Christian H. Krupke et al
Abstract
Populations of honey bees and other pollinators have declined worldwide in recent years. A variety of stressors have been
implicated as potential causes, including agricultural pesticides. Neonicotinoid insecticides, which are widely used and
highly toxic to honey bees, have been found in previous analyses of honey bee pollen and comb material. However, the
routes of exposure have remained largely undefined. We used LC/MS-MS to analyze samples of honey bees, pollen stored in
the hive and several potential exposure routes associated with plantings of neonicotinoid treated maize. Our results
demonstrate that bees are exposed to these compounds and several other agricultural pesticides in several ways
throughout the foraging period. During spring, extremely high levels of clothianidin and thiamethoxam were found in
planter exhaust material produced during the planting of treated maize seed. We also found neonicotinoids in the soil of
each field we sampled, including unplanted fields. Plants visited by foraging bees (dandelions) growing near these fields
were found to contain neonicotinoids as well. This indicates deposition of neonicotinoids on the flowers, uptake by the root
system, or both. Dead bees collected near hive entrances during the spring sampling period were found to contain
clothianidin as well, although whether exposure was oral (consuming pollen) or by contact (soil/planter dust) is unclear. We
also detected the insecticide clothianidin in pollen collected by bees and stored in the hive. When maize plants in our field
reached anthesis, maize pollen from treated seed was found to contain clothianidin and other pesticides; and honey bees in
our study readily collected maize pollen. These findings clarify some of the mechanisms by which honey bees may be
exposed to agricultural pesticides throughout the growing season. These results have implications for a wide range of largescale
annual cropping systems that utilize neonicotinoid seed treatments.
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) provide the means for other creatures to exist. For example the creatures may be the partridge whose young feed on sawfly larvae, but since the crops are sprayed against sawflies, the partridge population seems to be affected. The creatures may be those that have no direct connection with the human food chain, but just make the world nicer to live in.
