3 years ago



application period later

application period later into the growing season when milkweed is more susceptible to glyphosate. Additional monarch habitat is being lost due to the rapid conversion of grasslands and other milkweed-containing land types to corn and soybean fields to produce biofuels. Most remaining monarch habitat in the Midwest is on Conservation Reserve Program (CRP) lands. This habitat is threatened by ongoing conversion of these lands to corn and soybean production, a change driven by federal biofuels policy. Nationally, CRP acreage has shrunk by 11.2 million acres (30 percent) since 2007, with more than half of this decline occurring in the Midwest, which has lost 6.2 million CRP acres. This land-use change has resulted in the widespread elimination of milkweed from these habitats due to glyphosate use. Glyphosate used in conjunction with Roundup Ready crops has nearly eliminated milkweed from cropland throughout the monarch’s vital Midwest breeding range. It is estimated that in Iowa, for example, cropland lost 98.7 percent of its milkweed from 1999 to 2012. In just the 13 years from 1999 to 2012, it is estimated there was a 64 percent decline in overall milkweed in the Midwest, most of which was from croplands. Because cropland milkweed produces nearly four times as many monarchs as plants in other settings, milkweed loss in corn and soybean fields has had a disproportionate impact on monarch numbers. It is estimated that in 2012, the Midwest produced 88 percent fewer monarchs than it did in 1999. Monarch habitat is further threatened by the imminent introduction of new herbicide-resistant crops that are genetically engineered to now be resistant to multiple herbicides including for the first time 2,4-D and dicamba, which will be used in addition to glyphosate. Herbicides frequently drift beyond the boundaries of crop fields to affect wild plants growing nearby. These new genetically engineered crops will lead to sharply increased herbicide use, continued elimination of common milkweed from cropland, and reduction via herbicide drift of flowering plants that provide monarch adults with nectar, thereby threatening monarch nectaring habitat. Remnant monarch habitat outside of croplands is also being lost and degraded. Monarch breeding, nectaring, and wintering habitats have also been lost to development, and this threat is ongoing. Between 1982 and 2010, 43 million acres of land in the United States were newly developed, representing a 58 percent increase in developed land over a roughly 30-year period. Of note, more than 37 percent of developed land in the United States was developed during the last 28 years. East of the Rockies, it has been very roughly estimated that approximately 167 million acres of monarch habitat, an area about the size of Texas, may have been lost since the mid-1990s due to agricultural changes and development including nearly onethird of the monarch’s total summer breeding range. Monarch breeding habitat west of the Continental Divide is being lost due to urban and rural development, aggressive roadside management, herbicides, intensification of agriculture, and long-term drought. Glyphosate is also heavily used in the western portion of the monarch’s range, and may be degrading habitat there as well. The monarch is also threatened in its winter range. Monarch wintering habitat in California is threatened by development and natural senescence. Monarch wintering habitat in Mexico is Monarch ESA Petition 8

threatened by logging, forest diseases, and climate change. Though large-scale illegal logging in the Mexican winter range has largely been curtailed, the economy of the monarch butterfly region faces serious economic challenges which catalyze small-scale illegal logging as a shortterm option to cope with poverty. Finally, climate change poses a dire threat to monarch habitat. Several scientists have predicted that the monarch’s overwintering habitat in Mexico may be rendered unsuitable by global climate change, and that much of the monarch’s summer range may also become unsuitable due to increasing temperatures. Factor Two: Disease and Predation Disease and predation are significant sources of mortality for monarchs. In light of recent population declines and the major threats facing monarch habitat, either predation or disease or both could rise to population-level threats putting the monarch butterfly at risk of extinction. Numerous pathogens infect monarchs including viruses, bacteria, and protozoan parasites. The parasite Ophryocystis elektroscirrha (OE) is the most studied of monarch parasites and is of particular concern. Monarchs that are infected with these protozoa do not fly as well or live as long as uninfected butterflies. OE disproportionally affects female butterflies and may be responsible for the declining percentage of females in the population, which has long-term implications for monarch survival and recovery. The drastic reduction in milkweed availability in agricultural fields and other factors reducing monarch habitat pushes butterflies into smaller habitat patches where they may be at higher risk of disease transmission. Global climate change magnifies the threat posed to monarchs from disease. Climate change could influence butterfly disease prevalence by affecting pathogen development, survival rates of parasites and hosts, processes of disease transmission, and stress and host susceptibility. The release of commercially-reared monarchs also heightens the threat posed to wild monarchs by disease due to both increased exposure risk and the potential introduction of novel strains of pathogens or pathogens that have evolved higher virulence in captivity. Decreased monarch population sizes and reduced habitat availability exacerbate the threat of predation and parasitism to monarchs. The protective chemicals monarchs obtain from milkweeds provide some defense against predation, but monarchs have many natural predators, some of which are capable of consuming large numbers of eggs, caterpillars, and butterflies. Ants are a common predator on monarch eggs and have been recorded consuming 100 percent of eggs at some study sites. Monarch caterpillars are subject to high levels of predation and parasitism. A large suite of invertebrate predators including ants, spiders, crab spiders, and wasps prey on developing monarch larvae, and several species of flies and wasps parasitize larvae. Mortality rates as high as 100 percent at study sites have been reported for monarch caterpillars due to parasitism. Overall, only approximately 8 to 12 percent of monarch eggs and larvae survive to become adults. Adult monarch mortality rates as high as 44 percent from bird predation have been reported from winter colonies in Mexico. Overwintering adults are also subject to predation from mice, with mortality rates as high as 5 percent of an overwintering colony. Migrating and breeding adults face predation from birds, wasps, spiders, mantids, and dragonflies. While predation is a natural phenomenon, high levels of predation are of increasing Monarch ESA Petition 9

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