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1. The oviposition choices of phytophagous insects determine the environment that their offspring will experience, affecting both larval performance and host plant fitness. These choices, however, may be influenced by other activities, such as nectar foraging.

2. In the Sonoran Desert, Manduca sexta (Lepidoptera: Sphingidae) oviposits primarily on the perennial herb Datura wrightii. It has been reported to oviposit on the smaller-flowered, co-blooming, sympatric annual Datura discolor as well. Datura is also M. sexta’s most important source of nectar in this region. Nectaring and oviposition decisions thus determine M. sexta’s reproductive success, as well as the relative benefits (pollination) and costs (herbivory) that each Datura species derives from this interaction.

3. The nectaring and oviposition choices of adult M. sexta on these congeners were studied to investigate how nectar foraging influences oviposition. Larval performance on the two hosts was then assessed.

4. Nectaring and oviposition were behaviourally linked, with M. sexta preferring the perennial D. wrightii as both a nectar source and larval host when given a choice between the two species. This preference disappeared, however, when only D. discolor bore flowers.

5. In the laboratory, larvae developed at equal rates when fed D. wrightii or D. discolor leaves, but survival was higher on D. wrightii when larvae fed on intact plants.

6. These findings suggest that while female preferences match larval performance in most cases, the link between nectaring and oviposition may at times bias moths to lay eggs on inferior larval hosts.