Survival and growth of two Hydraecia species (Noctuidae : Lepidoptera) on eight midwest grass species

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 ser ious agriculture pests. Neonate larvae of both species (Noctuidae: Lepidopt era) were reared on eight selected grasses and corn for 14-18 days under gr eenhouse conditions to determine their survival and growth. These were quac kgrass (Agropyron repens), smooth bromegrass (Bromus inermis), orchardgrass (Dactylis glomerata), large crabgrass (Digitaria sanguinalis), barnyardgra ss (Echinochloa crusgalli), giant foxtail (Seteria faberii), wild prosso mi llet (Panicum millaceum), Johnsongrass (Sorghum halepense), and corn (Zea m ays). In a separate, concurrent experiment, H. immanis and H. micacea larva e were reared on quackgrass, smooth bromegrass and orchardgrass (narrow-ste mmed grasses) and sampled after 7, 10 and 14 days. H. immanis larvae genera lly grew more slowly and dispersed less quickly than H. micacea larvae. The fewest H. immanis and H. micacea larvae were recovered from giant foxta il. H. immanis larvae reared on quackgrass, smooth bromegrass and orchardgr ass (thin-stemmed grasses) "outgrew" their hosts by the third instar and ra pidly dispersed, particularly from quackgrass. Due to the unique internal s tem-feeding behavior of these larvae the stem thickness becomes a constrain ing factor regarding duration of suitability to serve as a larval host. Gra ss feeding has tremendous significance regarding the geographic spread, loc al population densities, phenological damage periods, and cultural control methods such as crop rotation for these two noctuid species.