New Larvicidal Acetogenin from the Red Alga Laurencia papillosa

A new C-15 acetogenin, cyclic enyne (12E)-cis-maneonene-E (1) and (12Z)-trans-maneonene-B (2), together with different secondary metabolites including sesquiterpenoid 2,10-dibromo-3-chloro-alpha-chamigrene (3) and fatty acid aldehydes (4-8) were isolated from the petroleum ether extract of a red alga, identified as Laurencia papillosa, collected from the Saudi Red Sea coast. The L. papillosa crude extract and its active ingredient acetogenin (1) have been evaluated for the ability to control two main economically important pests, the confused flour beetle larvae Tribolium confusum and Culex pipiens mosquito larvae. Compound 1 showed high potential as a natural insecticide against these two pests. In the case of T. confusum larvae, the LD50 values were 0.21 and 0.16% after 6 and 12 days of treatment with crude extract and acetogenin, respectively. On the other hand, the resulting LC50 values of mosquito larvae bioassay were 30.7, 36.9, and 41.8 ppm after 24 h treatment against 2nd, 3rd, and 4th larval instars, respectively. Also, an increase of the insecticidal effects against mosquito larvae was recorded after extending treatment time to 48 h.