Insect infestations in agricultural areas have been a major challenge for humanity since ancient times. The devastating locust swarms that invaded the fields of the Nile Valley, as described in the Books of Moses (ca. 1405 BCE), are among the earliest written references to this problem. The main objective of the project discussed here was to contribute to safe global food production by exploring fundamental principles related to odor-regulated oviposition behavior in one of the world’s most destructive insects, the noctuid moth species Helicoverpa armigera (the cotton bollworm).
A key contribution of the recently completed project was the discovery of a type of female-specific odor receptor linked to reproductive behavior in H. armigera. As described in the relevant 2023 publication in the internationally renowned journal Current Biology, we – together with our Chinese collaborators – identified a specific odor receptor on the female antennae, HarmOR56 (https://doi.org/10.1016/j.cub.2023.11.026). Activation of this receptor – which detects three methyl esters released from the surface of the species’ eggs, so-called oviposition deterrents (ODs) – was shown to inhibit female oviposition behavior. The article describes, for the first time, how a female-specific odor receptor recognizes chemical signals from the species’ own eggs. The data therefore explain the previously well-described biological phenomenon whereby gravid females avoid laying eggs where eggs are already present. While we have previously described male-specific olfactory pathways linked to reproduction in H. armigera, we have now contributed new insights into a female-specific system associated with reproduction. Experimental methods used in the relevant publication include CRISPR/Cas9 gene editing, extracellular recordings, and behavioral studies.
Another essential finding of the project demonstrates how carbon dioxide (CO2) influences oviposition behavior in gravid females. This study, also conducted in collaboration with our Chinese partners, was published in 2025 in the internationally recognized journal National Science Review (https://doi.org/10.1093/nsr/nwaf270). The article, entitled “Carbon dioxide drives oviposition in Helicoverpa armigera,” demonstrates that gravid females prefer to lay eggs on parts of a plant that release relatively high concentrations of CO2, i.e., areas that are metabolically most active.
It should also be noted that we have obtained data from a substantial number of experiments explaining how information from the three ODs mentioned above is encoded in central olfactory pathways. These findings have been fully analyzed and are ready for publication. The results include electrophysiological recordings from all categories of neurons that form glomeruli in the brain’s primary olfactory center – including sensory neurons, local interneurons, projection neurons, and centrifugal neurons. In addition, we have performed calcium imaging measurements of odor-induced responses in antennal-lobe projection neurons. Parts of this work, which reveal anatomical and physiological characteristics of a female-specific brain network linked to reproduction, have already been presented at various scientific conferences.
OUTCOMES AND IMPACTS: The principal scientific aim of our project was to “To contribute to world food safety by exploring basic principles associated with odor regulated egg laying behavior in one of the globally most harmful pest insects – the noctuid moth, Helicoverpa armigera”. See the first section in the original application, entitled Project info. Furthermore, we also expressed, in the sub-section ‘Novelty and ambition’, on page 7 of the original project description: “Our main ambition is to improve the knowledge about odor-regulated female oviposition and thereby contribute to development of improved strategies for reducing damage from pest insects in future. The modern pest control is at a turning point, clearly demonstrating that the traditional pesticides are devastating for our ecosystems. An environment-friendly alternative that is also effective is needed more than ever. To improve biological approaches, however, more comprehensive knowledge is required. We have addressed the principal scientific aim of the project in the following way:
Firstly, the finding of a female-specific odor receptor linked to reproductive activity in one of the world’s most serious pest insects, Helicoverpa armigera, is very relevant for developing more environment-friendly strategies for pest insect control. As we expressed in the original project description, in the first paragraph of the Impact section (page 7), “By turning the focus from male-detected pheromones to olfactory signals critically involved in female-specific oviposition behavior, we are at the core of the problem – the eating larva.” Furthermore, as predicted in the following sentence: “The academic impact of this approach should not be underestimated.” Of course, the identification of a female-specific odor receptor, HarmOR56, detecting chemical signals emitted from eggs laid by other conspecific females, led to publication in the highly acknowledged journal, Current Biology having impact factor 7.5.
Secondly, the new report on how external carbon dioxide (CO2) influences egg-laying behavior in H. armigera gravid females is also indeed significant. Elevated atmospheric CO2 is anticipated to affect insect biodiversity by influencing essential behaviors, and here we demonstrated that female H. 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. Our findings emphasize the important role of CO2 in moth reproductive behavior and reveal that rising anthropogenic CO2 levels may have significant ecological and agricultural implications.
In addition to the two above-mentioned publications, and three other articles, we have three more manuscripts that are ready for publication in 2026 – all will be submitted to acknowledged international journals.
For establishing sustainable agriculture and safe food production, the human society must change pest control strategies by reducing utilization of chemical pesticides and replacing them with environment-friendly alternatives. Despite introduction of biological strategies already several decades ago, including utilization of the insects' own odor signals, such as sex-pheromones, the effectiveness of these methods needs to be improved. It is therefore urgent to upgrade the knowledge about the olfactory pathways and the relevant signaling mechanisms. In this assignment, we aim to explore a system yet poorly described – i.e., the chemosensory circuit underlying regulation of female-specific egg laying behavior in the global pest insect, Helicoverpa armigera. The new knowledge may pave the way for innovation of novel pest control methods approaching the harmful larvae directly.
This proposal is linked to an ongoing research project on food safety, classified within the Sino-Norwegian program of the Research Council of Norway (RCN). Three recent high-ranked articles from our research unit on the ongoing project, entitled “Plant – insect relationships: imaging CO2, pheromones, and plant odors in the olfactory pathway of an herbivorous insect”, proves the academic ability of the Chemosensory lab and the suitability of the basic research approach. By continuing the well-established cooperation with our Chinese partners and including a national collaborator having extensive experience from applied research projects on the relevant topic, we have an ideal base for the new plan. The project will include behavioral tests of the local pest species, Pieris brassicae, as well. Regarding expert knowledge, the distinct groups complement each other perfectly as the Norwegian units are competent to explore the central pathways and the odor evoked behaviors, respectively, while the Chinese can uncover details of the peripheral signaling pathway.
