Insecticides-induced Life Table Parameters Of Nilaparvata Lugens Populations And Effects Of Low Temperatures On Development And Fecundity Of N.lugens

The brown planthopper, Nilaparvata lugens (St?l)is a serious pest of rice in Asia, which threats to rice production. The present study investigated life table parameters of the population of resistance to imidacloprid and susceptible population of N. lugens which exposed to sublethal doses of delmethrin and triazophos under laboratory condition using method of life table. The objective was to examine the mechanism of insecticide-induced resurgence of N. lugens. In addition, we also investigated effect of low temperature on developmental duration of egg, nymph and adult, and on fecundity of female. Results are as follows:1. Life tables of experimental population of N. lugens exposed to sublethal doses of deltamethrin and triazophos were constructed on two rice varieties, Xieyou 963 and Shenyou 1, and fitness of resistant and susceptible populations were compared. The results showed that life parameters of resistant and susceptible populations varied with rice variety, insecticide type and insecticide concentration. Range of population trend index(I)for resistant population was 13.1 to 484.3, that for susceptible population was 5.7 to 428.2. Relative fitness of resistant population for 6 of 28 treatment combinations were significantly higher than those of susceptible populations, relative fitness between two populations for other treatment combinations did show significant differences, indicating that the resistant population showed reproduction advantage under suitable environmental conditions.2. The present study also investigated developmental rate and fecundity of N. lugens under low temperature(s25, 22, 19, 16 and 13℃)and constructed mathematical models of developmental rate and active thermal accumulation. Results showed that there was a significant difference on developmental durations of different instars and adults under different temperatures. For a given instar, developmental duration increased with decline of temperature. The relationship between emperature and mean developmental durations of nymphs could be fitted to regression equations as follows: Y = 71.997-2.1603 X, R2 = 0.93, where X is temperature(℃), Y is developmental duration(day). At the same temperature, developmental durations of 1st and 5th instars were maximal values, in contrast, those of 3rd and 4th instars were minimual values. Longevity of adult female was longer than that of adult male under different temperatures. Developmental thresholds temperature and thermal accumulations(day degree)of 1st , 2nd , 3rd , 4th , 5th instars and nymph stage were 10.06, 11.89, 10.1, 10.9, 10.02 and 9.99℃, and 101.01,35.07,48.64,43.07,80.65 and 323.58 day degree, respectively.