Spatial and temporal patterns of catches in pheromone traps of Helicoverpa zea and Heliothis virescens in central Texas

Sex pheromone trapping was conducted in an agricultural area located primarily in Burleson and Brazos counties in Central Texas during 1990 and 1991 to determine the spatial and temporal patterns of catches of the corn earworm, Helicoverpa zea (Boddie), and the tobacco budworm, Heliothis virescens (F.). Traps for both species were spaced at about 3.2 km intervals and were operated in lines radiating from the center of a study area with a diameter of about 48 km (1,830 km super(2)) in 1990. In 1991, the number of traps was reduced by about half. The area represents a diverse agroecosystem with intensive irrigated and dryland cropped areas primarily in cotton, but with some acreage of corn, sorghum, and other crops. Uncropped areas consist of native and improved pastures, plantings for winter pastures, and areas with concentrations of wild hosts. Temporally, there were earlier and much higher catches of H. zea than H. virescens in the spring. Catches in traps of H. zea declined to a low point in mid-August; however, dramatic increases in late August and early September persisted until mid-October. Immigration from northern areas is suspected as the cause of the late season increases because local populations alone could not account for the magnitude of the captures. In contrast, catches of H. virescens were low starting with initial captures in early April and increased very gradually until July when numbers increased dramatically to the highest levels of the season from late August to mid-October. Initial captures in early April were synchronized with the period of expected H. virescens overwintering emergence. The pattern of H. virescens population build-up was keyed to the period of rapid cotton fruiting, especially in irrigated cotton, which appears to indicate a local origin for this species. The spatial pattern of catches indicated that H. virescens adult activity was significantly more concentrated than H. zea in the cropped than the uncropped areas at mid-season. Cotton, especially the intensively managed irrigated acreage, appears to play a major role in the activity patterns of H. virescens. Understanding the role of these proposed factors in the population dynamics of both species will aid in the development of areawide pest management approaches.