Larval development and adult life with particular reference to ovarian maturation in certain stoneflies (Plecoptera) of the upper part of the river Wear.

Abstract

The study was divided into three main sections dealing with larval life, the adults and the eggs. The growth rates of the larvae were investigated by constructing graphs of mean body length, mean head width and mean pronotum length against time; by construction of histograms of size group frequencies for samples taken on specific dates; and by the determining of the percentage change indices of the move up of larvae from one instar to the next over specified periods of time. These three methods of evaluating the growth rates of the larvae were used to determine the degree of retardation of growth in winter if indeed retardation occurred. They also made possible comparison of growth rates of larvae at high and low stations on the river. Studies on the adults were directed towards investigating the effect of feeding or starving on life expectancy and towards the importance of feeding in relation to maturation of the eggs in the sub-order filipalpia. Mature female larvae of both filipalpian species and setipalpian species were dissected together with adults to determine when maturation of the eggs was completed. Mating behaviour was observed and flight periods determined for the commonest species. Dissections of mature female flies were carried out and egg counts were made with a view to establishing some idea of the fecundity of the commonest species. The eggs were measured and described, some were drawn and others were photographed.