Susceptibility of Cydalima perspectalis (Lepidoptera: Crambidae) larvae to some reduced-risk insecticides in laboratory bioassays

Box tree moth (BTM) Cydalima perspectalis (Walker, 1859) is the most harmful pest of different boxwood species in Europe and Asia including Caspian boxwood Buxus hyrcana in the Hyrcanian forests of Iran. Accessible and effective eco-friendly insecticides are required for the pest control. Thus, susceptibility of 2^nd and 4^th instar larvae of BTM to commercial formulation of Bacillus thuringiensis (Bt), two plant extract formulations, Bio1^® and Matrine^®, and three insect growth regulator (IGR) insecticides, chlorfluazuron, chromafenozide and diflubenzuron were investigated in laboratory bioassay. Except for diflubenzuron, significant mortality of both instar larvae was observed. At the endpoint of the experiments (96 h), 75.2–90% of second and 80–85% of fourth instar larvae had already died, as a result of feeding on leaves treated with the highest concentration of the insecticides. Furthermore, based on Probit analysis, Matrine^® exhibited the highest efficiency (lethal concentration LC₅₀ = 2.87 μL·L^–1) on 2^nd instar larvae and followed by Bio1^® (8.07 μL·L^–1), chlorfluazuron (173.3 μL·L^–1) and Bt (326.3 mg·L^–1). The LC₅₀ of Matrine^® and Bt for 4^th instar larvae were 1.75 μL·L^–1 and 335.8 mg·L^–1, respectively. Our study revealed that Matrine^® and chromafenozide could be alternatively used against BTM in situations where there is a permission and need to use insecticides.