Remove or control non-native or problematic plants

Overall effectiveness category Evidence not assessed
Number of studies: 9
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Effectiveness

not assessed
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not assessed
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Background information and definitions

Invasive or dominant native plant species can alter habitat structure, outcompeting the host plants of butterflies and moths, or making the habitat otherwise unsuitable (Sinclair 2002). Removal of problematic plants may be conducted by hand, with machinery, or by targeted herbicide application (e.g. Glaeser & Schultz 2014). This action includes studies which have tested any of these methods, alone or in combination.

Note that herbicide application may also have negative effects on butterflies and moths (Russell & Schultz 2010) and the choice of which herbicide to use may be important for minimising harms (Schultz et al. 2016). For studies testing the effect of reducing herbicide application, see “Restrict certain pesticides or other agricultural chemicals” and “Reduce fertilizer, pesticide or herbicide use generally”.

^{Glaeser R.M. & Schultz C.B. (2014) Characterizing a contentious management tool: the effects of a grass-specific herbicide on the silvery blue butterfly. Journal of Insect Conservation, 18, 1047–1058.}

^{Russell C. & Schultz C.B. (2010) Effects of grass-specific herbicides on butterflies: an experimental investigation to advance conservation efforts. Journal of Insect Conservation, 14, 53–63.}

^{Schultz C.B., Zemaitis J.L., Thomas C.C., Bowers M.D. & Crone E.E. (2016) Non-target effects of grass-specific herbicides differ among species, chemicals and host plants in Euphydryas butterflies. Journal of Insect Conservation, 20, 867–877.}

^{Sinclair L.J. (2002) Distribution and conservation requirements of Notoreas sp., an unnamed Geometrid moth on the Taranaki coast, North Island, New Zealand. New Zealand Journal of Zoology, 29, 311–322.}

Study locations

Key messages

Nine studies evaluated the effects on butterflies and moths of removing or controlling non-native or problematic plants. Five studies were in the USA and one was in each of Poland, South Africa, Australia and Mauritius.

COMMUNITY RESPONSE (2 STUDIES)

Richness/diversity (2 studies): Two studies (including one replicated, paired, site comparison study and one controlled study) in Mauritius and the USA found that sites where invasive plants were removed by weeding or cutting and applying herbicide (in one case along with fencing to exclude non-native pigs and deer) had a greater species richness of butterflies than untreated sites. One of these studies also found that sites where Chinese privet was removed had a similar species richness of butterflies to sites which had not been invaded.

POPULATION RESPONSE (8 STUDIES)

Abundance (7 studies): Four of six studies (including three controlled studies, one before-and-after study and two site comparison studies) in Poland, South Africa, the USA and Mauritius found that sites where trees and shrubs were removed or invasive plants were cut to a similar height to native plants, or removed by weeding or cutting and applying herbicide(in one case along with fencing to exclude non-native pigs and deer), had a greater abundance of Apollo butterflies, a higher density of Fender’s blue eggs, or higher total abundance of butterflies, compared to before removal or untreated sites. One of these studies also found that sites where Chinese privet was removed had a similar abundance of butterflies to sites which had not been invaded. The fifth study found that in plots where herbicide was applied to control invasive grasses, the abundance of Columbia silvery blue eggs and caterpillars was similar to unsprayed plots. The sixth study found that, after prescribed burning, an area where bracken fern was also removed had fewer Brenton blue butterfly eggs than an area without removal. One study in Australia reported that a population of purple copper butterfly caterpillars translocated to an area where invasive plants had been removed, along with host plant translocation and other habitat management, increased in number compared to at the time of translocation.

Survival (2 studies): One replicated, randomized, paired, controlled study in the USA found that in plots where herbicide was applied to control invasive grasses, the survival of Columbia silvery blue eggs and caterpillars was similar to unsprayed plots. One replicated, randomized, controlled study in the USA found that one herbicide commonly used to control invasive grasses reduced the survival of snowberry checkerspot caterpillars, but two other herbicides did not affect the survival of snowberry checkerspot, Edith’s checkerspot or Baltimore checkerspot caterpillars.

