Evaluation of Coloured Sticky Traps for Monitoring Populations of Austroasca viridigrisea (Paoli) (Hemiptera: Cicadellidae) on Cotton Farms

Field tests on the colour response of Austroasca viridigrisea adults were conducted using square (30 × 30 cm) coloured sticky traps placed in a cotton field. Among the colours tested, adults were attracted most to yellow traps emitting light in the 500-600 nm region (peak reflectance at 560 nm), followed by green and orange, then red, deep blue, black, magenta and true blue. Dilution of yellow with white to produce yellow-white hues resulted in a significant decline in A. viridigrisea captures. Reflectance spectra of painted surfaces of enamel colours and also traps with different hues of yellow indicated that A. viridigrisea capture rates were directly related to the amount of light reflected in the 500-600 nm zone, the wavelength at which peak reflectance of green plants occurs. This positive behavioural response of A. viridigrisea to yellow suggests that the leafhopper can discriminate foliage-like hues (500-580 nm) from non foliage-like hues ( 580 nm) and therefore could detect herbaceous foliage on the basis of colour. Significantly higher numbers of adults were caught at heights between 25-75 cm than at 100, 125 and 150 cm above ground level. To monitor flight phenology and populations of A. viridigrisea, yellow sticky traps should be placed at heights between 25 and 75 cm above ground level.