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

ecruitment or depletion of prey can not be rule out as potential explanations. Following the
classification scheme for pesticide effects suggested by Hassan (1992), the lambda-
cyhalothrin effects can be considered moderately harmful (51-75% of mortality or
reduction on beneficial activity) and persistent (more than 30 days).
The B. bassiana isolate B-931 did not caused any significant adverse effects on studied
taxa, which agreed with several other studies carried out on different B. bassiana strains or
isolates. Predators showed a trend to decrease in B. bassiana plots ranging from 19-27%,
depending on which data set was considered (weighted mean = 22%), but these decreases
were not statistically significant in any date. In consequence, following the severity indexes
for non-target effects of biological control agents suggested by Lynch and Thomas (2000),
our field results ranked 0 or 1 (less than 5% of mortality induced by infection, with no
recorded significant population consequences). Therefore, the isolate B-931 posed a risk
lower than other B. bassiana isolates used at field, such as B. bassiana ARSEF 2883 (James
et al., 1995) or B. bassiana GHA (Jaronski et al., 1998). Spores were alive in significant
numbers less than one week on foliage and less than 15 days in soil. Therefore, they
degraded very quickly under field conditions and thus non-target species were exposed only
during a limited period of their life-span. This short exposure period and low dispersal
capability are fundamental to consider B. bassiana as a safe biological control agent and
could explain, at least partially, the lack of deleterious effects on non-target species. The
inherent selective properties of B. bassiana could play an important role as an explanatory
mechanism for the lack of adverse effects. In general, each strain has a narrow host range
and infectivity decreases in heterologous hosts.
The disturbance caused by lambda-cyhalothrin on predators may pose a threat both
biodiversity and the proper ecosystem functioning, including natural pest control. The level
of endemism in Chilean carabids is high (55%), despite of Chilean carabid fauna represents
just the 9% of the South American carabid species (Roig-Juñent and Domínguez, 2001).
Repeated insecticide inputs can result in the dominance of a few tolerant species, thereby
changing the predator community in the long term (Lee et al., 2001).
Despite of relatively few information is available on ecological structure and functioning of
Chilean pastures, in recent years gut contents and exclusion experiments (Carrillo,
unpubl.*) have given increasing evidence of the importance of ground-dwelling predators,
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