THE EGGSHELL OF THE ALMOND WASP EURYTOMA-AMYGDALI (HYMENOPTERA, EURYTOMIDAE) .1. MORPHOGENESIS AND FINE-STRUCTURE OF THE EGGSHELL LAYERS

The almond wasp Eurytoma amygdali (Hymenoptera: Eurytomidae) feeds and oviposits exclusively in almonds and therefore is characterized as an insect of economic importance. Its meroistic polytrophic ovaries incl ude follicles with a tri-partite configuration. The mature follicles e xhibit two filaments occupying the two poles of the egg. One is the mi cropylar filament while the other might serve for respiration since it is likely that its flattened end layers remain outside the almond fru it. The eggshell is formed by aposition and the follicle cells, which surround the follicle until the end of oogenesis, may be responsible f or protein synthesis and secretion which finally lead to the assembly of the eggshell. The eggshell comprises the thin vitelline membrane, p ossibly a 'wax' layer of waterproofing function. a transluscent layer which appears amorphous even al the end of choriogenesis, a granular l ayer, including large and small electron-dense granules, and finally a columnar layer very similar to layers found in other insect species o f the same or different orders. Peroxidase is histochemically found fo r the first time in an eggshell of the Hymenoptera order; the tranlusc ent layer in particular is positively stained (electron-dense). Two po ssible roles of this peroxidatic activity are discussed, first, in com parison to other fruit-infesting insects, we assume that elastic chori on is produced through the function of peroxidase induced bonds (resil in-type bonds): very important for avoiding premature breaking, while being oviposited through a narrow ovipositor. Second, referring to oth er studies, this layer can play a bactericidal role for additional emb ryonic protection.