Residual effect of imidacloprid and beta-cyfluthrin on Africanized Apis mellifera L. (Hymenoptera: Apidae) workers.

Canola has a long period of flowering in the winter season and this, associated with the lack of other flowers and the use of insecticides to control insect pests, means it may have a great impact on bee populations, such as Apis mellifera L. (Hymenoptera: Apidae). In this context, the use of insecticides with lower residuals and less harmful effects to bees is fundamental. Thus, the objective of the current work was to evaluate, in a laboratory bioassay, the residual toxicity and effect of imidacloprid, beta-cyfluthrin, and a mixture of both, when applied on canola in the field, on Africanized A. mellifera workers. Three commercial products were applied, formulated with imidacloprid, beta-cyfluthrin, and beta-cyfluthrin + imidacloprid. Each plot received one of the three treatments, in the concentration recommended by the manufacturer, at intervals between 14 and 0 days prior to conducting the bioassays. On the day of the bioassay, the bees were exposed to the plant material containing the treatments for a period of two hours, and were transferred to PVC cages, containing food and water. Mortality assessments were then performed at pre-established intervals until a 96 h post-exposure. Residuals on canola leaves of all tested products caused a significant reduction of honeybee worker longevity, which was less accentuated when the interval after treatment application increased. Safer pest management strategies are needed to ensure the preservation of bees. [ABSTRACT FROM AUTHOR]