Resistance Mechanisms in Sweetpotato Whitefly (Homoptera: Aleyrodidae) Populations from Sudan, Turkey, Guatemala, and Nicaragua

Publisher Website
Google Scholar
Abstract
Resistance mechanisms in populations of sweet potato whitefly, Bemisia tabaci (Gennadius), from Sudan, Turkey, Guatemala, and Nicaragua were investigated. Application of monocrotophos plus the synergist tricresylphosphate revealed the presence of highly active nonspecific est erases in the populations from Guatemala and Nicaragua but not in those from Turkey and Sudan. Est erase activity specific for cypermethrin was very high in the populations from Sudan and Guatemala but negligible in that from Turkey. Strong synergism of monocrotophos by piperonyl butoxide in sweet potato white flies from Guatemala and Nicaragua indicated high mixed-function oxidase (MFO) activity. Those from Sudan and Turkey had no measurable MFO. With cypermethrin, increased toxicity was caused by piperonyl butoxide in all four populations. In vitro est erase measurements yielded corresponding results; highest esterase levels were measured in populations from Nicaragua, followed by those from Guatemala and Sudan. The population from Turkey had somewhat similar est erase activity as the susceptible strain; however, a shoulder in the distribution indicated the presence of individuals with relatively high enzyme levels. Measurements of acetylcholine est erase (AChE) sensitivity to inhibition by monocrotophos and carbofuran revealed that populations from Turkey, Sudan, and Guatemala were insensitive to monocrotophos. AChE of sweet potato white flies from Nicaragua was less resistant to monocrotophos but considerably more resistant to carbofuran than that of the other three populations. The presence and expression of different components constituting the resistance mechanisms in the four populations vary but provide a total resistance level that is similar in all four cases.