Survival Tests on Submerged Green Rice Leafhopper : Nephotettix cincticeps UHLER, in Relation to Winter Mortality under Snow Cover in the Hokuriku District

概要

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In the Hokuriku district, there is heavy snow cover of more than 2 m, but air temperature remains usually above 0°C. The surface of fallow paddy fields is covered with water of 0°C under snow cover conditions. The overwintering nymphs of Nephotettix cincticeps UHLER are forced to submerge in the water. Laboratory experiments were conducted to clarify the factors affecting the mortality of nymphs under submerged conditions. The nymphs showed tolerance for starvation at 0°C, surviving for more thant 60 days under no food conditions. The 95% lethal periods for nymphs were 40.8 and 56.1 days when submerged in stationary and running water, respectively, at 0°C. The oxygen consumption of overwintering nymphs was minimal at 0°C, being 1/22 that of nondiapausing nymphs at 25°C. When the water was running and the melted oxygen concentration was high, the longevity of overwintering nymphs in water lengthened. These results suggested that the running water accelerated the exchange of the melted oxygen between water and around the surface of nymphs which could utilize the melted oxyegn for respiration. But they could not survive for more than 60 days under submerged conditions. Thus, the duration of continuous snow cover is one of the most important factors in determining the population density during the winter in the Hokuriku district.
日本応用動物昆虫学会の論文