Flavone-associated resistance of two species to duckweed weevil attack.

and are free-floating plants that often live in the same habitat. However, little is known about how they differ in response to herbivore attacks. In this study, we examined the species-specific resistance of two species to the duckweed weevil, . The female adults of preferred to lay eggs on over . In addition, the larvae of performed better when fed on than on . To understand the physiological basis of species-specific resistance in the two species, we measured the amounts of jasmonic acid (JA), phytosterols, and flavonoids. Attacks by duckweed weevils increased the levels of JA in the two species, but these levels did not differ significantly between the two species. Interestingly, the levels of flavones (isoorientin, vitexin, and isovitexin) in species were higher than those in . The in vitro bioassay showed that three flavones significantly decreased the survival rate of duckweed weevil larvae. Although was less resistant to duckweed weevil attack compared to , grew faster than regardless of the duckweed weevil attack. These results suggest that these two species have different defense strategies against the duckweed weevil.