Efficacy of inert dusts and plant powders against Sitophilus oryzae adults under laboratory conditions

Abstract: Bioassays were carried out to assess insecticidal efficacy of different inert dusts
and plant powders from Solidago canadensis and Solidago gigantea against rice weevil
(Sitophilus oryzae) adults. We evaluated insecticidal efficacy of inert dusts of local
(Slovenian) origin, i. e. zeolite, diatomaceous earth, quartz sand and wood ash from
Norway spruce. The efficacy was tested at 25 °C and at two different relative humidity
values (55 and 75 %). Mortality of rice weevil adults was evaluated at 7, 14 and 21 days
after exposure.When used in single formulation, inert dusts were applied at 450 and 900
ppm. SilicoSec® was used as positive control. Crushed leaves of Solidago species were
applied as 2.5 w%. When plant powders were used in combination, inert dusts were applied
at 300 ppm, and plant powders at 0.83 w%. Two different grain types were used in our
survey, wheat and corn grain. According to the results of our investigation, inert dusts and
plant powders of local origin proved to have low insecticidal efficacy in comparison to the
product SilicoSec®, with which mortality of Sitophilus oryzae adults at 900 ppm was
significantly the highest in both grain types: with corn mortality of adults reached 60 %,
and with wheat mortality was higher than 90 %.