Preference, performance, and impact of the water‐lily aphid on multiple species of duckweed

The role of herbivores in driving the structure of freshwater macrophyte communities remains poorly understood in comparison with terrestrial ecosystems. For instance, although duckweed (subfamily Lemnoideae) are globally distributed, can be locally highly abundant and ecologically dominant, and are of growing economic importance, their interactions with herbivores remain understudied. To address how herbivores may impact duckweed species composition, we here experimentally quantify the preference and performance of a common duckweed herbivore, the water‐lily aphid (Rhopalosiphum nymphaeae) on four widespread duckweed species. Our two‐way choice experiments reveal that aphids display a preference for Spirodela polyrhiza > Landoltia punctata = Lemna minor > > Wolffia brasiliensis. These results are rarely influenced by natal host species. By evaluating the growth of aphid populations on each duckweed species, we find that preference may be adaptive in certain ecological conditions. Quantifying the population growth rate of duckweed growing in the presence and absence of aphids revealed differential tolerance of herbivory across duckweed species. This study shows that aphids, through preferential feeding and significant differential effects on duckweed growth, can have a significant impact on duckweed population dynamics and potentially community composition. Our two‐way choice experiments reveal that water‐lily aphids prefer certain species of duckweed (Spirodela polyrhiza > Landoltia punctata = Lemna minor > > Wolffia brasiliensis) but this preference is rarely affected by the natal host. Aphids have the highest intrinsic per capita growth rate on S. polyrhiza and the highest carrying capacity on L. minor, indicating that preference may be adaptive in certain ecological conditions. Aphids severely reduce duckweed population growth measured as abundance and biomass, and there are interspecific differences in tolerance to aphid herbivory (S. polyrhiza > L. minor > L. punctata).