Development, fecundity and survival of the herbivore Lymantria dispar and the number of plant species in its diet

ABSTRACT.

• 1 Larval gypsy moth Lymantria dispar (L.) mortality depends upon the number and type of plant species consumed as well as the sequence in which they are consumed.
• 2 When a two-species diet is composed of a favourable and an unfavourable species, larval mortality is higher on the two-species diet than on the diet of the favourable species alone.
• 3 When a two species diet is composed of a favourable and unfavourable coniferous species, larval mortality is higher on the single conifer species diet than on the two-species diet.
• 4 Two-species diets, in which one species is a conifer, produce individuals with a greater fecundity than diets of either species alone.
• 5 The influence of diets composed of two favourable species, on development, size and fecundity, depends both on the relative quality of each of the two plant species and which of the two is consumed by older instars.

     

Effects of variation among plant species on the interaction between a herbivore and its parasitoid

Abstract.  1. Previous studies have demonstrated that phenotypic traits of plants have the potential to affect interactions between herbivores and their natural enemies. Consequently, the impact of natural enemies on herbivore vital rates and population dynamics may vary among plant species. This study was designed to investigate the potential for density-dependent parasitism of an aphid herbivore feeding on six different host plant species.
2. Population densities of the aphid Aphis nerii B de F (Homoptera: Aphididae) and its parasitoid Lysiphlebus testaceipes Cresson (Hymenoptera: Braconidae) were recorded within a single growing season on six different species of milkweed in the genus Asclepias L. (Asclepiadaceae). Asclepias species are known to vary in their quality as food for herbivores. Although data on plant quality were not available in this study, population data were analysed to determine the effects of different Asclepias species on rates of parasitism and aphid population growth.
3. Parasitism rates of A. nerii varied among Asclepias species but were temporally density dependent over at least some range of aphid density on all plant species. Aphid population growth rates also varied among Asclepias species, and declined with an increase in the maximum parasitism rates among plant species; however, in no case was density-dependent parasitism sufficient to prevent exponential population growth of aphids within the growing season. The results serve to emphasise that, if natural enemies are to regulate herbivore populations, density-dependent mortality is a necessary, but not sufficient, condition for regulation.     

Influence of host plant, foliar phenology and larval dietary history on Lymantria dispar larval nutritional indices

Quantitative nutritional indices were measured in 3rd instar gypsy moths, Lymantria dispar L. Analyses of the main and interactive effects of host plant consumed (oak or pine), foliar phenology (early or late season) and larval dietary history (whether fed artificial diet or foliage as second instars) indicate that larval performance was significantly affected by all three variables tested. Relative Growth Rate (RGR) was higher on oak than pine early in the season, but the reverse occurred one month later, owing largely to the slower Relative Consumption Rate (RCR) of late season oak feeders. Efficiency of Conversion of Digested food (ECD) was depressed in larvae fed pine foliage for two instars compared with those fed oak. The interaction between larval dietary history and foliar phenology produced significant effects on all indices measured. Foliar analyses showed that, as the season progressed, oak had a higher percent dry weight than did pine. On a dry weight basis, pine foliage had significantly less total and protein nitrogen than did oak collected at the same time.

