Electrophysiological and behavioral identification of a volatile blend involved in host location of female strawberry sap beetle,Stelidota geminata

The strawberry sap beetle (SSB), Stelidota geminata (Say) (Coleoptera: Nitidulidae), is a serious direct pest of strawberries in the northeastern USA. To date, however, no food or pheromone‐based attractants for SSB have been identified. A combination of solid‐phase microextraction, adsorbent sampling, gas chromatography coupled with electroantennographic detection (GC–EAD), and gas chromatography–mass spectrometry was used to identify volatile compounds from strawberry fruit acting as behavioral attractants for female SSB. Consistent EAD activity was obtained for 16 ester compounds. In Y‐tube olfactometer bioassays, the blend of these 16 compounds mixed at a ratio observed from strawberry headspace was significantly more attractive to adult female SSB than a control. Female SSB showed no difference in response levels between the 16‐component blend and a strawberry volatile adsorbent extract. Our data indicate that the combination of the ethyl acetate with some or all of the remaining 15 compounds is necessary for this ester blend to be attractive to female SSB. Previously identified host volatiles found for other species of sap beetles included mostly alcohols associated with over‐ripe fruit rather than the esters identified from ripe strawberries for SSB. A highly attractive synthetic food odor will be useful for developing new management options for SSB.     

Non‐host plant essential oil volatiles with potential for a ‘push‐pull’ strategy to control the tea green leafhopper,Empoasca vitis

The tea green leafhopper, Empoasca vitis Göthe (Hemiptera: Cicadellidae), is an economically important pest of tea crops, Camellia sinensis (L.) O. Kuntze (Theaceae), in China. The use of non‐host plant essential oils for manipulation of E. vitis was investigated for potential incorporation into a ‘push‐pull’ control strategy for this pest. The effectiveness of 14 plant essential oils in repelling E. vitis was investigated in laboratory assays. Rosemary oil, geranium oil, lavender oil, cinnamon oil, and basil oil repelled leafhoppers in a Y‐shaped olfactometer. We also compared the efficacy of these five plant essential oils to repel E. vitis in the presence of a host plant volatile‐based leafhopper attractant, (Z)‐3‐hexenyl acetate, in a tea plantation. In the treatment combination, four plates (north, south, east, and west) treated with an essential oil surrounded a central sticky plate treated with (Z)‐3‐hexenyl acetate. Fewer E. vitis were found on the plates treated with rosemary oil (12.5% reduction) than on the four water‐sprayed control treatment plates surrounding a central plate with (Z)‐3‐hexenyl acetate. We compared the distribution of E. vitis on the plates, and the relative numbers of E. vitis on each plate were compared with similar plates in the control treatment. When four plates treated with rosemary oil surrounded a central (Z)‐3‐hexenyl acetate‐treated plate, the distribution of E. vitis on the different plates changed significantly compared with that of the control. Relatively fewer E. vitis were found on the east (13.0% reduction) rosemary oil‐treated plates and more E. vitis (11.3% increase) were found on the central attractant‐treated plate. Our findings indicate that rosemary oil is a promising leafhopper repellent that should be tested further in a ‘push‐pull’ strategy for control of E. vitis.     

Behavioural and chemical ecology underlying the success of turnip rape (Brassica rapa) trap crops in protecting oilseed rape (Brassica napus) from the pollen beetle (Meligethes aeneus)

There is increasing interest in the use of trap crops as components of integrated pest management (IPM) strategies. Understanding the mechanisms underlying host plant preferences of herbivorous pests can lead to improved effectiveness and reliability of the trap crop. We investigated the behavioural and chemical ecology underlying the success of turnip rape, Brassica rapa, trap crops in protecting oilseed rape, Brassica napus, from the pollen beetle, Meligethes aeneus, which feeds in the flowers and lays its eggs in the buds causing yield loss. Using a semi-field arena bioassay, plant growth stage was found to be a major factor in the preference of this pest for B. rapa over B. napus. Plants at early-flowering growth stages were preferred over plants in the bud stage, irrespective of species. No preference was found when both species were flowering. As B. rapa develops faster than B. napus in the field, this could explain part of the mechanism of its success as a trap crop. However, B. rapa was preferred over B. napus when both species were in the bud stage, indicating some inherent preferences for B. rapa. Responses of M. aeneus in olfactometer tests to the odours of B. napus and B. rapa at the bud and flowering growth stages, reflected those of the semi-field arena bioassay. These behavioural responses can be explained by volatile compounds associated with the flowering stage. Phenylacetaldehyde, indole and (E,E)-α-farnesene were found to be present in air entrainment samples of both plant species at the flowering growth stage, but only in those of B. rapa at the bud stage. The former two compounds were behaviourally-active in olfactometer tests. These compounds are likely to be involved in host location by M. aeneus, and, at least partially, responsible for the attractiveness of B. rapa and its success as a trap crop to protect B. napus from this pest.     

