Ovicidal Activity of Larvin and Ammo Against Pyrethroid-Susceptible and Resistant Strains of Tobacco Budworm, 1987

Abstract

Abstract Two small-plot studies were conducted in the field at the Texas A&M University Research and Extension Center at Corpus Christi to measure the effects of 4 treatments on survival of eggs and freshly hatched larvae of tobacco budworm. In Test 1, treatments were evaluated on eggs obtained from a pyrethroid-susceptible strain (S-strain) of tobacco budworm (laboratory colony maintained at the USDA Field Crop Insect Management Laboratory at Stoneville, Miss.) Treatments in Test 2 were evaluated on a pyrethroid-resistant strain (R-strain) of tobacco budworm (laboratory colony [PEG-87] maintained at ICI Americas at Pikeville, N.C.). Experimental methods were identical for both tests. Treatments were compared in 1-row × 30-ft plots of cotton planted 19 Mar on 38-inch rows. Using a camel's hair brush moistened with distilled water, fresh eggs (3- to 10-h-old) were attached manually to the upper surfaces of leaves (10 eggs/leaf) located near the shoot terminal of each of 24 flowering cotton plants/treatment. Within 30 min following placement of eggs on plants, treatments were applied to plants by using a CO2-pressurized (35 psi) backpack sprayer. The sprayer was calibrated to deliver 4.5 gal total spray/acre through 2 size 3X hollow-cone nozzles/row. Based on visual estimation, coverage of leaves and eggs with treatment sprays was optimal. Four hours after application, all leaves containing eggs were collected and placed individually into covered plastic Petri dishes and held in a laboratory temperature cabinet for 72 h (constant 78°F and 80% RH) then inspected for unhatched eggs and dead or live larvae. Each treatment was replicated 6 times in a completely randomized design. A replicate consisted of 6 leaves and 47-57 eggs, depending on the number of eggs lost in the field.