Inhibitory effects of permethrin on flight responses,host‐searching,and foraging behaviour of Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of Plutella xylostella (Lepidoptera: Plutellidae)

Although it is well known that the application of broad‐spectrum synthetic insecticides reduces the effectiveness of natural enemies, the details of the actual mechanisms, including the lethal and sublethal effects of this reduction, are not fully understood. The inhibitory effects of a pyrethroid insecticide (permethrin), Adion 20% EC on the flight responses, host‐searching behaviour and foraging behaviour of Cotesia vestalis (Hymenoptera: Braconidae), a larval parasitoid of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), were investigated under laboratory conditions. In choice trials, the wasps showed significant preference for P. xylostella‐infested Komatsuna plants over insecticide‐treated plants, suggesting an inhibitory effect of the insecticide on the flight response of C. vestalis. When offered a pair of plants, the wasps showed a significant preference for P. xylostella‐infested plants compared to uninfested plants. However, significantly more wasps were attracted to infested permethrin‐treated plants than to uninfested plants, suggesting that the wasps are attracted to the volatile infochemicals from the infested plants, even if treated with permethrin. The searching time was significantly shorter and the mortality of C. vestalis adults on the insecticide‐treated plants significantly higher than in the control plants treated with distilled water. These results suggest that the application of the insecticide had an inhibitory effect on the wasps’‐searching behaviour and consequently reduced the effectiveness of C. vestalis as a biological control agent against P. xylostella. In addition, the strength of the inhibitory effect of permethrin on the attraction of the wasps to the plants is critical to the survival of C. vestalis. Our results suggest that the attraction of the wasps to the permethrin‐treated infested plants increases the risk of their exposure to this insecticide.     

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.     

Relative influences of plant type and parasitoid initial density on host–parasitoid relationships in a tritrophic system

To explore the effects of bottom-up and top-down forces on the relationships between a host, Plutella xylostella (L.) (Lepidoptera, Plutellidae), and its parasitoid, Cotesia vestalis (Haliday) (Hymenoptera, Braconidae), a short-term field experiment was established as a factorial experiment using three different host plants (Brassica pekinensis cv. Yuki F1, Brassica oleracea var. capitata cv. Midorimaru F1 and B. oleracea var. botrytis cv. Snow Crown) in the presence of C. vestalis at two different levels (low and high initial release). The tritrophic interactions were monitored by census counts of live adults 20?days after parasitoid release. The mean numbers of P. xylostella and C. vestalis adults were compared using log-linear analysis of deviance. Also, differences in the levels of parasitism were analysed using logistic analysis of deviance. There was a significant effect of host plant type on the abundance of P. xylostella, the abundance of C. vestalis and the percentage parasitism of P. xylostella by C. vestalis. The mean number of P. xylostella adults per cage on common cabbage or cauliflower was significantly greater than that on Chinese cabbage. The mean number of C. vestalis adults and the proportion of hosts attacked by C. vestalis per cage were significantly greater on Chinese cabbage compared with common cabbage or cauliflower. Indeed, initial parasitoid release did not significantly affect the abundance of P. xylostella but there was a significant influence of initial parasitoid release on the abundance of C. vestalis and the levels of parasitism of P. xylostella by C. vestalis. The mean number of C. vestalis adults and the proportion of P. xylostella parasitised by C. vestalis per cage were greater in high level of parasitoid release compared with low level of parasitoid release. However, there were no significant interacting effect of the factors (plant type?×?parasitoid initial abundance) on the abundance of P. xylostella, the population size of C. vestalis and parasitism of P. xylostella by C. vestalis.     

Plant Resistance Affects the Olfactory Response and Parasitism Success of Cotesia vestalis

Understanding the factors influencing host-selection behavior of parasitoids is essential in studies on host-parasitoid ecology and evolution, and in combining sustainable strategies of pest management, such as host-plant resistance and biological control. The effects of host-plant resistance on the olfactory response and parasitism success by Cotesia vestalis, a parasitoid of diamondback moth (Plutella xylostella) larvae were examined. Here, it was demonstrated that host-plant resistance can strongly influence foraging behavior and parasitism success of the parasitoid. In olfactometer experiments, C. vestalis did not differentiate between crucifer plant types with similar levels of susceptibility or resistance to P. xylostella but showed a strong preference for susceptible compared with partially-resistant host plants. The influence of previous oviposition activity varied with the host-plant type experienced by the parasitoid. In cage experiments, C. vestalis preferred to parasitize P. xylostella larvae on a susceptible plant compared with larvae on a partially resistant host plant when exposed to hosts for 24 h. However, this preference appeared to be transitory, and was not found after 96 h exposure. The present study suggests that combining partial host-plant resistance with biological control by C. vestalis for the control of P. xylostella may in some circumstances be antagonistic and negatively affect parasitism success.     

