Fig. 5. Manganese treatment induces precocious foraging. (A) Effects of MnCl₂, ZnCl₂ and 8-Br-cGMP on age at onset of foraging. % initiating foraging refers to the percentage of bees from each treatment group that were observed to initiate foraging (data pooled from six individual experimental colonies; pooled numbers shown in key). (B) Effects of MnCl₂, ZnCl₂ and 8-Br-cGMP on tendency to collect pollen. Bars represent means ± S.E.M. of the percent of foragers from each colony returning with pollen. There was a significant difference among the treatment groups (P<0.05; PROC GENMOD; counts of foragers converted to percentages solely for graphical purposes), but no consistent trends were evident when examining the data for each colony (N=6; line graphs). Differences in the proportion of bees starting to forage from each treatment group were evaluated with multiple factor survival analysis with Cox proportional hazards estimation (Ben-Shahar et al., 2002b).