Friday Weird Science: No Singing, or Sexing, in the Rain

Oct 04 2013 Published by under Friday Weird Science

*sings*
No siiiiinging in the rain,
No siiiinging in the rain!
But once the storm is over
Bugs are hooooorny again.

They're calling for mates
When the sun's out above
But when pressure's down
They're not ready for love.

Let's the stormy clouds chase
All the bugs from the place
Come on with the rain
And watch horny insects brace

They'll wait out the rain
Til the sun's out again
No singing
Or sexting in the raaaain.

Singing in the rain seems so romantic, doesn’t it? The childlike joy of dancing through the raindrops with your beloved certainly worked for Debbie Reynolds and Gene Kelly in the movie.

But there’s a difference between a light drizzle and a thunderstorm. And when red skies at morning make sailor’s take warning, it’s best to take the romancing indoors.

Unless of course, you’re an insect. Then, maybe you just want to pack it in for the day.

Pellegrino et al. “Weather Forecasting by Insects: Modified Sexual Behaviour in Response to Atmospheric Pressure Changes” PLoS ONE, 2013.

Water is essential for many insects to reproduce. And most of them are up to a light rain, with tough exoskeletons to ward off drops that might seem tiny to us, but are much larger when you’re less than an inch long. But heavy wind and rain are no good for insects, who can’t fly in the wind and could easily be drowned or squished by large drops (let alone hail!).

So it’s in a bug’s best interest to be able to get out of the way when a storm is coming, especially when mating is on the line. But how do they do it?

According to another article on this over at Nature News, the authors came to this study because they studied insects. But they found that some of their behavioral experiments just…didn’t work on some days. Being good observers, they noticed that it was the days when it was supposed to RAIN (maybe they caught themselves going home a few too many times going “$%&# experiment didn’t work and now it’s RAINING…wait…”). The lab, of course, was controlled for light, heat, and even humidity. But there’s one part of oncoming rain that it’s a lot harder to keep out: barometric pressure.

Was it the pressure getting the insect studies down?

To study this, the authors took three species they worked with: the curcurbit beetle (Diabrotica speciosa, pictured above), the true armyworm moth (Pseudaletia unipuncta, and yes, true is part of the name)

And the potato aphid (Macrosiphum euphorbiae)

bug 3
(Source)

They started with the curcurbit beetle. They put male beetles into a Y maze, where they could sense the pheromones of virgin females at one end of the maze. Under normal conditions, the males headed straight for the smell of lovely ladies. But when the scientists lowered the pressure (something that happens during a rainstorm), the beetles stopped moving, hunkering down for the storm. You can see them in the top panel of the figure below.

Figure 1

(Figure 1. Bonus points to the authors for cute little pics of the insects over significant findings!)

When they looked at the moths and aphids, they looked at both males and females. In both of these species, the males find the females and mate, but the females “call”, making noise to indicate where the males can find them for sweet, sweet action.

During normal conditions above (grey bars in the middle graph), you can see the female moths and aphids call a lot. But when the pressure fell (black bars) both species stopped calling. When the pressure increased (low pressure storm areas are often surrounded by high air pressure areas) the aphids also stopped calling, Don’t want your guys going out in the storm before your date!

Finally, they looked at actual mating (bottom graph).

You can see that mating was down for the moths and aphids when pressure was decreased (black bars) or increased (white bars). And when they looked at the beetle mating, they found that, while male beetles would still mate when given the opportunity when pressure was low…they were not nearly as charming about it. There were no preliminaries or foreplay, they just hopped on and got it done. Better mate fast, storm’s a comin!

All this means that a calm before the storm is more than just a drop in the wind. It’s also a drop in mating! Because when you can’t take it indoors, it’s probably safer to pack it in entirely.

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