Toxicity of castor bean (Ricinus communis) pollen to honeybees

Castor bean (Ricinus communis) is a tropical plant that is distributed widely across the world. In the semiarid region of northeastern Brazil, R. communis is largely cultivated mainly for the production of non-edible oil used in the manufacture of biodiesel. Considering the interest in expanded castor bean seed production for increasing biodiesel production in Brazil, the present study aimed to determine whether the pollen of R. communis is toxic to honey bees (Apis mellifera). Pollen samples were collected, dried, and added to food at doses of 0 (control), 2.5%, 5.0%, and 10%. Each dose of plant material was fed to 120 honey bees, which were observed daily until the last one died. Statistical comparison of the survival curves was performed using Kaplan–Meier survival analysis. The pollen of R. communis significantly (P < 0.0001) reduced the survival of honey bees. Therefore, expansion of castor bean production in the Brazilian semiarid region for bio fuel production might be potentially hazardous to native and domestic honey bees. New studies must be conducted under natural conditions.