Cover Caption

Cotesia vestalis has been used as a good biological control agent for management the pest of global cruciferous plants, Plutella xylostella. The successful parasitization strictly relies on C. vestalis olfactory perception, and odorant binding protein (OBP) play a key role in searching for hosts (see pages 1354-1368). The cover photo shows C. vestalis is parasitizing the host with the help of three OBP genes expressed in C. vestalis antennae for locating P. xylostalla larva. Photo provided by Xi-Qian Ye.     

Effect of insecticides on the mortalities of three whitefly parasitoid species, Eretmocerusmundus, Eretmoceruseremicus and Encarsiaformosa (Hymenoptera: Aphelinidae)

The toxicities of 24 insecticides for the biological control of whiteflies were evaluated for Eretmocerus mundus (Mercet), Eretmocerus eremicus Rose and Zolnerowich and Encarsia formosa Gahan using the residual film method (for adults) and the dipping method (for pupae). Mortalities from insect growth regulators (IGRs) (flufenoxuron and lufenuron), Bacillus thuringiensis (Bt), pymetrozine and sulfur were <30% for both pupae and adults of all three species, indicating that the parasitoids were not seriously affected by these insecticides. Neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid and nitenpyram), synthetic pyrethroids (etofenprox and permethrin), organophosphates (acephate and fenitrothion), chlorphenapyr, emamectin benzoate, spinosad and tolfenpyrad were seriously harmful (100% mortality) and acaricides (chinomethionat, milbemectin and pyridaben) were moderately harmful or seriously harmful to adult parasitoids (leading to mortalities of >92%). For each insecticide, the mortality of pupae was generally lower than that of adults, even though the toxicity classification for the two groups was similar. The results indicate that IGRs, Bt, pymetrozine and sulfur are relatively harmless, and are compatible with the use of parasitoids to help control whiteflies for integrated pest management in greenhouses.     

Application of synthetic herbivore‐induced plant volatiles causes increased parasitism of herbivores in the field

We previously reported that Cotesia vestalis (Hymenoptera, Braconidae), a parasitoid of diamondback moth (DBM) (Plutella xylostella; Lepidoptera, Plutellidae) larvae, was attracted to volatiles from crucifer plants infested by moth larvae kept in a desktop acrylic box, and that a blend of four DBM‐induced plant volatiles was responsible for this attraction. In this study, using a specially designed dispenser to release the four compounds, we demonstrated that the wasp was attracted to intact komatsuna plants (Brassica rapa var. perviridis). The experiments were performed in a climate‐controlled room, which was approximately 1000 times larger than the acrylic box used previously. Similarly, using the dispenser in the field, C. vestalis females were attracted to intact komatsuna plants with the dispenser from a distance of three metres. We also examined the effect of the volatile blend on the incidence of parasitism of DBM larvae in the field. Three small containers containing DBM‐infested komatsuna plants with dispensers, and three control containers containing only infested plants (control) were arranged in two lines running perpendicular to a komatsuna field in which both DBM larvae and C. vestalis populations were maintained, at distances of 12, 30 and 70 m. The results showed that the incidence of DBM parasitism was significantly higher in containers containing dispensers than in the control containers, suggesting that the blend could potentially be applied to DBM control in agroecosystems.     

Yeheb (<Emphasis Type="Italic">Cordeauxia</Emphasis><Emphasis Type="Italic">edulis</Emphasis>) extract deters feeding and oviposition of <Emphasis Type="Italic">Plutella xylostella</Emphasis> and attracts its natural enemy

The effects of yeheb (Cordeauxia edulis Hemsl.) leaf extract on feeding and oviposition by diamondback moth (DBM) (Plutella xylostella L.) and the behavior of DBM parasitoid, Cotesia vestalis (Haliday), were studied. Volatile organic compounds (VOCs) from the headspace of intact and DBM-damaged broccoli plants sprayed with yeheb extracts (YE) were also analyzed. Larval feeding and growth, and oviposition by adult DBM were strongly inhibited by the extract. Cotesia vestalis were attracted to volatile blends from intact or DBM-damaged broccoli plants sprayed with YE over intact plants sprayed with water or methanol. Analyses of VOCs in the headspace of broccoli plants revealed that both intact and DBM-damaged plants sprayed with YE showed remarkable differences in sesquiterpene compounds compared to intact control treatments. These combined negative effects of YE on DBM fitness together with positive effects on the parasitoid show that yeheb is a potential source of compounds for use in integrated pest management to control damage caused by DBM.     

