chemicals of the extrachorion which could be isolated by dichloromethane. Fractionation of the dichloromethane extract by TLC revealed a single active fraction which induced host recognition behavior. Since the eggs ofG. tanaceti contain anthraquinones and anthrones which are active as feeding deterrents against predators, we hypothesized that reproductive success ofO. galerucivorus is due to sequestration of these protective compounds. However, GC-MS analyses revealed that there was no transfer of them from the host egg into the adult parasitoid.     

Host plants alter their volatiles to help a solitary egg parasitoid distinguish habitats with parasitized hosts from those without

When attacked by herbivores, plants emit volatiles to attract parasitoids and predators of herbivores. However, our understanding of the effect of plant volatiles on the subsequent behaviour of conspecific parasitoids when herbivores on plants are parasitized is limited. In this study, rice plants were infested with gravid females of the brown planthopper (BPH) Nilaparvata lugens for 24 hr followed by another 24 hr in which the BPH eggs on plants were permitted to be parasitized by their egg parasitoid, Anagrus nilaparvatae; volatiles from rice plants that underwent such treatment were less attractive to subsequent conspecific parasitoids compared to the volatiles from plants infested with gravid BPH females alone. Chemical analysis revealed that levels of JA and JA-Ile as well as of four volatile compounds—linalool, MeSA, α-zingiberene and an unknown compound—from plants infested with BPH and parasitized by wasps were significantly higher than levels of these compounds from BPH-infested plants. Laboratory and field bioassays revealed that one of the four increased chemicals—α-zingiberene—reduced the plant's attractiveness to the parasitoid. These results suggest that host plants can fine-tune their volatiles to help egg parasitoids distinguish host habitats with parasitized hosts from those without.     

Choosy egg parasitoids: Specificity of oviposition-induced pine volatiles exploited by an egg parasitoid of pine sawflies

Generalist parasitoids are well‐known to be able to cope with the high genotypic and phenotypic plasticity of plant volatiles by learning odours during their host encounters. In contrast, specialised parasitoids often respond innately to host‐specific cues. Previous studies have shown that females of the specialised egg parasitoid Chrysonotomyia ruforum Krausse (Hymenoptera: Eulophidae) are attracted to volatiles from Pinus sylvestris L. induced by the egg deposition of its host Diprion pini L. (Hymenoptera: Diprionidae), when they have previously experienced pine twigs with host eggs. In this study we investigated by olfactometer bioassays how specifically C. ruforum responded to oviposition‐induced plant volatiles. Furthermore, we studied whether parasitoids show an innate response to oviposition‐induced pine volatiles. Naïve parasitoids were not attracted to oviposition‐induced pine volatiles. The attractiveness of volatiles from pines carrying eggs was shown to be specific for the pine and herbivore species, respectively (species specificity). We also tested whether not only oviposition, but also larval feeding, induces attractive volatiles (developmental stage specificity). The feeding of D. pini larvae did not induce the emission of P. sylvestris volatiles attractive to the egg parasitoid. Our results show that a specialist egg parasitoid does not innately show a positive response to oviposition‐induced plant volatiles, but needs to learn them. Furthermore, the results show that C. ruforum as a specialist does not learn a wide range of volatiles as some generalists do, but instead learns only a very specific oviposition‐induced plant volatile pattern, i.e., a pattern induced by the most preferred host species laying eggs on the most preferred food plant.     

Role of volatile semiochemicals in host location by the egg parasitoid Anagrus breviphragma

Recent investigations conducted on several tritrophic systems have demonstrated that egg parasitoids, when searching for host eggs, may exploit plant synomones that have been induced as a consequence of host oviposition. In this article we show that, in a system characterized by host eggs embedded in the plant tissue, naïve females of the egg parasitoid Anagrus breviphragma Soyka (Hymenoptera: Mymaridae) responded in a Y‐tube olfactometer to volatiles from leaves of Carex riparia Curtis (Cyperaceae) containing eggs of one of its hosts, Cicadella viridis (L.) (Hemiptera: Cicadellidae). The wasp did not respond to host eggs or to clean leaves from non‐infested plants compared with clean air, whereas it showed a strong preference for the olfactometer arm containing volatiles of leaves with embedded host eggs, compared with the arm containing volatiles of leaves from a non‐infested plant or host eggs extracted from the plant. When the eggs were removed from an infested leaf, the parasitoid preference was observed only if eggs were added aside, suggesting a synergistic effect of a local plant synomone and an egg kairomone. The parasitoid also responded to clean leaves from an egg‐infested plant when compared with leaves from a non‐infested plant, indicating a systemic effect of volatile induction.     

