桃蚜脱皮对球孢白僵菌毒力的影响

Effects of moulting in Myzus persicae on the virulence of the entomopathogenic fungus Beauveria bassiana

室内测定了球孢白僵菌BeauveriabassianaBBSG870 2菌株对桃蚜Myzuspersicae若蚜的毒力 ,并分析了若蚜脱皮与白僵菌有效侵染之间的关系。在 2 1℃、 1× 10 6 mL孢子浓度下 ,1～ 4龄若蚜感菌后的累积死亡率分别为 10 1%、 2 1%、 3 1%和4 0 2 % ,明显低于同样条件下成蚜的感菌死亡率 (98 4 % )。在若蚜各龄感菌死亡的个体中 ,1～ 4龄中分别有 8 1%、5 0 0 %、 4 4 4 %和 98 0 %的若蚜在死亡前发育到成蚜 ,且都能产下正常发育的后代。若蚜的感菌死亡率与接菌后到第一次脱皮的时间密切相关 ,脱皮早则感菌死亡率低 ,反之亦然。但试验中也发现有部分若蚜特别是低龄若蚜感菌后未完成第一次脱皮便死亡。观察了桃蚜在 1、 4龄早期感染球孢白僵菌后的发育、存活和生殖情况 ,结果表明 :1、 4龄早期若蚜接菌后第一次脱皮的时间早于未接菌若蚜 ,但提前幅度少于 5 % ,在羽化为成蚜之前被致死的概率分别只有 4 1%和 0 ,在羽化为成蚜后 8天内的生殖率与未接菌蚜虫的无明显差异。这些结果表明 ,若蚜的脱皮 ,尤其当蚜虫在低龄若蚜时受感染后的多次脱皮 ,可有效地摆脱球孢白僵菌分生孢子的侵染 ,降低该菌的毒力。

The effects of moulting by nymphs of the green peach aphid, Myzus persicae on the virulence of Beauveria bassiana BBSG8702, was bioassayed in the laboratory. At 21℃ and with a conidial suspension of 1×10 6/mL, aphids inoculated with the fungus at the 1st, 2nd, 3rd or 4thinstar suffered 10 1%, 2 1%, 3 1% and 40 2% cumulative mortality respectively, significantly lower than that observed in the aphids inoculated at the adult stage (98 4%). Among the individuals that eventually died of the infection following inoculation at the 1st, 2nd, 3rd or 4th instar, 8 1%, 50 0%, 44 4% and 98 0% of them developed to adulthood and produced healthy offspring prior to death. Mortality of the aphids inoculated with the fungus at the nymphal stages was closely related to the time interval between inoculation and first moult post inoculation; the earlier the moult, the lower the mortality. A small proportion of infected nymphs, especially those infected at early instars, died before the next moult post inoculation. Detailed observations were made on the development, survival and reproduction of aphids inoculated with the fungus during the very early stage of the 1st or the 4th instar, stages when nymphs were most susceptible to fungal infection. Compared to the duration of normal nymphal development, nymphs inoculated with the fungus had slightly shorter (<5%) development times for the instar in which they were inoculated. Pre adult mortality caused by the infection was only 4 1% and 0 when the aphids were inoculated with the fungus at the early 1st and 4th instar respectively. Moreover, the reproductive rates of those infected aphids that eventually died at the adult stage due to the fungus during the first 8 days of their adult life were similar to controls not inoculated. These findings demonstrate that moulting by this aphid, especially multiple moulting by the aphids following infection with B. bassiana at an early nymphal stage, is an effective mechanism for avoiding or delaying infection by this fungus, and thereby reduces the virulence of the fungus.