The influence of dietary l-azetidine-2-carboxylic acid on catecholamine levels in the hemolymph and cuticle of the corn earworm, Helicoverpa zea

Abstract

The influence of L-azetidine-2-carboxylic acid (AZC) on catecholamine levels in the hemolymph and cuticle of the corn earworm, Helicoverpa zea, was investigated. Feeding corn earworm larvae on a diet supplemented with AZC significantly reduced hemolymph levels of dopamine (DA) and N-β-alanyldopamine (NBAD) by at least 2–3-fold and to a lesser extent, the levels of N-acetyldopamine (NADA). This suggests that AZC has an inhibitory influence on the mechanisms involved in DA synthesis, catabolism or transport. NBAD was the major catecholamine in both hemolymph and cuticle of H. zea. Catecholamines were generally low in concentration during the larval feeding period but increased to highest levels during larval-pupal transformation. Conversely, catecholamine levels in cuticle were highest on day one of the fifth instar and then decreased to low levels thereafter. NBAD and other catecholamines were higher in day one cuticle of AZC fed larvae than in controls but not thereafter. DA and NBAD concentrations in the cuticle remained low throughout the larval instars, about 5–10 times lower than in the hemolymph. The pattern and temporal distribution of catecholamines during the larval-pupal transformation in this species was such that concentrations remained high in the hemolymph through post-wandering behavior, but low in the cuticle. Catecholamines became abundantly available in the cuticle for pupal sclerotization after pupation had occurred.