Ground Cover Influence on Microclimate and Trichogramma (Hymenoptera: Trichogrammatidae) Augmentation in Seed Corn Production

Abstract

As pest management practices include more biological control implementation, the effect of different cropping systems on microclimate and efficacy of natural enemies should be considered. In a 1993 experiment, physical and microolimatic differences between hybrid field corn, Zea mays L., and inbred seed corn were assessed. Seed corn fields had 4.2-fold less leaf surface area and higher maximum temperature at the soil surface than field corn fields. Emergence of Trichogramma brassicae Bezdenko from cardboard capsules was significantly lower in seed corn when capsules were placed at the soil surface, but was not significantly different when capsules were at canopy level. In 1994, a rye grass Lolium multiflorum Lambert intercrop planted with seed corn significantly reduced maximum soil surface temperature compared with seed corn plots in which soil was bare or was covered (62%) with corn residue. Soil surface temperature was significantly higher in corn residue plots than in bare soil plots. Minimum temperatures were not significantly affected by ground cover. The mean number of hours per day that temperatures were 35°C or higher (lethal to T. brassicae) was significantly higher in residue and bare soil microhabitats than in rye grass plots or the corn canopy. When T. brassicae inside cardboard capsules were put into plots in the same manner as an augmentative release (i.e., 2 developmentally staggered cohorts), emergence from both cohorts was not significantly different in rye grass than in the corn canopy, but was significantly reduced in bare soil and corn residue plots.