QIf cross pollination does not occur, why did the incident with milkweed occur thus killing off thousands of monarch butterflies?

If cross pollination does not occur, why did the incident with milkweed occur thus killing off thousands of monarch butterflies?

AExpert Answer

The Eastern monarch butterfly population fluctuates from year to year due to a variety of factors but has declined over the past two decades.  Pollen containing the insecticidal protein derived from Bacillus thuringiensis (Bt) and found in many varieties of corn is not a relevant factor since the vast majority of larvae are rarely exposed to harmful levels of Bt protein [see: Bt Corn and Monarch Butterflies – ARS].  However, there are several factors contributing to the decline that have been identified, including logging of overwintering sites in Mexico, weather events (e.g. freezing temperatures and drought), predation, pathogens and parasites, reduced availability of host plants (milkweed species) and nectar sources across their migration range, and climate change.  The combination of the above stressors has made this species ecologically vulnerable. 


One factor – a decline in milkweeds – has received a lot of attention because monarch butterflies depend on milkweeds for reproduction and population expansion as they migrate northward each year.   Agricultural production systems have been changing to become more productive and environmentally sustainable.  Prior to 1995, farmers already were incorporating more sustainable practices into production, including no-till and conservation tillage systems.  Reducing tillage has enormous benefits, such as less soil erosion, improved soil organic matter, less soil compaction, increased soil moisture, cleaner water, reduced energy use, more wildlife habitat, and less greenhouse emissions that contribute to climate change.  The principle barrier to reducing or eliminating tillage was the challenge of controlling weeds with available soil-applied herbicides.  The advent of herbicide-tolerant crops in the mid-1990s enabled farmers to control weeds better and to more widely adopt reduced tillage systems.  Since the introduction of herbicide-tolerant crops, farmers have increased no-till or reduced tillage systems by about 50 percent in the U.S.  Farmer emphasis on productivity and expansion of reduced tillage systems has led to better weed control (including milkweeds) in and around crop fields. 


To ensure a robust, resilient monarch population that is sustainable despite multiple environmental impacts, there is a growing interest in conservation programs to restore habitat and support monarch recovery.  Restoration and mitigation efforts can be initiated on public and private lands to increase the availability of monarch habitat and facilitate monarch population recovery during the spring-summer migration.  The priority areas include: Conservation Reserve Program (CRP) land, government-owned land, roadsides, utility rights-of-way, and on-farm conservation strips.  Incentive programs at the federal and state level exist to help farmers, U.S. state departments of transportation, and federal land managers to increase biodiversity through restoration programs.  These programs need to grow and expand.


The National Fish and Wildlife Foundation established the Monarch Butterfly Conservation Fund to work on short-term and long-term solutions to restore the monarch population to healthy levels.  Monsanto, government agencies and others in the private sector provided grants to fund Habitat Improvement and Best Management Practices, Organizational Coordination and Capacity, and Regionally Adapted and Native Plant Seed Supply.


Monsanto also announced additional funding support for habitat improvement, research and development of best management practices.  Recipients included:  the National Fish and Wildlife Federation; Monarch Watch, based at the University of Kansas; the Iowa Monarch Conservation Consortium, based at Iowa State University; the University of Illinois-Chicago; the University of Guelph (Canada); and Pheasants Forever.  Additional information about Monsanto’s commitment to collaborating with others to restore habitat for the monarch butterfly can be found in Restoring Natural Habitat for the Monarch Butterfly.

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