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. 2017 Feb 13;10:79. doi: 10.1186/s13071-017-2005-z

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© The Author(s). 2017

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 2 — Hormonal control of yolk formation. There are three invertebrate hormones that play major roles in yolk formation. Young females have a high level of juvenile hormone (JH), which is produced by corpora allata located in the arthropod brain and acts on fat body and ovaries (1). Upon a blood meal, the JH level drops in haemolymph, and egg development neurosecretory hormone (EDNH) (2) level increases to stimulate the release of ecdysone (Ec) (3) by ovaries that is converted in 20-hydroxyecdysona (20-HE) in the fat body. Together with 20-HE, the nutrients consumed during the blood meal stimulate the expression and secretion, by fat body cells, of yolk precursor proteins (YPP) (4) that are essential in vitellogenesis