Fluctuating asymmetry of Helicoverpa armigera (Hübner) in field populations with different levels of exposure to Bt-transgenic cotton
不同Bt棉种植年代棉铃虫种群的波动性不对称

Organisms are subject to three types of morphological asymmetry: Directional asymmetry, Antisymmetry and Fluctuating asymmetry, but only the latter is related to the environmental stress acting upon individuals during their developmental. Fluctuating asymmetry (FA), small random differences between left and right, with a low level of heritability, has been widely used as a measure of developmental stability. In this study, we test the levels of FA in populations of cotton bollworn (Helicoverpa armigera, CB) exposed to different stress levels of Bt-transgenic cotton. In 2002, thirteen field populations of CB moth were collected in light traps from four provinces in northern China, where transgenic Bt-cotton had been planted for one to five years. FA of the hind femurs of the light trap catches in response to the stress of Bt cotton was estimated. The results show that twelve of the field populations demonstrated FA, and that there was a tendency for the level of FA to decrease as the period over which Bt-cotton had been grown increased. Pearson's correlation coefficient weighted between levels of FA and history of Bt-cotton growing was -0.77, with this coefficient being highly significant. This trend means that the adaptation of field populations of CB to Bt cotton will increase with increasing exposure to Bt-cotton. The feasibility of FA as an indicator for monitoring the appearance of CB resistance to Bt-cotton is discussed.