Abundance of aphid natural enemies on flowering service plants is associated with aphid prey and floral resources

Abstract

Natural enemies of agricultural pests are dependent on alternative prey and floral food resources that may be scarce in intensively managed agricultural landscapes. Introduction of flowering service plants may provide food resources, but context-specific information on plant species and associated plant traits attractive and supportive to natural enemies is often lacking. Here, we assessed aphid natural enemies on 39 native and non-native service plant species in a replicated field experiment in Korla, Xinjiang, China, in 2020 and 2021. The natural enemy communities and aphid abundance on these plants were assessed using visual counts and sweepnetting. Flowering period, corolla type, and presence of extrafloral nectar on the plants were assessed as possible predictors for attractiveness to natural enemies. Gossypium hirsutum, Melilotus officinalis, Medicago sativa, Anethum graveolens, and Foeniculum vulgare were associated with relatively high natural enemy abundances, but G. hirsutum, M. officinalis and M. sativa also hosted cotton or cowpea aphids. Ladybeetles, predatory bugs and parasitoids showed positive responses to aphid densities on plants. Ladybeetle adults showed consistent positive responses to extrafloral nectar, open corollas and flowering across two years, while for other natural enemies this was only found in one out of two years. Our findings indicate that besides the provision of floral resources, aphid prey on service plants is an important characteristic that influences the attractivity of service plants to natural enemies. Service plants that host aphids that do not infest crops can therefore be useful for habitat management programs aiming to conserve and augment natural enemies.