BEHAVIOUR (4 STUDIES)

Use (3 studies): Two of three randomized, controlled studies (including two replicated, paired studies and one before-and-after study) in the USA found that sites where invasive oat-grass was cut to a similar height to native plants, or where Eastern white pine was removed, were used more by Fender’s blue and frosted elfin butterflies than untreated sites. The third study found that habitat use by Columbia silvery blue butterflies was similar in plots where herbicide was applied to control invasive grasses and in unsprayed plots.
Behaviour change (1 study): One before-and-after study in Poland found that removal of trees and shrubs, in addition to the release of captive bred adults and pupae, allowed adults from two previously separated populations of Apollo butterflies to mix.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

A before-and-after study in 1991–1994 in a limestone montane grassland reserve in southern Poland (Witkowski et al 1997) found that removing trees and shrubs, in addition to releasing captive bred adults and pupae, increased Apollo butterfly Parnassius apollo numbers, and allowed adults from two previously separated populations to mix. Removing trees and shrubs from an area with two small, separated populations of Apollo butterflies, along with releasing captive bred individuals, increased the total number of adults observed from 22 in 1991 to 60 in 1994. Mark-recapture surveys estimated that the total population increased from 44 adults in 1992 to 67 in 1994, and showed that the previously separated populations were mixing. In 1992, trees and shrubs were removed from an area of scree in the Pieniny Mountains, creating a corridor between the locations of two Apollo butterfly populations. From 1991–1994, captive bred butterflies were also released annually at the site (339 males, 362 females and four pupae in total). Butterfly numbers were recorded each year but survey details are not provided. Mark-recapture surveys were also conducted in 1992–1994 to estimate population size and determine connectivity between the original two populations.
Study and other actions tested
Referenced paper
Witkowski Z.J., Adamski P., Kosior A. & Plonka P (1997) Extinction and reintroduction of Parnassius apollo in the Pieniny National Park (Polish Carpathians). Biologia, 52, 199-208.
A site comparison study in 2000–2002 in one shrubland site in the Western Cape province, South Africa (Edge 2002) reported that after prescribed burning there were fewer Brenton blue butterfly Orachrysops niobe eggs in an area where bracken fern Pteridium aquilinium was removed compared to where it was not removed. In an area that had been burned, there were fewer Brenton blue eggs/Indigofera erecta host plant in the section with bracken fern control (November 2001: 0.035 eggs/100 plants; January–February 2002: 0.38 eggs/100 plants) than in the area with no control (November 2001: 0.32 eggs/100 plants; January–February 2002: 0.81 eggs/100 plants). Results were not tested for statistical significance. In September 2000, a 2,700 m² area of reserve was burned. Prior to the burn, in over 1,000 m² of the area bracken fern was cut and 0.2 m of topsoil was turned over (“skoffeled”). In that area and another 1,400 m², natural succession was allowed after the burn. In another 300 m²of the burned area, bracken fern was removed manually for 6 months after the burn. In a 1,500 m² area of reserve that was not burned, paths were cut with shears in July 2001, avoiding trees, large bushes and Indigofera erecta plants, and thereafter new bracken ferns were removed manually. In November 2001 and January–March 2002, all Indigofera erecta plants identified in the burned and unburned areas were checked for eggs and larvae.
Study and other actions tested
Referenced paper
Edge D. (2002) Some ecological factors influencing the breeding success of the Brenton Blue butterfly, Orachrysops niobe (Trimen)(Lepidoptera: Lycaenidae). Koedoe, 45, 19-34.
