Unbalanced dietary omega-6:3 ratio affects onset of nursing and nurse–larvae interactions by honey bees, Apis mellifera

Animals require a nutritionally balanced diet to support growth and reproduction. The geometric framework for nutrition asserts that animals actively balance their nutritional intake to maintain physiological homeostasis and optimize task performance to increase fitness. Both solitary and social animals will adjust their relative consumption of nutritionally distinct resources to meet their intake target ratio. Honey bees are eusocial insects whose primary source of macronutrients comes from floral pollen, including the essential fatty acids, omega-6 (linoleic acid) and omega-3 (alpha-linolenic acid). These must be actively balanced, as an unbalanced diet skewed towards a high omega-6:3 ratio reduces life span, reduces the size of the hypopharyngeal glands that produce jelly to feed larvae and impairs performance in cognition tests. As honey bees show a division of labour by age, we hypothesized that consuming an unbalanced diet would impact the timing of task transitions and nursing activity. To test this, we fed 1-day-old adult workers either a balanced (omega-6:3 ratio = 1) or unbalanced (omega-6:3 ratio = 5) diet for 7 days, after which they were released into a common-garden hive. Workers were tagged with barcodes and filmed continuously for 6 days, allowing analysis of nursing behaviour of individuals. The unbalanced diet delayed the onset of nursing, reduced the rate of nursing visits and affected the relative attention devoted between 3-day-old and 4-day-old larvae. We discuss these findings in the context of division of labour and nurse–larvae interactions, and identify novel avenues for further research linking fitness-related behaviours to nutritional balancing.