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

Abstract

The hawkmoth <i>Manduca sexta</i> and one of its preferred hosts in the North American Southwest, <i>Datura wrightii</i>, share a model insect-plant relationship based on mutualistic and antagonistic life-history traits. <i>D. wrightii</i> is the innately preferred nectar source and oviposition host for <i>M. sexta</i> Hence, the hawkmoth is an important pollinator while the <i>M. sexta</i> 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 <i>MsexOrco</i> 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 <i>D. wrightii</i> 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.