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Résumé Les indices nutritionnels larvaires ont été évalués sur des chenilles de L. dispar L. du troisième stade. L'analyse des effets et des interactions de la nature de la plante consommée (Quercus microcarpa) ou Pinus strobus, de la phénologie foliaire (en début de saison, c'est-à-dire seconde quinzaine de mai, ou en fin de saison, c'est-à-dire à la mi-juin), de l'alimentation antérieure (régime artificiel de germes de blé ou feuillage pendant le second stade) montre que les performances larvaires sont fortement modifiées par ces 3 variables. Le taux de croissance relative (RGR) est plus élevé sur chêne que sur pin en début de saison, mais s'inverse un mois plus tard avec une forte diminution sur chêne. L'efficacité de conversion de l'aliment (ECD) est diminuée sur pin pendant les second et troisième stades. L'interaction entre l'alimentation antérieure et le phénologie foliaire a des effets significatifs sur la digestibilité approchée (AD), sur l'efficacité de la conversion de l'aliment ingéré (ECI), et sur ECD, RCR et RGR.Les analyses foliaires ont montré que, lorsque la saison avance, le poids sec du chêne devient supérieur à celui du pin. En considérant le poids sec, le feuillage de pin contient moins d'aliments et de protéines que le chêne récolté au même moment. La teneur en azote tend à diminuer chez les deux espèces, de 17% pour le pin et 26% pour le chêne.Nous pensons que certains de ces facteurs déterminent la valeur de ces plantes pour L. dispar. Les chenilles âgées peuvent compenser plus ou moins la faible assimilation sur pin par des RCR plus élevés. Le même comportement ne semble pas possible sur chêne, une plus grande quantité de chêne avancé en saison que de feuilles jeunes ne pouvant être consommée pour compenser la diminution de la digestibilité.

     

Learning of host-infested plant volatiles in the larval parasitoid Cotesia kariyai

The ability to learn plant volatiles in Cotesia kariyai females was examined by wind tunnel bioassays. Searching experience on a host-infested corn plant increased subsequent flight responses of females to the infested plant. Females experiencing host by-products together with the volatiles extracted from infested leaves one time showed an increased response. However, such behavioral changes were not observed in females which experienced only the host by-products or the volatiles. Thus, the increased response is considered to be preference learning. Multiple experiences of C. kariyai with host by-products together with the volatiles did not increase their flight response to the volatiles. Furthermore, this learned response gradually decreased within 2 days. These behavioral modifications based on experience would be advantageous for C. kariyai to locate their polyphagous hosts efficiently.     

The influence of the host plant of diamond-back moth (Plutella xylostella) on the plant preferences of its parasitoid Cotesia plufellae in Sri Lanka

Abstract. In Y-tube olfactometer tests, female Cotesia plutellae Kurdjmov (Hymenoptera: Braconidae), a major parasitoid of Plutella xylostella (L.) in southeast Asia, preferred the odour of the brassica type (Blue Lake cabbage) on which they had developed.Such plants were even preferred to the odour of caterpillar-infested and damaged leaves of another brassica (Early Phenomenal cauliflower).However, within one brassica type, the odour of caterpillar-infested leaves was preferred to that of uninfested and undamaged leaves.Odours of both Blue Lake and Early Phenomenal were preferred to the control odour (water).However, following the transfer of the parasitoid from Blue Lake to another cabbage (Brunswick) for one generation, females no longer distinguished between Blue Lake and Early Phenomenal.     

Parasitism-induced effects of Glyptapanteles liparidis (Hym., Braconidae) on the juvenile hormone titer of its host, Lymantria dispar: the role of the parasitoid larvae

Parasitization by the gregarious larval endoparasitoid Glyptapantles liparidis induces a dramatic increase in the hemolymph juvenile hormone (JH) titer (especially JH III) of its host larva, Lymantria dispar. Here, we investigated the role of the parasitoid larvae in JH synthesis and release by in vitro and in vivo experiments. GC-MS analyses confirmed that the rising hemolymph JH titer coincided with the time at which the parasitoids molt to the second larval instar. Peak values in host hemolymph titers were observed prior to parasitoid emergence, and titers dropped to negligible levels within 24 h after parasitoid emergence. Whole body extracts from excised second instar parasitoids yielded JH III and trace amounts of JH II. The in vitro secretory activity of the corpora allata (CA) of L. dispar larvae was not enhanced by parasitization. When the host's CA were separated by neck ligation, we found elevated JH III titers, but no JH II in the hemolymph of the posterior section, which contained the parasitoids. Parasitoids that were kept in in vitro culture produced and released only JH III. The parasitoids’ ability to secrete JH and to molt independently from their host's molting cycles indicates that at least second instar parasitoids are hormonally self-reliant.     

