Credit: José Crespo, University of Utah

Even moths can’t escape the tribulations of being a virgin. New research by scientists at the University of Utah has revealed that when a male virgin Helicoverpa zea moth picks up the scent of a female, it will stop at nothing to get to her as soon as possible, even if that means taking off before its body is ready for sustained flight.

H. zea are found all over the world and are considered major agricultural pests. Their larvae are better known as corn earworms if they’ve been feeding on corn, cotton bollworms if they’ve been feeding on cotton, or tomato fruitworms if they’ve been feeding on tomatoes. The H. zea moth has an average wingspan of around 4cm, and its forewings coloured in a muted yellow or brown spotted with rust, olive green or grey.

They belong to the Noctuidae, or owlet, moth family, which is the largest family of moths and butterflies in the world. For these moths, successful reproduction is all about timing, because after a female is mated with once, she will stop calling for mates, and her receptivity and sex pheromone production will be suppressed for at least the next 24 hours. This means a female will very rarely mate twice in one night, so there is good reason for the males to locate one the instant they catch a whiff of her scent.

But the problem with this is that for a moth to achieve fast, powerful flight, it must first warm up its muscles by shivering. Insect flight muscles are one of the most metabolically costly types of muscles in the animal kingdom, requiring a lot of oxygen to generate enough power. So if a male moth does not take the time to properly warm up, it might not make it to the female, or it could be overtaken by another suiter. These virgin moths are ruled by a trade-off between a quick launch and a steady flight to the finish.

Biologists José Crespo and Neil Vickers examined the pre-flight behaviour of virgin male H. zea moths. They picked virgin males because having never mated or been exposed to pheromones, they woul produce the most accurate result. Vickers and Crespo cooled the males down to 8 to 10 degrees Celsius, which started them off in an inactive state, transported them to tiny wind tunnels, and once they were acclimatised, exposed them to six different kinds of odours. One was the normal pheromone scent of a female, another was a diluted version of the pheromone, and the other four were control odours that did not have any affect on the males. The reactions of the males to the different scents were recorded using an infrared video camera that could measure body temperature.

Corn earworm moth

Infrared video showing a moth's increasing temperature as it shivers. Credit: José Crespo, University of Utah

Publishing in the Journal of Experimental Biology, the researchers reported that when the males were exposed to the attractive pheromones, they started shivering significantly faster than those that were exposed to any of the other scents, and would take off with a lower thoracic (of the thorax) temperature. The males exposed to odours other than pheromones flew in random directions only after they had fully warmed their flight muscles. "These guys don't all heat up at the same rate," said Vickers. "The guys exposed to the pheromone odour go 'Wow!' and they warm up faster and take off more quickly. And that compromises the flight power they can produce."

The team also measured just how much the thoracic temperature affects the moths' flight by measuring the vertical flight power, or force. They did this by gently attaching an entomological pin to a moth's thorax. The other end of the pin was attached to a force sensor. The moth was then placed onto a small Styrofoam ball, which it relexively grasped onto with its legs, and when Crespo eased the ball away, the moth would reflexively fly upward, away from it. Attractive white and black lights were also placed above the moth, to ensure that it flew upwards with a maximum force, which was recorded and measured by the sensor.

The results showed that in order to achieve maximum flight power, the moths needed to heat their muscles to 32 degrees Celsius. The virgin males observed by Crespo and Vickers were taking off at just 27 degrees Celsius – much too cool to catch a female. "[Moths] are well-known for 'scramble competition’,” said Crespo. “When the female is advertising the pheromone in a field, that pheromone is probably going to be detected by several males, and they're going to try to compete and get to the female first. You can see how it might be advantageous to take off sooner and try to get to the female first."

But, he added, taking off with a lower temperature means less power to sustain flight, so there is a compromise in these virgin moths between heating up and taking off faster in order to reach the female first, or waiting and heating the muscles properly in the hopes of slowly and steadily winning the race. What is unclear at this stage is which option is better – the tortoise or the hare – until further research is done to compare the average success rate of each. What their results do show, said Vickers, is that "It's costly to fly, to jump into a relationship”.


Tuesday Jan 10

So Project X: In Which I Emancipate Myself from my Adolescent Virginal Hell by Sticking It in the Nearest Hot Chick is in full swing and has so far proved unsuccessful, despite the fact that I’m the fastest guy ever. That’s why they call me John, which distinguishes me from all the other moths whose name is not John, and alternatively The Flash, because I’m the fastest guy ever. Will continue with this strategy because being the fastest means I have to win.

Thursday Jan 12

Still haven’t made it to a female yet but have gotten pretty close. I actually saw one yesterday, and then I got too tired and had to sit down.

Friday Jan 13

Today Project X was a success. Now I am a man. On the other hand, I am now fully engaged in Project Y: In Which I Emancipate Myself from my Being Known as The Flash in a Sexual Context Hell. The strategy involves admitting I have a problem and applying topical anaesthetic cream.