This blog is the second of a three-part series about the effects on birds from treating Nova Scotia hemlock forests with neonicotinoids. Part 1 examined the latest findings on the impact of neonicotinoids on human and wildlife health and the regulatory responses in the Western world. Part 2 explores the potential effects of neonicotinoids on Nova Scotia hemlock forest birds, and Part 3 will report on what birds tell us about that forest’s future.

In 2017, scientists found that the Hemlock Woolly Adelgid had spread from the eastern seaboard of the United States to Yarmouth County in Nova Scotia. Realizing the threat posed by this event to birds of the hemlock forests, I began to organize a baseline breeding bird study throughout the province in areas of initial or pre-infestation. I hoped that these surveys could assist in developing a bird conservation management plan to mitigate the effects of the adelgid. By 2019, with the support of the Nova Scotia Bird Society, volunteer expert birders throughout the province commenced breeding bird surveys using a point-count methodology and passive acoustic monitoring over four years. These surveys became part of a broader citizen science initiative, the Listening Together project. I will present the full results of these bird surveys and their implications in Part 3 of this blog series.

At the same time as our surveys, governments and environmental organizations began planning to use neonicotinoids (or neonics for short) to control the adelgid. This approach started in 1993 in the United States to treat hemlocks in Pennsylvania (Steward and Horner 1994) and is the first known use of a neonic, imidacloprid, to treat hemlocks that I could find in the literature. Its use continues to be one of three key elements in pest management for the adelgid in that country (Jackson 2021). Those elements are chemical control for the short term, biological control and silvicultural practices for the long term. Biological control by introducing predatory beetles and silver fly species is mainly in the research and experimental stage. Silvicultural practices include thinning hemlocks in uninfested stands and reforestation with hemlocks resistant to the adelgid. The latter method is likely far into the future. Finally, where the adelgid has severely impacted the hemlock forest, natural regeneration or planting of other conifer species that can replace some of the ecological services of hemlocks are considered. Given the limitations of biological control and silviculture, there has been extensive application of neonics in the United States (Jackson 2021).

Thus, neonics quickly became the focus of adelgid pest management in Nova Scotia. In assessing the non-target impacts of neonic use, a paper produced by the Canadian Forest Service claimed that the use of neonics in hemlock stands would not impact birds (Sweeney 2021). Given the known adverse effects on birds in grasslands and agricultural habitats, how is it possible that there would be no effects in forests? This question became the spark for writing this three-part blog series.

First, it is essential to provide an overview of the insecticides used in Nova Scotia hemlock stands and how they are delivered. There are three types of insecticides used to treat hemlocks. The primary chemical is the neonic imidacloprid. One administers the chemical as an injection into the trunk of the tree. It moves through the tree’s vascular system, takes six to nine months to be fully effective, and provides four to five years of protection. Imidacloprid is also available as a basal bark spray, takes six to nine months to be effective, and provides protection for five to seven years. TreeAzin is a botanical pesticide made from the neem tree that is also an injection. It becomes effective in only one to two months but provides only one to two years of protection. Dinotefuran is also a neonic used as a basal bark spray. It becomes effective in one month and provides one to two years of protection. The choice of insecticide is related to the urgency of treatment and the proximity of bodies of water to the tree. The government requires a buffer zone of 30 metres from water for basal bark sprays (Province of Nova Scotia No date). You can watch a video on how hemlock trees are treated by injection and basal bark spray here (Medway Community Forest Coop 2024).

Now, we can return to the Canadian Forest Service’s (CFS) claim that the neonic treatment of hemlocks is harmless to birds (Sweeney 2021). The CFS based this conclusion on one paper (Falcone and DeWald 2010). The paper’s authors studied the effect of neonics on arthropods and insectivorous birds by comparing treated and untreated stands in the Great Smoky Mountains National Park in Tennessee and North Carolina. Arthropods are invertebrates with joined body segments and a hard shell. They include insects and spiders. The treatment method was applying imidacloprid in a soil drench around the tree’s base in one of two previous years. The researchers found no significant difference in the density of insectivorous birds feeding in the forest canopy between treated and untreated sites. They did, however, document a substantial decline in herbivorous Hemiptera (aphids, leafhoppers, etc.) and larval Lepidoptera (caterpillars of moths and butterflies) in the canopy. Although larval Lepidoptera is an important food source for insectivorous hemlock birds, the authors concluded that the birds found sufficient amounts of other insects to maintain their population levels. They also suggested that neonic treatments benefited the birds by preventing defoliation of the canopy.