Attraction of the specialist parasitoid Cotesia rubecula to Arabidopsis thaliana infested by host or non-host herbivore species

In this study we investigated whether in a two‐choice set‐up the parasitoid Cotesia rubecula (Marshall) (Hymenoptera, Braconidae) distinguishes between volatiles emitted by Arabidopsis thaliana (L.) Heynh. (Brassicaceae) infested with its host, Pieris rapae (L.) (Lepidoptera: Pieridae) and Arabidopsis infested with non‐host herbivores. Four non‐host herbivore species were tested: the caterpillars Plutella xylostella (L.) (Lepidoptera: Plutellidae) and Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae), both chewing insects, the spider mite Tetranychus urticae (Koch) (Acari: Tetranychidae), which punctures parenchymal cells, and the aphid Myzus persicae (Sulzer) (Hemiptera: Aphidoidea), which is a phloem‐feeder. Compared with undamaged plants, C. rubecula females were more attracted to Arabidopsis plants infested by P. rapae, P. xylostella, S. exigua, or T. urticae, but not to plants infested by M. persicae. The parasitoids preferred host‐infested plants to spider mite‐ or aphid‐infested plants, but not to plants infested with non‐host caterpillars (P. xylostella or S. exigua). The data show that when Arabidopsis plants are infested with a leaf tissue‐damaging herbivore they emit a volatile blend that attracts C. rubecula females and the wasps only discriminate between a host and non‐host herbivore when the type of damage is different (chewing vs. piercing). When Arabidopsis is infested with a herbivore that hardly damages leaf tissue, C. rubecula females are not attracted. These results may be explained by differences in the amount of damage and in the relative importance of different signal‐transduction pathways induced by different types of herbivores.     

Interactions among three trophic levels: the influence of host plant on performance of Pieris brassicae and its parasitoid, Cotesia glomerata

The relative suitability of four host plants was determined both for unparasitized Pieris brassicae L. caterpillars and for Cotesia glomerata (L.) developing in P. brassicae. For unparasitized P. brassicae, growth rate and pupal weight were highest on Brussels sprouts and Swedish turnip, intermediate on rape, and lowest on nasturtium. In contrast, C. glomerata larval developmental rate and adult longevity were greatest for wasps from P. brassicae reared on nasturtium.On all four plants, the host-parasitoid complex attained a lower final weight than unparasitized P. brassicae, and it is argued that this difference is due primarily to reduced consumption by parasitized P. brassicae. Among parasitized caterpillars, however, complex weight was positively correlated with clutch size, suggesting that C. glomerata larvae are able to partially counteract the effect of parasitization per se on host consumption.The host plants of P. brassicae appear to face an evolutionary dilemma: in order to increase the total mass of parasitoids produced, they must suffer greater loss of foliage. This trade-off, if common in nature, may represent a formidable constraint on coevolution between host plants and parasitoids.     

Host plants of the herbivorous insect Mythimna separata (Lepidoptera: Noctuidae) affect its susceptibility to parasitism by the larval parasitoid Cotesia kariyai (Hymenoptera: Braconidae)

Previous studies have shown that the food plant species consumed by herbivorous insects affect their parasitism by parasitoid wasps or flies, but this phenomenon has only been observed in a limited number of systems. Here, we investigate how feeding on different plant species affects the survival of the rice armyworm Mythimna separata (Walker) (Lepidoptera: Noctuidae) and its successful parasitism by the larval endoparasitoid Cotesia kariyai (Watanabe) (Hymenoptera: Braconidae). Survival rate and pupal weight of unparasitised M. separata fed with daikon Raphanus sativus L. var. longipinnatus was lower than with maize Zea mays L. In addition, caterpillars fed with daikon were less susceptible to parasitism by C. kariyai than those fed with maize, and parasitised M. separata larvae fed with daikon had higher survival rates than those fed with maize. These results indicate that while daikon is not an optimal food for unparasitised caterpillars, it may protect the larvae from death by C. kariyai parasitism.     

