Carbon dioxide drives oviposition in Helicoverpa armigera

The levels of carbon dioxide (CO₂), a powerful greenhouse gas, have risen dramatically over the past century, leading to widespread ecological effects on plants and animals alike, including insects that serve vital roles in many food webs. Elevated atmospheric CO₂ is anticipated to affect insect biodiversity by influencing essential behaviors, although the mechanisms remain poorly understood. Here, we demonstrate that female Helicoverpa armigera use plant-emitted CO₂ as a primary cue for egg-laying, showing a preference for younger leaves with higher CO₂ gradients to enhance offspring survival. Elevated environmental CO₂ disrupts this preference, reducing females' attraction to optimal egg-laying sites. Employing genome editing tools, we assessed the CO₂ receptors in this species and proved three gustatory receptors-HarmGR1, HarmGR2, and HarmGR3-that form a trimeric complex in the sensory neurons of the labial palp organ, essential for CO₂ detection. These neurons project to the labial pit organ glomerulus (LPOG) in the antennal lobe, which mediates CO₂-responsive behavior. Genetic disruption of any of these receptors impairs CO₂ sensing and alters oviposition behavior. Our findings underscore the essential role of CO₂ in moth reproductive behavior and reveal that rising anthropogenic CO₂ levels may have significant ecological and agricultural repercussions.