Natural mortality of bollworm in northern Texas Blacklands cotton

Abstract

To better understand the elects of natural mortality phics. on bookworm, Helicoverpa zea (Boddie), in short season cotton not receiving in-season insecticide applications, population data were collected for bookworm and its predators over two seasons. Life tables were construed for bookworm. An important egg predator, Orius spp., was assayed by enzyme-linked immunosorbent assay (ELISA) to determine the proportion of the Orius spp. population that had consumed bookworm eggs. The life tables for both seasons revealed a type III survivorship curve with over 93% of the cohort dying in the egg and first instar life stages. Egg parasitism was primarily by Trichogramma spp. and accounted for 1.7 and 2.8% of the age-specific mortality of the egg. Failure to hatch accounted for 9.0 and 6.4% of the egg mortality but the largest portion of generational mortality was the residual and was not accountable. Overall generational mortality was over 98%. Analysis by ELISA of Orius spp. indicated that Orius does prey upon bookworm eggs in this system, although only a low proportion of Orius sampled were deeded as egg feeders. Other common egg predators encountered were Pseudatomoscelis seriates (Reuter), Scymnus spp., Hippodamia convergens (Guerin-Meneville), and several species of spiders.