The life cycle of a sedentary endoparasite, root knot nematode, is depicted: (A) Egg stage. (B) First-stage juvenile within an egg. (C) A second-stage juvenile emerges from the egg. The second-stage juvenile must penetrate the root to feed. (D) Once inside the root, the second stage enlarges. (E) Third-stage male and female. (F) Fourth-stage male and female. (G) Adult stages. The vermiform male does not feed. The saccate female remains sedentary, producing eggs in a gelatinous matrix that usually develops external to the root surface.

Other nematode species have slightly different life cycles. Root lesion nematode, a migratory endoparasite, remains vermiform in the adult stages and either the second, third, fourth, or adult stages may penetrate or vacate a root. Stubby root nematode, ring nematode, needle nematode, pin nematode, and dagger nematode have life cycles similar to the root lesion nematode, except that they feed only at the root surface and do not enter roots.

Illustration from Grape Pest Management, 2nd edition. UC ANR Publication 3343.