This study of the hemlock birds of the Great Smoky Mountains National Park has two significant shortcomings. First, the authors understate the importance of lepidopteran abundance to hemlock birds. Their study focused on three bird species: the Black-throated Green Warbler, the Blue-headed Vireo, and the Black-throated Blue Warbler. The Black-throated Green Warbler is the second most common bird in the hemlock forests of Nova Scotia. Its scientific name is Setophaga virens, meaning “green moth-eater” from the ancient Greek and Latin words. Many of our warblers are in the genus Setophaga, and most of them, like the Black-throated Green Warbler, are neo-tropical migrants that winter in the Caribbean, Mexico, Central America, and South America. These warblers travel thousands of kilometres each year for one important reason: to raise their young where there is a high availability of Lepidopteran larvae. Studies show the foraging of the Black-throated Green Warbler concentrates on caterpillars, with the amount eaten ranging from 64%, 70%, and 83% of their total diet (Morse et al. 2024; Robinson and Holmes 1982).

While there are no percentages available of the number of caterpillars fed to the Black-throated Green Warbler nestlings, the literature highlights the importance of Lepidoptera in raising young birds. Studies show that parents feed small insects to the hatched birds in their first eighteen hours and then switch to caterpillars. The number of caterpillars increases daily and ends with the largest caterpillars coming just before fledging. Adults will even eat smaller insects to maximize the weight of larval food to the young while minimizing flying time to and from the nest (Nice and Nice 1932; Morse et al. 2024). Thus, a shortage of caterpillars might lead to the death of nestlings or poor body conditions of fledglings.

So important are Lepidoptera to the health of foliage-gleaning, neotropical, insectivorous birds that, according to one study, their population levels are in synchrony with the population levels of Lepidoptera in a region (Jones, Doran, and Holmes 2003). It might be all the more difficult for birds to recover from a population crash of caterpillars if other factors, such as neonic treatments, suppress the recovery of caterpillars. Thus, the Great Smokey Mountains National Park study fails to address the effect of hemlock treatments on nesting success and regional population dynamics of insectivorous birds.

The second shortcoming of the study is the failure to address the possible sublethal effects on insectivorous birds in treated hemlock stands. One of the main themes of the analysis of neonics in Part 1 of this blog series was the critical importance of sublethal effects on non-target species of insects and birds. The potential sublethal effects are especially significant to consider in the case of Nova Scotia hemlock stands since trunk injection is a commonly used application method of imidacloprid.

A study of hemlock treatments in the Cherokee National Forest in Tennessee tested the effects of each neonic treatment method on insects, namely soil drench, soil injection, and tree injection (Dilling et al. 2009). Lepidoptera mortality was highest with the soil drench and lowest with the tree injections. The basal bark spray was not one of the methods tested, so its effect on Lepidoptera is unknown.

The amount of imidacloprid reaching the foliage of hemlocks in Nova Scotia through tree injection is likely insufficient to kill herbivorous caterpillars. Studies have shown that imidacloprid is active in hemlock needles at concentrations of 0.2, 1.8, 2.0, and 1.4 micrograms per gram at 70, 435, 800, and 1165 days after tree injection compared to 0.14, 0.33, 3.1, and 2.4 micrograms per gram for the same periods in soil injected trees (Doccola et al. 2012; Doccola 2021). As shown in the Cherokee National Forest study, the soil injection method produced less decline in Lepidoptera abundance and species richness than soil drench but greater than tree injection (Dilling et al. 2009). Thus, the tree-injected foliage is the least likely to be lethal to caterpillars but still carries a sublethal dose of imidacloprid. The sublethal effects of imidacloprid on caterpillars include arrested pupal ecdysis (shedding of the outer cuticle) (Krishnan, Jurenka, and Bradbury 2021), increased vulnerability to predators (Dilling et al. 2009), and significantly reduced pupation duration and size of adults, indicating compromised adult fitness (Whitehorn et al. 2018).

