Submitted to: International Symposium on Biological Control of Arthropods
Publication Type: Proceedings
Publication Acceptance Date: 9/15/2005
Publication Date: 9/15/2005
Citation: Pfannenstiel, R.S. 2005. Nocturnal predators and their impact on lepidopteran eggs in annual crops: What we don't see does help us. In: Proceedings of the International Symposium on Biological Control of Arthropods, September 12-16, 2005, Davos, Switzerland. p. 463-471. Interpretive Summary: The predator complexes attacking moth eggs in cotton, corn, and soybean in south Texas, USA, were studied to compare day and night active predator groups, determine what percentage of eggs are eaten at night, and observe whether individual predator species are active during the day or night. The evaluations reported here focused on the predator complexes feeding on the corn earworm and the beet. We used direct observation to accurately measure and identify predation of moth eggs while removing the bias towards day active predators. Egg predation was high in all crops in all years, ranging from 25 to 99% per 24 hours. Predation at night was common in all crops. The day and night active predators observed feeding on eggs differed between crops. The proportion of predation observed at night varied among dates, but was similar to predation observed during the day in cotton, corn, and soybean in 2002, and soybean in 2003. Predation on eggs at night was higher than during the day in cotton in 2003. Predators observed feeding at night constituted nearly 72% of all observations in south Texas cotton, 52% in corn and 49% in soybean. At night, predators such as spiders and ants were particularly important. Few predators were active during both day and night. Nighttime observations revealed both known and unknown predators (e.g., cursorial spiders).
Technical Abstract: The predator complexes attacking lepidopteran eggs in cotton, corn, and soybean in south Texas were determined with the goal of characterizing diurnal and nocturnal predator complexes, determining the role of nocturnal predators in lepidopteran pest mortality, and quantifying diel predations. The evaluations reported here focused on the predator complexes attacking Helicoverpa zea (Boddie) and Spodopteran exigua (Hubner), Lepidoptera: Noctuidae. Egg predation was typically high in all crops in all years, although it ranged from 25 to 99% in any 24- hour period. Nocturnal predation was a significant component of this mortality in all crops. The diurnal and nocturnal predator complexes observed feeding on eggs differed between crops. The relative importance of nocturnal predation varied among dates, but on average was similar to diurnal predation in cotton, corn, and soybean in 2002 and soybean in 2003. Nocturnal predation was > 50% higher than diurnal predation in cotton in 2003. Nocturnal predation constituted nearly 72% of all observations in south Texas cotton, 52% in corn, and 49% in soybean. Nocturnal predators of particular importance included a group of cursorial spiders responsible for nearly 25% of all observations of predation in cotton, as well as the formicids (primarily Solenopsis invicta Buren). Few predators were commonly active during both day and night.