与中红侧沟茧蜂生境与寄主定位相关的玉米及棉铃虫幼虫体表挥发性成分的提取与鉴定

【目的】鉴定玉米Zea mays L.和棉铃虫Helicoverpa armigera (Hübner)幼虫体表挥发性成分中对中红侧沟茧蜂 Microplitis mediator (Haliday)具有生境与寄主定位作用的信息化合物,从化学生态学的角度研究玉米-棉铃虫-中红侧沟茧蜂三重营养关系,解释中红侧沟茧蜂寻找寄主的过程中的信息识别机制,为害虫的综合防治的“推-拉”方法提供一定的理论基础。【方法】利用触角电位仪(EAG)、触角电位联用仪(GC-EAD)、气质联用仪(GC-MS)及“Y”型嗅觉仪确定玉米和棉铃虫幼虫体表提取物的信息化合物。在室内利用玉米以及棉铃虫幼虫体表挥发物标准品化合物以及模拟混合物,使用“Y”型嗅觉仪进行中红侧沟茧蜂成虫行为反应试验。【结果】玉米挥发物中有11种化学成分,棉铃虫幼虫体表挥发物中有6种化学成分对中红侧沟茧蜂的触角具有电生理活性,其中4种成分在两种挥发物中都存在。室内行为反应试验发现：与正己烷对照相比,玉米的模拟组分对雌、雄蜂均表现出显著（P<0.05）的诱引作用;棉铃虫1龄幼虫体表模拟组分对雌蜂具有极显著的诱引作用（P<0.01）,对雄蜂具有显著的诱引作用（P<0.05）;棉铃虫2龄幼虫体表模拟组分对雌蜂具有显著的诱引作用（P<0.05）。【结论】本研究证明了玉米以及棉铃虫幼虫体表挥发物中分别存在11种（庚醛、2-己醇、1-己醇、1-辛烯-3-醇、壬醛、葵醛、苯甲醛、反式-2-壬烯-1-醇、己酸、苯基乙醇、月桂醇）和6种（2-己醇、己酸乙酯、1-己醇、壬醛、辛酸乙酯、癸醛）中红侧沟茧蜂生境及寄主定位的化学信息物质。     

Development of a synthetic plant volatile-based attracticide for female noctuid moths. II. Bioassays of synthetic plant volatiles as attractants for the adults of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

This paper reports olfactometer studies to determine the attractiveness of synthetic equivalents of plant volatiles to Helicoverpa armigera (Hübner) moths. Synthetic volatiles identified from host plants and other volatiles reported in literature as attractants to various noctuid species were tested in a two-choice olfactometer. Of 34 single chemicals tested, only seven were significantly attractive, and six were significantly repellent. However, when presented as blends of two or more volatiles, 21 of 31 blends tested were significantly attractive, and only one was significantly repellent. The most attractive blends were those containing four to six components, including aromatic volatiles primarily found in flowers, especially 2-phenylethanol and phenylacetaldehyde and volatiles found primarily in leaves, including green leaf volatiles and terpenoids. Some general principles in blending volatiles for developing attracticides for H. armigera are presented, including the need for blend complexity, the combination of volatiles from leaves and flowers, and early consideration of pragmatic factors such as price and toxicological profile.     

