INSECTICIDAL ACTIVITY OF FLORAL, FOLIAR, AND ROOT EXTRACTS OF TAGETES MINUTA (ASTERALES, ASTERACEAE) AGAINST ADULT MEXICAN BEAN WEEVILS (COLEOPTERA, BRUCHIDAE)

Experiments were conducted to determine speed of action and toxicities of extracts of Tagetes minuta L., a source of naturally occurring insecticidal compounds. LC(50) values for male and female Mexican bean weevils, Zabrotes subfasciatus (Boheman), were determined for floral, foliar, and root extracts of T. minuta. The 24-h LC(50) values ranged from 138 mu g/cm(2) for males exposed to the root extract (most susceptible) to 803 mu g/cm(2) for females exposed to the foliar extract (least susceptible). Increasing the duration of exposure to 48 h decreased all LC(50) values 20-30 mu g/cm(2). Males were more susceptible than females. The time to incapacitation for 50% of the test insects (IT50) for floral and foliar extracts indicated fast-acting, volatile components, whereas the root extract data indicated slower-acting components, likely a result of the interaction of photophase with time-dependent efficacy. Floral and foliar extracts of T. minuta may be useful as insecticides for controlling stored-product pests.