Changes in esophageal gland activity during the life cycle of Nacobbus aberrans (Nemata : Pratylenchidae)

Electron and light microscopy were used to study the dorsal gland (DG) and the two subventral glands (SvG) of seven developmental phases of Nacobbus a berrans: pre-parasitic second-stage juveniles (J2), parasitic J2, third- (J 3) and fourth- (J4) stages, migratory females, young sedentary females, and mature sedentary females. In each developmental phase the level of esophag eal gland activity was estimated by the abundance of organelles associated with secretory pathways, including endoplasmic reticulum, ribosomes, Golgi, multivesicular bodies, and secretory granules. All esophageal glands were metabolically active in all J2 examined, although only in parasitic J2 were there numerous secretory granules in the esophageal gland extensions and a mpullae. No evidence of secretory activity was observed in the esophageal g lands of the coiled and relatively inactive J3 and J4, nor in migratory fem ales; these stages apparently do not feed. Observations suggest that reserv es stored by J2 sustain three ecdyses and the migratory female's search for a feeding site and induction of a syncytium. Feeding activity is resumed i n young and mature sedentary females, in which the DG is highly active and enlarged. The SvG are metabolic ally active, but with little synthesis of s ecretory granules, suggesting that in sedentary females the SvG may have ph ysiological roles other than digestion.