Function of defensive volatiles in pedunculate oak (Quercus robur) is tricked by the moth Tortrix viridana

The indirect defences of plants are comprised of herbivore‐induced plant volatiles (HIPVs) that among other things attract the natural enemies of insects. However, the actual extent of the benefits of HIPV emissions in complex co‐evolved plant‐herbivore systems is only poorly understood. The observation that a few Quercus robur L. trees constantly tolerated (T‐oaks) infestation by a major pest of oaks (Tortrix viridana L.), compared with heavily defoliated trees (susceptible: S‐oaks), lead us to a combined biochemical and behavioural study. We used these evidently different phenotypes to analyse whether the resistance of T‐oaks to the herbivore was dependent on the amount and scent of HIPVs and/or differences in non‐volatile polyphenolic leaf constituents (as quercetin‐, kaempferol‐ and flavonol glycosides). In addition to non‐volatile metabolic differences, typically defensive HIPV emissions differed between S‐oaks and T‐oaks. Female moths were attracted by the blend of HIPVs from S‐oaks, showing significantly higher amounts of (E)‐4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) and (E)‐β‐ocimene and avoid T‐oaks with relative high fraction of the sesquiterpenes α‐farnesene and germacrene D. Hence, the strategy of T‐oaks exhibiting directly herbivore‐repellent HIPV emissions instead of high emissions of predator‐attracting HIPVs of the S‐oaks appears to be the better mechanism for avoiding defoliation.     

Olfactory response of Typhlodromus pyri (Acari: Phytoseiidae) to synthetic methyl salicylate in laboratory bioassays

The herbivore‐induced plant volatile (HIPV) methyl salicylate (MeSA) is widely present in the chemical profile of several plant species and is known to attract natural enemies, including predatory mites. In this study, the response of Typhlodromus pyri, a key predator of pest mites in west coast vineyards, to synthetically produced MeSA was tested using a Y‐tube olfactometer in laboratory bioassays. Six doses ranging from 0.002 to 200 μg of MeSA diluted in 0.1 ml hexane were tested. Significantly higher proportions of T. pyri preferred MeSA at doses 0.02, 0.2 and 20 μg. No differences in response to MeSA were detected at the highest (200 μg), intermediate (2 μg) and lowest (0.002 μg) doses. Mite response to MeSA was a function of dose when fitting polynomial and logistic regression models using dose and square of the log dose prediction factors. Results indicate that synthetic MeSA may be applied to attract predatory arthropod populations in vineyards to enhance biological control of pest mites.     

High‐throughput olfactory conditioning and memory retention test show variation in Nasonia parasitic wasps

Most of our knowledge on learning and memory formation results from extensive studies on a small number of animal species. Although features and cellular pathways of learning and memory are highly similar in this diverse group of species, there are also subtle differences. Closely related species of parasitic wasps display substantial variation in memory dynamics and can be instrumental to understanding both the adaptive benefit of and mechanisms underlying this variation. Parasitic wasps of the genus Nasonia offer excellent opportunities for multidisciplinary research on this topic. Genetic and genomic resources available for Nasonia are unrivaled among parasitic wasps, providing tools for genetic dissection of mechanisms that cause differences in learning. This study presents a robust, high‐throughput method for olfactory conditioning of Nasonia using a host encounter as reward. A T‐maze olfactometer facilitates high‐throughput memory retention testing and employs standardized odors of equal detectability, as quantified by electroantennogram recordings. Using this setup, differences in memory retention between Nasonia species were shown. In both Nasonia vitripennis and Nasonia longicornis, memory was observed up to at least 5 days after a single conditioning trial, whereas Nasonia giraulti lost its memory after 2 days. This difference in learning may be an adaptation to species‐specific differences in ecological factors, for example, host preference. The high‐throughput methods for conditioning and memory retention testing are essential tools to study both ultimate and proximate factors that cause variation in learning and memory formation in Nasonia and other parasitic wasp species.     

