| The migratory locust Locusta migratoria L. is a worldwide pest of agriculture. The cold hardiness strongly influences the population dynamics, dispersal and distribution of the locust. There are intensive studies on the cold hardiness of the locust eggs by Jing xiao-hong (2003) and Wang xian-hui (2004). Moreover, some problems are not yet thoroughly understood. Water is one of the major ecological factors that affect the cold hardiness of the locust, especially under the climate change scenarios. Therefore, the aim of this study is investigating the correlations between the soil water and cold hardiness of the locust eggs. We also studied the cryoprotectants of different geographic populations, trying to disclose the function of cryoprotectants.The capacity of supercooling of the locust eggs increased with the egg's development. 2-day-old eggs incubated at 30℃ in 15% water content soil were more cold hardy than other stages. The water content of the locust eggs also increased with the eggs' development. There was a strong correlations between the supercooling point and the water content (y=0.967ln(x)-23.64 R2=0.9314 p<0.001). The soil water content influences the eggs' water content. The water content of locust eggs increased with the increasing of soil water content. The water content of the eggs increased from 75.14% to 79.65% when the soil water content range from 7% to 23%. The soil water content influences the body water balance, in turn influences the physiology of cold hardiness of the locust. The supercooling point increased with the increasing of the eggs' water content (y = 0.6265x - 70.066 R2 = 0.3237 n=68). Generally, cold hardiness of eggs was inversely related to the egg's water content at low temperature. The mortality of eggs increased with its water content increasing at low temperature. The times for 50% mortality of eggs with lower water content at -5℃ (reared in 7% gross mass moisture soil) was 156.02h. Lethal time50 of the other type eggs (reared in 11%, 15%, 19% and 23% gross mass moisture soil) were 132.10h, 125.98h, 111.49h and 70.66h, respectively. This result was same to the influence of eggs' water content on the supercooling capacity. The mortality of eggs having the same water content chilled at low temperature within different moisture soil for various time were complicated. The trend of mortality of the locust eggs could be divided into two parts. During short-time chilling (<24h) at -5℃ and -10℃, mortality of eggs decreased with the increasing of soil moisture (range from 7% to 23% gross mass water content). Whereas, during long-time chilling (>24h) at -5℃ and -10℃, mortality of eggs increased with the increasing of soil moisture. The mortality of eggs with the same water content in 7%,11%,15%,19% and 23% gross mass water content chilled at -10℃ for 6h was 60.00%, 49.38%, 35.00%, 29.38% and 29.00%, respectively. The mortality decreased with the increasing of soil water content. However, after exposed for 72h, the mortality was 73.75%, 80.00%, 79.38%, 86.88% and 91.88%, respectively. The mortality increased with the increasing of soil water content.Mortality was strongly influenced by the soil's composition, the locust eggs' mortality was higher in the sand than that in the soil. The water potential may be a particular reason (the water potential was lower in soil than that in sand), the lower water content increases the survival of eggs by reducing the volume of ice.Soil salt content could influence the development and cold hardiness of the locust. It restrained the locust eggs' development when the soil salt content overrun 1.2%, and the eggs could not develop when the soil salt content reached 2.4%. The eggs that were reared in the higher salt content soil had stronger cold hardiness than the eggs reared in the lower salt content soil. The reason was likely to be that the higher salt content soil had the higher osmotic pressure than the lower salt content soil. The locust eggs obtain less water from the high osmotic pressure soil, therefore, the eg... |
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