Based on agricultural and grassland studies, one expects birds to experience severe sublethal sickness and adverse reproductive outcomes from eating contaminated insects (Mineau and Kern 2023). Yet, for the thirty years of neonic use in hemlock stands in the United States and the seven years in Canada, I could not find a single scientific study, either in the laboratory or under field conditions, tracing neonic residue activity from plant to insects and on to birds.

As Part 1 of this blog series noted,  27-gram White-crowned Sparrows showed signs of sickness from imidacloprid at a dose of 1.2 milligrams per kilogram of body weight. The equivalent dose for an 8-gram adult Black-throated Green Warbler would be 9.6 micrograms per gram. For a 1.3-gram nestling, the dose would be 1.56 micrograms per gram. While the level of contamination in the caterpillars is unknown, it is plausible that consuming many caterpillars every day over the breeding season could result in chronic, acute or even fatal illness, especially in young birds. Neotropical migrants will not stop eating caterpillars, even if it makes them sick or kills their nestlings; that is why they are here, for the Lepidoptera.

I have already described the heavy dependence of Black-throated Green Warblers on caterpillars. Among the other most common insectivorous canopy foraging birds breeding in hemlock stands, Blackburnian Warblers concentrate on Lepidoptera (Morse 2020), caterpillars were 42% of the diet of Blue-headed Vireos in one study and 73% in another (Morton and James 2020), and breeding Red-eyed Vireos diets were 50% Lepidoptera (Cimprich, Moore, and Guilfoyle 2020).

Another possible pathway of neonic contamination is from the seeds of hemlock cones. Hemlocks are the favoured food source of White-winged Crossbills in Northeastern North America (Benkman 2020) and are a staple in the diet of Red Crossbills (Benkman and Young 2020).

Bark-foraging hemlock birds may be at risk for an unknown amount of time following basal bark spraying. These birds are the Brown Creeper, Red-breasted Nuthatch, Pileated Woodpecker, and Black-capped Chickadee.

There are the forest floor-dwelling birds of the hemlock forest. These are the Swainson’s Thrush, the Hermit Thrush, and the Ovenbird. According to the Listening Together surveys by expert birders throughout the province, the Ovenbird was the most abundant breeding bird in Nova Scotia hemlock stands.

As a ground feeder, the diet of Ovenbirds consists of a variety of soil invertebrates, of which ants constitute a significant component. In one study, ants made up 62% of their food during the non-breeding season. The parents feed their nestlings mainly ground beetles and Lepidopteran larvae (Pomeluzi, Van Horn, and Donovan 2020).

Three recent studies supported by the Canadian Forest Service provide essential insights about the invertebrates in the soil and understory of hemlock stands. The three studies sought to understand the non-target effect of the basal bark spray on invertebrates and the resulting concentration of imidacloprid residues in the soil and vegetation.

In one study (Voscort 2024), the population of pollinators was not adversely affected in the year following treatment. However, concentrations of imidacloprid in flowers were potentially harmful to pollinators, especially within two metres of a sprayed tree. The second study (Chapman 2024) found a significant decline in the Spine-waisted Ant, a keystone forest species, in the treated stands compared to the untreated stands. The third study (Edge et al. 2024) demonstrated that the risk of adverse effects of basal bark spray on soil invertebrates is greatest within two metres of the tree. The authors write that these findings indicate the need for further research in hemlock stands.

All three studies shared the same study plots at two different sites in southwest Nova Scotia: Sissiboo Falls in Digby County and McKay Lakes in Shelburne County. The first application of basal bark spray was in October 2020, with 40 to 60 trees treated at each site. The peak deployment of autonomous recording units in the Listening Together project occurred in June 2021. One of the Canadian Forest Service research team members volunteered to set up a device at each study site. The Ovenbird is the bird species most likely to be exposed to contaminated soil insects. In analyzing all the Nova Scotia acoustic data in the 2021 breeding season, I chose sites with recordings in the peak singing period, the second and third weeks of June. Each morning has three ten-minute recordings one hour apart. I list the mean number of all songs recorded in the morning as the singing rate in Table 1. McKay Lakes and Sissiboo Falls had the lowest singing rates out of the thirteen sites.

