Native parasitoids and recovery of Spathius agrili from areas of release against emerald ash borer in eastern Tennessee,USA

The parasitoid Spathius agrili Yang, introduced in the USA to suppress populations of the emerald ash borer (EAB), Agrilus planipennis Fairmaire, has been recovered at a release site for the first time in eastern Tennessee after a single year of releases. Other native parasitoids, including Spathius floridanus Ashmead, undetermined species of Spathius (possibly Spathius elegans Matthews and Spathius parvulus Matthews) and Atanycolus cappaerti Marsh & Strazanac, also known to be associated with EAB, were recovered. These recoveries represent the first documentation of these four species, including the introduced S. agrili, associated with EAB in the southern USA. Implications for biological control efforts against EAB are discussed.     

Host-seeking behavior and parasitism by Spathius agrili Yang (Hymenoptera: Braconidae), a parasitoid of the emerald ash borer

Spathius agrili Yang (Hymenoptera: Braconidae) is a newly described and important idiobiont ectoparasitoid of the emerald ash borer (EAB) that has excellent potential as a biological control agent against EAB populations in the USA. In order to understand the ecological factors involved in the search and discovery of concealed hosts by S. agrili, we investigated the behavioral responses of adult female wasps to potential semiochemicals from host plants, hosts, and host frass as well as to vibration signals from host feeding and movement. Using a bioassay, we showed that S. agrili first finds the host’s habitats by detecting the volatile compounds emitted by ash. In the second phase of host location and acceptance, the parasitoids detect the mechanical vibrations produced by host feeding and movement under the surface of the bark and then probe to find the EAB larvae. Contact chemicals seem to play little or no role in short-range host finding. Female wasps avoided laying eggs on EAB larvae already parasitized and thus paralyzed. We hypothesized that female wasps were not attracted to these larvae due to their lack of feeding or movement. While an induced paralysis in the host is instrumental in avoiding superparasitism, we cannot rule out that S. agrili females also use an oviposition pheromone to deter conspecific females. Together, these results suggest that vibration and olfactory cues play significant roles in distinct phases of S. agrili host habitat and host location behaviors.     

Interactions between Spathius agrili (Hymenoptera: Braconidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae), larval parasitoids of Agrilus planipennis (Coleoptera: Buprestidae)

Three hymenopteran parasitoids native to China are being released in the United States as biological control agents for the emerald ash borer (EAB), Agrilus planipennis Fairmaire, an Asian buprestid species responsible for mortality of ash trees (Fraxinus spp.) in North America. Two of these hymenopterans, Spathius agrili Yang (Braconidae), a larval ectoparasitoid, and Tetrastichus planipennisi Yang (Eulophidae), a larval endoparasitoid, prefer late-instar EAB larvae. This overlapping host preference raises concerns that interspecific competition following field releases may compromise establishment of one or both species. In a series of laboratory and field experiments, we found S. agrili and T. planipennisi exhibited similar parasitism rates when presented alone with EAB larvae for 12–14 days. However, S. agrili was more efficient at locating and parasitizing hosts within the first 27 h, possibly explaining why S. agrili excluded T. planipennisi in the laboratory trials and nearly excluded T. planipennisi in field trials when the two species were presented together with EAB larvae. We found that S. agrili parasitized larvae previously parasitized by T. planipennisi but not the reverse. However, S. agrili offspring failed to complete development on hosts that were previously parasitized by T. planipennisi. We recommend releasing these species separately in time or space to avoid the antagonistic interactions observed in this study.     

Landing Surface Color Preferences of Spathius agrili (Hymenoptera: Braconidae), a Parasitoid of Emerald Ash Borer, Agrilus planipennis (Coleoptera: Buprestidae)

The color preferences for landing surfaces were examined for Spathius agrili (Hymenoptera: Braconidae), a parasitic wasp introduced for biocontrol of emerald ash borer, Agrilus planipennis (Coleoptera: Buprestidae). Lures with the 3-component pheromone blend of male S. agrili were used to activate upwind flight by virgin female S. agrili in a laminar flow wind tunnel. Paper discs with halves of two different colors (combination pairs of black, white, red, yellow, green, or purple), with the pheromone lure in the center, were tested to quantify preferences for landing on one color over another. Females landed preferentially on green, yellow, and white surfaces, and landed the least frequently on red, black, and purple surfaces. Changes in color preferences due to adjacent colors were observed and discussed.     

