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A flavone (5,7,4′-trihydroxy-3′,5′-dimethoxyflavone), a cyclohexenone (3-isopropyl-5-acetoxycyclohexene-2-one-1) and a liquid mixture of low polarity, containing long-chain and cyclic hydrocarbons, were isolated from leaves of allelopathic rice accession PI 312777 using column chromatography. Their structures and constituents were identified by means of HR-MS, NMR and GC/MS analyses, respectively. Bioassays showed that both the flavone and cyclohexenone significantly inhibited the growth of weeds Echinochloa crus-galli, Cyperus difformis and Cyperus iris, and the spore germination of fungal pathogens Pyricularia oryzae and Rhizoctonia solani at all tested concentrations. Moreover, the combination of the inactive mixture of low polarity and the active flavone or cyclohexenone significantly enhanced the inhibitory activities on weed growth. In addition, the two compounds and the mixture of low polarity from the leaves of PI312777 did not inhibit the rice growth at the same concentrations. It was also established that both compounds could be released into the soil, and was especially induced by E. crus-galli. The results suggest that 5,7,4′-trihydroxy-3′,5′-dimethoxyflavone and 3-isopropyl- 5-acetoxycyclohexene-2-one-1 may act as allelochemicals participating in the defense of rice against weeds and pathogens. [Copyright &y& Elsevier]

This paper studied the effects of Lantana camera fresh leaves aqueous extract and its contained phenolic compounds on the growth and physiologic-biochemical indexes of Eichhornia crassipes. The results showed that this extract had obvious inhibitory effects on the growth and development of E. crassipes. When the concentration was higher than 30 g FW x L(-1), it could kill E. crassipes after 6 days treatment. A total of seven phenolic compounds in the abstract were identified by HPLC, which were salicylic acid, gentisic acid, beta-resorcylic acid , coumarin, ferulic acid, p-hydroxybenzoic acid and 6-methyl coumarin, with the concentrations being, 50.95, 13.46, 5.28, 3.36, 2.92, 2.19 and 0.34 mg x L(-1), respectively. The mixture of the seven compounds had the strongest inhibitory effect, followed by salicylic acid, 6-methyl coumarin, coumarin, and p-hydroxybenzoic acid, while the effects of beta-resorcylic acid and gentisic acid were not significant.

In this study, crude lantadene was extracted from Lantana canmara leaves, and its antifeeding effects on Plutella xylostella and Spodoptera litura larvae were tested. In no-choice test, crude lantadene at 1.6 mg x ml(-1) concentration had antifeeding effects on the 2nd instar P. xylostella larvae and 1st instar S. litura larvae, with the antifeeding rate being 62.4% and 33.1%, respectively within 48 h. In choice test, even a low concentration (0.4 mg x ml(-1)) crude lantadene still had anti-feeding effects on the 2nd instar P. xylostella larvae, and the antifeeding rate at 0.4, 0.8 and 1.6 mg x ml(-1) concentration was 52.7%, 55.5% and 78.9%, respectively. Crude lantadene only at 1.6 mg x ml(-1) concentration had anti-feeding effects on the 1st instar S. litura larvae, and the antifeeding rate was 33.0%. For the 2nd instar S. litura larvae, crude lantadene had no antifeeding effects both in no-choice and in choice test.

Aulacophora fermoralis chinensis and Aulacophora cattigarensis are the two related Aulacophora beetles, but their host selectivity and feeding behavior are significantly different. A. fernzoralis chinensis usually feeds upon Cucumis sativus and Cucurbita moschata, but never upon Luffa acutangula, Momordica charantia and Citrullas lanatus. Its feeding behavior on hosts is to snip a circular trench on their leaves, and then, to feed the leaf tissues isolated by the trench. On the contrary, A. cattigarensis only feeds L. acutangula, and its trenching behavior rarely occurs. This study showed that the host selectivity and feeding behavior of the two beetles were significantly correlated with the types of cucurbitacin biosynthesized by host melon crops. C. sativus and C. moschata might be induced to produce cucurbitacin I by A. fermoralis chinensis feeding, and this compound was responsible for feeding deterrent on A. fermoralis chinensis. Therefore, the feeding behavior of A. fermoralis chinensis was to block the translocation of cucurbitacin I to feeding sites. M. charantia and C. lanatus contained deterrent cucurbitacin D, and thus, both beetles never fed upon them, while L. acutangula contained stimulants cucurbitacin B and E, and made A. cattigarensis directly feed upon it without trenching. The results suggested that the taste responses of insects on specific allelochemicals from plants may play an important role in host selectivity and feeding behavior.

