Natural mortality of Helicoverpa zea (Lepidoptera : Noctuidae) in short-season cotton

The population dynamics of the bollworm, Helicoverpa tea (Boddie), and its associated natural enemies were studied in insecticide-free. commercial, sh ort-season cotton fields from 1991 to 1995 in the southern Blacklands of Te xas. Bollworm had one discernable generation per season in cotton. Partial ecological life tables constructed for each annual generation indicated tha t 71-95% mortality could be consistently expected in the egg and first-inst ar life stages. Intrageneration mortality ranged from 93 to 99%. Unexplaine d mortality was the leading cause of mortality in 1991-1993, but not in 199 1 and 1995 when predation due to Or-ius spp. was partitioned. Unexplained m ortality included abiotic as well as biotic factors. Parasite activity was consistently low. Egg parasitization by Trichtogramma spp. averaged 3.4%. L arval parasitization rarely exceeded 5% and no lan;al parasitization was fo und in 1993. Microplitis croceipes (Cresson) was the most common lan al par asite collected. Predation of bollworm eggs by Orius insidiosus (Say), the numerically dominant predator in the system, was estimated using ELISA in 1 994 and 1995. O. insidiosus was the most important mortality factor when me asured consuming 84 and 71% of the eggs in 1994 and 1995, respectively.