Ovicidal Activity Trial, 1995

Abstract Treatments were applied to cotton grown in small plots at Stoneville, Miss. Plot size was 30 ft X 4 rows arranged in a RCBD with 4 replicates/treatment. Treatments were applied on 12 Jul (Test 1) and 18 Aug (Test 2) by a high-clearance spray machine equipped with a compressed-air spray system. Total spray volume was 6 gpa at 5 mph and 35 psi using two TX10 nozzles/row. TB eggs were obtained from cultures maintained in the laboratory. Test 1 eggs were obtained from a susceptible STV-LAB strain and Test 2 eggs were from a resistant G2-95 strain. The STV-LAB strain had been in culture without insecticide selection pressure since collection from cotton in 1984; the G2-95 strain was collected from cotton 13-16 Jun, 1995, and had been shown to have multiple resistance by standard bioassays. All eggs used were laid the previous night on tulle cloth material. Eggs were not washed or subjected to chemical treatments before use and were easily removed by crumpling the material. Eggs treated in the field were placed on the upper surface of the last 3-4 expanded leaves in the terminal of 4 plants in each replication by brushing a weak solution of xanthan gum and water on the leaves and sprinkling eggs on the surface. Plots were sprayed 30 min after application of the eggs. Eggs were sprinkled on the leaves in an effort to get at least 10 eggs/leaf. Eggs remained in the field for 2 h after treatment and were then taken to the laboratory to determine mortality. The number of viable eggs was counted on each leaf in the laboratory 24 h after being sprayed. The number of eggs averaged 15.0 ± 5.5 (S.D.). Leaves were held in Petri dishes on water-moistened filter paper at 82° F. The number of unhatched eggs was determined at 48 and 72 h after eggs were applied. Eggs were considered dead when black and shriveled. Cumulative egg mortality (EM) 72 h after treatment is reported. Hatched larval mortality (LM) was observed at 48 and 72 h after treatment and is reported as cumulative larval mortality at 72 h after treatment. Larval mortality was used to calculate total mortality (TM) at 72 h.