Movement of transgenic plant-expressed Bt Cry1Ac proteins through high trophic levels

The movement of Bacillus thuringiensis (Berliner) (Bt) Cry1Ac endotoxin through high trophic levels was assessed to help elucidate the effects of Bt toxin on non‐target insects. The diamondback moth (Plutella xylostella L., Lepidoptera: Plutellidae), the parasitic wasp (Cotesia vestalis Haliday, Hymenoptera: Braconidae) and the predatory green lacewing Chrysoperla carnea (Stephen) (Neuroptera: Chrysopidae) were used as a model system in this laboratory study. Bt‐resistant P. xylostella larvae fed Cry1Ac‐expressing transgenic oilseed rape (OSR, Brassica napus L., Cruciferae), before and after parasitization by C. vestalis, consumed Cry1Ac with the ingested plant material but only a proportion of Cry1Ac consumed was recovered from the bodies and faeces of P. xylostella larvae. Cry1Ac was not detected in newly emerged parasitoid larvae. In contrast, Cry1Ac was detected in C. carnea larvae fed on resistant P. xylostella larvae reared on Bt OSR. However, no Cry1Ac could be detected in C. carnea larvae when the lacewings were transferred to P. xylostella larvae reared on conventional OSR and tested 24–48 h. The metabolizing ability of Cry1Ac is discussed for the larvae of P. xylostella and C. carnea.     

Offering honey containing a selective insecticide as food for pests and parasitoids: another effective use

We investigated the effects of the presence of a selective insecticide, pyridalyl, in aqueous solutions of honey as food for adults of diamondback moth (DBM) Plutella xylostella (L.) and its larval parasitoid Cotesia vestalis (Halliday) on their performances. We used a commercial formulation of pyridalyl which contained 10% pyridalyl. Survival times of DBMs reared with honey solution with pyridalyl at 10 000‐fold dilution were not significantly different from those of DBMs reared with pure honey solution. However, at 1000‐fold and 100‐fold dilutions of pyridalyl in honey solution, survival times were significantly shorter than those with honey solution alone. By contrast, survival times of C. vestalis reared with honey solution with pyridalyl at 1000‐fold and 100‐fold dilution were not significantly different from those of C. vestalis reared with pure honey solution. Offering honey solution with pyridalyl at 100‐fold dilution to C. vestalis did not affect its parasitization ability or offspring sex ratio. The novel aspects of the use of selective pesticides to control DBMs using C. vestalis are discussed.     

The effect of insecticides on the distribution of foracing parasitoids,Diaeretiella rapae [Hym.: Braconidae] on plants

Foraging aphid parasitoids,Diaeretiella rapae M'Intosh, were exposed to sublethal doses of the insecticides pirimicarb, permethrin and malathion on brusslls sprouts plants. Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and, while on these plants, tended to concentrate activity on unsprayed surfaces. For permethrin and malathion, pesticide residues reversed the stereotypic upward foraging pattern of the wasp. Negative consequences of sublethal pesticide doses for parasitoid foraging efficiency are discussed.      

