Cellular immune response of brown soft scale Coccus hesperidum L. (Hemiptera: Coccidae) to eggs of Metaphycus luteolus Timberlake (Hymenoptera: Encyrtidae)

The parasitic wasp, Metaphycus luteolus Timberlake, is an endoparasitoid of various soft scale insects including brown soft scale, Coccus hesperidum L. Development of this parasitoid in scale hosts is hindered by encapsulation. In the present study, using transmission and scanning electron microscopy, we show that hemocytes are responsible for encapsulation, which is mediated by the direct deposition of cells and melanin on the surface of M. luteolus eggs. By 12 h post-oviposition, scale hemocytes, presumably granulocytes, aggregate, spread and directly lyse on the surface of parasitoid eggs. This process continues for at least 1 day and results in the gradual formation of a capsule. Two to three days post-oviposition, a melanized capsule is well formed and signs of chemical deposition are evident by examination of the outer surface of the capsule. These results demonstrate that soft scale insects are fully capable of melanotic encapsulation of foreign material mediated by hemocytes.