The pollen of Caesalpinia pyramidalis Tul. is toxic to honeybees (Apis mellifera)

Caesalpinia pyramidalis Tul. (syn. Caesalpinia gardneriana Benth.) is an endemic tree from northeastern Brazil whose flowers are visited by a number of bee species, including the honeybee (Apis mellifera). The present study aimed to determine whether the pollen of C. pyramidalis is toxic to honeybees. Pollen samples were collected, dried, and added to food at doses of 0 (control), 2.5, 5.0, and 10 %. Each dose of food was fed to 60 honeybees, which were observed daily until the last one died. Statistical comparison of the survival curves was performed using the log-rank test. The mean survival times of the bees fed with C. pyramidalis pollen were 6.40 ± 0.28 days for the 2.5 % group, 5.70 ± 0.18 days for the 5.0 % group, 5.72 ± 0.23 days for the 10.0 % group, and 13.7 ± 0.61 days for the control group. All the pollen concentrations of C. pyramidalis significantly (P < 0.0001) reduced the survival of honeybees in comparison with control group. In conclusion, the results of our study show that the pollen produced by C. pyramidalis is toxic to A. mellifera under laboratory conditions.