FAIRFAX CA - SEPTEMBER 12: O'Donnell and Son Nursery advertises milkweed plants and seeds to support monarch butterflies in Fairfax, Calif. on Monday, Sept. 12, 2022. (Alan Dep/Marin Independent Journal)

Some monarch butterfly researchers are questioning Marin County and other counties’ recent decision to ban tropical milkweed sales as a way to protect the state’s dwindling populations of the iconic orange-and-black insects.

Marin — along with Contra Costa, San Mateo and Ventura counties — prohibited nurseries from selling a species of tropical milkweed known as Asclepias curassavica after the California Department of Agriculture recategorized it as a noxious weed. The “B” classification by the state allows county agricultural commissioners to enact bans on the sale of the plant. Ventura County had initially requested the state to reclassify the plant, according to California Department of Agriculture spokesman Jay Van Rein.

Milkweed plants are vital for monarch butterflies, which lay their eggs exclusively on the plants. The hatched caterpillars eat the milkweed, imbuing them with the plant’s protective toxins.

The rationale for Marin County’s ban, endorsed by the Xerces Society for Invertebrate Conservation nonprofit group, is that tropical milkweed species do not die off during the winter months as native milkweed species typically do. As a result, the butterflies can be exposed to harmful microscopic protozoan parasites that can kill monarch caterpillars and butterflies, which have had steep population declines in the past few decades.

Tropical milkweed also does not die back during the winter as native milkweed typically does. The Xerces Society and the Marin agriculture commissioner’s office said this works to both prolong exposure to parasites and encourages butterflies to breed during a time when they should be migrating or roosting in their overwintering sites.

Hugh Dingle, a retired University of California at Davis entomology professor who has studied monarch butterfly migration for more than two decades, said the bans are “basically a wasted effort” and that the focus should be on larger threats such as pesticide and herbicide use. All species of milkweed carry …read more

Source:: East Bay – Entertainment

      

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