A team of scientists in Ohio has discovered a new way to control Helicoverpa zea, or corn earworm. They have developed a chemical that interrupts the insect’s dormancy.
Helicoverpa zea, also known as the cotton bollworm, corn earworm and tomato fruitworm, is a major pest throughout the U.S. It is typically controlled through insecticides and Bt-crops.
Most insects enter a period of dormancy, or diapause, when environmental conditions are close to a dramatic change and food is scarce. In many insects, diapause is triggered by an internal diapause hormone. This hormone responds to changes in the environment that indicate the imminence of harsh conditions, whether in temperatures that are intolerable to the insect, or the lack of food. The insect goes into a period of “sleep” and “wakes up” when its hormonal levels return to a specific point.
Disturbing that period of dormancy can mean death to an insect. If an insect does not enter diapause at the recommended time, or if it does not complete the entire cycle, the insect is vulnerable to environmental stresses that diapause usually protects it from.
Scientists at the Ohio State University have found a way to use a synthetic diapause hormone to disturb the diapause period of the pest Helicoverpa zea. The chemistry is not completely new; scientists have been using the hormone to initiate diapause in the silkworm. However, in H. zea, the hormone has the opposite effect.
The team has developed hormone chemistries for various interruptions of diapause. One hormone chemistry will prevent the larvae from entering pupal diapause and pupating. Another affects the pupae itself, interrupting its dormancy during the pupal stage. A third keeps the pupae from ever exiting the dormancy stage, preventing it from developing into a moth and laying eggs.
In H. zea, seven core amino acids usually terminate the diapause. The team re-created that chemical compound and then tested the chemistry on the larvae and pupae. The insect responded as it would if its own biological chemistry was giving them the signal. In fact, the synthetic compounds are more potent than the insect’s own amino acids.
In the laboratory, researchers David Denlinger and Qirui Zhang, two lead scientists on the project, injected the larvae and pupae with the diapause hormone. Zhang, a postdoctoral researcher and entomology and evolution and first author on the paper, is currently experimenting with delivery methods in the insect’s food.
“My guess is that these particular compounds won’t be the ones that solve the world’s problems, but this points us in the direction that could lead to some next-generation control agents,” said Denlinger.
Ohio State University (2011, September 27). Killing crop-eating pests: Compounds work by disrupting bugs’ winter sleep. ScienceDaily. Retrieved September 30, 2011, from http://www.sciencedaily.com/releases/2011/09/110928110014.htm
Q. Zhang, R. J. Nachman, K. Kaczmarek, J. Zabrocki, D. L. Denlinger. Disruption of insect diapause using agonists and an antagonist of diapause hormone. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1113863108.