6种杀虫剂对南美番茄潜叶蛾的毒力及田间防效

[目的]研究6种杀虫剂对南美番茄潜叶蛾卵、幼虫和成虫的毒力及其在温室番茄上的防治效果,为南美番茄潜叶蛾防治提供高效杀虫剂和施药技术。[方法]采用浸渍法和药膜法测定了6种杀虫剂对南美番茄潜叶蛾卵、幼虫和成虫的毒力,田间调查毒力较高杀虫剂对温室番茄上南美番茄潜叶蛾防效。[结果] 6种杀虫剂中的乙基多杀菌素、甲氨基阿维菌素苯甲酸盐和阿维菌素对南美番茄潜叶蛾卵有毒力作用,致死中浓度（LC₅₀）分别为1.415、13.588和23.194 mg·L^-1。6种杀虫剂对南美番茄潜叶蛾幼虫的LC₅₀分别为：阿维菌素0.026 mg·L^-1、四唑虫酰胺0.052 mg·L^-1、甲氨基阿维菌素苯甲酸盐0.057 mg·L^-1、乙基多杀菌素0.072 mg·L^-1、氯虫苯甲酰胺0.484 mg·L^-1和呋虫胺2.039 mg·L^-1。对于南美番茄潜叶蛾成虫,24 h时,仅甲氨基阿维菌素苯甲酸盐和四唑虫酰胺对成虫有较高毒力;72 h时,6种杀虫剂对成虫的LC₅₀分别为：甲氨基阿维菌素苯甲酸盐0.390 mg·L^-1、乙基多杀菌素1.646 mg·L^-1、四唑虫酰胺2.630 mg·L^-1、呋虫胺5.577 mg·L^-1、阿维菌素22.502 mg·L^-1和氯虫苯甲酰胺39.636 mg·L^-1。在成虫盛发期第4天施药,阿维菌素、四唑虫酰胺、甲氨基阿维菌素苯甲酸盐、乙基多杀菌素在南美番茄潜叶蛾危害严重的温室番茄上防效达80%以上。[结论]阿维菌素、四唑虫酰胺、甲氨基阿维菌素苯甲酸盐、乙基多杀菌素、氯虫苯甲酰胺和呋虫胺对南美番茄潜叶蛾卵、幼虫或成虫有较高毒力,其中阿维菌素、四唑虫酰胺、甲氨基阿维菌素苯甲酸盐和乙基多杀菌素田间防效较好。     

Tritrophic Choice Experiments with Bt Plants,the Diamondback Moth (Plutella xylostella) and the parasitoid Cotesia plutellae

Parasitoids are important natural enemies of many pest species and are used extensively in biological and integrated control programmes. Crop plants transformed to express toxin genes derived from Bacillus thuringiensis (Bt) provide high levels of resistance to certain pest species, which is likely to have consequent effects on parasitoids specialising on such pests. A better understanding of the interaction between transgenic plants, pests and parasitoids is important to limit disruption of biological control and to provide background knowledge essential for implementing measures for the conservation of parasitoid populations. It is also essential for investigations into the potential role of parasitoids in delaying the build-up of Bt-resistant pest populations. The diamondback moth (Plutella xylostella), a major pest of brassica crops, is normally highly susceptible to a range of Bt toxins. However, extensive use of microbial Bt sprays has led to the selection of resistance to Bt toxins in P. xylostella. Cotesia plutellae is an important endoparasitoid of P. xylostella larvae. Although unable to survive in Bt-susceptible P. xylostella larvae on highly resistant Bt oilseed rape plants due to premature host mortality, C. plutellae is able to complete its larval development in Bt-resistant P. xylostella larvae. Experiments of parasitoid flight and foraging behaviour presented in this paper showed that adult C. plutellae females do not distinguish between Bt and wildtype oilseed rape plants, and are more attracted to Bt plants damaged by Bt-resistant hosts than by susceptible hosts. This stronger attraction to Bt plants damaged by resistant hosts was due to more extensive feeding damage. Population scale experiments with mixtures of Bt and wildtype plants demonstrated that the parasitoid is as effective in controlling Bt-resistant P. xylostella larvae on Bt plants as on wildtype plants. In these experiments equal or higher numbers of parasitoid adults emerged per transgenic as per wildtype plant. The implications for integrated pest management and the evolution of resistance to Bt in P. xylostella are discussed.     

Organic and conventional fertilizer effects on a tritrophic interaction: parasitism,performance and preference of Cotesia vestalis

Interest in sustainable farming methods that rely on alternatives to conventional synthetic fertilizers and pesticides is increasing. Sustainable farming methods often utilize natural populations of predatory and parasitic species to control populations of herbivores, which may be potential pest species. We investigated the effects of several types of fertilizer, including those typical of sustainable and conventional farming systems, on the interaction between a herbivore and parasitoid. The effects of fertilizer type on percentage parasitism, parasitoid performance, parasitoid attack behaviour and responses to plant volatiles were examined using a model Brassica system, consisting of Brassica oleracea var capitata, Plutella xylostella (Lepidoptera) larvae and Cotesia vestalis (parasitoid). Percentage parasitism was greatest for P. xylostella larvae feeding on plants that had received either a synthetic ammonium nitrate fertilizer or were unfertilized, in comparison to those receiving a composite fertilizer containing hoof and horn. Parasitism was intermediate on plants fertilized with an organically produced animal manure. Male parasitoid tibia length showed the same pattern as percentage parasitism, an indication that offspring performance was maximized on the treatments preferred by female parasitoids for oviposition. Percentage parasitism and parasitoid size were not correlated with foliar nitrogen concentration. The parasitoids did not discriminate between hosts feeding on plants in the four fertilizer treatments in parasitoid behaviour assays, but showed a preference for unfertilized plants in olfactometer experiments. The percentage parasitism and tibia length results provide support for the preference–performance hypothesis.     

