2.5.2. Field trials
A locality, where residents store water in cement tanks for bathing
and washing purposes, was selected from the Kurunegala municipal
area. These cement tanks (180 x 120 x 90 cm) have been
reported as good breeding sites for Aedes species (13). Temephos
(1%) sand granules were applied into 148 cement tanks in 148
households to give approximately 1 ppm concentration. Required
amount of insecticide was wrapped in a piece of cloth and allowed
to float on the water surface of each tank. Bioassays were conducted
at weekly intervals using ten randomly selected tanks out
of 148 tanks. Larval cages, made from 5 L capacity buckets, were
used to hold and expose larvae to the water in tanks. Bottom of
each bucket was covered with 100-mesh nylon strainer cloth to allow
water circulation and the top of the bucket was covered with a
net. The bucket was fixed to a hole in a polystyrene board enabling
the larval cage to float in the water of the cement tank (one cage
per tank). Twenty late 3rd instar larvae of both Ae. aegypti and
Ae. albopictus were introduced separately into each of larval cages
placed in 10 randomly selected tanks. After a 24 h exposure the
buckets were removed from the tank and dead/live larvae were
counted. Bioassays were repeated so that a minimum of 200 larvae
from each species were tested against 1 ppm temephos. Control
experiments were done using the tanks filled with water alone.