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 assessed in the laboratory using various administrative routes: 10 ml of 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 the 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 three treatments. Mortality was concentration-dependent in nymphs exposed to treated leaves and in nymphs sprayed directly. The potency of destruxin 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 directly. 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 exposed to treated leaves. Analysis of data (100 ppm) showed that there was no significant difference in mortality due to either of the three bioassay procedures. Mortality rates were 87.5% in nymphs sprayed directly, 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.