Abstract:
Rice weevil, Sitophilus oryzae (L.) is one of the major pests of rice both in the field after
harvest and during storage. Previous studies have revealed that plants are a potentially
rich source of pesticides. Therefore, the present study was designed to evaluate the
repellent activity of selected medicinal plants, Acalypha indica, Murraya koenigii, Juticia
gendarussa, Pongamia sp. and Piper longam against rice weevil, Sitophilus sp. Repellent
activity of leaf powder (1:10 w/w) and leaf paste (1:4 w/w) from these five plants were tested
using a six- armed olfactometer based on the number of insects oriented towards each
treatment.
Ten grams of infestation free rice grains were mixed with the leaf powder (1 g) from the
selected plants and placed on a filter paper (2 inch diameter) and kept separately within
each bottle (250 ml) of the six-armed olfactometer. The sixth bottle contained 1 g of
untreated sound rice as the control. One hundred 1-3 day old adult Sitophilus sp. from the
laboratory culture were introduced into the centre bottle of the six-armed olfactometer. The
number of insects in each bottle was counted at 24 hrs and 48 hrs of exposure. This was
replicated five times. Similarly 1:4 (w/w) fresh leaf paste from the above said plants were
prepared and placed in each bottle of the olfactometer. Data were analyzed by using
analysis of variance and LSD. The percentage repellency was compared with the control.
Orientation of Sitophilus sp. towards leaf powder and leaf paste from all tested plants was
significantly less in numbers (P<0.05) than the untreated control after 24 hrs and 48 hrs of
exposure. From the LSD analysis, the leaf paste of P. longam showed less repellent effect
than the other plants tested. However, leaf powder of M. koenigii, J. gendarussa and P.
longam showed high repellent activity followed by A. indica and Pongamia sp. After 48 hrs
of exposure percentage repellency ranged from 44 % to 92 % for leaf powder but for leaf
paste it ranged from 66 to 89 %. It was concluded that the leaf powder of M. koenigii,
J.gendarussa, P.longam, A. indica and Pongamia sp at 1:10 (w/w) and leaf paste of M.
koenigii, J.gendarussa, Pongamia sp and A. indica at 1:4 (w/w) has a potential repellent
effect against Sitophilus sp. and could be considered for integration with other control
options in the control of Sitophilus sp..
