Evaluation of seaweed extracts for the control of the Asian citrus psyllid Diaphorina citri

Insecticidal and repellent activities were evaluated on extracts from three macroalgae (Caulerpa sertularioides, Laurencia johnstonii and Sargassum horridum) against Diaphorina citri adults. The ethanolic extracts were obtained by maceration, filtration, and concentration under reduced pressure at 40 °C. Each extract was fractionated by solid-liquid methods, followed by column fractionation. The fractions obtained were analyzed by phytochemical tests to determinate their chemical composition. The three extracts showed alkaloids, terpenes, phenols, tannins, flavonoids, anthraquinones and saponins, which are associated with insecticidal and repellent activity. The repellency assay with S. horridum extract showed repellent activity over 24 h (Index of Behavioral Tendency, IBT = 0.376 ± 0.047), L. johnstonii extract showed repellency during 18 h (IBT = 0.240 ± 0.034). Although C. sertularioides extract at the beginning produced an attractant effect (during the first 4 h), it was followed by a repellent effect after 12 h (IBT = 0.297 ± 0.041). The repellent control used was Neemix 4.5 (azadirachtin) and it has a longer repellency of over the 24 h, however S. horridum had a higher repellent activity over the control during all the assay. In the insecticidal activity assay, lethal doses were calculated for each species: L. johnstonii (LD₅₀ = 284 μg mL⁻¹), S. horridum (LD₅₀ = 364 μg mL⁻¹), and C. sertularioides (LD₅₀ = 3703 μg mL⁻¹). Additionally, three terpenic compounds isolated from L. johnstonii were identified by GC/MS; debromolaurinterol, isolaurinterol, and laurinterol as potential insecticidal and repellent compounds. The results suggest that seaweed extracts represent an alternative in the development of agrochemicals for pest control.