Effect of chlorpyrifos added to beeswax on Apis mellifera honey bees

Abstract

Chlorpyrifos is a widely used organophosphate insecticide for controlling insects and mites in economically important crops. In honey bees, it reduces foraging efficiency and delays the acquisition of olfactory memory. In larvae exposed to contaminated food, it increases mortality rates. Chlorpyrifos can be detected in field-collected resources such as honey, as well as incorporated into beeswax within the combs.However, there are few studies investigating beeswax as a potential route of exposure and contamination of the hive by this insecticide. Therefore, this study evaluated the effect of chlorpyrifos, at an environmentally relevant dose, added to beeswax and how it affected colony population development and adult bee mortality. For this purpose, the wax was melted in a water bath (70°C), and chlorpyrifos was added at a concentration of 24,95 µg/kg (environmentally relevant dose). Wax sheets were prepared using a manual sheet and cell mold press and inserted into standard American brood frames. These frames, either with contaminated or uncontaminated wax, were placed in the experimental colonies (5 with chlorpyrifos and 5 control colonies). After the combs were built and the queen began laying eggs, colony population development was monitored weekly over a 60-day period. The brood frames were photographed, and the areas of open and sealed brood were measured (cm²). To assess adult bee mortality, “underbasket” type dead bee collectors were installed below the entrance of the experimental hives, and dead bees were counted daily over the 60-day period. Data were analyzed using ANOVA followed by Student’s t-test (p<0.05). No significant differences were observed between control and treated colonies in open brood area (116.4±148.4 vs. 101.2±135.6 cm²), sealed brood area (360.8±273.2 vs. 345.2±270.4 cm²), or adult bee mortality (6.4±4.3 vs. 6.5±4.8 bees/day). These results suggest that, at the tested concentration, chlorpyrifos did not affect colony population development or adult bee mortality