COLOR PATTERN PLASTICITY IN THE HOVERFLY, EPISYRPHUS-BALTEATUS - THE CRITICAL IMMATURE STAGE AND REACTION NORM ON DEVELOPMENTAL TEMPERATURE

Episyrphus balteatus is phenotypically plastic with respect to abdomin al colour pattern, It was hypothesized that developmental temperature was the environmental cue governing this plasticity. The length of dif ferent immature stages was manipulated by altering the rearing tempera tures. It was shown that all stages of the pupal developmental period were equally important in influencing adult phenotype. Lengthened pupa l period, achieved by reducing rearing temperature, resulted in darker individuals. Adjusting the length of the larval period had no affect on adult colour pattern. Colour pattern was quantified using image ana lysis, Reaction norms of black pigment on each tergite against pupal d evelopmental temperature were constructed, All reaction norms were app roximately linear. Females were darker than males at comparable temper atures. In both sexes tergite 2 was the most plastic, whereas tergite 3 was the least plastic. The results are discussed in connection with the colour plasticity having a possible thermoregulatory function. (C) 1998 Elsevier Science Ltd. All rights reserved.