The Effect of Application Rate of GF-120 (Spinosad) and Malathion on the Mortality of Apis mellifera (Hymenoptera: Apidae) Foragers.

Beneficial organisms like the honey bee, Apis mellifera L. (Hymenoptera: Apidae), are heavily affected by pest control practices that incorporate insecticides. Safer alternatives as the spinosad-based formulation GF-120 have been developed to overcome this issue. Though both the low concentration of spinosad and the ultra-low-volume application rate of GF-120 are supposed to have a low acute toxicity in honey bee foragers, to our knowledge such claims have not been explicitly proven. We thus carried out a series of experiments to assess the effect of GF-120, malathion, and Spintor (spinosad) on honey bee foragers when applied at two concentrations (80 and 1,500 ppm) and two application rates (low density rate [LDR]—80 drops of 5 mm diameter per square meter; high density rate [HDR]—thousands of 200 -µm-diameter droplets per square meter). Interestingly, the three pesticides caused low mortality on foragers when applied at LDR-80, LDR-1,500, or HDR-80. However, HDR-1,500 caused a very high mortality. Based upon these results, we developed a computer program to estimate the average number of foragers that are exposed at LDR and HDR. We found that more foragers receive a lethal dose when exposed at HDR than at the other rates. Our results support the hypothesis that the impact of GF-120 and malathion upon honey bees is minimal when applied at LDR and that computer simulation can help greatly in understanding the effects of pesticides upon nontarget species.