Protozoan-enhanced toxicity of Bacillus thuringiensis var. Israelensis δ-endotoxin against Aedes aegypti larvae

Robert Manasherob, Eitan Ben-Dov, Arieh Zaritsky, Ze'ev Barak

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


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 δ-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.

Original languageEnglish
Pages (from-to)244-248
Number of pages5
JournalJournal of Invertebrate Pathology
Issue number3
StatePublished - 1 Jan 1994


  • Bacillus thuringiensis var. israelensis
  • Bioencapsulation
  • Larvicidal mortality
  • Mosquito biocontrol
  • Tetrahymena pyriformis
  • Δ-endotoxin

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics


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