Laboratory evaluation of the efficacy of inert dusts against adults of rice weevilSitophilus oryzae (L.) and red flour beetle Tribolium castaneum (Herbst)in treated wheat

Abstract: Inert dusts have a prominent place in IPM programmes for protection of cereal grainsfrom stored-product insects. The intention in this study was therefore to conduct preliminary testsof the insecticidal potential of several inert dusts in protecting wheat from Sitophilus oryzae andTribolium castaneum adults, namely: (a) natural zeolite originating from Serbia (Minazel andMinazel plus with 63-68% SiO2), (b) bentonite originating from Bosnia and Herzegovina(Bentonit, with 48.4% SiO2), and (c) diatomaceous earths originating from Serbia (DE S-1 with79.8% SiO2, and DE S-2 with 63.2% SiO2) (roughly purified at the Institute of Technology ofNuclear and Other Raw Materials, Belgrade). The efficacy of dusts was tested in the laboratory(24±1°C and 60±5% r.h) by exposing insects to wheat treated with 0.75g/kg of each product,using modified methods OEPP/EPPO (2004) and Collins (1990). Mortality was determined after7 and 14 days of insect contact with threated wheat, while total mortality after 7 more days ofrecovery on untreated wheat. After seven days of exposure and the additional seven days ofrecovery of S. oryzae and T. castaneum, the highest efficacy was observed in treatments with DES-1: 72% and 47%, and 78% and 61%, respectively. The highest efficacy after 14 days wasachieved by DE S-1 (96%) and DE S-2 (91%) against S. oryzae, and DE S-1 (94%) and DE S-2(89%) against T. castaneum. Total mortality of rice weevils reached 100% after contact with DES-1 and DE S-2 dusts, while the highest mortality of red flour beetle reached 94% and 91%,respectively. Total mortality of both insects in wheat treated with Minazel was 86-89%. Underthe trial conditions and application rate, none of the bentonite treatments achieved efficacyexceeding 15%, while Minazel plus reached a maximum of 53%, which indicates that higherapplication rates would be required to secure significant efficacy.