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The Hoya Question

Two of our New Zealand correspondents, Kenn and Noeline Bates, indicated that monarchs use yet another plant (maybe a whole group of plants) known as a wax plant in the genus Hoya

http://www.succulent-plant.com/hoya.html

Hoyas are widely cultivated as ornamental plants and there are several web sites such as

http://www.teessidecacti.org/BCSS/GALLERY/PICTURES/HOYA/hoya_004.htm

illustrating the different cultivars available commercially (e.g. Hoya carnosa). As it turns out, the Hoyas are in the milkweed family, Asclepiadacae (now Apocynaceae). The Bates' report that female monarchs lay eggs on this plant and that larvae feed and reach the pupal stage on Hoya bella. Unfortunately, the monarch pupae died from what might have been an outbreak of the protozoan Ophryocystis or exposure to the cold before they emerged so it is still not clear whether they would have become normal adults. Nevertheless, this is an interesting observation and one which should be validated. Hoyas are slow growing and expensive so whatever the outcome, these plants will not become a useful host for monarch culture. Even so, the chemistry of the plant with respect of oviposition and feeding stimuli as well as the presence of toxic compounds that might be used by monarchs feeding on this plant would be of interest.