Evaluation of tree mortality and parasitoid recoveries on the contiguous western invasion front of emerald ash borer

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Population responses of hymenopteran parasitoids to the emerald ash borer (Coleoptera: Buprestidae) in recently invaded areas in north central United States

Populations of hymenopteran parasitoids associated with larval stages of the invasive emerald ash borer (EAB) Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) were surveyed in 2009 and 2010 in the recently invaded areas in north central United States (Michigan), where two introduced EAB larval parasitoids, Tetrastichus planipennisi Yang and Spathius agrili Yang were released for classical biological control. Results from two years of field surveys showed that several hymenopteran parasitoids have become associated with EAB in Michigan. Among these parasitoids, the gregarious species T. planipennisi was the most abundant, accounting for 93% of all parasitoid individuals collected in 2009 (immediately after field release) and 58% in 2010 (a year later after field releases). Low levels (1–5%) of parasitism of EAB larvae by T. planipennisi were consistently detected at survey sites in both years. Separately, the abundance of the native parasitoid, Atanycolus spp., increased sharply, resulting in an average parasitism rate of EAB larvae from <0.5% in 2009 to 19% in 2010. Other parasitoids such as Phasgonophora sulcata Westwood, Spathius spp., Balcha indica Mani & Kaul, Eupelmus sp., and Eurytomus sp. were much less abundant than T. planipennisi and Atanycolus spp., and each caused <1% parasitism. Besides hymenopteran parasitoids, woodpeckers consumed 32–42% of the immature EAB stages present at our study sites, while undetermined biotic factors (such as microbial disease and host tree resistance) caused 10–22% mortality of observed EAB larvae. Relevance of these findings to the potential for biological control of EAB in the invaded areas of North America is discussed.     

Effects of rearing conditions on reproduction of Spathius agrili (Hymenoptera: Braconidae), a parasitoid of the emerald ash borer (Coleoptera: Buprestidae)

Spathius agrili Yang (Hymenoptera: Braconidae) can be successfully reared on emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), larvae feeding in chambers drilled in small ash twigs that are wrapped with floral tape. Females maintained in groups with males for one week can receive enough sperm for production of female progeny throughout their lives. Volatiles released by emerald ash borer adults feeding on ash foliage increased parasitoid fecundity over ash foliage alone or no stimulus. The temperature at which the parasitoids were reared ranged from 20 to 25 degrees C in a daily cycle; however, raising the daily maximum temperature to 28 degrees C did not affect parasitoid longevity or fecundity. Adult females lived between 12 and 127 d, with an average of 60.8 +/- 4.5 d. Males lived slightly longer, with an average of 66 +/- 4.5 d. The first clutch of eggs was laid when the female was between 2 and 42 d old, with the average preoviposition period lasting 11.4 +/- 1.4 or 19.5 +/- 2.0 d in 2007 and 2009 trials, respectively. A higher proportion of the emerald ash borer larvae were feeding and thus attractive to parasitoids in the 2009 trial, and female S. agrili laid an average of 9.5 +/- 1.0 clutches containing 5.4 +/- 0.2 eggs, for an average of 51.2 eggs per female. Approximately three quarters of the progeny were female. The number of eggs per clutch was significantly greater when deposited on larger emerald ash borer larvae, further highlighting the need for quality larvae in rearing. Chilling S. agrili pupae at 10 degrees C to stockpile them for summer release was not successful; chilling resulted in lower survival and lower fecundity of emerging progeny. Female S. agrili proved capable of attacking emerald ash borer larvae through even the thickest bark of an ash tree that was 30-cm diameter at breast height. Even emerald ash borer larvae that were creating overwintering chambers in the outer sapwood of the tree were successfully attacked, suggesting that S. agrili could be reared on field collected logs infested with emerald ash borer.     

