The environmental control of colouration in a bushcricket, Mygalopsis marki Bailey (Orthoptera: Tettigoniidae)

Abstract

The environmental factors proximately influencing variable colouration in the bushcricket, Mygalopsis marki, were studied in natural populations and under controlled laboratory conditions. Two major components of variable colouration were identified; a green/brown dimorphism in ground colour hue (dominant wave length) and continuous variation in the darkness of brown insects, representing a contrast between ground colour value (brightness) and the intensity of overlying black pattern. Ground colour hue differed between natural populations in different seasons and at different localities. The proportion of brown individuals was greater in populations developing over late summer than over spring at the same locality, and in populations from drier localities, as indicated by vegetation type, in the same season. Experimental studies showed that colour change occurred at moults, with green colouration promoted by increased water intake in developing nymphs. Ground colour value and pattern differed between natural populations at different localities, but not in different seasons. Ground colour value was less, and pattern was greater, in populations from localities with a dense cover of forbs and grasses. Experimental studies showed that ground colour value and pattern were influenced by the intensity of incident radiation received by developing nymphs, with decreased intensity promoting lower value and greater pattern.