Decline in Monarch butterfly population

There has been a decline in the population of Monarch butterflies.
The study favours the declining numbers due to the ‘milkweed limitation’ hypothesis.
The hypothesis has a view that the decline in habitat loss was because of the increasing use of glyphosate herbicide on corn and soybean fields in the Upper Midwest region of the US.
The monarch butterfly is the most familiar North American butterfly.
It is considered an iconic pollinator species.
Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9 – 10.2 cm.
Famous for their seasonal migration, millions of monarchs migrate from the US and Canada south to California and Mexico for the winter.
Monarchs have been bred on the International Space Station.