Comparable insecticidal efficacy of three locally obtained inert dusts and commercial formulation of diatomaceous earth against adults of bean weevil (Acanthoscelides obtectus [Say], Coleoptera, Chrysomelidae)

Abstract We studied the contact efficacy (surface treatment) of six types of inert dusts in controlling the bean weevil ( Acanthoscelides obtectus [Say], Coleoptera: Chrysomelidae), including zeolite, quartz sand, Slovenian diatomaceous earth (DE), wood ash of fir trees ( Abies alba L.), wood ash of Norway spruce trees ( Picea alba L.), and Silicosec®; the latest being a commercial brand of DE. The two concentrations of dust of 10 and 20 g/m 2 were tested, in which the dust was used to treat common beans ( Phaseolus vulgaris L.) as a contact treatment inside a Petri dish. Fifteen adult weevils were introduced into each Petri dish, and the weevil mortality was counted on days 2, 3, 4, 5, and 7. On the 7th day, the surviving weevils were transferred into a new Petri dish filled with beans without the dust treatment, and then the delayed mortality of the weevils was counted on days 8, 9, 10, 11, and 14. A set of experiments consist of nine repetitions, and four sets were made to observe them under four combinations of two storage temperatures (20 and 25 °C) and two storage RH (55 and 75%). The analysis shows that the corrected mortality and delayed mortality were influenced by the day of exposure, dust type, concentration, storage temperature, and RH. The lower concentration of 10 g/m 2 was effective enough to control the bean weevil, while the corrected mortalities were higher at 25 °C compared to 20 °C. The efficacy of fir and Norway spruce wood ashes and Slovenian DE was as high as that of SilicoSec®, which can cause 100% weevil mortality after 4 days. Those three types of inert dusts are strongly recommended as a non-chemical material to control bean weevils A. obtectus in common bean storage.