Responses of Tribolium castaneum to olfactory cues from cotton seeds,the fungi associated with cotton seeds,and cereals

We tested, in an olfactometer, whether or not Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) responds preferentially to the volatiles that emanate from the fungi associated with cotton [Gossypium hirsutum L. (Malvaceae)] seed over those that emanate from cereals, because cereals are usually portrayed as the primary resources of these beetles. Pairwise comparisons were conducted between cotton seed, wheat (Triticum aestivum L.), and sorghum [Sorghum bicolor (L.) Moench] (both Poaceae); volatiles were tested from intact seeds and from both water and ethanol extracts. The results demonstrate that T. castaneum is attracted more strongly to cotton seeds with its lint contaminated with fungi, than to the conventional resources of this species (i.e., wheat and sorghum). Further tests prove that it is the fungus on the lint that produces the active volatiles, because the beetles did not respond to sterilized cotton lint (i.e., without the fungi typically associated with it when cotton seed is stored). Tests with five fungal cultures (each representing an unidentified species that was isolated from the field‐collected cotton lint) were variable across the cultures, with only one of them being significantly attractive to the beetles. The others were not attractive and one may even have repulsed the beetles. The results are consistent with the beetles having a strong ecological association with fungi and suggest it would be worth investigating the ecology of T. castaneum from this perspective.     

Phloem‐specific resistance in Brassica oleracea against the whitefly Aleyrodes proletella

The cabbage whitefly [Aleyrodes proletella L. (Hemiptera: Aleyrodidae)] is becoming a serious pest in Brassica oleracea L. (Brassicaceae) crops. However, almost nothing is known about the interaction of this insect with its host plants. Previous studies have shown differences in the natural occurrence of adults, eggs, and nymphs on the closely related B. oleracea cultivars Christmas Drumhead and Riviera grown in the field. In this study, we aimed to identify the nature of these differences and to gain insight into the resistance mechanisms against A. proletella. We used no‐choice experiments on field‐ and greenhouse‐grown plants to show that the differences between the two cultivars are mainly based on antibiosis (traits that reduce herbivore performance) and not on antixenosis (traits that deter herbivory). This was further supported by laboratory choice experiments that indicated little or no discrimination between the two cultivars based on plant volatiles. We showed that resistance is dependent on plant age, that is, resistance increased during plant development, and is mainly independent of environmental factors. Analysis of probing behaviour revealed that the resistance trait affects A. proletella at the phloem level and that morphological differences between the two cultivars are most likely not involved. We suggest that compounds present in the phloem reduce sap ingestion by the whitefly and that this explains the observed resistance.     

A six-arm olfactometer permitting simultaneous observation of insect attraction and odour trapping

Abstract.  Behavioural assays to study insect attraction to specific odours are tedious, time consuming and often require large numbers of replications. Olfactometer and flight tunnel tests can usually only be conducted with one or two odour sources at a time. Moreover, chemical information on the odour sources has to be obtained in separate analytical studies. An olfactometer was developed in which six odours can be tested simultaneously for their relative attractiveness while during the assays, part of each test odour can be trapped for further analyses. The effectiveness of this six-arm olfactometer was tested by observing the responses of the solitary endoparasitoid Cotesia marginiventris (Cresson) to host-induced odours from young maize plants. For statistical analyses, we used log-linear models were adapted to account for overdispersion and possible positional biases. Female wasps responded extremely well in tests where they were offered a single odour source, as well as in tests with multiple choices. The responses of wasps released in groups were the same as those released individually and it was found that females did not attract or repel each other, but males preferred arms in which females had been released. Dose–response tests with varying numbers of plants or host larvae on plants revealed that the wasps responded in a dose-related manner, thus showing that the system is well suited to measure relative preference. The clear choices of the insects amongst six possibilities provided substantial statistical power. Gas chromatographic analyses of sampled air revealed clean and effective odour trapping, which largely facilitates the comparison of results from behavioural assays with the actual blends of volatiles that were emitted by the various odour sources. Advantages and disadvantages compared to other methods are discussed.     

Behavioural responses of wheat stem sawflies to wheat volatiles

1 Adult wheat stem sawflies Cephus cinctus, pests of cultivated cereals that also infests wild grasses, migrate into wheat fields where they oviposit in elongating, succulent stems.
2 Volatiles released by wheat plants at susceptible stages were analyzed to determine potential semiochemical compounds. Seven major compounds were identified and quantified.
3 A Y-tube bioassay was developed to evaluate upwind orientation of adult sawflies in response to an airstream that passed over elongated wheat plants. The bioassay was also conducted with synthetic volatile compounds. The compounds were tested using a range of concentrations spanning those identified in the airstream passing over wheat plants.
4 A significant number of adult females were attracted to wheat plants when given a choice of either purified air or the air passing over plants.
5 A significant number of female C. cinctus were attracted to ( Z )-3-hexenyl acetate, β-ocimene, and ( Z )-3-hexen-1-ol, but were repelled by 6-methyl-5-hepten-2-one. Females did not respond to ( E )-2-hexenal, or ( E )-2-hexenyl acetate. The behavioural responses were concentration dependent; the highest tested concentration of ( Z )-3-hexenyl acetate was repellent to females of this species.
6 Adult males did not discriminate between air passing over wheat plants and air from a purified airstream. Males did not respond to any tested synthetic compound at any concentration.
7 The present study demonstrates for the first time that adult females of wheat stem sawfly display innate behaviours in response to synthetic volatiles. These results provide a basis for the potential development of resistant wheat varieties and for the development of semiochemically-based pest management.     

