Abstract. Morphological and electrophoretic variation is evaluated in 272 female and 424 male specimens of Aphidius reared from known hosts representing seventeen aphid-host species. Much of this material was reared under experimental conditions in order to examine the effects of environmental conditions such as temperature and different host species, and to induce as much variation as is possible in known single populations. Multivariate analysis and electrophoresis are used to demonstrate the degree to which entities defined by morphological characters and electrophoretic bands correspond to collection from a common host.
Many characters commonly used in the identification of this group, e.g. sculpturing on the propodeum, are shown to be very variable. Despite this, several morphologically and electrophoretically definable groups of Aphidius are demonstrated, many of them corresponding to individual aphid-hosts, while others, especially those parasitizing pea and cereal aphids were found to occur on more than one host. The possible nominal species associated with each defined group are discussed and morphological keys given to these complexes, and to the species of of Aphidius known to parasitize pea and cereal aphids.