Bioassay, Effect of Field-Aged Residues of Spinosad, Abamectin and Bacillus Thuringiensis on Neonate Leafroller Larvae, 1995

Using a leaf-disk bioassay, Spinosad DE-105 1.6% (DowElanco), Abamectin 0.15 EC (Merck & Co, Inc.) and Bacillus thuringiensis (Bt) (Dipel 2X, Abbott Laboratories) were evaluated for residual effects on PLR and OBLR neonate larvae. The test was conducted in an apple orchard at the Tree Fruit Research and Extension Center. The trees were 15-yr-old spur type Delicious on dwarfing roots. Treatments were applied on 14 Jul with a handgun sprayer at 300 psi to the point of drip, simulating a dilute spray of approximately 400 gal/acre. Each treatment was replicated three times with one tree in each. Ten leaves were collected from the interior canopy of each tree at 1, 4, 7, 14 and 21 DAT. Two punches (2.3 cm diameter) were taken from each leaf. Four punches were placed in a Petri dish (Falcon 1006, 50X9 mm), keeping the leaves from each replication separate. Petri dishes were chosen randomly, and five 1- to 2-d-old leafroller larvae were placed on the leaves. Five Petri dishes were prepared for each tree and each leafroller species (75 larvae per treatment). The Petri dishes were placed inside a food storage container and kept at 75°F (±2°F) constant temperature and 16:8 photoperiod. Petri dishes were examined after 7 d and larval survival recorded.