Vitellogenesis is the process of yolk formation via nutrients being deposited in the oocyte

Oocyte

An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in the ovary during female gametogenesis. The female germ cells produce a primordial germ cell which undergoes a mitotic...

, or female germ cell

Germ cell

A germ cell is any biological cell that gives rise to the gametes of an organism that reproduces sexually. In many animals, the germ cells originate near the gut of an embryo and migrate to the developing gonads. There, they undergo cell division of two types, mitosis and meiosis, followed by...

 involved in reproduction. It starts when the fat body stimulates the release of juvenile hormones and produces vitellogenin

Vitellogenin

Vitellogenin is a synonymous term for the gene and the expressed protein. The protein molecule is classified as a glycolipoprotein, having properties of a sugar, fat and protein...

 protein. It occurs in all animal groups lower than the mammals. In cockroaches, for example, vitellogenesis can be stimulated by injection of juvenile hormone

Juvenile hormone

Juvenile hormones are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. JHs regulate development, reproduction, diapause, and polyphenisms....

 into immature females and mature males.

In mosquitoes infected with Plasmodium

Plasmodium

Plasmodium is a genus of parasitic protists. Infection by these organisms is known as malaria. The genus Plasmodium was described in 1885 by Ettore Marchiafava and Angelo Celli. Currently over 200 species of this genus are recognized and new species continue to be described.Of the over 200 known...

, vitellogenesis may be manipulated by the parasites to reduce fecundity (Hurd, 2003).