Cuticular chemistry and food rewards in the honeybee, Apis mellifera

ANDRÉS GONZÁLEZ; MARÍA SOL BALBUENA; WALTER M FARINA

Natal

Congreso; EBEQ; 2013

EBEQ

When a honeybee (Apis mellifera) collects nectar with high sucrose concentration from flowers, she returns to the hive and dances vigorously to communicate the discovered food source. During this conspicuous display her body temperature raises, which may result in chemical changes at the cuticular level, with potential communicational value inside the hive. Temperature rising also occurs upon nectar collection, and is affected by the food profitability found at the feeding site. To evaluate if food quality results in changes in the cuticular chemistry at the feeding site, we used artificial feeders with high and low levels of sucrose concentration (2 and 0.5 M), to which a group of foraging bees were trained and captured upon feeding (filled-crop foragers). Bees captured in empty feeders (emptied-crop foragers) and inside the colony (hive bees) served as controls. The bees were killed with CO2, and the surface compounds were extracted in dichloromethane and analyzed by GC-MS. The identification of cuticular hydrocarbons and other extracted compounds associated with exocrine glands, was based on mass spectra and retention indices, as well as hydrogenation and DMDS-derivatization of the samples. The compounds were quantified relative to an internal standard, and statistically analyzed by Principal Component Analysis (PCA) to compare the surface chemistry of bees from different treatments. We analyzed 51 chromatographic peaks corresponding to 56 compounds, including cuticular hydrocarbons as well as compounds associated to the Nasanov and sting glands. We found significant differences in the composition of the cuticular extracts of the hive bees with those of foraging bees. Among the latter, filled-crop foragers collected at high and low profitable feeders resulted in no observable differences, but emptied-crop foragers did show higher amounts of non-hydrocarbon compounds, especially of Z-11-eicosenol and compounds associated with Nasanov gland. Our results are not in line with previous studies reporting that four hydrocarbons, namely (Z)-9-tricosene; tricosane; (Z)-9-pentacosene and pentacosane, are produced in larger amounts by foraging bees advertising a profitable food source.