华北大黑鳃金龟对桃树挥发物的电生理反应

【目的】华北大黑鳃金龟Holotrichia oblita是一种分布范围广,寄主种类多的农业害虫。本研究鉴定了桃树顶空挥发物中对华北大黑鳃金龟雌虫具有触角电生理活性的化合物,并探索桃树挥发物活性成分的剂量对华北大黑鳃金龟雌、雄虫触角电生理反应的影响。【方法】采用顶空吸附法收集桃树枝叶挥发物,用气相色谱 触角电位联用技术(GC-EAD)和气相色谱 质谱联用技术(GC-MS)鉴定有电生理活性的桃树挥发物成分,最后用触角电位(electroantennograph, EAG)技术测试这些挥发物在0.01,0.1, 1, 10和100 μg剂量下引起的华北大黑鳃金龟雌、雄成虫EAG反应。【结果】桃树挥发物中能引起华北大黑鳃金龟雌成虫触角电生理反应的成分有7种,包括Z-β-罗勒烯、顺-3-己烯乙酸酯、顺-3-己烯醇、壬醛、水杨酸甲酯以及2种未知化合物。所测试的对华北大黑鳃金龟雌成虫触角具有电生理活性的5种桃树挥发物成分在各剂量下都能引起雌、雄成虫明显的EAG反应。雌、雄虫对同种物质的EAG反应随着剂量的增加而有增大的趋势,并且雌虫的EAG反应显著高于雄虫。【结论】桃树挥发物中,罗勒烯、顺-3-己烯乙酸酯、顺-3-己烯醇、壬醛、水杨酸甲酯均能引起华北大黑鳃金龟雌、雄成虫的剂量依赖性的触角电生理反应,而且存在显著的性别差异。可利用这些化合物开展行为反应和田间诱集试验,进一步验证其对华北大黑鳃金龟的引诱活性。     

复配杀虫剂BtA对棉铃虫的杀虫效果及对天敌中红侧沟茧蜂蛹和成虫的触杀毒性(英文)

为了科学施药, 合理保护和利用天敌对棉铃虫Helicoverpa armigera进行综合防治, 本研究在室内测定和比较了复配杀虫剂BtA和7种常用杀虫剂（阿维菌素、 Bt、 β-氯氰菊酯、辛硫磷、定虫隆、氰戊菊酯和丁硫克百威）对棉铃虫的杀虫效果及对其天敌中红侧沟茧蜂Microplitis mediator蛹和雌成虫的触杀毒性。采用浸叶法测定杀虫剂在室内72 h内对棉铃虫3龄幼虫的杀虫效果, 结果表明： 与其他杀虫剂相比, BtA对棉铃虫幼虫具有更高的毒性和致死效应 (LC₅₀=0.7364 mg/mL)。将棉铃虫3龄幼虫接到用浓度4 mg/mL上述杀虫剂分别处理过的大白菜上24, 48和72 h, 发现其死亡率之间存在显著差异（P≤0.05）。但在72 h后, BtA和其他杀虫剂对棉铃虫幼虫的杀虫效果之间并无显著差异(P>0.05)。BtA施药后, 随着时间的延长, 棉铃虫幼虫的死亡率也在增加。另外, 通过杀虫剂对寄生蜂中红侧沟茧蜂蛹和雌成虫的触杀毒性的生物测定发现： 与β-氯氰菊酯、 氰戊菊酯和丁硫克百威相比, BtA对中红侧沟茧蜂蛹和雌成虫的毒性较低, 对其蛹和雌成虫致死率分别仅为13.82%和7.33%。本研究证明BtA对鳞翅目害虫具有中等毒性, 而对寄生蜂中红侧沟茧蜂则具有较低毒性。     

