Trap cropping effect on oviposition behaviour of the leek moth Acrolepiopsis assectella and the diamondback moth Plutella xylostella

The potential of trap cropping as a pest control strategy was explored for two specialist moth species, where oviposition behaviour determines larval distribution. Oviposition behaviour was studied at three different scales: Individual plants in the laboratory, small scale field experiments with and without cages, and medium scale field trials. The study insects were the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a specialist on Brassica species and the leek moth, Acrolepiopsis assectella (Z.) (Lepidoptera: Acrolepiidae), a specialist on Allium species. The diamondback moth preferred Indian mustard, Brassica juncea (L.) over white cabbage, B. oleracea var alba (L.). The leek moth did not show preference when offered leek, Allium porrum (L.) and chives, A. schoenoprasum (L.). However, the leek moth did prefer to oviposit on plants of a larger biomass over smaller plants. In both the small scale and the medium scale field studies the trap crops reduced the number of eggs laid on the primary crop. The total number of eggs laid in the monoculture and the trap crop treatments were the same in the small scale field cage study, but the females distributed their eggs differently. More eggs were laid on trap crops compared with primary crops and this pattern was also validated in the medium scale field trials. In this study only the direct effects of trap cropping were considered. Indirect effects of vegetation diversity such as enhancement of natural enemies could potentially increase the efficacy of trap cropping.     

Chemoreception of oviposition inhibiting terpenoids in the diamondback moth Plutella xylostella

The effects of six terpenoids and two terpenoid containing extracts of the neem tree (Azadirachta indica A. Juss.) on oviposition by the diamondback moth (Plutella xylostella L., Yponomeutidae: Lepidoptera) were tested. Two drimane terpenoids, the sesquiterpenoid polygodial and the neem extract Margosan-O exerted significant inhibitory effects at the dosages tested. Ablation experiments showed that both antennae and fore-tarsi contributed to mediation of the inhibition by a drimane. Location of chemosensilla on prothoracic tarsi and ovipositor was examined by scanning electronmicroscopy. Electrophysiological recordings from ovipositor and tarsal taste sensilla showed that distilled water produced distinct responses from one neuron. In tarsal sensilla, ethanol and drimane solutions produced responses from two neurons, one of which might be the water cell that fired at a reduced rate. A drimane significantly decreased the responses of tarsal chemoreceptors to a cabbage leaf extract, which is a possible sensory mechanism leading to behavioural avoidance of this compound.     

小菜蛾幼虫偏好表达的microRNA鉴定及功能研究

[目的]microRNA(miRNA)在昆虫生长发育中发挥重要功能,本研究拟通过鉴定小菜蛾不同发育阶段的miRNA,挖掘幼虫偏好表达的miRNA及其潜在功能.[方法]对小菜蛾卵、3龄幼虫、蛹和成虫的miRNA开展高通量测序,结合生物信息学分析方法,筛选在幼虫期偏好表达的miRNA;借助实时荧光定量PCR技术,验证候选m...     

Superparasitism and host size effects in Oomyzus sokolowskii, a parasitoid of diamondback moth

Many aspects of a parasitoid's biology may be affected by its host. Host size, for example, could affect parasitoid fitness, especially in gregarious parasitoids, in which the resource is used by multiple siblings. Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae) is a gregarious larval–pupal endoparasitoid of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), a major pest of crucifers worldwide, and is able to superparasitize the host. This study focuses on the hypothesis that because resource availability is higher in larger hosts, parasitoids developing in larger hosts will fare better. However, superparasitized hosts are expected to yield larger numbers of parasitoid offspring of smaller body size. Results showed that superparasitism increased the number of parasitoid offspring produced per host and increased offspring longevity, but decreased offspring body size. However, developmental time and sex ratio of parasitoid offspring was similar among hosts parasitized once, twice, or three times. Regardless of superparasitism, parasitoids emerging from larger hosts that were fed honey solution lived longer than similarly fed progeny from smaller hosts (36.4 vs. 22.1 days). The results partially support the hypothesis that Oomyzus gained fitness from an increase in host size; moreover, superparasitism seems advantageous for Oomyzus due to increased offspring numbers and longevity.     