Could resistance to insecticides in Plutella xylostella (Lep., Plutellidae) be overcome by insecticide mixtures?

Abstract: To investigate if synergism occurs between pyrethroids, organophosphates and new insecticides, we tested representatives of these compounds (bifenthrin, chlorpyrifos, spinosad, indoxacarb and emamectin) against the diamondback moth (Plutella xylostella). Larvicidal activity of these insecticides was assessed separately and together on a susceptible strain (Lab‐UK) of P. xylostella as well as a field population collected from Multan. The field population showed significant resistance to chlorpyrifos (331 100‐fold), bifenthrin (45 200‐fold), emamectin (1800‐fold), spinosad (11‐fold) and indoxacarb (5600‐fold) when compared with the Lab‐UK population. When insecticides were mixed based on LC₅₀ and tested at serial concentrations against Lab‐UK, significant synergy (CI < 1) occurred between bifenthrin, spinosad and emamectin. In contrast, the interaction between bifenthrin and indoxacarb was additive (CI = 1). The toxicity of bifenthrin against the field population increased significantly (P < 0.01) when combined with spinosad, emamectin and indoxacarb. Synergistic effects could be attributed to the complementary modes of action by these insecticide classes acting on different components of nerve impulse transmission (which are not identical for bifenthrin and indoxacarb either). However, chlorpyrifos/bifenthrin mixture was not significantly different either from bifenthrin or chlorpyrifos alone, indicating an additive affect. In combination with spinosad and emamectin, tested against the resistant field population, the toxicity of chlorpyrifos increased significantly and even more so with indoxacarb. Mixtures could also give rise to multiple resistance that may extend across other chemical classes and thus become difficult to manage. Therefore, alternative strategies such as mosaics or rotations should be considered. That is, though synergistic effects have been found, this should not be followed up as a strategy to manage resistant field populations.     

西花蓟马抗噻虫胺种群对杀虫剂的交互抗性及机制

噻虫胺是具有内吸和触杀等多种作用方式的新烟碱类杀虫剂,常用于防治入侵害虫西花蓟马。为明确抗性风险,本文研究了西花蓟马抗噻虫胺种群对多种杀虫剂的交互抗性及其机制。经过45代筛选,西花蓟马对噻虫胺产生了高水平抗性(56.8倍)。生物测定结果表明: 西花蓟马高抗噻虫胺种群与噻虫嗪、吡虫啉、毒死蜱、三氟氯氰菊酯、甲维盐存在中等水平交互抗性(18.6>RR₅₀>11.3),对辛硫磷及灭多威具有低水平交互抗性,与溴虫腈和多杀菌素不存在交互抗性。胡椒基丁醚(PBO)与磷酸三苯酯(TPP)对杀灭西花蓟马抗噻虫胺种群(CL)、云南田间种群(YN)和敏感种群(S)均有显著增效作用。西花蓟马抗噻虫胺种群细胞色素P₄₅₀含量(3.6倍)、细胞色素b₅含量(2.9倍)及O-脱甲基酶活性(4.9倍)和羧酸酯酶活性(2.5倍)均显著高于敏感种群,表明多功能氧化酶及羧酸酯酶活性增强是西花蓟马对噻虫胺产生抗性的重要机制。     

Effect of Bt broccoli and resistant genotype of <Emphasis Type="Italic">Plutella xylostella</Emphasis> (Lepidoptera: Plutellidae) on development and host acceptance of the parasitoid <Emphasis Type="Italic">Diadegma insulare</Emphasis> (Hymenoptera: Ichneumonidae)

