FMRF‐amide immunoreactivity and the midgut of the corn earworm (Heliothis zea)

The midgut of the larval corn earworm, Heliothis zea, was examined using light microscopy and immunocytochemistry. Many endocrine‐like midgut cells exhibit immunoreactivity to the molluscan cardioactive peptide FMRF‐amide (FMRFa), and bovine pancreatic polypeptide (BPP). Cross‐reactivity studies demonstrate the immunoreactive material is more FMRFa‐like than BPP‐like. Immunocytochemical surveys and radioimmunoassay of midguts from fed or starved individuals show that the fed animals contain a significantly greater amount of FMRFa immunoreactivity. Radioimmunoassay of hemolymph reveals a significant increase in the amount of FMRFa immunoreactivity in the starved animals. These observations indicate that the changes in the levels of FMRFa immunoreactivity in the midgut and hemolymph may be a midgut endocrine response to changes in the feeding state.