Neonicotinoid insecticides can cause a variety of adverse sub-lethal effects in bees. In social
species such as the honeybee, Apis mellifera, queens are essential for reproduction and
colony functioning. Therefore, any negative effect of these agricultural chemicals on the
mating success of queens may have serious consequences for the fitness of the entire colony.
Queens were exposed to the common neonicotinoid pesticides thiamethoxam and
clothianidin during their developmental stage. After mating, their spermathecae were dissected
to count the number of stored spermatozoa. Furthermore, their worker offspring
were genotyped with DNA microsatellites to determine the number of matings and the genotypic
composition of the colony. Colonies providing the male mating partners were also
inferred. Both neonicotinoid and control queens mated with drones originating from the
same drone source colonies, and stored similar number of spermatozoa. However, queens
reared in colonies exposed to both neonicotinoids experienced fewer matings. This resulted
in a reduction of the genetic diversity in their colonies (i.e. higher intracolonial relatedness).
As decreased genetic diversity among worker bees is known to negatively affect colony
vitality, neonicotinoids may have a cryptic effect on colony health by reducing the mating frequency
S1 Table. Raw data of the worker offspring genotyping for each mated honeybee queens
(Apis mellifera). Tweenty to 24 worker offspring (individuals) per queen were genotyped
using five closely linked microsatellite loci (HB007, HB005, HB004, SV240 and HB15). Alleles
were scored as fragment lengths in base pairs. Colony source refers to the colony from which
queens were reared. Treatments are noted ªPº when the queens were exposed to neonicotinoids
(thiamethoxam and clothianidin) during developmental stage, or ªCº for controls.