Circadian Rhythm of Emergence in the Mosquito Wyeomyia mitchellii and the Effects of Light Cycles on the Pupation Rhythm of Culex nigripalpus1

Abstract

The rhythmic control of emergence was studied in 2 Florida mosquitoes, Wyeomyia mitchellii (Theobald) and Culex nigripalpus Theobald. In W. mitchellii, there were no indications of a pupation rhythm in the various light cycles tested but there was a pronounced emergence rhythm. This rhythm proved to be an endogenous circadian rhythm of the kind reported in Drosophila pseudoobscura. It showed distinct phase shifts and resetting under altered light regimes, was synchronized by a non-repeated light signal of 12 h, and, once initiated during the pupal stage, continued in DD for at least 4 days. This is the 1st report of an endogenous circadian rhythm of emergence, as opposed to a pupation rhythm, in mosquitoes. In C. nigripalpus, where a pupation rhythm occurred in LD 12:12, other light cycles during the pupal stage shifted the onset and the mean time of the emergence peak 1–3 h. This slight shift was not due to entrainment, however, but the result of the light cycles affecting the developmental period, and hence, the timing of the pupation and emergence peaks.