UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

JUN 07 2012 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: BEAD Chemical Profile for Registration Review: Resmethrin (pC # 097801) 

FROM: Nikhil Mallampalli, Entomologist /lilt;( ~ '/ ~/ z.., rzBiological Analysis Branch ~ 

Jihad Alsadek, Economist V t--,W It. tP,la...,..M t /7 ! 20 J ZScience Information and Analysis Branch 

ElizabethHill,Economist, r~_ ~\NJ~ Economic Analysis Branch \" Y" "---J] 

Biological and Economic Analysis Division (7503P) 

THRU: Arnet Jones, Chief 

Biological Analysis Branc 

Diann Sims, Chief • {;~~ Science Information and Analysis Branch 

Timothy Kiely, Chief 4- I)v\..I (0 Economic Analysis Branch '--1' U l/("~ Biological and Economic Analysis Division (7503P) 

TO: Katherine StClair, Chemical Review Manager 

Risk Management and Implementation Branch 4 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: December 7, 2011 

INTRODUCTION 

The purpose of this document is to convey usage information and a broad overview of the pest 

management roles of pesticides that are beginning to undergo registration review. The 

anticipated audience consists of the team of EPA staff currently evaluating the registration status 

of resmethrin, and eventually the general public. This document builds upon the data already 

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provided in the "Usage and Label Use Data Packages" that are also provided to Registration 

Review teams by BEAD. The document is based on information and data available to BEAD as 

of November 2011. 

Two chemicals are included in the Agency's "resmethrin" chemical review, resmethrin and 

bioresmethrin. Resmethrin was nrst registered in the u.s. in 1967, while bioresmethrin was first 

registered in the U.s. in 1973. Resmethrin and bioresmethrin are in the same chemical review 

because of their very similar chemical structures and use patterns. The rest of this document will 

refer to both chemicals under the term "resmethrin". It underwent Agency risklbenefIt review in 

2006, when a Reregistration Eligibility Decision (RED) was issued (EPA 2006). BEAD did not 

conduct any formal benefits assessments for this RED. 

The Insecticide Resistance Action Committee (IRAC), comprised of technical personnel from 

various large agrochemical and public health companies, classifies resmethrin as a member of 

the Mode of Action Group 3 (subgroup 3A).This group of insecticides acts as sodium channel 

modulators, thus 'causing disruption of nerve impulses in the target insects. All pyrethroids 

"initially stimulate nerve to produce repetitive discharges and subsequently cause paralysis" 

(Narahashi, 1976). Like other compounds derived from the chemical structure of pyrethrum, it is 

most toxic to the target pest on contact, and has a quick "knockdown" effect, which is the initial 

paralysis and quick intoxication caused by nerve stimulation (DoulI1976). 

Resmethrin is sometimes formulated with a synergist compound, such as piperonyl butoxide 

(PBO) or MGK-264, to extend its active life and increase its toxic effect on target insects (Jones 

1998). It is also sometimes formulated with pyrethrins or synthetic pyrethroids for the same 

purpose. Resmethrin is currently classified as a restricted use chemical for wide area mosquito 

abatement. 

USE SITES 

Currently, resmethrin is registered for use on Athletic fields, Camp areas, Domestic dwellings 

(outdoor), Eating establishments (outdoor inedible), Industrial areas (outdoor), Livestock feed 

lots, Marshes (surrounding vegetation-foliar treatment), Marshland (surrounding vegetation), 

Mosquito abatement districts, Municipalities Ornamental turf (golf courses), Parks, Playgrounds, 

Ponds (surrounding vegetation), Recreational areas, Restaurants (outdoor), Roadsides, 

Shorelines, Stagnant pools (surrounding vegetation-foliar treatment), Stores (outdoor inedible), 

Swamps/marsheslbogs/standing water (vegetation), Tidal marshes (surrounding vegetation), 

Urban outdoor, Warehouses (outdoor), Woodland .areas, Zoos. 

All other uses have been voluntarily cancelled by the registrant (Bayer). 

COMMON FORMULATIONS AND APPLICATION METHODS 

Resmethrin is formulated as soluble concentrate. The 2006 RED summarized application 

methods as follows: ApplicatlOIis [can be] made with hand held equipment such as ready-to-use 

spray containers, aerosol cans, thermal fog generators, electric foggers, backpack sprayers, and 

hand held sprayers. Applications are also made with aircraft and ground ·equipment such as 

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truck-mounted [ultra-low volume (ULV)] sprayers." The RED eliminated use ofresmethrin in 

residential products intended for use with indoor metered spray systems and automatic misting 

systems. All other application methods described above remain on current resmethrin labels. 

USAGE 

BEAD has very limited information on the use of resmethrin. Usage for mosquito abatement 

ranged from 17,000 lbs in 2003 to 34,000 lb in 2005. A small amount of resmethrin use has also 

been reported for containerized nursery applications. There was less than 100 lbs. of resmethrin 

used in 2002 in nurseries and greenhouses (Kline and Company, Inc. 2003-2005). It is not clear 

what the most commonly used application rates or frequencies are for resmethrin. 

BIOLOGICAL ASPECTS RELEVANT TO RESMETHRIN 

Resmethrin is one if several synthetic pyrethroids that were commercially developed early in the 

history of this class of insecticides (Casida 1980, Wickham 1995). It is one ofa group of older 

pyrethroids that are used in "much the same manner as pyrethrum extract", the crude mixture of 

pyrethrins that is derived from chrysanthemum flowers (Casida 1980). As such, resmethrin is 

"highly insecticidal but not [environmentally] persistent enough for [outdoor] agricultural use" 

(Casida 1980). Resmethrin, like cismethrin and D-phenothrin (aka sumithrin) has "poor stability. 

in sunlight" but continues to playa role as an indoor space spray option for controlling urban 

pests such as cockroaches (Wickham 1995). It continues to be one of a small set of insecticides 

recommended by some state-level experts for suppressing populations of adult mosquitoes 

(Brattsten and Hamilton 2011). 

