The high titre of free amino acids in the larval haemolymph of the moth, Spodoptera mauritia boisduval

Host-pathogen interactions: proline gives insect pathogens the green light

How does a quiescent symbiont of a nematode worm know when to turn nasty? Metabolic analysis and genetic knockouts confirm that model insect pathogens can sense L-proline in insect blood. This not only serves as a wake-up call, activating secondary metabolite virulence factors, but also provides an energy source for a metabolic shift appropriate for adaptation to the host environment.

Changes in protein content and free amino acid composition in metal-contaminated gypsy moth larvae (Lymantria dispar L., Lymantriidae, Lepidoptera)

Larvae of Lymantria dispar (Lymantriidae, Lepidoptera) were either reared on oak foliage or on an uncontaminated and metal-contaminated wheat germ diet from hatching to the end of experiment. Cd, Pb, Cu and Zn were separately applied, each at two concentrations in the range of no-observed-effect concentrations recently published for this species. Hemolymph was collected from day 3 fourth instar larvae, and total protein content and free amino acid composition were determined along with total body protein content (TBP) of the corresponding larvae. Clear diet-dependent differences were observed: total protein content of the larvae and of the hemolymph was higher in foliage-fed (281.2 micrograms/mg; 13.6 mg/ml) than in diet-fed control individuals (200.5 micrograms/mg; 10.5 mg/ml), whereas the opposite applied to the total free amino acid (TFAA) concentration (64.78 mM, 108.81 mM). Chronic exposure to Cd, Cu and Zn in the diet generally resulted in a decrease of total hemolymph protein but enhanced TFAA concentrations and TBP compared with artificial-diet-fed control group. Sixteen free amino acids were identified and quantitated by high-performance liquid chromatography. Concentrations of single amino acids and/or their relative abundance depended on the diet and the metal applied. For example, the concentration of histidine, the most abundant amino acid (40-53% of total amino acids), was lower in the oak-leaf-fed group (26.04 mM, 40.8% of total amino acids) than in the wheat germ control group (47.89 mM, 44%), but in most metal-contaminated specimens histidine increased significantly (56.58-69.78 mM, 46-53%). The phenylalanine concentration was not diet dependent but was the only amino acid elevated in all contaminated groups.