Effects of cutting Phragmites australis on the density of the scale insect Nipponaclerda biwakoensis Kuwana and multiparasitism relationships of its five parasitoids
Author of the article:MA Hua1, 2** , PAN Hui2, WU Jie2*** , LI Kai1***, SUN Ying3 , CHEN Xiu-Zhi3
Author's Workplace：(1. School of Life Science, East China of Normal University, Shanghai 200241, China; 2. Shanghai Entomological Museum,Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Science, Chinese Academy of Sciences, Shanghai 200032, China; 3. Shanghai Jiuduansha Wetland National Nature Reserve Administration, Shanghai 200135, China
Key Words：Phragmites australis cutting, Nipponaclerda biwakoensis, parasitoids, parasitism rate, multiparasitism
Abstract：
[Objectives] The aim of this paper is to investigate the effects of reed cutting on the density of the scale insect Nipponaclerda biwakoensis and the parasitism rates and multiparasitism relationships between the five parasitoids that parasitize it. [Methods] Sixteen experimental plots in an uncut Phragmites australis (Cav.) Trin. ex Steudel community and twenty plots in a cut P. australis community on ShangshaIslandin the Jiuduansha wetland nature reserve,Shanghai, were repeatedly sampled in July and September of 2011. Differences in the scale insect density, parasitism rates, multiparasitism relationships and female ratios of the five parasitoids between the cut (C) and uncut (UC) plots were statistically compared. [Results] Reed cutting significantly decreased scale insect density (P<0.001); the total parasitism rate of the five parasitoids significantly increased from July to September. The total parasitism rate was not significantly different between C and UC plots in July (P>0.05), but was significantly higher in C than in UC plots in September (P<0.001). The total parasitism rate of the five parasitoids was not significantly related to scale insect density. Responses of the five parasitoids to reed cutting were different and varied with sampling season. In July, the parasitism rate of Aprotocetus sp. was higher than that of all other parasitoids, and was significantly higher in C than in UC plots (P<0.05) when the parasitism rates of other parasitoids were low. In September, the parasitism rate of Aprotocetus sp. decreased, while the parasitism rates of other parasitoids increased. Except for the Encyrtidae sp., the parasitism rates of other parasitoids were significantly different between UC and C plots (P<0.001). Reed cutting significantly increased the multiparasitism rate of Boucekiella depressa and Astymachus japonicus (P<0.001), and decreased the multiparasitism rate of B. depressa and Aprotocetus sp. (P<0.001). Except for Aprotocetus sp. (P<0.05), reed cutting had no significant effects on the female ratios of other parasitoids. [Conclusion] Responses of five parasitoids to reed cutting not only depend on scale insect density but also to their own biological characteristics such dispersal and competitive ability. Therefore, reed cutting can affect interactions between parasitoids and N. biwakoensis through many different mechanisms.