The influence of host plant on gut conditions of gypsy moth ( Lymantria dispar) caterpillars

We examined the pH and E h (redox potential) of the lumen of the digestive tract of gypsy moth caterpillars on six different host plants to understand the physiochemical conditions under which plant nutrients are extracted and allelochemicals are detoxified. To identify potential plant characteristics associated with the gut conditions, we determined the plant pH, E h , pH buffering capacity, and level of reducing phenolic groups for each host. We found (1) host plants differ in specific traits such as leaf pH, pH buffering capacity, E h , and the level of phenolic reducing groups; (2) the pH of the midgut is alkaline and independent of host plant, but the pH of the foregut and hindgut is acid to neutral and host plant dependent; (3) the E h of foregut, midgut, and hindgut are oxidizing and determined by both plant and insect traits; and (4) the plant trait that best predicts midgut E h is the level of phenolic reducing groups. We argue that the alkaline and oxidizing midgut conditions of gypsy moth caterpillars improve nutrient digestion and influence the activity of host plant allelochemicals, especially foliar phenolics.