Acclimation of entomopathogenic nematodes to novel temperatures: trehalose accumulation and the acquisition of thermotolerance.

The effect of thermal acclimation on trehalose accumulation and the acquisition of thermotolerance was studied in three species of entomopathogenic nematodes adapted to either cold or warm temperatures. All three Steinernema species accumulated trehalose when acclimated at either 5 or 35 degrees C, but the amount of trehalose accumulation differed by species and temperature. The trehalose content of the cold adapted Steinernema feltiae increased by 350 and 182%, of intermediate Steinernema carpocapsae by 146 and 122% and of warm adapted Steinernema riobrave by 30 and 87% over the initial level (18.25, 27.24 and 23.97 microg trehalose/mg dry weight, respectively) during acclimation at 5 and 35 degrees C, respectively. Warm and cold acclimation enhanced heat (40 degrees C for 8h) and freezing (-20 degrees C for 4h) tolerance of S. carpocapsae and the enhanced tolerance was positively correlated with the increased trehalose levels. Warm and cold acclimation also enhanced heat but not freezing tolerance of S. feltiae and the enhanced heat tolerance was positively correlated with the increased trehalose levels. In contrast, warm and cold acclimation enhanced the freezing but not heat tolerance of S. riobrave, and increased freezing tolerance of only warm acclimated S. riobrave was positively correlated with the increased trehalose levels. The effect of acclimation on maintenance of original virulence by either heat or freeze stressed nematodes against the wax moth Galleria mellonella larvae was temperature dependent and differed among species. During freezing stress, both cold and warm acclimated S. carpocapsae (84%) and during heat stress, only warm acclimated S. carpocapsae (95%) maintained significantly higher original virulence than the non-acclimated (36 and 47%, respectively) nematodes. Both cold and warm acclimated S. feltiae maintained significantly higher original virulence (69%) than the non-acclimated S. feltiae (0%) during heat but not freezing stress. In contrast, both warm and cold acclimated S. riobrave maintained significantly higher virulence (41%) than the non-acclimated (14%) nematodes during freezing, but not during heat stress. Our data indicate that trehalose accumulation is not only a cold associated phenomenon but is a general response of nematodes to thermal stress. However, the extent of enhanced thermal stress tolerance conferred by the accumulated trehalose differs with nematode species.

Effect of temperature on the activities of glucose-6-phosphate dehydrogenase and hexokinase in entomopathogenic nematodes (Nematoda: Steinernematidae).

The kinetic properties of two metabolic enzymes, glucose-6-phosphate dehydrogenase and hexokinase, were studied in four strains of entomopathogenic nematodes that had been recycled for two years at various temperatures: Steinernema feltiae NF strain, Steinernema feltiae Umeå strain, Steinernema carpocapsae All strain, Steinernema riobravis TX strain. The recycling temperatures influenced the activities of glucose-6-phosphate dehydrogenase and hexokinase in an adaptive fashion in all the strains. At each assay temperature (5-35 degrees C), the maximum specific activity of both the enzymes was greater in the nematodes that had been recycled at lower temperatures than in those reared at higher temperatures. In three enzyme-nematode strain combinations, the lowest K(m) values measured at each assay temperature occurred in nematodes that had been recycled at the lower temperatures. However, the assay temperatures at which the minimum K(m) values occurred were > or = 15 degrees C. The capacities of these nematodes to adjust to different recycling temperatures is discussed in relation to the physiological mechanisms involved.

Use of cellulose acetate electrophoresis in the taxonomy of steinernematids (rhabditida, nematoda).

