Over a decade, declines in honey bee colonies have raised worldwide concerns. Several
potentially contributing factors have been investigated, e.g. parasites, diseases, and pesticides.
Neonicotinoid pesticides have received much attention due to their intensive use in
crop protection, and their adverse effects on many levels of honey bee physiology led the
European Union to ban these compounds. Due to their neuronal target, a receptor
expressed throughout the insect nervous system, studies have focused mainly on neuroscience
and behaviour. Through the Geometric Framework of nutrition, we investigated effects
of the neonicotinoid thiamethoxam on survival, food consumption and sucrose sensitivity of
honey bees (Apis mellifera). Thiamethoxam did not affect protein and carbohydrate intake,
but decreased responses to high concentrations of sucrose. Interestingly, when bees ate
fixed unbalanced diets, dietary protein facilitated better sucrose detection. Both thiamethoxam
and dietary protein influenced survival. These findings suggest that, in the presence
of a pesticide and unbalanced food, honey bee health may be severely challenged.
Consequences for foraging efficiency and colony activity, cornerstones of honey bee health,
are also discussed.
S1 Fig. Daily nutrient intake is influenced by the amount of dietary protein, but not by the
THX pesticide dose. The panels show the effect of THX doses among different diets. The top
panel is the choice experiment, where bees were able to regulate their nutrient intake. The four
panels below the line represent the no-choice experiment with the four different fixed diets
(indicated at the top-left corner of each panel). For each panel, days are indicated on the x-axis,
from day 1 to day 14, while the four THX doses are represented on the y-axis. Nutrient intake
(in mg/bee) is colour-scaled. Maximal intake is achieved during the choice experiment, around
day 6, independent of THX dose. The patterns of daily consumption of P:C ratios 1:30 and 1:3
diets are similar to those in the choice experiment, although the maximum intake is around
day 7. In contrast, when dietary protein is low or absent, daily consumption is reduced, especially
on the second week.
S3 Table. Cumulative consumption and details of the different amount of nutrient eaten
during the Choice Experiment. Every values are in mg/bee ±s.e.m., except for the P:C ratio
columns. The “Cumulative Consumption” column is the same as the last column in Table 1.
Honey bees were offered the choice between two unbalanced diets, differing in their P:C ratios
(1:3 and 1:30). First, consumption of each diet is assessed and proportions of protein and carbohydrate
are calculated. The total protein consumption is the addition of the protein parts
eaten from the 1:3 diet and the 1:30 diet; the same goes for the carbohydrate part. P:C ratios are
calculated by dividing the total protein consumption by the total carbohydrate consumption.