Grasses play a critical role in the life cycles of both the hop vine borer (Hydraecia immanis) and potato stem borer (H. micacea), two potentially serious agriculture pests. Neonate larvae of both species (Noctuidae: Lepidoptera) were reared on eight selected grasses and corn for 14-18 days under greenhouse conditions to determine their survival and growth. These were quackgrass (Agropyron repens), smooth bromegrass (Bromus inermis), orchardgrass (Dactylis glomerata), large crabgrass (Digitaria sanguinalis), barnyardgrass (Echinochloa crusgalli), giant foxtail (Seteria faberii), wild prosso millet (Panicum millaceum), Johnsongrass (Sorghum halepense), and corn (Zea mays). In a separate, concurrent experiment, H. immanis and H. micacea larvae were reared on quackgrass, smooth bromegrass and orchardgrass (narrow-stemmed grasses) and sampled after 7, 10 and 14 days. H. immanis larvae generally grew more slowly and dispersed less quickly than H. micacea larvae.
The fewest H. immanis and H. micacea larvae were recovered from giant foxtail. H. immanis larvae reared on quackgrass, smooth bromegrass and orchardgrass (thin-stemmed grasses) outgrew their hosts by the third instar and rapidly dispersed, particularly from quackgrass. Due to the unique internal stem-feeding behavior of these larvae the stem thickness becomes a constraining factor regarding duration of suitability to serve as a larval host. Grass feeding has tremendous significance regarding the geographic spread, local population densities, phenological damage periods, and cultural control methods such as crop rotation for these two noctuid species