星天牛对青皮垂柳挥发物的电生理及行为反应

【目的】考察星天牛Anoplophora chinensis对不同生理状态青皮垂柳Salix ohsidare挥发物的选择偏好性,深入探究星天牛对虫害青皮垂柳与健康青皮垂柳行为选择差异的原因。【方法】利用动态顶空吸附法,分别收集虫害和健康两种生理状态下的青皮垂柳枝条挥发物,通过气相色谱 质谱联用仪(GC-MS)对收集的挥发物样品进行鉴定与分析,采用触角电位仪(EAG)和Y型嗅觉仪分别分析星天牛对挥发物样品中鉴定的主要化合物的标准化合物的电生理以及行为反应,通过大笼行为实验和林间诱捕试验分析单一挥发性化合物及其双组分和三组分配方对星天牛成虫的诱捕效果。【结果】健康青皮垂柳枝条挥发物中共鉴定出3种主要化合物,包括α-蒎烯、3-蒈烯和樟脑,而虫害青皮垂柳枝条挥发物中鉴定出5种主要化合物包括α-蒎烯、β-蒎烯、3-蒈烯、β-罗勒烯和樟脑。另外虫害青皮垂柳枝条挥发物中的樟脑含量显著高于健康青皮垂柳枝条中的,3-蒈烯在两种挥发物中含量差异不显著,而健康青皮垂柳枝条挥发物中的α-蒎烯含量显著高于虫害青皮垂柳枝条中的。EAG实验表明,星天牛成虫对α-蒎烯、3-蒈烯和β-罗勒烯3种化合物的EAG反应相对值较高,并且随这3个化合物浓度的升高而逐渐增大;星天牛成虫对β-蒎烯和樟脑的EAG反应相对值差异不大,且这2个化合物浓度变化对EAG反应相对值无明显影响。Y型嗅觉仪实验表明,在1 mg/mL浓度下,α-蒎烯、3-蒈烯和β-罗勒烯吸引星天牛雄成虫数量均显著高于对照组（石蜡油）,β-罗勒烯吸引的星天牛雌成虫数量显著高于对照组;在10 mg/mL浓度下,3-蒈烯吸引的星天牛雄成虫数量显著高于对照组。大笼行为实验表明,三组分虫害配方D(α-蒎烯∶3-蒈烯∶β-罗勒烯=42∶30∶103)、α-蒎烯和β-罗勒烯吸引的星天牛成虫数量最多,显著高于双组分健康配方H(α-蒎烯∶3-蒈烯=105∶38)和3-蒈烯吸引的成虫数量。林间诱捕试验表明,α-蒎烯和虫害配方D对星天牛成虫的诱捕效果最好,诱捕的成虫数显著高于β-罗勒烯和健康配方H诱捕的成虫数,而3-蒈烯和空白对照组没有诱捕到星天牛成虫。【结论】虫害和健康青皮垂柳枝条挥发物中共有的α-蒎烯和虫害青皮垂柳枝条挥发物中特有的β-罗勒烯是对星天牛成虫具有引诱作用的两种重要寄主植物挥发性化合物,而3-蒈烯抑制了α-蒎烯对星天牛成虫的引诱作用。我们推测,虫害青皮垂柳挥发物中特有的β 罗勒烯是造成虫害青皮垂柳比健康青皮垂柳更容易受到星天牛危害的原因之一。     

烟草挥发物对2近缘种夜蛾产卵行为的影响及其成分分析

寡食性烟夜蛾Helicoverpa assulta (Guenée)和广食性棉铃虫H.armigera (Hübner)是铃夜蛾属2近缘种,烟草是其共同寄主.室内实验测定了1个普通烟草品种和4个黄花烟草品种叶片挥发物对二者电生理和行为反应的影响.结果表明,烟夜蛾处女雌蛾和交配雌蛾对4个黄花烟草品种叶片挥发物的EAG反应均显著高于普通烟草,而棉铃虫对普通烟草叶片挥发物的反应显著高于黄花烟草;二者的行为反应与EAG测试结果相似,黄花烟草叶片挥发物对烟夜蛾有较强的引诱作用,棉铃虫对普通烟草叶片挥发物有较强趋性;两种夜蛾雄蛾对这些挥发物的EAG和行为反应均没有雌蛾强烈,性别差异显著;GC-MS分析表明,与K326相比,马合烟叶片挥发物中尼古丁的相对含量高(76.91%),绿叶气味种类多但芳香族化合物种类少,挥发物种类和含量的不同是否与两种夜蛾产卵趋性差异相关,有待进一步研究.     

Development of a synthetic plant volatile-based attracticide for female noctuid moths. I. Potential sources of volatiles attractive to Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

This paper is the first of a series which will describe the development of a synthetic plant volatile-based attracticide for noctuid moths. It discusses potential sources of volatiles attractive to the cotton bollworm, Helicoverpa armigera (Hübner), and an approach to the combination of these volatiles in synthetic blends. We screened a number of known host and non-host (for larval development) plants for attractiveness to unmated male and female moths of this species, using a two-choice olfactometer system. Out of 38 plants tested, 33 were significantly attractive to both sexes. There was a strong correlation between attractiveness of plants to males and females. The Australian natives, Angophora floribunda and several Eucalyptu s species were the most attractive plants. These plants have not been recorded either as larval or oviposition hosts of Helicoverpa spp., suggesting that attraction in the olfactometer might have been as nectar foraging rather than as oviposition sources. To identify potential compounds that might be useful in developing moth attractants, especially for females, collections of volatiles were made from plants that were attractive to moths in the olfactometer. Green leaf volatiles, floral volatiles, aromatic compounds, monoterpenes and sesquiterpenes were found. We propose an approach to developing synthetic attractants, here termed 'super-blending', in which compounds from all these classes, which are in common between attractive plants, might be combined in blends which do not mimic any particular attractive plant.     

