Diversidad y control biológico de insectos - CyberTesis UACh ...

Treatments were applied on 15 October 2003, after 18:00 h, with weather conditions of
12.5 (air) and 16.4 (soil) °C, cloudy day with weak showers (rainfall is showed in Figure
1). The pasture was 15-20 cm high. All applications were made by tractor-mounted sprayer
at 200 L per ha.
Data collection.
Pitfall trapping. Pitfall traps are widely used for ground-dwelling arthropod sampling
(Spence and Niemelä, 1994). Because many factors aside from abundance influence pitfall
trap captures, we adopted the term activity-density following Thiele (1977) to record and
show our results. Pitfall traps were made from one 370 mL blank plastic cup (10 cm high, 5
cm diameter), with no cover. The cups had very small holes drilled in the bottom for
drainage. Twelve traps per plot were buried in the soil so that the lip was flush with the soil
surface and arranged on a grid, on 3 columns by 4 rows. The traps were put in the center of
the plot and the grid area was covered by a net to prevent bird foraging on caught
arthropods. The unbaited traps were 0.5 m each other and were active for a 4-days period in
each sampling date. When the traps were not active, they were inverted. The arthropods
were removed from traps every morning. Sampling was performed four times during the
study: before spraying and 1, 30 and 60 days after spraying. Activity-density from pitfall
trap captures was shown as the average number of individuals per trap in each 4-d sampling
period.
Soil cores. Thirty soil cores (9 cm diameter, 10 cm high) were extracted at random in each
plot, although they were not extracted close to the plot borders to avoid potential edge
effects. The cores were bagged to prevent arthropod escape or loss. Invertebrate were
extracted by Berlese-Tullgren method for 96 h. The cores were put inverted in extractor
over a layer of cheese-cloth over screen of extractor to prevent soil particles being
dislodged into the extractant. A mix of water and a soft detergent were used as extractant.
The content was sifted over a 2 mm mesh screen and then sifted again over a finer mesh
screen. Large specimens were separated by hand or with forks, while the remaining content
was rinsed with tap water over a