LIFE SYSTEM OF STEGASTA BOSQUEELLA (CHAMBERS) ON PEANUTS IN OKLAHOMA

Scope of Study. The rednecked peanutworm, Stegasta bosqueella (Chambers) is the most common lepidopterous insect pest on peanuts, Arachis hypogaea L. in Oklahoma. It can cause considerable defoliation and stunting of plants when population densities are high. The purpose of this investigation was to develop life tables in order to follow the development of this insect in the field and determine the impact of larval feeding on peanuts. Eggs, larvae, pupae, and adults were reared in the laboratory at constant temperatures to establish developmental thresholds and thermal requirements for development. Field sampling for larvae, pupae, and adults was conducted in order to construct life tables of this insect. Artificial and actual rednecked peanutworm damage was inflicted on field grown peanuts to ascertain the plant response to foliar damage.;Findings and Conclusions. Eggs, larvae, and pupae had developmental thresholds of 11.7(DEGREES)C, 11.0(DEGREES)C, and 12.2(DEGREES)C, respectively. The mean C(DEGREES) day accumulations required for completion of life stages were: 66.5 - egg, 156.0 - larva (to prepupa), 25.1 - prepupa, and 94.2 - pupa. None of the life stages completed development at 12.8 (+OR-) 1(DEGREES)C. There were no significant differences (P = 0.05) between the degree day accumulations required for completion of life stages at 18.3 (+OR-) 1, 23.9 (+OR-) 1, and 29.4 (+OR-) 1(DEGREES)C. The total generation time for S. bosqueella was calculated to be approximately 440(DEGREES)C days. Life table studies of S. bosqueella indicated that 3 generations a year occur in Oklahoma. Larval numbers were very great at times (over 3 million/hectare) and typically reached maximum numbers in the second generation. Twelve parasitic species were recovered from this host, the most numerous being Orgilus modicus Mues., Chelonus (Microchelonus) sp., and Invreia spp. Disappearance was the major cause of S. bosqueella mortality and appeared to be a combination of biological and climatic factors. Peanut plant response to foliar damage varied with the type of damage inflicted. Although simulated rednecked peanutworm damage appeared very similar to actual damage caused by larval feeding, the plant response was not the same. Artificially damaged plants produced significantly fewer (P = 0.05) pegs, nuts, and terminals and reduced weight of leaves than plants damaged by larval feeding. However, peanutworm damaged plants produced significantly shorter stems as compared to artificially damaged or undamaged plants. Peanut leaflets demonstrate the ability to compensate for damage as they enlarge from terminals. Damage to very small leaflets (area < 150 mm('2)) results in much more compensation than the same extent of damage to larger leaflets (150 - 450 mm('2)). Feeding of S. bosqueella through the larval stage results in a mean reduction in mature leaf area of 3993 mm('2) (ca. 4 leaflets)/individual. The potential for economic damage to peanuts from foliar feeding of the rednecked peanutworm appears to be minimal except for the period of time when plants are 50 - 90 days of age.