Remove or control non-native or problematic plants
Overall effectiveness category Awaiting assessment
Number of studies: 6
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.
Supporting evidence from individual studies
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
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
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
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
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
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