Risk Assessment for Adult Butterflies Exposed to the Mosquito Control Pesticide Naled

Environmental Toxicology and Chemistry # 2012 SETAC Printed in the USA DOI: 10.1002/etc.1757 Hazard/Risk Assessment RISK ASSESSMENT FOR ADULT BUTTERFLIES EXPOSED TO THE MOSQUITO CONTROL PESTICIDE NALED TIMOTHY A. BARGAR* Southeast Ecological Science Center, U.S. Geological Survey, Gainesville, Florida (Submitted 22 June 2011; Returned for Revision 11 October 2011; Accepted 23 November 2011) Abstract—A prospective risk assessment was conducted for adult butterflies potentially exposed to the mosquito control insecticide naled. Published acute mortality data, exposure data collected during field studies, and morphometric data (total surface area and fresh body weight) for adult butterflies were combined in a probabilistic estimate of the likelihood that adult butterfly exposure to naled following aerial applications would exceed levels associated with acute mortality. Adult butterfly exposure was estimated based on the product of (1) naled residues on samplers and (2) an exposure metric that normalized total surface area for adult butterflies to their fresh weight. The likelihood that the 10th percentile refined effect estimate for adult butterflies exposed to naled would be exceeded following aerial naled applications was 67 to 80%. The greatest risk would be for butterflies in the family Lycaenidae, and the lowest risk would be for those in the family Hesperidae, assuming equivalent sensitivity to naled. A range of potential guideline naled deposition levels is presented that, if not exceeded, would reduce the risk of adult butterfly mortality. The results for this risk assessment were compared with other risk estimates for butterflies, and the implications for adult butterflies in areas targeted by aerial naled applications are discussed. Environ. Toxicol. Chem. # 2012 SETAC Keywords—Butterflies Naled Risk assessment Mosquito control INTRODUCTION impacts on nontarget insects have provided mixed indications The mosquito control pesticide Trumpet EC (AMVAC of risk. One investigation reported that survival of late-instar Chemical Corporation), containing the active ingredient naled Cyclargus thomasi bethunebakeri larvae following aerial naled (1,2-dibromo-2,2-dichloroethyl dimethyl phosphate), is aerially applications was reduced 26% compared with a reference applied as an ultralow-volume spray in the Florida Keys, USA, location [7]. Another reported that the mean abundance for to control adult mosquitoes. This has been an issue for resource A. troglodyte floridalis, but not S. acis bartrami, was greater at management agencies responsible for conservation of imperiled locations not treated by mosquito control pesticides relative to butterflies residing within or adjacent to areas of active mos- sprayed locations [1]. In a study not targeting butterflies, aerial quito control. In fact, it has been suggested that the application naled applications reduced abundance for several nontarget of mosquito control pesticides is partially responsible for the insect families but did not affect diversity [8]. Therefore, it decline of butterfly communities in the Florida Keys [1–3]. appears that naled impacts on insects in the field vary depending Reintroduction efforts for the state-listed and federal candidate on the family of interest. Miami blue butterfly (Cyclargus thomasi bethunebakeri) are The prospective risk assessments that estimate pesticide occurring adjacent to areas of active mosquito control. In impacts on nontarget terrestrial insects might not be applicable addition, aerial naled applications are permitted over the for adult butterflies exposed to an insecticide applied as an Key Deer National Wildlife Refuge on Big Pine Key, Florida, ultralow-volume spray, because they consider exposure only as where two resident butterfly taxa (Florida leafwing butterfly a result of the insect walking across or landing on a contami- [Anaea troglodyta floridalis] and Bartram’s hairstreak nated surface [4,9,10]. Naled is a very labile compound with a butterfly [Strymon acis bartrami]) are candidates for federal half-life ranging from 1.4 to 8.2 h depending on incident light listing under the Endangered Species Act of 1973.) Aerial and relative humidity, with it being least persistent in direct applications of naled may be adversely impacting populations sunlight and most persistent under dark conditions with low of those butterflies. relative humidity [11]. At least in the Florida Keys, aerial Naled is a broad-spectrum organophosphate insecticide that naled applications occur just before sunrise and extend for a is potentially toxic to a variety of insects [1–4]. Based on naled short period after sunrise, meaning that naled residues on toxicity to honey bees, the U.S. Environmental Protection foliage are likely to degrade rapidly, before