A study in 2004–2007 in one shrubland in New South Wales, Australia (Mjadwesch & Nally 2008) reported that, three years after translocation, a population of purple copper butterfly Paralucia spinifera caterpillars that had been moved from land designated for development to an adjacent area of retained habitat and compensatory habitat where invasive plants had been removed, along with host plant translocation and other habitat management, increased in number compared to the time of translocation. A site designated for development and adjacent retained and compensatory habitat initially had an estimated purple copper caterpillar population size of 2,000. After the development, habitat management and translocation of butterflies into the retained and compensatory habitat, the estimated caterpillar population size reduced to 1,600 in the following year but increased to an estimated 1,995 two years and 2,780 three years after translocation. Of the caterpillars found in the third year, 39% were in the compensatory habitat and 61% were in the area of retained original habitat. In 2004–2005, two thirds of an area of purple copper butterfly habitat was cleared for road-building and an area adjacent to the retained third was designated as compensatory habitat. Invasive plants, including hawthorn Crataegus monogyna, radiata pine Pinus radiata, cotoneaster Cotoneaster sp., blackberry Rubus fruticosus sp. and briar rose Rosa rubiginosa were cleared from the retained and compensatory habitat and caterpillars and their host plant blackthorn Bursaria spinosa var. lasiophylla were moved from the land about to the cleared to the retained and compensatory habitat. Over 12 nights in December 2004–January 2005, a total of 1,260 caterpillars were moved. In 2005–2007 blackthorn plants in the retained and compensatory habitats were surveyed for caterpillars, signs of their feeding, and their mutualistic ants Anonychomyrma itinerans. Estimated caterpillar population sizes were calculated by multiplying the number of caterpillars found by five.
Study and other actions tested
Referenced paper
Mjadwesch R. & Nally S. (2008) Emergency relocation of a Purple Copper Butterfly colony during roadworks: Successes and lessons learned. Ecological Management & Restoration, 9, 100-109.
A replicated, randomized, paired, controlled study in 2004 in two upland prairies in Oregon, USA (Severns 2008) found that plots where non-native tall oat-grass Arrhenatherum elatius had been cut were used by Fender’s blue Icaricia icarioides fenderi more than uncut plots. In plots where oat-grass had been cut, Fender’s blue butterflies were more likely to bask (76–80% of 166 butterflies) or lay eggs (69% of 71 females) and less likely to fly straight over (17–24% of 166 butterflies) than in plots where oat-grass had not been cut (bask: 13–49% of 105 butterflies; lay eggs: 13% of 45 females; fly over: 47–87% of 105 butterflies). In cut plots, the density of eggs (2.5 eggs/leaf) was higher than in uncut plots (1.0 eggs/leaf). In May 2004, four pairs of plots (1-m radius, 2.5 m apart) were selected in each of two remnant prairies (1–5 ha). In one plot/pair, oat-grass was cut with shears to the same height as the native Kincaid’s lupine Lupinus sulphureus kincaidii leaves. In the remaining plots oat-grass was not cut. In May 2004, three pairs of plots/prairie were observed for 50 minutes, and butterflies flying over, basking, or laying eggs in each plot were recorded. In June 2004, all lupines within each plot were searched for eggs.
Study and other actions tested
Referenced paper
Severns P.M. (2008) Exotic grass invasion impacts fitness of an endangered prairie butterfly, Icaricia icarioides fenderi. Journal of Insect Conservation, 12, 651-661.
A randomized, controlled, before-and-after study in 2001–2006 in a heathland in New York, USA (Pfitsch & Williams 2009) found that areas where eastern white pine Pinus strobus had been removed were used more by frosted elfin butterflies Callophrys irus. In areas where eastern white pine trees were removed, the number of elfins seen after removal (11% of all butterflies recorded) was higher than before removal (3% of all butterflies), but there was no significant change in areas where trees were not removed (before: 12% of all butterflies; after: 8% of all butterflies). After tree removal, there were 12 male territories on a 1-ha dune, compared to nine territories before removal. In May 2002, seventeen white pines growing over lupine plants were selected and, in January 2003, eight were randomly removed. From April–June 2001–2006, frosted elfins were surveyed along a 12-minute transect 10–15 times/year. The location of each butterfly, and each male territory, was mapped, and the number within 3 m of the removed and not removed trees was counted.
