Use of odor by host-finding insects: the role of real-time odor environment and odor mixing degree

Olfaction plays a major role in the host-finding behaviors of insects. However, the irregularity of insect responses to odor interactions has hindered our efforts to draw broad conclusions about how a host-finding insect uses the complex mixture of various odor plumes in natural environments. Particularly, it is still unclear so far why the use of non-host odors to control insect pests in practices have met with mixed results. To further understand the host-finding of a specific insect, we highlight the role of the real-time odor environment (ROE) that the host-finding insect is passing through. The ROE may contain various odors with different ranks and changes during the insect’s host finding. A host-finding insect may always prone to switch to the higher rank odor plumes in each ROE regardless of the distance is “short” or “long” from the odor source. For a specific herbivorous insect, only mixing degree of the given host and non-host plant odors reaches some certain level (threshold value), can the non-host odors significantly affect its ability to locate host plants. When the odor mixing degree is low, masking effects may not occur or the non-host plant odors’ “attractive” effects at long distances and “repellent” effects at short distances can even increase the pest loads. In forests, the mixing degree of different plant odors is determined by turbulence intensity which is mainly affected by plant structures. These may further advance our understanding of herbivorous insects’ host finding and have important implications for the development of pest management strategies.