SummaryThe influence of diet upon the development of prothoracic gland cells and oenocytes in honeybee larvae reared in colonies and in the laboratory was assessed at the age of 4 days by measuring nuclear diameters. Laboratory diets included the following: freshly collected worker jelly, both unaltered and with (1) added fructose and glucose, (2) ether extract of royal jelly, and (3) dialysate of royal jelly; freshly collected royal jelly; and royal jelly which had been stored for several years.On unaltered worker jelly, which has a low sugar content, there was little or no glandular development beyond the stage reached by colony-reared worker larvae (CW) aged 72 hours; increasing the sugar concentration to that of royal jelly supported development similar to that in CW.An addition of an ether extract of royal jelly to the worker jelly produced less glandular development than in CW. In larvae fed on a diet with added dialysate of royal jelly, the oenocytes were not significantly less developed than those in CW, but the prothoracic gland cells had significantly smaller nuclei. When sugar was also added to the diet containing the ether extract, glandular development was similar to that in CW; the addition of sugar to the dialysate diet resulted in a significantly greater level of glandular development, which was similar to that of colony-reared queen larvae (CQ). This last result was interpreted as an interaction between sugar and another water-soluble component of royal jelly.Nuclei of larvae reared in the laboratory on fresh royal jelly were similar in size to those in CQ, whereas nuclei of larvae reared on the stored royal jelly resembled those in CW. These results are compatible with an hypothesis of endocrine mediation between diet and form with respect to both maturation and caste development.