GROUND COVER INFLUENCE ON MICROCLIMATE AND TRICHOGRAMMA (HYMENOPTERA,TRICHOGRAMMATIDAE) AUGMENTATION IN SEED CORN PRODUCTION

As pest management practices include more biological control implement ation, the effect of different cropping systems on microclimate and ef ficacy of natural enemies should be considered. In a 1993 experiment, physical and microclimatic 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 B ezdenko from cardboard capsules was significantly lower in seed corn w hen capsules were placed at the soil surface, but was not significantl y different when capsules were at canopy level. In 1994, a rye grass L olium multiflorum Lambert intercrop planted with seed corn significant ly reduced maximum soil surface temperature compared with seed corn pl ots in which soil was bare or was covered (62%) with corn residue. Soi l surface temperature was significantly higher in corn residue plots t han in bare soil plots. Minimum temperatures were not significantly af fected by ground cover. The mean number of hours per day that temperat ures were 35 degrees C or higher (lethal to T. brassicae) was signific antly 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 w as not significantly different in rye grass than in the corn canopy, b ut was significantly reduced in bare soil and corn residue plots.