Patch-exploitation patterns in an egg parasite of elm leaf beetle

Eggs of elm beetle,Pyrrhalta luteola (Muller), normally occur in masses which can be viewed as discrete host patches in space and time. Analysis of>800 egg masses from 3 field sites in northern California revealed that the number of eggs/mass varied from 2 to>40 and that the imported egg parasiteTetrastichus gallerucae (Fonsc.) exploited a relatively large proported of the egg masses at certain times. The spatial relationship between parasitization and number of eggs/egg mass was assessed in 2 ways-i.e., for exploited masses only and for all masses combined (exploited+nonexploited). Percent parasitization was density independent in most cases for both data sets. It is suggested that both methods of analysis can provide patterns which are relevant to biological control of insect pests.      

桑天牛卵长尾啮小蜂的寄主选择定位行为

本文对桑天牛卵长尾啮小蜂Aprostocetus prolixus LaSalle et Huang的寄主选择定位行为进行了系统研究。已有研究表明,寄主植物-寄主昆虫复合体释放的挥发物对寄生蜂有显著的引诱作用。为了查明寄主植物 寄主昆虫复合体中挥发性引诱物质的来源,对不同处理桑枝（正常桑枝、机械损伤桑枝、系统枝、桑天牛Apriona germari（Hope）咬食和产卵桑枝）、桑天牛虫粪及雌雄两性桑天牛所释放的挥发物分别进行了测定。结果显示：不同处理桑枝对寄生蜂都具有显著的引诱作用,而且产卵桑枝的引诱活性最大;桑天牛虫粪的气味对寄生蜂有引诱活性,而雌、雄桑天牛体表挥发物对寄生蜂的引诱效果不明显。桑天牛爬行痕迹对寄生蜂的微栖境接受行为没有影响,而桑天牛虫粪中的信息物质在寄生蜂的微栖境接受过程中起着重要作用。寄生蜂对产卵桑枝段的选择几率明显高于正常桑枝段和咬食桑枝段,而对不同植物上产卵刻槽的选择没有差异; 刻槽表面存在着与此卵寄生蜂寄主识别相关的信息物质。     

Semiochemical and physical stimuli involved in host recognition by Telenomus podisi (Hymenoptera: Scelionidae) toward Euschistus heros (Heteroptera: Pentatomidae)

The egg parasitoid, Telenomus podisi, was shown to recognize its host, Euschistus heros, through both chemical and physical cues. These were determined in short-range bioassays. The cues comprised fertile and infertile host eggs, egg extracts, crude extracts of adult males and females and successive dilutions of the synthetic racemic mixture of methyl 2,6,10-trimethyltridecanoate, a male-produced pheromone of E. heros. Some of the treatments used induced a selection process in T. podisi, through host recognition behaviour, indicating a consistent response of this species to E. heros. The possibility that some of these compounds could be exploited as long-range kairomones, by T. podisi, is discussed. Using GC analysis, an unidentified compound (Rt 24.8 min), possibly from the egg adhesive material, was detected from E. heros egg extracts. Its retention time compared to the methyl 2,6,10-trimethyltridecanoate showed a lower volatility, suggesting that the egg adhesive may act as a short-range kairomone. Physical cues appeared to be an important component in the host selection process by T. podisi. The parasitoid discriminated infertile eggs which are differently shaped and smaller than fertile eggs.     

