The geomagnetic field affects all living organisms on the Earth.  In this study we investigated the developmental and behavioral effects of rearing Mythimna separata in a near-zero magnetic field (<500 nT) compared to the local geomagnetic field (approximately 50 μT).  The near-zero magnetic field produced by a Helmholtz coil system significantly lengthened larval and pupal development durations, increased male longevity, and reduced pupal weight, female reproduction, and the relative expression level of the vitellogenin (Vg) gene in newly emerged females.  Moreover, the near-zero magnetic field had a considerable negative effect on the mating ratio of M. separata adults.  In addition, the moths in the near-zero magnetic field displayed less flight activity late in the night than those in the Earth’s normal geomagnetic field, indicating that the flight rhythm of M. separata may be affected by the near-zero magnetic field.  Reduction in magnetic field intensity may have negative effects on the development and flight of oriental armyworm, with consequent additional effects on its migration.

Insect migratory flight differs fundamentally from most other kinds of flight behavior, in that it is non-appetitive.  The adult is not searching for anything, and migratory flight is not terminated by encounters with potential resources.  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.  The migratory nature of these pests is somewhat easy to recognize because of their sudden appearance in areas where they had been absent only a day or two earlier.  Many other serious pests survive hostile winter conditions by diapausing, and therefore do not require migration to move between overwintering and breeding ranges.  Yet there is evidence of migratory behavior engaged in by several pest species that inhabit high latitudes year-round.  In these cases, the consequences of migratory flight are not immediately noticeable at the population level, because migration takes place for the most part within their larger year-round distribution.  Nevertheless, the potential population-level consequences can be quite important in the contexts of pest management and insect resistance management.  As a case study, I review the evidence for migratory flight behavior by individual European corn borer adults, and discuss the importance of understanding it.  The kind of migratory behavior posited for pest species inhabiting a permanent distribution may be more common than we realize.