Functional response of abamectin and bifenazate resistant and native populations of Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae)

This study aimed to investigate the impact of acaricides on the predatory capacities of native (NP) and acaricide-resistant (RP) populations of Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae). The RP was obtained in a previous study through six successive selections of abamectin and bifenazate from the NP of A. swirskii, resulting in a 25-fold resistance level. The functional and numerical responses of the NP and RP populations were evaluated under untreated conditions (control) and after treatment with the recommended concentration (100 ml/100 L distilled water) of an abamectin+bifenazate mixture at 27 ± 1 °C, under a 16:8 (L:D) photoperiod and 80 ± 5% relative humidity. The functional and numerical responses, as well as the related parameters of NP and RP females, were analyzed in response to different egg densities of Tetranychus urticae Koch (Tetranychidae). Logistic regression analysis indicated that the untreated RP and NP and the treated RP exhibited a Type II functional response, whereas the treated NP exhibited a Type III functional response. The handling times for T. urticae eggs were recorded as 0.0454 and 0.0376 hours for the untreated NP and RP, respectively, while they were calculated as 0.0420 and 0.0381 hours for the treated NP and RP, respectively. The handling time (Th) increased significantly in NP after acaricide treatment. The Th value of RP was not affected by acaricide treatment. The attack rate coefficients (α) varied considerably among the populations and treatments, with the highest value observed in the untreated RP (1.27), followed by the treated RP (1.13), the untreated NP (1.00), and the treated NP (0.71). Under untreated conditions, A. swirskii exhibited a higher α value in the RP population than the NP population. Our findings indicate that the resistant A. swirskii population can effectively feed on T. urticae eggs and oviposit, even at low prey densities and under acaricide-treated conditions.