Study and other actions tested
Referenced paper
Pfitsch W.A. & Williams E.H. (2009) Habitat restoration for lupine and specialist butterflies. Restoration Ecology, 17, 226-233.
A replicated, paired, site comparison study in 1998 in eight lowland forest sites in Mauritius (Florens et al. 2010) found that areas where invasive plants had been removed, together with fencing to exclude non-native pigs and deer, had a higher abundance and species richness of butterflies than sites where invasive species control had not been conducted. In sites where invasive plants had been removed and exclusion fencing installed, both the abundance (5.9 individuals/100 m) and species richness (9 species) of native butterflies was higher than in sites where no weed removal or fence installation had been conducted (abundance: 0.3 individuals/100 m; richness: 3 species). From 1986–1996, eight Conservation Management Areas (0.4–6.0 ha) were fenced to try to exclude non-native pigs and deer, and were regularly hand-weeded (1–3 times/year) to remove invasive plants, primarily strawberry guava Psidium cattleianum, rose apple Syzygium jambos, Ossaea marginata and Christmas berry Ardisia crenata. From April–June 1998, butterflies were surveyed on point counts along four to six 100-m transects in each weeded plot and in adjacent, non-weeded plots with an equivalent number of native canopy trees.
Study and other actions tested
Referenced paper
Florens F.B.V., Mauremootoo J.R., Fowler S.V., Winder L. & Baider C. (2010) Recovery of indigenous butterfly community following control of invasive alien plants in a tropical island's wet forests. Biodiversity and Conservation, 19, 3835-3848.
A controlled study in 2005–2012 in seven riparian forests in Georgia, USA (Hudson et al. 2013) found that areas where Chinese privet Ligustrum sinense had been removed had a higher abundance and species richness of butterflies than areas infested with privet. Five years after privet removal had finished, removal sites had a higher abundance (121–146 individuals/plot) and species richness (10–12 species/plot) of butterflies than privet-infested sites (abundance: 30 individuals/plot; richness: 4 species/plot). Butterfly abundance and species richness in removal sites were also similar to reference sites with no privet invasion (abundance: 190 individuals/plot; richness: 14 species/plot). In October 2005, Chinese privet was removed from two infested 2-ha plots. At one site, a mulching machine ground up the privet and at the other site privet was hand-cut with chainsaws. Privet stumps were sprayed with herbicide (30% triclopyr or 30% glyphosate) after cutting, and sprouts and seedlings were sprayed with 2% glyphosate in December 2006. Removal sites were compared with two infested sites where privet was not removed, and three reference sites with little or no privet invasion. From March–October 2012, butterflies were sampled for one week/month using five blue and five yellow pan traps/plot. Traps were filled with soapy water and suspended 30 cm above ground.
Study and other actions tested
Referenced paper
Hudson J.R., Hanula J.L. & Horn S. (2013) Removing Chinese privet from riparian forests still benefits pollinators five years later. Biological Conservation, 167, 355-362.
