Tenebrio beetle pupae show a conditioned behavioural response to pulse rotations of a geomagnetic field

Pupae of holometabolous insects are not motionless and insensitive developmental stages. Their behavioural display is restricted to rotations or contractions of the abdomen in a range of movements from the clearly visible to the microscopic of the order of tenths of microns. Pupae react spontaneously and surprisingly sensitively to mechanical, light or sound stimuli. In the present study, reactions of yellow mealworm beetle ( Tenebrio molitor , L.) pupae to a geomagnetic field rotation are examined. By means of a micromechanical recording technique, peaks of abdominal contractions are monitored before and after magnetic treatment and show that spontaneous behavioural reaction to a magnetic pulse is insignificant. Nevertheless, using negative reinforcement training, a conditioned magneto-sensitive reaction is elicited. These surprising sensory and behavioural capacities of an insect pupa are discussed.