Larvicidal efficacy of Adiantobischrysene from Adiantum latifolium against Oryctes rhinoceros through disrupting metamorphosis and impeding microbial mediated digestion.

BACKGROUND

Oryctes rhinoceros Linn. (Coleoptera: Scarabaeidae) is a serious pest of coconuts and other palms. Symbiotic gut bacteria play significant roles in the digestion of cellulosic materials as well as in some other physiological processes essential for the existence of O. rhinoceros larvae. The study was undertaken to isolate a compound with antibacterial and larvicidal activities from the leaves of Adiantum latifolium Lam. following a bioassay-guided method.

RESULTS

Methanol extract (ME) of dry leaf powder of A. latifolium showed larvicidal activity against third-instar O. rhinoceros (LD50 , 5018 mg/kg) with antibacterial activity on its gut microbiota. An in vitro study showed the bacteria Bacillus cereus, Micrococcus lylae, Stenotrophomonas maltophilia, Kocuria rosea, Burkholderia mallei, Staphylococcus epidermidis, S. arlettae and Corynebacterium afermentans identified from the larval gut were sensitive to ME. Bioactivity-guided isolation of the compound by liquid-liquid extraction and column chromatography resulted in Adiantobischrysene which showed antibacterial and larvicidal activity (LD50 , 8.4 mg/kg) and led to weight loss and precocious metamorphosis in larvae. An enzyme immunoassay showed a large peak in 20-hydroxyecdysone that commits larvae to precocious metamorphosis.

CONCLUSIONS

This study demonstrated that the antibacterial and metamorphosis disrupting activity of Adiantobischrysene make it a natural pesticidal compound against O. rhinoceros. © 2018 Society of Chemical Industry.