High resistance to pyrethroid insecticides associated with ineffective field treatments in Triatoma infestans (Hemiptera, Reduvidae) from the north of Argentina.

PICOLLO M.I. ; C.V. VASSENA; P. SANTO-ORIHUELA; E. ZERBA

Journal of Medical Entomology

Entomological Society of America.

Lugar: Lanham, Maryland; Año: 2005 vol. 42 p. 637 - 642

Field populations of Triatoma infestans were collected during 2002 from four villages in the north of Argentina (El Chorro, La Toma, El Sauzal and Salvador Mazza), after application of deltamethrin and other pyrethroids was ineffective. High levels of resistance to the pyrethroid insecticides deltamethrin, â-cypermethrin, â-cyfluthrin, and lambda-cyhalothrin, were detected in all of the evaluated populations. The resistance ratio (RR) to pyrethroids determined by topical application ranged from 50.5 (deltamethrin, El Sauzal) to 667.6  (â-cyfluthrin, Salvador Mazza). None of the pyrethroid resistant insects was resistant to the organo-phosphorus insecticide fenitrothion. Topical application of piperonyl butoxide (PBO) to the most deltamethrin resistant population (Salvador Mazza), led to slight reduction in levels of resistance. Activity of  P450 monooxygenase measured in individual insects through ethoxycoumarine O-Deethylase (ECOD), showed a slight but noticeable difference in the distribution of activities between susceptible and resistant populations. The total percentage of insects below 0.48 pmol 7-OH coumarine/ m./ i. Was 36.4 for Salvador Mazza population and 64.3 pm 7-OH coumarine/m./i. Whereas a low level of resistance to deltamethrin was previously related to monooxygenase activity in T. infestans, the high levels of resistance shown by these populations, appears to involve monooxygenase in combination with other resistance mechanisms, for example insensitivity of nervous membrane (kdr). Researches on T. infestans resistance are now in progress to improve Chagas vector control programs in Latin America and to implement resistance management strategies.