Identification and diel activity patterns of predators attacking Helicoverpa zea (Lepidoptera: Noctuidae) eggs in soybean and sweet corn

Predation on lepidopteran eggs in soybean and corn and the temporal partitioning of predation among the predator species were examined in soybean Glycine max (L.) and sweet corn Zea mays (L.). The complex of predators feeding on lepidopteran eggs [Helicoverpa zea (Boddie)] and the key predators discovered in this study were different in each crop. The dominant predator in each crop was consistent from year to year but the secondary predators varied in importance. Nabids were the dominant predator group in soybean contributing 51 and 50% of the observed predation events in 1993 and 1994, respectively. The coccinellid, Coleomegilla maculata (DeGeer), was the dominant predator in corn contributing 43.9 and 46.3% of the observed predation events in 1993 and 1994, respectively. Other predators causing greater than or equal to10% of the observed predation events included Geocoris punctipes Say and the Phalangiidae in soybean, and the nabids, Orius insidiosus Say and Lygus lineolaris (Palisot de Beauvois) in sweet corn. All predators observed feeding exhibited taxa specific diel patterns of predation. C. maculata, O. insidiosus and G. punctipes were primarily day active, with 75, 85.7, and 100% of observed predation events occurring during daylight hours, respectively. Nabids were primarily nocturnal with 84.2% of predation events happening at night. Phalangiids, Clubiona abbotii Koch, Lygus lineolaris, and the elaterids were only observed preying upon H. Zea eggs nocturnally. Because the dominant predators and their diel activity varied between crops, the period of peak egg predation did also. Egg predation was usually higher during the day in corn and at night in soybean. Crop, date, and time of day all affected intensity of predation on H. zea eggs. Predation in both crops increased through the beginning of August and then declined on the last sampling date. Predation was usually higher in corn than in soybean (three of four sample dates). However, when anthesis was occurring in corn plots, predation rates in soybean and corn were similar. Apparently the availability of sweet corn pollen as an alternative food source for C. maculata caused a reduction in egg predation.