A new study by the Xerces Society showed a 74 percent decrease in the number of monarch butterflies (Danaus plexippus) over the last two decades. Butterfly conservationists at the Pacific Grove Museum of Natural History monitor the monarch numbers on the Monterey Peninsula and said the study's results come as no surprise. They are similar to a trend conservationists are seeing locally. Their numbers are going down," museum representative Patrick Whitehurst said. Whitehurst said that between 2014 and 2015, the monarch population at Pacific Grove's sanctuary was cut in half. "Historically speaking, their numbers are much lower than they were in the early '90s," he said.
According to the study, back in 1990, there were about a million monarch butterflies spending their winter on the California coast and that number is down to a little more than 200,000 butterflies.
A possible reason for the decline is a shortage of milkweed, which is the plant on which the butterflies lay eggs and the plant they eat while in the caterpillar stage. Some conservationists say pesticides and overdevelopment may be to blame for their shrinking habitat.
"Here, locally, it's got something to do with development and pesticide use and this is an ag area, lots of agriculture, and there's a lot of pesticides being used so that can definitely hamper their growth and their numbers," Whitehurst said.
Source: KSBW, July 11th, 2016
http://www.ksbw.com/news/monarch-butterfly-population-declines-on-calif…
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