Predicting When, Why and Where Asian citrus psylllids move to increase effectiveness of insecticide sprays

Predicting When, Why and Where Asian citrus psylllids move to increase effectiveness of insecticide sprays

Report Date: 12/12/2016
Project: 15-024   Year: 2016
Category: ACP Vector
Author: Lukasz Stelinski
Sponsor: Citrus Research and Development Foundation

We have continued to investigate movement of Asian citrus psyllid (ACP) as it relates to biotic and abiotic factors. We have continued to investigate how previous experience and learning affects ACP movement behavior as it relates to developing practical pest management tools for managing this pest with behavior modifying chemicals. We designed three experiments to test whether males learn about female odor, specifically in the context of mating, where copulation acts as a biologically significant unconditioned reinforcer. First, we compared the responses of mated and virgin males to female odor (proxy for volatile cuticular hydrocarbons thought to function as sex pheromone). If male attraction is experienced-dependent, we expected only mated males to show preference for female odor. Then, we compared the acquisition of response of a novel olfactory stimulus, vanillin, in males exposed to the odor under different conditions: as an environmentally derived odor, an odor associated with females directly, and an odor associated with a food source. If the learned responses were explicitly linked to mating experience, we speculated that only the males exposed to vanillin associated with females directly should demonstrate a learned response. Finally, we compared antennal responses of virgin and mated males to female cuticular extracts electrophysiologically to determine if changes in male response to female odor are caused by peripheral sensitization or true learning. In the ACP stimulatory cuticular hydrocarbons act as sex pheromone attractants. Male psyllids locate aggregations of females using those olfactory cues, as well as vibrational communication on the plant surface. Although previous research has indicated that learning plays a role in modulating female reproductive behaviors in psyllids, it is unknown whether males similarly use learning to increase fecundity. We used an olfactometer-based bio-assay to study the effects of experience on male response to female odor. First, we compared male attraction to female odor in virgin and previously mated males. Second, we tested the effect of several modes of experience with a novel odor, vanillin, to determine whether mating, feeding, or general environmental exposure elicited a learned response. We found that male attraction to female odor significantly increased after mating experience. In addition, we found that males learn about odor specifically in the context of mating, rather than feeding or general exposure. Electrophysiological measurements of antennal response to odorants confirmed that mating status did not affect the sensitivity of the peripheral nervous system to volatile stimuli implicating learning at the level of the central nervous system. These results suggest that male response to female odor is not an innate behavior. Males require mating experience with female conspecifics to develop attraction to those olfactory cues in the environment. This adaptive plasticity may allow males to detect females in an ever-changing environment and promote diversification and further specialization on different host genotypes. Our results may have implications for development of behaviorally based management tools for ACP. Semiochemical-based management tools for ACP are currently under development. Non-traditional control methods are also being explored, given the importance of this pest. If male attraction to female odor is experience-dependent, it may be possible to manipulate male behavior in such a way that mate detection and reproduction is suppressed. For example, appetitive learning in insects is specifically mediated by octopamine (RS-4-(2-amino-1-hydroxy-ethyl) phenol), a biogenic amine neurotransmitter found almost exclusively in invertebrate species. While octopamine occurs in vertebrates, it does not appear to have a major role as compared with norepinephrine. Indeed, appetitive learning is significantly suppressed in insects when octopamine antagonists are administered. It therefore may be possible to introduce a novel form of mating disruption in agricultural settings by disrupting a target species´┐Ż ability to learn. While the potential for such application is distant and would require significant effort to develop a safe and target-specific method of application, pest control options are expanding with better understanding of the target species´┐Ż ecology and behavior.


Your browser does not support pdfs, click here to download the file.