抗生素和肠道细菌对小菜蛾适合度的影响

【目的】小菜蛾是危害十字花科蔬菜的世界性重要害虫。通过分析抗生素对小菜蛾的毒性效应,了解肠道细菌对小菜蛾适合度的影响,有助于更好地阐明小菜蛾肠道细菌的功能。【方法】利用抗生素处理含有高丰度肠道细菌的萝卜苗饲养品系(FZss)小菜蛾幼虫,同时利用抗生素处理饲料饲养的无肠道细菌(SLss)小菜蛾幼虫,分析抗生素及肠道细菌对小菜蛾适合度的影响。【结果】抗生素处理FZss品系小菜蛾导致了小菜蛾发育历期延长,虫重、蛹重、化蛹率、产卵量和成虫寿命降低。利用抗生素处理无肠道菌的SLss品系小菜蛾幼虫,小菜蛾化蛹率和单雌产卵量均显著降低,而对发育历期、虫重和蛹重则无影响。【结论】综合两个研究的结果发现抗生素处理后宿主适合度的降低一方面是由于抗生素的毒性效应导致,另一方面是由于小菜蛾肠道细菌的缺失引起。抗生素的毒性效应主要表现为对化蛹率和单雌产卵量的影响,而肠道细菌则对小菜蛾的发育历期、虫重、蛹重以及成虫寿命具有重要的促进作用。     

Trap cropping effect on oviposition behaviour of the leek moth Acrolepiopsis assectella and the diamondback moth Plutella xylostella

The potential of trap cropping as a pest control strategy was explored for two specialist moth species, where oviposition behaviour determines larval distribution. Oviposition behaviour was studied at three different scales: Individual plants in the laboratory, small scale field experiments with and without cages, and medium scale field trials. The study insects were the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), a specialist on Brassica species and the leek moth, Acrolepiopsis assectella (Z.) (Lepidoptera: Acrolepiidae), a specialist on Allium species. The diamondback moth preferred Indian mustard, Brassica juncea (L.) over white cabbage, B. oleracea var alba (L.). The leek moth did not show preference when offered leek, Allium porrum (L.) and chives, A. schoenoprasum (L.). However, the leek moth did prefer to oviposit on plants of a larger biomass over smaller plants. In both the small scale and the medium scale field studies the trap crops reduced the number of eggs laid on the primary crop. The total number of eggs laid in the monoculture and the trap crop treatments were the same in the small scale field cage study, but the females distributed their eggs differently. More eggs were laid on trap crops compared with primary crops and this pattern was also validated in the medium scale field trials. In this study only the direct effects of trap cropping were considered. Indirect effects of vegetation diversity such as enhancement of natural enemies could potentially increase the efficacy of trap cropping.     

Dynamics of diamondback moth oviposition in the presence of a highly preferred non-suitable host

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), highly prefers to oviposit on yellow rocket, Barbarea vulgaris (R. Br.) (Cruciferae) var. arcuata, despite larvae not being able to survive on it, suggesting it may have potential as a trap crop. In a no‐choice greenhouse experiment, P. xylostella laid 28% more eggs on B. vulgaris than on cabbage. Within the B. vulgaris plant, P. xylostella laid 3.7 times more eggs on younger than older leaves. Furthermore, we demonstrated that in the presence of B. vulgaris volatiles, P. xylostella laid 23% more eggs on cabbage plants than when B. vulgaris volatiles were absent. Because increased oogenesis in the presence of B. vulgaris could complicate the use of this host as a trap crop for P. xylostella, we wanted to examine levels of oogenesis in varying mixtures of cabbage and B. vulgaris. In outdoor screenhouse experiments, P. xylostella laid a decreasing percentage of eggs on cabbage as the percentage of B. vulgaris increased. However, the total number of eggs laid on cabbage did not differ among treatments, suggesting that the presence of B. vulgaris may have stimulated P. xylostella oviposition. In the field, total oviposition in cabbage plots containing B. vulgaris was 6.3 times higher than in cabbage plots without B. vulgaris. However, in plots with B. vulgaris, P. xylostella laid 99% of the eggs on B. vulgaris and oviposition on cabbage plants was 6.2 times lower than in the plots without B. vulgaris. The results of this study are discussed according to P. xylostella egg‐laying behavior and life history as it relates to its interaction with B. vulgaris.     

