Back to search

BIONÆR-Bionæringsprogram

Plant - insect relationships: imaging CO2, pheromones, and plant odors in the olfactory pathway of an herbivorous insect

Alternative title: Insekt - plante relasjoner: avbildning av CO2, feromoner og plantedufter i herbivore insekters luktebaner

Awarded: NOK 5.0 mill.

Evolution of insect-plant relationships has been one of the central topics of science for more than 150 years. Charles Darwin pointed out the interplay between flowering plants (angiosperms) and plant-eating (herbivore) insects as early as 1859, in 'Origin of Species'. In fact, when Darwin saw the long spur on an orchid from Madagascar, he predicted the existence of a pollinating moth with a very long proboscis. Final evidence for the coevolution involving the orchid and the long-tongued moth, named Xanthopan morganii praedicta, did not appear until the 1990s. Angiosperms, which appeared 130 million years ago, have always required a specific form of pollination. Among all Earth's terrestrial organisms that interact with angiosperms, insects are the most important group. Cultivated plants include to a large extent angiosperms and are therefore fundamentally dependent on these small creatures. On the other hand, certain herbivorous insects represent a serious problem for agriculture just because they are plant-eaters. Although these pests make up only 1% of all insects, they are responsible for a significant loss of crops. To establish a sustainable agriculture, it is necessary to minimize the extent of insect pests and at the same time preserve the insects' biological diversity. This requires, above all, increased knowledge about insects. In this project, which lasted from 2019 to 2022, we have studied the olfactory system of the noctuid moth, Helicoverpa armigera – one of the most serious insect pests in the world. In line with the project title - 'Insect–plant relations: imaging of CO2, pheromones and plant scents in the olfactory paths of herbivorous insects', we contribute new knowledge that has been published both in recognized scientific journals and in popular science channels. 1. New scientific data on the olfactory pathway linked to male-specific reproductive behavior 1.1 A unique target area for pheromone signals in the male brain: We have acquired new knowledge about the pheromone system by identifying a group of second-order olfactory neurons ending up in a delimited brain area, completely separated from the target area of the previously described and well-known 'sister neurons'. The sister neurons resemble the human Mitral cells and, like them, end up in areas linked to memory formation. We hypothesize that the new population of neurons is specifically involved in the characteristic flight behavior of a male seeking a potential mate. The article is published in the renowned journal, Frontiers in Cellular Neuroscience, 2020, https://www.frontiersin.org/articles/10.3389/fncel.2020.00147/full. In a subsequent article, we compare the two populations of male-specific pheromone neurons with two groups of visual neurons that make up the mammalian ventral ('what') and dorsal ('where') streams. 1.2. Valence-based odor processing in higher-order brain areas: In an article in the internationally renowned journal eLife, 2021, we present how female-produced odor signals linked to attraction and rejection, respectively, are coded in higher-brain centers in the male. We demonstrate that the two categories of scent signals, each linked to a specific behavior – attraction versus repulsion – are processed in separate brain areas. The findings provide new insight into higher-order olfactory pathways linked to reproductive behavior. The data are very relevant to the entire field of olfactory research as we describe neural principles linked to the 'pleasure/displeasure' classification typifying the olfactory system. https://elifesciences.org/articles/65683 2. New scientific data on neural networks processing input from CO2 and plant odors 2.1. Mapping the peripheral CO2 pathway: Like other species of lepidoptera, the moth has a separate sensory organ on its mouthparts for the detection of CO2. By using different color techniques, we have carried out a precise mapping of the peripheral sensory pathway for CO2. The data is published in the journal Frontiers in Physiology, 2020, https://www.frontiersin.org/articles/10.3389/fphys.2020.00202/full. 2.2. Second-order CO2 pathways in the moth brain: We demonstrate, for the first time, how input from CO2 is represented in second-order neurons. This type of signal essentially follows different tracts than the ordinary olfactory neurons. However, the CO2 projections end up in a brain area that also includes terminals of plant odor neurons - which makes sense as the insect uses CO2 input to detect the most nutritious parts of a host plant. https://www.nature.com/articles/s41598-020-76918-1 The new knowledge from this project will contribute to promoting human awareness of the advanced nervous system of insects - which is a prerequisite for the conservation of species diversity and sustainable development. The data will also enable new strategies for reducing pests where use of traditional pesticides is replaced with control mechanisms based on biologically relevant signal.