长足大竹象成虫体表信息化学物质的提取和鉴定

为了确定我国南方竹林主要害虫长足大竹象Cyrtotrachelus buqueti Guerin-Meneville雌虫是否存在诱引雄虫的化学信息素以及所释放的相关化学信息素的成分, 本研究利用风洞和“Y”型嗅觉仪测试到长足大竹象雄虫对雌虫及雌虫体表提取化合物具有正趋向行为反应, 随后用GC-EAD和GC-MS对雌虫体表提取化合物进行了分析。在GC-EAD分析时发现雄虫触角对雌虫体表粗提液和体表物质标准品化合物的触角电位反应时有5个GC峰有电生理活性; 通过质谱法确定这5个电生理活性GC峰的化学成分分别为苯酚、己酸乙酯、2-壬酮、壬醛和十五酸甲酯。风洞和GC-EAD分析表明, 这5种成分的标准品化合物对长足大竹象雄虫具有诱引生物活性和触角电生理活性。结果说明长足大竹象雌虫体表粗提液中存在的苯酚、己酸乙酯、2-壬酮、壬醛和十五酸甲酯是长足大竹象成虫的化学信息素物质。     

青杨脊虎天牛对植物源挥发物的EAG和行为反应

测定了青杨脊虎天牛Xylotrechus rusticus （L.）雌、雄成虫对其寄主杨树中的水杨醛（0.95 μmol/μL）和非寄主植物中0.3 μmol/μL的叶绿醇、0.4 μmol/μL的水芹烯和0.6 μmol/μL的 R 型α-蒎烯、S 型α-蒎烯、S型β-蒎烯、3-蒈烯、罗勒烯、香草烯和松节油等10种植物挥发性气味物质的触角电位（EAG）反应。结果表明,与对照相比,这10种植物挥发物多能引起成虫明显的EAG反应( P<0.05,P<0.01 ),其中雌虫对松节油、水杨醛、R 型α-蒎烯和 S 型α-蒎烯的EAG反应较强; 雄虫对 R 型α-蒎烯的EAG反应最强,松节油次之。根据雌虫对这10种挥发物EAG反应的强弱,进一步测定了雌虫对0.00006、0.0006、0.006、0.06、0.6、0.12 μmol/μL的松节油、R 型α-蒎烯、S 型α-蒎烯以及0.000095、0.00095、0.0095、0.095、0.95、0.19 μmol/μL的水杨醛的EAG和行为反应。结果表明,雌虫对松节油、水杨醛和 R 型α-蒎烯的EAG反应随气味物质浓度的增加而增加,水杨醛浓度增加到0.95 μmol/μL、松节油和 R 型α-蒎烯浓度增加到0.6 μmol/μL以后,EAG反应值趋于平稳;对 S 型α-蒎烯的反应随浓度的增加而呈线性增加。水杨醛浓度低于0.095时,对雌虫没有明显的定向作用( P>0.05 ),高于此浓度时表现为驱避作用( P<0.05 ); 松节油在浓度低于或等于0.6 μmol/μL时对雌虫表现为驱避作用,浓度为0.6时驱避效果最佳（ P<0.01 ）。雌虫对 R 型α-蒎烯和 S 型α-蒎烯没有明显的定向行为反应。     

EAG and behavioural responses of the larger grain borer, Prostephanus truncatus, and its predator, Teretriosoma nigrescens, to the borer‐produced aggregation pheromone

Abstract.Electroantennogram (EAG) and behavioural studies were conducted with Prostephanus truncatus (Horn) (Col.: Bostrichidae) and the predatory beetle, Teretriosoma nigrescens Lewis (Col: Histeridae) in regard to their responses to the components of the prey‐produced aggregation pheromone. There were hardly any differences between species or sexes regarding perception thresholds. In field and olfactometer experiments, female P. truncatus were more responsive to the pheromone than males, and both sexes reacted more strongly to the minor pheromone component, T2, than to T1. Sex ratios among trap catches of T. nigrescens were slightly male‐biased. The predator did not differentiate behaviourally between the pheromone components.