Since the audio data were not part of the study design of the soil and understory studies at McKay Lakes and Sissiboo Falls, one cannot say that they are some level of proof of adverse effects from basal bark spray. Nonetheless, they provide enough circumstantial evidence to wonder if Ovenbirds may have been too sick to sing or abandoned their territories due to lack of food. Thus, the audio data reinforce the researchers’ conclusions that more study is needed.

The final pathway for the contamination of avian food with neonics is through the leaching of imidacloprid into streams, which can sublethally affect aquatic invertebrates, which emerge at later stages of their life history to become available to aerial insectivores, including bats and birds. This possibility is especially worrying for forest species at risk, like the Common Nighthawk, Chimney Swift, and Eastern Wood-Pewee.

Studies on runoff from hemlock stands in the United States have suggested low risk to invertebrates while noting that imidacloprid concentrations in streams can temporarily exceed regulatory limits after rain events (Churchel et al. 2011; Benton et al. 2017; Wiggins et al. 2018). The most recent study takes a more precautionary approach, showing that water samples may not represent actual ecosystem effects. Tissue samples from salamanders and their food, macroinvertebrates, have contained levels of imidacloprid that adversely affect body condition in the salamanders. Concentrations of imidacloprid in these same streams were lower than in other studies, which showed no effects on aquatic fauna. The authors suggest that small concentrations of imidacloprid may lead, through bioaccumulation, to sublethal effects in invertebrates and higher trophic levels (Crayton et al. 2020). These findings imply that regulatory benchmarks for aquatic invertebrates are too high.

Regulatory benchmarks are the chemical concentrations in the water that will adversely affect organisms. The lower the benchmark value, the greater the protection afforded to aquatic life. Table 2 shows the freshwater benchmarks for adverse effects on aquatic invertebrates for Canada, the United States and the European Union (Mineau 2024). The Pest Management Regulatory Authority (PMRA) of Health Canada sets the benchmarks in Canada. Canada’s benchmarks for acute and chronic conditions are higher than those set by the Environmental Protection Agency (EPA) in the United States and much higher than those of various countries in the European Union. This fact means Canada provides less protection to aquatic invertebrates and higher trophic levels than the United States and Europe.

As noted in Part 1 of this blog, these kinds of decisions on the part of the PMRA have caused great concern among national environmental organizations. In December 2024, an environmental coalition led by the David Suzuki Foundation called for an independent panel to review decision-making in the PMRA. According to Birds Canada, on January 22, 2025, the federal Minister of Health responded and “did not commit to any urgent action but did leave the door open to an independent review (Birds Canada 2025).”

Finally, this blog did not discuss several studies in the United States concerning changes in the composition of bird populations in infested hemlock stands. These bird habitat studies involve a complex set of questions related to such issues as invasive species, climate change, and forestry practices. I will discuss these issues in Part 3 of this blog series and describe what Nova Scotia hemlock birds tell us about them.

In conclusion, this blog has shown an almost total absence of scientific studies on the effects of neonics on the health of hemlock birds and their nestlings. To say that hemlock treatments do not affect birds is misleading the public. The public, in good faith, will assume there is a scientific basis for that claim. It is now time to take action to stop us from creating a hemlock forest that is forever silent.

 

References

Benkman, C.W. 2020. “White-winged Crossbill (Loxia leucoptera), version 1.0.” Birds of the World, edited by S.M. Billerman. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/whwcro/1.0.

Benkman, C.W., and M.A. Young. 2020. “Red Crossbill (Loxia curvirostra), version 1.0.” Birds of the World, edited by S.M. Billerman, B.K. Keeney, P. G. Rodenwald and T.S. Schulenburg. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/redcro/1.0.

Benton, Elizabeth P., Jerome F. Grant, Rebecca J. Nichols, R. Jesse Webster, John S. Schwartz, and Joseph K. Bailey. 2017. “Risk assessment of imidacloprid use in forest settings on the aquatic macroinvertebrate community.” Environmental Toxicology and Chemistry 36 (11): 3108-3119. https://doi.org/10.1002/etc.3887.

Birds Canada, 2025, “The Hidden Threat: Why Neonics Are Still Putting Birds at Risk.” https://www.birdscanada.org/the-hidden-threat-why-neonics-are-still-putting-birds-at-risk?utm_medium=email&utm_source=engagingnetworks&utm_campaign=2025FebEnews&utm_content=2025+February+Enews+-+EN+2077233491.

