Mutagenesis of orco impairs foraging but not oviposition in the hawkmoth Manduca sexta

Plant volatile detection through olfaction plays a crucial role in insect behaviors. In vivo, the odorant receptor co-receptor 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) orco in a neurophysiological model species, the hawkmoth Manduca sexta. M. sexta and its host, the Sacred Datura (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. We generated an orco KO through CRISPR-Cas9 to test the consequences of a loss of OR-mediated olfaction in this 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. However, when testing the oviposition behavior of mated females encountering a non-flowering plant, there was no difference between orco KO and wild type females regarding upwind flight orientation and number of eggs laid. Overall, OR-mediated olfaction is essential for foraging and pollination behaviors, but plant-seeking and oviposition behaviors appear largely unaffected.