Insecticidal activity of volcanic ash against Sitophilus oryzae L. (Coleoptera: Curculionidae) under laboratory conditions

Abstract

This study assessed the acute toxicity and repellence as well as feeding deterrence effect of volcanic ash (VA) on Sitophilus oryzae adults under laboratory conditions. VA resulted in significant adult mortality of S. oryzae. Acute toxicity of the VA was similar to that of commercially available diatomaceous earth DiatomiD ® demonstrating its insecticidal potential. Median lethal concentration values (LC 50 ) obtained were 1610 [1449, 1778] mg/kg for VA and 1046 [916, 1168] mg/kg for DiatomiD ® .Similarly to other inert dusts, VA particle size shows a bi-modal distribution and porosity which increases its surface area. Among the smallest particles, the highest volumetric loading was close to 5 µm with a distribution of smaller particles peaking at 0.5µm. Results indicate that VA is not repellent to S. oryzae. An "engagement" response or increased interaction of the insects with the VA treated surface was observed. However, feeding deterrence indices showed that both VA and diatomaceous earth had strong feeding deterrent action. Contact of insects with VA may lead to mortality by adherence of the VA particles to the insect cuticle. However, insects prefer feeding on sites without VA covered substrates and this could have a positive impact on its use for pest management.

Diatomaceous earth as insecticide: physiological and morphological evidence of its underlying mechanism

“…This phenomenon holds significant ecological importance, as it can profoundly impact insect populations in the affected area following a volcanic eruption. 46 In this study we took SEM images of individual abdomens of T. castaneum treated with DE and observed that DE particles have direct interaction with the wax layer of its cuticle. Images show a liquid substance composing the wax layer and covering the insect's body that is being absorbed by DE particles (Fig.…”

“…Another natural occurrence with insecticidal properties, leading to insect mortality through desiccation, is the deposition of volcanic ashes. This phenomenon holds significant ecological importance, as it can profoundly impact insect populations in the affected area following a volcanic eruption 46 …”