Fitness-related traits in a parasitoid fly are mediated by effects of plants on its host

Plants can affect parasitoids directly, by reducing or enhancing their ability to locate hosts, or indirectly by affecting the fitness of herbivores and thus of parasitoids. Tritrophic interactions between three host plants (cucumber, tomato, sweet pepper), a polyphagous herbivore Trichoplusia ni and a generalist parasitoid Compsilura concinnata were assessed. Plants had a strong effect on T. ni larval survival, as well as on C. concinnata fitness-related traits: cucumber-fed hosts yielded parasitoids with shorter larval development time and females had heavier pupal weights than parasitoids from host larvae that were fed tomato. Furthermore, C. concinnata was more efficient at finding cucumber-fed than tomato-fed T. ni . These results suggest that C. concinnata has different efficiency and potential as a biocontrol agent on the different crops. This highlights the importance of assessing tritrophic interactions in systems where an inundative biological control agent may be released against generalist targets on more than one crop plant.     

外源茉莉酸诱导的青杨生化抗性及其对舞毒蛾幼虫食物利用的影响

【目的】为探讨外源茉莉酸(jasmonic acid, JA)诱导的青杨 Populus cathayana Rehd.抗性对舞毒蛾 Lymantria dispar (L.)幼虫食物利用的影响。【方法】在室内对青杨苗木喷施0.001和0.1 mmol/L两种浓度的茉莉酸,对照喷0.2%的丙酮水溶液,喷施后1, 5和10 d分别采集叶片,分析其初生和次生物质含量的变化。另选喷施0.1 mmol/L茉莉酸的青杨苗木,喷施后1, 5和10 d分别接舞毒蛾2龄幼虫,单头饲养,测定其取食量、体重和排粪量及发育历期,统计分析其食物消化率、转化率和利用率。【结果】两种浓度茉莉酸处理均使青杨叶片中的蛋白质和可溶性糖含量降低,而木质素、单宁、黄酮和酚类物质含量增加。蛋白质和可溶性糖在处理第10天时含量最低,其中高浓度茉莉酸处理较对照分别降低46.5%和49.1%,低浓度处理分别降低30.6%和22.8%。叶片中酚类物质含量在高浓度处理第10 天时增幅最大,较对照增加102%。木质素、黄酮和单宁酸在处理第5天时的含量最高,其中高浓度处理分别较对照增加113%, 75%和57%。用0.1 mmol/L茉莉酸诱导处理后,舞毒蛾2龄幼虫对叶片的消化率、转化率和利用率均有所降低, 取食处理后1, 5和10 d的青杨叶片的食物利用率较对照分别降低了29.4%, 27.6%和28.2%,且幼虫体重降低、发育历期延长。【结论】结果提示外源茉莉酸诱导青杨可对舞毒蛾产生明显的生化抗性,实践中可利用这种生化抗性防治舞毒蛾的危害。     

舞毒蛾卵寄生蜂大蛾卵跳小蜂发育与温度的关系及利用替代寄主柞蚕卵繁育的子代品质评价

舞毒蛾Lymantria dispar (L.)是国际性检疫害虫。大蛾卵跳小蜂Ooencyrtus kuwanae (Howard)是舞毒蛾卵的重要寄生蜂, 对舞毒蛾有一定的控制作用。为了在规模化繁育大蛾卵跳小蜂时控制小蜂的发育进度, 设置不同的温度梯度研究了该蜂发育与温度的关系; 同时, 为了对替代寄主繁育出的天敌质量进行评价, 对利用其自然寄主舞毒蛾卵和替代寄主柞蚕Antheraea pernyi卵繁育出的子代成蜂的寿命、 胸宽、 雌雄性比进行了比较。结果显示： 大蛾卵跳小蜂的发育起点温度和有效积温分别为10.50±1.41℃和260.74±25.09日·度, 温度与发育速率的关系为T=10.50+260.74V。当采用30%的蜂蜜水饲喂成蜂时, 柞蚕卵繁育出的大蛾卵跳小蜂雌、 雄蜂的平均寿命分别为15.01和10.38 d, 采用原寄主舞毒蛾卵繁育出的雌、 雄蜂平均寿命分别为20.94和15.95 d, 两者差异显著; 采用柞蚕卵繁育出的雌蜂个体显著大于用舞毒蛾卵繁育出的雌蜂个体; 柞蚕卵和舞毒蛾卵繁育出的大蛾卵跳小蜂雌雄性比没有显著差异, 分别为2.42∶1和2.57∶1。结果表明, 在野外开展舞毒蛾的生物防治时, 释放利用柞蚕卵繁育出的大蛾卵跳小蜂具有可行性。     

