Aop: 4


A descriptive phrase which references both the Molecular Initiating Event and Adverse Outcome.It should take the form “MIE leading to AO”. For example, “Aromatase inhibition leading to reproductive dysfunction” where Aromatase inhibition is the MIE and reproductive dysfunction the AO. In cases where the MIE is unknown or undefined, the earliest known KE in the chain (i.e., furthest upstream) should be used in lieu of the MIE and it should be made clear that the stated event is a KE and not the MIE. More help

Ecdysone receptor agonism leading to incomplete ecdysis associated mortality

Short name
A name that succinctly summarises the information from the title. This name should not exceed 90 characters. More help
EcR agonism leading to incomplete ecdysis associated mortality

Graphical Representation

A graphical representation of the AOP.This graphic should list all KEs in sequence, including the MIE (if known) and AO, and the pair-wise relationships (links or KERs) between those KEs. More help
Click to download graphical representation template Explore AOP in a Third Party Tool


The names and affiliations of the individual(s)/organisation(s) that created/developed the AOP. More help

You Song1 and Knut Erik Tollefsen1,2 1 Norwegian Institute for Water Research (NIVA), Section of Ecotoxicology and Risk Assessment, Gaustadalléen 21, N-0349 Oslo, Norway 2 Norwegian University of Life Sciences (NMBU), Faculty of Environmental Science and Technology, Department of Environmental Sciences (IMV). P.O. Box 5003, N-1432 Ås, Norway


Point of Contact

The user responsible for managing the AOP entry in the AOP-KB and controlling write access to the page by defining the contributors as described in the next section.   More help
Knut Erik Tollefsen   (email point of contact)


Users with write access to the AOP page.  Entries in this field are controlled by the Point of Contact. More help
  • Knut Erik Tollefsen
  • You Song


Provides users with information concerning how actively the AOP page is being developed, what type of use or input the authors feel comfortable with given the current level of development, and whether it is part of the OECD AOP Development Workplan and has been reviewed and/or endorsed. OECD Status - Tracks the level of review/endorsement the AOP has been subjected to. OECD Project Number - Project number is designated and updated by the OECD. SAAOP Status - Status managed and updated by SAAOP curators. More help
Author status OECD status OECD project SAAOP status
Open for citation & comment Under Development
This AOP was last modified on June 04, 2021 10:07

Revision dates for related pages

Page Revision Date/Time
Increase, Ecdysone receptor agonism May 24, 2018 16:30
Decrease, Circulating ecdysis triggering hormone May 24, 2018 16:34
Increase, Incomplete ecdysis May 24, 2018 16:41
Decrease, Abdominal muscle contraction May 24, 2018 16:41
Increase, Nuclear receptor E75b gene expression May 24, 2018 16:32
Increase, Fushi tarazu factor-1 gene expression May 24, 2018 16:33
Decrease, Circulating crustacean cardioactive peptide May 24, 2018 16:37
Decrease, Ecdysis motoneuron bursts May 24, 2018 16:38
Decrease, Excitatory postsynaptic potential May 24, 2018 16:39
Increase, Mortality October 26, 2020 05:18
Increase, EcR agonism leads to Increase, E75b expression February 09, 2017 03:33
Increase, E75b expression leads to Increase, Ftz-f1 expression February 09, 2017 03:33
Increase, Ftz-f1 expression leads to Decrease, Circulating ETH February 09, 2017 03:34
Decrease, Circulating ETH leads to Decrease, Circulating CCAP February 09, 2017 03:34
Decrease, Circulating CCAP leads to Decrease, Ecdysis motoneuron bursts February 09, 2017 03:35
Decrease, Ecdysis motoneuron bursts leads to Decrease, Excitatory postsynaptic potential February 09, 2017 03:35
Decrease, Excitatory postsynaptic potential leads to Decrease, Abdominal muscle contraction February 09, 2017 03:36
Decrease, Abdominal muscle contraction leads to Increase, Incomplete ecdysis December 03, 2016 16:38
Increase, Incomplete ecdysis leads to Increase, Mortality December 03, 2016 16:38
Tebufenozide February 09, 2017 03:06
20-hydroxyecdysone February 09, 2017 03:06
Ponasterone A February 09, 2017 03:06
Methoxyfenozide February 09, 2017 03:42
Halofenozide February 06, 2017 12:28
Chromafenozide February 09, 2017 03:41
Cyasterone February 09, 2017 03:42
Makisterone A February 09, 2017 03:43
Inokosterone February 09, 2017 03:43
Ecdysone February 09, 2017 03:43
RH-5849 February 09, 2017 03:43


