Systematicity, persistence and efficacy of selected insecticides used in endotherapy to control the red palm weevil Rhynchophorus ferrugineus (Olivier, 1790) on Phoenix canariensis

The control of the invasive red palm weevil (RPW) Rhynchophorus ferrugineus (Olivier, 1790) is a challenge. This pest has a cryptic behavior, as it achieves most of its life cycle within host tissues, where larval instars are endophytic and are out of reach from insecticides applied as cover sprays. In order to increase the efficacy of chemical control, stem injection technique, known also as endotherapy, has been implemented and recommended as an alternative approach, which requires the use of highly systemic and persistent insecticides. In this paper, we report the results of endotherapy essays carried out on ornamental palm trees, Phoenix canariensis Chabaud in Carthage, Tunis (Tunisia) and Catania, Sicily (Italy), between 2015 and 2018, using thiamethoxam, emamectin benzoate and imidacloprid. The mobility, persistence and efficacy of these insecticides were evaluated. We found that emamectin benzoate is more systemic and persistent (up to 5 months) in palm tissues than thiamethoxam and imidacloprid. Maximum residues of emamectin benzoate (1.87 mgkg) were detected in leaf base samples, 10 days after its injection. Residues of imidacloprid were detected 10 days after application (0.194 mgkg), with a maximum (0.277 mgkg) registered 2 months after its injection with a persistence period up to 3 months. Residues of thiamethoxam were detected (0.123 mgkg) only once, 10 days after application. Then values were below the limit of detection (0.1 mgkg). Field essays with selected insecticides applied as preventive and curative endotherapy treatments showed that emamectin benzoate is able to protect palm trees from RPW infestation up to 9 months.