Effects of parental and progeny rearing densities on locomotor activity of 1st-stadium nymphs in the migratory locust, Locusta migratoria: An analysis by long-term monitoring using an actograph

The effects of parental and progeny rearing densities on locomotor activity in 1st-stadium nymphs of the migratory locust, Locusta migratoria, were observed over a 24- or 36-h period using an actograph. Newly hatched nymphs showed a small activity peak shortly after hatching and the peak level was significantly higher in offspring (gregarious nymphs) of crowd-reared adults than in those (solitarious nymphs) of isolated-reared adults. However, no significant difference was found between the two groups in maximum activity levels exhibited after the initial peak. Post-hatching crowding enhanced locomotor activity during 2–5 h of measurements in 2-day-old nymphs. In this case, the parental density resulted in no significant influence on locomotor activity. However, the maximum activity level shown later in the observation period was higher in gregarious nymphs than in solitarious nymphs. Interestingly, this parental effect was more pronounced in nymphs reared in group than in those reared in isolation. The parental density appeared to affect the degree of response to crowding in the progeny. No evidence was found for the phase accumulation in terms of locomotor activity. The variation observed in locomotor activity among geographical populations did not correspond to their phylogenetic relationships.