Geomagnetic field absence reduces adult body weight of a migratory insect by disrupting feeding behavior and appetite regulation

The geomagnetic field (GMF) is well documented for its essential role as a cue used in animal orientation or navigation. Recent evidence indicates that the absence of GMF can trigger stress-like responses such as reduced body weight, as we have previously shown in newly emerged adults of the brown planthopper, Nilaparvata lugens. To test the hypothesis that reduced feeding in the absence of the GMF leads to a decrease of N. lugens body weight, we compared magnetic responses in feeding behavior, glucose levels, and expression of magnetoreception- and appetite-related genes in brown planthopper nymphs exposed to either a near-zero magnetic field (NZMF, i.e., GMF absence) or typical GMF conditions. In addition to observing the expected responses in the expression of the potential magnetosensor cryptochromes, the food intake of 5th instar nymphs was significantly reduced in insects reared in the absence of GMF. Insects that exhibited reduced feeding reared in the absence of the GMF also had higher glucose levels which is associated with food aversion. Expression patterns of appetite-related neuropeptide genes were also altered in the absence of GMF in a manner consistent with diminishing appetite. These findings support the hypothesis that strong changes in GMF intensity can affect insect feeding behavior and underlying regulatory processes. Our results provide further evidence that magnetoreception and regulatory responses to GMF changes can affect a wide variety of biological processes.