Protein content in larval diet affects adult longevity and antioxidant gene expression in honey bee workers

In honey bees, adult longevity is strongly dependent on the quantity of dietary protein ingested after emergence, but relatively little is known about the role played by the protein content of larval diet. In total, 15 colonies of Apis mellifera ligustica Spinola (Hymenoptera: Apidae) bees with sister queens were randomly allocated to one of three groups (five colonies per group), provided with pollen substitutes (PS) with protein concentrations of 15, 25, or 35%, designated as PS15, PS25, and PS35, respectively. In a field experiment, we measured the PS consumption and collected samples for analyzing body protein content and gene expression. On day 29, groups of 50 newly emerged workers from each colony were obtained and confined in cages for measuring survival and longevity. Results showed that bees consumed significantly more PS15 and PS25 than PS35. However, the total protein intake of PS15 was less than that of the others. Increasing the protein available to larvae (PS35) significantly increased total accumulated protein before emergence, adult survival, and longevity. Furthermore, bees fed PS25 or PS35 tended to have higher mRNA levels for genes encoding antioxidant enzymes, providing a potential physiological mechanism for observed survival differences among the three dietary treatments. We conclude that protein content in larval diet could positively influence worker longevity likely because of the increased related antioxidant gene expression.