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

a dose of 10 12 spores per ha was selected. Finally, no treated plots remained as control. All
treatments were applied on 15 October 2003, spraying an equivalent to 200 L of tank mix
per ha using a standard horizontal bar mounted on a tractor. Control plots were sprayed
with water.
Predator sampling.
Surface predators were sampled by dry pitfall traps. Pitfall trap capture of individuals of the
same taxa at different locations of the same habitat during the same time period can be
compared as a measure of the relative abundance at each location (Maloney, 2002). Plastic
cups (370 mL, 10 cm high, 5 cm diameter) drilled at bottom for drainage were used as
traps. Sampling was performed once before spraying and three times after spraying (Fig. 1).
In each sampling date, traps were active for 4 days and they were checked daily. We put
twelve traps per plot, arranging them on 3 rows by 4 columns. The traps were put in the
center of each plot and wide mesh plastic net supported by wooden sticks was used to avoid
bird foraging on insects captured. Trap catches were pooled over each plot.
All collected arthropods were placed into a 70% ethanol solution and stored until the
samples could be sorted under a dissecting microscope. Arthropods were identified
comparing them to a reference collection held at Entomology Laboratory, Universidad
Austral de Chile and with the help of specialists (see Acknowledgements).
Statistical analysis.
We use one-way analysis of variance to test for differences in relative abundance for each
of the five predominant carabid species and two spider families as well as for all seven
combined (see Table 1). No statistical analyses were performed on the rare species,
although they were included in total trap analysis. When significant treatment effects were
detected, means were compared by Fisher’s least significant difference test (p=0.05). Data
were transformed (log(x+1)) before analysis, which were performed in S-Plus software.
Analyses were done separately in each sampling date.
Results
A total of 1608 individuals were captured in the sampling period. Ground predators were
comprised by carabid beetles (11 species, 71%) and spiders (two families, 29%). The
carabid assemblage was dominated by four species accounting by 89% of the captures:
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