Reservoirs forAphidius erviHaliday (Hymenoptera: Aphidiidae), a polyphagous parasitoid of cereal aphids (Hemiptera: Aphididae)

Abstract

AbstractAphidius erviHal. parasitised natural populations ofAcyrthosiphon pisum(Harris),Sitobion avenae(F.) andMicrolophium carnosum(Buckt.) in Britain but parasitised few examples ofS. avenaeplaced on trap plants in winter wheat, nettle-grass edge areas or lucerne-wheat strip crops. In laboratory experiments,Aphidius ervireared fromAcyrthosiphon pisumdid not parasitiseM. carnosum, and significantly fewer mummies were formed onS. avenaethan onA. pisum. After rearingAphidius ervifor 4–5 generations onS. avenae, similar numbers of mummies were formed on both hosts. The switch of hosts fromAcyrthosiphon pisumtoS. avenaewas associated with the loss of certain parasitoid esterase enzyme bands revealed following electrophoretic separation of parasitoid proteins. Slow adaptation to new aphid hosts by polyphagous parasitoids such asAphidius ervimay reduce the usefulness of reservoirs as a source of beneficial species.