Heavy domestic and peridomestic infestations of Triatoma infestans were
controlled in two villages in southern Bolivia by the application of
deltamethrin SC25 (2.5% suspension concentrate) at a target dose of 25 mg
a.i./m^2. Actual applied dose was monitored by HPLC analysis of filter
papers placed at various heights on the house walls, and was shown to range
from 0 to 59.6 about a mean of 28.5 mg a.i./m^2. Wall bioassays showed high
mortality of T. infestans during the first month after the application of
deltamethrin. Mortality declined to zero as summer temperatures increased,
but reappeared with the onset of the following winter. In contrast,
knockdown was apparent throughout the trial, showing no discernible
temperature dependence.
House infestation rates, measured by manual sampling and use of paper
sheets to collect bug faeces, declined from 79% at the beginning of the
trial to zero at the 6 month evaluation. All but one of the houses were
still free of T. infestans at the final evaluation 12 months after
spraying, although a small number of bugs were found at this time in 5 of
355 peridomestic dependencies. Comparative cost studies endorse the
recommendation of large-scale application of deltamethrin, or pyrethroid
of similar cost-effectiveness, as a means to eliminate domestic T.
infestans populations in order to interrupt transmission of Chagas
disease.