Importance of host oviposition pattern and plant size for the selection of Trichogramma strains to control the diamondback moth

The aim of this work was to select a candidate strain of Trichogrammatidae (Hymenoptera: Chalcidoidea) to control the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae), an important pest of cabbage in Europe. The parasitic efficiency of Trichogramma chilonis Ishii from Japan and Réunion Island, Trichogramma evanescens Westwood from Egypt, Trichogramma ostriniae Pang & Chen from Japan, and Trichogramma semblidis (Aurivillius) from France was studied with sentinel eggs in greenhouse‐grown cauliflower. The percentage of parasitized eggs was measured 1 m from the release point and 3 days after release. Two factors were studied: host‐egg density (three eggs per stem vs. 50 eggs per stem) and plant size (50–100 cm high plants vs. 100–150 cm high plants). Trichogramma evanescens from Egypt achieved the best parasitism. Parasitism efficiency of T. ostriniae from Japan and T. chilonis from Réunion Island was not influenced by egg density. In contrast, parasitism efficiencies of the three other strains were higher at the lower egg density than at the higher egg density. Parasitism efficiency was lower when the plants were bigger, with the exception of T. chilonis from Réunion Island, for which the level of parasitism was not affected by plant size. Thus, T. chilonis from Réunion Island appeared to be the most suitable Trichogramma strain for use in controlling P. xylostella, regardless of the growth stage of the crop. However, T. ostriniae from Japan may also be more suitable for use on cauliflower crops at the early stage of crop development. If potential problems related to the introduction of exotic species are taken into consideration, it is possible to consider the native T. evanescens.     

Greenhouse and field evaluations of transgenic canola against diamondback moth, shape Plutella xylostella, and corn earworm, shape Helicoverpa zea

Canola (Brassica napus L.) cultivars Oscar and Westar, engineered with a Bacillus thuringiensis (Bt) cryIA(c) gene, were evaluated for resistance to lepidopterous pests, diamondback moth, Plutella xylostella L. (Plutellidae) and corn earworm, Helicoverpa zea (Boddie) (Noctuidae) in greenhouse and field conditions. In greenhouse preference assays conducted at vegetative and flowering plant stages, transgenic plants recorded very low levels of damage. A 100% diamondback moth mortality and 90% corn earworm mortality were obtained on transgenic plants in greenhouse antibiosis assays. The surviving corn earworm larvae on transgenic plants had reduced head capsule width and body weight. Mortality of diamondback moth and corn earworm were 100% and 95%, respectively, at different growth stages (seedling, vegetative, bolting, and flowering) on the transgenic plants in greenhouse tests. In field tests conducted during 1995–1997, plots were artificially infested with neonates of diamondback moth or corn earworm or left for natural infestation. Transgenic plants in all the treatments were highly resistant to diamondback moth and corn earworm larvae and had very low levels of defoliation. Plots infested with diamondback moth larvae had greater damage in both seasons as compared with corn earworm infested plots and plots under natural infestation. After exposure to defoliators, transgenic plants usually had higher final plant stand and produced more pods and seeds than non-transgenic plants. Diamondback moth injury caused the most pronounced difference in plant stand and pod and seed number between transgenic and non-transgenic plants. Our results suggest that transgenic canola could be used for effective management of diamondback moth and corn earworm on canola.     

The roles of olfaction and vision in host-plant finding by the diamondback moth, Plutella xylostella

Abstract.  The relative roles of olfaction and vision in the crepuscular host-finding process of a major lepidopteran pest of cruciferous crops, the diamondback moth Plutella xylostella are investigated in a series of laboratory and semi‐field experiments. Flying female moths use volatile plant chemical cues to locate and to promote landing on their host, even in complex mixed-crop environments in large cages. Multiple regression analysis shows that both the plant position (front, middle or back rows) and the type of plant (host plant, nonhost plant) are needed to explain the distribution of insects in such a mixed-crop situation. This strong plant position effect indicates that, when host plants are present in a mixture, foraging P. xylostella are more likely to alight on the first row of the plants. The findings are discussed with regard to current theories of host-plant location by phytophagous insects and the possible implications for integrated pest management.     

Influence of plant sulphur nutrition on oviposition and larval performance of the diamondback moth

We measured adult oviposition preference, larval growth, and feeding behaviour of the crucifer specialist Plutella xylostella (L.) (Lepidoptera: Plutellidae) on plants of Brassica napus (L.) cv. Express (Brassicaceae), grown under three different sulphur regimes. The nutrient solutions used were the following: one sulphur‐free (S₀), one normal sulphur (S_n, normal field concentration), and one sulphur‐rich (S₊, double concentration of S_n). Females laid more eggs on S_n than on S₀ plants, while only a slight, non‐significant difference was observed between S_n and S₊ plants. Moreover, the development time from hatching to emergence was significantly shorter, and adults were heavier on S_n than on S₀ plants. Comparing these same two parameters from S_n and S₊ plants, we found a shorter development time on plants rich in sulphur, although this trend was not statistically significant. Larval feeding preferences were tested in a dual choice assay using leaf discs. A significantly higher number of larvae preferred leaf discs of S_n plants than those of S₀ plants. Furthermore, the larvae preferred S₊ to S_n discs. An optimal supply of sulphur to oilseed rape is necessary for a good seed harvest, and it also plays an important role in acceptance by P. xylostella of the host plant. Maintaining higher levels of sulphur in the plant nutrient solution benefits insect performance, both at the adult and larval stage.     

