Mosquito-borne diseases are a major component of the worldwide burden of infectious diseases in humans.
In the wild, A. aegypti has begun to show resistance to insecticides, revealing a need for new types of pesticides for targeting this species.
“Flavonoids – a type of metabolic product from plants, fungi, and other organisms – can interfere with insect development and physiology, and can kill larvae of A. aegypti,” says senior author of the study, Professor Ryusuke Niwa.
To investigate how flavonoids can kill mosquito larvae, the researchers analyzed the activities of several flavonoids in A. aegypti, including daidzein, which has previously been identified as a larvicide for this species.
The team found that the flavonoids inhibit the activity of glutathione S-transferase Noppera-bo (Nobo); in A. aegypti, Nobo is an enzyme involved in the biosynthesis of the hormone ecdysone.
Ecdysone is an insect steroid hormone, or ecdysteroid, required for the initiation of metamorphosis and regulation of molting.
Because ecdysteroids are key to the life cycle of insects, chemical inhibitors of enzymes involved in making these hormones, including Nobo, are thought to be insect growth regulators (IGRs) that disrupt development in insects without affecting other organisms.
The high prevalence of resistance in mosquitoes to current insecticides in some areas urgently requires the development of new insecticides with different chemical structures and targeting pathways from those currently in use.
The results of this study offer a new avenue for developing new IGRs that are environmentally friendly and can be used for the control of mosquito populations by inhibiting the biosynthesis of ecdysteroids.