CONTACT TOXICITY OF THE MYCOTOXIN DESTRUXIN-E TO EMPOASCA-VITIS (GOTHE) (HOM, CICADELLIDAE)

The toxicity oi destruxin E for nymphs of Empoasca vitis (Gothe) was a ssessed in the laboratory using various administrative routes: 10 ml o f a given concentration of the toxin (30, 100, 300 and 1000 ppm) were sprayed either on potato leaves or directly onto the insects, and 1 mu l of a 100 ppm concentration of toxin was applied onto the nora of th e insects. Checks were made daily for 4 days and mortality in E. vitis was recorded. Natural mortality was less than 5%. Nymphs of E. vitis were susceptible to the insecticidal activity of destruxin E in all th ree treatments. Mortality was concentration-dependent in nymphs expose d to treated leaves and in nymphs sprayed directly. The potency of des truxin E was reflected in the low LC(50) values obtained: 46.4 ppm for insects exposed to treated leaves and 38.2 ppm for insects sprayed di rectly. The LT(50) values were 3.2 days (at 30 ppm) and 0.2 days (1000 ppm) for nymphs sprayed directly, and slightly higher for nymphs expo sed to treated leaves. Analysis of data (100 ppm) showed that there wa s no significant difference in mortality due to either of the three bi oassay procedures. Mortality rates were 87.5% in nymphs sprayed direct ly, 93.8% in nymphs exposed to treated leaves, and 78.1% in nymphs in the topical application test. The LT(50) value in the latter test (at 100 ppm) was 1.3 days. Contact insecticidal activity of destruxin E is demonstrated here for the first time.