4 years ago



Corn Belt region

Corn Belt region (Wassenaar and Hobson 1998, Oberhauser et al. 2001, Brower et al. 2012a, b; Flockhart et al. 2013, Pleasants and Oberhauser 2012). Due to the loss of common milkweed, Pleasants (in press) estimates that in 2012, the Midwest produced 88 percent fewer monarchs than it did in 1999. Increased herbicide use and drift with new herbicide-resistant crops further threatens continuing loss of milkweed for monarch larvae and loss of nectar resources for monarch adults. Remnant monarch habitat outside of croplands is also shrinking. Habitat loss in the monarch’s U.S. breeding grounds threatens the monarch with extinction because of the significance of this portion of the range to the redundancy, resiliency, and representation of Danaus plexippus plexippus overall, as discussed further in the Significant Portion of Range section of this petition. The rapid loss of milkweed attributable to increased pesticide use and land cover changes puts the monarch at risk of extinction in the foreseeable future (Hartzler 2010, Brower et al. 2012a, b; Pleasants and Oberhauser 2012, Flockhart et al. 2014, p. 18). Extensive loss of milkweed due to increased use of glyphosate and near ubiquitous planting of Roundup Ready crops has contributed substantially to the drastic population decline of eastern monarchs of 90 percent from the twenty-year average, and glyphosate use in California has also likely contributed to the decline of western monarchs. Because monarch survival is dependent on maintaining a large population size, the relatively low remaining population size puts the species at heightened risk of extinction from global climate change, stochastic weather events, disease, predation, and other habitat-destroying activities including further loss of nectar sources from next-generation genetically engineered, herbicide-resistant crops. Development Monarchs are also threatened by habitat loss due to residential, industrial, commercial, and other development activities that cause conversion of habitat. Between 1982 and 2010, 43 million acres of land in the United States were newly developed, bringing the total acreage of developed land to approximately 113 million acres, a 58 percent increase in developed land over a roughly 30-year period (U.S. Department of Agriculture 2013, p. 8). Of note, more than 37 percent of developed land in the 48 conterminous states, Hawaii, Puerto Rico and the U.S. Virgin Islands was developed during the last 28 years, with every one of the 48 conterminous states, Hawaii, and the Caribbean having statistically significant increases in developed land area since 1982 (U.S. Department of Agriculture 2013, p. 8). Development causes direct loss of monarch butterfly habitat. It threatens monarch overwintering sites in coastal California and breeding, nectaring, and roosting sites throughout the country. For example, trees required for winter roosts are uprooted to make way for housing and other urban and suburban infrastructure. Areas with milkweed are converted to lawns, covered with concrete and asphalt, and otherwise made unsuitable for breeding and nectaring. Development also contributes to increased pesticide use which can be harmful to monarchs. More than two decades ago, a California statewide report documented the loss or destruction of 38 overwintering sites in the state, 16 of which were lost to housing developments (Sakai and Calvert 1991). Then, in the 1990s, housing developments replaced 11 additional monarch overwintering sites (Meade 1999). At present, at least three California overwintering sites are slated for housing developments (Sarina Jepsen personal observation). Though the total area of monarch habitat that has been lost to development has not been quantified, it is certainly substantial and is a threat factor that has been noted by several authors. Monarch ESA Petition 66

Brower et al. (2012a) identify loss of breeding habitat due to land development as one of the primary factors implicated in the drastic downward trend in monarch abundance in recent years (in conjunction with other threat factors, including severe weather events and loss of milkweed due to increased herbicide use caused by the cultivation of genetically-engineered, herbicideresistant crops) (p. 96). Flockhart et al. (2014) also identify urbanization as a contributing factor in the land-use change that is driving monarch declines (p. 4). Development of roads causes direct loss of monarch habitat, and chemicals sprayed on roadsides can also be harmful to monarchs including herbicides. Road maintenance and other related activities may also impact the butterflies. For instance, the application of road salt to melt snow and ice during winter can affect butterflies the following summer. Road salts are applied widely during winter months. For example, in Minnesota in the metropolitan area of Minneapolis and St. Paul, approximately 300,000 tons of sodium chloride are applied to roads each winter (Snell- Rood et al. 2014, p. 1). Sodium is important for the function of neural and muscle tissue and influences brain size and other traits, but can have varying effects at different life stages. Sodium availability is limited in most ecosystems, which likely led to the evolution of sodium cravings and sodium foraging behaviors. For example, adult male butterflies of many species engage in “puddling” to get sodium that they then transfer to females as part of mating practices (Snell-Rood et al. 2014, p. 1). Changes in sodium availability translate into physiological effects on butterflies including effects on neural and muscle tissue development. Excessive sodium, however, appears to have detrimental impacts on monarch larvae. Snell-Rood et al. (2014) reared monarchs on milkweed collected from roadsides or milkweed collected from prairies and found that milkweeds readily take up roadside sodium which is then taken up by larvae. They found that the survival rates of monarch caterpillars were significantly lower on roadside milkweed leaves than on milkweed leaves from prairies (40.5% vs. 58.2%, P = 0.02). In surviving butterflies, the fitness effects of the induced physiological changes were unclear. They also reared cabbage white butterflies (Pieris rapae) on diets with varying levels of sodium and found that butterfly survival was significantly lower on a high-sodium artificial diet than on a medium- or low-sodium diet (high: 10.9%; medium: 34.3%; low: 41.7%; P < 0.0001). Due to widespread loss of milkweed in agricultural fields attributable to increased use of herbicides resulting from near-ubiquitous planting of genetically engineered, herbicide-resistant corn and soybeans, roadside milkweeds are becoming increasingly important habitat for monarchs. Flockhart et al. (2014) estimate that roadside habitats now harbor 10 percent of all milkweeds in eastern North America (p. 16). It is estimated that in Iowa, which is representative of the monarch’s Midwest breeding grounds, roadsides harbored 13 percent of milkweed in 1999, and 36 percent of milkweed in 2012 (based on data supplied by John Pleasants). Reduced caterpillar survival due to road salt could thus have significant effects on monarch populations, particularly so given the newly heightened reliance on roadside milkweed for recruitment. Loss and Degradation of Overwintering Habitat in Mexico The eastern monarch population primarily overwinters in oyamel (sacred) fir (Abies religiosa) forests in the mountains of the Trans-Mexican Volcanic Belt in Central Mexico. The high Monarch ESA Petition 67

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