How do solitary bees reproduce?

Answer

Dear Veerle,

In our country alone there are at least 300 species of solitary bees or “wild bees”, all with their own life cycle, which is very often very similar. Usually there is one generation per year, but there are also species with two generations per year.

After mating, the female of the solitaire bee is responsible for building the nest, usually in some tunnel in the ground, in a hollow of eg a reed, or in a hollow in a tree trunk, pole, or wall. Once the “mother bee” has found a nest cavity, she goes in search of pollen. This pollen is carried to the nest cavity on the hairs of the hind legs or the abdomen. The pollen is mixed with some nectar to make a “bee bread”. A fertilized egg is initially laid on this, then this “brood cell” is closed with a wall of mud and saliva. This creates a first cell. In this way, the entire nest cavity is further filled with similar cells (clump of pollen/nectar + egg). The number of brood cells in a nest cavity is usually limited to 10 to 15 cells.

In the front cells (outer cells) unfertilized eggs are laid. Finally, the outside of the nest cavity is closed off with a wall of mud and saliva, plant material or sand so that the nest cavity is well protected against natural enemies and weather conditions.

From each egg emerges a larva that feeds on the pollen and once mature turns into a pupal stage. Over time, the adult solitary bee emerges from this. The female that laid the eggs only lives for a few weeks; after egg laying she dies, her energy is exhausted and her wings are worn out, so solitary bees never see their offspring. The males live even shorter than the female bees and die shortly after mating.

In many species of solitary bees, the males appear several days to several weeks earlier than the females; they are therefore also at the front of the nest cavities. It is the males who then patrol in places where the chance of encountering females is greatest, for example near nest cavities and flowers. For example, dozens of mating males can sometimes fly just above the bottom surface near nesting sites until the “virgin females” emerge from the nest cavity. As you could already observe, the males sit on top of the females during mating.

Often chemical signals also play an important role in finding a female. Newly hatched virgin females produce a type of volatile substance (sex pheromone) that attracts the males and stimulates mating. The males of various species, in turn, use their jaw glands to spread so-called scent flags on plants and other places in the landscape, which attract females of the same species. These “scent flags” are a bit like a dog that marks its territory while peeing against trees.

After mating, the cycle starts again: the female immediately starts building a nest cavity. The inseminated female initially lays fertilized eggs (sexual reproduction) which develop into females; at the end of the nest cavity (outside) unfertilized eggs are also laid, from which the males then develop.

kind regards,

Hans