Subacute and delayed toxicity of iminoctadine liquid formulation, which contains iminoctadine triacetate as an antifungal component on a nontarget domesticated insect, the silkworm, Bombyx mori L. (Lepidoptera: Bombycidae)

We investigated insecticidal effects of iminoctadine liquid formulation, a fungicide containing iminoctadine triacetate, on the silkworm Bombyx mori that is an important domesticated insect. Iminoctadine liquid formulation was incorporated in an artificial diet and fed to silkworms for 24 h on the first day of either the third or fourth instar, thereafter reared without the fungicide. Third instar larvae that ingested the diet containing 1% (wt/wt) iminoctadine liquid formulation died within 24 h (subacute toxicity), and those that ingested either 0.1% or 0.3% iminoctadine liquid formulation developed to the pharate fourth stage and then became deficient in molting (delayed toxicity). In fourth instar larvae, iminoctadine liquid formulation exhibited subacute toxicity and delayed toxicity at 0.3% and >1%, respectively. Furthermore, we fed the larvae a diet with iminoctadine liquid formulation for 24 h at different intervals in the inter-molting period of the third and fourth instar. Iminoctadine liquid formulation administered at an earlier stage in the inter-molting period exerted a more severe effect than a later administration. Iminoctadine triacetate, an anti-fungal ingredient in the iminoctadine liquid formulation, exhibited toxicity similar to that of the liquid formulation.

Silkworm larvae were fed Befran while the first day in the third instar and fed normal diet on the second day or later. They developed to the pharate fourth stage that looked normal. Then, they failed to molt. There was a substantial time lag between the chemical administration and actualization of the toxicity. A common cutworm Spodoptera litura ingesting Befran developed to the adult stage, which is different from the results obtained by using Bombyx mori.Figure optionsDownload as PowerPoint slideHighlights
► Unique toxicities of a fungicide iminoctadine triacetate on the silkworm Bombyx mori.
► Subacute death of the larvae ingesting the chemical at high doses.
► Delayed death of the larvae after a substantial time lag ingesting low doses of the chemical.
► More severe effects of the chemical administered at an earlier stage in the inter-molting period than later administrations.