普通大蓟马聚集信息素的分离和鉴定

【目的】普通大蓟马Megalurothrips usitatus是我国华南地区重要的豆科害虫,给我国豇豆种植产业带来巨大损失。开发利用基于聚集信息素的引诱剂是普通大蓟马的绿色防控措施之一,对于普通大蓟马生物防治具有重要意义。【方法】采用Y型嗅觉仪测定普通大蓟马雌雄成虫对其雌虫和雄虫气味源的嗅觉反应;用顶空固相微萃取法(head space solid-phase microextraction, HS-SPME)和溶液浸提法提取普通大蓟马雌雄成虫挥发物;应用气质联用仪(gas chromatography-mass spectrometry, GC-MS)对收集的气体挥发物和正己烷提取物进行活性成分分离鉴定;应用Y型嗅觉仪测定人工合成聚集信息素组分对雌雄成虫的引诱效果。【结果】行为学试验结果表明,普通大蓟马雄成虫气味源对其雌雄成虫均具有显著的引诱作用,而雌成虫气味源则没有。顶空固相微萃取法和溶液浸提法均可提取雄成虫挥发物主要组分,但顶空固相微萃取法获得的TIC图基线平稳,杂峰少,提取效果优于溶剂浸提法。GC-MS分析结果表明,普通大蓟马雄成虫挥发物中主要含有 1种化合物,为反式,反式-金合欢醇乙酸酯［(E,E)-farnesyl acetate］,该化合物在雌成虫挥发物中不存在。室内行为学实验结果表明,特定剂量的人工合成的(E,E)-farnesyl acetate对普通大蓟马雌雄成虫均具有显著的引诱作用。【结论】本研究证明了普通大蓟马雄成虫可以释放聚集信息素,并鉴定了其主要组分(E,E)-farnesyl acetate,为应用聚集信息素开展普通大蓟马的监测和诱杀提供了基础。     

不同季节黑杨萎蔫叶片挥发物的化学成分分析

采用水蒸气蒸馏法和气相色谱-质谱联用技术,分析黑杨不同季节的叶片,即嫩叶、成熟叶和衰老叶萎蔫后释放的气味物质成分.结果表明,嫩叶挥发物主要成分为顺-3-己烯醇、-甲基-1-戊醇和邻羟基苯甲醛,其相对含量分别为44.81%、21.85%和15.19%;成熟叶挥发物主要组分也是顺-3-己烯醇,相对含量28.71%,其次为邻羟基苯甲醛,相对含量10.35%.邻羟基苯甲醛为衰老叶挥发物的主要组分为,其相对含量为28.81%,其次是苯甲醇,相对含量15.06%;随着叶龄增长,挥发物中顺-3-己烯醇含量显著减少,而具有芳香性化合物种类及其含量显著增加.     

Analysis of volatiles from black pine (Pinus nigra): significance of wounding and egg deposition by a herbivorous sawfly

