Patterns of relationships between certain leafhoppers and plants, part iii. range and interaction of sensory stimuli

Information on the range and interaction of certain sensory stimuli determining the orientational responses of Empoasca devastans to the host (cotton) and nonhost (castor) plants is given. These responses of the leafhoppers, resulting in their arrival on various plants during host selection, are determined by the sensory stimuli from both the plants and from their background. The responses differ qualitatively and quantitatively according to the combination patterns of the different sensory stimuli perceived. The humidity (water vapour) and odour stimuli from the plants attract the insects up to only 1 cm. The humidity from the background of the plants in an irrigated bed attracts the insects from a longer distance (180 cm). The visual stimuli from the plants, particularly colour, attract the insects from the maximum distance (360 cm). When presented the same stimuli, e.g., cotton plants, in two different directions at different distances, the insects show a greater attraction to the nearer plants. The background stimuli which influence the insects' orientational responses to the plants include light and humidity. The insects show a greater attraction to a plant in a higher intensity of light or humidity than to the plant in a lower intensity of light or humidity. Even the nonhost (castor) plant, under high intensity conditions, attracts the insects more than the host (cotton) plant under low intensity conditions. The possibility of manoeuvring the orientational behaviour of the leafhoppers for their control is considered. (Baumwollpflanzen) in entgegengesetzter Richtung und verschiedenem Abstand geboten, so wurden die näheren Pflanzen bevorzugt. Wirksame Umgebungsreize waren Licht und Feuchtigkeit: die Insekten wurden zu Pflanzen im Bereich höherer Lichtintensität oder höherer Feuchtigkeit stärker angelockt. Bei solchen Bedingungen wirkte sogar ein Nichtwirt (Rizinus) stärker anlockend als ein Wirt bei schwächerem Licht oder geringerer Feuchtigkeit. Die Möglichkeit, diese Verhaltensweisen der Zwergzikaden für die Bekämpfung auszunutzen, wird erörtert.