Levels of insecticide resistance in Phthorimaea absoluta (Meyrick) populations collected from South India

Phthorimaea absoluta (Meyrick) has become a serious threat to global tomato production. Management of an invasive pest mainly relies on insecticides because of immediate effect. In this study, susceptibility of second instar larvae of P. absoluta collected from different locations of south India to seven insecticides belonging to different chemical groups was evaluated to determine the lethal concentration (LC) values. Leaf dip bioassay method revealed that the LC₅₀ values in P. absoluta varied to different tested insecticides among different populations collected from south India. The median lethal concentrations of all the insecticides against P. absoluta ranged from 1.4 to 106.0 ppm. Among tested insecticides, chlorantraniliprole showed more toxicity to second instar larvae of P. absoluta which recorded lowest LC₅₀ values, followed by cyantraniliprole, spinosad, indoxacarb, flubendiamide and the least susceptibility of P. absoluta larvae were recorded to neonicotinoids (acetamiprid and imidacloprid). Regarding resistance ratio, maximum of 7.8-fold resistance to acetamiprid was recorded when compared to remaining six insecticides.