IMPACT OF DIETARY ALLELOCHEMICALS ON GYPSY-MOTH (LYMANTRIA-DISPAR) CATERPILLARS - IMPORTANCE OF MIDGUT ALKALINITY

Midgut pH of gypsy moth larvae was depressed artificially with buffere d diet to examine the impact of alkalinity on the caterpillars' abilit y to tolerate a dietary polyphenol and a quinone. A 2 x 3 factorial de sign was used, with 2 levels of succinate buffer and 3 dietary amendme nts (tannic acid, juglone, or control). Development was monitored duri ng the third and fourth instars, with consumption, food passage rates, midgut pH, and midgut redox potential (Eh) measured in the fourth ins tar. Diet buffering successfully depressed midgut pH to hypothetically suboptimal acidic levels without reductions in survivorship, but it d id reduce larval growth and impede development. Buffering dramatically reduced survivorship of fourth instar larvae eating diets containing tannic acid or juglone. Growth increased on unbuffered diet amended wi th tannic acid, but not with juglone. Caterpillars passed food through the gut more slowly when feeding on buffered tannic acid diet or on u nbuffered juglone diet. These results indicate that maintenance of mid gut alkalinity is critical to tolerance of dietary tannic acid and jug lone, and that these allelochemicals have very different activities in the caterpillar gut. (C) 1997 Elsevier Science Ltd. All rights reserv ed.