A replicated, randomized, paired, controlled study in 2013 in an upland prairie in Oregon, USA (Glaeser & Schultz 2014) found that applying herbicide to control invasive grasses in the early spring did not increase use of the habitat by Columbia silvery blue butterflies Glaucopsyche lygdamus columbia, or the number or survival of eggs or caterpillars. In sprayed plots, the number of butterfly visits (12 individuals/plot), the time spent in the plot (34–154 seconds/visit), and the proportion of butterflies which landed (18–73%) did not differ significantly from unsprayed plots (visits: 10 individuals/plot; time: 40–98 seconds/visit; landed: 16–67%). Similarly, in sprayed plots, the number of eggs (3.9/subplot), caterpillars (1.3/subplot) and survival of eggs to large caterpillars (15%) did not differ significantly from unsprayed plots (eggs: 4.1/subplot; caterpillars: 1.3/subplot; survival: 14%). In March 2013, thirty-two plots (20 × 20 m) were paired based on equal host plant (Kincaid’s lupine Lupinus oreganus) cover (>15 m²/plot). In each pair, one plot was randomly assigned to the herbicide treatment (sprayed in March with 326 g/ha Fusilade DX® grass-specific herbicide and 425 g/ha Nufilm®) and the other was left unsprayed. In May 2013, the time spent in each plot by adult butterflies, and whether or not they landed, was recorded during 15-minute observations in 30 plots. From late April 2013, hatched and unhatched eggs were counted five times, and the number and size of caterpillars was counted eight times, at 4–5 day intervals in each of three 60 × 60 cm subplots/plot, centred on randomly selected flowering lupines.
Study and other actions tested
Referenced paper
Glaeser R.M. & Schultz C.B. (2014) Characterizing a contentious management tool: The effects of a grass-specific herbicide on the silvery blue butterfly. Journal of Insect Conservation, 18, 1047-1058.
A replicated, randomized, controlled study in 2013–2014 in a greenhouse in Washington, USA (Schultz et al. 2016) found that one of three herbicides commonly used to control invasive grasses reduced the survival of snowberry checkerspot Euphydryas colon caterpillars, but not Edith’s checkerspot Euphydryas editha colonia or Baltimore checkerspot Euphydryas phaeton caterpillars. The survival of snowberry checkerspot caterpillars sprayed with sethoxydom and NuFilm (78%) was lower than caterpillars sprayed with water (98%), but the survival of caterpillars sprayed with clethodim and NuFilm (85%), fluazifop-p-butyl and NuFilm (88%) or NuFilm alone (93%) was not significantly different from those sprayed with water. The survival of caterpillars sprayed with fluazifop-p-butyl and NuFilm (snowberry checkerspot: 51–89%; Edith’s checkerspot: 87–88%; Baltimore checkerspot: 91–95%) was not significantly lower than unsprayed caterpillars (snowberry: 55–92%; Edith’s: 84–92%; Baltimore: 96–98%). Eggs were collected from wild-caught females (snowberry and Edith’s checkerspot) or wild-laid egg clusters (Baltimore checkerspot), and caterpillars were reared on ribwort plantain Plantago lanceolata. In August 2014, forty snowberry checkerspot caterpillars were exposed to each of five treatments: one of three herbicides used regularly for prairie restoration (fluazifop-p-butyl, sethoxydim and clethodim) applied using their most common formulations (Fusilade DX^®, Poast^® and Envoy Plus^®, respectively) in combination with a “sticker-spreader” (adjuvant NuFilm IR^®); the NuFilm alone; or a water treatment (see paper for details). Caterpillars were kept in containers and fed fresh plantain exposed to the same treatment. In August–September 2013, caterpillars of three species were randomly assigned to two treatments, sprayed with Fusilade and NuFilm or unsprayed, and placed in groups of 20 in 5–6 host plant microcosms/treatment/species. In both experiments, survival to overwintering was recorded.
Study and other actions tested
Referenced paper
Schultz C.B., Zemaitis J.L., Thomas C.C., Bowers M.D. & Crone E.E. (2016) Non-target effects of grass-specific herbicides differ among species, chemicals and host plants in Euphydryas butterflies. Journal of Insect Conservation, 20, 867-877.

Please cite as:

Bladon A.J., Bladon, E. K., Smith R.K. & Sutherland W.J. (2023) Butterfly and Moth Conservation: Global Evidence for the Effects of Interventions for butterflies and moths. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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This Action forms part of the Action Synopsis:

Butterfly and Moth Conservation

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