Bioassay, Effect of Commonly Applied Pesticides on C. Florus in North Central Washington, 1994
Abstract Various insecticides were evaluated for direct toxicity and the effects of field-aged residues on adult females of the leafroller parasitoid Cf. The chemicals tested for direct toxicity were those listed in the “Predator Toxicity Guide-Apple” chart in the “1994 Crop Protection Guide for Tree Fruits in Washington.” B. thuringiensis products (Dipel, Javelin and MVP), growth regulators (Comply, Dimilin, RH-5992 and RH-2485) and M-Pede were tested at the full field rate and the neurotoxins at 10% of the field rate. Ten microliters of a wetting agent (Triton B-1956) were added to each of the B. thuringiensis formulations. Cf females were taken from a colony maintained at the WSU Tree Fruit Research and Extension Center for the assay. The age of Cf adults was standardized at 2-5 d after emergence from the pupal stage. Fifty females reared from at least five separate host larvae were selected for each of the chemicals tested. These females were anesthetized with CO2, placed on a piece of 11-cm filter paper and transferred to a Potter spray tower. The tower applied 4 ml of pesticide at 6 psi of pressure to the parasites. Cf were transferred to petri dishes with snap-on lids (Falcon 1006, 50 × 9 mm). Honey water and a small cube of artificial diet used to rear leafrollers were added to the petri dishes. The diet worked very well for controlling the moisture in the petri dishes, and honey water had been shown to extend Cf life span by providing nutrition. Five Cf were placed into 10 petri dishes for each of the chemicals (50 Cf per treatment) and kept at 75°F (±2°F) constant temperature and a photoperiod of 16:8 (L:D) h. Surviving parasites were counted at 24 and 48 h after treatment. Treatments with significant Cf survival at 10% field rate were then tested at 50% of the field rate. Treatments with survivors at 50% of the field rate were tested at the full field rate. The residue degradation 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 insecticides were applied at the recommended field rates (see below) 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 as a single tree. Ten mature leaves were collected from each tree (replicate). One punch (2.3 cm diameter) was taken from each leaf (10 total from each tree), and two were placed in a small petri dish (Falcon 1006, 50 × 9 mm). A small quantity of diluted honey water was smeared on the lid for a carbohydrate source, and a small piece of artificial diet used to rear leafrollers was placed in the petri dish to help keep humidity at acceptable levels. There were five petri dishes for each replicate (15 for each treatment). After the leaves were placed in the petri dish and each dish was labeled with a replicate and treatment code, one was chosen at random and five adult Cf females, age 2-3 d old, were placed inside (75 females 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. The no. of survivors was counted at 24 and 48 h. This bioassay was repeated at 1, 3, 7, 14 and 21 d after treatment (DAT) for treatments where Cf mortality was significantly different than the untreated check.
