Summary. This paper describes a study on the relation between the composition of larval food and the development of female castes in bumblebees. The first aim was to evaluate the significance of glandular secretions in the larval diet as a possible factor involved in larval feeding and caste differ-entiation. Small amounts of proteinaceous secretions were found to be added during the ingestion of sucrose but not while discharging food to the larvae. It is discussed that these secretions are digestive in function rather than food additives that would possibly play a role in the process of caste dif-ferentiation. Secondly, a comparative analysis was made of the gen-eral composition of food samples obtained from larvae of dif-ferent castes and ages and from various periods in the social development of the colony. No significant differences in the total amount of pollen, sucrose and protein were detected between the castes or different age groups. Unlike honeybee workers, individual bumblebee workers did not change the composition of the diet they supplied to the brood in relation to their own age, nor to the social development of the colony. These findings suggest that all larvae receive the same nourishment during their total development and indicate that differences in development between queen larvae and worker larvae are neither caused by variations nor by a qualitative modification of their food with respect to the amount of pollen, protein and carbohydrates
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