A RAPID, NONDESTRUCTIVE TECHNIQUE FOR ASSESSING CHLOROPHYLL LOSS FROMGREENBUG (HOMOPTERA, APHIDIDAE) FEEDING DAMAGE ON SORGHUM LEAVES

A rapid and nondestructive technique was developed to estimate the los s of chlorophyll in sorghum leaves caused by the feeding of greenbugs, Schizaphis graminum (Rondani). A SPAD-502 chlorophyll meter (Minolta Corporation, Ramsey, NJ) was used to measure chlorophyll content of un infested and infested leaf areas. A SPAD Index was calculated by divid ing chlorophyll loss (SPAD reading for uninfected tissue-SPAD reading for greenbug-infested tissue) by the SPAD reading for uninfested tissu e. SPAD Index values theoretically could range from 0.0 (no loss of ch lorophyll) to 1.0 (total loss of chlorophyll); the higher the index, t he greater the proportional loss of chlorophyll. Chlorophyll loss incr eased as the feeding duration of the greenbugs increased, but did not increase further after seven days of feeding. Interestingly, tissue fe d upon by greenbugs for only one day (greenbugs removed after one day of feeding), continued to lose chlorophyll each day for up to 22 days after removal of the feeding aphids. The likelihood of toxins, injecte d by feeding greenbugs, eliciting a continuing cascade of responses in the plant after removal of the aphids, is discussed.