Long-term monitoring of the introduced emerald ash borer (Coleoptera: Buprestidae) egg parasitoid,Oobius agrili (Hymenoptera: Encyrtidae), in Michigan,USA and evaluation of a newly developed monitoring technique

Emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a serious invasive pest of ash trees (Fraxinus spp.) in North America from China. The egg parasitoid Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) was introduced from China as a biological control agent for this pest in Michigan and throughout the infested area of the United States. A critical component of any biological control program is post-release monitoring and evaluation; however, because of the small size and cryptic nature of O. agrili, evaluation of its impact is difficult. We compared two methods for measuring parasitism of emerald ash borer eggs: (1) timed visual searches of bark on standing ash trees and (2) bark collection, sifting, and sorting. Both methods were carried out in paired parasitoid-release and control plots, the visual search method over a six-year period (2008–2013) and the more recently developed bark-collection and sifting method for 2 years (2012–2013). The visual search method found parasitism in release plots remained low (0.7–4.2%) in samples taken from 2008 to 2012 and reached 10.6% in 2013. In comparison, the bark-sifting method found that rates of egg parasitism were considerably higher in release plots, 21.8% and 18.9% for samples taken in 2012 and 2013, respectively. These findings indicate that the population-level impact of O. agrili is increasing and may be an important source of mortality for EAB populations. We recommend the bark-collection and sifting method as the more effective method to recover parasitoids and estimate parasitism rates of O. agrili.     

Compound effects of induced plant responses on insect herbivores and parasitoids: implications for tritrophic interactions

1. Induced plant responses can affect herbivores either directly, by reducing herbivore development, or indirectly, by affecting the performance of natural enemies. Both the direct and indirect impacts of induction on herbivore and parasitoid success were evaluated in a common experimental system, using clonal poplar trees Populus nigra (Salicales: Salicaceae), the gypsy moth Lymantria dispar (L.) (Lepidoptera: Lymantriidae), and the gregarious parasitoid Glyptapanteles flavicoxis (Marsh) (Hymenoptera: Braconidae). 2. Female parasitoids were attracted to leaf odours from both damaged and undamaged trees, however herbivore‐damaged leaves were three times more attractive to wasps than undamaged leaves. Parasitoids were also attracted to herbivore larvae reared on foliage and to larval frass, but they were not attracted to larvae reared on artificial diet. 3. Prior gypsy moth feeding elicited a systemic plant response that retarded the growth rate, feeding, and survival of gypsy moth larvae, however induction also reduced the developmental success of the parasitoid. 4. The mean number of parasitoid progeny emerging from hosts fed foliage from induced trees was 40% less than from uninduced trees. In addition, the proportion of parasitised larvae that survived long enough to issue any parasitoids was lower on foliage from induced trees. 5. A conceptual and analytical model is provided to describe the net impacts of induced plant responses on parasitoids, and implications for tritrophic interactions and biological control of insect pests are discussed.     

Exploitation of the Fecal Shield of the Lily Leaf Beetle, Lilioceris lilii (Coleoptera: Chrysomelidae), by the Specialist Parasitoid Lemophagus pulcher (Hymenoptera: Ichneumonidae)

We investigated signal sources used by the parasitoid Lemophagus pulcher in locating and accepting larvae of its host, the lily leaf beetle, Lilioceris lilii. Olfactometer bioassays revealed that larvae with fecal shields, larvae without shields, the shield alone, and lily leaves damaged by L. lilii were all attractive to female parasitoids. In contact bioassays, L. pulcher females were attracted to shields and showed ovipositor probing independently of whether the larva underneath was L. lilii or a nonhost, suggesting that the shield plays a primary role in short-range host location and host acceptance by L. pulcher. The attractiveness of the shield is at least partly of a chemical nature, since shield extracts applied to dummies increased contact duration and induced ovipositor probing by L. pulcher. Another putative defense system of L. lilii, i.e., oral discharge which is emitted by disturbed larvae, was also attractive to experienced, but not to naive, female parasitoids. In all other tests, naive and experienced female L. pulcher responded to the same signal sources tested, suggesting that the host-selection behavior of this biological control candidate is governed largely by innate responses to host-associated cues.     

