It was another normal day of collecting and examining insect eggs in the lab for New Mexico State University grad student Danielle Lara and entomology professor Scott Bundy. On this particular day though, something happened that caused Lara to distrust her own eyes.
An assassin bug that the duo had collected earlier had laid eggs over the weekend. Bundy collected the eggs and placed them in a petri dish and told Lara to take a look at the egg mass the assassin bug had laid.
“I placed the eggs under the microscope and noted the eggs looked similar to other assassin bug egg masses I had seen,” Lara said. “Upon further examination, I realized the tops of the egg masses all started to open up like flowers, in sync”
Doubting her eyes and sanity, Lara asked Bundy to look at the eggs to check to see if he was seeing the same thing.
“Sure enough, he saw them react the same way,” Lara said.
Bundy explained that assassin insects are common in North America and around the world and many are beneficial insects because they eat other insects. This has drawn interest to them from researchers, but a lot about their biology is not known.
“When we first witnessed these tiny eggs reacting in such a bizarre manner, we thought surely this has been researched or written about before,” Lara said. “We were only able to find one paper on the subject matter, but we got excited because we knew we could expand on what was going on with the eggs. The paper we found was rather brief but it gave us a starting point on where to begin our research.”
Bundy said that’s when the detective work started.
“The fact that the top part of the egg moved while the rest of it stayed still is so fascinating,” Bundy said. “We had to figure out the mechanism. The way it moved, we thought it had to be something that’s living that was causing it, but we had eggs that were about two years old that were also moving the same way. So, we looked at them up close, used lasers to reflect off of their structures, and started putting the pieces together.”
The researchers initially thought it could be light that was causing the top of the eggs to react.
“I think we both thought the eggs were reacting to light, especially since when we first observed the eggs moving, they were under a microscope light. We ran a few trials to test this theory and soon realized this wasn’t the case,” Lara said.
After many test trials to rule out potential causes of movement, they finally found their answer.
“When we finally figured out water was the mechanism behind the movement of the eggs, I remember feeling relieved and excited. I thought: ‘Yes! Finally, an answer!’” Lara said.
Images from a microscope helped Lara and Bundy to see what the cell was doing and how the water was traveling through the egg.
“The flower-like part of the egg is called the corolla. The cells there receive the water and funnel it through the egg and allow water to be sucked in and out of the egg,” Bundy said. “The fact that an egg that was two years old was still moving shows that this is a physical property of the egg, which is so interesting.”
Bundy explained that other assassin bugs have unusual eggs, but nothing like this, as it is only a certain genus of the assassin bug’s eggs that does this.
Bundy’s and Lara’s research appeared in the April issue of Proceedings of the Entomological Society of Washington. Bundy said he would like to look more into the evolutionary reasons of why this mechanism evolved, but doesn’t have any immediate plans to work on it now.