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Title: Congener response reduces risks from bottom-up and top-down forces: Behavioral parsimony by Xylophage

Author
item MIZELL, R - University Of Florida
item ANDERSEN, P - University Of Florida
item BRODBECK, B - University Of Florida
item Hunter, Wayne

Submitted to: American Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2012
Publication Date: 7/28/2012
Citation: Mizell, R.F., Andersen, P.C., Brodbeck, B.V., Hunter, W.B. 2012. Congener response reduces risks from bottom-up and top-down forces: Behavioral parsimony by Xylophage. American Entomologist. 58:106-115.

Interpretive Summary: Understanding how insect pests respond to the quality of their host plants and to predation is critical to formulating pest management strategies. As organisms must find food and avoid enemies, we examined these behaviors of the glassy-winged sharpshooter leafhopper: Homalodisca vitripennis (Germar) which is a primary vector of the plant-infecting bacterium, Xylella fastidiosa, which is the causal agent of Pierce's disease, a deadly disease of grapevines, fruit trees, and other woody plants. H. vitripennis feeds on xylem tissue which is scarce in nutrients and has evolved many specialized physiological and behavioral adaptations to overcome this limitation. Bottom-up mortality risks, those imposed by the host plant, to H. vitripennis include starvation and reduced fecundity through loss of high quality hosts. Top-down risks include predation, egg parasitism by Hymenoptera, and mortality from fungal pathogens. Visual behavior of H. vitripennis in response to congeners, common heterospecifics, and artificial models of conspecifics was investigated. Behaviors and the physical properties of the visual cues involved were characterized. H. vitripennis adults exhibited highly significant, positive responses to the presence of other conspecifics, a heterospecific leafhopper species, like Oncometopia nigricans, and artificial models which were of similar size of adult leafhoppers. Significant response was not observed to a congeneric, Homalodisca insolita, with a smaller body size, or to models of sizes, shapes, and colors other than black and red. Cadavers of leafhoppers placed on a novel and nutritionally poor host plant stimulated H. vitripennis adults to land on branches containing the cadavers. H. vitripennis also landed preferentially on branches containing conspecific cadavers despite the presence of a cadaver of a major predator, Anolis carolinensis lizards, or artificial lures resembling spiders. This consistent visual response was independent of variable bottom-up (host quality) and top-down (predator presence) risks, and it suggests for the first time such parsimonious behavior in insects, i.e., sole use of a live visual cue, other leafhoppers of the same size, as a means to reduce mortality risks from bottom-up and top-down forces.

Technical Abstract: Organisms must find food and avoid enemies. Homalodisca vitripennis (Germar), the glassy-winged sharpshooter leafhopper, is a primary vector of Xylella fastidiosa, the causal agent of Pierce's disease, a deadly disease of grapevines, fruit trees, and other woody plants. H. vitripennis feeds on xylem tissue depauperate in nutrients and has evolved many specialized physiological and behavioral adaptations. Bottom-up mortality risks to H. vitripennis include starvation and reduced fecundity through loss of quality hosts. Top-down risks include predation, egg parasitism by Hymenoptera, and fungal pathogens. Visual behavior of H. vitripennis in response to congeners, common heterospecifics, and artificial models of conspecifics was investigated. Behaviors and the physical properties of the visual cues involved were characterized. H. vitripennis adults exhibited highly significant, positive responses to conspecifics, a heterospecific species, Oncometopia nigricans, and artificial models the size of adult leafhoppers. Significant response was not observed to a congeneric, Homalodisca insolita, with a smaller body size, or to models of sizes, shapes, and colors other than black and red. Cadavers of leafhoppers placed on a novel and nutritionally poor host plant stimulated H. vitripennis adults to land on branches containing the cadavers. H. vitripennis also landed preferentially on branches containing conspecific cadavers despite the presence of a cadaver of a major predator, Anolis carolinensis lizards, or artificial lures resembling spiders. This consistent visual response was independent of variable bottom-up (host quality) and top-down (predator presence) risks, and it suggests for the first time such parsimonious behavior in insects, i.e., sole use of a live visual cue as a means to reduce mortality risks from bottom-up and top-down forces.