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

Adverse effects of pesticides on ground beetles have been widely documented in the
Northern Hemisphere, but little is known about the response of other populations, such as
the highly endemic Chilean carabid fauna. The level of endemism in Chilean carabids is
high (55%) and they are distinctive from the carabid fauna of the rest of South America
(Roig-Juñent and Domínguez, 2001). Reducing the use of broad-spectrum insecticides can
be a particularly effective mean to conserve generalist predators (Koss et al., 2005).
Conservation biological control may rarely be successful as a stand-alone tactic, but rather,
needs to be combined with other pest management strategies (Koss et al., 2005). The use of
entomopathogenic fungus such as Beauveria bassiana rises as a good potential alternative
to design an IPM program for pastures considering D. pallens as a primary pest and
promoting actions that avoid the outbreaks of other herbivores. Some negative effects of
Beauveria spp. on non-target species have been reported (Lynch and Thomas, 2000) and it
is desirable to compare the risk posed by this fungus with the risks of the insecticides
currently used against D. pallens, before to advocate scaling up its use.
This study was conducted to accomplish two objectives: to compare the effects on
generalist predators of both a new biopesticide based on B. bassiana and a standard
chemical insecticide; and to increase the knowledge of the generalist predator assemblage
in Southern Chilean pastures.
Materials and methods.
The study was conducted from October to December 2003 at the experimental field of the
Universidad Austral de Chile, Valdivia, Chile. The naturalized pasture was comprised
primarily of ryegrass (Lolium perenne L.) and Yorkshire fog (Holcus lanatus L.), with
broad-leaf weeds covering less than 10% of the surface. The ca. 4 ha field was surrounded
by a road (one side), pastures (two sides) and a riparian area (one size). Climate is typical
of temperate zones and data are shown in Figure 1.
Three treatments were arranged in a completely randomized design, with four replicates (30
x 30 m unfenced plots). One treatment corresponded to the standard chemical insecticide
used against Dalaca spp., the synthetic pyrethroid lambda-cyhalothrin (7,5 active
ingredient per ha, Zero, ANASAC, Santiago, Chile). The second treatment was a new
biopesticide developed by the Instituto de Investigaciones Agropecuarias (INIA), consisting
of dried spores of the fungus Beauveria bassiana coded B-931. Based on previous studies,
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