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

Multivariate statistics. Principal response curves (PRC) were used to analyze the time and
treatment-dependent multivariate response of non-target assemblages. Background of this
multivariate analysis is given by van den Brink and ter Braak (1999). In brief, this method
summarizes all the information of the recorded assemblage simultaneously. The principal
response, which is a weighted sum of the abundances of the taxa, was expressed as a
canonical coefficient and reflected the behavior of the treated assemblages relative to the
untreated control (Dively and Rose, 2002). In addition, PRC makes assemblage-level
responses easier to plot and interpret and can deal with the large number of zeros often
found in ecological community data.
Monte-Carlo permutation tests (1999 permutations) were used to test the significance of the
treatment effects (departures from the zero control line) at each sampling date. The partial
redundancy analysis and MC testing were performed on CANOCO software version 4.53
(ter Braak and Smilauer, 1998). Input data were log(x+1) transformed for analysis.
CANOCO outputs were used to calculate the PRCs in a spreadsheet using the formula:
Cdt = (TAU x Regr:AX1) / SD (1)
Where Cdt = standardized canonical coefficients; TAU = total standard deviation of the
species data; Regre:AX1 = Regression/canonical coefficients for standardized variables;
and SD = standard deviations of environmental variables.
Results.
Over 4111 specimens were enumerated and the numerically most important taxa were the
carabid beetles (42%), oribatid mites (20%), gnaphosid spiders (16%) and curculionid
weevils (8%). The remaining taxa accounted by the 14%. In terms of ecological
functionality, 61 % of the invertebrates were predators, 11 % were herbivores and 28 %
were decomposers.
Spore persistence.
The spore persistence on foliage and soil is shown in Figure 1. Before treatment, B.
bassiana spore number was 1,7 x 10 4 CFU/dry soil gram. One day after treatment, B.
bassiana spores increased by 70% (2,8 x 10 4 CFU/dry soil gram), but numbers dropped to
pre-treatment level by day 15. Spores in foliage peaked 82 CFU/cm 2 , but the number
decreased to almost zero one week after spraying.
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