Caterpillar guts and ammonia volatilization: retention of nitrogen by gypsy moth larvae consuming oak foliage

The gypsy moth (Lymantria dispar L.), a major defoliator of hardwood forest s in the eastern U.S., has a highly alkaline midgut pH. We hypothesized tha t the high pH would cause high rates of ammonia (NH3) volatilization as lar vae consumed foliage, leading to potentially large losses of N from the eco system to the atmosphere during gypsy moth outbreaks. We measured NH3 emiss ion during the consumption of oak foliage by larvae in the laboratory. Surp risingly, we found very low amounts of NH3 release of about 0.1% of the N c onsumed in foliage. We speculate that digestive mechanisms may limit NH3 pr oduction in the midgut, and that the acidic environment of the hindgut trap s most of the small amount of NH3 that is produced, effectively preventing a potentially very large N loss from both larvae and ecosystem. The estimat ed rate of NH3 emission from a defoliated forest is small compared to other inputs and outputs of N from the ecosystem, but could potentially enhance the neutralization of atmospheric acidity during the defoliation period.