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

Jingjing Xu,Fajun Chen,Wei Pan,Weidong Pan,Yue Li,Guijun Wan,Yingchao Zhang,Gregory A Sword

doi:10.1242/bio.022954

Abstract

ABSTRACTProgress 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.

Highlights

The geomagnetic field is an environmental cue that varies predictably across the surface of the globe
The positional information of the geomagnetic field can be used as a magnetic map, whereas the directional information can be used as a magnetic compass (Lohmann et al, 2007)
Flight orientation distribution of a single armyworm moth To detect the availability and reliability of the self-made system, we first tested the tethered flight of a moth in the spring

Summary

Introduction

The geomagnetic field is an environmental cue that varies predictably across the surface of the globe. It provides animal with two potential types of information. The magnetic intensity and inclination can serve as a component of the navigational ‘map’, and specific magnetic conditions of local regions may act as ‘sign posts’. Organisms have evolved sensory systems to detect and exploit these cues in their environment to use information about the geomagnetic field to guide their movements in ways that enhance fitness (Lohmann et al, 2007)

Methods

Results

Conclusion