EFFECTS OF LEAF SURFACE MOISTURE AND RELATIVE-HUMIDITY ON THE EFFICACY OF SUGAR ESTERS FROM NICOTIANA-GOSSEI AGAINST THE TOBACCO APHID (HOMOPTERA, APHIDIDAE)

The effects of leaf surface moisture and relative humidity on tile tox icity of sugar esters extracted from Nicotiana gossei Domin to the tob acco aphid, Myzus nicotianae Blackman, were examined in the laboratory and the field. The efficacy of sugar esters applied at a concentratio n of 1 mg/ml against tobacco aphids was >5 times higher under moist co nditions (either wet leaf surface or wet filter paper in petri dishes) than under dry conditions (dry leaf surface plus dry filter paper) in the laboratory. The effect of moisture an tile efficacy of sugar este rs was greater as the lethal concentration value increased from LC30 t o LC90. There was no significant difference in aphid mortality between the red and green color forms of tobacco aphids at tile same moisture and relative humidity levels. Regression analysis showed a linear rel ationship between aphid mortality front sugar esters and relative humi dity: The toxicity of sugar esters to aphids increased with higher rel ative humidity. Preliminary field evaluations also demonstrated increa sed aphid mortality under higher relative humidity.