Mate finding in the forest cockchafer, Melolontha hippocastani, mediated by volatiles from plants and females

The response of the forest cockchafer, Melolontha hippocastani F. (Coleoptera, Scarabaeidae), towards volatiles emitted by different host plants and conspecifics was tested in field experiments during the flight period at dusk. Funnel traps containing artificially damaged leaves from the host plants Carpinus betulus L. and Quercus rubra L., as well as from the non‐host plant Prunus serotina Ehrh. caught significantly more beetles than empty control traps. On the other hand, traps baited with undamaged leaves from Q. rubra did not catch significantly more beetles than empty controls. Leaves from C. betulus damaged by beetle feeding did not attract more beetles than artificially damaged leaves. By use of gas chromatography coupled with electroantennographic detection (GC‐EAD) electrophysiological responses of males and females were shown for 18 typical plant volatiles. A synthetic mixture of selected typical green plant volatiles was also highly attractive in the field. A total of 9982 beetles was caught during the field experiments, among them only 33 females. This suggests that attraction to damaged foliage during flight period at dusk is male‐specific. Field experiments testing the attractiveness of female M. hippocastani towards conspecific males by employing caged beetles and beetle extracts indicated that males of M. hippocastani use a female‐derived sex pheromone for mate location. On wired cages containing either unmated feeding females, or unmated females without access to foliage, or feeding males in combination with extracts from unmated females, significantly more males landed during the flight period than on comparable control cages containing feeding males or male extracts. A possible scenario of mate location in M. hippocastani involving feeding‐induced plant volatiles and a female‐derived sex pheromone is discussed.     

Hunting for moving hosts: Cephalonomia tarsalis, a parasitoid of free-living grain beetles

The parasitic wasp Cephalonomia tarsalis parasitizes larvae of the saw-toothed grain beetle Oryzaephilus surinamensis, which feed on wheat grains. In contrast to most other host–parasitoid systems studied so far, the grain beetles are highly mobile within their habitat, bulk of grains in grain stores. This should increase the wasps’ problem to locate the hosts. To study the host-finding strategy of C. tarsalis females, the reaction of wasps to different grain and host-derived odour sources was tested in a four-chamber-olfactometer. These experiments revealed that wasps were attracted by healthy grains and mechanically damaged grains. In direct comparison, healthy and mechanically damaged grains are equally attractive. Both potential sources of host-derived odours, host faeces and trail-traces of larvae on filter paper were attractive to the wasps. The response to trail-traces vanished 30 min after larvae had been removed from the filter paper. With respect to the specificity of the odours, it turned out that wasps were attracted to odours from the seed–host complexes from O. surinamensis and Oryzaephilus mercator and the non-host complex of larvae of the granary weevil Sitophilus granarius in wheat grains. Odours from the seed–host complex were preferred. From these results, we hypothesize that host habitat location in C. tarsalis is achieved by using grain-derived odours. Within the habitat, wasps search for kairomones from host faeces and host trails. Following these larval trails finally leads wasps to their hosts.     

Evaluation of systemic insecticides as a treatment option in integrated pest management of the elm leaf beetle, Xanthogaleruca luteola (Müller) (Coleoptera: Chrysomelidae)

This study evaluates the efficacy of two systemic insecticides (imidacloprid and abamectin) in an operational setting and their suitability to be incorporated into an integrated pest management program. Elm leaf beetle abundance and leaf damage were compared between treated trees and untreated control trees from 1995 through 1999. Laboratory bioassays using first-instar larvae were also used to measure the toxicity of leaves collected from treated trees at varying times after treatment. Trunk injections of abamectin and imidacloprid reduced the defoliation caused by elm leaf beetle when applied after monitoring at the peak density of elm leaf beetle eggs. Treatment in the first generation appeared to provide protection against damage in that generation as well as the second and third beetle generations. Both of these materials become active within the tree canopy very quickly and are therefore compatible with a management program that determines the need for treatment based on monitoring for egg clusters at peak density of eggs. Laboratory bioassays showed no toxicity of leaves in the year following treatment.     

Biology of the Eucalyptus leaf beetle Paropsisterna selmani (Chrysomelidae: Paropsini): a new pest of Eucalyptus species (Myrtaceae) in Ireland

相似文献   

Primary attraction and kairomonal host discrimination in three species of Dendroctonus (Coleoptera: Scolytidae)

