AbstractBACKGROUNDCamptothecin (CPT), a monoterpene indole alkaloid from Camptotheca acuminate (Nyssaceae), is toxic to some insect pests but insoluble in water. Here we show that an aqueous CPT‐Na+ solution can kill the phytophagous mites Tetranychus urticae (TU), Acaphylla theae (AT) and Brevipalpus obovatus (BO) under laboratory and field conditions.RESULTSModelling of 10 day time–concentration–mortality responses of female adults to 2 mL tower sprays of three CPT‐Na+ dilutions generated LC50 and LT50 values that decreased over post‐spray days and sprayed amounts respectively. CPT‐Na+ sprays required to kill 50% BO, TU and AT were 35, 41 and 124 µg mL−1 on day 1 post‐spray, but rapidly decreased to 2.2, 2.5 and 3.6 µg mL−1 on day 5, and to 0.69, 0.77 and 1.17 µg mL−1 on day 7 respectively. In summer field trials, a spray rate of 7.5 g CPT‐Na+ ha−1 provided better control efficacy against TU (81–85%) on cotton or AT (90–93%) and BO (83–88%) in tea gardens than aramite (commercial acaricide) at the labelled rate of 56.25 g ha−1. Half of the CPT‐Na+ rate controlled the mites as effectively as aramite.CONCLUSIONWater‐soluble CPT‐Na+ is a promising plant‐sourced acaricide to combat wide‐spectrum pest mites. © 2015 Society of Chemical Industry