Chapman, Cody. 2024. “Arthropods in mature eastern hemlock forests: assessing the non-target effects of basal bark imidacloprid application for control of hemlock woolly adelgid on forest floor and canopy arthropod fauna in southwestern Nova Scotia.” Master of Science (Biology), Biology, Acadia University. https://scholar.acadiau.ca/node/4255.

Churchel, Melissa A., James L.  Hanula, C. Wayne Berisford, James M. Vose, and Mark J. Dalusky. 2011. “Impact of Imidacloprid for Control of Hemlock Woolly Adelgid on Nearby Aquatic Macroinvertebrate Assemblages.” Southern Journal of Applied Forestry 35 (1): 26-32. https://academic.oup.com/sjaf/article-abstract/35/1/26/4774810.

Cimprich, D.A., F. R. Moore, and M.P. Guilfoyle. 2020. “Red-eyed Vireo (Vireo olivaceus), version 1.0.” Birds of the World, edited by P. G. Rodenwald. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/reevir1/1.0

Crayton, Sara M., Petra B. Wood, Donald J. Brown, Alice R. Millikin, Terence J. McManus, Tyler J. Simpson, Kang-Mo Ku, and Yong-Lak Park. 2020. “Bioaccumulation of the pesticide imidacloprid in stream organisms and sublethal effects on salamanders.” Global Ecology and Conservation 24: e01292. https://doi.org/https://doi.org/10.1016/j.gecco.2020.e01292. https://www.sciencedirect.com/science/article/pii/S2351989420308337.

Dilling, Carla, Paris Lambdin, Jerome Grant, and Rusty Rhea. 2009. “Community Response of Insects Associated with Eastern Hemlock to Imidacloprid and Horticultural Oil Treatments.” Environmental Entomology 38 (1): 53-66. https://doi.org/10.1603/022.038.0108. https://doi.org/10.1603/022.038.0108.

Doccola, Joseph J. 2021. “Activity of Stem-Injected and Soil Applied Imidacloprid Against Hemlock Woolly Adelgid in the Great Smoky Mountains.” Arboriculture & Urban Forestry (AUF) 47 (1): 25-33. https://doi.org/10.48044/jauf.2021.003. https://auf.isa-arbor.com/content/isa/47/1/25.full.pdf.

Doccola, Joseph J., William Hascher, John Joseph Aiken, and Peter M. Wild. 2012. “Treatment Strategies Using Imidacloprid in Hemlock Woolly Adelgid (Adelges tsugae Annand) Infested Eastern Hemlock (Tsuga canadensis Carrière) Trees.” Arboriculture & Urban Forestry. https://www.semanticscholar.org/paper/Treatment-Strategies-Using-Imidacloprid-in-Hemlock-Doccola-Hascher/595696e410af335d41b0f4b3be46b32dc9a591a0.

Edge, Christopher, Shane Hertz, Anthony  Lagalante, Andrew  Lewis, and Jon Sweeney. 2024. “Risk of imidacloprid to soil invertebrates when applied as basal bark spray for the control of Hemlock Woolly Adelgid.” Canadian Journal of Forest Research. https://cdnsciencepub.com/doi/abs/10.1139/cjfr-2024-0267.

Falcone, Josephine F., and Laura E. DeWald. 2010. “Comparisons of arthropod and avian assemblages in insecticide-treated and untreated eastern hemlock (Tsuga canadensis [L.] Carr) stands in Great Smoky Mountains National Park, USA.” Forest Ecology and Management 260 (5): 856-863. https://doi.org/10.1016/j.foreco.2010.06.003. https://www.sciencedirect.com/science/article/abs/pii/S0378112710003269?via%3Dihub.

Jackson, David R. 2021. Integrated Approach to Hemlock Woolly Adelgid Mitigation. https://extension.psu.edu/integrated-approach-to-hemlock-woolly-adelgid-mitigation.

Jones, Jason, Patrick J. Doran, and Richard T. Holmes. 2003. “Climate and Food Synchronize Regional Forest Bird Abundances.” Ecology 84 (11): 3024-3032. https://doi.org/https://doi.org/10.1890/02-0639. https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/02-0639.

