Nocturnal Predators and Their Impact on Lepidopteran Eggs in Annual Crops: What We Don’t See Does Help Us!

Predation is often a key factor maintaining insect populations below pest status in annual crops. However, in many cases, the predators causing significant mortality to particular pests in the field are not well understood. In particular, the complex of nocturnally active predators feeding on pest species is usually unknown. The predator complexes attacking lepidopteran eggs in cotton, corn and soybean in south Texas, U.S.A., 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 patterns of predation. The evaluations reported here focused on the predator complexes feeding on Helicoverpa zea (Boddie) and Spodopteran exigua (Hübner), (Lepidoptera: Noctuidae). This work has been conducted using direct observation to accurately measure and identify predation of lepidopteran eggs while removing the bias towards day-active predators. Egg predation was typically high in all crops in all years, although it ranged from 25 to 99% in any 24 h 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. Mortality due to nocturnal predation was >50% higher than diurnal predation 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. 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) Of the four spider species most frequently observed feeding on eggs, only one had previously been reported as an important predator in agricultural settings (Cheiracanthium inclusum [Hentz]). Few predators were commonly active during both day and night. Nocturnal observations revealed both predators that were previously suspected to be important mortality factors as well as those that had not been perceived to be important (e.g., cursorial spiders).