Mutagenesis oforcoimpairs foraging but not oviposition in the hawkmothManduca sexta

Abstract

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. Significance statement Insects detect plant volatiles mainly through the expression of ORs and IRs on the antennal olfactory sensory neurons (OSNs). In vivo, Orco is an obligate partner for OR, but not IR function and ORs mediate a vast spectrum of olfactory perception. We applied CRISPR-Cas9 in M. sexta to mutate the orco gene and determine the physiological and behavioral implication of a loss of Orco receptor function in a semi-ecological interaction with D. wrightii. We found that while behaviors related to foraging were largely disrupted, other sensory modalities outside Orco function determine the relationship between an ovipositing female and its plant host. These results have implications toward understanding the olfactory basis of insect-plant interactions shaping our ecological and agricultural landscapes.

Complex plant metabolomes guide fitness-relevant foraging decisions of a specialist herbivore

“…Plants produce complex chemical mixtures, and herbivores likely combine many of these chemicals to make appropriate foraging decisions (11,12,29). In line with this idea, recent in vivo work shows that, while individual compound classes and insect gustatory receptors can be of major importance for specific behavioral patterns, their disruption is not sufficient to fully suppress these behaviors (22)(23)(24). In the case of the western corn rootworm, we find that even the suppression of two major foraging cues does not fully abolish its ability to find and accept a host plant, at least under laboratory conditions.…”

“…Over the past decades, herbivores have been found to respond to a multitude of plant primary and secondary metabolites in artificial diet experiments (13,16,17). An increasing number of studies now also document the importance of these metabolites in planta through molecular manipulative approaches (20)(21)(22)(23)(24)(25)(26).…”

Insights Into Chemosensory Proteins From Non-Model Insects: Advances and Perspectives in the Context of Pest Management

“…Their results suggested that ionotropic responses are followed by membrane depolarization and, ultimately, metabotropic responses are unleashed. More recently, the use of CRISPR-Cas9 to disrupt the expression of Orco in the hawkmoth M. sexta showed that Orco is crucial for sexual communication but not for host location ( Fandino et al, 2019 ). Despite all these advances based on model insects, the study of a non-model insect established a milestone in insect olfaction.…”