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

predators extracted from soil cores followed the same pattern that predator activity density
from pitfall trapping. The soil cores estimation was performed 30 days after spraying, thus
it comprised the first two sampling dates of pitfall trapping estimates.
The predator guild was numerically dominated by carabid beetles (68%) and spiders (26%).
Much research efforts have been focused in these two groups because a) most of the species
are polyphagous predators and thus the taxonomic groups as a whole are considered
beneficial (Duelli et al., 1999); and b) they have properties for biodiagnostic purposes and
thus have an bioindicative value (Marc et al., 1999).
Negative effects of lambda-cyhalothrin on ground-dwelling predators, especially carabids
and lycosid spiders, have been widely reported on literature (Wehling and Heimbach, 1991;
Brown et al., 1990; Krause et al., 1993; Hof et al., 1995). Some authors have characterized
the effects as weak or transient (Candolfi et al., 2004; White et al., 1990; Wick and Freier,
2000; Berg et al., 1998), while others reported that the effects were strong or persistent
(Dinter and Poehling, 1992; Dinter and Poehling, 1995; Rose, 2005). Some groups
increased after lambda-cyhalothrin application (Wick and Freier, 2000).
On the other hand, some B. bassiana strains have caused mortality on non-target predator at
the laboratory level, but in general field effects of this fungus are negligible or non existent
(Riedel and Steenberg, 1998; Wang et al., 2001, but see James et al., 1995; Jaronski et al.,
1998; Flexner et al., 1986), even when a dose as high as 10 14 spores per ha was applied in
forests (Parker et al., 1997). Limited epizootic of B. bassiana on staphylinids were reported
by Steenberg et al., 1995.
In our study, lambda-cyhalothrin decreased the predator guild by 49-74%, depending on the
collecting method (weighted mean = 54%). This effect was almost constant throughout the
experiment, as the magnitude of the decrease was similar in each sampling date. No
recovery was observed at the last sampling date.
Insecticide application reduced predator activity-density immediately beginning from 1 day
after treatment. This instantaneous effect could be attributed to direct toxicological
properties of lambda-cyhalothrin on predators, but the persistent decrease (at least 60 days)
could be the result of more complex ecological mechanisms. Acute toxicity of lambda-
cyhalothrin could not persist for 60 days in the pasture, especially if high temperatures and
organic matter are present. Therefore, mechanisms such as loss of habitat quality, lack of
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