棉铃虫蛹期土壤水分对其种群发生的影响

Effects of soil moisture during pupal stage on population development of cotton bollworm, Helicoverpa armigera (Hübner)

1 999～ 2 0 0 0年在室内通过模拟试验研究了棉铃虫蛹期的不同阶段土壤水分状况对其入土化蛹和羽化出土的影响 ,以及对出土成虫的后效应。结果表明不同的土壤相对含水量和不同时间土壤浸水对棉铃虫的入土和化蛹无影响 ,但却能显著影响其羽化和出土。此期土壤干燥 (土壤相对含水量≤ 2 0 % )对棉铃虫的羽化出土十分有利 ,大于 40 %的土壤相对含水量对其羽化出土不利 ,饱和的土壤相对含水量对棉铃虫的影响则是毁灭性的 (羽化出土率≤ 1 0 % ) ;而棉铃虫入土后的第 2天、第 3天和第 1 0天土壤浸水对其羽化出土的影响也很大 ,羽化出土率分别为 1 6.33%、9.2 8%和 2 1 .0 5 %。此外 ,土壤水分状况通过影响棉铃虫的土中虫态而间接影响出土成虫的存活、卵巢发育、交配和产卵 ,乃至下代卵的孵化 ,进而影响下代种群的发生。

Soil moisture during the pupal stage is a key factor of affecting the population dynamics of cotton bollworm, Helicoverpa armigera (Hübner). From 1999 to 2000, indoor experiment was implemented to study the effects of soil moisture on procedures of pupation and eclosion of the cotton bollworm in the soil, as well as the consequent performance of the adults after they came up out of the soil. Based on the pupation behavior and the development duration of the pupae in the soil, the whole period of pupation was divided into seven phases i.e., before entry, the 2nd, 3rd, 5th, 8th, 10th and 12th day after they entered the soil. Six soil moistures were set in the experiment. They were 10%, 20%, 40%, 60%, 80% and 100%. In addition, a soil soaking treatment (making moisture beyond saturation and then vaporizing naturally) was made in the experiment. There were 49 treatments all together and the individuals exposed in the air as the control. 50 larvae (5th or 6th-instar larvae) were tested in each treatment. The results showed that different relative moisture of soil and different time of soil soaking did not affect entry and pupation of the cotton bollworm, but influence the eclosion and excavation significantly. Soil moisture lower than 20% was favorable for the eclosion and excavation of adults, while the soil moisture higher than 40% was unfavorable, saturated soil moisture was detrimental for adults (rate of eclosion and excavation was less than 10%). Moreover, the experiment of soil soaking indicated that the emergence rates of the adults were greatly reduced. If the pupae on phase of 2nd, 3rd and 10th day were exposed to the soaked soil, the emergence rate of moths was only 16.3%, 9.3% and 21.1%, respectively. In addition to above direct effects, soil moisture during the pupal stage also played a very important indirect role on the survival,ovary development,mating and oviposition of adults of the cotton bollworm after they came up out of soil, and even on egg hatching and other biologcal procedures of the next generation. Based on a set of analysis of the effects of soil moisture on different biological procedures of the cotton bollworm, four conclusions were derived. (1) The survival rate of the adults decreased apparently when the pupae that remained in the soil for 3 to 8 days exposed to relative moisture of ≥40%. Similarly, the survival rate was also influenced negatively if any phase of pupae exposed to soaked soil. (2) The ovarian development was significantly delayed and the mortality rate of female adults increased before oviposition peak, if the relative moisture of the soil was above 60% or the soil was soaked during any phase of pupae. (3) The mating ability of moths decreased if the relative moisture of soil was over 40% during the 3rd to 10th day or over 60% on the 2nd and 12th day. However, the ability of mating reduced only if the relative moisture of soil arrived to 100% before the old larvae entered the soil. (4) The fecundity of the adult decreased when the relative moisture of soil was ≥20% before entry and after they entered soil for 2 and 3 days or ≥10% for 5 days. Similarly, the hatching rate of offspring eggs obviously decreased when the relative moisture of soil was ≥10% on the 8th day or ≥ 60% on the 3rd day after entry. In addition, hatching rate of eggs was significantly reduced by soil soaking on the 3rd and 10th day after they entered the soil.