Nectaring and oviposition preferences of Manduca sexta on two co-blooming Datura species in the Sonoran Desert

Background/Question/Methods

As the oviposition choices of female insects ultimately determine the environment their larvae will experience, appropriate host plant selection is exceedingly important for larval fitness. In the Sonoran Desert, the hawkmoth Manduca sexta both nectars and oviposits on the large perennial Datura wrightii. Previous work has focused on M. sexta’s mutualistic and antagonistic interactions with D. wrightii, but there are anecdotal reports that M. sexta also visits the small annual congener Datura discolor, which co-occurs and co-blooms with D. wrightii. As the host-plant quality likely differs between the annual and perennial, the host-plant foraging choices of female moths likely have consequences for larval fitness. Despite their consequences, these choices may be modified by the presence of nectar-rich flowers on the potential hosts, as nectar foraging is known to influence oviposition. In this pilot study, using mixed-species greenhouse flight arrays, we investigate (i) whether M. sexta visits both Datura species for nectar and oviposition, (ii) what are its nectaring and oviposition preferences between the two species, and (iii) whether nectaring and oviposition are linked in females foraging on the two species. 

Results/Conclusions

We report three key results. (1) M. sexta adults used both D. wrightii and D. discolor as nectaring resources and oviposition sites in our flight arrays. (2) There were no significant differences in the number of moths that nectared at or oviposed on D. wrightii versus D. discolor.  Interestingly, however, moths spent a significantly longer time nectaring and ovipositing on D. wrightii and laid significantly more eggs on D. wrightii. This suggests that moths sampled multiple plant species within our array “patch”, but ultimately preferred to nectar and oviposit on D. wrightii rather than D. discolor. This preference may imply that D. wrightii is a higher quality larval host, a prediction being answered by ongoing research. Finally, (3) for both Datura species, here was no significant relationship between the amount of time moths spent nectaring or nectaring bouts versus time spent ovipositing or the number of eggs laid. This suggests that nectar foraging and host plant foraging may not be as tightly correlated as previously reported.  Taken together, these results indicate that the nectaring and oviposition behaviors of hawkmoths may be more flexible than previously thought, which may change the predicted fitness consequences of flowering for host plants.