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

particularly carabids. Most of the studied carabids feed on a range of prey, including animal
(spiders, aphids, coleopterans, dipterans, Lepidoptera larva and hymenopterans) and not
animal materials (pollen and fungi). The gut content analysis showed that 65-80% of
content was animal, therefore the species studied (T. unistriatus, A. chilensis, F. aerea)
were predominantly carnivorous. These studies would corroborate previous findings (Lövei
and Sunderland, 1996; Kromp, 1999) on importance of carabids as natural pest control
agents. Augmenting generalist predator populations could potentially aid in the
establishment of balanced ecosystems that are less susceptible to pest outbreaks (Mathews
et al., 2004), while enhancing or retention of an assemblage of generalist predators rather
than a single species, has the potential for increasing the biological control of diverse and
multi-generation pest complexes (Brown and Adler, 1989).
To our knowledge, lycosid and gnaphosid spiders have been not quantified in Chilean
pastures, but radio-nucleotide predation experiments conducted in other grassland systems
have shown that spiders consumed a high proportion of the herbivores biomass, even over
coleopteran predation (Riechert, 1999 and included references). Most of the spiders have
long life cycles and generalist feeding habits, therefore they have limited abilities to exhibit
density-dependent tracking of their preys (Riechert, 1999). On the other hand, spiders fit
better to a equilibrium point model which can be applied to relative stable systems as
perennial pastures. Therefore, the substantial decrease on spider numbers could alter the
arthropod community dynamics and it is unclear if other groups could play the same
function, considering they exert influence on prey dynamics through ways different from
predation such as to cease feeding by the predator presence, to forage at less favorable sites
and to drop off host plants altogether in an escape response (Riechert, 1999), with a final
slowing of prey population growth.
The lost of predator species could lead to outbreaks of secondary pests, considering that the
predator species could be act as a keystone species or that intra-guild predation could relax
natural control of some herbivore species present in the pasture.
In our study oribatid mites tended to increase in lambda-cyhalothrin plots. This kind of
resurgence after pyrethroid application has been found by other authors (Dively and Rose,
2002). Profusion of decomposer, including mites, has been linked to increases in predator
densities (Badejo et al., 1995), as they are potential prey items (Lövei and Sunderland,
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