The population dynamics of the bollworm, Helicoverpa zea (Boddie), and its associated natural enemies were studied in insecticide-free, commercial, short-season cotton fields from 1991 to 1995 in the southern Blacklands of Texas. Bollworm had one discernable generation per season in cotton. Partial ecological life tables constructed for each annual generation indicated that 71–95% mortality could be consistently expected in the egg and first-instar life stages. Intrageneration mortality ranged from 93 to 99%. Unexplained mortality was the leading cause of mortality in 1991–1993, but not in 1994 and 1995 when predation due to Orius spp. was partitioned. Unexplained mortality included abiotic as well as biotic factors. Parasite activity was consistently low. Egg parasitization by Trichogramma spp. averaged 3.4%. Larval parasitization rarely exceeded 5% and no larval parasitization was found in 1993. Microplitis croceipes (Cresson) was the most common larval parasite collected. Predation of bollworm eggs by Orius insidiosus (Say), the numerically dominant predator in the system, was estimated using ELISA in 1994 and 1995. O. insidiosus was the most important mortality factor when measured consuming 84 and 71% of the eggs in 1994 and 1995, respectively.
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