四种植物酚类物质对舞毒蛾生长发育及繁殖的影响

【目的】为明确植物酚类次生物质对舞毒蛾Lymantria dispar (L.) 的影响,并为应用其防治害虫奠定基础。【方法】本研究选用4种酚酸（水杨酸、丁香酸、绿原酸和水解单宁酸）分别加入人工饲料中饲养舞毒蛾2龄幼虫,调查其对幼虫生长发育及繁殖的影响。【结果】不同酚酸对舞毒蛾的影响差异显著。单宁酸处理第12天时幼虫死亡率达到22.2%,显著高于对照（取食不添加任何酚酸的人工饲料）死亡率（3.3%）（P＜0.01）及其他酚酸处理时的死亡率。到第22天单宁酸及绿原酸使幼虫死亡率迅速上升,至第34天时死亡率达到100%;二者处理的幼虫虫体瘦小,发育历期显著延长,不能正常蜕皮,到4龄期时全部死亡。取食含丁香酸或水杨酸饲料的幼虫可幸存至蛹和成虫,雌性蛹重较对照显著增加,但产卵量和卵受精率均显著降低。其中,取食含丁香酸饲料的成虫产卵量和卵受精率分别比对照减少近90粒和降低约35%,雌性成虫比例下降。【结论】结果说明不同酚酸在害虫体内的积累会对其生长发育及繁殖产生不同程度的影响。     

Cotesia plutellae parasitizing Plutella xylostella: Host-age dependent parasitism and its effect on host development and food consumption

The braconid Cotesia plutellae(Kurdjumov) (Hymenoptera: Braconidae) is amajor solitary, larval endoparasitoid of thediamondback moth, Plutella xylostella(L.) (Lepidoptera: Plutellidae). Parasitism oflarvae of different host instars and fourdevelopmental ages of the 4th instar ofthe pest was examined. The effects of hostinstar at initial parasitization on thedevelopment, survival, size and fecundity ofthe parasitoid were determined in thelaboratory at 25 °C. The effects ofparasitism on host development and foodconsumption were investigated at 28 °C.Cotesia plutellae could parasitize larvaeof all four instars of P. xylostella, butpreferred 2nd and 3rd instars. In achoice test, the relative parasitism indicesfor 2nd, 3rd and 4th instarswere 0.37, 0.39 and 0.24, respectively.Parasitism decreased sharply with increasinghost age in the 4th instar and approachedzero in host larvae that had gone beyond 37%of 4th stadium. The development time andthe final adult size of the parasitoid variedwith the host instar at initial parasitization.Parasitoids with initial parasitism in the4th instar hosts had the shortestdevelopment time, followed by those in the3rd instar, and then by those in the2nd instar. Parasitoids startingparasitism in 2nd instar hosts weresmaller in body size than those starting in the3rd or 4th instar. However, resultantfemales starting parasitism in 3rd instarhosts had the highest fecundity. Parasitizedlarvae exhibited longer development time andincreased food consumption compared withunparasitized ones. This study presents thefirst record that a solitary parasitoidregulates host behavior leading to an increasein food consumption by the host.     

Induced plant responses to multiple damagers: differential effects on an herbivore and its parasitoid