The ecological implications on biological control of insecticidal transgenic plants, which produce crystal (Cry) proteins from the soil bacterium Bacillus thuringiensis (Bt), remain a contentious issue and affect risk assessment decisions. In this study, we used a unique system of resistant insects, Bt plants and a parasitoid to critically evaluate this issue. The effects of broccoli type (normal or expressing Cry1Ac protein) and insect genotype (susceptible or Cry1Ac-resistant) of Plutella xylostella L. (Lepidoptera: Plutellidae) were examined for their effects on the development and host foraging behavior of the parasitoid, Diadegma insulare (Cresson) (Hymenoptera: Ichneumonidae) over two generations. Parasitism rate and development of D. insulare were not significantly different when different genotypes (Bt-resistant or susceptible) of insect host larvae fed on non-Bt broccoli plants. D. insulare could not discriminate between resistant and susceptible genotypes of P. xylostella, nor between Bt and normal broccoli plants with different genotypes of P. xylostella feeding on them. No D. insulare could emerge from Bt broccoli-fed susceptible and heterozygous P. xylostella larvae because these larvae were unable to survive on Bt broccoli. The parasitism rate, developmental period, pupal and adult weights of D. insulare that had developed on Bt broccoli-fed Cry1Ac-resistant P. xylostella larvae were not significantly different from those that developed on non-Bt broccoli-fed larvae. Female D. insulare emerged from Cry1Ac-resistant P. xylostella that fed on Bt plants could successfully parasitize P. xylostella larvae. The life parameters of the subsequent generation of D. insulare from P. xylostella reared on Bt broccoli were not significantly different from those from non-Bt broccoli. The Cry1Ac protein was detected in P. xylostella and in D. insulare when hosts fed on Bt broccoli. These results are the first to indicate that Cry1Ac did not harm the development or host acceptance of an important endoparasitoid after two generations of exposure. We suggest that using other Bt crops and resistant insect species would likely lead to similar conclusions about the safety of the presently used Bt proteins on parasitoids.     

Evaluating new insecticides for the control of Helicoverpa spp. (Lepidoptera: Noctuidae) on capsicum and zucchini

Abstract  The efficacy of insecticides in controlling Helicoverpa spp., predominantly H. armigera (Hübner), on capsicum and zucchini was tested in small plot trials. Indoxacarb, methoxyfenozide, spinosad, emamectin benzoate and novaluron provided control, as measured by the percentage of damaged fruit, equal to or better than standard treatments of methomyl or methomyl alternated with methamidophos on capsicum. The Helicoverpa nucleopolyhedrovirus gave control equivalent to the standard treatment, as did Bacillus thuringiensis aizawai , but B. thuringiensis kurstaki was ineffective. Helicoverpa armigera larvae were present in zucchini flowers but did little damage to the fruit. None of the insecticides significantly reduced the percentage of damaged zucchini fruit compared with the untreated control. Bifenthrin, spinosad, emamectin benzoate and methoxyfenozide were effective in controlling larvae in flowers, while methomyl, B. thuringiensis aizawai , B. thuringiensis kurstaki and novaluron were not effective. Data indicated that all the insecticides effectively controlled larvae of Diaphania indica (Saunders), cucumber moth, in the zucchini flowers. There has been a limited range of insecticides available to manage Helicoverpa spp. in these vegetable crops, but these trials demonstrate the effectiveness of a number of newer insecticides that could be used and that would be compatible with integrated pest management programs in the crops.     

An ecogenomic analysis of herbivore‐induced plant volatiles in Brassica juncea

Upon herbivore feeding, plants emit complex bouquets of induced volatiles that may repel insect herbivores as well as attract parasitoids or predators. Due to differences in the temporal dynamics of individual components, the composition of the herbivore‐induced plant volatile (HIPV) blend changes with time. Consequently, the response of insects associated with plants is not constant either. Using Brassica juncea as the model plant and generalist Spodoptera spp. larvae as the inducing herbivore, we investigated herbivore and parasitoid preference as well as the molecular mechanisms behind the temporal dynamics in HIPV emissions at 24, 48 and 72 h after damage. In choice tests, Spodoptera litura moth preferred undamaged plants, whereas its parasitoid Cotesia marginiventris favoured plants induced for 48 h. In contrast, the specialist Plutella xylostella and its parasitoid C. vestalis preferred plants induced for 72 h. These preferences matched the dynamic changes in HIPV blends over time. Gene expression analysis suggested that the induced response after Spodoptera feeding is mainly controlled by the jasmonic acid pathway in both damaged and systemic leaves. Several genes involved in sulphide and green leaf volatile synthesis were clearly up‐regulated. This study thus shows that HIPV blends vary considerably over a short period of time, and these changes are actively regulated at the gene expression level. Moreover, temporal changes in HIPVs elicit differential preferences of herbivores and their natural enemies. We argue that the temporal dynamics of HIPVs may play a key role in shaping the response of insects associated with plants.