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minutes before peak of minutes after peak oscillation peak

FIGURE 3 Oscillation underlying the feeding behavior of the migratory locust, L. migratoria. (A) Feeding record of an individual during a 12-h light phase. Notice that each meal begins close to the peak of a 14.5-min oscillation. (B) Times at which feeding started relative to the peak of the oscillation for eight insects on one 12-h day. [Reproduced, with permission, from Simpson, S. J. (1981). An oscillation underlying feeding and a number of other behaviours in fifth-instar Locusta migratoria nymphs. Physiol. Entomol. 6, 315-324.]

minutes before peak of minutes after peak oscillation peak

FIGURE 3 Oscillation underlying the feeding behavior of the migratory locust, L. migratoria. (A) Feeding record of an individual during a 12-h light phase. Notice that each meal begins close to the peak of a 14.5-min oscillation. (B) Times at which feeding started relative to the peak of the oscillation for eight insects on one 12-h day. [Reproduced, with permission, from Simpson, S. J. (1981). An oscillation underlying feeding and a number of other behaviours in fifth-instar Locusta migratoria nymphs. Physiol. Entomol. 6, 315-324.]

tions are rare, and the extent to which similar rhythms occur in other insects is not known because observations are lacking.

The effects of these varying factors on feeding can be accounted for by an, as yet hypothetical, excitatory state in the central nervous system first postulated for the blow fly and subsequently elaborated for the migratory locust (Fig. 4). Only when the central excitatory state exceeds a certain threshold can feeding occur, but feeding is not an automatic consequence of reaching the threshold; it is a probabilistic event. At the end of a meal, the central excitatory state is assumed to be depressed below threshold. As time since the previous meal increases, so does the level of the central excitatory state so that it approaches and ultimately exceeds threshold. Rhythmic changes in the central excitatory state are presumed to account for the basic rhythmicity of feeding, and other events, such as defecation, may temporarily elevate it, while others (disturbance) may depress it.

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