Guy Bonnot

The effect of cold acclimation and deacclimation on cold tolerance, trehalose and free amino acid levels in Sitophilus granarius and Cryptolestes ferrugineus (Coleoptera)

Canadian and French laboratory strains of Sitophilus granarius (L.) and Cryptolestes ferrugineus (Stephens) were cold acclimated by placing adults at 15, 10 and 5 degrees C successively for 2wk at each temperature before deacclimating them for 1wk at 30 degrees C. Unacclimated S. granarius had an LT(50) (lethal time for 50% of the population) of 12days at 0 degrees C compared with 40days after the full cold acclimation. At -10 degrees C, unacclimated C. ferrugineus had an LT(50) of 1.4days compared with 24days after the full acclimation. Cold acclimation was lost within a week after returning insects to 30 degrees C. Trehalose, as well as the amino acids proline, asparagine, glutamic acid and lysine were higher in cold acclimated insects for both species. For S. granarius, glutamine was higher in cold acclimated insects and isoleucine, ethanolamine and phosphoethanolamine, a precursor of phospholipids, were lower in cold acclimated insects. For C. ferrugineus, alanine, aspartic acid, threonine, valine, isoleucine, leucine, phenylalanine and phosphoethanolamine were higher in cold acclimated insects. For both species tyrosine was lower in cold acclimated insects. There were small but significant differences between Canadian and French strains of S. granarius, with the Canadian strain being more cold hardy and having higher levels of trehalose. There were small but significant differences between male and female S. granarius, with males being more cold hardy and having higher levels of proline, asparagine and glutamic acid. In conclusion, high levels of trehalose and proline were correlated with cold tolerance, as seen in several other insects. However, correlation does not prove that these compounds are responsible for cold tolerance, and we outline further tests that could demonstrate a causal relationship between trehalose and proline and cold tolerance.

EFFECT OF DIET ON THE FREE AMINO ACID POOLS OF SYMBIOTIC AND APOSYMBIOTIC PEA APHIDS, ACYRTHOSIPHON PISUM

Abstract Free amino acid pools were analysed in Acyrthosiphon pisum reared on Vicia faba L. and on three artificial diets with different amino acid profiles: diets A and B copying the very unbalanced profiles of phloem saps of alfalfa and broad bean respectively, diet C deriving from aphid carcass analysis. Total free amino acid levels ranged from 46.9 ± 2.3 nmol·mg−1 fresh weight for aphids maintained on host plant to 86.0 ± 3.6 nmol·mg−1 for those reared on diet B. Whatever the food source was, the free amino acid pools of aphids displayed roughly similar patterns, except for lysine and arginine. The role played by the intracellular symbionts in this homeostasis was investigated with aposymbiotic aphids reared on the same diets. The treated aphids had significantly higher free amino acid content (119.2 ± 1.7 to 140.0 ± 7.7 nmol·mg−1 fresh weight) than control aphids. In contrast to the symbiotic situation, the well balanced free amino acid pools were not maintained in aposymbiotic aphids: four amino acids were found in higher concentrations in aposymbiotic aphids (asparagine, aspartic acid, glutamine and proline), while isoleucine, leucine, tyrosine, phenylalanine, threonine and glutamic acid were in lower concentrations. These results are consistent with the hypothesis that symbiotic bacteria contribute to the nutrition of aphids by the synthesis of essential amino acids. The observed negative correlation of free amino acid levels with aphid performances suggested a possible use of this parameter as an indirect criteria to measure the quality of a natural food for aphid development, and to test the nutritional fitness of an aphid population to its host plant.

Physiological considerations of importance to the success of in vitro culture: An overview

Abstract The implications of the main physiological host-parasitoid relationships on artificial diet rearing are considered. Based on their own experience and some literature, the authors have emphasized some points such as larval growth and development with hormonal implications, osmotic pressure, respiration, nutrition and toxicity. Many parameters control each physiological function and its was shown that all the parameters act simultaneously. To take into account the multiple interactions, use of multifactorial analysis and design is proposed.