Use of lichen secondary metabolites as antifeedants to protect higher plants from damage caused by slug feeding

Extracts of 15 species of lichen were tested for antifeedant properties against the field slug Deroceras reticulation (Müller) (Mollusca: Pulmonata). All but three showed some activity and two of these were from endolithic species. The most effective extract was from Letharia vulpina. The major active compound from this species, vulpinic acid, was tested for dose response, applied as a foliar spray to turnip plants and as a dressing to wheat seeds in laboratory experiments. It provided effective protection against slug feeding under these conditions.     

A bioassay for screening materials influencing feeding in the field slug Deroceras reticulatum (Müller) (Mollusca: Pulmonata)

Test materials were incorporated in wheatflour pellets to measure their effect on slug feeding. The dry weights of individual pellets were measured before and after exposure for 24 h to starved slugs. The method gave consistent results, and can accommodate test materials with different physical properties. The phagostimulant effect of sucrose was confirmed. An extract of the herb tarragon (Artemisia dracunculus) was the most effective antifeedant of the materials used at the concentrations tested. The method is compared with other published techniques.     

Host plant defenses of black (Solanum nigrum L.) and red nightshade (Solanum villosum Mill.) against specialist Solanaceae herbivore Leptinotarsa decemlineata (Say)

Black nightshade (Solanum nigrum, S. nigrum L.) and red nightshade ( Solanum villosum, S. villosum Mill.) are medicinal plants from the Solanaceae family that synthesize glycoalkaloids and other secondary metabolites. To recognize the potential insecticide activity of these compounds, leaf extracts (containing glycoalkaloid and methanol fractions) were tested for enzyme inhibition, antifeedant activity and toxicity. For in‐vitro glutathione S‐transferase (GST) inhibition activity, we used insecticide‐resistant Colorado potato beetle, Leptinotarsa decemlineata ( L. decemlineata; Say) midgut and fat‐body homogenate. In‐vivo toxicity and the antifeedant activity were performed using larval bioassays. The methanol extracts had greater GST inhibitory activity compared to the glycoalkaloids, as well as greater 2nd instar larvae mortality and antifeedant activity. Furthermore, the green leaf volatile compound, cis‐hex‐3‐enyl acetate, at the concentration of 5 ppm, caused 50% mortality of 2nd instar larvae. Our findings suggest the potential usefulness of S. nigrum and S. villosum extracts to control L. decemlineata.     

龙柏精油对小菜蛾的生物活性

龙柏精油对小菜蛾Plutella xylostella(L.)的室内生物活性测定结果表明,熏蒸作用是龙柏精油对小菜蛾的主要作用方式,熏蒸实验中当龙柏精油浓度为5.00 mg/L2、.50 mg/L时,处理后48 h小菜蛾2龄幼虫的校正死亡率分别为92.33%、80.29%。龙柏精油对小菜蛾具有较强的非选择性拒食作用和产卵忌避作用,但由于精油的挥发性效果不持久。当龙柏精油浓度为5.00 mg/L和2.50 mg/L时,24 h小菜蛾的产卵忌避率分别为80.45%和77.42%;而48 h则降为72.30%和61.79%。当龙柏精油浓度为5.00,2.50和1.25 mg/L时,24 h的非选择性拒食率分别为86.70,74.36和70.93%,48 h的非选择性拒食率分别降为82.36,71.40和60.40%。龙柏精油对小菜蛾具有一定的触杀活性,当龙柏精油浓度为5.00 mg/L时效果最好,24 h和48 h的校正死亡率分别为60.00%和76.67%。     

广藿香精油对檀香粉蝶和荔枝卷叶蛾生物活性研究

试验采用不同浓度广藿香(Pogostemon cablin(Blanco)Benth.)精油,研究其对檀香粉蝶和荔枝卷叶蛾幼虫拒食和忌避作用。使用2.5~40 mg/mL广藿香精油分别对檀香粉蝶和荔枝卷叶蛾幼虫进行饲喂试验,檀香粉蝶幼虫的选择性和非选择性拒食率都为100%,荔枝卷叶蛾的选择性拒食率为18.36%~100%,24 h和48 h非选择性拒食率分别为51.45%~100%和53.34%~100%。忌避试验发现,随着浓度提高,忌避作用越强,其中最大忌避率分别为80.30%和93.81%;随着时间推移,各浓度精油对檀香粉蝶和荔枝卷叶蛾幼虫的忌避效应呈现不同程度的下降趋势。试验表明,广藿香精油对檀香粉蝶和荔枝卷叶蛾幼虫有较好的防治作用。     

Insect antifeedant secoaromadendrane-type sesquiterpenes from Plagiochila species

The characteristic pungency of the liverworts Plagiochila species P. fruticosa, P. hattoriana, P. ovalifolia and P. yokogurensis is due to a new ent-secoaromadendrane-type sesquiterpene hemiacetal, plagiochiline A, which exhibits very strong antifeedant activity against the African army worm, Spodoptera exempta at 1–10ng/cm². Two new secoaromadendranes, plagiochilide and furanoplagiochilal A, together with the previously known plagiochiline C were isolated from P. yokogurensis. Plagiochilal A, which may be a precursor of plagiochilide and its related hemiacetals, and a bitter principle, plagiochiline B were also isolated from P. hattoriana. P. ovalifolia contained plagiochilines A, B and C. From P. fruticosa, plagiochilide and plagiochilines A, B and C were isolated. The structures of the new secoaromadendrane-type sesquiterpenes were elucidated by extensive ¹H NMR and ¹³CNMR studies.     