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.     

Development of methods for the field evaluation of Oobius agrili (Hymenoptera: Encyrtidae) in North America,a newly introduced egg parasitoid of the emerald ash borer (Coleoptera: Buprestidae)

A field study was conducted in forested plots near Lansing, Michigan in 2008 and 2009 to evaluate the newly introduced egg parasitoid Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) for control of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). To measure parasitism by O. agrili, laboratory-reared “sentinel EAB eggs” were deployed under bark flaps on trunks of selected ash trees in both parasitoid-release and non-release control plots. In addition, naturally occurring EAB eggs were collected in both parasitoid-release and control plots to measure parasitism. While no parasitism was detected with either sentinel or naturally occurring EAB eggs in control plots in either 2008 or 2009, a low level of parasitism by O. agrili was detected in the parasitoid-release plots in both artificially deployed sentinel eggs (?1%) and field-collected, naturally occurring eggs (1.1–4.2%) in both years. In addition to losses due to parasitism by O. agrili, a large proportion (37–52%) of the field-deployed sentinel eggs disappeared, possibly due to predators such as ants, in both parasitoid-release and control plots. While no statistical differences in parasitism by O. agrili were detected between parasitoid release and control plots, other sources of egg mortality such as disappearance due to predation on eggs, varied significantly across study sites in both 2008 and 2009. The relevance of these findings to future release and evaluation strategies for O. agrili for biological control of the invasive emerald ash borer in the US is discussed.     

An improved method for monitoring parasitism and establishment of Oobius agrili (Hymenoptera: Encyrtidae), an egg parasitoid introduced for biological control of the emerald ash borer (Coleoptera: Buprestidae) in North America

Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae) is a solitary egg parasitoid that has been released in the United States since 2007 for biocontrol of the invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae). Field and laboratory trials with ash logs infested with EAB eggs were conducted in Michigan between 2009 and 2010 to improve methods for monitoring the establishment of O. agrili. Naturally occurring EAB eggs were collected in both parasitoid-release and control (non-parasitoid-release) plots to compare with the EAB egg-sentinel log (ESL) technique. In three parasitoid-release plots, >50% of ESLs had O. agrili-parasitized eggs ranging from 3.9% to 48.2% egg parasitism after one week of field exposure. No EAB eggs were attacked by O. agrili on the ESLs deployed in control plots. In the laboratory, 100% of ESLs exposed to O. agrili inside rearing jars for one week had parasitized-eggs (68.5% egg parasitism). Deployment of ESLs detected low levels of parasitism by O. agrili in all three ash stands where O. agrili was released in previous years. In contrast, collection of naturally occurring EAB eggs detected the parasitism in only one of these three parasitoid-release ash stands. No parasitism was detected in control ash stands with either method. These findings indicate that populations of O. agrili released in previous years had successfully overwintered and established in the released ash stands by 2010, but had not yet dispersed to the control stands.     

Recent advances in biological control of important native and invasive forest pests in China