Herbivore-induced plants responses can affect the preference and performance of herbivores and their natural enemies. These responses may vary depending on the identity and number of herbivore species feeding on the plant so that when herbivores from different guilds feed on plants, the interactions between plants, herbivores, and natural enemies may be disrupted. Tomato plants were damaged either by the caterpillar Spodoptera exigua, or the aphid Macrosiphum euphorbiae, or damaged by both herbivores, or undamaged controls. We measured the preference and performance of S. exigua and its parasitoid Cotesia marginiventris, and activity of proteinase inhibitors (PI) as an indicator of induced resistance. Compared to undamaged plants, caterpillar damage reduced the number of eggs laid by S. exigua adults, reduced growth, consumption, and survival of larval S. exigua and C. marginiventris, and increased activity of PIs 43%; but did not increase attraction of C. marginiventris. While pupal mass of S. exigua was not affected, the pupal mass of C. marginiventris decreased on caterpillar-damaged plants compared to controls. In contrast, plants damaged by aphids were preferred for oviposition by S. exigua, and had increased larval consumption and survival, compared to controls. Aphid feeding did not affect the preference or performance of C. marginiventris, or PI activity, compared to controls. While oviposition was deterred on caterpillar-damaged plants, plants damaged by both herbivores received the same amount of oviposition as controls. The attraction of C. marginiventris to plants damaged by caterpillars and aphids was increased compared to controls. However, plants damaged by both herbivores had similar PI activity, larval growth and survival of S. exigua and C. marginiventris, as plants singly damaged by caterpillars. Overall, the preference component for both the herbivore and parasitoid was more strongly affected by damage due to multiple herbivores than the performance component.     

Alterations in carbohydrate and fatty acid levels of Lymantria dispar larvae caused by a microsporidian infection and potential adverse effects on a co-occurring endoparasitoid,Glyptapanteles liparidis

Infection of Lymantria dispar host larvae by the entomopathogenic microsporidium Vairimorpha sp. has a negative impact on the performance of the endoparasitic braconid Glyptapanteles liparidis. To investigate possible causes for this effect, we studied to what extent nutritional host suitability is altered by the microsporidium. Therefore, we analyzed carbohydrates and fatty acids in host larvae after Vairimorpha infection and/or parasitism by G. liparidis. Trehalose levels were significantly reduced in the hemolymph of infected hosts. After day five post infection, it was detected only in traces. Four to six days later, the glycogen resources were depleted in infected larvae. Parasitism by G. liparidis, on the other hand, led to increased hemolymph trehalose levels during the early endoparasitic phase but to a significant decrease at the end of its larval development. No effect of parasitism on the glycogen content was ascertained. Hemolymph levels of the fatty acids analyzed, such as palmitic, stearic, oleic, linoleic, and linolenic acid, were significantly reduced in microsporidia-infected L. dispar. Vairimorpha sp. develops as an intracellular parasite in the fat body of the host larva and synthesis of trehalose and fatty acids may be disturbed. Moreover, microsporidia may also harness metabolites or energy produced by host cells. We conclude that the microsporidia-induced decrease in hemolymph carbohydrates and fatty acids adversely affects growth and development of parasitoid larvae.     

Effect of Bt corn leaf suspension on food consumption by Chilo partellus and life history parameters of its parasitoid Cotesia flavipes under laboratory conditions

Laboratory scale experiments were conducted in order to assess the potential effect of Bacillus thuringiensis‐corn leaf material on the parasitized herbivore Chilo partellus Swinhoe (Lepidoptera: Crambidae) and on its parasitoid Cotesia flavipes (Cameron) (Hymenoptera: Braconidae). Food consumption and relative consumption rate of parasitized hosts exposed to Bt‐corn leaf‐material were strongly reduced compared to the control. The number of hosts allowing parasitoid larvae to complete their development was also reduced in the Bt group. Moreover, the fresh weight of parasitoid pupae and the dry weight of parasitoid adults was lower than in the control. Only in the Bt group, were strong negative correlations found between food intake by the host, and the number of parasitoid cocoons. Strong positive correlations were also only found in the Bt group, between food intake and parasitoid development time. As effects of Bt on the oviposition behaviour of C. flavipes could be excluded, differences between the Bt group and the control could only be due to the effect of Bt toxin on the parasitoid larva developing inside the host. Whenever food consumption can be measured, the methods used in this study are proposed as a model for future risk assessments on different types of insect‐resistant transgenic plants, herbivores, parasitoids, and predators.     

