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Key Event Title
Increase, Premature molting
Key Event Components
|ecdysis, chitin-based cuticle||decreased|
Key Event Overview
AOPs Including This Key Event
|AOP Name||Role of event in AOP||Point of Contact||Author Status||OECD Status|
|SAM depletion leading to population decline (2)||KeyEvent||You Song (send email)||Under development: Not open for comment. Do not cite|
|SAM depletion leading to population decline (1)||KeyEvent||You Song (send email)||Under development: Not open for comment. Do not cite|
|Chitinase inhibition leading to mortality||KeyEvent||Simon Schmid (send email)||Under development: Not open for comment. Do not cite|
|Chitobiase inhibition leading to mortality||KeyEvent||Simon Schmid (send email)||Under development: Not open for comment. Do not cite|
|CHS-1 inhibition leading to mortality||KeyEvent||Simon Schmid (send email)||Open for comment. Do not cite|
|SUR binding leading to mortality||KeyEvent||Simon Schmid (send email)||Under development: Not open for comment. Do not cite|
Key Event Description
This key event is measured on the level of the individual. In order to grow and develop, arthropods need to shed their exoskeleton periodically (Heming 2018). If they are not able to molt properly, the organism will eventually die. Premature molting summarizes a variety of effects related to molting disruption. It describes the unsuccessful molting where the organism is not able to shed the old cuticle, but also other effects related to molting in an immature stage where the new cuticle is not mature enough for the molt, such as rupture of the new cuticle and associated desiccation, deformities, higher susceptibility to pathogens or impaired locomotion.
How It Is Measured or Detected
Premature molting can be determined by observation. For example, during an OECD 202 Daphnia sp. Acute immobilization test (OECD 2004), the cumulative number of molts can be assessed as an additional endpoint. One could even prolong the test to 96h to get a clearer result of this endpoint. Additionally, one could apply histopathological methods to monitor the maturity of the newly synthesized cuticle (e.g. thickness of procuticle).
Domain of Applicability
Taxonomic: Effect data for the occurrence of this KE exist from Pieris brassicae and Lucilia cuprina, defining its taxonomic applicability. However, all arthropods undergo molting, so it is highly likely that this KE is applicable to the whole phylum of arthropods.
Life stage: This KE is applicable for organisms that undergo molting in order to grow and develop, namely larval stages of insects and all life stages of crustaceans and arachnids.
Sex: This KE is applicable to all sexes.
Chemical: Substances known to induce premature molting are of the family of pyrimidine nucleosides (e.g. polyoxin D and nikkomycin Z) (Gijswijt et al. 1979; Tellam et al. 2000; Arakawa et al. 2008).
Evidence for Perturbation by Stressor
Arakawa T, Yukuhiro F, Noda H. 2008. Insecticidal effect of a fungicide containing polyoxin B on the larvae of Bombyx mori (Lepidoptera: Bombycidae), Mamestra brassicae, Mythimna separata, and Spodoptera litura (Lepidoptera: Noctuidae). Appl Entomol Zool. 43(2):173–181. doi:10.1303/aez.2008.173.
Gijswijt MJ, Deul DH, de Jong BJ. 1979. Inhibition of chitin synthesis by benzoyl-phenylurea insecticides, III. Similarity in action in Pieris brassicae (L.) with Polyoxin D. Pestic Biochem Physiol. 12(1):87–94. doi:10.1016/0048-3575(79)90098-1.
Heming BS. 2018. Insect development and evolution. Ithaca: Cornell University Press.
OECD. 2004. Test No. 202: Daphnia sp. Acute Immobilisation Test. OECD Guidel Test og Chem Sect 2.(April):1–12. doi:10.1787/9789264069947-en. [accessed 2020 Jun 5]. https://www.oecd-ilibrary.org/environment/test-no-202-daphnia-sp-acute-immobilisation-test_9789264069947-en.
Tellam RL, Vuocolo T, Johnson SE, Jarmey J, Pearson RD. 2000. Insect chitin synthase. cDNA sequence, gene organization and expression. Eur J Biochem. 267(19):6025–6043. doi:10.1046/j.1432-1327.2000.01679.x.