Effect of GCSC-BtA biocide on abundance and diversity of some cabbage pests as well as their natural enemies in southeastern China.
The effect of Germany-China Scientific Cooperation-Bacillus thuringiensis-Abamectin (GCSC-BtA) biocide on abundance and diversity of some important cabbage pests, i.e., Plutella xylostella, Pieris rapae, Brevicoryne brassicae, Liriomyza sativae, Phyllotreta vittata, as well as their natural enemies, i.e., Apanteles plutellae [Cotesia plutellae], Erigonidium graminicola [Hylyphantes graminicola], Coccinella septempunctata, were determined in comparison to that of methomyl insecticide in cabbage fields in Fuzhou region of the southeastern China in 2001. GCSC-BtA biocide showed high efficacy in reducing abundance of all the tested pest species while very low harmfulness to their natural enemies. GCSC-BtA treatment resulted in significantly lower abundance of all the pests with 10.32, 6.10, 2.11, 8.68 and 1.02% of Plutella xylostella, Pieris rapae, Brevicoryne brassicae, L. sativae and Phyllotreta vittata, compared to methomyl treatment with 26.68, 26.33, 25.18, 33.89, 32.08% or the control with 62.99, 67.55, 71.74, 57.42, 46.41%, respectively. On the other hand, abundance of all the natural enemies was significantly higher in GCSC-BtA treatments with 40.80, 32.42, 36.52% for E. graminicola, A. plutellae, C. septempunctata, than in methomyl treatment with 9.53, 5.60, 12.87%, respectively. Species evenness of the different cabbage pests was in the range of 0.3302 to 0.8382 and of their enemies from 0.1017 to 0.8499. Both GCSC-BtA and methomyl resulted in higher species evenness of the two main pests P. xylostella as well as B. brassicae with values of 0.5231, 0.5221 and 0.4938, 0.5179 compared with 0.4611, as well as 0.3302 in the control, respectively, while values for Pieris rapae was higher in the control with 0.8382 than the biocide with 0.5886 or methomyl with 0.6811. Species evenness of L. sativae and Phyllotreta vittata were not significantly different among the treated and non-treated treatments. The biocide gave higher species evenness of the natural enemies than the methomyl or control treatments. The values were 0.7934 for E. graminicola, 0.6442 for A. plutellae and 0.8499 for C. septempunctata in the biocide treatment compared to 0.3241, 0.1017 and 0.4011 in the methomyl and 0.7520, 0.3907 and 0.7775 in the control treatments, respectively. After application, Shannon-Wiener diversity index was higher with a value of 2.4111 with GCSC-BtA treatment than 1.1859 with methomyl or 1.2166 in the control treatment. It can be concluded from this study that GCSC-BtA has high efficacy against cabbage pests and low harmfulness to their natural enemies compared to methomyl.