Mutagenesis of odorant coreceptor Orco fully disrupts foraging but not oviposition behaviors in the hawkmoth Manduca sexta

Significance

Insects detect plant volatiles mainly through the expression of odorant receptors (ORs) and ionotropic receptors (IRs) in olfactory sensory neurons. In vivo, Orco is an obligate partner for OR but not for IR function. We applied CRISPR-Cas9 in the hawkmoth Manduca sexta to mutate the Orco gene and investigate the physiological and behavioral implication of a loss of Orco receptor function in a semiecological interaction with its preferred host plant, the Western Jimsonweed, Datura wrightii. We found foraging behaviors were largely disrupted. Oviposition behaviors were also affected, but the hawkmoth was capable of exhibiting directed flight toward the nonflowering plant. These results enhance our understanding on the olfactory basis of insect–plant interactions shaping our ecological and agricultural landscapes.

Abstract

The hawkmoth Manduca sexta and one of its preferred hosts in the North American Southwest, Datura wrightii, share a model insect–plant relationship based on mutualistic and antagonistic life-history traits. D. wrightii is the innately preferred nectar source and oviposition host for M. sexta. Hence, the hawkmoth is an important pollinator while the M. sexta larvae are specialized herbivores of the plant. Olfactory detection of plant volatiles plays a crucial role in the behavior of the hawkmoth. In vivo, the odorant receptor coreceptor (Orco) is an obligatory component for the function of odorant receptors (ORs), a major receptor family involved in insect olfaction. We used CRISPR-Cas9 targeted mutagenesis to knock out (KO) the MsexOrco gene to test the consequences of a loss of OR-mediated olfaction in an insect–plant relationship. Neurophysiological characterization revealed severely reduced antennal and antennal lobe responses to representative odorants emitted by D. wrightii. In a wind-tunnel setting with a flowering plant, Orco KO hawkmoths showed disrupted flight orientation and an ablated proboscis extension response to the natural stimulus. The Orco KO gravid female displayed reduced attraction toward a nonflowering plant. However, more than half of hawkmoths were able to use characteristic odor-directed flight orientation and oviposit on the host plant. Overall, OR-mediated olfaction is essential for foraging and pollination behaviors, but plant-seeking and oviposition behaviors are sustained through additional OR-independent sensory cues.