Communication is essential to any successful relationship, and insect relationships are no different. In insect (as in human) relationships, much of this communication is non-verbal. Chemical cues in the form of pheromones help females of many insect species decide when to mate, who to make with and, when the deed is done, other chemicals let them know it’s time to stop dating and get serious about making some babies.
Joachim Ruther and colleagues at the University of Regensburg in Germany published an article in 2010 that describes how the switch from “let’s do it!” to “I gotta find a place to lay my eggs” happens in the jewel wasp Nasonia vitripennis. Now, Dr. Ruther and Theresa Hammerl have found the exact chemicals that make this happen.
The romantic period of a female jewel wasp’s life is very brief. Females normally only mate one time, and then they flutter off to continue the miraculous circle of life by laying their eggs inside the pupal case of a developing fly so that their babies can eat the fly alive from the inside out. Beautiful, isn’t it?
But what about the dating scene?
There is no OK Cupid for wasps, so they have to use other means to find each other. Males produce a pheromone that is released from their anus, and virgin female wasps find this irresistible. Once the female has found this sexy smelling male, he immediately mounts her and starts his courtship act. This is a complicated set of movements, including head nodding and rapid wing movements. He also rubs his mouth up and down her antennae while making chewing movements with his mouth.
Those chewing movements are actually really important: they release an aphrodisiac that the female senses through her antennae. If she likes what she smells, she signals the male that she’s ready by lowering her head and unlocking her genitals. You can see this in action in the video below:
Video: Male Nasonia mounts female and exchanges an aphrodisiac pheromone, resulting in female acceptance response and a switch to host-seeking behavior after mating. From Ruther et al. 2010. Copyright Elsevier. Posted with permission. http://www.journals.elsevier.com/animal-behaviour
After mating, the male will mount the female a second time and spread some more of that aphrodisiac pheromone from his mouth to her antennae. She will often signal again that she’s in the mood, but they won’t mate twice. Instead, a switch will flip in the female’s brain, making her completely ignore the anal secretion from the male that she previously found so attractive. Instead, she’ll go into hunt mode and start looking for fly pupae to lay her eggs in.
In many insect species, like Drosophila (fruit flies), the switch flipper is actually transferred to the female with sperm. But in the case of jewel wasps, no sperm, or anything else in the male ejaculate for that matter, is needed for the switch to occur. Dr. Ruther and colleagues found out that the secretions from the male’s mouth—the same secretions that act as an aphrodisiac before mating—make the female stop being attracted to males and start caring about where to lay her eggs. In fact, by disrupting the courtship process they found that the moment she signals the male that she’s accepted him is the exact moment she stops caring about the attractiveness pheromone.
To prove that it’s a pheromone from the mouth, and not something in the semen or anything else, that turns off the attractiveness signal, the researchers isolated the pheromone from males and determined its exact chemical composition. They found that the pheromone is made up of 3 distinct chemicals. To show that this chemical cocktail makes females stop responding to the attractant pheromone (the one from the male’s anus), they took virgin female wasps and lightly dabbed their antennae in the isolated pheromone. These females were no longer attracted to male scent, even though they had never encountered a male. Virgins who had their antennae dabbed in a control chemical, on the other hand, acted just like normal virgins would—they moved toward the male anal pheromone, looking for love.
These experiments proved that female jewel wasps don’t need to get sperm from males in order to flip the switch from mate-finding to host-finding. They just need to come in contact with a 3-chemical cocktail (ethyl oleate, ethyl linoleate and ethyl α-linolenate). Still to be discovered is how this chemical actually works. How does the signal get from the female’s antennae into her brain? And how does it do both jobs, aphrodisiac and switch-flipper? Or are there different chemicals in the oral secretions from the male that act as the aphrodisiac?
The studies on wasp chemical communication are important for understanding the evolution of insects and their mating systems. The chemicals discovered may even one day prove useful for developing pesticides or other insect population-management tools. But I think the most important aspect is the decoding of the insect language. That way, when they take over the world, at least we’ll know what they’re saying…
Ruther J, & Hammerl T (2014). An oral male courtship pheromone terminates the response of Nasonia vitripennis females to the male-produced sex attractant. Journal of chemical ecology, 40 (1), 56-62 PMID: 24369389
Ruther, J., Thal, K., Blaul, B., & Steiner, S. (2010). Behavioural switch in the sex pheromone response of Nasonia vitripennis females is linked to receptivity signalling Animal Behaviour, 80 (6), 1035-1040 DOI: 10.1016/j.anbehav.2010.09.008