Testing the insecticidal efficacy of individual and combined use of four different natural substances against granary weevil (Sitophilus granarius L.) adults under laboratory conditions

Abstract: Laboratory experiment was carried out to evaluate the impact of different environmentally acceptable substances on the mortality of the granary weevil (Sitophilus granarius L.). We treated wheat grains with diatomaceous earth, quartz sand, leaf powder of neem tree, and wood ash. Wheat grains were also treated with combinations of diatomaceous earth and wood ash, leaf powder of neem tree and wood ash, quartz sand and wood ash, and with a combination of all four different. Substances were applied at different concentrations. Mortality of granary weevil adults was tested at 3 different temperatures (20, 25, and 30 °C) and 2 different relative humidity levels (55 and 75%). Mortality was evaluated 7th, 14th and 21st day after exposure. We have detected significant impact of different substances on the mortality of granary weevil adults. Significantly the highest mortality of the beetles was established in treatments with individual use of 2.5 w% wood ash (69.73 ± 2.52%), with combined use of diatomaceous earth (450 ppm) and 2.5 w% wood ash (71.94 ± 2.40%), and with combined use of quartz sand (450 ppm) and 2.5 w% wood ash (68.72 ± 2.80%). Combination of 4 different substances (diatomaceous earth [225 ppm], wood ash [1.25 w%], leaf powder of neem tree [0.625 w%], quartz sand [225 ppm] provoked 68.76 ± 2.75% mortality. We established that wood ash in single or combined use can perform environmentally acceptable alternative to synthetic insecticides in controlling granary weevil adults, however for final confirmation of this thesis we have to study the activity of the substances against the eggs and the larvae of the pest.