The leaves of the two plants were dried in the shade, then ground to a fine powder. The powders were mixed with sterilized rice at varying application rates. The mixed rice was tested for toxicity, repellency, and its effect on progeny development in seven-day tests.
Toxicity was tested with seven different application rates: 1.0, 2.5, 5, 10, 15, 20, and 25g leaf powder/100 g rice. The guava leaf powder was found more toxic to both weevil species than eucalyptus when both powders were applied at 2.78g leaf powder/100g rice. Both powders were found to be more toxic to S. oryzae than S. granarius. Toxicity of the powders may be attributed to one or more of the following factors where insects fed on the treated grain: fumigation effect, contact effect, or stomach poisoning effect.
In testing repellency at an application rate of 2.5g leaf powder/100g rice, the repellent effect of the powders was sustained for the seven days. Eucalyptus served as a stronger repellent to both insect species than did guava. Olfactory and gustatory sensation of the weevils may be largely responsible for the powder’s effectiveness.
The impact of the powders on progeny development was evident in first generation progeny. Rates of 5, 10, and 15g leaf powder/100g rice were used. With 15g of either powder, no first generation weevils reached adulthood. The number of insects that developed into adults decreased as the powder application rate increased. It was concluded that guava and eucalyptus powders may be effective in protecting small quantities of stored rice.
Laboratory of Plant Protection
National Research Center
Dokki, Cairo, Egypt