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Thursday - March 14, 2013

From: Springfield, VA
Region: Mid-Atlantic
Topic: General Botany, Non-Natives
Title: Native vs Non-native Insect Host Plants
Answered by: Anne Van Nest

QUESTION:

My understanding of a host plant is that it is a plant that an insect will lay its eggs on. Is this correct? If this is so then can a cultivar be a host plant for the same insect? I have read Mr. Doug Tallamy's book, Bringing Nature Home and several others on native plants and am not sure of the answers to these questions.

ANSWER:

Thanks for this interesting question and concern for the nature of insect host plants. It has long been know that insects vary in their host food preference from being a generalist to a very specific "picky" eater. At the one extreme, is the gypsy moth caterpillar which feeds on hundreds of different types of plants (native and cultivated) within many plant families. This hugely diverse group of food plants has allowed this destructive insect to multiply and become a noxious pest over a wide area. On the other extreme are the insects that feed on only one plant genus (or even rarer on only one plant genus and species).  These insects are exhibiting oligophagy – feeding on a restricted range of food.  An example is the Heliconius melpomene butterfly that feeds specifically on one type of passionflower, Passiflora oerstedii.

Now back to your question.  There are many occasions where insects can feed and reproduce on host plants that are cultivars of native plants.  There are also situations where an insect has adapted to a new host plant (including cultivars) when their native food was not available. There are also examples when an insect has been reduced in numbers because it could not adapt to new food when their original host plants were scarce.  Whether an insect will adapt or die when their native food plants become scarce or non-existent varies from one insect type to the next. But this is a concern.

Dr. Tallamy, author of Bringing Nature Home, Professor and Chair of Entomology and Wildlife Ecology at the University of Delaware, and Director of the Center for Managed Ecosystems has published some interesting information to draw attention to the use of non-natives in our landscapes and reduction in native host plants that results.

He has a website investigating Lepidopteran Use of Native & Alien Ornamental Plants.  Here’s the introduction to this issue:

Landscaping paradigms have promoted the use of alien ornamentals over native plants with ornamental value for over a century. The bias toward landscaping with alien ornamentals has been so complete that the first trophic level in suburban/urban ecosystems throughout U.S. is now dominated by plant species that evolved elsewhere. If alien ornamentals are not the ecological equivalents of native species, particularly in their palatability to herbivores that transfer energy to higher-level consumers, herbivore productivity, as well as the biomass of organisms that depend on herbivores will be compromised in landscapes in which alien plants comprise a large portion of the plant biomass.

Dr. Tallamy has posted a spreadsheet list of native and alien plant genera on this website that gives their ability to support insect herbivores (overall biodiversity). He has ranked all native genera (woody and herbaceous) in terms of the number of Lepidoptera species recorded using them as host plants. Ultimately, He would like this ranking to be used as one criterion for plant selection.

Also Dr. Tallamy has published an article in Conservation Biology on this subject.

Tallamy, D. W. and K. J. Shropshire. 2009. Ranking Lepidopteran use of native versus introduced plants. Conservation Biology 23: 941–947.

 Further information on the host plants of Lepidoptera can be found in HOSTS - a database of the world’s lepidopteran hostplants. This is a project of the National History Museum in London.

 

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