The composition of headspace volatiles of black pine (Pinus nigra) was analysed by coupled gas chromatography-mass spectrometry (GC-MS). It has been shown in a previous study that egg deposition of the sawfly Diprion pini on P. sylvestris induces a quantitative change of the pine volatile blend . Chrysonotomyia ruforum, an egg parasitoid of D. pini, is known to be attracted by volatiles from egg-carrying P. sylvestris, but not by odour from egg-laden P. nigra. Therefore, the present study focused on the question whether also P. nigra as another host plant of this sawfly responds to egg deposition by change of its volatile blend. The headspace of untreated, egg-carrying, and artificially wounded P. nigra twigs were compared. The artificial damage inflicted to the twigs mimicked the damage by the sawfly female prior to egg deposition. Thirty five mainly terpenoid compounds that were identified in more than 50% of the egg-carrying P. nigra twigs could also be detected in the headspace of untreated and artificially wounded twigs. Quantitative differences of the blends of volatiles from differently treated P. nigra twigs were compared by multivariate data analyses. PLS-DA (projection to latent structures-discriminant analysis) revealed that blends of volatiles from differently treated P. nigra differed significantly. When comparing volatiles from egg-carrying and artificially wounded P. nigra with respective P. sylvestris samples, qualitative and quantitative differences were detected. The differences in volatile composition of P. nigra and P. sylvestris are discussed with special respect to the egg parasitoid's response to odours of egg-carrying pine twigs.     

Electrophysiological and Behavioral Responses of Male Fall Webworm Moths (Hyphantria cunea) to Herbivory-Induced Mulberry (Morus alba) Leaf Volatiles

Volatile organic compounds (VOCs) were collected from damaged and intact mulberry leaves (Morus alba L., Moraceae) and from Hyphantria cunea larvae by headspace absorption with Super Q columns. We identified their constituents using gas chromatography-mass spectrometry, and evaluated the responses of male H. cunea antennae to the compounds using gas chromatography-flame ionization detection coupled with electroantennographic detection. Eleven VOC constituents were found to stimulate antennae of male H. cunea moths: β-ocimene, hexanal, cis-3-hexenal, limonene, trans-2-hexenal, cyclohexanone, cis-2-penten-1-ol, 6-methyl-5-hepten-2-one, 4-hydroxy-4-methyl-2-pentanone, trans-3-hexen-1-ol, and 2,4-dimethyl-3-pentanol. Nine of these chemicals were released by intact, mechanically-damaged, and herbivore-damaged leaves, while cis-2-penten-1-ol was released only by intact and mechanically-damaged leaves and β-ocimene was released only by herbivore-damaged leaves. Results from wind tunnel experiments conducted with volatile components indicated that male moths were significantly more attracted to herbivory-induced volatiles than the solvent control. Furthermore, male moths'' attraction to a sex pheromone lure was increased by herbivory-induced compounds and β-ocimene, but reduced by cis-2-penten-1-ol. A proof long-range field trapping experiment showed that the efficiency of sex pheromone lures in trapping male moths was increased by β-ocimene and reduced by cis-2-penten-1-ol.     

茉莉酸甲酯处理对棉铃虫生长和解毒能力的影响

【目的】为明确茉莉酸甲酯（methyl jasmonate, MeJA）的不同处理方式对昆虫生长和解毒代谢能力的影响,以及MeJA熏蒸处理昆虫对植物防御和昆虫解毒代谢之间关系的影响。【方法】本文比较了取食MeJA和MeJA熏蒸等两种处理对棉铃虫Helicoverpa armigera 3龄末幼虫生长和解毒代谢酶活性的影响,并系统研究了经MeJA熏蒸处理的棉铃虫3龄末幼虫,再取食经MeJA喷雾处理的棉叶,其中肠解毒酶活性的变化。【结果】取食MeJA和MeJA熏蒸两种不同处理,对棉铃虫幼虫的生长及解毒能力的影响有所不同。取食含2.9 μg/g MeJA的人工饲料显著抑制了棉铃虫的生长,同时诱导棉铃虫幼虫P450活性增加了1.92倍,而MeJA熏蒸虽然没有影响棉铃虫幼虫的生长,但MeJA熏蒸处理使棉铃虫幼虫P450活性和羧酸酯酶活性分别增加了2.94倍和1.16倍。经MeJA熏蒸处理后的棉铃虫幼虫,再取食正常的或经MeJA喷雾处理的棉叶,其幼虫P450活性显著增加,其中经MeJA熏蒸处理的棉铃虫,再取食经MeJA喷雾处理的棉叶,其P450酶显示了最高活性。【结论】MeJA熏蒸处理棉铃虫,不仅使棉铃虫中与P450酶相关的解毒能力显著增加,而且增加了棉铃虫对于MeJA所诱导的棉花防御反应的解毒能力。     