Abstract 1 Synthetic blends of bole and foliage volatiles of four sympatric species of conifers were released from pheromone‐baited multiple‐funnel traps to determine if three species of tree‐killing bark beetles (Coleoptera: Scolytidae): (i) exhibited primary attraction to volatiles of their hosts and (ii) discriminated among volatiles of four sympatric species of host and nonhost conifers. 2 Bole and foliage volatiles from Douglas‐fir, Pseudotsuga menziesii (Mirb.) Franco, increased the attraction of coastal and interior Douglas‐fir beetles, Dendroctonus pseudotsugae Hopkins, to pheromone‐baited traps. Primary attraction to bole volatiles was observed in interior D. pseudotsugae. Beetles were significantly less attracted to the pheromone bait when it was combined with volatiles of lodgepole pine, Pinus contorta var. latifolia Engelm. or interior fir, Abies lasiocarpa × bifolia. 3 The monoterpene myrcene synergized attraction of mountain pine beetles, Dendroctonus ponderosae Hopkins, to their aggregation pheromones, but there was no evidence of primary attraction to host volatiles or discrimination among volatiles from the four conifers. 4 There was significant primary attraction of the spruce beetle, Dendroctonus rufipennis Kirby, to bole and foliage volatiles of interior spruce, Picea engelmannii × glauca, but beetles did not discriminate among volatiles of four sympatric conifers when they were combined with pheromone baits. 5 Our results indicate that host volatiles act as kairomones to aid pioneer Douglas‐fir beetles and spruce beetles in host location by primary attraction, and that their role as synergists to aggregation pheromones is significant. For the mountain pine beetle, we conclude that random landing and close range acceptance or rejection of potential hosts would occur in the absence of aggregation pheromones emanating from a tree under attack.     

Oviposition‐induced plant cues: do they arrest Trichogramma wasps during host location?

Plants can defend themselves against herbivorous insects before the larvae hatch from eggs and start feeding. One of these preventive defence strategies is to produce plant volatiles, in response to egg deposition, which attract egg parasitoids that subsequently kill the herbivore eggs. Here, we studied whether egg deposition by Pieris brassicae L. (Lepidoptera: Pieridae) induces Brussels sprouts plants to produce cues that attract or arrest Trichogramma brassicae Bezdeko (Hymenoptera: Trichogrammatidae). Olfactometer bioassays revealed that odours from plants with eggs did not attract or arrest parasitoids. However, contact bioassays showed that T. brassicae females were arrested on egg‐free leaf squares excised from leaves with 72 h‐old egg masses, which are highly suitable for parasitisation. We tested the hypothesis that this arresting activity is due to scales and chemicals deposited by the butterflies during oviposition and which are thus present on the leaf surface in the vicinity of the eggs. Indeed, leaf squares excised from egg‐free leaves, but contaminated with butterfly deposits, arrested the wasps when the squares were tested 1 day after contamination. However, squares from egg‐free leaves with 72 h‐old butterfly deposits had no arresting activity. Thus, we exclude that the arresting activity of the leaf area near 72 h‐old egg masses was elicited by cues from scales and other butterfly deposits. We suggest that egg deposition of P. brassicae induces a change in the leaf surface chemicals in leaves with egg masses. A systemic induction extending to an egg‐free leaf neighbouring an egg‐carrying leaf could not be detected. Our data suggest that a local, oviposition‐induced change of leaf surface chemicals arrests T. brassicae in the vicinity of host eggs.     

Behavioral responses of the parasitoid Psyllaephagus pistaciae (Hymenoptera: Encyrtidae) to host plant volatiles and honeydew

The behavioral responses of the parasitoid Psyllaephagus pistaciae, the major biocontrol agent of the common pistachio psylla, Agonoscena pistaciae, to volatiles emanating from its host plant and host honeydew, were examined using a four‐arm airflow olfactometer. In addition, the arrestment behavior of this parasitoid on clean and honeydew‐treated leaves of the pistachio, Pistacia vera, was monitored. The infested pistachio leaves were the most favored source of the volatile attracting the parasitoids. The parasitoid clearly distinguished and responded to infochemicals emitted by psyllid honeydew but at a lower level than to the volatiles from infested host plants. However, the searching time, locomotory behavior, antennal drumming and ovipositor probing were all affected when they encountered honeydew‐contaminated zones on pistachio leaves. These findings suggest that the psyllid honeydew releases kairomones that stimulate the parasitoids to greater searching activity, as well as providing a directional cue. The intensive searching activities in the presence of the volatiles tested were very similar to responses by the parasitoid females when encountering patches treated with psyllid honeydew. Such behavior could retain the parasitoid in a favorable area, thereby increasing the probability of additional host encounters.