Honeybees Produce Millimolar Concentrations of Non-Neuronal Acetylcholine for Breeding: Possible Adverse Effects of Neonicotinoids.
The worldwide use of neonicotinoid pesticides has caused concern on account of their involvement in the decline of bee populations, which are key pollinators in most ecosystems. Here we describe a role of non-neuronal acetylcholine (ACh) for breeding of Apis mellifera carnica and a so far unknown effect of neonicotinoids on non-target insects. Royal jelly or larval food are produced by the hypopharyngeal gland of nursing bees and contain unusually high ACh concentrations (4-8 mM). ACh is extremely well conserved in royal jelly or brood food because of the acidic pH of 4.0. This condition protects ACh from degradation thus ensuring delivery of intact ACh to larvae. Raising the pH to ≥5.5 and applying cholinesterase reduced the content of ACh substantially (by 75-90%) in larval food. When this manipulated brood was tested in artificial larval breeding experiments, the survival rate was higher with food supplemented by 100% with ACh (6 mM) than with food not supplemented with ACh. ACh release from the hypopharyngeal gland and its content in brood food declined by 80%, when honeybee colonies were exposed for 4 weeks to high concentrations of the neonicotinoids clothianidin (100 parts per billion [ppb]) or thiacloprid (8,800 ppb). Under these conditions the secretory cells of the gland were markedly damaged and brood development was severely compromised. Even field-relevant low concentrations of thiacloprid (200 ppb) or clothianidin (1 and 10 ppb) reduced ACh level in the brood food and showed initial adverse effects on brood development. Our findings indicate a hitherto unknown target of neonicotinoids to induce adverse effects on non-neuronal ACh which should be considered when re-assessing the environmental risks of these compounds. To our knowledge this is a new biological mechanism, and we suggest that, in addition to their well documented neurotoxic effects, neonicotinoids may contribute to honeybee colony losses consecutive to a reduction of the ACh content in the brood food.
Institute of Pathology, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstr. 1, D-55101 Mainz, Germany.
Ignaz
I
Wessler
Institut für Bienenkunde, Polytechnische Gesellschaft Frankfurt am Main, Fachbereich Biowissenschaften, Goethe Universität Frankfurt am Main, Karl-von-Frisch-Weg 2, D-61440 Oberursel, Germany.
Hedwig-Annabel
HA
Gärtner
Institute of Pathology, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstr. 1, D-55101 Mainz, Germany.
Rosmarie
R
Michel-Schmidt
Institute of Pathology, University Regensburg, Franz-Josef-Strauss Allee 11, D- 93053 Regensburg, Germany.
Christoph
C
Brochhausen
Institute of Pathology, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstr. 1, D-55101 Mainz, Germany.
Luise
L
Schmitz
Institute of Pathology, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstr. 1, D-55101 Mainz, Germany.
Laura
L
Anspach
Institut für Bienenkunde, Polytechnische Gesellschaft Frankfurt am Main, Fachbereich Biowissenschaften, Goethe Universität Frankfurt am Main, Karl-von-Frisch-Weg 2, D-61440 Oberursel, Germany.
Bernd
B
Grünewald
Institute of Pathology, University Medical Center, Johannes Gutenberg University Mainz, Langenbeckstr. 1, D-55101 Mainz, Germany.
Charles James
CJ
Kirkpatrick
D000109:Acetylcholine / Q000032:analysis / Q000096:biosynthesis*; D000691:Anabasine / Q000009:adverse effects* / Q000031:analogs & derivatives; D000818:Animals; D001516:Bees / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002795:Choline O-Acetyltransferase / Q000032:analysis / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D007013:Hypopharynx / Q000187:drug effects / Q000378:metabolism; D007306:Insecticides / Q000009:adverse effects* / Q000494:pharmacology; D007814:Larva / Q000187:drug effects; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009474:Neurons / Q000378:metabolism; D009574:Nitro Compounds / Q000494:pharmacology; D054817:Pollination / Q000187:drug effects; D012098:Reproduction / Q000187:drug effects* / Q000502:physiology*
D007306:Insecticides; D009574:Nitro Compounds; D002795:Choline O-Acetyltransferase; D000691:Anabasine; D000109:Acetylcholine