 with a map of those ratios in rainwater, researchers have developed a clearer picture of how and where the moths migrate across North and South America. The findings advance understanding of gene flow and insecticide resistance spread among corn earworms and can improve integrated pest management practices. The researchers found a pronounced pattern of south-to-north migration and also found evidence of north-to-south reverse migration. (Photo courtesy of Silvana Paula-Moraes, Ph.D.)</p><p>” data-image-caption=”</p><p>By comparing ratios of hydrogen isotopes in corn earworm moths (<em>Helicoverpa zea</em>) with a map of those ratios in rainwater, researchers have developed a clearer picture of how and where the moths migrate across North and South America. The findings advance understanding of gene flow and insecticide resistance spread among corn earworms and can improve integrated pest management practices. The researchers found a pronounced pattern of south-to-north migration and also found evidence of north-to-south reverse migration. (Photo courtesy of Silvana Paula-Moraes, Ph.D.)</p><p>” data-medium-file=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?fit=325%2C217&ssl=1″ data-large-file=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?fit=1024%2C683&ssl=1″ class=”size-large wp-image-22426″ src=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=1024%2C683&ssl=1″ alt=”Close-up of a corn earworm moth resting on a green leaf. The moth has a pale body and large, green compound eyes. The background consists of blurred green leaves, with the moth partially hidden among them.” width=”1024″ height=”683″ srcset=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=1024%2C683&ssl=1 1024w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=325%2C217&ssl=1 325w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=768%2C512&ssl=1 768w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=1536%2C1024&ssl=1 1536w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=2048%2C1365&ssl=1 2048w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-helicoverpa-zea.jpg?resize=1200%2C800&ssl=1 1200w” sizes=”(max-width: 1000px) 100vw, 1000px” data-recalc-dims=”1″/>By comparing ratios of hydrogen isotopes in corn earworm moths (Helicoverpa zea) with a map of those ratios in rainwater, researchers have developed a clearer picture of how and where the moths migrate across North and South America. The findings advance understanding of gene flow and insecticide resistance spread among corn earworms and can improve integrated pest management practices. The researchers found a pronounced pattern of south-to-north migration and also found evidence of north-to-south reverse migration. (Photo courtesy of Silvana Paula-Moraes, Ph.D.)</p><p>By John P. Roche, Ph.D.</p><p>The corn earworm (Helicoverpa zea) is a moth pest that feeds on a wide range of host plants, including corn, cotton, and soybeans. It causes immense economic damages each year to North America’s agriculture industry. To inform control efforts, a group of researchers across North America uncovered migration patterns of corn earworms using a clever chemical analysis and reported their findings in April in Environmental Entomology.</p><p>As adults, corn earworm moths often migrate long distances among geographic locations, and understanding their migration patterns is important for designing optimal pest-control strategies. Migration allows earworms to overwinter in a region with suitable temperatures and then move to temperate regions in the warmer months to take advantage of resources that are seasonably available farther north. But how can researchers measure migration in such small creatures? It is difficult to mark and recapture individual moths, but scientists have devised an ingenious way to track individual moths without the need for marking them—through the measurement of hydrogen isotope ratios.</p><p>Two stable isotopes of hydrogen are found in nature: protium (1H), which has a proton and no neutron, and deuterium (2H), which has a proton and one neutron. On Earth, deuterium is far less common—about only one in 6,400 hydrogen atoms in the ocean are 2H. However, the ratio between protium and deuterium in precipitation varies geographically around the globe, and this variation allows entomologists to measure migration patterns.</p><p><img decoding=)
” data-image-caption=”
These maps show examples of northward migration of corn earworm moths (Helicoverpa zea). One sampled moth is shown on each panel, with the red circle indicating its collection location in southern Ontario. The scale on the right shows the probability (p-values) of the geographic origin of each sampled moth, with p-values above 0.5 and closer to 1 (yellow to green colors) being more likely sites of origin. (Image originally published in Paula-Moraes et al 2024, Environmental Entomology)
” data-medium-file=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?fit=325%2C102&ssl=1″ data-large-file=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?fit=1024%2C320&ssl=1″ class=”size-large wp-image-22430″ src=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=1024%2C320&ssl=1″ alt=”A series of six maps shows longitudinal data with colored intensity ranging from 0.00 to 1.00, indicating different migration values within North and Central America. Each map is labeled CAN followed by a different number (1, 2, 3, 4, 9, 10). A red dot is marked on each map.” width=”1024″ height=”320″ srcset=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=1024%2C320&ssl=1 1024w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=325%2C102&ssl=1 325w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=768%2C240&ssl=1 768w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=1536%2C480&ssl=1 1536w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=2048%2C640&ssl=1 2048w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?resize=1200%2C375&ssl=1 1200w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/corn-earworm-origin-maps.jpeg?w=3000&ssl=1 3000w” sizes=”(max-width: 1000px) 100vw, 1000px” data-recalc-dims=”1″/>These maps show examples of northward migration of corn earworm moths (Helicoverpa zea). One sampled moth is shown on each panel, with the red circle indicating its collection location in southern Ontario. The scale on the right shows the probability (p-values) of the geographic origin of each sampled moth, with p-values above 0.5 and closer to 1 (yellow to green colors) being more likely sites of origin. (Image originally published in Paula-Moraes et al 2024, Environmental Entomology)
In Minnesota, there are generally two migratory flight periods per year, one in June and then one in late July to early August. In the first flight period, moths migrate in from southern latitudes. In the second flight period, multiple flights occur among a mixture of migrant moths and local offspring of migrating moths from the first flight period. Therefore, the local moths sampled in Minnesota, which were collected in September, might have been young produced by migrant moths arriving in the warm months and not from moths that overwintered.
