| The brown planthopper, Nilaparvata lugens Stal (Hemiptera:Delphacidae), belongs to a category of insect pests whose resurgence has been induced by pesticides. The pesticide-induced resurgence of N. lugens has been attributed to the destruction of natural enemies and the stimulation of reproduction. Extreme temperatures are thought to be one of the main factors suppressing natural population growth of the brown planthopper. In contrast, sublethal doses of some pesticides stimulate reproduction of adult males and females of N. lugens. However, the combined effects of high or low temperature and sublethal doses of pesticides on the reproduction of adult males or females have not been investigated. Accordingly, the further research the on changes of protein levels in both male accessory glands (MAGs) and female ovaries induced by the insecticides with different temperatures as well as the stimulating effect of treated-males on the fecundity of adult female via mating, the combined effects of temperature and insecticide on the development and reproduction of adult males and adult females will be valuable for understanding the ecological mechanisms of the N. lugens resurgence.This study examined the effect of sublethal doses of triazophos (one of the insecticides that typically induce resurgence) or indoxacarb under different temperatures, i.e., high, low and suitable temperatures, on the development and the reproduction of adult males and adult females of N. lugens. Experimental results are as follows:1The combined effects of temperature and insecticide on the protein content of male accessory glands (MAGs) and of adult female ovaries and the transference effect on the fecundity of adult femalesThis study examined the effects of temperature and the insecticide triazophos on the protein content of male accessory glands (MAGs) and adult female ovaries and on the fecundity of adult females. The study demonstrated that temperature and triazophos concentration significantly influence the protein content of MAGs and of female ovaries before and after mating. The protein content in MAGs before mating attained a maximum value at26℃(45.1μg per adult male, grand mean of all concentrations), followed by an intermediate value of38.0μg at20℃and a minimum value of10.4μg at34℃.These results indicate that the reproduction of males is more sensitive to high temperature compared to females. Protein content in MAGs after mating at26℃remained at a maximum value (25.6μg per adult male, grand mean of all concentrations), followed by21.9μg at20℃and a minimum value of8.3μg at34℃.The protein content of MAGs decreased with increasing triazophos concentration at three temperatures.This result indicates that treated males transferred more MAG protein to adult females through mating. For example, MAG protein after mating at26℃for0,10,20,40and80mg/L triazophos treatments decreased by16.5,39.2,42.8,53.5and58.2%, respectively, compared with the corresponding values before mating. The protein content of female ovaries both before and after mating at three temperatures for all concentrations was significantly higher than in the control. However, the increase of ovary protein (percent) both before and after mating for all concentrations attained its maximum value at34℃, an intermediate value at26℃, and its minimum value at20℃, compared with the control. Similarly, percent increases in the number of eggs laid for10,20,40and80mg/L triazophos treatments at34℃and20℃(except for80mg/L) were greater than those at26℃. These results indicate that triazophos treatment enhanced the resistance of the insect to high-temperature stress. The findings of this study provide a scientific basis for understanding the resurgence of N. lugens populations.2Effects of variable high temperature and insecticides on development and fecundity of N.lugensNatural population growth of N. lugens is influenced by temperature, especially, high temperature significantly suppressed population growth. In addition, insecticides are frequently applied at high temperature season (from July to August) in rice-producing regions of the middle and lower reaches of the Yangtze River. It has been demonstrated that some insecticides stimulate the reproduction of N. lugens. Here, there is a scientific issue to be answered, i.e, how effect of insecticide application on N. lugens outbreak at high temperature season. The present study examined life parameters of experimental population of N. lugens treated with two insecticides triazophos and indoxacarb under two group temperatures (variable temperature and constant temperature). Statistical analysis showed that temperature, insecticides and insecticide concentrations significantly influenced survival rate of nymphs, mating rate of adults, lifespan of adult females and the number of eggs laid. Insecticide treatments are more beneficial to survival and reproduction of N. lugens under variable temperature compared to constant temperature. For example, All nymphs and adults treated with the two insecticides under constant temperature38℃can not survive. However, survival rate of the nymphs and fecundity of adult females treated with the two insecticides under variable temperature38℃were still higher, for example, the number of eggs laid by adult females treated with10,20,40and80mg/L triazophos was163.2,171.8,208.8and173, increasing by45.7,53.4,86.4and54.5%, respectively compared to control (untreated); the number of eggs laid by adult females treated with7.5,15,30and60mg/L indoxacarb was223,200.2,184.2and109.4and was significantly higher than control (except for60mg/L), increasing by99.1,78.8and64.5%, respectively, compared to control. In addition, all eggs at constant temperature38℃did not hatch, but hatchability at variable temperature38℃was over50%. For constant temperature35℃and variable temperature35℃, survival rate, fecundity and hatchability showed a similar outcome. The present findings demonstrated that insecticide-treated N. lugens at variable high temperature was more beneficial to its population growth. In the other words, the pesticide application in high temperature season may result in the occurrence of N. lugens resurgence. |
PDF Full Text Request