. Untersuchungen im Feld von Bacillus thuringiensis zur Steuerung von Western Hemlock looper. Hemlock looper Kontrolle; Bacillus thuringiensis. Ergebnisse Muster der Larven Sterblichkeit Zahlreiche distressed Larven auf Laub Proben 4 und 7 Tage bemerkt wurden nach dem Spritzen, und die ersten Toten Larven im Boden Fächer 6 Tage nach dem Spritzen gefunden wurden. Mortalität schnell erreicht eine Spitze 8 Tage nach dem Spritzen, mit 20 Larven in den Fächern gefunden, dann allmählich, bis ein deutlicher Rückgang in der 16. Tag (Bild zurück. 5). Nur 94 tote Larven wurden in den Fächern im Laufe der 20-tägigen Frist gefunden. 30 . Abbildung 5 - Zahl der toten Larven f

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. Field testing of Bacillus thuringiensis for control of western hemlock looper. Hemlock looper Control; Bacillus thuringiensis. Results Pattern of Larval Mortality Numerous distressed larvae were noticed on foliage samples 4 and 7 days after spraying, and the first dead larvae in ground trays were found 6 days after spraying. Mortality quickly reached a peak 8 days after spraying, with 20 larvae found in the trays, then decreased gradually until a sharp decline on the 16th day (fig. 5). Only 94 dead larvae were found in the trays over the 20-day period. 30_. Figure 5.—Numbers of dead larvae found in ground trays during a 20-day period after spraying with B. thuringiensis. O 5 10 15 20 Number of days after spraying An additional 47 dead larvae were found on branch tips removed by pole-pruner; approximately equal numbers were found in each of five samplings up to the 16th day after spraying. Dislodgment of dead larvae was apparently a gradual process. Bacillus infections were found in varying percentages of larvae obtained 6 to 18 days after spraying. From the 8th to the 12th day after spraying, around 70 percent of the dead larvae were infected; in collections on the 14th and 16th days after spraying, around 50 percent were infected. On the 18th day after spraying, one out of five larvae found (20 percent) was infected with Bacillus . The decline in detectable Bacillus infections after the 12th day was also indicated by analysis of dead larvae found on tips cut by pole-pruner. Of 1 6 larvae collected 13 days after spraying, 50 percent were infected. Amount of Larval Mortality Numbers of larvae found on 18-inch branch tips before spraying and at intervals after spraying (table 1) indicated generally low and variable mortality in the treated area. Larval mortality 19 days after spraying ranged from 0 to 66 percent for the 20 plots, averaging 30 percent for the area. Six plots showed a range of 49 to 66 percent mortality; seven plots, 11 to 43 percent mortality; and

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