Behavioral evidence for a magnetic sense in the oriental armyworm,Mythimna separata

Abstract

Progress has been made in understanding the mechanisms underlying directional navigation in migratory insects, yet the magnetic compass involved has not been fully elucidated. Here we developed a flight simulation system to study the flight directionality of the migratory armyworm Mythimna separata in response to magnetic fields. Armyworm moths were exposed to either a 500 nT extreme weak magnetic field, 1.8 T strong magnetic field, or a deflecting magnetic field and subjected to tethered flight trials indoors in the dark. The moths were disoriented in the extreme weak magnetic field, with flight vectors that were more dispersed (variance=0.60) than in the geomagnetic field (variance=0.32). After exposure to a 1.8 T strong magnetic field, the mean flight vectors were shifted by about 105° in comparison with those in the geomagnetic field. In the deflecting magnetic field, the flight directions varied with the direction of the magnetic field, and also pointed to the same direction of the magnetic field. In the south-north magnetic field and the east-west field, the flight angles were determined to be 98.9° and 166.3°, respectively, and formed the included angles of 12.66° or 6.19° to the corresponding magnetic direction. The armyworm moths responded to the change of the intensity and direction of magnetic fields. Such results provide initial indications of the moth reliance on a magnetic compass. The findings support the hypothesis of a magnetic sense used for flight orientation in the armyworm Mythimna separata.

Central Projections of Antennal and Labial Palp Sensory Neurons in the Migratory Armyworm Mythimna separata

“…My. separata might actually possess corresponding arrangements as well, since it is reported to maintain consistent directions when migrating ( Xu et al, 2017 ). Generally, the antennal sensilla of My.…”

The Earth’s Magnetic Field and Visual Landmarks Steer Migratory Flight Behavior in the Nocturnal Australian Bogong Moth

“…Although the importance of a magnetic compass for long-distance migration in birds [9], sea turtles [12], and fish [13] has been long established, its role in long-distance migration in insects is unknown. Tentative evidence suggests that some migratory moths may sense magnetic fields [14][15][16], as may some butterflies [17,18], such as the diurnal long-distance migratory monarch butterfly, Danaus plexippus [18], although in many of these studies very strong (unnatural) magnetic fields were used to show effects and the evidence is also conflicting [7,19]. Hitherto studied migratory butterflies instead appear to rely primarily on a sun compass [7,[20][21][22], and it remains unclear how, or whether [19], they use the Earth's magnetic field for navigation in natural circumstances.…”

Peer Review #2 of "Removal or component reversal of local geomagnetic field affects foraging orientation preference in migratory insect brown planthopper Nilaparvata lugens (v0.1)"

“…Accordingly, it has been confirmed that a magnetic compass was involved in both species (Srygley et al 2006；Guerra et al, 2014. It is also the case for some migratory moths as the Mythimna separata that maintain migratory direction in the night sky (Xu et al, 2017). The use of magnetic compass has also been found in foraging of insects, including honeybee and ants.…”