Bioassay, Effect of Commonly Applied Pesticides on T. Platneri in North Central Washington, 1994

Abstract

Abstract Various insecticides were evaluated for direct toxicity and the effects of field-aged residues on adult females of the leafroller egg parasite Tp. Tp were received from Rincon-Vitova (Ventura, CA) on a card containing approximately 100,000 parasitized host eggs (Sitotroga cerealella reared on grain). 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.” The B. thuringiensis products (Dipel, Javelin and MVP), the growth regulators (Comply, Dimilin, RH-5992 and RH-2485) and M-Pede were tested at the full field rate and the neurotoxins at 10% the field rate. Ten microliters of a spreader (Triton B-1956) were added to each of the B. thuringiensis formulations. The card with the parasitized eggs was sectioned into 1-square-inch pieces containing approximately 1,000 Tp. The Tp females used for the tests were reared from these pieces in small petri dishes (Falcon 1006, 50 × 9 mm). The age of Tp females was standardized at 1-3 d after emergence from the pupal stage. Fifty females from one of the petri dishes 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. Tp were transferred to additional petri dishes (Falcon 1006, 50 × 9 mm). A small cube of artificial diet used to rear leafrollers and a thread dipped in honey were added to the petri dishes. The diet worked very well for controlling the humidity and moisture in the petri dishes, and honey had been shown to extend Tp life span by providing nutrition. Five Tp were placed into 10 petri dishes for each of the chemicals (50 Tp per treatment). Surviving parasites were counted 24 and 48 h after treatment. Treatments with significant survival at 10% of the 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. Means from the 10% field rate application covered a wide range of values and the standard deviations were proportional to the means so statistics were run on transformed data (log X + 1). 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 in each .Ten mature leaves were collected from each replicate (tree). One punch (2.3 cm diameter) was taken from each leaf (10 total from a tree), and two were placed in a small petri dish (Falcon 1006, 50 × 9 mm). A small cube of artificial diet used to rear leafrollers and a thread dipped in honey were added to the petri dishes. There were 15 petri dishes for each treatment (five for each tree). 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 Tp females, age 1-3 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 test was repeated at 1, 3, 7, 14, and 21 d after treatment for those that were significantly different than the untreated check.