Analysis of the volatile components of five Turkish Rhododendron species by headspace solid-phase microextraction and GC-MS (HS-SPME-GC-MS)

Volatile constituents of various solvent extracts (n-hexane, CH2Cl2, H2O) of 15 different organs (leaves, flowers, fruits) of five Rhododendron species (Ericaceae) growing in Turkey were trapped with headspace solid-phase microextraction (HS-SPME) technique and analyzed by GC-MS. A total of 200 compounds were detected and identified from organic extracts, while the water extracts contained only traces of few volatiles. The CH2Cl2 extract of the R. luteum flowers was found to exhibit the most diverse composition: 34 compounds were identified, with benzyl alcohol (16.6%), limonene (14.6%) and p-cymene (8.4%) being the major compounds. The CH2Cl2-solubles of R. x sochadzeae leaves contained only phenyl ethyl alcohol. This study indicated appreciable intra-specific variations in volatile compositions within the genus. Different anatomical parts also showed altered volatile profiles. This is the first application of HS-SPME-GC-MS on the volatiles of Rhododendron species.     

艾草和窃衣挥发物的提取鉴定及其对烟粉虱MED隐种成虫选择性的影响

[目的]在前期研究中,我们发现艾草Artemisia argyi和窃衣Torilis scabra都有吸引或驱避昆虫的作用.然而还未见有研究报道艾草和窃衣以及它们的挥发物对烟粉虱Bemisia tabaci MED隐种成虫的作用.本研究旨在检测能否利用艾草和窃衣及其挥发物对烟粉虱MED隐种成虫实施绿色防控.[方法]通过...     

Chemical signatures affecting host choice in the Eucalyptus herbivore,Gonipterus sp. (Curculionidae: Coleoptera)

It is well known that herbivorous insects respond to host plant volatiles. Yet details of how these insects perceive the complex profile of volatiles from different potential host plants have not been studied for most insects. Gonipterus spp. are important pests of Eucalyptus worldwide, but differ in their preference for different species of this host. In this study, we consider whether host volatiles affect the host choice for a Gonipterus sp. and we characterize the response of the female insect to the volatile profiles from these hosts in an electro-antennographic experiment. We sampled volatiles from freshly damaged leaves of three Eucalyptus species and analysed the profiles by gas chromatography coupled to electro-antennography (GC-EAD) and gas chromatography coupled to mass spectrometry. Female weevils gave a mixed range of electro-physiological responses to volatile puffs from leaves of different tree species. This suggests that differences in volatile profiles of different trees play a role in how these beetles discriminate between potential hosts. GC-EAD analysis showed that responses were as complex as the volatile chemical compositions of the leaves. A number of these chemicals were identified, and responses were mostly due to general green leaf volatiles. This was also evident from the fact that the insects showed a markedly greater response to the total volatile profile from freshly damaged leaves for all species. The females of the Gonipterus sp. can therefore detect damaged leaves, which may indicate host quality. Host specificity information is further expected to lie in the relative differences in emission ratios and synergism between different host chemical compounds, rather than specific individual compounds.     

Induced volatiles in elicitor-treated and rice blast fungus-inoculated rice leaves

The volatiles released from elicitor (copper chloride, jasmonic acid, UV, L-methionine and chitosan oligomer)-treated and rice blast fungus-inoculated rice leaves were collected by the solid-phase microextraction technique and analyzed by GC-MS. (Z)-3-Hexen-1-ol, monoterpenes, methyl salicylate, and sesquiterpenes were identified as elicitor-induced volatiles by a comparison of their GC retention times and mass spectra with those of authentic compounds. The different elicitors resulted in some qualitative and quantitative differences in the production of volatiles. Monoterpenes and sesquiterpenes were identified as the rice blast fungus-induced volatiles.     

