A device ("ADCAS") is described, the use of which improves upon the usual dipper and eyedropper method of assaying water surfaces for the presence of aquatic mosquito stages. The ADCAS is essentially a portable, (hand-carried), metal conduit leading into and out of a detachable glass bottle. The entrance is funnel-shaped and is protected by a hardware cloth cover against leaves, twigs, etc. The exit is in the form of a self-activating siphon, the intake end of which is covered with a fine wire mesh to prevent passage of mosquito eggs, larvae, and pupae. Each successive sample of water poured into the ADCAS is automatically discharged by siphon action and simultaneously is relieved of its burden of aquatic mosquito stages; the latter being retained within the confines of the glass bottle. The ADCAS is simply and easily constructed of universally available metal and glass parts. The economy of time and the increase in accuracy gained by the use of the ADCAS in routine field surveys is considerable.