Some effects of Mermis nigrescens on the hemolymph of Schistocerca gregaria

The sugar, free amino acid, and lipid fatty acid components of the hemolymph of adult Schistocerca gregaria parasitized by the larvae of the entomophilic nematode Mermis nigrescens were examined at intervals during the 4-week infection period. Glucose levels remained low, relative to trehalose, and at no time during the infection was there a significant difference in the glucose concentrations of controls and parasitized locusts. Trehalose was maintained at high levels (75–80 mM) in controls but fell to less than 25 mM between 7 and 10 days after parasitization and continued at a low level until day 17, when it began to rise in the parasitized group. Total free amino acid levels doubled in the parasitized group by day 21. By day 7 the concentration of methionine doubled, by day 14 both methionine and ornithine were at high levels, and by day 21, 13 of the 21 ninhydrin-positive substances were different from controls. There was no significant difference in the relative lipid fatty acid composition at day 14 between parasitized and control locusts.It is suggested that the nematode modifies its host's metabolism to favour production of small molecules such as glucose and amino acids from carbohydrate and protein reserves and it is also suggested that the host cell's ability to sequester nutrients is impaired during parasitism.