Long-term monitoring of body size and morphometric ratios in the migratory locust, Locusta migratoria (Orthoptera: Acrididae)

Body size is influenced by various environmental and genetic factors. The migratory locust, Locusta migratoria L., exhibits phase polyphenism in which nymphs change body coloration and adult body dimensions undergo specific changes in response to different population densities experienced during nymphal development. In this study, I collected adults of the migratory locust L. migratoria in solitarious (low-density) populations in central Japan over 16 years to determine how adult body size changed with years and how stable their body dimensions were. Four size parameters including head width (C), hind femur length (F), forewing length (E) and total body length (TBL) were highly correlated with each other. None of these parameters correlated with years except for E with a marginally significant correlation. None of these parameters showed a significant correlation with mean annual temperatures. The classical morphometric ratios, F/C and E/F, which are often used to separate different phases, showed no significant differences among years, suggesting that they may serve as reliable phase indicators for solitarious populations. The sexual size dimorphism (SSD) was confirmed and consistently larger variances in adult body size were observed in females than in males. When the mean values of the two sexes in different years were plotted, no significant correlation was observed in any of the body size parameters including C, F and E, indicating that the two sexes varied these parameters independently. The present data may provide a basis to analyze body size changes in relation to global climate changes in the future.