| Tea aphid (Toxoptera aurantii Boyer) is one of the serious pests in our country and other neighboring tea-producing countries, like Vietnam and Burma. It pierces and sucks young tea shoots, and excretes honeydew infesting Neocapnadium theae Kara. Again it has a strong migrating habit. In order to find some useful method in the uncontaminated management of tea aphid, we made a continuous survey on the population dynamics of tea aphid in spring, and studied the communicating function of semiochemicals in the tritrophic level of tea plant-tea aphid-tea aphid's natural enemies.Tea aphid's population increased sharply from March 29 to April 13. Population peak emerged around April 3. There was a time lag between the natural enemies' population and tea aphid's population. Natural enemies' population peak was found on 8 April.Richness, diversity indices, evenness degree and dominant degree of the natural enemies' community were calculated and analyzed. Species richness of the community changed from 2 to 7. Diversity indices and evenness degree increased in spring, domination degree was high in early spring, then, decreased.Temporal niche width, spatial niche width and the overlap of the two niches of tea aphid and its natural enemies were calculated. Temporal niche width of tea aphid was small. Spiders' temporal niche width was the greatest among all the natural enemies, however, it had the smallest niche overlap with tea aphid. Syrphids' niche overlap with tea aphid was the greatest. No significant difference among Propylaeajapoinca (Thunberg), Lets axyridis (Pallas), Coccinella septempunctata L., Chrysopa septempunctata Wesmeal and C. sinica Tjedea was found. Tea aphid had a small spatial niche width. Spiders had the greatest one among all the natural enemies, while syrphids had the smallest. Lacewings' niche width was also small. Syphids had the greatest niche overlap with tea aphids, beetles' had smaller niche overlap with tea aphid, and spiders and lacewings had the smallest niche overlap with tea aphid.The behavioral reactions of winged tea aphid to 15 various odor sources were" tested in a four-armed olfactometer. Winged Tea aphid had significant olfactory responses to most of the odor sources in the olfactometer. At 10-4ug/ul dose level, those odor sources are: (Z)-3-hexen-l-ol, (Z)-3-hexen-l-ol acetate,Trans-2-hexen-l-yl, (E)-4-hexen-l-ol, Linalool, Aallyl isothiocyanate, Nerolidol, a -caryophyllene, Hexenal, Benzaldehyde, n-octanol, Methyl Salicylate. Those odor sources also have significant effects on tea aphid at 10-2ug/ul dose level. Attracting ability of different ordours varies. New multiple range test found that, among all the odor sources, Methyl Salicylate had the most significant effect on tea aphid at both of the two dose level. It was also found that the effect of Linalool and a -caryophyllene had varied effects at the two dose levels respectively. The linalool affected alatae adversely at the two consistency levels i.e. it attracted tea aphid significantly at 10-4ug/ul, while it affected tea aphid adversely at 10-2ug/ul; a -caryophyllene was found to be more attractive to alatae at 10-2ug/ul than at 10-4ug/ul.Y-shaped olfactometer was used to test taxis of syrphid Sphaerophoria menthastri L. and lacewings to various odor sources. Those odor sources are: (Z)-3-hexen-l-ol, (Z)-3-hexen-l-ol, acetate, (E)-2-hexen-l-ol, Linalool, Trans-2-hexen-l-yl, (E)-4-hexen-l-ol, l,3,6-octatriere-3,7- dimethyl, Geraniol, Aallyl isothiocyanate, Nerol, a -caryophyllene, Hexanal, Benzaldehyde, n-octanol, Methyl Salicylate. Most of them are volatiles from tea aphid infested tea shoots. It was found that syrphids were attracted at 10-4ug/ul dose level to odor sources such as (E)-2-hexen-l-ol, Linalool, Trans-2-hexen-l-yl, l,3,6-octatriere-3,7-dimethyl, Geraniol, Nerol, n-octanol, Methyl Salicylate. At 10-2ug/ul dose level, syrphids had significant taxis towards Hexenal and Benzaldehyde. Y-shaped olfactometer was also used to test taxis of lacewing (Chiysopa septempunctata Wesmeal), one of tea aphid's e... |
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