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

Lemna perpusilla and Lemna minor 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 Lemna species to the duckweed weevil, Tanysphyrus lemnae. The female adults of T. lemnae preferred to lay eggs on L. perpusilla over L. minor. In addition, the larvae of T. lemnae performed better when fed on L. perpusilla than on L. minor. To understand the physiological basis of species-specific resistance in the two Lemna species, we measured the amounts of jasmonic acid (JA), phytosterols, and flavonoids. Attacks by duckweed weevils increased the levels of JA in the two Lemna species, but these levels did not differ significantly between the two species. Interestingly, the levels of flavones (isoorientin, vitexin, and isovitexin) in L. minor species were higher than those in L. perpusilla. The in vitro bioassay showed that three flavones significantly decreased the survival rate of duckweed weevil larvae. Although L. perpusilla was less resistant to duckweed weevil attack compared to L. minor, L. perpusilla grew faster than L. minor regardless of the duckweed weevil attack. These results suggest that these two Lemna species have different defense strategies against the duckweed weevil.