苍耳甾醇物质对菜青虫取食、血淋巴和中肠酶活性及中肠组织的影响

甾醇是植物体内的重要次生物质,具有多种生物活性。为探明植物甾醇类物质对害虫的作用机理,采用叶碟饲喂法进行取食处理后研究了苍耳Xanthium sibiricum中分离纯化的甾醇类组分（甾醇A和甾醇B）对4龄菜青虫Pieris rapae的取食、酶活性以及中肠组织的影响。结果表明： 苍耳甾醇类组分甾醇A和甾醇B能明显抑制菜青虫的取食,拒食中浓度AFC50分别为0.0229 和0.0147 mg/mL;同时,显著降低菜青虫中肠蛋白酶、淀粉酶和羧酸酯酶活性,其中,甾醇B的作用效果较强,处理后24 h和36 h, 对蛋白酶活性抑制率分别为23.74%和58.59%,对中肠羧酸酯酶的活性抑制率分别为49.01%和83.03%;降低血淋巴蛋白质含量,诱导菜青虫血淋巴羧酸酯酶活性的提高;破坏昆虫中肠上皮组织,微杆模糊不清呈消融状,杯状细胞的杯腔基部微绒毛消失。这些结果说明苍耳甾醇类物质对菜青虫的取食抑制可能与对中肠消化酶活性的抑制以及对中肠上皮组织的破坏有关,植物甾醇组分的不同配比影响其对昆虫的作用效果。     

不同生物药剂对稻水象甲的毒力、拒食活性及防效分析

【目的】防治稻水象甲的现有常规化学药剂的大量施用所引发的环境问题越发突出,而其生物药剂单一,加之天敌匮乏,故开展符合绿色生产标准的低毒、低残留、无污染生物药剂的筛选已成为稻水象甲防治工作所面临的首要任务。【方法】以越冬代稻水象甲成虫为试虫,采用室内点滴、田间喷雾等方法,对5种符合绿色生产标准药剂的毒力、拒食活性、防效及药后取食量等指标进行了测定和综合评价。【结果】室内生测方面:72 h后对处理稻水象甲成虫的室内毒力显著;此外,对试验前后的取食斑面积进行比较,发现药后各药剂拒食活性差异显著,均表现出较好的拒食作用。田间药效方面:除0.6%苦参碱AS外,其他药剂对稻水象甲均表现出较好的防效,100亿个孢子·m L~(-1)白僵菌OD、1.5%除虫菊素AS、7.5%鱼藤酮EC和6%乙基多杀菌素SC这4种药剂15 d的田间防效为51.24%~82.55%;3 d后各处理组田间新增取食斑数、取食长度均显著低于对照组。【结论】在绿色水稻生产中,100亿个孢子·m L~(-1)白僵菌OD、1.5%除虫菊素AS、7.5%鱼藤酮EC和6%乙基多杀菌素SC均具有较好的推广价值,可用于稻水象甲的防治。     

A toxin protein from Xenorhabdus nematophila var. pekingensis and insecticidal activity against larvae of Helicoverpa armigera

Xenorhabdus nematophila var. pekingensis, which is highly virulent for many insects, is a symbiotic bacterium of Steinernema carpocapsae isolated from Beijing soil in China. Previous studies demonstrated that the bacterium had high antifeedant activity against larvae of Helicoverpa armigera, Plutella xylostella and Spodoptera exigua. Herein, we report the purification, molecular cloning and antifeedant activity of an intracellular toxic protein from the bacterium. The purified protein displayed a single band and a relative molecular weight of over 212 kDa determined by SDS-PAGE. We designated the protein as XnAFP2. Peptide segments were obtained by MALDI-TOF and covered 40% of the amino acid sequence of a toxin protein from X. nematophilus PMFI1296. The full cDNA sequence encoding for XnAFP2 (Genbank accession number FJ222606) was amplified from X. nematophlia var. pekingensis and consists of 7575 bp. The gene showed homology with up to 99% identity to the A2 gene from X. nematophila strain BP (GenBank accession number AY282763) and 92% identity to the insecticidal toxin xptA2 gene from X. nematophila PMFI 1296 (GenBank accession number AJ308438). The protein caused a rapid cessation in feeding and reduction in larval weight of H. armigera. When fed to third instar larvae of H. armigera in an artificial diet at 6.0 µg/g (w/w) toxin protein, growth reduction reached 97.9%. The insecticidal protein greatly decreased fourth instar larval weight, lengthened larval stage, and reduced pupation and emergence rates. The antifeedant rate in choice and no-choice leaf disk tests against fifth instar larvae was 78.4 and 87.6% in 24 h, respectively.     

Biological activities of lignans and stilbenoids associated with plant-insect chemical interactions

Lignans and biogenetically-related secondary metabolites derived from phenylpropanoid precursors play a significant role in the defence of plants against insects. They act largely as regulators of insect feeding, but in a few cases they can influence also specific physiological functions of insects. The antifeedant activities of a series of lignans are summarised and compared with previously published data. The compounds represent either natural substances isolated from plants or their chemically transformed structural analogues. The precise mode of action of such compounds is mostly unknown. One possible mechanism might be interaction with, and disruption of, the endocrine system, which is crucial for proper development of insects and is dependent on the action of moulting hormones (ecdysteroids). This hypothesis has been tested using the specific Drosophila melanogaster B_II cell line bioassay for ecdysteroid agonists and antagonists, in which the potency of the test compound reflects the affinity of binding to the ligand-binding site of the D. melanogaster ecdysteroid receptor. The activity data are evaluated in terms of a structure-activity relationship. To explore this phenomenon, the compounds were prepared and tested alongside ecdysteroid analogues and some insect ecdysis/metamorphosis-disturbing steroidal and non-steroidal natural compounds. Several phenylpropanoids, including lignans and stilbenoids (derived from resveratrol), were evaluated with promising results. The results indicate that such phenylpropanoid-derived compounds can possess ecdysteroid antagonistic activity, which could potentially influence insect development.