Étude de la variation intrastade au cours du développement postembryonnaire de Enallagma hageni (Walsh) (Zygoptera: Coenagrionidae): facteurs agissant sur la différenciation des types de développement

INTRA-STAGE VARIATION DURING POST-EMBRYONIC DEVELOPMENT OF ENALLAGMA HAGENI (WALSH) (ZYGOPTERA: COENAGRIONIDAE): FACTORS INFLUENCING DIFFERENTIATION OF GROWTH PATTERNS — Data were obtained from a laboratory rearing of larvae, from hatching to emergence, of Enallagma hageni in a controlled environment (25 C ; 16 hours of light). These were used to analyse variation occurring in larval growth. Five different growth patterns were observed, each characterized by a particular number of instars (i.e. 9, 10, 11, 12 and 13 instars). Five variables were considered for this study: head width, length of prementum, length of metathoracic femora, length of dorsal gill and length of mesothoracic wingpads. By means of principal component analysis, size variation is compared to shape variation. The relative importance of size and shape variation during development is analysed for each growth pattern observed. Comparisons are made with what was observed in the case of E. ebrium and E. vernale along with the possible adaptive value.