Effect of ichthyomycin on the ultrastructure of tissues of Culex pipiens.

A new antibiotic ichthyomycin produced by Streptomyces sp. strain 1107 was tested for its toxicity and effect on the ultrastructure of tissues of larvae of Culex pipiens autogenicus. Concentrations used were 5 x 10(-7), 2.5 x 10(-7), 1.5 x 10(-7) and 1 x 10(-7) g ml-1. The mortality of larvae after 24 h exposure was 90, 30, 0 and 0%, and after 48 h was 100, 100, 87 and 0%, respectively. The effect of the antibiotic was most evident on mitochondria. They distended and ruptured with subsequent dissolution of their cristae. The microvilli of the brush border of the midgut cells and cell membranes were unchanged, and the peritrophic membrane remained coherent. Cisternae of the rough endoplasmic reticulum and microbodies filled the cytoplasm. Chromatin of the nuclei was aggregated into amorphous masses on the wall, but the nucleolus remained intact. Some cells showed large vacuoles in their cytoplasm from destroyed mitochondria. In muscle cells the mitochondria were in the process of dissolving and the sarcoplasmic reticulum formed elongate cisternae.