Eco-friendly biocontrol of the red palm weevil using the local brown alga Hormophysa cuneiformis

The red palm weevil (RPW), Rhynchophorus ferrugineus (Olivier) is a major destructive pest of date palms. The aqueous extract of a local brown alga was tested for the biocontrol of this insect. In that regard, we evaluated the insecticidal effects of aqueous extract of the brown alga, Hormophysa cuneiformis, against larvae and adults of R. ferrugineus through dietary bioassay. The FTIR of both the dried algal biomass and its aqueous extract was performed to reveal some of the functional groups present which are indicative of bioactive compounds. The insecticidal efficacy of its aqueous extract was assessed at three concentrations. Adult R. ferrugineus showed a concentration-dependent response to H. cuneiformis extract. After 10 days of exposure, mortality reached 80% at 10%, compared with 66.67% and 53.33% at 5% and 2.5%, respectively. Exposure of larval and pupal stages to the 5% aqueous extract significantly reduced survival, disrupted development, and impaired adult emergence, resulting in up to 68% larval mortality. In addition, the treatment significantly affected key biological traits, including larval weight and developmental duration of R. ferrugineus. The FTIR of the extract revealed the presence of functional groups related to broad range of metabolites and GC analysis showed diversity of compounds related to alcohols, secondary metabolites and other bioactive compounds which have insecticidal and larvicidal activities but are reported for the first time in this brown alga. This pest management strategy is both eco-friendly and cost-effective. The insecticidal effects observed show the potential application of H. cuneiformis extract as an eco-friendly biocontrol agent against R. ferrugineus. Algal aqueous extract can be easily supplied in irrigation water to plants, thereby deterring insects while being nutritious to plants.