Honey Bee Biology

 

  Honey Bee Biology  - September 2014


Bee Larvae: Busier than You Think

by Dr. Wyatt A. Mangum

(excerpt)

Healthy brood should not be taken for granted. During colony inspections, I always check to make sure the colony has plenty of glistening white worker larvae, at all ages, which tend to catch my eye.

Healthy larvae are white, and the older ones, covering the bases of the cells, glisten in sunlight, when held there briefly (see Figure 1). Larvae appearing off white, especially brownish, indicate various problems from chilled brood or different diseases or perhaps indirectly a connection with varroa infestations.

The honey bee larva is a specialized development stage for feeding, little else, except for pheromone production. However, larvae do move in their cells. The larva, curled in a “C” shape, can move slowly in a circle. The larva needs no external limbs for such moment, which can bring it to food placed in the cell by nurse bees. Notice in Figure 1 the larvae are in different rotational positions. Those positions would change in the next hour or so. The folds of the body surface on their sides and back are thought to provide the movement.

Observations from older research report the folds in a larva contract and then expand in an advanced position, which apparently pull the larva forward, in somewhat of a crawling movement. For example, three-day-old worker larvae can turn (rotate) twice in their cells every one and three quarter hours. Larvae move forward (head first) in their cells, although backwards-moving larvae have been reported. When moving in reverse, the larva pushes against the cell with its mouthparts (Jay, 1963). I have seen older larvae, near capping age, crawl out of their brood cells when the bee coverage was removed, and the comb kept warm. That may be due to a lack of food as brief comments in older research suggest. Anyway, those larvae being sedentary and immobile are an illusion – nurse bee magic. I have seen a similar behavior in older hornet larvae leaving their cells when I removed the comb from the nurse hornets. Out wiggle the older larvae. Going nowhere.

For feeding, larvae are essentially little eating machines made to grow quickly. Insects have their skeletal structure on the outside of their bodies, called an exoskeleton. In contrast mammals, reptiles and birds have internal skeletons supporting their bodies, called an endoskeleton. Given the rapid growth, an external skeleton, no matter how thin around a larva, cannot contain its expanding body. In terms of size, the old exoskeleton becomes out of date and must be shed, or molted. A developing bee has six molts. Five of them occur during the fast-growing larval stage. For queens and workers the first four molts occur approximately once a day allowing rapid growth by shedding old exoskeletons.

For digestion, internally larvae are mostly a mid gut and a hind gut, which comes to a dead end inside them while feeding. So the larvae do not defecate while the nurse bees feed the larvae. In addition, the nurse bees help digest the food before they give it to the larvae. Once larvae finish feeding with the cells open, nurse bees provision the cells with a little more food for worker larvae and probably drone larvae. Then bees cap their cells (see Figure 2).

Queen larvae are much different. Nurse bees put massive quantities of royal jelly in their cells. The entire base of the cell becomes coated in a thick layer of white material, which under optimum feeding conditions, cannot all be consumed by a larva. Some will be left over. Later on during pupation and right after the queen leaves her cell, the once white jelly-like consistency turns to a tough thick brown resin-like material. Even after the queen has emerged from a cell, the presence of the brown gooey material tells me the nurse bees gave the developing queen a proper feeding. I cut open the empty queen cell and look for the old royal jelly at the base of the cell. When letting a nuc rear its own queen, rearing under stressful conditions, sometimes the emergency queen cells do not have any extra old royal jelly or there is a little bit that perhaps the larva could not reach. Then I would expect the new queens to be under-fed and that would damage their development and the colony’s honey production.

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