Synergism to acaricides in resistant Neoseiulus californicus (Acari: Phytoseiidae), a predator of Tetranychus urticae (Acari: Tetranychidae)

Tetranychus urticae Koch is one of the most important phytophagous mite species worldwide, and Neoseiulus californicus (McGregor) is the main predatory mite species marketed for control of this pest in Brazil. The present study aimed to evaluate the toxicity of acaricides on both prey and predator mites and to assess mechanisms of resistance to acaricides in the predator. Concentration-response curves for the mite populations were established using the acaricides abamectin, chlorfenapyr, diafenthiuron, spiromesifen and fenpyroximate. Acaricide field dose effect on predator survival was also assessed. Additionally, synergism of PBO, TPP and DEM to fenpyroximate and chlorfenapyr was performed on the predator to preliminarily assess the involvement of detoxification enzymes on their toxicities. Ovicidal effects of acaricides were also evaluated on N. californicus eggs. Abamectin was the most toxic acaricide for both T. urticae (LC50 varying from 0.02 to 0.24 mg/L) and N. californicus (LC50 varying from 3.92 to 4.94 mg/L). Chlorfenapyr, diafenthiuron, fenpyroximate and spiromesifen are promising acaricides for the integrated management of T. urticae in combination with N. californicus. However, spiromesifen efficacy is stage dependent. Resistance of N. californicus to chlorfenapyr (RR50 = 14.69-times) and fenpyroximate (RR50 = 113.96-times) was observed for Bonito and Brejão populations, respectively. Synergism of chlorfenapyr toxicity in both N. californicus populations suggested an involvement of CYP450-dependent monooxygenases in the resistance, while these and esterases seem to be involved in the resistance to fenpyroximate. Survival of N. californicus was reduced to zero in a maximum of 12 h, to abamectin only. Excepting abamectin, the other acaricides must have their use encouraged regarding chemical-biological control association.