Aseasonal, undirected migration in insects: 'invisible' but common

Authors: Sappington, Thomas

Submitted to: iScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2024
Publication Date: 5/20/2024
Citation: Sappington, T.W. 2024. Aseasonal, undirected migration in insects: 'invisible' but common. iScience. 27. https://doi.org/10.1016/j.isci.2024.110040.
DOI: https://doi.org/10.1016/j.isci.2024.110040

Interpretive Summary: Insect migration usually conjures images of long-distance, multi-generation, seasonal movement between overwintering and breeding ranges. However, some species, perhaps many, that overwinter at high latitudes still engage in true migratory behavior. This phenomenon includes a number of major crop pests including European corn borer, western corn rootworm, and boll weevil, species not normally thought of as migratory. Migratory flight is a specialized behavior that is straightened-out, undistracted by resources like food or mates, and is not triggered by immediate conditions such as poor habitat or crowding. Such migratory movement occurs over substantial but relatively short distances, is spatially undirected, is not associated with host-plant abundance, and does not result in seasonal population shifts in location. Instead, it results in population mixing without changing the dimensions or location of the population. Nevertheless, the potential population-level consequences can be quite important in the contexts of pest management and insect resistance management. This information will be useful to academic and government scientists interested in the role of pest movement in designing more effective pest management tactics and strategies.

Technical Abstract: Many insect pests of agricultural crops are long-distance migrants, moving from lower latitudes where they overwinter to higher latitudes in the spring to exploit superabundant, but seasonally ephemeral, host crops. After one or more generations of breeding in the summer habitat, the descendants migrate to the species' overwintering range at lower latitudes. The migratory nature of these pests is relatively easy to recognize because of their sudden appearance in areas where they had been absent; or conversely, by their sudden disappearance from areas where they had been abundant. Radar can often detect directional movement of masses of insects high in the atmosphere during such migrations. These seasonal long-distance migration events justifiably receive a great deal of attention by researchers and ecologists because of their huge impact on ecosystems and agriculture. In contrast, many insect species, including a number of serious pests, survive hostile winter conditions at high latitudes via diapause, and therefore do not require migration to move between overwintering and breeding ranges. Yet there is evidence that individuals of several pest species that inhabit high latitudes year-round engage in migratory behavior not associated with seasonal displacement, including, for example, European corn borer (Ostrinia nubilalis), western corn rootworm (Diabrotica virgifera virgifera), and boll weevil (Anthonomus grandis grandis). In these cases, migratory flight is somewhat "invisible", because displacement is nondirectional and takes place within the larger year-round distribution where others of its species already exist making it difficult to detect. The evidence is related to recognizing true migratory flight behavior, which differs fundamentally from most other kinds of flight in that it is non-appetitive. A migrating adult is not searching for resources and migratory flight is not terminated by encounters with potential resources such as host plants, mates, or sheltering habitat. The reasons for migratory movement neither associated with tracking seasonal host plant distributions, nor with escaping lethally harsh seasonal conditions are unclear. But the result of such movement is a spatial mixing of individuals within the larger metapopulation, and this mixing has important implications for pest management and insect resistance management.