In a recently published review article, researchers from the Czech Republic and Belgium investigated courtship strategies in different bumblebee species and highlighted a plethora of chemical structures used by males to attract young queens to mate. Here they explain how the recipe for success is in the combination of compounds used to create a male bumblebee’s marking pheromone.
By Irena Valterová & Nicolas Brasero
Bees play a crucial role in the life cycle of flowering plants by transferring pollen from flower to flower, thus fertilizing the plants and allowing them to reproduce. In particular, bumblebees are irreplaceable for many plants due to their commonness and well-developed fur, which is especially good at transporting pollen. Their importance is clear in the case of some economically important crops, such as tomatoes, which are fully dependent on bumblebees as specific pollinators.
Bumblebee societies consist of worker bees responsible for maintaining the colony, and a queen, who is the only sexually mature, egg-laying member of the colony. In temperate zones, like Europe, the annual cycle of a bumblebee colony is divided into three phases; hibernation and nest foundation, a growth phase, and mating and overwintering preparations.
A queen who mated the previous summer emerges from her overwintering shelter (called a hibernaculum) in early spring and searches for a nesting site, such as an abandoned nest of a small mammal or a patch of soil surface protected by dense vegetation. She then stocks her nest with nutrient reserves in the form of pollen and nectar before laying her first eggs. She spends 4-5 weeks caring for her larvae and foraging before the first workers are born. This marks the beginning of the second phase, where the workers help to collect nectar and pollen whilst also maintaining the nest. The queen continues to lay eggs, and the colony grows.
After several weeks of this growth phase, the queen begins to lay new types of eggs from which next generation queens and males will emerge – this moment is called the “switch-point”. Both males and young queens leave the maternal nest with the goal of finding a mate. Males perform their courtship display and mate with the virgin queens, who then dig a hibernaculum of their own and insulate themselves until the following spring.
Males perform a conspicuous pre-mating behaviour with two distinct behavioural components: scent marking and patrol flying. In patrol flying, males establish flight paths along which they mark leaves, branches or stones with a pheromone to attract virgin queens. All day, they fly along these paths or perch at one specific spot in the hope of encountering a queen of their own species to mate with. Virgin queens choose their partner based on his marking pheromone and, as a recently published review article in Zeitschrift für Naturforschung C explains, males with the wrong perfume will not succeed!
The male marking pheromone is a blend of many chemical compounds, but its composition is specific to each bumblebee species. While the queen uses this perfume to recognise her mate, researchers use it to recognise the bumblebee species by analysing its molecular components. This is useful because bumblebees are sometimes difficult to recognise based on aspects of their appearance. For example, coloration sometimes varies dramatically between individual males within a species, but variation is not always so easily noticed between different species.
Read the original article here: