REACTIONS OF CARPOPHILUS SPP (COLEOPTERA NITIDULIDAE) TO HUMIDITY WITH REFERENCE TO GRADIENT STEEPNESS

Gradient steepness has hitherto been confused with other gradient terminology and this may account for the failure of investigations to obtain a definite result regarding its significance in humidity behaviour studies. In this study gradient steepness is regarded as a relationship between the humidity range and the distance over which it operates. Adults of C. dimidiatus and C. hemipterus were preconditioned so as to select the moist region in gradients in which the steepness was varied as a result of altering the distance over which the humidity range operated. It was found that at 0·12 per cent R.H. per cm, in the humidity range 46·5-52·5 per cent R.H., adults were unable to select the moist region as they did at a steepness of 0-·24 per cent R.H. per cm. In the humidity range 67·5-72·5 per cent R.H., at a steepness of 0·1 per cent R.H. per cm, C. hemipterus adult females exhibited a selection for the moist region of the gradient. Gradient steepness, i.e. humidity increment per unit distance, is thus an important physical factor of the gradient, warranting careful evaluation in humidity behaviour studies. © 1969.