Noxious components of venom from the pupa-specific parasitoid pimpla hypochondriaca
Venom from the endoparasitoid wasp Pimpla hypochondriaca induced a lethal paralysis when injected into the hemocoel of larval, pupal, and adult stages of the tomato moth Lacanobia oleracea and was also toxic to the adult stages of the housefly Musca domestica and the cockroach Blatella germanica. Heating the venom to 58 degreesC did not reduce its potency against M. domestica. Phenoloxidase activity was detected in diluted venom using dihydroxyphenylalanine as the substrate and occurred independently of activators. Enzyme activity was strongly inhibited by 2.0 &mgr;M phenylthiocarbamide (PTC), a known inhibitor of phenoloxidase, and was not detectable in venom that had been heated to 58 degreesC for 10 min. Venom treated to remove phenoloxidase was shown to inhibit phenoloxidase activity in untreated venom, with a potency likely to be sufficient to prevent enzyme activity in the parasitoid's venom sac. The venom was found to be cytotoxic to an insect cell line (SF21) from Spodoptera frugiperda, and this activity was not reduced when the cells were cultured in the presence of 20 &mgr;M PTC. Venom constituents were separated according to size using high-resolution gel filtration. Three venom components: phenoloxidase, a factor which caused paralysis of M. domestica, and a factor which was cytotoxic to SF 21 cells were detected and found to have maximum activity in fractions 19, 40-42, and 50-51, respectively. Phenoloxidase and the factor causing paralysis of M. domestica had estimated apparent molecular masses of 390 and 27 kDa, respectively, while the cytotoxic factor had an apparent molecular mass of less than 13 kDa. Assay for inhibitors of venom phenoloxidase identified two major inhibitory components having highest activity in fractions 48 and 60, respectively. The larger of these two factors had an estimated apparent molecular mass of 12 kDa, but the other factor was considerably smaller than the lowest molecular mass standard (13.7 kDa) used to calibrate the column. Copyright 1999 Academic Press.
Parkinson
NM
Central Science Laboratory, Sand Hutton, York, YO41 1LZ, United Kingdom.
Weaver
RJ