Arthropods infesting grain sorghum panicles: Parasitism, partial life tables, and sampling

Grain sorghum panicles were collected and examined for corn earworm, Heliothis zea (Boddie); sorghum webworm, Celama sorghiella (Riley); and arthropod predators during 1986-1988 in seven sorghum fields. The incidence of parasitism of H. zea eggs and larvae and C. sorghiella eggs was determined. Trichogramma exiguum (Pinto and Planter) and T. pretiosum Riley were the predominant egg parasites. Seven parasite species were reared from H. zea larvae; one eulophid, three tachinids, and three braconids.; Partial life tables were prepared for H. zea egg and larval stages. Total mortality was high ({dollar}>{dollar}97.0%). Mortality of eggs, first and second instar larvae accounted for more than 86.0% of the total mortality, with a majority occurring during the egg stage. Parasitism by Trichogramma spp. was the most significant egg mortality factor, particularly when host eggs were available throughout the growing season. The minute pirate bug, Orius insidiosus (Say), was the most frequently encountered predator during the study and predation was an important egg mortality factor and the most significant biotic factor affecting first instar larvae. Larval parasitism was very low, accounting for less than 0.6% of total mortality. Elasmus setosiscutellatus Crawford, was the most common larval parasite recovered; Archytas marmoratus (Townsend) was second most common. Mortality from unknown factors was the major contributor to overall mortality and was attributed to abiotic factors and/or undetected predation. Larval populations of H. zea were generally maintained below economically damaging levels by natural enemies and/or abiotic factors.; A modification of the beat-bucket sample method was evaluated for H. zea and O. insidiosus in grain sorghum panicles. Panicles were cut and twirled inside a 19-liter plastic bucket. Based on absolute density estimates, the method recovered greater than 50.0% of the H. zea larvae and O. insidiosus adults and 35.0% of the O. insidiosus nymphs. The method provided reliable estimates of population trends of H. zea larvae and O. insidiosus nymphs and adults. The method was calibrated for H. zea larvae and relative density estimates (y) may be converted to absolute density estimates (x) by the formula, x = y/b (b = slope of regression line).