[Stream ecosystem health assessment based on the measurement of leaf litter breakdown: a case study in Hengshishui River of Guangdong Province].

Based on the Gessner' s model of leaf litter breakdown, the functional integrity and ecosystem health of Hengshishui River in Guangdong Province were assessed, and the breakdown rates of Castanopsis fissa and Schima superba leaf litters at the sites unpolluted and polluted by acid mine drainage were compared. The leaf litters of the two tree species had a significantly lower breakdown rate at polluted than at unpolluted sites (P < 0.05). According the Gessner's model, all polluted sites had an ecosystem health score 0, while all unpolluted sites had a score 2, indicating that the health status of polluted river reaches were severely damaged. The biological assessment of stream ecosystem health was consistent with the results of water quality analysis, indicating that the leaf litter breakdown model was a suitable index of stream status.

[Roles of infochemicals in host-selection process of Anastatus japonicus].

By using a Y-tube olfactometer, this paper studied the selection behavior's responses of Anastatus japonicus to the volatiles and their individual components emitted from isolated leaves and live plants of different litchi varieties, and to Tessaratoma papillosa. The results showed that among the test litchi varieties, Sanyuehong and Huaizhi had more significant attracting effects to A. japonicus than Nuomici, Guiwei, Feizixiao and Heiye. The two main components of the volatiles from litchi leaves, alpha-humulene and beta-caryophyllene, had no distinct attraction to A. japonicus, but displayed synergistic effect on the host-searching process of natural enemy. When the two components were mixed in equal concentration of 0.3 microl x microl(-1), the attracting effect was most remarkable. In a dual-choice experiment, the selectivity of A. japonicus to T. papillosa eggs was not significant, but very remarkable to T. papillosa female adults and to the water extracts from adult abdomen-tip. In a vessel experiment, the numbers of A. japonicus which made selection to T. papillosa eggs and the settling frequency of A. japonicus on the place of T. papillosa eggs were more than those of other treatments. (E)-2-hexenal, one of the most important components of the volatiles of T. papillosa adult, didn't have evident attracting effect on the adults of A. japonicus.