Samples in southern regions were not found to originate in northern regions. But they were sampled in July and August, so northern moths may not yet have reached these sampling areas.
The hydrogen-isotope-ratio measurements made by Paula-Moraes and colleagues suggest that corn earworms migrate south to north from Central America, the Caribbean, and the Southeastern U.S. to the Midwest and Canada as weather conditions improve with the advent of spring and summer. They also observed reverse migration of the moths, from north to south.
 with a map of those ratios in rainwater, researchers have developed a clearer picture of how and where the moths migrate across North and South America. Shown here is a light trap used to collect corn earworm moths. (Photo courtesy of Silvana Paula-Moraes, Ph.D.)</p><p>” data-image-caption=”</p><p>By comparing ratios of hydrogen isotopes in corn earworm moths (<em>Helicoverpa zea</em>) with a map of those ratios in rainwater, researchers have developed a clearer picture of how and where the moths migrate across North and South America. Shown here is a light trap used to collect corn earworm moths. (Photo courtesy of Silvana Paula-Moraes, Ph.D.)</p><p>” data-medium-file=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?fit=325%2C433&ssl=1″ data-large-file=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?fit=768%2C1024&ssl=1″ class=”size-medium wp-image-22431″ src=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?resize=325%2C433&ssl=1″ alt=”A wooden pole stands in a grassy field at dusk, fitted with a glowing blue and green light device. The background is dark with the silhouette of trees and a cloudy sky, slightly illuminated by the fading light.” width=”325″ height=”433″ srcset=”https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?resize=325%2C433&ssl=1 325w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?resize=600%2C800&ssl=1 600w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?resize=450%2C600&ssl=1 450w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?resize=300%2C400&ssl=1 300w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?resize=150%2C200&ssl=1 150w, https://i0.wp.com/entomologytoday.org/wp-content/uploads/2024/06/light-trap.jpg?w=768&ssl=1 768w” sizes=”(max-width: 325px) 100vw, 325px” data-recalc-dims=”1″/>By comparing ratios of hydrogen isotopes in corn earworm moths (Helicoverpa zea) with a map of those ratios in rainwater, researchers have developed a clearer picture of how and where the moths migrate across North and South America. Shown here is a light trap used to collect corn earworm moths. (Photo courtesy of Silvana Paula-Moraes, Ph.D.)</p><p>The migratory patterns of corn earworms suggested by this study have important implications for integrated pest management. When the moths migrate, the migration can create gene flow that reintroduces insecticide-resistant alleles to populations where insecticides were used. This pattern has been observed for pyrethroid insecticides, and with Bacillus thuringiensis (Bt) toxins used for corn earworm control.</p><p>The investigators note that this and similar studies made conclusions based on only one biogeochemical marker. Future studies on natal origin of insects could be made even more accurate by combining multiple biogeochemical markers. They also suggest that studies of frequencies of alleles for resistance to insecticides and Bt toxins should take into consideration gene flow from migratory corn earworm moths. “I feel that future studies will continue to explore the use of isotopic gradients,” Paula-Moraes says, “and should be combined with region-specific information to refine predictions of arrival and annual colonization of crops in areas where this pest does not overwinter.”</p><p>Looking to the future, climate change may affect corn earworm migration patterns. With warmer temperatures, the pests could overwinter further north, and more moths could migrate north in the first seasonal flight, leading to larger numbers of moths in the population. This could make information about migration patterns even more important for successful integrated pest management.</p><p>In summary, Paula-Moraes says, “Our study added insights into the continental-scale migratory behavior and geographic origins of H. zea populations, which is crucial for developing effective pest management strategies and understanding the potential for gene flow and insecticide resistance spread.” Measurement of hydrogen isotope ratios is an elegant and innovative technique, and it offers promise for helping optimize control of corn earworm infestations.</p><p>John P. Roche, Ph.D., is an author, biologist, and science writer with a Ph.D. and postdoctoral fellowship in the biological sciences and a dedication to making rigorous science clear and accessible. He authors books and articles, and prepares materials for universities, scientific societies, and publishers. Professional experience includes serving as a scientist and scientific writer at Indiana University, Boston College, and the UMass Chan Medical School; serving as a visiting professor at four tier-one schools; and developing concept-based science curricula for universities and publishers.</p><p>
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