Context dependency of nectar reward‐guided oviposition

Abstract

AbstractNectar is the most common floral reward used to recruit pollination services. Changes in nectar volume may affect not only pollination services, but also the attraction of antagonists such as herbivores, especially if the same insect species acts as herbivore and pollinator. Plants compete with each other for the best pollination services, at the same time employing various strategies to avoid herbivory. Datura wrightii Regel and Nicotiana attenuata Torr. ex Watson, two sympatric solanaceous species, compete for the same hawkmoth pollinator, Manduca quinquemaculata (Haworth) (Lepidoptera: Sphingidae), although standing nectar volume per flower differs 50‐fold (70 vs. 1.3 μl, respectively) between these species. This large difference may also result in differences in oviposition rates. I conducted a detailed analysis of diurnal changes in nectar volume and sugar concentration in field‐ and glasshouse‐grown D. wrightii and N. attenuata plants, and tested how well nectar production is buffered against the loss of large amounts of foliar tissue that frequently occurs due to M. quinquemaculata larval herbivory. I examined the influence of nectar volume on herbivore damage in the field and compared the results with previously published data from N. attenuata which were collected simultaneously. Oviposition by M. quinquemaculata moths increased significantly in D. wrightii plants whose nectar volume had been experimentally increased five‐fold compared to untreated control plants, and correlated with the numbers of flowers per plant in native populations. The results suggest that a hawkmoth mother may use standing nectar volume of a potential host plant to estimate its size, and possibly health, to make the optimal decision for her progeny. This mode of assessment, however, is apparently not used with another plant species, as other more herbivory‐related cues, such as olfaction or vision, are more influential in determining oviposition rates on other plant species. Yet within a plant species, regulating nectar volume strongly influences future herbivory.