Ovipositional preference ofSiphoninus phillyreae and its fitness on seven host plant species

The relationship between ovipositional preference ofSiphoninus phillyreae (Haliday) (Homoptera: Aleyrodidae) and host plant suitability on seven host plant species (Citrus sinensis (L.) cv. ‘Washington’ [navel orange],Fraxinus uhdei (Wenz.) [shamel ash],Heteromeles arbutifolia Roemer [toyon],Malus domestica Mill. cv. ‘Granny Smith’, [apple],Pistacia vera L. cv. ‘Kerman’ [pistachio],Prunus persica (L.) cv. ‘O’Henry’ [peach], andPyrus communis L. cv. ‘Bartlett’ [pear]) was evaluated. Ovipositional preference ofS. phillyreae was determined by measuring egg density after adult female whitefies were given a simultaneous choice of all host plants for oviposition. Immature survival, developmental time, and adult size were examined to determine host plant suitability forS. phillyreae. All studies were performed under greenhouse conditions.S. phillyreae showed distinct ovipositional preference among host plant species. Host plant species had a significant effect on immature survival, but little or no effect on developmental time or forewing length. For four of the seven host plant species tested, there was an association between ovipositional preference and survival.     

Impact of a glossy collard trap crop on diamondback moth adult movement, oviposition, and larval survival

One component of developing a systematic approach for deployment of trap crops is to understand how the trap crop modifies pest behavior. Glossy‐leafed collards, Brassica oleracea L. var. acephala (Brassicaceae), were evaluated as a potential trap crop for diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), because they are attractive to P. xylostella adults and are a poor host for P. xylostella larvae compared to cabbage, Brassica oleracea L. var. capitata. We used large field plots to measure the changes in adult, egg, and larval P. xylostella densities in cabbage when the trap crop was planted in the field. Furthermore, we planted the trap crop in dispersed and concentrated spatial arrangements to determine the impact of trap crop arrangement on the behavior of P. xylostella. In 2002, results showed that the presence of collards within a cabbage field reduced larval density on cabbage. In 2003, neither trap crop arrangement had a significant impact on P. xylostella larval density on cabbage. Adult moths aggregated in proximity to collards in 2002, but not in 2003. Egg and larval data in both years in all treatments showed that total oviposition was highest near a central release point, indicating that females lay many eggs before dispersing very far when suitable host plants are available. The mean direction of P. xylostella movement and oviposition from a central release point was not consistent or correlated to wind direction. Plant size of the trap crop in relation to the main crop and environmental factors may have been responsible for the inconsistent effectiveness of the trap crop.     

Diamondback moth egg susceptibility to rainfall: effects of host plant and oviposition behavior

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field.     

低温对小菜蛾实验种群的影响

研究了低温(<8℃)对小菜蛾的发育、存活和繁殖的影响.结果表明,卵和蛹在4℃和6℃下死亡率随处理时间的延长而增加,在分别处理55d和70d后,卵和蛹全部死亡;经4℃和6℃处理的蛹,在16℃下羽化成虫的平均产卵量随处理时间的延长而减少,处理45d时,产卵量均为0.小菜蛾幼期各虫态在0℃以下,死亡率随低温强度加大和处理时间的延长而增高.就耐寒力而言,3龄幼虫和蛹最强,其次是2龄和4龄幼虫,卵和1龄幼虫的耐寒力最弱.不同低温和时间处理小菜蛾幼期虫态对其后继虫态的发育历期有较大影响,总体说来,经过处理的小菜蛾幼期虫态,其后继虫态的发育历期普遍延长,一般处理某一虫态对其相邻虫态发育历期的影响最大.小菜蛾蛹经低温处理后其羽化成虫的产卵量随着蛹期所经历低温强度的增强和时间延长而减少.     