In recent decades, China has suffered severe attacks by both native and invasive forest pests. We have carried out a series of research projects on biological control of these pests. The fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Arctiidae) has been sustainably controlled by an effective gregarious pupal endoparasitoid, Chouioia cunea Yang (Chalcidoidea: Eulophidae), which is native to China, and spraying HcNPV virus against the pest’s larval stage. Pine wilt disease, caused by the pine wood nematode (Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle) (Aphelenchida: Aphelenchidae), is currently the number one pest in China. The strategy for controlling the disease is to manipulate the nematode’s vector, Monochamus alternatus Hope (Coleoptera: Cerambycidae). We discovered that Dastarcus helophoroides (Fairmaire) (Coleoptera: Bothrideridae) is the most important natural enemy in China pine forests. Mass rearing and release techniques were studied and developed. By releasing the parasitoid, 92.6% of the M. alternatus were parasitized in the first year. Meanwhile, three elaterid beetle species were found to prey on the larva of M. alternatus. The red turpentine beetle, Dendroctonus valens (LeConte) (Coleoptera:Scolytidae) was suppressed by a predator, Rhizophagus grandis Gyllenhal (Coleoptera: Rhizophagidae) introduced from Belgium and a total 3334 ha. of pine forests were protected. The oak longhorned beetle, Massicus raddei (Blessig) (Coleoptera: Cerambycidae) is the number one pest in the northeast forests of China, where it damages trunk of oaks, mainly Quercus liaotungensis and Q. mongolicus. An integrated management technique was developed for controlling the longhorned beetle: a special black light was invented for trapping the adults; the parasitoid Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae) was released against young larvae; and the parasitoid Dastarcus helophoroides eggs and/or adults were released when the hosts were mature larvae and/or pupae. By applying the technique for five years in northeastern China oak forests, the oak longhorned beetle has been controlled to a large extent. The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is native to eastern Asia, including China, and feeding by larvae damages ash trees. Natural enemies of the emerald ash borer were investigated and seven species were found in China, of which Spathius agrili Yang (Hymenoptera: Braconidae), Tetrastichus planipennisi Yang (Hymenoptera: Eulophiae), Sclerodermus pupariae Yang et Yao and Oobius agrili Zhang et Huang (Hymenoptera: Encyrtidae) are predominant and have high potential for biocontrol of the pest. The biology, behavior, ecology and mass rearing techniques of the parasitoids were studied.     

Short-range cues mediate parasitoid searching behavior on maize: The role of oviposition-induced plant synomones

Host searching by egg parasitoids faces a main constraint due to low detectability of cues from host eggs. Therefore egg parasitoids have developed distinctive strategies by exploiting cues that originate from non-target instars of the host and/or from plants. The scelionid Telenomus busseolae is specialized on concealed eggs of Sesamia nonagrioides and other noctuid stemborers. In this paper we show that oviposition by S. nonagrioides induces changes in the cues present on maize leaf surface, which arrest naïve females of T. busseolae. The induction appears to be systemic as the parasitoid also responds to leaves and leaf portions that are not directly affected by ovipositing females. Such oviposition-induced, short-range, plant synomones, acting in sequence with the kairomonal cues from scales left on the plant by the ovipositing host female, significantly increases parasitoid efficiency during host finding. The elicitor of plant response originates from the host female reproductive system, being contained both in the host’s ovarian eggs and in the colleterial gland secretion. Induction starts 24 h after oviposition and lasts at least till 72 h. The ecological role of this oviposition-induced plant synomone in host searching by T. busseolae is discussed.     

Effects of learning experience on behaviour of the generalist parasitoid Sclerodermus pupariae to novel hosts

Massicus raddei Blessig (Coleoptera: Cerambycidae), also referred to as the oak long‐horned beetle (OLB), is a non‐natural host for the generalist parasitoid Sclerodermus pupariae Yang et Yao (Hymenoptera: Bethylidae). To determine whether this generalist parasitoid might be a suitable agent for the control of OLB, the adaptive learning experience of adult female parasitoids to OLB larvae was investigated in the laboratory. A Y‐tube olfactometer bioassay was used to examine the effects of adaptive learning experience on the foraging ability of parasitoids for OLB larvae. The results indicated that parasitoids were significantly attracted by the volatiles of ash bark, Fraxinus velutina, with emerald ash borer (EAB), Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) larvae and larval frass, after exposure to ash bark mixed with EAB larval frass (learning condition A). In contrast, after exposure to oak bark, Quercus liaotungensis, mixed with OLB larval frass (learning condition C), parasitoids showed significant preference for the volatiles of oak bark with OLB larvae and larval frass. On the basis of the results of no‐choice tests, we found that parasitoids exposed to learning condition C had greater paralysis efficiency and higher OLB larvae parasitism rates than those exposed to learning condition A or no experience. Furthermore, parasitoids fed on OLB larvae in learning condition C had significantly greater paralysis efficiency and higher OLB larvae parasitism rates than other parasitoids tested. Parasitoids fed on EAB larvae in learning condition A had the lowest paralysis efficiency and OLB larvae parasitism rates among the parasitoids tested. These findings suggested that adaptive learning significantly enhanced the ability of a generalist parasitoid to utilize a novel host. This may provide a new approach to controlling non‐natural hosts using generalist parasitoids.     

