Photofrin II (PII) accumulates and fluoresces in the alimentary canal, anal papillae, malpighian tubules, rectum, and gastric caeca at greater concentrations (>10 microg/ml) and accumulates (fluoresces) in (along) the alimentary canal only at lower concentrations (< or =10 microg/ml). Initial experiments with larvae exposed to different osmotic conditions and PII indicated that cells of osmoregulation were most susceptible to life-threatening cell damage. Larvae that lacked anal papillae and were exposed to different osmotic conditions and PII indicated that cells of osmoregulation may not be the most deleterious site for cell damage. Larvae ligated around the neck and exposed to PII survived significantly longer than larvae ligated after the 4th abdominal segment and after the 6th abdominal segment while also being exposed to PII. Pupae are unaffected by PII at any concentration and they do not ingest during their development. These experiments indicate the midgut gastric epithelia could be the most deleterious site for cell damage caused by PII.