Volatiles from soil‐borne fungi affect directional growth of roots

Volatiles play major roles in mediating ecological interactions between soil (micro)organisms and plants. It is well‐established that microbial volatiles can increase root biomass and lateral root formation. To date, however, it is unknown whether microbial volatiles can affect directional root growth. Here, we present a novel method to study belowground volatile‐mediated interactions. As proof‐of‐concept, we designed a root Y‐tube olfactometer, and tested the effects of volatiles from four different soil‐borne fungi on directional growth of Brassica rapa roots in soil. Subsequently, we compared the fungal volatile organic compounds (VOCs) previously profiled with Gas Chromatography–Mass Spectrometry (GC–MS). Using our newly designed setup, we show that directional root growth in soil is differentially affected by fungal volatiles. Roots grew more frequently toward volatiles from the root pathogen Rhizoctonia solani, whereas volatiles from the other three saprophytic fungi did not impact directional root growth. GC–MS profiling showed that six VOCs were exclusively emitted by R. solani. These findings verify that this novel method is suitable to unravel the intriguing chemical cross‐talk between roots and soil‐borne fungi and its impact on root growth.     

枸杞红瘿蚊对寄主植物挥发物的电生理和行为反应

植物挥发物是植食性昆虫定位寄主的重要信息物质。枸杞红瘿蚊是宁夏枸杞的主要成灾害虫,野外发现其雌虫对枸杞幼嫩花蕾具有更强的产卵趋性。为明确枸杞红瘿蚊对枸杞不同阶段花蕾挥发物的选择差异性,解析吸引其选择产卵的关键信息化学物质,采用顶空固相微萃取法和气相色谱-质谱联用技术(GC-MS),系统研究枸杞幼嫩花蕾和成熟花蕾挥发物的成分差异,选择幼嫩花蕾挥发物中的特有成分及其与成熟花蕾挥发物共有成分共8种作为候选挥发物;通过气相色谱-触角电位联用仪(GC-EAD)和Y型嗅觉仪,测定枸杞红瘿蚊对上述挥发物的电生理和行为反应,筛选关键活性挥发物。结果显示: 枸杞幼嫩花蕾和成熟花蕾挥发物的种类和释放量存在明显差异;8种化合物能激发枸杞红瘿蚊产生持续触角电生理反应,其中,有5种[3-蒈烯、莰烯、萜品油烯、d-柠檬烯和(+)-α-蒎烯]能刺激枸杞红瘿蚊产生显著趋向或躲避行为。利用枸杞挥发物设计枸杞红瘿蚊引诱剂或忌避剂,可为田间安全防控红瘿蚊提供新的途径。     

Aggregation pheromone in Sternechus subsignatus (Coleoptera: Curculionidae): olfactory behaviour and temporal pattern of emission

The Brazilian soybean stalk weevil, Sternechus subsignatus Boehman (Coleoptera: Curculionidae), is a pest of economic importance in many regions of Brazil. Volatiles from both sexes of S. subsignatus were collected by aeration and the behavioural response of males and females was evaluated using a Y‐olfactometer. The results obtained demonstrate that the communication in S. subsignatus is mediated by aggregation pheromone as both sexes were attracted to host plant (HP) volatiles, and this attraction was increased by the addition of male volatiles. At least five male‐specific compounds (1–5) were detected in the chromatographic analysis, providing chemical support to the behavioural data. Release of these volatiles is dependent on the presence of the HP as the amount of compounds differs significantly when volatiles are collected from weevils with or without access to food. The release takes place mainly during photophase, showing a peak between 4 and 6 h after its beginning, which is also a peak of the insect activity in the field. Studies are underway to elucidate the structures of these putative aggregation pheromone components, in order to evaluate their biological activity under laboratory and field conditions.     

