Structure des caboxines: Alcaloïdes oxindoliques du Cabucala fasciculata

The structures of three new 11-monomethoxy pentacyclic oxindole alkaloids have been elucidated by chemical correlations with reserpinine: caboxine-A was assigned to the allo C₁₉-méthyl α series: 3S, 4R, 7S, 19S; isocaboxine-A and B to the epi-allo C₁₉-methyl α series and have, respectively, the following configurations 3R, 4S, 7S, 19S and 3R, 4S, 7R, 19S.     

Density dependence of Anaphes sordidatus (Hymenoptera: Mymaridae) parasitism on eggs of Listronotus oregonensis (Coleoptera: Curculionidae)

Listronotus oregonensis (LeConte) (Coleoptera: Curculionidae) oviposits in carrot leaves and the larvae feed in carrot roots. Its eggs are parasitized by Anaphes sordidatus (Girault) (Hymenoptera: Mymaridae) throughout its oviposition period. This parasitoid is the major biotic mortality factor for L. oregonensis. Parasitism by A. sordidatus was studied for three years in sequentially sown plots of carrots, Daucus carota var. sativa. Over the scason, significantly fewer L. oregonensis eggs were oviposited in later sown carrots than in earlier sown carrots because oviposition started later in late sown plots of carrots. A positive temporal density-dependent relationship was observed each year between parasitism rates and host densities. This positive density dependence occurred in early and mid-summer for earlysown carrots where host density reached 1–2 host eggs per plant but disappeared in late summer when host density decreased while parasitism remained high. Latesown carrots had low host egg density (0.2 host egg per plant) and contributed little to the total number of eggs. In these late sown plots, parasitism increased rapidly to over 80% but no density dependence was observed. Spatially, few statistically significant regressions were found but all indicated a positive spatial density-dependence. Most non-significant regressions occurred because the range of egg density was too small between plots for a given date.     

A spatial panel statistical analysis on cultivated land conversion and chinese economic growth

The conflict between cultivated land protection and economic development has become increasingly acute in recent years. Despite, intensive researches made on this conflict, little attention has been paid to the spatial correlation of variables. In view of this, the paper introduces the spatial panel regression model to estimate, and test whether the relationship between economic growth and cultivated land conversion conforms to Kuznets curve. Research results show that the area of converted cultivated land in China exhibits strong spatial auto-correlation; the spatial panel model with time effect and fixed effect is more stable and significant than conventional panel mode, and that the relationship between economic growth and cultivated land conversion agrees with the inverted U-shape of Kuznets curve, with inflection point occurring when average per capita GDP reaches ¥31330.93 (calculated at comparable price of 1999). On the basis of analysis, it is suggested that the government, with a view to developing economy alongside protecting cultivated land, should attach more importance to land use and planning in the future, pay more attention to the spatial correlation of cultivated land planning in adjacent areas and make greater efforts to increase the input–output ratio of land.