In vitro evaluation of acaricidal activity of novel green silver nanoparticles against deltamethrin resistance Rhipicephalus (Boophilus) microplus

•2, 3 Dehydrosalannol and quercetin dihydrate coated silver nanoparticles were showed acaricidal properties against Rhipicephalus (B.) microplus.•First time to find and prove the superior acaricidal activity of deltamethrin neem coated silver nanoparticles against deltamethrin resistant R. (B.) microplus in vitro.•The results confirm the neem chemilloids in the form of green silver nanoparticles have better acaricidal activity against R. (B.) microplus.

An investigation was undertaken to study, for the first time, in vitro acaricidal activity of green silver nanoparticles on deltamethrin resistance Rhipicephalus (Boophilus) microplus. The compounds tested were neem coated silver nanoparticles (N-Ag NPs), deltamethrin neem coated silver nanoparticles (DN-Ag NPs), 2, 3 dehydrosalannol (2,3 DHS), 2, 3 DHS coated silver nanoparticles (2, 3-DHS-Ag NPs), Quercetin dihydrate (QDH) and QDH coated silver nanoparticles (QDH-Ag NPs). Also included in this study, for the purpose of comparison, were neem leaf extract (NLE), silver nitrate (AgNO3) and deltamethrin (D). Acaricidal activity on larvae and adults of R. (B.) microplus was tested by larval packet test (LPT) and adult immersion test (AIT) respectively. In the LPT, 100% mortality was obtained at concentrations (ppm) of 360, 6000, 260, 200, 50, 300, 85, 600 and 200 for the compounds, D, NLE, Ag NO3, N-Ag NPs, DN-Ag NPs, 2, 3 DHS, 2, 3 DHS-Ag NPs, QDH, QDH-Ag NPs respectively. In AIT, the proportions of mortality and oviposition inhibition were proportionate but the reproductive index was inversely proportional to the concentration of the compounds used. The effect of DN-Ag NPs on mortality was the highest (93.33%) at 50 ppm concentration. The mean reproductive index (0.01) and oviposition inhibition (99.16%) values were statistically significant when compared to control group. DN-Ag NPs showed significantly (P < 0.05) lower LC50 (3.87 ppm; 21.95 ppm) and LC99 (53.05 ppm; 90.06 ppm) values against both the larvae and adults of R. (B.) microplus. The oviposition inhibiting ability of various compounds was determined to assess the reproductive performance of adult female ticks. The DN-Ag NPs had potent oviposition inhibitory activity with significantly lower IC50 and IC99 values compared to the rest of the treatments at 0.034 and 51.07 ppm respectively. These results showed that the DN-Ag NPs had significant acaricidal activity against R. (B.) microplus.