Characterization and purification of insecticidal bioactive small molecules from fruit

Natural products, or derivatives thereof, are widely used in human medicine to fight numerous diseases, including bacterial, viral and fungal infections, cancer, and immune system disorders.  They also continue to be the source of new modes of action and chemistry surrounding drug discovery for veterinary and human medicine as well as crop protection (i.e. insecticides, fungicides and antimicrobials). Mosquitoes are one of the many insects that are controlled with these products.  Control of the mosquito populations is not only significant at the global level since mosquitoes are primary vectors for numerous human and animal infectious diseases (e.g. West Nile virus, Western equine encephalitis, Chikungunya and malaria), it is also of importance to communities located throughout South Dakota and the Great Plains where West Nile is especially prevalent.

Citrus fruit compounds such as limonene provide natural protection against predator insects. Other fruits, such as cantaloupe and avocado, may present similar characteristics that trigger insect mortality. Peels of oranges, key limes, strawberries, avocados and cantaloupe were homogenated with acetone or water.  Crude extracts were evaporated under reduced pressure using a rotary evaporator.  Distilled extracts were collected and examined using insect-bioassays of Aedes aegypti (mosquito) and Trichoplusian ni (cabbage looper) larvae tracking growth inhibition and mortality.  Extracts were then fractionated using UV absorption spectrometry and subjected to follow-up insect-bioassays. Fractions maintaining insecticidal activity were further characterized using Quadrupole Time-of-Flight (Q-TOF) LC/MS in order to precisely elucidate the composition of the small molecule bioactives. Insect cell-based assays combined with forward chemical identification schemes are a critical component towards discovering, characterizing and understanding bioactive small molecules.  It is anticipated that the successful identification and characterization of bioactives will provide new biotechnology opportunities for crop protection and fighting infectious diseases.