BIOCHEMISTRY OF THE EXOCRINE SECRETION FROM GYPSY-MOTH CATERPILLARS (LEPIDOPTERA, LYMANTRIIDAE)

Gypsy moth, Lymantria dispar (L.), caterpillars have unpaired dorsal a bdominal glands on the 6th and the 7th segments, and pairs of smaller glands on the Ist to 4th abdominal segments. Normally, material from t hese glands becomes sticky and is regularly dispersed onto setae by th e caterpillars, but if larvae are held at saturated humidity for 3-4 d , droplets accumulate on the glands and remain fluid. The secretion is an aqueous mixture of low molecular weight molecules including the bi ogenic amine, gamma-aminobutyric acid, short-chain hydroxy acids (e.g. , alpha-hydroxyisobutyric acid), and Krebs cycle acids (e.g., isocitri c acid), plus higher molecular weight compounds (equal to or greater t han 30,000 MW). 2-Isobutyl-3-methoxypyrazine, considered to be a warni ng odor in many aposematic insects, also occurs in the secretion in mi nute amounts (equal to or less than 1 picogram per larva), yet is main ly responsible for the exudate odor which is detectable from individua l caterpillars. Natural secretion from L. dispar larvae was a feeding deterrent to foraging fire ants, Solenopsis geminata (F.), in a labora tory bioassay. All Lymantriidae have dorsal abdominal glands; therefor e, it is likely that secretion from these glands contributes to the ir ritating and allergenic properties associated with setae from tussock moth caterpillars.