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The Effects Of Bt Toxin (Cotton) On Sex Pheromone Communication System Of Helicoverpa Armigera (Hübner)

Posted on:2006-03-23Degree:MasterType:Thesis
Country:ChinaCandidate:L F MuFull Text:PDF
GTID:2133360152993945Subject:Agricultural Entomology and Pest Control
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Transgenic Bt cotton (Bt cotton) has been effectively used in many cotton-producing countries to prevent economic injury by H. armigera in fields in recent years. However, the most common used Bt cotton varieties now all over the world still have two serious problems: 1) the decreasing in resistance of the Bt cotton to H. armigera on later cotton development stage, when the 3rd and 4th generation bollworm occur in China, which made it needed to carry on the essential chemical spraying; 2) the resistance risk of H. armigera to the Bt cotton which threat the sustainable use of the Bt cotton as an effective means of cotton bollworm control. Our objectives of this study are aimed to elucidate 1) the effects of sublethal treatment of the cotton bollworm larvae (from 3-instar to pupation) with Cry 1 Ac toxin (same as that in Bt cotton) on the sex pheromone communication system, and 2) the variation of this communication system in resistant cotton bollworm strain to the susceptible one.The major results for the first part of the researches are:1. The calling behavior of female survivors from the artificial diet containing sublethal dose of Bt toxin is suppressed. The calling percent, the mean onset time of calling and the mean time spent calling of survivors are all decreased over the first to seven scotophases, especially significant difference in 3rd and 4th scotophases for the mean onset time of calling (P<0.05) and in all 7 scotophases for the mean time spent calling (P<0.01). In the 3rd and 4th scotophases, the mean onset time of calling of female survivors is 3.25±0.93 and 4.07±0.91 hr after the initiation of scotophase, whereas that of control is 2. 5±0.84 and 3.45±0.97hr, respectively. In all 7 scotophases, the mean time spent calling of female survivors are 1. 8±0.61, 3.1±0.56, 4.25±1.04, 3.53±0.74, 2.43±0.76, 2.05±0.74 and1.12±0.36hr; whereas that of control are 3.15±0.73, 4.25±0.70, 5.57±0.89, 4.18±0.92, 3.38±0.81, 2.73±0.80 and 2.25±0.92hr, respectively. However, the calling periodicities (day periodicity and hour periodicity) of both control and treated females are same, with the peak calling time at 8-9 hr after the initiation of 3rd-scotophase.2. The titers of sex pheromones produced by female survivors from the artificial diet containing sublethal dose of Bt toxin are decreased, but not significantly different to thecontrol for Zll-16:Ald. The titers of Zll-16:Ald and Z9-16:Ald females are 47.45±3.91 and 3.76±0.46ng/(?) in control, and 42.88±12.86 and 3.30±0.84 ng/(?) in female survivors, respectively. Similarly, the ratio of Zll-16:Ald to Z9-16:Ald is not significantly different between control (12.70±1.21) and female survivors (12.99±2.17).3. The EAG responses of male survivors to a series dosages of binary sex pheromone mixtures ( 1, 10, 100, 1 000, 10 000 and 100 000ng) increase to 7.31±1.63, 8.84±2.67, 9.73±2.59, 12.72±2.22, 15.47±3.65 and 18.61±3.84mV from 6.30±1.01, 6.42±0.83, 7.15±1.09, 7.91±1.41, 9.77±1.86 and 11.02±2.34mV in control, respectively. When the dosage are 1 000ng and above, the EAG responses between them are significant difference(P<0.01).4. The behavioral response in wind tunnel to sex pheromone lure (300ng) of male survivors is slightly increased than the control males, but there are no significant difference in regard to the percentages of 'taking flight', 'orientation', 'up-wind flight', 'approaching' and 'contacting' behaviors.5. Assortative mating between control and survivor cotton bollworms indicated there is no evidence for assortative mating between them.In the second part of this research, we have carried on a comparative study on the difference of sex pheromone communication systems between Bt cotton-susceptible (S) and Bt cotton-resistant (R) H. armigera The major results as follows:1. The calling behaviors of S and R female are similar not only in the calling periodicities (day periodicity and hour periodicity) with the peak calling time at 8-9 hr after the initiation of 3rd-scotophase, but also in the calling percent, the m...
Keywords/Search Tags:Bt cotton, Helicoverpa armigera, sex pheromone, calling behavior, EAG response, wind tunnel, assortative mating, 'refuge'
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