• amino acids
• haemolymph composition
• honeybees
• laboratory rearing
• mason bees

Nectar is the main food resource of adult bees and it fuels their flight. Amino acids are the most abundant solutes present in nectar, second only to sugars. All the essential amino-acids have been found almost ubiquitously in nectar. Among them, the protein amino acid proline has received more attention because of its role in the insect flight metabolism and because it is the most abundant amino-acid found in the honeybee haemolymph.
Also several non-protein amino acids have been found in nectar, within the so-called class of “nectar secondary compounds”. Among the non-protein amino acids, γ-amino butyric acid (GABA) and β-alanine are the most common and abundant in floral nectar.

Amino acids affect bees physiology, thereby their pollination activity, but their role is still unclear. Bees amino acids requirements are still to be fully investigated, especially for wild bees. Honeybees are one of the most efficient and wide-spread pollinators on a world scale. Among the solitary bees, mason bees are important pollinators of fruit trees and they are managed in several countries for orchards pollination. Due to the possibility to be easily kept in cages, both honeybees and mason bees are suitable genera for laboratory experiments.

Experiments were performed in order to investigate effects of a single amino acids enriched diet on food consumption, survival, behaviour and haemolymph composition on three bees species. Proline, GABA at natural concentration, GABA at twentyfold increased concentration (GABA 20x) and -alanine were tested separately on Apis mellifera (L.) workers (both newemerged and foragers), just emerged Osmia cornuta (Latreille) females and just emerged Osmia bicornis (L.) females and males, all reared in laboratory conditions using two types of cages (small cages or tubes and big bowls).
 
Syrup consumption and survival rate were recorded daily in all the experiments. Behavioural observations were performed using the scan sampling method for bees reared in bowls. Haemolymph was sampled from bees at different time and analysed by gradient HPLC.

Different responses to a diet enriched with single amino acids were observed among the different bees species and also, within the same species, between different sexes and ages. A “cage-dependent” effect was also hypothesized.
Proline increased food consumption by O. cornuta females and newemerged honeybees, both reared in cages. This amino acid positively affected survival of newemerged honeybees reared in bowls while it decreases the lifespan of newemerged honeybees reared in cages, as well as the one of O. cornuta females reared in tubes.
High concentration of GABA (GABA 20x) increased syrup consumption by foragers honeybees reared in bowls and positively affected survival of O. cornuta females reared in bowls. GABA 20x showed also an interesting affect on forager honeybees behaviour, resulting in an increased motor activity of these bees during the first week of rearing. GABA at natural concentration negatively affected the lifespan of newemerged honeybees reared in cages.
-alanine increased the newemerged honeybees lifespan when they were reared in cages.
Haemolymph composition differed among different bees species, and also within the same species, and resulted to be affected by diet. Especially proline and GABA showed curious trends in both mason bees and honeybees haemolymph suggesting the existence of some unexpected metabolic interactions that need to be further investigated.