Outcomes This assignment was a joint Sino-Norwegian project, where the Chinese partners were financed by the National Natural Science Foundation of China and the Norwegian partners by the Research Council of Norway (RCN). The members formally involved in the proposal of the Norwegian team included - in addition to the PI, one young co-PI and a young associate professor from another department. The co-PI has been engaged in a three-year 100% position in the project, together with another research fellow. As demonstrated by the publications obtained from the project, both research fellows have contributed significantly to the success of the project. This project has been an important facilitator for improving their experimental competence, analytical ability, and programming skills. The associate professor has been involved in designing several of the new scientific articles. He has also served as co-supervisor for a PhD in our lab. This PhD was not formally connected with the project, but thematically it was, since the doctoral candidate explored the accessory olfactory pathway, conveying input about CO2. In total, the project has been of priceless value for several young promising researchers at NTNU and for the general reputation of our research unit. Besides, the solid cooperation has been significant for scientific development of several young researcher involved in the Chinese team. Finally, as stated in the dissemination plan of our original proposal, we have communicated the scientific topic on olfaction to young people. During this year’s event of “Forskningsdagene”, we have presented our research for large groups of schoolchildren between the ages of 10 and 14 as well as for the general population locally. https://www.ntnu.no/forskningsdagene/torget/program Impact The overriding aim of this project was to contribute to new knowledge on sustainable agriculture and to improve international exchange of expertise between China and Norway. As can be seen from the publication list, formalization of the connection with the Chinese groups has further amended the scientific cooperation. Notably, a new research project financed by the RCN has just started up. In this project, entitled “Chemosensory pathways underlying oviposition behavior in the pest insect, Helicoverpa armigera – peripheral and central mechanisms”, we have maintained the collaboration with the Chinese groups. Besides, we have established cooperation with the Norwegian company, "Norsk senter for økonomisk landbruk" (NORSØK), in this project. Finally, our participation in a recently awarded EU/Horizon project starting up in 2023, entitled “Purpest” and managed by “Norsk institutt for bioøkonomi” (NIBIO), may also relate to the success of the recently ended RCN project.

In this joint proposal including research groups at the Chinese Academy of Agricultural Sciences, Beijing; Henan Agricultural University, Zhengzhou; and Chemosensory laboratory, Norwegian University of Science and Technology (NTNU), we will extend our already well established cooperation on the olfactory system of a plant feeding insect representing one of the worldwide pests. The fruitfulness of this cooperation has been demonstrated by numerous international publications. The expert competence in the distinct groups complements each other in an optimal manner as the Chinese groups focus on the peripheral arrangement of the insect's chemosensory system and the Norwegian group on the central pathways. For establishing a sustainable agriculture, the human society has to balance between the two factors of preserving biodiversity of pollinating insects and at the same time minimizing the extent of pests. Therefore, the knowledge about insects in general and pest species specifically is utterly important. In this assignment, we aim to explore chemosensory signal processing including CO2, plant odors, and pheromones in the noctuid moth, Helicoverpa armigera. As larvae, these organisms damage reproductive organs of important crops. Adult insects measure CO2 emission from plants in search for optimal hosts. This ability is based on a specific gaseous-sensing organ located on the tip of two mouthpart structures. The project presented here, includes three work packages (WPs), each of which corresponds to distinct levels of the chemosensory pathway: 1) WP1 to detection and processing at the peripheral level, 2) WP2 to coding principles in the primary olfactory center (the antennal lobes), and 3) WP3 to modulation of odor-evoked behavior. In addition to the scientific outcome in the form of publications and presentations, this project will contribute to regulate populations of insect pests in an environmentally sound way.

Publications from Cristin

No publications found

No publications found

Funding scheme:

BIONÆR-Bionæringsprogram