Dramatic expansion of the range of the invasive ash pest,buprestid beetle Agrilus planipennis Fairmaire, 1888 (Coleoptera,Buprestidae) in European Russia

The emerald ash borer (Agrilus planipennis Fairmaire, 1888) is a dangerous invasive pest of ashes. It was previously believed that in European Russia it occurs only in Moscow, Moscow Province, and in the eastern regions of Smolensk Province. An examination of ash trees in 12 cities of European Russia has revealed a much wider area of the emerald ash borer invasion. The pest was found in Konakovo (Tver Province), Tula, Kaluga, Orel, and Voronezh. We have found that A. planipennis damages not only Fraxinus pennsylvanica (an American species which is commonly planted in cities), but also the aborigine European ash Fraxinus excelsior. Ashes in the European forests and in the protective forest belts are badly endangered.     

Response of the fruit fly parasitoid Diachasmimorpha longicaudata to host and host‐habitat volatile cues

Chemical information is crucial to insect parasitoids for successful host location. Here, we evaluated the innate response of Diachasmimorpha longicaudata (Ashmead) (Hymenoptera: Braconidae), a fruit fly larval parasitoid, to cues from host and host habitat (i.e., fruit infested with host larvae). We first assessed the preference of female parasitoids between oranges infested with Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) and non‐infested fruit. Females were highly attracted towards infested oranges on the basis of volatile chemical cues. After this initial experiment, we aimed at revealing the potential sources of volatile cues present in an infested fruit. To this end, we considered five potential sources: (1) punctured fruit; (2) fly feeding, frass, or host‐marking pheromone deposited on the orange surface; (3) larval activity inside the fruit; (4) the larvae themselves; and (5) fungi associated with infestation of oranges. Habitat cues associated with host activity and those produced by rotten oranges or oranges colonized by fungi were highly attractive for female wasps, whereas odours associated with the activity of the adults on the surface of the fruit, and those released by the fruit after being damaged (as happens during fruit fly egg‐laying) were not used as cues by female parasitoids. Once the female had landed on the fruit, direct cues associated with larval activity became important although some indirect signals (e.g., products derived from larval activity inside the fruit) also increased host searching activity. Our findings indicate that naïve D. longicaudata uses chemical cues during host habitat searching and that these cues are produced both by the habitat and by the host larvae.     

稻纵卷叶螟绒茧蜂对寄主的搜索行为

稻纵卷叶螟绒茧蜂是稻纵卷叶螟幼虫的重要天敌。以Y形嗅觉仪测定了稻纵卷叶螟2—3龄幼虫虫粪、4—5龄幼虫虫粪、健康水稻、稻纵卷叶螟幼虫为害后水稻在纵卷叶螟绒茧蜂对寄主的搜索过程中的作用。结果表明已交配的雌蜂显著趋向稻纵卷叶螟2—3龄幼虫虫粪和4—5龄幼虫虫粪,不趋向健康水稻、稻纵卷叶螟幼虫为害后的水稻。雄蜂、处女雌蜂不显著趋向健康水稻、稻纵卷叶螟幼虫为害后水稻、稻纵卷叶螟2—3龄幼虫虫粪、稻纵卷叶螟4—5龄幼虫虫粪。利用固相微萃取(SPME)及气相色谱/质谱(GC/MS)联用分析稻纵卷叶螟2—3龄幼虫虫粪的化学成分,并通过Y-形嗅觉仪测试已交配雌蜂对稻纵卷叶螟2—3龄幼虫虫粪化学成分标准品的嗅觉反应,结果表明已交配的雌蜂显著趋向1-十一烯和异缬草醛,稻纵卷叶螟幼虫虫粪中的1-十一烯和异缬草醛可能是稻纵卷叶螟绒茧蜂搜索寄主的利他素。     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.