Partial ecological life table of immature Helicoverpa zea (Lepidoptera: Noctuidae) in an irrigated cotton cropping system in the Trans-Pecos region of Texas, USA

During the summers of 1996 and 1997 cotton bollworm, Helicoverpa zea (Boddie), life stages were sampled in insecticide-free, irrigated cotton, Gossypium hirsutum L., in the Trans-Pecos region of Texas. Partial ecological life tables were constructed for one generation of H. zea in each of the two growing seasons. Partial generation mortality (egg to fifth-instar) surpassed 97% in both years. The egg stage exhibited the greatest amount of real (r_x) and apparent (q_x) mortality followed by the third-instar. One hundred percent of the collected life stages consisted of H. zea. Egg parasitism ranged from 4.1 to 6% and egg predation by Orius tristicolor (White) was 4.1% in 1996 and 13.2% in 1997. Unexplained factors made the greatest contribution to H. zea mortality regardless of the life stage sampled. Each cotton bollworm generation monitored in 1996 and 1997 exhibited a Type III survivorship curve. As a result of the extensive early life stage mortality, rescue management tactics associated with contemporary H. zea control in the region appears to be generally unnecessary for cotton grown under irrigation in the Trans-Pecos region.