| Transgenic Bt cotton has effectively controlled Lepidoptera pests such as cotton bollworm Helicoverpa armigera Hubner with reductions in the amount of chemical pesticides used in cotton fields. The status of the pests in cotton fields has changed, and non-target insect Aphis gossypii became the new problem because of its serious damage to cotton plants. In order to effectively control A. gossypii with the nature enemies, we surveyed the species and populations of the main predatory and parasitical enemies to A. gossypii in cotton fields. And we chose the predatory enemy Propylea japonica and parasitical enemy Lysiphlebia japonica of A. gossypii as the research object to study their biology habits and host choice behavior. We also explored volatiles and their proportions of different treatments among the different cotton varieties. The results were as follows.Field survey showed that the number of A. gossypii in three transgenic cotton fields of GK12,33B, SGK321were638,469and588,9.4%,4.9%and5.9%increase respectively compared with the normal cotton fields, but no significant difference. The main predatory enemies of A. gossypii were ladybirds, lacewings, spiders and the main parasitical enemy was L. japonica. The results of field survey showed that there was no significant difference of the populations of the predatory enemies between transgenic cotton fields and conventional cotton ones. The number of L. japonica in transgenic Bt cotton fields GK12and33B were both23, increased significantly by31.6%and20.8%increase compared with their correspoonding controls. The number of L. japonica in transgenic CpTI+Bt cotton fields was17, decreased by4.0%compared with its contrast, but no significant difference. Compared with transgenic Bt cotton GK12and33B, the number of L. japonica in transgenic CpTI+Bt cotton decreased significantly by25.8%and26.7%. The relationship of populations between ladybirds and A. gossypii had significant synchronous follow effect in conventional cotton fields SM3,33, SY321and bivalent transgenic cotton field SGK321, the correlation coefficient were0.7674,0.8310,0.7070and0.6420respectively. In transgenic Bt cotton fields GK12and33B the populations of ladybirds and A gossypii had a week of hysteresis. Lacewings had no significant follow phenomenon to A. gossypii. The control of spiders to A. gossypii had hystereticnature. The correlation coefficient of populations between L. japonica and A. gossypii in SM3, GK12,33,33B, SY321and SGK321cotton fields were0.7044,0.7779,0.9394,0.9154,0.8366and0.8677 respectively with significant differences. This showed. japonica had close synchronization follow effect to A. gossypii. The results of2010were similar to those of2009.Research showed that the number of P.japonica in transgenic cotton fields GK12,33B and SGK321were23,21and18, increase by3.6%,3.5%and2.8%respectively compared with the conventional cotton fields, and no significant difference. The biology habits research showed there were no negative influence on larvae development, survival and sex ratio of P. japonica feeding on A. gossypii in transgenic cotton fields. Compared with the conventional cotton, the number of eggs laid by P. japonica feeding on A. gossypii in bivalent transgenic cotton decreased by34.3%with significant difference. Compared with the conventional cotton, the number of eggs laid by P.japonica feeding on A. gossypii in transgenic Bt cotton GK12and33B increased by133.3%(P<0.01) and42.7%(P<0.05). Compared with the conventional cotton, the hatching of P. japonica feeding on A. gossypii in transgenic cotton decreased by5.9%(P>0.05),4.0%(P>0.05) and11.0%(P<0.05) respectively. Predating numbers of P. japonica each instar larva increased with the density increase of A. gossypii in different cotton varieties. Most of the predating numbers of P. japonica feeding on A. gossypii in transgenic cotton were higher than those in conventional cotton. Predatory functional response of P. japonica each instar larva was consistent with Holling II model pattern. Parasitism preference of each instar larva and adult female of Propylaea japonica to Aphis gossypii feeding on different cotton varieties had no significant difference.The parasitic rate of L. japonica to A. gossypii feeding on transgenic cotton was not significant differencant compared with their control no matter indoor or in field. The eclosion rate of L. japonica adults parasitising in A. gossypii feeding on transgenic cotton increased by8.8%,9.1%and5.7%respectively compared with that on conventional cotton, but no significant difference. The difference of the life time of L. japonica adults from parasitic transgenic cotton and normal cotton were not obvious. The sex ratio of L. japonica was higher than1in cotton field. But indoor the sex ratio of L. japonica tended to1:1. This showed there was no negative influence in parasitism, eclosion, sex ratio of L.japonica and life time of L. japonica female.L. japonica can’t indentify healthy transgenic cotton and normal cotton. L.japonica tended to choose transgenic cotton for the damaged cotton without host and there was significant difference between transgenic cotton and normal cotton. In the treatment of damaged cotton with A. gossypii larvae, transgenic Bt cotton GK12had the same attraction compared with its contrast to L. japonica, transgenic Bt cotton33B and transgenic CpTI+Bt cotton SGK321had more attractive than the normal cottons. In this research we collected18volatiles of6cotton varieties with different treatments by solid phase microextraction (SPME), including10kinds of terpenes,4kinds of aldehyde,2kinds of alcohols,1kind of acetates and1kind of alkanes. The volatiles of transgenic cotton were similar to those of the conventional cottons under the same treatment, and there were some differences among the three treatments of healthy cotton, damaged cotton with A. gossypii larvae and damaged cotton without A. gossypii larvae and different cotton varieties. In transgenic Bt cotton GK12the relative content of α-pinene,β-pinene and limonene were higher than those in the contrasts but the relative content of β-myrcene and β-ocimene were lower than the contrasts among three treatments. The relative content of α-pinene ware significantly higher than the contrasts in three treatments of transgenic Bt cotton33B. In transgenic Bt cotton33B the content of limonene was significantly increased after A. gossypii damaged, and there was difference of the healthy cotton between the transgenic Bt cotton33B and its contrast. The relative content of α-pinene ware significantly higher than the contrasts in three treatments of transgenic CpTI+Bt cotton SGK321. The content of limonene,3,7-dimethyl,1,3,6-octatriene and (Z)-3-hexen-1-ol, acetate were significantly increased after A. gossypii damaged. In the three treatments of33B and SGK321the relative content of β-myrcene were decreased significantly. |
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