Insecticide efficacy was determined by estimating densities of
L. oryzophilus larvae and pupae three to four weeks after establishment
of permanent flood. Root/soil core samples were collected into
plastic bags haphazardly by walking through the cuts or plots of
each treatment from one corner to another in an S-shaped pattern
and pulling core samples at approximately equally spaced intervals
of at least 25 m. Samples were not taken close to the edge or the
levee of the plot or cut. The core sampler was a metal cylinder with a
diameter of 9.2 cm and a depth of 7.6 cm attached to a metal handle.
Root/soil cores were then placed into 40 mesh screen sieve buckets
and soil was washed from roots. Buckets were placed into basins
with salt water, and larvae and pupae were counted as they floated
to the water surface. In 2008, 5 to 14 core samples were taken from
each cut. In 2009, 6 to 10 cores were taken per cut; in 2010, 10 cores
were taken per cut. In 2011, 10 cores were taken per plot.