Development of the lateral palatal brush in larvae of Aedes aegypti (L.) (Diptera: Culicidae)

Abstract

Light and electron microscopy were used to observe development of the lateral palatal brush in Aedes aegypti (L.) larvae. Development was sampled at 4-h intervals from second- to third-instar ecdyses. Immediately after second-instar ecdysis, the epidermis apolyses from newly deposited cuticle in the lateral palatal pennicular area to form an extensive extracellular cavity into which the fourth-instar lateral palatal brush filaments grow as cytoplasmic extensions. On reaching their final length, the filaments deposit cuticulin, inner epicuticle, and procuticle sequentially on their outer surfaces. The lateral palatal crossbars, on which the lateral palatal brush filaments insert, form after filament development is complete. At the beginning of development, the organelles involved in plasma membrane and cuticle production are located at the base and middle of the cells. As the filament rudiments grow, most rough endoplasmic reticulum, mitochondria, and Golgi apparatus move to the apex of the epidermal cells and into the filament rudiments. After formation of the lateral palatal brush filaments and lateral palatal crossbars, extensive organelle breakdown occurs. Lateral palatal brush formation is unusual in that no digestion and resorption of old endocuticle occurs prior to deposition of new cuticle. No mucopolysaccharide secretion by the lateral palatal brush epidermis was observed, nor were muscle fibres observed to attach to the lateral palatal crossbars, as has been suggested by other workers.