Volatiles of two chemotypes of Majorana syriaca L. (Labiatae) as olfactory cues for the honeybee

Summary A study of olfactory discrimination by honeybee has been set up in order to understand the role of volatiles of the aromatic plant Majorana syriaca in attracting pollinating insects. The honeybee's response to volatiles from leaves and inflorescences of two M. syriaca chemotypes, which differ in the thymol carvacrol ratio of their volatiles, was tested using a bioessay method based on associative conditioning and recruitement techniques. Behavioural data show that a honeybee identifies and reacts selectively to olfactory signals from leaves and from inflorescences of the two chemotypes. Such data suggest that the volatiles from all parts of the aromatic plant M. syriaca may have a role in attracting pollinators. The vegetative parts produce a volatile emission which attracts the pollinators from a distance towards the whole plant. At close range these are directed by the flower signal which is amplified by the volatiles of bracts and leaves in the inflorescence.     

Effects of Neem Leaf Volatiles on Submerged Cultures of Aflatoxigenic Aspergillus parasiticus

Microbe-free compressed air was passed continuously for a 3-day test period through an enclosed system containing fresh neem leaves; the resultant emitted volatiles were passed over the surface of submerged liquid cultures of a wild-type aflatoxigenic isolate of Aspergillus parasiticus. Aflatoxin determinations for the fungal culture that received neem-derived volatiles, after a 3-day incubation period, resulted in a 90% overall reduction in aflatoxin production and a 51% reduction in fungal biomass when compared with cultures that did not receive neem volatiles. In a separate experiment but in a similarly enclosed system, volatiles from fresh neem leaves were collected on a small Tenax column and were thermally desorbed and cryogenically focused on a capillary gas chromatography column. The neem volatiles were subsequently separated and identified by gas chromatography-mass spectrometry. Sixty-eight compounds were identified by comparison of retention times and mass spectra with either authentic compounds or spectra from a computer-assisted library database of mass spectra. It was found that 10% of the total headspace volatiles were composed of C₃ to C₉ alkenals, which are toxic to aflatoxigenic Aspergillus spp., which could explain the bioactivity that resulted in reduced biomass in the neem-treated cultures.     

C(15)H(24) Volatile Compounds Unique to Aflatoxigenic Strains of Aspergillus flavus

Headspace volatiles from eight strains of Aspergillus flavus (four aflatoxigenic strains and four nonaflatoxigenic strains), grown for 1, 2, 3, 4, 8, and 10 days in submerged cultures, were collected in Tenax GC traps. The traps were desorbed onto a 50-m gas-liquid chromatography capillary column by heat and gas purge from an external direct injector device. The column was interfaced with a mass spectrometer data acquisition system. Peaks were identified by comparing retention times and mass spectra with those obtained from authentic compounds and by using a computer-assisted mass spectral data base. Aflatoxigenic strains of A. flavus produced several C(15)H(24) compounds (e.g., alpha-gurjunene, trans-caryophyllene, and cadinene) which peaked in 3-day cultures and were not present in earlier (1- and 2-day) or later (8- and 10-day) cultures. None of these volatiles were detected in nonaflatoxigenic strains of A. flavus. There was an apparent correlation between the release of C(15)H(24) volatile compounds and the initiation of aflatoxin biosynthesis, and a correlation between decline of aflatoxin synthesis and the disappearance of the C(15)H(24) compounds unique to aflatoxigenic A. flavus also existed.     

Antennal response of cotton bollworm (Heliocoverpa armigera) to volatiles in transgenic Bt cotton

Abstract:  Volatile compositions in transgenic Bt cotton variety 'GK-97' and its parental variety 'Simian No. 3' were analysed, and antennal response of cotton bollworm ( Heliocoverpa armigera ) to the volatiles were investigated. Volatile components in Bt cotton and regular cotton were almost same, except for absence of a sesquiterpene and a minor unknown compound in regular cotton. The results of gas chromatography-electroantennographic detection (GC-EAD) experiments showed that cotton bollworm antennae responded to seven compounds and two minor unknown compounds in Bt volatiles, among which concentrations of α -pinene and β -pinene in Bt cotton were relatively higher than those in regular cotton, and one minor unknown compound was absent in regular cotton.