Interestingly, beekeepers dealing with infestations of American foulbrood (Paenibacillus 

larvae), a bacterial disease, sometimes have had to depopulate the colony with an over-thecounter formulation ofresmethrin, applied with aerosol spray cans (synthetic pyrethroid) (USDA 

2004,2006). No other pesticide appears to be recommended for this purpose, although other 

control strategies, such as treatment of hives with an antibiotic such as terramycin, are among 

recommended options (USDA 2004, 2006). Note that this use is no longer possible since overthe-counter products have been cancelled by the registrant. 

A search of the database on arthropods resistant to pesticides (maintained online by Michigan 

State University and accessible at www.pesticideresistance.org) indicates that many insects have 

evolved resistance to resmethrin (formulated with and without synergists) over the many years 

that the products have been in use. The list is diverse, covers both cases within and outside the 

U.S., and includes urban pests such as German cockroaches and houseflies, as well as 

widespread agricultural and stored commodity pests such as the the diamondback moth (Plodia 

interpuncte/la) and red flour beetle (Tribolium castaneum). BEAD's initial assessment, based on 

a scan of the literature mentioned in the database and other internet accessible sources, is that 

such resistance has not become consistently widespread in the U.S.; rather, it develops repeatedly 

in isolated instances-. 

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mSTORY OF BEAD ASSESSMENTS FOR RESMETHRIN 

In 2005 and 2006, the California Environmental Protection Agency, Department of Pesticide 

Regulation (CADPR) requested a Public Health Exemption for the use ofresmethrin on all crops 

grown in the state except for almonds, pasture, rice, and walnut to control for mosquitoes 

vectoring the West Nile virus (see Attachment 1). In both years California was granted use-of 

resmethrin for this purpose, as the rapid spread of the West Nile virus coupled with the lack of 

effective aerially applied insecticides for adult mosquito control resulted in an urgent, nonroutine situation. Resmethrin is currently registered for use as a wide area mosquito abatement 

insecticide. 

No other assessments for resmethrin have been conducted by BEAD. In addition, according to 

the EPA's Official Section 18 Action Database, no other emergency exemptions have been 

issued for this chemical (EPA, 2011). 

INFORMATION THAT MAY BE USEFUL FOR BEAD'S FUTURE WORK ON 

RESMETHRIN 

Obtaining additional information on the following items would improve future BEAD 

assessments of the importance of resmethrin and may be required as part of the registration 

review of this pesticide. 

Usage data (ideally, in GIS-mappable format) on recent (post 2006) use ofresmethrin as a 

mosquito adulticide. 

REFERENCES: 

Brattsten, L.B. and G.C. Hamilton. 2011. Insecticides Reco~ended for Mosquito Control in 

New Jersey in 2011. New Jersey Agricultural Experiment Station Publication No. P08001-01-11. 

Cas ida. J. 1980. Pyrethrum Flowers and Pyrethroid Insecticides. Environmental Health 

Perspectives Vol. 34, pp. 189-202. 

Doull, J. 1976. The Treatment of Insecticide Poisoning. Ch. 16 in: C.F. Wilkinson (ed.), 

-Insecticide Biochemistry and Physiology. 753 pp. Plenum Press, New York. 

EPA. 2006. Reregistration Eligibility Decision for Resmethrin. Available at 

http://wWw.epa.gov/oppsrrdlIREDs/resmethrin red.pdf. [Accessed November 16,2011]. 

Environmental Protection Agency (EPA). 2011. Section 18 Action Database. Located at: 

http://cfpub 1.epa.gov/oppref/section 18/search.cfm. 

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Jones, D.G (ed.). 1998. Piperonyl Butoxide: The Insecticide Synergist. 323 pp. Academic Press, 

San Diego, CA. 

Kline and Company, Inc. 2002-2005. 

Narahashi, T. 1976. Effects of Insecticides on Nervous Conduction and Synaptic Transmission. 

Ch. 9 in: C.F. Wilkinson (ed.), Insecticide Biochemistry and Physiology. 753 pp. Plenum 

Press, New York. 

USDA. 2004. Crop Profile for Honey Bees in New Jersey. Available on the web at 

www.ipmcenters.org [Accessed November 16,2011]. 

USDA. 2006. Crop Profile for Honey in Virginia. Available on the web at www.ipmcenters.org 

[Accessed November 16,2011]. 

Wickham, J.C. 1995. Conventional Insecticides. In: Understanding and Controlling the 

German Cockroach. M.K. Rust, lM. Owens, and D.A. Reierson (eds). 430 pp. Oxford 

Univ. Press, New York. 

ATTACHMENT 1 

EPA Section 18 Actions for Resmethrin ~ 

"" al!B~e 

Site; .f.! I!' P~st ~pplieant Recej;ved ReSllo~ Status- rOj: BJiiAEl :~ IF Date Date seS§n!.ents, ~ ff@o..tmuefed 

VARIOUS MOSQUITO CALIFORNIA 9/12/2005 7/1112006 ISSUED 321734 

VARIOUS ' MOSQUITO CALIFORNIA 5/1112006 7/1112006 ISSUED 

Source: EPA (2011); BEAD OffiCIal Records. 

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