Department of Physics, University of Trento, 38120, Trento, Italy.
Center for Mind/Brain Sciences (CIMeC), University of Trento, 38068, Rovereto, Italy.
Sci Rep. 2023 Mar 8;13(1):3851. doi: 10.1038/s41598-023-30796-5.
Geosmin is an odorant produced by bacteria in moist soil. It has been found to be extraordinarily relevant to some insects, but the reasons for this are not yet fully understood. Here we report the first tests of the effect of geosmin on honey bees. A stinging assay showed that the defensive behaviour elicited by the bee's alarm pheromone component isoamyl acetate (IAA) is strongly suppressed by geosmin. Surprisingly, the suppression is, however, only present at very low geosmin concentrations, and disappears at higher concentrations. We investigated the underlying mechanisms at the level of the olfactory receptor neurons by means of electroantennography, finding the responses to mixtures of geosmin and IAA to be lower than to pure IAA, suggesting an interaction of both compounds at the olfactory receptor level. Calcium imaging of the antennal lobe (AL) revealed that neuronal responses to geosmin decreased with increasing concentration, correlating well with the observed behaviour. Computational modelling of odour transduction and coding in the AL suggests that a broader activation of olfactory receptor types by geosmin in combination with lateral inhibition could lead to the observed non-monotonic increasing-decreasing responses to geosmin and thus underlie the specificity of the behavioural response to low geosmin concentrations.
土臭素是一种由潮湿土壤中的细菌产生的气味物质。它被发现与某些昆虫有着非常密切的关系，但原因尚不完全清楚。在这里，我们首次测试了土臭素对蜜蜂的影响。刺痛试验表明，蜜蜂报警信息素成分异戊酸乙酯（IAA）引起的防御行为受到土臭素的强烈抑制。令人惊讶的是，这种抑制作用只在非常低的土臭素浓度下存在，而在较高浓度下则消失。我们通过触角电生理学研究了嗅觉受体神经元水平的潜在机制，发现土臭素和 IAA 的混合物的反应低于纯 IAA，表明这两种化合物在嗅觉受体水平上相互作用。对触角叶（AL）的钙成像表明，神经元对土臭素的反应随浓度的增加而降低，与观察到的行为非常吻合。AL 中气味转导和编码的计算模型表明，土臭素与侧抑制相结合，更广泛地激活嗅觉受体类型，可能导致对土臭素的观察到的非单调增加-减少反应，从而为对低浓度土臭素的行为反应的特异性提供了基础。
