Search

Flaveria bidentis (L.) Kuntze, an invasive plant, poses a serious threat to the structure and function of the native ecosystem in Hebei Provience, China. However, little is known about the allelopathic activity of the residues of this plant species. In this study, the impact of the phytotoxicity of unburnt (UR) and burnt (BR) residues of the exotic invasive weed on the growth of wheat (Triticum aestivvm L.) was assessed. Extracts prepared from both UR and BR reduced the shoot length, root length and dry weight of wheat significantly compared with the control, thereby indicating the presence of some water-soluble allelochemicals in F. bidentis residues. Growth studies conducted in soil amended with UR and BR extracts or residues also revealed phytotoxic effects towards wheat. A significant amount of phenolics was detected in the residue extracts and in residue-incorporated soil. The phenolic content rose with increasing residue concentration, thereby showing their direct involvement in the observed growth inhibition. The inhibition of wheat growth by the burnt residue and its water extracts was similar to that of unburnt residue, so burning it is not a good way to eliminate the allelopathic effects of the residue of F. bidentis on native plants. [ABSTRACT FROM PUBLISHER]

Since insects are ectothermic, they are highly vulnerable to the sudden increase of temperature. Indeed, it has been hypothesized that the survival, development, fecundity, and even population expansion of insects are all affected significantly by extremely high temperature. We studied the effect of short-term high temperature stress on the survival and development of different stages, adult longevity and fecundity of Ophraella communa (Coleoptera: Chrysomelidae), a biological control agent of the invasive plant, the common ragweed, Ambrosia artemisiifolia (Asterales: Asteraceae) in the laboratory. The results showed that egg, larval, pupal and adult survival rates were significantly affected after 2 hour-short-stress at high temperatures (35 to 47°C) when compared to the 28°C control. With the exceptions of the control and 35°C stress, survival rate of females was significantly higher than that of males after short-stress at any high temperature. Short-term high temperature stress also significantly impacted longevity and fecundity of adult beetles. Except for control, female longevity was significantly longer than male's after short-stress at any high temperature. The survival rates of different stages, and adult longevity and fecundity of the beetle decreased significantly with the increase of short-term stress temperature. Based on the results of the present study, we conclude that the development and population expansion of O. communa may be significantly affected when they are exposed to a high temperature stage in a summer day in the areas invaded by common ragweed, in southern China. [ABSTRACT FROM AUTHOR]

Understanding distribution and diversity of invasive weeds is essential for the development of efficient control measures against it. In the present study, inter-simple sequence repeat (ISSR) markers were used to assess the biogeographic relationships among populations of the invasive Crofton weed (Ageratina adenophora (Spreng.)) during 2004-2006 in China. A total of 100 ISSR primers with di-, tri-, tetra- and penta-nucleotide repeats were screened, from which 20 polymorphic and informative primers were selected. Amplification of the 20 primers generated a total of 479 polymorphic bands among the 64 weed populations, and a high level of genetic diversity (HE = 0.1541 ± 0.0193) was detected in A. adenophora. Neighbor-joining (NJ) cluster analysis based on genetic distances among populations grouped the populations according to their geographical origin, i.e. (1) populations of southwestern Guizhou, (2) populations of Liangshan city in Sichuan, (3) populations of western Guizhou, (4) Guangxi populations plus Chongqing populations, (5) populations of southern Yunnan, and (6) populations of Yangtze River Valleys in Sichuan plus populations of western Yunnan. A significant positive correlation between geographical and genetic distance was detected by the Mantel test (r = 0.183, p = 0.0012). Based on the divergence relationships revealed by ISSR markers, it was assumed that A. adenophora mainly dispersed through wind and water in China. [ABSTRACT FROM AUTHOR]

Ambrosia artemisiifoliaL. is native to North America, and was unintentionally introduced into China in the 1930s, where it has become invasive. The two insect speciesEpiblema strenuanaandOphraella communahave been considered as biological control agents ofA. artemisiifoliain China. The purpose of this study was to examine the control effect ofO. communa+E. strenuanaonA. artemisiifoliain the field. The mortality ofA. artemisiifoliaplants increased with time and increasing initial release densities ofO. communaand/orE. strenuanain 2008 and 2009. The treatments of 0.53O. communa+ 0.53E. strenuanaper plant and 12O. communa+ 16E. strenuanaper plant at early (60–70 cm tall) and later (90–100 cm tall) growth stages could subsequently kill all plants prior to seed production in both 2008 and 2009. Thus, the two initial densities of the two insect species may be recommended when they are jointly used for biological control ofA. artemisiifoliaat the two growth stages. However, all or some plants could survive and bear seeds in any other treatment and in the non-treated control plots. This implies that biological control ofA. artemisiifoliawith the two biological control agents will be recommended in the areas invaded byA. artemisiifoliain China. [ABSTRACT FROM AUTHOR]

Highlights: [•] China has the largest area in the world under greenhouse vegetable. [•] Whiteflies, aphids, spider mites and thrips cause 18% production loss. [•] 14 Natural enemies used against 8 pests in 8 crops between 1988 and 2007. [•] More than 40 species of predators and parasitoids have been applied in greenhouse. [•] The importance of using native species rather than non-native agents is increasing. [ABSTRACT FROM AUTHOR]