Relative and Allometric Growth of two Gerrids (Hemiptera: Gerridae)

Gerrids are ideal for studying relative growth and allometry since their nymphal phases are clearly defined. In order to assess and compare the relative growth and ontogenetic allometry, body measurements of Gerris spinolae and Limnometra fluviorum were examined in the present study. At each developmental stage (nymph to adult), an analysis of the link between total body length and various body parts, viz., head length, head width, antenna, rostrum, fore leg, mid leg, and hind leg was conducted. Majority of the measured structures in the current investigation displayed allometric growth, and changes in the proportions of many body components during growth were noted. The morphometric measurements (in mm) for G. spinolae from the first nymphal stage to adult with regard to total body length, head length, head width, antenna, rostrum, fore leg, mid leg and hind leg ranged from 2.87 to 13.23, 0.60 to 2.20, 0.80 to 2.30, 1.90 to 7.90, 1.20 to 3.47, 1.63 to 8.93, 2.97 to 19.30, 2.50 to 18.00, respectively. For L. fluviorum, they were 1.67 to 10.20, 0.43 to 1.53, 0.60 to 2.05, 1.30 to 7.20, 0.93 to 3.27, 1.10 to 7.20, 2.13 to 19.17, and 1.60 to 15.00. Amongst the legs in the case of both nymphs and adults for both the gerrid species, the mid leg was considered to be more in measurement. The rate of change was found to be high in head width (7.80 mm) and low in mid leg (0.40 mm) for G. spinolae, and high in head length and width too (7.40 mm) and low in mid leg (0.20 mm) for L. fluviorum. The coefficient of determination was maximum for rostrum (98.84 and 94.00 %), respectively, and minimum for antenna (89.66 %) in G. spinolae, and hind leg (71.61 %) in L. fluviorum. The results of this study showed that morphometric differentiation amplified during growth and indicated that a significant portion of the morphological changes that occurred in nymphs during ontogeny were connected to morphological adaptations to move from a juvenile to an adult state.