This Thanksgiving, we’re taking a moment to share some gratitude for an aspect of animal behavior that, well, affects some of the platters one might come across during a typical Thanksgiving feast. And I’m not talking about our feathered friends (though we’ve written about turkey behavior too).
Have you ever bit into some nice fresh sweet corn on the cob, only to find that someone got there before you…? Helicoverpa zea, AKA the corn earworm, is a moth that frequently lays its eggs on corn silk. When hatched, the larvae proceed to munch away at the young corn kernels and bore into the cob [1]. If you spend a lot of time eating corn, you might have noticed that you typically only find one worm per ear of corn – that’s because they cannibalize each other if there’s a competitor [2, 3]! After a few weeks [4], they pupate in the ground, and a dusty tan, lightly speckled moth emerges another couple weeks later, flying about for 15-30 days, continuing the cycle of life (and destruction), with individual females laying up to 3,000 eggs [1] ! The adult moths feed on tree sap and nectar [1], so, while they’re considered a major pest, they do also contribute to pollination of some crops, like citrus [5].
The moth of the Corn Earworm is normally active at night, but here is seen (at left) feeding on lantana flower nectar, in Arizona, and (at right) in Georgia, demonstrating its wide geographical range and behavioral flexibility. Left photo by Lon&Queta [Source]. Right photo by Judy Gallagher [Source].
This hungry caterpillar is considered one of the main agricultural pests in North America. While they specialize on corn, they eat a wide variety of food and fiber crops, ranging from tomatoes to lettuce to cotton and more. They’re often the reason why growers apply pesticides and search for resistant crop varieties. So, there’s a lot of interest in their behavior. Another utility of behavioral research concerns what predators might be able to target them as biocontrol agents [6]. For example, some parasitoid wasps and pirate bugs kill corn earworm eggs and larvae [7] and bats are efficient consumers of the moth stage, in places where bats aren’t pushed out by human activities [8].
Corn earworms live in every US state (except Alaska, but including Hawaii!) [9]. A recent study found that the moths migrate northward throughout the US in the spring and summer [10]. To figure this out, the authors sampled moths from throughout the US. They then essentially measured what type of elements they were made out of in the different places. Specifically, the heaviness (isotope) of the element hydrogen that is incorporated into biological tissue depends on where that tissue is formed because of rainfall patterns. So, if you look at the tissue of a moth, who ate plants that grew from water from precipitation, you know where that moth grew up. This method is called stable isotope biogeochemistry. In short, you can use chemistry to “watch” how animals migrate!
Beyond the methodological coolness, understanding corn earworm movement patterns and other aspects of their behavior can help identify ecosystem-friendly management tools. In addition, using Native American agricultural practices improve ecosystem health and farming yields [11]. For example, companion planting, where corn is planted alongside beans and squash, promotes healthier corn plants that suffer less damage from pests [12].
Importantly, as a possible corn-consumer this Thanksgiving, note that the part of the corn not eaten by the corn earworm is completely safe for consumption [7]. Sharing is caring! I’ll round this out by thanking native insect pollinators and biocontrollers for enabling the vast majority of food and fiber crops to exist.
Main featured image by Scot Nelson [Source].
Written by: Alice Michel is a PhD candidate in the Animal Behavior Grad Group. She studies gorilla communication and ranging behavior. When she’s not wading through the swamp forest or wading through virtual mountains of acoustic data, she enjoys spending time in the California sun.
References:
[1] Corn Earworm—Helicoverpa zea. Retrieved November 28, 2024, from https://entnemdept.ufl.edu/creatures/veg/corn_earworm.htm
[2] Bentivenha, J. P. F., Baldin, E. L. L., Montezano, D. G., Hunt, T. E., & Paula-Moraes, S. V. (2017). Attack and defense movements involved in the interaction of Spodoptera frugiperda and Helicoverpa zea (Lepidoptera: Noctuidae). Journal of Pest Science, 90(2), 433–445. https://doi.org/10.1007/s10340-016-0802-3
[3] Boyd, B. M., Daniels, J. C., & Austin, G. T. (2008). Predaceous Behavior by Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae: Heliothinae). Journal of Insect Behavior, 21(3), 143–146. https://doi.org/10.1007/s10905-007-9113-0
[4] Corn Earworm in Missouri | MU Extension. Retrieved November 28, 2024, from https://extension.missouri.edu/publications/g7110
[5] Monasterolo, M., Ramírez-Mejía, A. F., Cavigliasso, P., Schliserman, P., Chavanne, V., Carro, C. M., & Chacoff, N. P. (2024). Animal pollination contributes to more than half of citrus production. Scientific Reports, 14(1), 22309. https://doi.org/10.1038/s41598-024-73591-6
[6] Olmstead, D. L., Nault, B. A., & Shelton, A. M. (2016). Biology, Ecology, and Evolving Management of Helicoverpa zea (Lepidoptera: Noctuidae) in Sweet Corn in the United States. Journal of Economic Entomology, 109(4), 1667–1676. https://doi.org/10.1093/jee/tow125
[7] Corn Earworm, Helicoverpa zea. Wisconsin Horticulture. Retrieved November 28, 2024, from https://hort.extension.wisc.edu/articles/corn-earworm-helicoverpa-zea/
[8] McCracken, G. F., Westbrook, J. K., Brown, V. A., Eldridge, M., Federico, P., & Kunz, T. H. (2012). Bats track and exploit changes in insect pest populations. PloS One, 7(8), e43839. https://doi.org/10.1371/journal.pone.0043839
[9] Helicoverpa zea. Retrieved November 28, 2024, from http://www.extento.hawaii.edu/kbase/crop/Type/helicove.htm
[10] Paula-Moraes, S. V., Calixto, E. S., Santos, A. A., Reay-Jones, F. P. F., Reisig, D. D., Farhan, Y., Smith, J. L., & Hutchison, W. D. (2024). Continental-scale migration patterns and origin of Helicoverpa zea (Lepidoptera: Noctuidae) based on a biogeochemical marker. Environmental Entomology, 53(3), 487–497. https://doi.org/10.1093/ee/nvae034
[11] Kapayou, D. G., Herrighty, E. M., Hill, C. G., Camacho, V. C., Nair, A., Winham, D. M., & McDaniel, M. D. (2023). Reuniting the Three Sisters: Collaborative science with Native growers to improve soil and community health. Agriculture and Human Values, 40(1), 65–82. https://doi.org/10.1007/s10460-022-10336-z
[12] Liao, H., Zhou, Z., Liu, Y., Luo, Y., Zhang, C., Feng, Y., Shu, Y., & Wang, J. (2024). ‘The Three Sisters’ (maize/bean/squash) polyculture promotes the direct and indirect defences of maize against herbivores. European Journal of Agronomy, 155, 127118. https://doi.org/10.1016/j.eja.2024.127118
[Edited by Jacob Johnson]