Changes in free amino acids in Alphitobius diaperinus (Coleoptera: Tenebrionidae) during thermal and food stress

Temporal changes in free amino acid pools are examined in starved and cold-exposed (10 degrees C) beetles (Alphitobius diaperinus) (control beetles; 4, 7, 14, 28 and 56 days of cold-exposure). The range of individual responses and the effect of gender on survival and free amino acid levels are evaluated. Females survived significantly longer (Lt50 and Lt90) than males under stressing conditions. Pro, Gln, Ala, Arg and Thr are the major components of the free amino acid pool in the whole body of adult beetles. Multivariate analysis indicates that the duration of exposure explains most of the observed variation in amino acid levels, while sex effect is not significant. Moreover, amino acid levels fluctuate strongly within each sampled date, revealing a high inter-individual heterogeneity. However, this heterogeneity decreases after four weeks of cold-exposure and starvation. The increase in Ala level and the concomitant decrease of Pro after four weeks suggest that Pro might be an important fuel for metabolism when fat reserves are reduced. We conclude that changes in free amino acid pools are due to a combination of reduced individual heterogeneity, cold-acclimation and amino acid degradation for energetic purposes.