不同作物田烟粉虱发生的时空动态

2008～2009年连续2年系统调查了番茄、茄子、棉花、大豆、玉米等寄主植物上烟粉虱种群发生的时间与空间动态。结果表明：不同寄主植物上的烟粉虱成虫及其伪蛹数量有显著性差异，其密度大小依次为：茄子>棉花>番茄>大豆>玉米。其中，在玉米上除了发现极少量的成虫逗留外，没有发现烟粉虱的卵及若虫。在发生的时间序列上，烟粉虱成虫及伪蛹的数量呈现为先逐渐上升后又下降的变化过程，发生高峰期集中在8月5日到8月31日，9月初以后烟粉虱数量慢慢减少。在空间分布上，表现为烟粉虱成虫喜食寄主的上部叶片。统计分析显示，寄主对烟粉虱成虫和伪蛹的数量的影响极显著，而年份对其数量的影响没有显著差异。由此得出的烟粉虱发生和达到高峰的时间，可为烟粉虱预测预报和区域性综合治理提供重要理论依据。

Temporal and spatial distribution of Bemisia tabaci on different host plants

Insect pests have long been recognized as a significant threat to agriculture. Bemisia tabaci was described over 100 years ago and has since become one of the most important pests worldwide in subtropical and tropical agriculture as well as in greenhouse production systems. It adapts easily to new host plants and geographical regions and has now been reported from all continents except Antarctica. In the last decade, international transport of plant materials and people has contributed to geographical spread. B. tabaci has been recorded from more than 400 plant species and there may be many additional hosts not yet formally documented. Excessive B. tabaci-induced losses worldwide occur in ?eld, vegetable and ornamental crop production. Several studies have examined B. tabaci populations in cotton, tomato, eggplant and so on, which appear to increase nearly exponentially during the middle part of the growing season. Historically, heavy infestations in cotton fields often resulted in significant dispersal to other field crops and vegetables following termination of the cotton crop. Whiteflies exhibit a degree of holometabolism. They oviposited preferentially in young leaves which are generally located on the apical parts. Ninety percent of B. tabaci adults emerged from their pupal cases between 6:00 am and 9:30 am. Few emerged during hours of darkness. During summer months, copulation takes place within 1- 8 h following eclosion of B. tabaci from the pupal cases. Studies of the population dynamics of whiteflies in natural settings are still lacking. Here we investigated the abundance of B. tabaci on different host plants, including tomato, eggplant, soy, cotton, corn, between 2008 and 2009. The results indicated that the abundance of the adults and pupae of B. tabaci on different hosts was remarkably different. The densities of B. tabaci on different hosts were in decreasing order as follows: eggplant, cotton, tomato, soy and corn. Only a few adults but no eggs and nymphs were found on the corn plants. Moreover, the adults of whiteflies preferred the upper leaves of the host plants. The number of whiteflies first increased gradually, followed by decrease on the five host plants. The highest abundance was observed between 5th and 31th of August. However, no significant difference was found in the abundance of the aduts and pupae between 2008 and 2009. The results presented in this study may provide important theoretical basis for the prediction and regional comprehensive management of B. tabaci and economically efficient control of B. tabaci. In China, there are at least four di?erent genetic groups of B. tabaci such as B biotype, Q biotype and some other local biotypes. Both B biotype and Q biotype of B. tabaci are the most important invasive biotypes. Status change of the two biotypes has important effects on whitefly populations. White?ies reproduce rapidly and tend to live on the underside of leaves, making it a difficult pest to manage effectively with chemicals. Heavy use of older insecticides, such as organophosphates, on whitefly populations on crops, including field crops and vegetables, has fostered their resistance to those chemicals. This has increased the need for and value of innovations in chemical control. It has been reported that natural enemies such as Encarsia formosa may play important roles in regulating whitefly population dynamics. Cultural and biological control techniques were indispensable against infestations of the whitefly. Therefore, chemical insecticides and biological control are both important to an effective whitefly control program.