Abstract: A one-year experiment on the prevention of the barnacles on planted Rhizophora stylosa- Griff seedlings with malathion was conducted at Yingluo bay of Guangxi, China. Four pesticide concentrations (1/200, 1/400, 1/600, and 1/800 seawater solution of the original malathion concentration (45%)) and four spraying frequencies (every 3, 7, 14, and 28 days) were installed. The results showed that with increasing pesticide concentration and spraying frequency, the barnacle biomass on the seedlings decreased significantly, and all the treatments had a significantly lower barnacle biomass than the control (P<0.001). The seedlings stem biomass and height did not have definite patterns of responses to the pesticide concentration and spraying frequency. At the same pesticide concentration, spraying it every 28 days gave the lowest root biomass, leaf biomass and leaf area, and the more the spraying frequency, the more the leaves preserved. Also at the same pesticide concentration, spraying it every 28 days gave the highest mortality (11%-22%) of the seedlings, while spraying every 3, 7 and 14 days only gave 0-5% of the mortality. However, the mortality in control group reached 39%. Statistical analysis indicated that the seedlings mortality had a significant positive correlation with barnacle biomass (P<0.001), significant negative correlations with leaf biomass, leaf number, root biomass, and neonatal biomass (P<0.001), but no significant correlations with seedlings stem height, stem biomass, and remained propagule biomass. Spraying malathion decreased the seedlings leaf chlorophyll content, but increased the leaf Chl (a/b) ratios and SOD and POD activities. It was proposed that in case of mangrove forestation on tidal flats at mean sea level, spraying malathion at the concentration of 1/800 and with a frequency of every 14 days could prevent barnacle effectively.

Key words: Chinese cabbage, Plutella xylostella, Volatiles