A concise and informative summation of the AOP under development that can stand-alone from the AOP page. The aim is to capture the highlights of the AOP and its potential scientific and regulatory relevance. More help

Molting is a natural biological process in arthropods. During a molt cycle, the animals generate new exoskeletons by the epidermis and shed the old ones in order to grow. Successful molting is key to survival, development and reproduction. Over half a century research on arthropod endocrinology reveals that molting is precisely controlled by complex multi-hormone systems, with 20-hydroxyecdysone (20E) being the key effective hormone to mediate different biological processes that are necessary for molting. The hormonal actions of 20E are exerted through binding and modulation of the ecdysone receptors (EcR), which are nuclear transcriptional factors that regulate a wide range of physiological and behavioral changes. Based on this knowledge, endocrine disrupting chemicals (EDCs) targeting at the EcRs are developed as pesticides and anti-parasite pharmaceuticals in order to disrupt the molting cycles of “harmful” arthropods and protect the agriculture and aquaculture. However, environmental residues of these EDCs may also affect non-target species, such as a number of crustaceans (e.g. crabs and lobsters) with great ecological and economical values, due to highly conserved endocrine systems in arthropods. Substantial efforts are therefore needed to assess the environmental hazards and risks of EDCs on non-target species. Due to the high number (over a million described) of species in the phylum of Arthopoda, it is not feasible to perform toxicity testing for each species as well as EDC. Construction of universal models on basis of systems (eco)toxicology and phylogenetic similarities for understanding the environmental endocrine disruption (ED) effects may serve as a potential solution. The current AOP is therefore developed based on available information in the databases to identify knowledge gaps in this research field. The conceptual AOP will be further expanded using a combination of laboratory studies and advance in sillico predictions of potential EcR ligands and taxonomic appllicablity to inform environmental risk assessment as an ultimate goal.

AOP Development Strategy


Used to provide background information for AOP reviewers and users that is considered helpful in understanding the biology underlying the AOP and the motivation for its development.The background should NOT provide an overview of the AOP, its KEs or KERs, which are captured in more detail below. More help


Provides a description of the approaches to the identification, screening and quality assessment of the data relevant to identification of the key events and key event relationships included in the AOP or AOP network.This information is important as a basis to support the objective/envisaged application of the AOP by the regulatory community and to facilitate the reuse of its components.  Suggested content includes a rationale for and description of the scope and focus of the data search and identification strategy/ies including the nature of preliminary scoping and/or expert input, the overall literature screening strategy and more focused literature surveys to identify additional information (including e.g., key search terms, databases and time period searched, any tools used). More help

Summary of the AOP

This section is for information that describes the overall AOP. The information described in section 1 is entered on the upper portion of an AOP page within the AOP-Wiki. This is where some background information may be provided, the structure of the AOP is described, and the KEs and KERs are listed. More help


Molecular Initiating Events (MIE)
An MIE is a specialised KE that represents the beginning (point of interaction between a prototypical stressor and the biological system) of an AOP. More help
Key Events (KE)
A measurable event within a specific biological level of organisation. More help
Adverse Outcomes (AO)
An AO is a specialized KE that represents the end (an adverse outcome of regulatory significance) of an AOP. More help
Type Event ID Title Short name
MIE 103 Increase, Ecdysone receptor agonism Increase, EcR agonism
KE 1264 Increase, Nuclear receptor E75b gene expression Increase, E75b expression
KE 1265 Increase, Fushi tarazu factor-1 gene expression Increase, Ftz-f1 expression
KE 988 Decrease, Circulating ecdysis triggering hormone Decrease, Circulating ETH
KE 1266 Decrease, Circulating crustacean cardioactive peptide Decrease, Circulating CCAP
KE 1267 Decrease, Ecdysis motoneuron bursts Decrease, Ecdysis motoneuron bursts
KE 1268 Decrease, Excitatory postsynaptic potential Decrease, Excitatory postsynaptic potential
KE 993 Decrease, Abdominal muscle contraction Decrease, Abdominal muscle contraction
KE 990 Increase, Incomplete ecdysis Increase, Incomplete ecdysis
KE 350 Increase, Mortality Increase, Mortality

Relationships Between Two Key Events (Including MIEs and AOs)

This table summarizes all of the KERs of the AOP and is populated in the AOP-Wiki as KERs are added to the AOP.Each table entry acts as a link to the individual KER description page. More help

