Does catechin make the Mediterranean palm tree Chamaerops humilis L. an unsuitable host for Rhynchophorus ferrugineus?

The Red Palm Weevil (RPW), Rhynchophorus ferrugineus (Coleoptera: Curculionidae), is an insect pest native to Southeast Asia, which has become the major threat to palms in the Mediterranean Basin, mainly due to the movement of infested planting material. In case of infestation, the exotic weevil is difficult to control effectively and host plants often die. Chamaerops humilis (Arecales: Arecaceae) palms are reported as resistant to RPW, but little is known about the chemical basis of this resistance and about the identity of the endogenous metabolites that may be involved. In the present study, we focused on the potential toxic effect of catechin against RPW larvae. In laboratory bioassays, purified catechin from C. humilis leaves was provided to two- and five-week old RPW larvae at three different concentrations. We found that catechin can impair the survival of RPW, causing toxicity at concentrations as low as 0.03 mg g-1. Larval mortality was concentration-dependent, and furthermore larval age influenced the effect of catechin, older larvae being more susceptible than younger ones. The observed toxicity of catechin on RPW larvae agrees with the hypothesis that this compound contributes to C. humilis being an unsuitable host for this insect pest.