Scientists discover a bee that's half female, half male

A team of scientists led by Cornell University (USA) has identified a bee that is male on its left side and female on its right side. This is a rare condition known as gynandromorphism and occurs in several groups of insects, such as Coleoptera, Hymenoptera and Diptera, among others. It is also found in certain crustaceans and arachnids (although practically unknown in mammals); but this is the first known example of gynandromorphism in the bee species.

The first gynandromorph of its species

The bee in question (Megalopta amoena) is four millimetres long and is a nocturnal insect native to Central and South America. Specifically, the researchers found the bee inside a nest in Panama, in a forest on the island of Barro Colorado. 

When the bee was discovered, scientist saw that on its left side, it is physiologically a male: it has a small and delicate jaw, a long antenna and a hind leg with few hairs.

On its right side, it is a female: it has a shorter antenna, a jagged and well-pronounced jaw and a thick and hairy hind leg.

This bee is so special because, generally, the rare genetic condition of bilateral gynandromorphism is only seen when the insect is already dead and on display in a museum.

"Finding M. amoena was like finding gold or winning the Darwinian lottery," said Erin Krichilsky, a Cornell University student and lead author of the study published in the Journal of Hymenoptera Research.

Although this bee has bilateral gynandromorphism, as its sex differences are halved, gynandromorphism can also be axial, with the front of the body being one sex and the back is the other. It can also appear as a mosaic, with male and female features mixed and dispersed throughout the animal's body.

The determination of the sex in the order of insects, which includes bees, ants and wasps, is really peculiar. If the eggs are fertilized, worker bees (female bees) will be born. The unfertilized ones will be drones (male bees). But there can be double fertilization: if the sperm of a second and even a third individual enters an egg that is already fertilized, a female embryo, it can divide to produce male tissue, resulting in a gynandromorphic specimen.

How does he behave?

The researchers followed her for four days and found that she tends to wake up a little earlier than the male and female bees. However, her periods of increased activity were more like female behaviour.

"More studies are needed to better understand whether there is a difference in circadian rhythm based on sex in this species, and to distinguish what the pattern of deviant activity of the gynandromorph is derived from," the authors explain.

Reference: Erin Krichilsky et al, The first gynandromorph of the Neotropical bee Megalopta amoena (Spinola, 1853) (Halictidae) with notes on its circadian rhythm, Journal of Hymenoptera Research (2020). DOI: 10.3897/jhr.75.47828