Long-duration feedings and caste differentiation in Bombus terrestris larvae

Abstract

The duration of feedings received by Bombus terrestris larvae was studied using video-recordings. In the last days of development all larvae received feedings mainly of long duration. Worker larvae of the third brood received significantly longer feedings than worker larvae reared in the other broods. Throughout the development queen larvae and worker larvae received feedings of similar duration. Male larvae received shorter feedings than both kinds of female larvae. Therefore, the duration of feedings seems to be associated to the sex and stage of development of the larvae. The causes of the long-duration feedings seem not to be related to the amount of food provided, workers age and size, to the workers abdominal contraction or to the amount of pollen in the larval food. Perhaps the feeding duration is caused by the viscosity of the food, which is a consequence of the presence of pollen grains, sugar and glandular material. Although the precise amount of pollen was not measured, the differences in colour showed clearly that the larval food samples contained variable quantities of pollen grains. Some of the samples did not contain any pollen at all. It is suggested that the duration of feedings may be related (among other factors) to the presence of glandular material (proteins and enzymes) which is added to the larval food. This could be especially important for queen larvae in the last phase of their development. Because they have a long development and are fed with a high frequency they might receive large amounts of these substances. This could help them to grow more efficiently using a relatively smaller amount of pollen than expected.