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

knowledge of South Chile grassland functioning precludes us from identifying which
fraction of the total diversity is needed to saturate most of the processes present in this
agroecosystem. Therefore, until the trophic relationships between the different species
could be revealed, we advocate for a conservative approach to diversity loss.
Our studies were not designed to test hypotheses about specific functional groups or
species, thus we can not identify the mechanism(s) that explain(s) the observed decreased
diversity. In spite of this, we raise concerns about continued use of these kind of
insecticides because several cases of natural regulation disruption have been recorded in
intensified agricultural systems much before explicit mechanisms that explain natural
herbivore regulation had been revealed (Hardin et al., 1995). In fact, there are several well
documented cases of release of herbivore insects from control after removing their natural
enemies (Hills and Taylor, 1951; Kenmore et al., 1984) or non-target herbivores acting like
alternative prey when the pest is scarce and contributing to support early season build-up of
generalist natural enemies (Settle et al., 1996). In an oversimplified system like pastures,
any additional biodiversity loss could exacerbate this process, reduce the system stability
and increase the reliance on external inputs, especially insecticides, to maintain its
productivity.
It remains a challenge to identify the several roles that the different species play in the
pasture. However, as it was mentioned above, negative effects on ecosystem processes with
declining biodiversity could be serious much before knowledge about explicit mechanisms
could be gathered.
Growers must be aware of how their pest practices may influence ecological processes
before to make management decisions. Inundative biological control of Dalaca pallens
using Beauveria bassiana spores did not affect grassland diversity and its components
(species richness and evenness), at least in the short term. Lambda-cyhalothrin, one of the
most common insecticides used for D. pallens control, affected all the community metrics
(diversity, richness, evenness and dominance), with unknown consequences for the
grassland agroecosystem. It was clear that the community-level impact of this broad-
spectrum insecticide was far greater that any effect of Beauveria bassiana on arthropod
community.
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