THE SEVEN LARVAL INSTARS OF SIMULIUM ARCTICUM (DIPTERA: SIMULIIDAE)

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Abstract
The larvae of Simulium arcticum Malloch in three collections from the North Saskatchewan River of May and June 1969, 1971, and 1974 showed seven instars. The first instar larva possessed an egg burster and the seventh instar larva possessed separated cervical sclerites. The intervening instars, however, could be decisively identified only by measuring the lengths of the postgenae. The observed mean postgenal lengths for all but the seventh instar were near those predicted by the regression line logeY = 4.1216 +.2927X. The observed mean lengths of whole larvae of all seven instars were near those predicted by the regression line logeY = −.5234 +.3238X but with relatively large standard deviations. Thus there were geometric increases in size between successive instars.

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