Parasitoids in low-level populations ofLymantria dispar [Lep.: Lymantriidae] in different forest physiographic zones

A 2-year study was conducted on the distribution of parasitoids of gypsy moth,Lymantria dispar (L.) (Lep.: Lymantriidae), in mesic and adjacent higher elevation transition and xeric forest habitats in Vermont (U.S.A.). In both years, overall parasitism ranged from 12–18% in each habitat. When analyzed according to the life stage at which the host was collected, parasitism rates of greater than 40% were obtained among the late instars.Parasetigena silvestris (Robineau-Desvoidy) andPhobocampe disparis (Viereck) were recovered most commonly from the mesic habitat, andCotesia melanoscelus (Ratzeburg) andBlepharipa pratensis (= Sturmia scutellata) (Meigen) were most common in collections from the xeric area. Parasitism byCompsilura concinnata (Meigen) occurred at similar levels in all three habitats, and this species was responsible for the highest parasitism rates on the site, reaching 40% among the late instars in 1985. Percent parasitism byC. concinnata increased three-four-fold from 1984 to 1985, while parasitism by other species declined.     

Chirality differences in amino acid retention and release from the acid-extractable pool of cultured mammalian cells

In previous work, no chiral differences were found between D and L enantiomers of Leu in their ability to displace one another from the acid-extractable pool in mammalian cells. Recent evidence suggested otherwise. Our aim is to examine whether, in physiological range, D-amino acids have an equivalent ability to displace L-amino acids from the acid-extractable pool of HeLa cells, and vice versa. In the millimolar range, D-Leu and L-Leu have similar uptake and displacement properties with regard to the acid-extractable pool in HeLa cells, despite only the latter isomer being incorporated into protein. Below millimolar concentrations however, a distinct difference was found in the displacement of tritium-labelled L-Leu from the pool by unlabelled D-Leu compared with unlabelled L-Leu. Thus, unlabelled L-Leu in the external medium at 10⁻⁴ or 10⁻⁵ M displaced an equivalent amount of label from the pool as D-Leu introduced at a concentration approx. one order of magnitude higher, respectively. Reciprocal experiments, in which the acid-extractable pool was preloaded with ³H-D-Leu, confirmed this finding. The chirality difference was noted whether pool prelabelling was carried out at 37 or 0°C; but in order to avoid the complications of active transport mechanisms, the competition work reported here was done at 0°C. Similar chirality differences were observed with other hydrophobic amino acids, including His, Ile and Phe, such as, preferential displacement by the L-Leu racemer compared with the D-Leu racemer below mM levels. This was also true for the D and L forms of the non-utilisable isomer of Leu, norleucine (nLeu). We conclude that D-forms of hydrophobic amino acids have lower affinity for similar or the same intracellular binding sites involved in the acid-extractable pool than their L-forms. The significance of these chirality findings to amino acid pools in cells, and to the predominance of L-forms of amino acids in the biosphere is considered.     

High Levels of Ascorbic Acid, Not Glutathione, in the CNS of Anoxia-Tolerant Reptiles Contrasted with Levels in Anoxia-Intolerant Species

Abstract: Ascorbic acid and glutathione (GSH) are antioxidants and free radical scavengers that provide the first line of defense against oxidative damage in the CNS. Using HPLC with electrochemical detection, we determined tissue contents of these antioxidants in brain and spinal cord in species with varying abilities to tolerate anoxia, including anoxia-tolerant pond and box turtles, moderately tolerant garter snakes, anoxia-intolerant clawed frogs (Xenopus laevis), and intolerant Long-Evans hooded rats. These data were compared with ascorbate and GSH levels in selected regions of guinea pig CNS, human cortex, and values from the literature. Ascorbate levels in turtles were typically 100% higher than those in rat. Cortex, olfactory bulb, and dorsal ventricular ridge had the highest content in turtle, 5–6 µmol g^?1 of tissue wet weight, which was twice that in rat cortex (2.82 ± 0.05 µmol g^?1) and threefold greater than in guinea pig cortex (1.71 ± 0.03 µmol g^?1). Regionally distinct levels (2–4 µmol g^?1) were found in turtle cerebellum, optic lobe, brainstem, and spinal cord, with a decreasing anterior-to-posterior gradient. Ascorbate was lowest in white matter (optic nerve) in each species. Snake cortex and brainstem had significantly higher ascorbate levels than in rat or guinea pig, although other regions had comparable or lower levels. Frog ascorbate was generally in an intermediate range between that in rat and guinea pig. In contrast to ascorbate, GSH levels in anoxia-tolerant turtles, 2–3 µmol g^?1 of tissue wet weight, were similar to those in mammalian or amphibian brain, with no consistent pattern associated with anoxia tolerance. GSH levels in pond turtle CNS were significantly higher (by 10–20%) than in rat for several regions but were generally lower than in guinea pig or frog. GSH in box turtle and snake CNS were the same or lower than in rat or guinea pig. The distribution GSH in the CNS also had a decreasing anterior-to-posterior gradient but with less variability than ascorbate; levels were similar in optic nerve, brainstem, and spinal cord. The paradoxically high levels of ascorbate in turtle brain, which has a lower rate of oxidative metabolism than mammalian, suggest that ascorbate is an essential cerebral antioxidant. High levels may have evolved to protect cells from oxidative damage when aerobic metabolism resumes after a hypoxic dive.