Effects of Insecticides on the Mid–gut Wall of a Larva

    THE specific action of insecticides on the tissues of various insects is a little–explored field. Knowledge of this kind may prove of value in the selection, improvement and appliction of methods of insect control. A review of the physical and chemical effects of poisons on insect tissues cells and secretions is given by Trappmann (Z. Pflanzenkrank., 48; 1938), while the most recent contribution to this subject is by P. A. Woke, of the U.S. Department of Agriculture. In the Journal of Agricultural Research, 61, 321–29 (1940), this writer discusses the effects of certain insecticides on the walls of the mid–intestine of the larva of the “southern army worm” (Prodenia eridania). Lethal doses of the poisons were fed to the larvae in turnip–leaf or sweet potato–leaf “sandwiches”. The subjects of the trials were then killed and fixed after different intervals and the tissues examined histologically for comparison with control individuals. It appears that the action of arsenicals was followed by disintegration of the epithelial lining of the mid–intestine and damage to the visceral muscle–fibres. Ingestion of sodium fluoride resulted in disintegration of the substance of the cytoplasm and the nuclei. The epithelial cells of those larvæ that had ingested sodium fluoaluminate were greatly disintegrated and the cross–striations of the muscle–fibres were faint or obliterated. On the other hand, no changes in the epithelium or muscle–fibres followed the ingestion of barium fluosilicate, phenothiazine or rotenone that could be attributed with certainty to the substances named. Rotenone, it may be added, varies remarkably in its toxic action on different species of insects. Silkworm larvæ, for example, died within two hours from the effects of taking in minute quantities of this substance, whereas southern armyworm larvse readily ingested 5–10 mgm. without showing ill effects. With regard to sodium fluoride, the observation of Hockenyos that this compound can be absorbed in lethal amounts directly through the integument of cockroaches, requires fuller exploration.

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    RESEARCH ITEMS. Nature 148, 318–319 (1941) doi:10.1038/148318a0

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