Krishnan, Niranjana, Russell A. Jurenka, and Steven P. Bradbury. 2021. “Neonicotinoids can cause arrested pupal ecdysis in Lepidoptera.” Scientific Reports 11 (1): 15787. https://doi.org/10.1038/s41598-021-95284-0. https://doi.org/10.1038/s41598-021-95284-0.

Medway Community Forest Coop. 2024. “HWA Video Series” https://www.youtube.com/playlist?list=PLxJ2nQxQ_ld-1TnnyYsncKhoMb0hXqkW1.

Mineau, Pierre. 2024. Neonic Pesticides in Minnesota Water: Their Contamination of and Threats to the State’s Aquatic Ecosystems. https://www.nrdc.org/sites/default/files/2024-12/neonic-pesticides-in-minnesota-water.pdf.

Mineau, Pierre, and Hardy Kern. 2023. Neonicotinoid insecticides: Failing to come to grips with a predictable environmental disaster. (American Bird Conservancy). https://www.researchgate.net/publication/372413480_Neonicotinoid_insecticides_Failing_to_come_to_grips_with_a_predictable_environmental_disaster.

Morse, Douglass H. 2020. “Blackburnian Warbler (Setophaga fusca), version 1.0. .” Birds of the World, edited by A.F. Poole. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/bkbwar/1.0.

Morse, Douglass H., Joe P. Poston, Peter Pyle, and Alan F. Poole. 2024. “Black-throated Green Warbler (Setophaga virens), version 1.2.” Birds of the World, edited by P. G. Rodenwald and N. D. Sly. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/btnwar/1.2/.

Morton, E. S., and R.D. James. 2020. “Blue-headed Vireo (Vireo solitarius), version 1.0.” Birds of the World, edited by A. Poole. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/buhvir/1.0.

Nice, Margaret, and L.B. Nice. 1932. “A Study of Two Nests of the Black-throated Green Warbler.” Bird-Banding 3 (3): 95-105. https://www.jstor.org/stable/20699029.

Pomeluzi, P., M.A. Van Horn, and T. M. Donovan. 2020. “Ovenbird (Seiurus aurocapilla), version 1.0.” Birds of the World, edited by A.F. Poole. Ithaca, New York: Cornell Lab of Ornithology. https://birdsoftheworld.org/bow/species/ovenbi1/1.0.

Province of Nova Scotia. No date. Hemlock Woolly Adelgid Management Program Factsheet. https://novascotia.ca/natr/forestprotection/foresthealth/sheets/hemlock-woolly-adelgid.pdf.

Robinson, Scott K., and Richard T. Holmes. 1982. “Foraging Behavior of Forest Birds: The Relationships Among Search Tactics, Diet, and Habitat Structure.” Ecology 63 (6): 1918-1931. https://doi.org/https://doi.org/10.2307/1940130. https://esajournals.onlinelibrary.wiley.com/doi/abs/10.2307/1940130.

Steward, Bruce V., and Tracey A. Horner. 1994. “Control of Hemlock Woolly Adelgid Using Soil Injections of Systemic Insecticides.” Journal of Arboriculture 20 (5): 287-288. https://auf.isa-arbor.com/content/20/5/287.

Sweeney, Jon. 2021. Review of non-target impacts of imidacloprid. Canadian Forest Service. https://nshemlock.ca/sites/nshemlock.ca/files/JS_Review%20of%20nontarget%20impacts%20of%20imidacloprid_wf.pdf.

Voscort, Luca Joshua. 2024. “Pollinators in Eastern Hemlock Forests: Non-target Effects of Imidacloprid Basal-bark Spray for Hemlock Woolly Adelgid Management and Efficacy of Sampling Methods.” Masters of Science, Acadia University. https://scholar.acadiau.ca/node/4269.

Whitehorn, Penelope R., George Norville, Andre Gilburn, and Dave Goulson. 2018. “Larval exposure to the neonicotinoid imidacloprid impacts adult size in the farmland butterfly Pieris brassicae.” PeerJ 6: e4772. https://doi.org/10.7717/peerj.4772. https://doi.org/10.7717/peerj.4772.

Wiggins, Greg, Elizabeth Benton, Jerome Grant, Marie Kerr, and Paris Lambdin. 2018. “Short-term Detection of Imidacloprid in Streams after Applications in Forests.” Journal of Environmental Quality 47 (3): 571-578. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/jeq2017.11.0446.