Effect of Systemic Insecticides Applied via Drench on the Mortality of Diaphorina citri on Curry Leaf

SIMPLE SUMMARY: Huanglongbing (HLB), a disease associated with the bacteria Candidatus Liberibacter spp. and transmitted by the Asian citrus psyllid (ACP) Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is the primary and most destructive disease that affects citrus crops. The disease management tactics can target both the causal agent and the insect vector. Studies have demonstrated the potential of the curry leaf tree (Bergera koenigii L.) as a trap plant for D. citri, as it is more attractive than commercial citrus plants, in addition to being immune to the bacteria that cause HLB. The use of the trap plant technique, combined with systemic insecticides, creating an attract-and-kill system, can significantly increase the effectiveness of disease and pest management. The systemic insecticides thiamethoxam, thiamethoxam + chlorantraniliprole, and imidacloprid, frequently used in citriculture, were tested on adults of D. citri in the curry leaf tree by the drench method. The results demonstrated efficacy in controlling D. citri, showing the high mortality (>90%) of adults and a prolonged effect of biological activity after application in field and protected cultivation experiments. Low concentrations of insecticides affected D. citri oviposition. The results indicate that it is possible to combine the use of the curry leaf tree as a trap plant with systemic insecticides in citrus, increasing control efficacy and reducing the application of insecticides used in commercial groves. ABSTRACT: Huanglongbing (HLB), the most serious disease in citriculture, is caused by the bacteria Candidatus Liberibacter spp., which is transmitted by the Asian citrus psyllid (ACP) Diaphorina citri. HLB is mainly controlled with insecticides, necessitating the development of alternative methods, e.g., the use of trap plants such as curry leaf Bergera koenigii, which is highly attractive to the ACP. We evaluated the effects of the main systemic insecticides used by citrus growers, applied via drench to adults of D. citri on the curry leaf tree. We tested the persistence of three pesticides: thiamethoxam, thiamethoxam + chlorantraniliprole, and imidacloprid in protected cultivation and the field condition at 7, 14, 28, 42, 56, 70, 98, and 154 days after the application. Different concentrations of insecticides containing the active ingredient thiamethoxam were tested on adults to determine the LC(10) and LC(50). Finally, we assessed the sublethal effects on the oviposition and development of D. citri. The insecticides controlled the adults for long periods. However, in the field experiment, from 42 days after application there was a decrease in mortality caused by pesticides applied via drench, while in the protected cultivation, mortality did not decline until the last day of evaluation. The median lethal concentration (LC(50)) for thiamethoxam was 0.031 g of active ingredient per plant, and for thiamethoxam in a mixture, the LC(50) was 0.028 g a.i. per plant. In the experiment with sublethal doses, D. citri did not oviposit on the treated plants. Our findings suggest that the attract-and-kill system using the curry leaf tree and systemic insecticides is effective for the control of D. citri and contributes to the integrated management of HLB.