Host recognition by the gypsy moth [Lymantria dispar] [Lep.: Lymantriidae] hyperparasite,Eurytoma appendigaster [Hym.: Eurytomidae] of cocoons ofCotesia melanoscela [Hym.: Braconidae]

Artificial and modified natural hosts were exposed to females of the gypsy moth [Lymantria dispar (L.)] hyperparasite,Eurytoma appendigaster (Swederus), to investigate its host recognition behavior on the primary host, which are cocooned larvae of the gypsy moth parasite,Cotesia melanoscela (Ratzeburg). Material(s) which caused drilling behavior by the hyperparasite on host cocoons were extracted with both polar and non-polar solvents. However, cocoons washed with large volumes of solvent still caused substantial drilling activities by females, suggesting that additional cues may be important. Results suggest that host recognition in this hyperparasite involves a variety of host characteristics.      

In situ modification of herbivore-induced plant odors: a novel approach to study the attractiveness of volatile organic compounds to parasitic wasps

Many parasitic wasps (parasitoids) exploit volatile organic compounds (VOCs) emitted by herbivore-infested plants in order to locate their hosts, but it remains largely unknown which specific compounds within the volatile blends elicit the attractiveness to parasitoids. One way of studying the importance of specific VOCs is to test the attractiveness of odor blends from which certain compounds have been emitted. We used this approach by testing the attraction of naive and experienced females of the two parasitoids Cotesia marginiventris and Microplitis rufiventris to partially altered volatile blends of maize seedlings (Zea mays var. Delprim) infested with Spodoptera littoralis larvae. Adsorbing filter tubes containing carbotrap-C or silica were installed in a four-arm olfactometer between the odor source vessels and the arms of the olfactometer. The blends breaking through were tested for chemical composition and attractiveness to the wasps. Carbotrap-C adsorbed most of the sesquiterpenes, but the breakthrough blend remained attractive to naive C. marginiventris females. Silica adsorbed only some of the more polar VOCs, but this essentially eliminated all attractiveness to naive C. marginiventris, implying that among the adsorbed compounds there are some that play key roles in the attraction. Unlike C. marginiventris, M. rufiventris was still attracted to the latter blend, showing that parasitoids with a comparable biology may employ different strategies in their use of plant-provided cues to locate hosts. Results from similar experiments with modified odor blends of caterpillar-infested cowpea (Vigna unguiculata) indicate that key VOCs in different plant species vary greatly in quality and/or quantity. Finally, experienced wasps were more strongly attracted to a specific blend after they perceived the blend while ovipositing in a host. Considering the high number of distinct adsorbing materials available today, this in situ modification of complex volatile blends provides a new and promising approach pinpointing on key attractants within these blends. Advantages and disadvantages compared to other approaches are discussed.     

外源茉莉酸诱导的青杨叶片保护性酶活性变化及其对舞毒蛾幼虫生长发育的影响

为探讨外源茉莉酸对青杨Populus cathayana的诱导抗性及其对舞毒蛾Lymantria dispar的影响, 室内对青杨扦插苗喷施不同浓度的茉莉酸（对照为0.17%丙酮）, 分别在喷施后1, 5和10 d采集叶片分析其保护性酶活性的变化, 并接舞毒蛾幼虫于青杨苗木上观测其长发育情况。结果表明： 0.1 和0.001 mmol/L两种浓度的茉莉酸（JA）处理均使青杨叶过氧化物酶（POD）、 多酚氧化酶（PPO）、 苯丙氨酸解氨酶（PAL）、 胰凝乳蛋白酶抑制剂（CI）和胰蛋白酶抑制剂（TI）活性较对照增加(P<0.05)。取食茉莉酸诱导的青杨苗木后, 舞毒蛾幼虫的发育历期延长, 体重降低。0.1 mmol/L茉莉酸诱导的青杨苗木5 d后接虫, 使舞毒蛾幼虫的发育历期显著延长, 较对照长8 d; 接虫21 d后称重时, 取食茉莉酸诱导的青杨叶片的幼虫体重较对照组降低了50%~100%, 该结果说明外源茉莉酸诱导青杨产生了对舞毒蛾明显的抗虫性。