Thread by @BugQuestions

Bed bug sex is incredibly violent, and never voluntary.

The male's penis is a dagger he uses to forcibly inseminate the female, puncturing her body wall and injecting sperm directly into the bloodstream.

So how does he know when he's found a female?

He doesn't.

#DeepDive

Again, before we continue...bed bug sex does not resemble anything human sex should resemble.

See disclaimer:

https://twitter.com/BugQuestions/status/1011072704978485248

Early on in bed bug research, it was apparent to researchers that something wasn't right with the mating recognition systems of these insects.

Male bed bugs didn't seem to be too discriminatory, and would attempt to mount pretty much any well fed insect...male and female.

So...at first glance, it would seem that bed bugs exhibited some bisexual behavior.

However, the attempts to mate with males were a bit different than what you'd see with females.

When mounting other males, they'd get right up to the point of insertion...and then quit.

So, clearly there's something weird going on here.

Most bugs can tell the boys from the girls from afar...but bed bugs can't recognize females until they're pretty much touching them.

There's another thing...same-sex mating attempts produced a distinct odor.

Bed bug sex is a traumatic event.

Traumatic events in insects living in groups are typically associated with alarm pheromones.

So in 2009, Camilla Ryne asked a really obvious question.

What happens when you block the pheromones w/nail polish?

Blocking the male's ability to release alarm pheromones doesn't change the frequency of mountings, however it does change their behavior.

Males which can't produce pheromones are mounted longer and more violently.

When you take mating male/female pairs of bed bugs, and flood the chamber with the scent of male bed bug alarm pheromones, mating tends to end pretty quickly.

It ends in 1/4th the time.

So...alarm pheromones regulate sex-specific patterns in bed bugs.

Case closed, right?

Well, there's another layer of complication here.

Male bed bugs aren't the only bed bugs which produce alarm pheromones.

Female bed bugs, and nymphs produce alarm pheromones as well.

The males seem to only react to the alarm pheromones of other males, and nymphs.

We know what's in the bed bug pheromones, and we can detect those smells.

Adults produce a mix of (E)-2 Hexenal (think green apple flavoring), and (E)-2-octenal (a mix of citrus and cucumber).

The nymphs produce 4-5 different things, but the main one is (E)-4-oxo-2-hexenal.

I'm not entirely sure what that last one smells like, by the way.

So...when we see male/male mating attempts, we see them emitting a specific pattern of chemicals.

They're mainly producing that chemical which smells a bit like apples.

Females, however, seem to produce these two chemicals in a ratio that's a bit more even.

However, in general, they're releasing more of the citrusy-type chemical when mounted by a male.

Nymphs, on the other hand, drive off the males using 4-oxo-(E)-2-hexenal...which is a compound that's a bit different than what we see in male/male pairings.

So...why is this important?

Sex is something that's frequently happening in bed bug colonies, and it only happens with living insects. By definition, it only happens in breeding colonies.

If we know what bed bug sex smells like, we can design better diagnostic tests.

From a pure science perspective, it also explains why an insect with such a bizarre and violent mating system would not only occasionally pair with members of the same sex...but also explains why we see the pattern of backing off.

Bed bug sex makes a little more sense now.

Again, I want to re-state the disclaimer we began this thread with.

Insect sex is a bit horrifying, and we should not draw any conclusions about how humans should act from the ways insects do act.

We are different from insects, and they are not role models.