Gut contents in molting lepidopteran larvae: a source of error in nutritional studies

It is generally assumed that larval insects allow the gut to clear of all food prior to each molt (Waldbauer, 1968; Kogan, 1986; Ayres & MacLean, 1987). This premise has been important in the standardization of insect starting weights in growth experiments; the food in feeding larvae may account for up to 50 ~o of the dry weight of phytophagous insects (Wightman, 1981; Kogan, 1986). The only published reference that we found of a lepidopteran species which does not clear its gut during molting was Spodoptera eridania (Cram.) (Soo Hoo, 1962 in Waldbauer, 1968). The finding that Paratrytone melane Edwards larvae also consistently contain a substantial amount of food in the midgut during and following a molt (Barbehenn, 1989) prompted us to make a survey of molting lepidopteran larvae in order to generalize about the prevalence of this putatively rare phenomenon. We also present a method for estimating the correct initial dry weights (DW) of larvae of species which retain food in their guts during a molt.