Plant volatiles mediate attraction to host and non-host plant in apple fruit moth, Argyresthia conjugella

Plant volatiles mediate host finding in insect herbivores and lead to host fidelity and habitat‐specific mating, generating premating reproductive isolation and facilitating sympatric divergence. The apple fruit moth, Argyresthia conjugella Zeller (Lepidoptera: Argyresthiidae), is a particularly suitable species to study the cues and behavioural mechanisms leading to colonization of a new host: it recurrently oviposits on the non‐host plant, apple Malus domestica Borkh. (Rosaceae), where the larvae cannot complete their development. The larval host of the apple fruit moth (Lepidoptera, Argyresthiidae), is rowan Sorbus aucuparia L. (Rosaceae). Fruit setting in rowan, however, fluctuates strongly over large areas in Scandinavia. Every 2–4 years, when too few rowanberries are available for egg laying in forests, apple fruit moth females oviposit instead on apple in nearby orchards, but not on other fruits, such as pear or plum. This poses the question of which cues mediate attraction to rowan and apple, and how apple fruit moth discriminates rowan from apple. Chemical analysis and antennal recordings showed that 11 out of 15 rowan volatiles eliciting an antennal response in A. conjugella females co‐occur in rowan and apple headspace, in a different proportion. In the field, A. conjugella was attracted to several of these plant volatiles, especially to 2‐phenyl ethanol, methyl salicylate, and decanal. Addition of anethole to 2‐phenyl ethanol had a strong synergistic effect, the 1 : 1 blend is a powerful attractant for A. conjugella males and females. These results confirm that volatiles common to both plants may account for a host switch in A. conjugella from rowan to apple. Some of the most attractive compounds, including 2‐phenyl ethanol, anethole, and decanal, which have been found in several apple cultivars, were not present in the headspace of the apple cultivar, Aroma, which is also susceptible to attack by A. conjugella. This supports the idea that the odour signal from apple is suboptimal for attraction of A. conjugella, but is nonetheless sufficient for attraction, during times when rowan is not available for egg laying.     

Moving on hairy surfaces: modifications of Gratiana spadicea larval legs to attach on its host plant Solanum sisymbriifolium

Both larvae and adults of Gratiana spadicea (Klug) (Coleoptera: Chrysomelidae: Cassidinae) feed exclusively on leaves of Solanum sisymbriifolium Lamarck (Solanaceae), which have simple and stellate trichomes. The simple trichomes can be non-glandular or glandular. The stellate trichomes present a long central ray that secretes a viscous exudate when broken. Trichome effects on movement of G. spadicea larvae were evaluated in the laboratory. Larval speed on intact petioles of S. sisymbriifolium was compared to those where the exudates and/or stellate trichomes were removed. Exudates had no effect on larval speed. Stellate trichomes mechanically slowed down first instar movement. Gratiana spadicea larval legs have a modified distal portion, the tarsungulus, whose rounded aperture shape matches that of the cylindrical pointed rays of S. sisymbriifolium stellate trichomes. The first three instars anchor the tarsungulus to the trichome rays, and get both attachment to the leaf surface and support to body impulsion. Morphological comparisons showed that the legs in the first larval instars are shorter than the central ray of the stellate trichome, so larvae have to walk above them. Fifth instar larvae have longer legs and walk by inserting the sharp tip of their tarsungulus directly into the leaf epidermis. The dimensions of the tarsungulus aperture vary in such a way that it can clasp every thickness of trichome ray for any larval instar. Contrary to other tarsungulus portions and larval body features, where growth is allometric, growth of the tarsungulus aperture is isometric throughout the larval stage. Thus, it is suggested that this G. spadicea leg structure is adapted for moving on hairy leaf surface of S. sisymbriifolium.     

Regulation of reproductive behaviour and egg maturation in the tobacco hawk moth, Manduca sexta

ABSTRACT. The virgin female tobacco hawk moth, Manduca sexta, flies during the early scotophase in an LD 16:8 cycle at 24C then begins 'calling' within 2h. Mating lasts 3–4 h. Oviposition occurs in the succeeding scotophases if a tobacco plant is present. The switch from virgin 'calling' behaviour to mated ovipositional behaviour is mediated by the presence of sperm and/or associated testicular fluids in the bursa copulatrix. The corpora allata, which are necessary for egg maturation in this species, are activated via the NCC I and II around the time of eclosion. Feeding increases the activity of the corpora allata in the virgin female (as judged by the number of eggs matured in 4 days) but mating brings about a further stimulation of the activity of the corpora allata. The stretching of the bursa copulatrix by the insertion of the spermatophore during mating is probably the trigger for this response. Continued neural input from the bursa copulatrix to the brain is necessary to maintain the increased activity of the corpora allata.