Effects Of Elevated Nocturnal Temperature On Experimental Population Of Cereal Aphids

The effects of global warming on insects have been widely concerned. Insects as ectotherms are widespread distribution and large abundance. The effects of climate warming on insects have become significant issues in recent years. We can predict future population development of insects by studying the relationships between temperature change and insects. Previous studies on the influence of climate warming on insects mainly focused on the impact of daily mean or maximum temperature increase on insect population, by using man-made climatic chambers to simulate warming. However, little attention was paid to the most important factor i.e. nocturnal temperature increase that played the most significant role in climate warming. In this study, by setting24-h temperature cycle and simulating the natural temperature change, we investigated:(1) the effects of different nocturnal minimum temperature on development, survival, reproduction, life-span and population parameters of Sitobion avena;(2) the differences of ecological traits among the three aphid species i.e. S. avena, Schizaphis graminum and Rhopalosiphum padi under different nocturnal temperatures;(3) the differences of ecological parameters in different generations under different nocturnal temperatures. The objective of this study is to reveal the effects of nocturnal warming on populations of cereal aphids at the ecological level. Main conclusions were as followed:The ecological parameters of S. avenae were maximized at the nocturnal minimum temperature of16or19℃, and then gradually decreased, indicating that aphid populations were adversely affected by relative higher nocturnal temperatures. The lowest temperature at night were assigned as:13、16、19、22and25℃, the developmental time and survival rate of pre-adult aphids and were increased then reduced with the increasing of lowest temperature. Reproductive quantity and lifetime are maximum at16℃of the lowest temperature, and then reduced with the raise of the lowest temperature at night, which showed that, the development and survival rate could be restrained seriously by the increased temperature at night, parameter of population on the innate capacity, fecundity and population doubling time displayed trend of advantageousness firstly and disadvantageousness secondly with changes of temperature at night, which showed.xorbitant lowest temperature at night leaded to negative effects to development of S. avena population.When nocturnal minimum temperature was increased from16℃to22℃, R. padi had higher developmental rate, reproduction, longevity and intrinsic rate of increase than other species, suggesting a stronger ability to nocturnal warming in R. padi. The reaction of three aphids exposed to16and22℃indicated that:the development of R. padi and S. graminum was faster at22℃than16℃. The opposite was ture for S. avenae. The survival rate of R. padi (60%) was highest at16℃; the low survival rate (3%-10%) was found in all the three aphids when the temperature increased to22℃. The differences of fecundity and longevity of adult among three aphids were significant with the increase of lowest temperature at night. The fecundity of R. padi (31.84±3.99/female) was the largest followed by S. graminum (9.56±4.49/female), and finally, that of S. avenae was the smallest (9.56±4.49/female). The longevity of R. padi was higher than the other two aphids obviously, which was identical with the rule of fecundity. On the whole, the negative effect on grain aphids would be developed by the condition of high lowest temperature at night and less daily range. Among three grain aphids, R. padi had the strongest capacity of adaption to the changing temperature.The effects of nocturnal warming on aphid population showed differences between generations. The second generation grew faster and survived for longer, indicating an adaptation of the aphids to nocturnal warming. There was significant difference among the mean generation time and mean adult longevity of aphids at13,19and25℃..The longevity of pre-adult in the second generation (7.14d) was shorter obviously than that of the first generation (8.71d), but that of adult had the reverse conclusion. The net reproductive rate of second generation was higher than that of the first generation. In addition, the survival rate of nymph of R. padi offspring was higher than the parental generation, which may be attributed to the adaption to the environmental stress.