QUIESCENCE IN THE COLORADO POTATO BEETLE, LEPTINOTARSA-DECEMLINEATA

Quiescence (death feigning) was induced in the Colorado potato beetle, Leptinotarsa decemlineata by mechanical disturbance of live and artif icial plants on which beetles were walking, feeding or grooming. The r esponse consisted of a sudden cessation of activity lasting 12 to 500 s. Recovery from this immobile state was usually preceded by either an tennal or leg movement. The time taken for beetles to come out of the immobile state (i.e. recovery time) was not dependent on age or sex of beetles or on stimulus duration, but was dependent on degree of displ acement and on satiation level. Repeated stimulations led to longer re covery times and to a smaller proportion of responding beetles. Stimul ation within the immobile state also prolonged recovery time. The most effective frequency of mechanical disturbance for startling beetles w as 30 Hz. This response is presumed to be part of the extensive defens e repertoire of this beetle, but we have so far been unable to discove r a natural enemy that will elicit it.