Micro analysis of the egg shell of Adela metallica (Poda) (Lepidoptera : Adelidae) by energy-filtering transmission electron microscopy (EFTEM)

The egg shell of the incurvarioid moth Adela metallica (Lepidoptera : Adelidae) was studied by conventional (cTEM) and energy-filtering transmission electron microscopy (EFTEM). The shell of the laid egg consists of 3 envelopes. The vitelline envelope is 0.1–0.2μm thick and homogeneous, thus exhibiting the non-exoporian character state. The single-layered chorion, which is covered by a fibrogranular mucous layer, is 0.5–0.9μm thick and homogeneous, thus exhibiting the non-ditrysian character state. The chorion is highly electron-lucent. Neither cTEM nor EFTEM revealed any sub-structural details. However, electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS), revealing the elemental composition of the egg shell, indicate that the chorion and vitelline envelope are proteinaceous and hence, similar to the egg shells of other lepidopteran species. The presence of high sulphur signals associated with the vitelline envelope and the thin basal lamella of the chorion indicates that these components may be stabilized via sulphur-bridges.