Abstract :
[en] Various aspects have been considered to study bee health, especially immune and detoxification responses. Research in these areas has been conducted at the cellular (e.g., haemocyte) and humoral (e.g., antimicrobial peptide (AMP), melanisation and detoxification pathway) levels. However, focusing on these metrics requires costly devices (e.g., quantitative PCR instruments) and highly trained experimenters. As an alternative, scientists have focussed on fat body content as a proxy for immunocompetence, since this tissue is known to be the main site for AMP and detoxification enzyme production, and since required equipment are cheap and easy to use. Yet, no research has ever properly demonstrated a link between fat body content and immune-related metrics. Motivated by incongruencies found in the literature and in previous research in our laboratories, we exposed bumblebee Bombus terrestris microcolonies to various stressors (i.e., nutrition, xenobiotic, infection and physical) and then assessed fat body content together with more direct immune-related parameters. In the haemolymph, we determined (i) phenoloxidase activity (i.e., an enzyme involved in the melanisation process), (ii) bacterial growth inhibition (i.e., due to AMP) and (iii) haemocyte populations (i.e., involved in several immune responses). Our preliminary results showed no significant differences among treatments, neither in phenoloxidase activity nor in fat body content, while haemocyte counts varied significantly. In addition to demonstrating that fat body content may fail to accurately reflect the immune status, it definitely showed that fat body content failed to capture discrepancies among treatments. We argue that fat body content should be interpreted carefully in future studies.
