Impostor among us: Beetles that lie to Bees

by Jagath V – Insects navigate their environment using a variety of cues – an important one of which is their sense of smell, olfaction. Insects not only sniff their surroundings in search of food and to avoid danger but also to find potential mates. A subset of these odours, called sex pheromones, convey infomation about an insect’s species and its availability to mate. Love is literally in the air.

One of the downsides of this odour-based communication is that it is an open system. Insect pheromones that are wafting through the air are open to prying noses and antennae. Since pheromones are often specific molecules, not all organisms are able to tune-in to this chemical signal, and it may not be relevant to those that are able to smell these signals either. Some eavesdroppers however, use this to their own advantage or may even hijack the system.

Sunset in the Mojave Desert
Mojave desert

In the deserts of the south-western United States there exist several desert-dwelling organisms, one of which is the blister beetle – Meloe franciscanus. Its life cycle begins as an egg on the Astragalus plant. Female beetles lay eggs at the base of the plant. These eggs develop at the same time and hatch simultaneously. The newly hatched larvae, called triungulins form aggregations of 200-2000 individuals on the vegetation. They move up and down leaf blades as a unit and can remain as such for up to 14 days.

The same environment is co-habited by the solitary honeybee, Habropoda pallida. Being solitary, these bees do not live in colonies but females do have nests where they lay their eggs. Triungulins that are perched on vegetation draw attention to male bees of the species – because the cluster of triungulins resemble a female bee. Not just that, they also smell like the female bee! The male bee is tricked into following a pheromone trail which he thinks will lead him to a mate. The male bee approaches the cluster to investigate it, or may even try mating with it. Before he realizes what’s happened, within a time span of 2 seconds, the beetle larvae latch onto his body. They wait there, hanging on for dear life until he finds a real female bee to mate with.

Triungulins on bee body (photo from https://doi.org/10.1038/35011129)

The triungulins grab onto the female bee when opportunity strikes. They then piggyback on her till she reaches her nest. Once in the nest, the larvae detach from her body and get cosy in their new home. They live there as parasites, feeding on any food that the adult bee brings, but also on her larvae. Once they reach adulthood they leave the bee’s nest behind, continuing their life cycle.

This phenomenon by which these beetles entice male bees is an example of what is called aggressive chemical mimicry.

To me, this is reminiscent of the popular video game Among Us. Especially when impostors are waiting at key locations looking for unsuspecting crewmates. If you go into electrical and see someone ‘sus’, it is already too late.

References:

1) Deceptive signals and behaviors of a cleptoparasitic beetle show local adaptation to different host bee species

Leslie Saul-Gershenz, Jocelyn G. Millar, J. Steven McElfresh, Neal M. Williams

Proceedings of the National Academy of Sciences Sep 2018, 115 (39) 9756-9760; DOI: 10.1073/pnas.1718682115

2) Phoretic nest parasites use sexual deception to obtain transport to their host’s nest

Leslie S. Saul-Gershenz, Jocelyn G. Millar

Proceedings of the National Academy of Sciences Sep 2006, 103 (38) 14039-14044; DOI: 10.1073/pnas.0603901103

3) Beetle larvae cooperate to mimic bees

Hafernik, J., Saul-Gershenz, L.. Nature 405, 35–36 (2000). https://doi.org/10.1038/35011129

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: