Does queen age affect the quality of her eggs?
Answer: Yes, both in size and mortality, although the latter is more important
Ask any beekeeper how to quickly evaluate the queen in a given colony, and they will undoubtedly check her "brood pattern". With experience and a keen eye, one can fairly and readily assess how good a queen is without even finding her. The arrangement, consistency, and even-spacing of the developing young within the combs can tell you a lot about the quality of the queen, her productivity, and whether or not you should replace her. This subjective measure of a queen's brood pattern is therefore part science, and part artistic judgement.
There are many factors that influence a queen's brood pattern, some within her "control" and others that she can't do anything about. For example, a queen could have a discontiguous (unevenly spaced) brood pattern—which is often a sign that the queen is poor—but the colony may be "honey bound" or be congested within the brood nest. In such a case, the queen simply can't find ample space in which to lay, so she hunts around laying eggs in different areas that results in a helter-skelter pattern of brood ages that is not her fault. Similarly, a queen may have a "spotty" brood pattern—also a sign of trouble—but it can either be due to poor mating (diploid drone production, for example, which is the fault of the queen) or due to disease (chalkbrood, for example, which can be cleared up by the workers and therefore not the fault of the queen).
But what happens if you take a closer look at the brood? Are there any patterns in how queens affect the eggs that they lay? It is this question that a German research team recent asked by looking at the potential relationship between queen age and the quality of the eggs that they lay. They tested 76 queens in total, some of them newly mated (0 years old), some young (1 year old), and some old (2 years old). They then allowed the queens to lay into comb and grafted out eggs from each queen's brood well before they hatched. They then measured the physical size of each egg, as well as whether or not it finally hatched from its chorion (egg casing).
The researchers found a significant effect of queen age on both the size of the eggs as well as the average viability of eggs. Newly mated queens laid the largest eggs, the size of which decreased as queen age increased. The likelihood that an egg would hatch, however, was not affected by size. Nonetheless, egg viability was also a strong function of queen age. Newly mated queens had 9.1% mortality in their eggs, one-year-old queens had 12.5% mortality, and two-year-old queens had 30.7% mortality. This decrease of egg viability is highly significant and demonstrates that older queens may be constrained by how fecund they can be.
These findings are more evidence for why older queens can be less productive than younger queens. We already know that younger queens tend to be more productive than older queens, but it is not just because they have more sperm and tend to swarm less frequently. It appears also that the eggs that they lay are subject to more stress and hatch less often. This is even more reason to take the time and be sure to mark your queens so that you know how old they are, and to replace the queens before they peter out from old age.
Al-Lawati, H., and K. Bienefeld. (2009). Maternal age effects on embryo mortality and juvenile development of offspring in the honey bee (Hymenoptera: Apidae). Annals of the Entomological Society of America, 102: 881-888.