"Less than 20 years ago, a billion butterflies from east of the Rocky Mountains reached the oyamel firs, and more than a million western monarchs migrated to the Californian coast to winter among its firs and eucalypts."In 2013, the numbers reached rock bottom in the Midwest and Mexico with about 80-90% drop in numbers. Although the numbers in the fall of 2014 appeared to be encouraging, both Ms Satterfield and Ms Sonia Altizer, an ecologist at Georgia and Ms Satterfiled's adviser, were cautious not to be too hopeful that the good numbers represented a recovering migration. In fact, they were concerned that the well-meaning efforts of butterfly lovers may be accountable for the monarch's current plight.
In a typical year, the first generation Monarch butterflies fly from Mexico to the Southeast when spring approaches and the native milkweeds start to grow. By fall, when the milkweeds die back, up to two more generations of sexually immature Monarchs develop. That is when they make the flight back to Mexico to avoid the approaching winter before the cycle repeats.
The Monarch butterfly's life cycle is intricately synchronized with the native milkweed species such that their migratory patterns are split amongst several generations. The exotic tropical milkweed is now widely used, over the native species, by amateur conservationists to replenish declining populations of milkweed in an attempt to raise the butterfly populations, which may bring about unseasonal breeding, increase the butterfly's exposure to diseases and lead to reproductive failure.
It is reported in the 2012 journal Insect Conservation and Diversity that 60% of native milkweeds disappeared over a span of 10 years between 1999 and 2009. This was documented to be the result of increased applications of Roundup, a broad spectrum Glyphosate systemic herbicide, used to control weeds amongst commercial crops such as corn and soybean, which are genetically engineered to tolerate the weedkiller. Whilst the native milkweeds die, they are replaced by the tropical milkweeds where the migrating Monarchs lay their eggs and spread the spores of an obligate protozoan parasite Ophryocystis elektroscirrha (OE), which was discovered in Florida in the 1960s, that infects the Monarch and Queen butterflies by killing foraging caterpillars or affecting the adults' ability to fly or reproduce normally, thereby reducing their survival rates and fitness.
However, some optimists are positive that the tropical milkweeds make up only a small fraction of all the milkweeds available in the landscape and are hopeful that the Monarchs have sufficient native milkweeds in the abundant landscape of Eastern U.S. to feed when they return in spring.
Meanwhile, Ms Satterfield is continuing her research work on tracing the migratory breeding of Monarchs at tropical milkweed sites to determine if they have abandoned their migratory patterns and hopes to be able to do her part to protect the great North American journey of the Monarchs while there is still hope.