Manasherob R, Ben-Dov E, Zaritsky A, Barak Z
Department of Life Sciences, Ben-Gurion University of the Negev, Be'er-Sheva, Israel.
J Invertebr Pathol. 1994 May;63(3):244-8. doi: 10.1006/jipa.1994.1047.
The toxicity of Bacillus thuringiensis var. israelensis (Bti) in mosquito larvae was enhanced by encapsulation in the protozoan Tetrahymena pyriformis. Aedes aegypti larvae which fed on T. pyriformis loaded with Bti died about three times faster than when fed on the same concentrations of Bti alone due to ingestion of higher toxin concentrations, reflected by shorter death times of exposed populations. The best larvicidal activities were achieved at ratios of cell/spore numbers in the range of 1:200 to 1:500. This enhancement of mortality by preincubation with T. pyriformis was higher at low Bti concentrations or in late third-instar larvae. Ninety minutes of preincubation yielded the best enhancement effect. Toxicity enhancement is very likely a consequence of concentrating large quantities of Bti spores and crystals (containing delta-endotoxin) by T. pyriformis cells and delivering them to the larvae. Shortening larval mortality time by encapsulation in T. pyriformis should reduce the exposure time of Bti to unfavorable field conditions that inactivate its larvicidal activity. Whether this method will indeed improve Bti efficacy is still to be determined.
通过包裹在梨形四膜虫原生动物中，苏云金芽孢杆菌以色列变种（Bti）对蚊虫幼虫的毒性得以增强。以负载有Bti的梨形四膜虫为食的埃及伊蚊幼虫，其死亡速度比仅以相同浓度Bti为食的幼虫快约三倍，这是由于摄入了更高浓度的毒素，表现为暴露群体的死亡时间更短。在细胞/孢子数量比例为1:200至1:500的范围内可实现最佳杀幼虫活性。在低Bti浓度或三龄晚期幼虫中，通过与梨形四膜虫预孵育提高死亡率的效果更明显。预孵育90分钟可产生最佳增强效果。毒性增强很可能是梨形四膜虫细胞浓缩大量Bti孢子和晶体（含有δ-内毒素）并将它们递送至幼虫的结果。通过包裹在梨形四膜虫中来缩短幼虫死亡时间，应可减少Bti暴露于使其杀幼虫活性失活的不利田间条件的时间。这种方法是否真的会提高Bti的功效仍有待确定。
