Aetiology of melanized inclusions in the body cavity of Neodiprion sertifer (Geoffroy) (Hym., Diprionidae) adults

The aetiology of large melanized inclusions occurring in the haemocoel of a dults of some diprionid sawflies is not fully understood. Their occurrence has been associated with nuclear polyhedrosis virus (NPV), but also with ex treme temperatures, parasitism, and prolonged diapause. High frequencies of inclusions are found most often during NPV epizootics. In laboratory exper iments with Neodiprion sertifer larvae, ingestion of large doses of a commo n bacterium, Enterobacter cloacae, was shown to induce inclusions indisting uishable from those associated with NPV infection. It is argued that a bact erial aetiology is not contradicted by the other conditions reported to be associated with inclusions. The bacterial aetiology provides an explanation for the low frequencies of inclusions in N. sertifer populations with no N PV infection. It is proposed that the ability to form inclusions may have e volved as a defence against bacterial infection.