Ecological Mechanism Of Effects Of High Temperature Patterns On Laboratory Population Of Cereal Aphid

Temperature is one of the most important factors to influence development, reproduction and survival. The results from experiments at constant temperatures showed that the temperature over 27.5℃have detrimental effects on cereal aphids. However, the tested cereal aphids were forced to live under uniform temperature conditions in most experiments for studying effects of constant high temperatures on aphids. Results from those experiments cannot demonstrate how fluctuant temperatures influence the population development of aphids. We designed a set of experiments simulating the fluctuant high temperatures in the field to reveal the effects of daily maximum temperature, high temperature pattern and interval time between heat pulses on population dynamics of cereal aphids. We also studied the trend of acetylcholinesterase activity (AChE) and trehalose level of Sitobion avenae. The results are potentially useful for improving prediction accuracy and innovating new control strategies of cereal aphids. The main rests were displayed as follows:1 Degree-day model was inapplicable under high temperatures patterns. When population of Sitobion avenae, Rhopalosiphum padi and Schizaphis graminum were tested in the fluctuant high temperature patterns with daily maximum temperature between 35℃and 39℃, the developmental time of these aphids was longer than those that calculated with degree-day model. It indicates that degree-day model is inapplicable under high temperatures.2 Effects of high temperature patterns with the same temperature accumulation on cereal aphids was confirmed. The level of longevity, fecundity and survival of nymph of Sitobion avenae, R. padi and S.graminum are significantly decreased as maximum temperature increased.3 Effects of high temperature pluses with different maximum temperature on cereal aphids were confirmed. When population of Sitobion avenae, R.padi and S.graminum were in the temperature mode which the maximum temperature was above 36℃, the longevity, fecundity and survival of nymph significantly decreased as maximum temperature increased. 36℃may be the critical high temperature of these aphids.4 Effects of high temperature patterns with different interval time on cereal aphids were confirmed. The developmental time of Sitobion avenae and R. padi was shortest under the pattern with one heat pulse per 3 days. The period of heat pulse have no significant influence on the longevity and survival of nymph of Sitobion avenae and R. padi when the daily maximum temperature was 36℃. When the population of R. padi is under the pattern with one heat pulse per 3 days, the data of fecundity per female is the largest. No nymph of S.graminum could grow to adult under the pattern with one heat pulse per 3 days.5 The trends of the acetylcholinesterase (AChE) activity and trehalose level of Sitobion avenae according to the high temperature degree were confirmed. The AChE activity of Sitobion avenae was affected by the high temperature. The regression curve of the two accorded with "Lorentzian" function. The regression curve of trehalose level and high temperature accorded with quadratic function. The AChE activity and trehalose level reached the maximum at 36℃.