Action of the microbial metabolite and chitin synthesis inhibitor nikkomycin on the mite Tetranychus urticae; an electron microscope study

Abstract

Chitinous structures of Tetranychus urticae K., after treatment with the microbial metabolite nikkomycin, were examined using an electron microscope. The results were compared with published information on the mechanisms of action of this antibiotic. Application of the drug resulted in an inhibition of moulting, due to a deficient or abnormal differentiation of the procuticle during ecdysis. Damage to the procuticle caused disorders in the muscle attachments, preventing the chrysalis stages leaving their exuviae after treatment with the metabolite. Application of nikkomycin to an adult female caused plug‐like accumulations below the procuticle of the prosoma and cranial opisthosoma, as well as inside the hypodermis. The egg shell was another site of action of nikkomycin; depending on when drug treatment began, an abnormally thickened or incomplete plaque‐like egg shell was produced. The deposition of affected eggs was strongly inhibited, if they were laid at all. The electron micrographs supported the suggestion that a competitive inhibition of chitin synthetase results in inhibition of cuticle synthesis. However, such a mechanism of action cannot explain the results on egg shell damage after nikkomycin treatment, which indicates some other influences of the antibiotic.