A steinernematid nematode was isolated from soil samples collected near St. John's, Newfoundland, Canada. On the basis of its morphometry and RFLPs in ribosomal DNA spacer, it was designated as a new strain, NF, of Steinernema feltiae. Cellulose acetate electrophoresis was used to separate isozymes of eight enzymes in infective juveniles of S. feltiae NF as well as four other isolates: S. feltiae Umeå strain, S. feltiae L1C strain, Steinernema carpocapsae All strain, and Steinernema riobravis TX strain. Based on comparisons of the relative electrophoretic mobilities (mu) of the isozymes, one of the eight enzymes (arginine kinase) yielded zymograms that were distinctive for each of the isolates, except for the Umeå and NF strains of S. feltiae, which had identical banding patterns. Four enzymes (fumarate hydratase, phosphoglucoisomerase, phosphoglucomutase, and 6-phosphogluconate dehydrogenase) yielded isozyme banding patterns that were characteristic for all isolates, except for the L1C and NF strains of S. feltiae, which were identical. Two enzymes (aspartate amino transferase and glycerol-3-phosphate dehydrogenase) yielded zymograms that permitted S. carpocapsae All strain to be discriminated from the other four isolates, while the remaining enzyme (mannose-6-phosphate isomerase) was discriminatory for S. riobravis TX strain. Except for one enzyme, the isozyme banding pattern of the NF isolate of S. feltiae was the same as in the L1C strain, isolated 13 years previously from Newfoundland. Cellulose acetate electrophoresis could prove invaluable for taxonomic identification of isolates of steinernematids, provided that a combination of enzymes is used.

Distribution of catecholamine(s) in the nervous system of a mermithid nematode, Romanomermis culicivorax.

The nervous system of the mermithid nematode Romanomermis culicivorax was investigated at different developmental stages for the distribution of catecholamine(s). The catecholaminergic nervous system increased in complexity during development. In the adult nematode, catecholamine(s) occurred in the nerve ring and associated ganglia, cephalic nerves, ventral and dorsal nerve cords and mid-body region ganglia. The distribution of catecholaminergic ganglia in the tail region was different for each sex. The tail region of males contained 16-20 catecholaminergic ganglia, whereas the tail of females contained only 2 ganglia. The catecholamine widely distributed throughout the nervous system of R. culicivorax is not dopamine, since immunoreactivity to dopamine was observed only in the amphids. The results suggest that the catecholamine(s) is widely distributed within the nervous system of R. culicivorax and might function as a neurohormone or neurotransmitter in controlling physiological and developmental processes.

Distribution of FMRF-amide-like peptide in the nervous system of a mermithid nematode, Romanomermis culicivorax.

The nervous system of the mermithid nematode Romanomermis culicivorax was investigated at different developmental stages for the distribution of the neuropeptide FMRF-amide. An FMRF-amide-like peptide was detected by an indirect immunofluorescence technique. The peptidergic nervous system increased in complexity during development. In adults, FMRF-amide-like peptide was present in the nerve ring, cephalic papillary ganglia, cephalic nerves, amphids, ganglia posterior to the nerve ring, longitudinal nerve cords and several mid-body region ganglia. The distribution of peptidergic ganglia in the tail region was different for each sex. Four clusters of ganglia were present in the tail of females, whereas such ganglia were absent in the tail of males. The results suggest that FMRF-amide-like peptide is widely distributed within the nervous system of R. culicivorax and might function as a neurohormone or neurotransmitter in controlling physiological and developmental processes.

Role of Catecholamines in the Reproduction of Romanomermis culicivorax.

The relative concentrations of catecholamine in the nervous system of the entomophilic nematode Romanomermis culicivorax were measured under different experimental conditions by a glyoxylic acid-induced fluorescence procedure. A greater concentration of catecholamine was recorded in the nervous system of adult males and females than in postparasitic juveniles. A higher concentration of catecholamine occurred in adults maintained in physical contact with the opposite sex than in those maintained in isolation. Adult males maintained with females in the same aqueous medium but physically separated by a barrier displayed a greater concentration of catecholamine in their nervous systems than did males maintained in isolation, but the catecholamine fluorescence intensity of such males was less than in males allowed physical contact with females. In adult males, the fluorescence intensity of catecholamine declined progressively during and after copulation. In adult females, the intensity of catecholamine remained constant before, during, and after copulation. Catecholamine(s) may play a role in regulating copulatory behavior, egg production, or oviposition.

Caudal Papillae in Romanomermis culicivorax.

Distribution of caudal papillae in adult Romanomermis culicivorax was determined by scanning electron microscopy. Ninety eight caudal papillae, each containing one pore, were present in males but absent in females. Papillae were arranged in three longitudinal rows, one ventral, two ventrolateral; the middle ventral row bifurcated anterior to the spicule. The appearance of the papillae was different anterior and posterior to the spicule. The role of the caudal papillae in mediating copulatory behavior was discussed.