Network View

This network graphic is automatically generated based on the information provided in the MIE(s), KEs, AO(s), KERs and Weight of Evidence (WoE) summary tables. The width of the edges representing the KERs is determined by its WoE confidence level, with thicker lines representing higher degrees of confidence. This network view also shows which KEs are shared with other AOPs. More help

Prototypical Stressors

A structured data field that can be used to identify one or more “prototypical” stressors that act through this AOP. Prototypical stressors are stressors for which responses at multiple key events have been well documented. More help

Life Stage Applicability

The life stage for which the AOP is known to be applicable. More help
Life stage Evidence
Juvenile High
Adult High

Taxonomic Applicability

Latin or common names of a species or broader taxonomic grouping (e.g., class, order, family) can be selected.In many cases, individual species identified in these structured fields will be those for which the strongest evidence used in constructing the AOP was available. More help
Term Scientific Term Evidence Link
insects insects High NCBI
crustaceans Daphnia magna Moderate NCBI

Sex Applicability

The sex for which the AOP is known to be applicable. More help
Sex Evidence
Unspecific Moderate

Overall Assessment of the AOP

Addressess the relevant biological domain of applicability (i.e., in terms of taxa, sex, life stage, etc.) and Weight of Evidence (WoE) for the overall AOP as a basis to consider appropriate regulatory application (e.g., priority setting, testing strategies or risk assessment). More help

Domain of Applicability

Addressess the relevant biological domain(s) of applicability in terms of sex, life-stage, taxa, and other aspects of biological context. More help

Essentiality of the Key Events

The essentiality of KEs can only be assessed relative to the impact of manipulation of a given KE (e.g., experimentally blocking or exacerbating the event) on the downstream sequence of KEs defined for the AOP. Consequently, evidence supporting essentiality is assembled on the AOP page, rather than on the independent KE pages that are meant to stand-alone as modular units without reference to other KEs in the sequence. The nature of experimental evidence that is relevant to assessing essentiality relates to the impact on downstream KEs and the AO if upstream KEs are prevented or modified. This includes: Direct evidence: directly measured experimental support that blocking or preventing a KE prevents or impacts downstream KEs in the pathway in the expected fashion. Indirect evidence: evidence that modulation or attenuation in the magnitude of impact on a specific KE (increased effect or decreased effect) is associated with corresponding changes (increases or decreases) in the magnitude or frequency of one or more downstream KEs. More help

Evidence Assessment

Addressess the biological plausibility, empirical support, and quantitative understanding from each KER in an AOP. More help

Known Modulating Factors

Modulating factors (MFs) may alter the shape of the response-response function that describes the quantitative relationship between two KES, thus having an impact on the progression of the pathway or the severity of the AO.The evidence supporting the influence of various modulating factors is assembled within the individual KERs. More help

Quantitative Understanding

Optional field to provide quantitative weight of evidence descriptors.  More help

Considerations for Potential Applications of the AOP (optional)

Addressess potential applications of an AOP to support regulatory decision-making.This may include, for example, possible utility for test guideline development or refinement, development of integrated testing and assessment approaches, development of (Q)SARs / or chemical profilers to facilitate the grouping of chemicals for subsequent read-across, screening level hazard assessments or even risk assessment. More help


List of the literature that was cited for this AOP. More help

Song, Y.; Villeneuve, D. L.; Toyota, K.; Iguchi, T.; Tollefsen, K. E., 2017. Ecdysone receptor agonism leading to lethal molting disruption in arthropods: review and adverse outcome pathway development. Environ Sci Technol, 51, (8), 4142-4157.

Song, Y., Evenseth, L.M., Iguchi, T., Tollefsen, K.E., 2017. Release of chitobiase as an indicator of potential molting disruption in juvenile Daphnia magna exposed to the ecdysone receptor agonist 20-hydroxyecdysone. J Toxicol Environ Health A, 1-9

Fay, K. A., Villeneuve, D. L., LaLone, C. A., Song, Y., Tollefsen, K. E. and Ankley, G. T., 2017. Practical approaches to adverse outcome pathway (AOP) development and weight of evidence evaluation as illustrated by ecotoxicological case studies. Environ. Toxicol. Chem. 36(6):1429-1449.

Miyakawa, H., Sato, T., Song, Y., Tollefsen, K.E., Iguchi, T., 2017. Ecdysteroid and juvenile hormone biosynthesis, receptors and their signaling in the freshwater microcrustacean Daphnia. J Steroid Biochem Mol Biol. pii: S0960-0760(17), 30370-30379.