丽蚜小蜂寄生对Q型烟粉虱生长发育的影响

为明确丽蚜小蜂寄生对Q型烟粉虱的影响,通过室内饲养观察不同龄期Q型烟粉虱被丽蚜小蜂寄生后的生长发育,并比较了被寄生后烟粉虱若虫的个体大小及死亡率。结果表明,2龄、3龄和4龄烟粉虱若虫被寄生后均能继续发育,2龄若虫蜕皮进入3龄和3龄若虫蜕皮进入4龄的时间与对照间无显著差异,而被寄生若虫的4龄期显著延长。对于同一龄期的烟粉虱若虫,丽蚜小蜂偏向于选择较大的个体寄生,2龄和3龄被寄生若虫发育后期个体比未被寄生个体大,但4龄时被寄生的个体在发育后期略小于未被寄生个体,显示丽蚜小蜂对不同龄期若虫的生长发育影响不同。2龄若虫死亡率为61.64%,显著高于3龄和4龄若虫;4龄若虫褐蛹率最高,为48.84%。表明无论寄生哪一发育阶段的烟粉虱若虫,丽蚜小蜂的寄生均为容性寄生,田间应用丽蚜小蜂防治Q型烟粉虱时在其若虫3~4龄时释放更适宜。

Effects of parasitization by Encarsia formosa on development of biotype Q Bemisia tabaci nymphs

In order to clarify the effects of parasitization of Encarsia formosa on biotype Q Bemisia tabaci nymphs, the development of B. tabaci nymphs parasitized at the 2nd, 3rd, and 4th instars by E. formosa were observed in the laboratory, respectively. The results showed that the nymphs continued to develop despite the parasitization. The molting from 2nd to 3rd instars and 3rd to 4th instars of parasitized nymphs was synchronous with that of non-parasitized ones. The developmental time of the 4th-instar nymphs was prolonged. E. formosa preferred bigger B. tabaci nymphs of the same instars. The body size of parasitized 2nd and 3rd instars were bigger than that of non-parasitized ones during the observation period. However, the body size of parasitized 4th-instar nymphs was smaller than that of non-parasitized ones at the seventh day after parasitization, although the former was bigger than the latter when the parasitization happened. These results indicated that the host instar at parasitization affected the effects of parasitization on the development of B. tabaci. The mortality of nymphs exposed at 2nd instar (61.64%) was significantly higher than that exposed at 3rd or 4th instar. The percentage of brown pupae (48.84%) was higher when the 4th instars were exposed to wasps than that when the 2nd or the 3rd instars were used. These results denoted that the parasitization by E. formosa was koinobiont, and E. formosa should be released when biotype Q B. tabaci developed into 3rd to 4th instars in the field.