Can resistance in Bemisia tabaci (Homoptera: Aleyrodidae) be overcome with mixtures of neonicotinoids and insect growth regulators?

Tobacco whitefly, Bemisia tabaci is an important polyphagous insect pest which has developed resistance to various insecticides worldwide. Mixtures of insecticides with different modes of action may delay the onset of resistance. Bioassays were performed to investigate the effects of various mixtures of neonicotinoid and insect growth regulator (IGR) insecticides against a susceptible and a resistant strain. The results of the study showed that potentiation ratio (PR) of all neonicotinoids + buprofezin or pyriproxyfen mixtures at 1:1, 10:1 and 20:1 ratios was greater than 1 suggesting synergistic interactions between insecticides. Maximum potentiation occurred at the 1:1 ratio (PR = 1.69–7.56). The PRs for mixture of acetamiprid, thiamethoxam, thiacloprid or nitenpyram with buprofezin or pyriproxyfen at 1:10 and 1:20 ratios were less than 1 indicating antagonistic interactions. Addition of synergists, S, S, S, tri-butyl phosphorotrithioate (DEF) or piperonyl butoxide (PBO) in the insecticide solutions largely overcame the resistance to all tested neonicotinoids, indicating that the resistance was associated with esterases or mono-oxygenases, respectively. Likewise, addition of both DEF and PBO in mixture with neonicotinoids and IGRs also suggested a similar mechanism of resistance in B. tabaci to the tested insecticide groups. The mechanism of synergism between neonicotinoids and IGRs is unclear. Implications of using mixtures to counteract pesticide resistance are discussed. Mixtures of neonicotinoids with buprofezin or pyriproxyfen at a 1:1 ratio could be used to restore the efficacy of these neonicotinoids against B. tabaci.

► Mixture of neonicotinoids with IGRs with and without inhibitors at different ratios was tested against acetamiprid selected strain of whitefly.
►  Combinations of neonicotinoids and IGRs at 1:1, 10:1 and 20:1 ratios produced synergistic effects.
► The PBO largely overcame the resistance to acetamiprid, imidacloprid, thiathoxam, nitenpyram and thiacloprid indicating that the resistance was associated with the esterase or monooxygenases.
► Addition of both DEF and PBO in mixture with neonicotinoids and IGRs also suggested a similar mechanism of resistance in B. tabaci to the tested insecticide groups.
► The mechanism of synergism between neonicotinoids and IGRs is unclear.