竹横锥大象对寄主及虫体挥发物的行为和触角电位反应

为了探明竹横锥大象Cyrtotrachelus buqueti Guerin-Meneville是否存在两性间的引诱作用,以及寄主植物慈竹Neosinocalamus affinis笋对两性行为的影响,采用Y型嗅觉仪测定了竹横锥大象雌、雄成虫对4种虫体及寄主挥发物不同处理（雌、雄成虫,慈竹笋与雌、雄成虫的复合体）的行为反应,测定了触角不同部位对雌雄成虫3种虫体的提取物（整体、鞘翅、后肠）及其与寄主植物挥发物质联合作用的触角电位反应（EAG）。结果表明：雌成虫挥发物对雄虫有较高的引诱活性,对雌虫有驱避作用;雄成虫挥发物对雌虫有一定的引诱作用。雌、雄成虫对虫体与竹笋复合体气味的行为和电生理反应均显著或极显著高于对相应虫体挥发物的反应。经EAG测定,触角各部位对虫体不同部位挥发物的EAG值差异明显,触角端部对虫体与植物挥发性物质的联合作用EAG反应差异极其显著（P＜0.01）。竹横锥大象对沾染雌雄成虫虫体提取物的玻璃棒有一定的兴奋表现,雌虫兴奋率为6.67%,雄虫为26.67%。结果提示,竹横锥大象种内存在信息素,雌虫释放的信息素对同类雄虫有很强的引诱作用,而雄虫所释放的信息素对同类雌虫有引诱作用,添加寄主植物能够增强两性间的引诱效果。     

苹毛丽金龟对植物挥发物成分的触角电位及行为反应

为筛选适宜的苹毛丽金龟Proagopertha lucidula (Faldermann)引诱剂化学物质, 对已报道的金龟子科两性引诱剂单一组分进行了触角电位（EAG）和Y型嗅觉仪中的嗅觉反应测定。结果表明: 在10 μg刺激剂量下测试的11 种植物挥发物中, 只有顺-3-己烯-1-醇、香叶醇、茴香脑和丁香酚有明确的EAG反应值, 其他7种化合物具有弱反应值。剂量反应曲线表明, 具有明确的EAG活性的4种化合物激发的反应强度与化合物的剂量呈正相关。在Y型嗅觉仪中, 顺-3-己烯-1-醇、香叶醇、茴香脑和丁香酚4种化合物在1, 10, 100 μg剂量下的行为反应百分率都显著高于对照溶剂正己烷, 且雌雄之间无显著差异。该研究结果可为开发苹毛丽金龟田间引诱剂奠定基础。     

Effects of leaf conditions and flight activity on the behaviour of Platypus quercivorus (Murayama) (Coleoptera: Platypodidae)

The important role of semiochemicals in the interactions between plants and insects has been extensively investigated. The volatiles produced by oak trees are thought to attract the ambrosia beetle Platypus quercivorus (Murayama), which causes wilt disease in Quercus trees, resulting in widespread damage. In the present study, we hypothesized that (a) P. quercivorus is attracted to the leaf volatiles emitted by host trees and (b) the response of P. quercivorus to leaf volatiles is affected by flight. An experiment was performed to survey the preferences of both sexes of P. quercivorus for the leaf volatiles of Quercus crispula Blume at various stages of leaf deterioration, represented by different number of days after cutting. Additionally, the effect of flight on both sexes was evaluated by testing the beetle flight on a flight mill. The results showed that P. quercivorus was attracted to the volatiles emitted from fresh leaves and was not attracted to those emitted from dry leaves. This suggests that leaf volatiles from healthy hosts are primary attractants for P. quercivorus. Further, males exhibited increased olfactory responses to leaf volatiles as their flight duration increased, whereas the opposite pattern was observed in females. These results suggest that the different ecological roles of the sexes contribute to differences in olfactory responses.     

How to find a needle in a haystack – host plant finding of the weevil Ceratapion onopordi

The weevil Ceratapion onopordi Kirby (Coleoptera: Apionidae) shows a mutualistic interaction with the rust fungus Puccinia punctiformis (Str.) Röhl (Pucciniaceae). One of the weevil’s host plants, the thistle Cirsium arvense (L.) Scop. (Asteraceae), is also the host of the rust fungus. It has been argued that weevils prefer rust‐infected thistle shoots for egg deposition and consequently should be able to detect such shoots. Olfactory, visual, and gustatory orientation was tested using a four‐chamber olfactometer, a visual testing arena, and feeding choice tests. Whereas the weevils used olfactory cues to find their host plants, visual orientation does not seem to be important. Rust‐infected thistle shoots were not preferred over healthy shoots in any of the tests. We conclude that host plants infected with rust fungi, which are rather rare in the field, appear to be found more or less by chance.