Determination of the number of instars and size variation in the larvae and pupae of Simulium chutteri Lewis 1965 (Diptera: Simuliidae) and some possible bionomical implications

Morphometric studies show that there are seven larval instars in Simulium chutteri. A guide for separating instars of S. chutteri is included. Seasonal and sexual size variation and seasonal variation in biomass in larvae and pupae of S. chutteri are statistically analysed and discussed. Water temperature is a major factor in determining larval and pupal size variation and duration of the pupal stage. Growth in S. chutteri follows a geometric pattern and is in agreement with previous works on other species. An overlap of larger and smaller larvae at the same developmental stage resulted from the coexistence of early winter and late summer generations, respectively. Larger larvae and pupae can result in autogenous and more fecund adult females. This is important in the population dynamics of this pest species and can lead to sudden unexpected population explosions. It is suggested that population explosions could be controlled by sharply reducing the population of large individuals of S. chutteri in the spring.