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How the situation of milkweed influences egg laying and the survival of monarchs



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Among the results of a study on the habitat preferences of Monarch butterflies ( Danaus plexippu ) for laying eggs and the rate of predators of their eggs, researchers found The first 24 hours after oviposition indicate that weekly egg examinations are not sufficient to differentiate the preference for the egg-laying habitat from the losses due to predators. (Credit: Steven Katovich, USDA Forest Service, Bugwood.org)

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The results of a study Based on the habitat preferences of Monarch butterflies ( Danaus plexippu ) for laying eggs and the rate of robbery of their eggs, Michigan State University researchers found that most predators appeared in the first 24 hours after laying eggs, suggesting that weekly egg surveys are not enough (Photo: Steven Katovich, USDA Forest Service, Bugwood.org)

By Paige Embry

A monarch butterfly ( Danaus plexippus ) weighs about as much as a paperclip, but the summer is coming to an end These tiny animals begin a hike that can cover up to 4,800 kilometers, with the eastern population traveling to Mexico and the western one dividing into two wipe off the trip to the California coast or further south to Mexico. After the monarchs have made their way through the winter, they fly north, but this journey is more of a relay race than a marathon in which successive generations each cover one stage -id = "11261" data-permalink = "https: // entomologytoday .org / 2019/05/14 / how-milkweed-location-influencing-monarch-butterfly-egg-laying-survival / paige-embry / "data-orig-file =" https://i1.wp.com/entomologytoday .org / wp-content / uploads / 2019/05 / Paige-Embry.jpg? fit = 125% 2C143 & ssl = 1 "data-orig-size =" 125,143 "data-comments-opens =" ​​1 "data-image -meta = "{" Aperture ":" 10 "," Credit ":" "," Camera ":" Canon EOS 70D "," Caption ":", "created_timestamp": "1461177681", "copyright": ", "focal_length": "92", "iso": "400", "shutter_speed": "0.033333333333333", "title": "," guidance ":" 1 "}" data-image-title = "Paige Embry" data -image-description = "

Paige Embry

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Paige Embry

Over the last 20 years, the eastern monarch population has fallen by an estimated 80 percent, with one theory of decline being the emergence of herbicides. also called "Roundup-Ready") corn and Soybeans in 1996, the primary host plant of the monarch, the ordinary m milkweed ( Asclepias syriaca ), from fields of the Midwest. According to one study, between 1999 and 2014, the Midwest lost more than 860 million spurge, mainly on agricultural fields.

Surprisingly, some studies have shown that the survival rates of monarch eggs in spurge are higher in row crops than in prairie areas. Andrew Myers, Ph.D. The Michigan State University (MSU) Landis Lab candidate says it was this "fascinating mystery" that led to a study published in Environmental Entomology last week.

Myers and Christie Bahlai, Ph.D. from Kent State University and Dr. Ing. Douglas Landis of MSU wanted to find out if this difference in habitat was due to monarchs laying more eggs in row crops or that predation rates were lower there – or both. They had some unexpected results.

A Two-Phase Experiment

The fieldwork took place in 2016 and 2017 at the MSU Kellogg Biological Station and was divided into two parts: habitat preference for oviposition and predation rates in each habitat. In both phases, potted wolfgrass plants were used, which were placed in four different habitat blocks: corn, soy, raw food and prairie.

In 2016, the monarchs laid the most eggs on spurge in corn, followed by prairie and bare ground.In 2017, the butterflies preferred spurge during the barren ground and joined the corn habitats for second place were. Perhaps the biggest surprise was that this was the case for both years. Last ybean came, a different result than previous studies.

For the predator study, the researchers pasted eggs (with the school's favorite glue, Elmer's glue) onto the milkweed. During the first 24 hours, the team checked the eggs every two to three hours and counted and identified the predators throughout the night. Myers notes, "On the prairie plots crawled both arthropod herbivores and predators that I rarely saw during the day." He was surprised "how effectively predators and parasitic arthropods regulate the herbivore populations. … [It] has really increased my awareness and appreciation for the biological control services offered by insects. "

Food stalls

  • Both predation rates and oviposition preferences varied from one habitat to another.
  • Maize was the best habitat when both the preference for oviposition Myers also notes that corn has other risk factors, such as pesticides.
  • Several factors may contribute to the conflicting habitat outcomes, including the weather, which was significantly different between the two years
  • Most of the predators occurred in the first 24 hours, weekly egg replacements are not enough to differentiate the preference for oviposition of losses due to predators. [1965902] 4] Regarding what people should know about monarchs in general or the newspaper in particular, Myers says, "Monarchs are intriguing and beautiful and precious to themselves, but I think it is helpful to them Recent research indicates that insect wealth is declining as a common phenomenon, and this trend should really force us to question what goes wrong when we look at agriculture and our responsibility to nature

    Paige Embry is a freelance science journalist from Seattle and author of Our Native Bees: North America's Endangered Pollinators and the Battle for Their Salvation Email: paembry @ comcast. net.

    Editor's Note: This article was updated on May 15 to discuss the migration objectives of the Eastern and Western describe more closely the populations of the monarch butterflies.

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