Stink¹ bug² mothers will lay darker or lighter³ eggs depending on how much light is reflecting off of a surface. The newly discovered adaptation is likely related to how some species of stink bugs⁴ are able to deposit their eggs on top of leaves, as the darker-colored eggs are better protected from UV radiation. Surprisingly, the eggs are not darkened by melanin, but by a previously⁵ unknown pigment⁶. The findings, published July 23 in Current Biology, were driven by the curiosity of a University of Montreal PhD student, who uses the stink bugs as hosts for parasitic⁷ wasps⁸. Egg color variation exists in other species of animals, but how Podisus maculiventris (the spined⁹ solider stink bug, commonly found in fields and backyard gardens across North America) selectively controls egg pigmentation based on light perception is a new take on the trait. Certain birds and insects will lay subtly differently colored eggs, but typically in response to changes in age or diet, not a sensory¹⁰ cue from the environment. 

 

"We suspect that these bugs possess some kind of physiological¹¹ system that receives visual input¹² from the environment and then modulates¹³ the application of a pigment in real time," says lead author and Paul Abram, who is working toward his PhD in entomology. "This is the first animal found that can selectively control egg color in response to environmental conditions, but we really doubt that it's the only one."

 

Abram was inspired to pursue this line of research by the crossword¹⁴ puzzle of a newspaper lining¹⁵ the bottom of a stink bug cage. He noticed that darker-colored eggs tended to appear on the black squares of the puzzle and the lighter-colored eggs on the light squares. He then replicated¹⁶ this observation in the lab using Petri dishes that were painted black or white. This was the tip-off of a relationship between surface brightness and stink bug egg color.

 

"We did a whole suite¹⁷ of experiments to determine whether females control egg color or whether eggs themselves are responding to the light," Abram says. "What we show is that color is likely influenced by how a female stink bug perceives the ratio of amount of light reflecting off of a surface to the amount of light coming down from above her head."

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