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.