Bioassay, Effect of Field-Aged Residue Degradation of Bacillus Thuringiensis, 1994

Abstract

Abstract Using a leaf-disk bioassay, B. thuringiensis products (Dipel and Troy Bt), and B. thuringiensis with feeding stimulants (Konsume and Coax) were evaluated for residue 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 ‘Red Delicious’ on dwarfing roots. The treatments were applied on 8 Sep at the recommended rate 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, 6 and 8 (OBLR) DAT. Two punches (2.3 cm diameter) were taken from each leaf. Four punches were placed in a petri dish (Falcon 1006, 50 × 9 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 replicate and each leafroller species (75 larvae per treatment). The petri dishes were placed inside a food storage container and kept at 20°C constant temperature and a photoperiod of 16:8 (L:D) h. Petri dishes were examined after 7 d and larval survival recorded.