Wasp Larvae "Jump" To Shadier Spots To Avoid High Temperatures and Bright Lights

While humans shade themselves with large hats and apply sunscreen to avoid getting burned by the sun, its not that easy for young insects – especially those in the larvae stage. But a now study has shown that a few species of parasitic wasp larvae literally "jump" to shadier spots in order to develop properly and survive to adulthood, researchers from Kyushu University in Japan report. 

One species that has developed this rather unique behavior is the three millimeter-long Bathyplectes anurus, which is a parasite often used as a biological pest control against alfalfa weevil (Hypera postica), a destructive agricultural pest that attacks legumes. Generally, an adult Bathyplectes anurus wasp will lay its eggs in alfalfa weevil larvae, so when the wasp larva develops, it emerges from its host and feeds on it. For the following ten months, the larva continues to develop in a self-spun cocoon in which they preform whip-like twitches to move themselves roughly five centimeters at a time if need-be to escape bright lights, according to a news release.

To study this movement, researchers observed a total of 100 Bathyplectes anurus larvae to test if this behavior is primarily a survival technique and what specific costs and benefits are involved. To do this they examined the effects of different light intensities, temperatures, as well as levels of humidity under different laboratory and field conditions.

"We hypothesized that jumping has the fitness benefits of enabling habitat selection by avoiding unfavorable environments," researchers wrote in their study. "We conducted laboratory experiments, which demonstrated that jumping frequencies increased in the presence of light, with greater magnitudes of temperature increase and at lower relative humidity."  

Specifically, researchers found Bathyplectes anurus cocoons "jumped" three times more often when exposed to light and increased temperatures, compared to those kept in the darkness. Jumping activity also increased 60 percent when humidity was low. Researchers confirmed this was a survival technique because many of the larvae opted for shadier areas when able to move freely, and those that did relocate were more likely to survive, compared to those that were left to fry under bright lights.

The cocoons were also 83 percent more likely to jump when they were placed near Japanese giant ants, which are known predators of this type of larvae, suggesting once again that this behavior is a survival technique.

Being able to jump to more a more favorable environment does come with its own set of liabilities, researchers say.  Not only does it require more energy, but jumping individuals also had a lower body mass on average. 

However, further research is needed to better understand how the physical mechanisms that allow for such cocoon jumping. The recent study was published in the journal The Science of Nature.

A video of their findings can be found online. 

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