SDNHM Monarca: Butterfly Beyond Boundaries

Threats to the Monarch Population

Red Gum Eucalyptus and the Lerp Psyllid
The red gum lerp psyllid, a new pest on California's red gum eucalyptus trees, was discovered in 1998 in Los Angeles County, and has currently spread throughout much of the state. These psyllids form a lerp, a term derived from an Australian aboriginal language describing the protective structure produced by the nymphs. The psyllids are small insects that suck sap from leaves causing leaf damage and drop. Prolonged leaf loss hinders photosynthesis, the tree's primary food source. After two or three years of sustained leaf loss, the tree essentially dies of starvation.

Coastal Development
The number of overwintering sites in California is shrinking as Monarch oases vanish under coastal development. It is unclear how further habitat destruction will affect the Monarch migration in California, as Monarchs have proved resilient enough to weather the destruction of trees native to California by utilizing Eucalyptus groves, native to Australia, as their winter homes.

Human Interference In Overwintering Sites
Although parks are protected from developmental threats, they are not necessarily safe Monarch overwintering sites. Areas adjacent to a park are subject to development and cutting, which reduces wind protection and alters the delicate microclimate of the site. Further, well-known sites suffer as large numbers of visitors disturb the Monarchs through vegetation destruction, physical intrusion, and other bothersome activity.

Oyamel Fir Deforestation
With skyrocketing population growth in Mexico, arable land and wood are in great demand. Local farmers are moving further and further up the mountainside into Monarch habitat, cutting trees for fuel and construction as well as to provide land for their crops. Illegal commercial logging is also on the increase, destroying Monarch habitat through relentless selective cutting and some clear cutting. Bad weather has always been a threat to the Monarch. By destroying the Oyamel Fir forest canopy, humans alter the delicate microclimate and put large Monarch populations as risk for freezing. Fewer trees allow strong winds to further dry out the forest, thereby reducing possible overwintering sites for Monarchs.

Genetically Altered Crops
Researchers have found that wind-borne pollen from genetically altered corn may kill Monarch butterflies. This Bt corn was developed to protect itself from the European Corn Borer with a toxin it produces in its tissues. While the developers succeeded in creating an insect resistant crop strain, researchers state that Monarch caterpillars fed milkweed leaves dusted with Bt pollen ate less, grew more slowly, and suffered a higher mortality rate than those reared on milkweed leaves dusted with pollen from a non-Bt corn strain. Milkweed, which is the Monarch caterpillars' only food, grows near many of those fields in America's Corn Belt, the heart of the Monarch's breeding range.

Monarca | Exhibits