Susceptibility of Phthorimaea operculella (Zeller) to Insecticides

Seven technical grade insecticides were evaluated against a susceptible population and against two field populations of the potato tuberworm Phthorimaea operculella (Zeller) by topical application to third-instar larvae. Using a standard susceptible laboratory colony, we calculated median lethal doses (LD50) of 0.39, 0.059, 0.12, 0.00022, 0.18, 0.010 and 0.0007 μg/larvae for the insecticides DDT, methyl parathion, ethyl parathion, azinphosmethyl, malathion, carbaryl and permethrin, respectively. By comparison, we found that a wild population from Oyameles, Puebla was susceptible to the insecticides while a population from Leon, Guanajuato was susceptible to DDT, methyl parathion, ethyl parathion, malathion and permethrin, but was resistant to azinphosmethyl and carbaryl.