Sublethal dosage effects of carbaryl on honey bee (Apis mellifera (L.)) colonies

Abstract

The sublethal dosage effects of carbaryl were studied in honey bee (Apis mellifera L.) colonies. Carbaryl was fed to colonies during a 14-day period in a 0.95 M sucrose solution. Carbaryl dosages were based on 0.0036, 0.0178, and 0.0356 ug/bee/day, and concentrations approximated 0.09, 0.44, and 0.86 ppm, respectively. Five potential areas of sublethal effect were examined: brood production, brood mortality, adult mortality, colony weight change, and worker resistance to the toxicant.

The carbaryl dosages appeared to fall within the sublethal range. No significant differences (P≤0.05) in adult mortality were found between Control and carbaryl treatments during or following carbaryl application. Statistically-significant increases in brood production and brood mortality were observed at the median dosage, but no significant differences were found at the highest dosage. The lowest dosage also caused no significant differences in brood production. A significant increase in worker resistance to carbaryl was observed at the median dosage, but a significant decrease occurred at the highest dosage and the Control. No significant differences in colony weight change were observed during the treatment or post-treatment periods at any dosage.

Although statistically-significant differences were observed, they were not felt to be biologically significant. Intra-treatment colony variation was considered to be partly responsible for the differences observed. This variation is great enough to make honey bee colonies unsuitable for general insecticide screening, although they may be useful when prior evidence of sublethal effects exists