The ecological and economic impacts of exotic invasive weeds have been followed with interest. A successful invasion of exotic weeds depends not only on their bio-ecological traits, but also on some specific mechanisms of invasion. The clarification of the invasive mechanism of exotic weeds will be beneficial to predict and manage on them. In the process of establishment, reproduction and spreading, an exotic species has to become dominant in the interactions with native ones at new habitats, and then invades successfully. Among invasive mechanisms, the chemical interaction between exotic and native weeds should not be neglected. Previous studies showed that allelopathy plays an important role in exotic weed invasion. In fact, plants are able to defend or inhibit animals, plants and microbes from new habitats by using some specific chemicals. The chemical mechanism of exotic weed invasion might involve each aspect of plant chemical ecology. Therefore, chemical ecological characteristics of exotic weeds should be regarded as one of the most significant factors on predicting invasive species. The studies on chemical mechanism of exotic weed invasion will be one of the important aspects in future.

This study showed that the volatile oils from Myoporum bontioides had a significant repellent action on Plutella xylostella. When Plutella xylostella adults entered into the 4-arm selective olfactometer, the preferred times and average staying duration, in the order from more to less, were 3, 1, 4, and 2 arms, which showed a tendency of keeping away from the treatment arms. The males were more sensitive to the volatile oils than the females, when the velocity of flow was 200 ml.min-1. On the first day of the 3rd bioassay, the oviposition deterrent rate and IIPC of the volatile oils on Plutella xylostella adults was 94.48% and 0.0552, respectively. A liquid component of the volatile oils from Myoporum bontioides was isolated, purified, and identified as myoporone.

The volatile oil from C. odorata had a significant effect on the growth of plants, fungi and insects. The result showed that the seedling growth of five test plants was obviously inhibited, in the order of ryegrass > Chinese cabbage > radish > snap been > rice. The inhibitory effect of the oil at its middle concentration (800 mg.L-1) for Pyricularia grisea was the strongest, the next was to Phytophthora nicotianae, and the weakest was to Fusarium axysporum. The inhibitory percentage was 61.40%, 29.27% and 14.44%, respectively. The volatile oil from C. odorata at the dose of 10-20 microliters.plant-1 had a significant oviposition deterrent effect on Phyllotreta striolata and Plutella xylostella. The volatile oil from C. odorata was analyzed by GC/MS and thirty components were identified. Terpenoids compounds were major components of the volatile oil, such as trans-caryophyllene (16.58%), delta-cadinene (15.85%), alpha-copaene (11.58%), caryophyllene oxide (9.63%), germacrene-D (4.96%), and delta-humulene (4.32%).

The chemical components of volatile oil from Mikania micrantha were analyzed by GC/MS. Twenty-two compounds were identified, and monoterpenes and sesquiterpenes as well as alcohol and ketone with their derivatives were major components. Biological activity of volatile oil on insect was investigated. The results showed that the volatile oil had significant deterrent effect on oviposition of Plutella xylostella, Phyllotreta striolata and Phaedon brassicae at dose of 5-10 microliters.plant-1. They also possessed established contracting toxicity, and their rectifying reduce rates for Lipaphis erysimi were 50.0%, 59.86%, 62.51% at concentration of 500, 750, and 1000 mg.L-1, respectively. However, they had not fumigating toxicity for virginogeniae, L. erysimi, 2nd instar larvae of P. xylostella, and adult of P. striolata at concentration of 500 mg.L-1.

Mikania micrantha, an exotic plant species, is an important weed in south China. The volatile oil of the weed species had significant biological activities on plants and their pathogens, particularly Pyricularia grisea. The results showed that the seeding growth of 6 plant species decreased obviously when exposed to increasing concentration (200, 400, 800, 1600 mg.L-1) of the volatile oil. The fresh weight of all test plants decreased, and the emergence of all test plants delayed for 1-2 days under soil treatment (2500 g.hm-2). The inhibitory effect of volatile oil of M. micrantha at its medium concentration was the most strong on Pyricularia grisea; secondary on Fusarium oxysporum; but weak on Phytophthora nicotianae. The inhibitory rate was 53.38%, 28.66% and 18.69% for the three plant pathogens, respectively.