The Indirect Effect Of Stress From Propylaea Japonica Thunberg And Lysiphlebia Japonica Ashmead On Development, Fecundity And Fitness Of Aphis Gossypii Glover

Natural enemies not only directly influence prey density by predation and parasite but they can also indirectly cause the modification of fitness in their victims by modifying the development and fecundity of their victims. However, little is known about the indirect effect of natural enemies on their preys so far. We examined the response of the development, fecundity and fitness in A. gossypii exposed to P. japonica and L. japonica in two sets of experiments. The results were as follows:1) The indirect effect of stress from P. japonica on the development, fecundity and fitness of A. gossypii.Studies about the effects of stress from P. japonica with different action modes, time and stages on the development, fecundity and fitness of A. gossypii were conducted in laboratory. The results indicated that the intrinsic rate of increase and fitness of A. gossypii enhanced with the action time of stress from P. japonica caged prolonging. The longer the action time was, the shorter the development and mean generation time of A. gossypii was. While the absolutely different results were observed in the experiment of A. gossypii caged in the presence of stress from P. japonica with different action time, only 4-hours action time of stress have a significant influence on the development and mean generation time of A. gossypii caged.Different action stages of stress also played an important role in A. gossypii. The growth rate of A. gossypii obviously more accelerated when their maternal generation was exposed in predation risk of P. japonica than the offspring. Furthermore, the responses of the fresh ones were more susceptive to this stress than the old ones. Consequently, our results clearly demonstrated that the stress of P. japonica could indirectly increase fitness of A. gossypii and their population density, which leads to auto-regulation of A. gossypii population so that they can successfully survive.2) The impacts of stress from L. japonica on the development, fecundity and fitness of the three successive generational A. gossypiiThe second experiment was studied to evaluate adaptation of the development, fecundity and fitness on the three successive generational A. gossypii in response to exposure of L. japonica and caged L. japonica. Compare to the first-three-instars larvae, the 4-instar larvae stressed by L. japonica had the least fecundity and the shortest longevity. There was no significant difference in total and net reproduction of the 1st generational A. gossypii whatever they were threatened by L. japonica or caged L. japonica. However, the successive direct stress evidently produced more offsprings in the second generation of A. gossypii, whereas the indirect stress remarkably produced more numbers of nymphae in the second generation and third generation of A. gossypii. Both direct stress and indirect stress of L japonica didn't influent significantly the mean generation time of the 2nd and 3rd generational A. gossypii, but only their mean generation time of the 1st generational A. gossypii encountered indirect stress was shortened. Therefore, it has been suggested that direct stress from L. japonica have no obvious effects on the intrinsic rate of increase in the three successive A. gossypii, and the indirect stress implicitly promoted the fitness of successive generational A. gossypii. Here, we emphasized on the indirect effect to population dynamics of successive generational A. gossypii.3) The impacts of stress from L. japonica on the development, fecundity and fitness of the three successive generational A. gossypii in elevated CO₂.Furthermore, the effects of elevated CO₂ (375μl / L VS 750μl / L) on the system of cotton - A. gossypii - L. japonica were studied used OTCs. The experiment would be desirable to show that a stronger effect of L. japonica-stress was seen in the first-two-instars A. gossypii in elevated CO₂, which would cause a lower fecundity and longevity. In addition, a notable trade-off interaction among CO₂ levels, generation and L. japonica-stress determined the reproduction, mean generation time and intrinsic rate of increase in cotton aphids. Here, our results suggested that the L. japonica-stress did a more forceful function to the three successive aphids that the caged L. japonica-stress in elevated CO₂, further, induced a lower aphid-population.