butterflies (adults Agency’s Office of Pesticide Programs classified naled as or larvae) can accumulate naled as a result of walking across or highly toxic to nontarget terrestrial invertebrates, implying that consuming contaminated foliage. As a result, direct deposition naled impacts on butterflies are possible given sufficient expo- of naled onto the exoskeleton is the most likely route of sure [5]. Available acute toxicity data for several butterfly efficacious exposure for adult butterflies. Therefore, assessing species suggest that honey bee acute toxicity data may not risk to butterflies from ultralow-volume spray applications of be applicable to butterflies [6]. Field studies investigating naled naled requires considering direct deposition in the exposure assessment. The present study presents a prospective risk assessment * To whom correspondence may be addressed ([email protected]). method for adult butterflies exposed to mosquito control insec- Published online 25 January 2012 in Wiley Online Library ticides containing the active ingredient naled that are applied as (wileyonlinelibrary.com). an ultralow-volume spray. Naled is used by several mosquito 1 2 Environ. Toxicol. Chem. 31, 2012 T.A. Bargar control districts in the state of Florida and elsewhere and is (nearest 0.001 g) were coupled as a metric of surface area per also registered by the U.S. Environmental Protection Agency unit mass (cm2/g, the exposure metric), which was combined for the control of black flies and leaf-eating insects on a variety in Equation 1 with deposition data to estimate a weight- of agricultural crops. Although the focus of this risk assessment normalized exposure for adult butterflies in the field. is on impacts on butterflies in the Florida Keys, it has implications for other areas where pesticides containing naled are Exposure ðmg=gÞ used. ¼ deposition ðmg=cm2Þexposure metric ðcm2=gÞ (1) MATERIALS AND METHODS The product of the deposition and exposure metric data has the same units as the toxicity data, which facilitates risk Field studies were conducted to measure naled deposition estimation. Toxicity data for insects are often reported as following aerial applications over the Key Deer National Wild- chemical mass per organism rather than per unit body weight. life Refuge, Florida, USA (hereafter, Refuge). Two residue Therefore, use of the term ‘‘exposure’’ in the present study sampler types were used to assess naled deposition at each test refers to weight-normalized exposure to avoid confusion. location immediately following aerial applications, glass fiber 2 Effects were estimated based on published acute toxicity filter papers (452.4 cm , Whatman No. 4 qualitative) pinned to data and on unpublished data determined by the author aluminum foil-covered Styrofoam blocks and placed flat on the Â (Table 1). The range of toxicity values in this data set (four ground and acrylic yarn (0.47 cm 5.79 m) stretched within orders of magnitude) is not unusually small given the variability polyvinylchloride frames set approximately 1 m above the of acute toxicity data sets typically available for organisms ground. Yarn samplers were also used to assess naled deposition exposed to organophosphate insecticides [12]. Most of the because small droplets typical of ultralow-volume sprays are toxicity data available for butterflies were derived using the unlikely to settle onto the filter papers before the samplers honey bee acute contact toxicity method, in which the chemical are retrieved. During each of two field trials, three yarn and is applied to the dorsal side of the thorax. However, adult three paper samplers were placed at each of eight locations in butterflies are responsive to naled deposition onto wings [6], the Refuge. The samplers were deployed less than 1 h before the indicating that exposure routes other than deposition onto the applications. Applications began shortly before dawn (15– thorax should be considered in the risk assessment. To this end, 20 min), when an airplane flew over the Refuge at an elevation a refined effect estimate was generated for this risk assessment of approximately 30.5 m and sprayed (Micronair AU4000 atom- using Equation 2. The refined effect estimate incorporates izer) Trumpet EC at a rate of 70 g a.i./ha (840.6 g end-use relative surface areas of the body and wings and the toxicity product/ha). Four teams of personnel were responsible for as a result of exposure on the body and wings. residue sampler recovery to hasten sampler retrieval after the sprays. Each team was responsible for separate pairs of loca- Effect ðmg=gÞ tions beginning approximately 50 min after the application had ¼ð Â þð Â Þ ceased. The 50-min delay allowed for droplet settling to the Propwing LD50wing Propthorax LD50thorax (2) ground following the sprays.

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