New Worlds: How the jewel wasp enslaves its prey

Researches at Ben-Gurion University make discovery on tiny parasitic wasp.

By JUDY SIEGEL-ITZKOVICH
Jewel wasp. (photo credit: Wikimedia Commons)
Jewel wasp.
(photo credit: Wikimedia Commons)
You don’t have to be a neurosurgeon to perform brain surgery. A tiny parasitic wasp (Ampulex compressa), called the jewel wasp, uses sensors on its stinger to find and inject a venom “cocktail” right into cockroach brains. This was recently discovered by Prof. Frederic Libersat and Dr. Ram Gal from Ben-Gurion University of the Negev.
The wasp feeds its offspring live cockroaches, which are much larger than the parents. To subdue the much larger prey, the wasps sting it, causing the cockroach to completely lose its will to move away. Instead of fighting or fleeing, the stung cockroach follows the wasp into its nest, then waits until the wasp lays an egg on its leg, seals the nest and leaves. The cockroach does not try to escape its tomb even as the wasp’s offspring hatches, devours the cockroach alive and pupates inside its abdomen.
In a paper recently published in PLoS One, the researchers wondered how the wasp locates the cockroach’s brain. First, using an electron microscope, they found minute sensory organs on the wasp’s stinger. Then they implanted an electrode in the wasp’s nervous system and found that these sensory organs are highly sensitive to bending of the stinger, for instance during penetration of a “brain” made of rubber. This implied that the wasp feels its way through the cockroach’s exoskeleton.
To prove this, the researchers utilized several approaches, including tricking the wasp into stinging an artificial brain.
When they implanted into a cockroach a rubbery lump that mimics the cockroach brain in texture, the wasp couldn’t tell the difference and readily injected venom. However, when the rubbery lump was softer than a real brain, or when the cockroach’s brain was removed completely or ground up, the wasp immediately felt the difference and did not inject venom.
Taken together, these results highlight an exquisitely evolved sensory organ that is adapted to navigate the wasp’s stinger through the interior of a cockroach’s head. In less than a minute, these “brain sensors” help the wasp to essentially perform brain surgery, using a two millimeter-long stinger-scalpel.
IN ONE EAR AND OUT THE OTHER
Remember that sound bite you heard on the radio this morning? The grocery items your spouse asked you to pick up? Chances are, you don’t. University of Iowa researchers have found that when it comes to memory, we don’t remember things we hear nearly as well as things we see or touch. “As it turns out, there is merit to the Chinese proverb ‘I hear, and I forget; I see, and I remember,” said graduate student and lead author James Bigelow.
“We tend to think that the parts of our brain wired for memory are integrated. But our findings indicate our brain may use separate pathways to process information. Even more, our study suggests the brain may process auditory information differently than visual and tactile information, and alternative strategies – such as increased mental repetition – may be needed when trying to improve memory,” explained psychology Prof. Amy Poremba, a corresponding author on the paper, published this week in the journal PLoS One.
Bigelow and Poremba discovered that when over 100 university undergraduates were exposed to a variety of sounds, visuals and tactile stimuli, the students were least apt to remember the sounds. In an experiment testing short-term memory, participants were asked to listen to pure tones via headphones, to look at various shades of red squares and to feel low-intensity vibrations by gripping an aluminum bar. Each set of tones, squares and vibrations was separated by time delays ranging from one to 32 seconds. Although students’ memory declined across the board as time delays grew longer, the decline was much greater for sounds and began as early as four to eight seconds after exposure.
While this seems like a short time span, it’s akin to forgetting a phone number that wasn’t written down, notes Poremba. “If someone gives you a number, and you dial it right away, you are usually fine. But do anything in between, and the odds are you will have forgotten it,” she said.
In a second experiment, Bigelow and Poremba tested participants’ memory using things they might encounter on an everyday basis. Students listened to audio recordings of dogs barking, watched silent videos of a basketball game, and touched and held common objects blocked from view, such as a coffee mug. The researchers found that between an hour and a week later, students were worse at remembering the sounds, but that their visual and tactile memory was about the same.
Both experiments suggest that the way your mind processes and stores sound may be different from the way it process and stores other types of memories – and that could have big implications for educators, design engineers and advertisers alike.
“As teachers, we want to assume students will remember everything we say. But if you really want something to be memorable you may need to include a visual or hands-on experience, in addition to auditory information,” says Poremba.
The authors believe humans’ weakness for remembering sounds likely has its roots in the evolution of the primate brain.