Colony-level simulation models

U.S. Environmental Protection Agency 1

Keith Sappington, M.S.

Environmental Fate and Effects Division

Office of Pesticide Programs
Outline

• Potential utility of colony-level simulation models for 

proposed risk assessment framework

• Current State of the Science

U.S. Environmental Protection Agency 2

• Discussion of select models
Why consider colony simulation models? 

• Understanding interdependent biological processes

• Interpret and relate sublethal measurement endpoints to 

assessment endpoints 

(e.g., colony strength and survival, quantity of hive products) 

U.S. Environmental Protection Agency 3

• Inform the design of higher tier studies 

(e.g., timing, scale, replication, duration)

• Assist interpretation of Tier II and III study results

Account for observed variability in endpoints (e.g., season)

Account for other non-chemical factors (e.g., weather)

• Incorporate data from multiple assessment Tiers

• Integrate chemical and non-chemical stressors
Current State of the Science

• SETAC Pellston1 Conclusion (Executive Summary): 

“None of the existing honey bee models seems suitable for regulatory 

risk assessment because...” (p 37)

 Lack of linkage between foragers and surrounding landscape

 Most are insufficiently tested with empirical data 

U.S. Environmental Protection Agency 4

 Most are insufficiently tested with empirical data 

 Most lack sensitivity analysis to understand controlling factors

 Multiple stressors are not included

 Insufficient documentation with some models 

1 Fischer, D. and T. Moriarty. 2011. Pesticide risk assessment for pollinators: summary of a SETAC Pellston Workshop. Edited 

by D. Fischer and T. Moriarty. SETAC Press. 

http://www.setac.org/sites/default/files/executivesummarypollinators_20sep2011.pdf
Attributes of Select Models 

U.S. Environmental Protection Agency 5

Model Scale Key Model Output Key Model Inputs and Processes

Becher et al. 2010 Colony Colony size and composition Impact of comb temperature on 

egg laying, brood development, 

colony strength

DeGrandiHoffman et al. 

1989 (BeePoP)

Colony Colony size and composition Impact of initial colony size, 

weather, photoperiod, queen 

fertility on brood development, 

colony dynamics

Khoury et al. Colony Colony size and composition Impact of forager death rate on

2011

Colony Colony size and composition Impact of forager death rate on

onset of foraging; task division, 

brood and forager survival

Makela et al. 

1993 (AHBsim)

Colony and 

population

Colony size and spatial 

distribution of Africanized 

and European honey bees

Food quantity, task division, queen 

fertility, brood development, 

swarming, migration, genotype

Schmickl & 

Crailsheim 2007 

HoPoMo)

Colony Colony size and composition, 

amount of pollen and honey

Food quantity &processing, task 

division, queen fertility, brood 

development, foraging, larval 

cannibalism

Thompson et al. 

2005

Colony Colony size and composition Pesticide impacts on egg laying,

brood rearing, onset of foraging, 

worker longevity, colony strength
Attributes of Select Models 

U.S. Environmental Protection Agency 6

Model Spatially 

Explicit?

Sensitivity

analysis?

Model Verification Application to 

Pesticides?

Becher et al. 2010 No No Timing of peak hive strength, 

minimum hive strength for 

overwintering

No

DeGrandi-Hoffman 

et al. 1989 (BeePoP)

Yes* Yes Limited comparison to 

literature studies

Yes 

(Web version)

Khoury et al. 2011 No Limited Onset of foraging, forager No

age

No

Makela et al. 1993 Yes No None No

Schmickl & 

Crailsheim 2007 

(HoPoMo)

Yes* Limited Selected model components 

and output compared to 

literature data

No

Thompson et al. 

2005

No No Limited comparison to 

colony-level toxicity studies

Yes

* Based on geographic differences in weather conditions 
Desired Features of a Colony-level Simulation 

Model

• Account for major factors that determine colony dynamics 

• intra-colony and eventually, inter-colony

• Quantitatively link various measurement endpoints to

assessment endpoints

• colony strength & colony survival, production of hive products

• Readily parameterized, using existing biological and pesticideU.S. Environmental Protection Agency 7• Readily parameterized, using existing biological and pesticidespecific data

• Adaptable to pesticide uses that differ across regions

• Account for geographic variation in use pattern, crops, climate, landscape

• Scientifically defensible, transparent, well documented, 

publically available1

• Sensitivity and uncertainty analysis

• Evaluation relative to empirical data

1 Guidelines for environmental model development have been published by the USEPA Council on Regulatory Environmental Models (CREM) 

http://www.epa.gov/crem/index.html. Guidelines for “Mechanistic Effects Models” are under development as part of an European Commission 

CREAM project (http://cream-itn.eu/ ) 
Summary

• Current colony-level simulation models do not appear ready for 

regulatory use

• Once fully developed and evaluated, colony level models have 

potential to serve as an important line of evidence as part of risk 

characterization

• They may also be useful for problem formulation, designing and 

U.S. Environmental Protection Agency 8

• They may also be useful for problem formulation, designing and 

interpreting empirical studies, and integrating data generated at 

multiple risk assessment tiers 

• EPA is interested in SAP feedback on the concept of using colonylevel models in pesticide ecological risk assessments and their 

current state of the science. (Charge Question 14a&b)

• EPA seeks SAP comments on critical model elements that should be 

considered in a honey bee colony-level model for use in pesticide 

ecological risk assessments. (Charge Question 14c)