中华稻蝗长沙种群的生活史及其卵滞育的进化意义

中华稻蝗Oxya chinensis为重要的水稻害虫,在我国除青海、西藏、新疆、内蒙古等未见报道外,南起海南北至东北均有分布,在许多的分布区域1年发生1代。为探索中华稻蝗长沙种群的生活史及其季节适应特征,通过野外和实验室的研究,调查了其发生代数、孵化率和卵滞育率的季节变化及越冬卵的存活率。结果显示,中华稻蝗长沙种群为1年2代和1年1代混合发生:第1代卵产卵后大部分孵化为若虫而1年完成2代,但亦有19.4% -4.1%的卵不孵化而1年只能完成1世代。第1代成虫于6月上旬至8月上旬羽化,6月下旬至8月中旬产卵;第2代若虫于7月初开始孵化,9-10月羽化为成虫,10月上旬至11月下旬产卵。在室外自然条件下,中华稻蝗长沙种群6-8月(第1代)和10-11月(第2代)所产卵块均为部分滞育,滞育率为30%左右,皆无显著差异。然而,其卵滞育率在12月以后显著降低,仅为6.6%或以下,卵滞育快速地得以解除。因此,包括非滞育卵和滞育解除卵,中华稻蝗长沙种群的越冬卵皆以非滞育状态度过其后的寒冷季节。即使是遭遇长江流域2007年末至 2008年初异常寒冷的冬季,在长沙地区越冬后其卵的存活率亦在98%以上。非滞育状态的中华稻蝗长沙种群越冬卵完全能安全地越冬,其滞育的发生并非是为了提高其耐寒性而安全度过不适环境。并探讨了中华稻蝗长沙种群卵滞育的进化意义。

Life history and the evolutionary significance of egg diapause in Changsha population of the rice grasshopper, Oxya chinensis (Orthoptera: Catantopidae)

The Chinese rice grasshopper, Oxya chinensis Thunberg (Orthoptera: Catantopidae), is an important pest in rice paddy fields, and is widely distributed throughout China except for the cold and dry northwestern provinces and autonomous regions of Qinghai, Tibet, Xinjiang, and Inner Mongolia. It is known to be univoltine in northern China and bivoltine in southern China, and it shows a complex pattern of latitudinal variation in diapause induction. Eggs of both the northern and southern populations of O. chinensis enter diapause and overwinter. The incidence of diapause is genetically determined in the northern populations and regulated by maternal photoperiod and incubation temperature in the southern populations. In populations at intermediate latitudes, diapause is only affected by the incubation temperature of eggs. To understand the life cycle and seasonally adaptive traits of O. chinensis in a Changsha population (28.2°N, 113.0°E), we investigated the number of generations per year, seasonal variation in egg hatching and diapause rate, and survival of overwintering eggs in the field and laboratory. The results indicated that the Changsha population of O. chinensis showed a uni-bivoltine mixed life cycle with non-diapause and diapause eggs in the first generation. Non-diapause eggs subsequently hatched and completed two generations per year. Diapause eggs overwintered and completed only one generation per year. Adults of the first generation appeared from early June to early August and oviposited from late June to mid-August. Nymphs of the second generation started appearing in early July and emerged as adults from September to October, with most individuals finishing oviposition by late November. In the field, eggpods obtained from June to August (the first generation) or from October to November (the second generation) were all enter diapause partially in this Changsha population of O. chinensis. The diapause rate was about 30% and it did not significantly differ among different months. However, the diapause rate of eggs exposed to field conditions significantly decreased after December, to only 6.6% at most, indicating that the eggs had terminated their diapause spontaneously because of the low temperatures before the end of winter. Thus, both non\\diapause and diapause O. chinensis eggs overwintered in a non-diapause state through the subsequent cold season in Changsha. Freezing rain swept across large areas south of Yangtze River from the end of 2007 to early 2008 and the winter was unusually cold at our experimental site. However, the survival rate of overwintered eggs was more than 98%, as assessed in the following spring. These results reveal that non-diapause eggs are able to safely overwinter, and diapause does not seem to be an adaptation to improve the cold tolerance of eggs in the Changsha population of O. chinensis. Additionally, this paper also discusses the evolutionary significance of egg diapause in Changsha population of O. chinensis.