Ultrastructure of the Head Region of Molting Second-Stage Juveniles of Heterodera glycines with Emphasis on Stylet Formation.

The morphology and alterations of infective juvenile (J2) body components with emphasis on the body wall, stomatal wall, stylet, and sensilla of Heterodera glycines were observed. During the molt of J2 to J3, the J2 hypodermis separates from the J2 cuticle and forms an extracellular space, continuous with an invagination of the anterior, center of the J3. The space between the J2 cuticle and the enlarged J3 hypodermal cells is filled with electron-dense material resembling a fluid observed in insects during molt. Regeneration of the J2 during molt was traced in a series of ultrathin sections. The site of stylet regeneration is in the hypodermal and myoepithelial tissues of the invaginated anterior, center of the J3. Four arcade-like cells are related to specific components of the stomatal wall, the stylet cone, and the stylet shaft of the J3. The first and second arcade-like cells are primarily related to stomatal wall development, whereas the third and fourth arcade-like cells are related to stylet cone and shaft development. Spherical, electron-translucent vacuoles that occur in myoepithelial cells just posterior to the arcade-like cells appear to be progenitors of the stylet knobs. Early stages of protractor muscle attachment to the vacuolar membrane were observed.