Where have all the insects gone? Long time passing-When will they ever return? A Case for Native Gardens

The President’s Hoot
by Richard H. Baker, Ph.D.
March 2010

Most folks know little about the most diverse group of organisms ever to evolve on our planet.  And if they do, it is usually regarding a negative experience with mosquitoes, no-see-ums, cockroaches, wasps, termites, fire ants, or crop eating caterpillars.  Usually the solution is to hire a pest control firm to try to eradicate them.  These pesky insects actually are just a small percentage of the more than 920,000 described insects species found in the world. Thousands more are described yearly, and some researchers estimate that there are 15 to 30 million insect species still not described.  Insects have been here a long time beginning about 350 million years ago, while humans first appeared about 100,000 years ago.

Grasshopper by Bob Montanaro.

Insects represent 85 percent of all animal species (Mammals 4,000, Birds 9,000, Reptiles and Amphibians 5,500, and Fishes 18,000).  There are more species of dragonflies than mammals and almost twice as many butterflies as birds.  Insects play a vital role, as they are critical food sources low on the food chain for many species.

Plants are essential to life on this planet.  With few exceptions, neither we nor anything else can live without them.  They provide the oxygen we breathe, capture the sun’s energy, which though photosynthesis turns this energy into food.  Plants often are referred to as a primary producer of the “food web,” and they provide animals, including humans with shelter.  

Worldwide, 37 percent of animal species are plant-eating insects.  These species convert plant tissue to insect tissue that provides food in the form of themselves for other species.  As E. O. Wilson points out: “a land without insects is a land without most forms of higher life.”  Nearly all (96%) terrestrial bird species in North America rely on insects and other arthropods to feed their young.  In other words, insects provide energy to animals that can’t eat plants. Part of the nearly 50% population reduction in many of our bird species, within the space of 50 years, is the result of the loss of native plants that serve as food for insects that birds require to rear their young.

For the last 100 years we have created our gardens with one thing in mind: aesthetics. A new book entitled Bringing Nature Home-How You Can Sustain Wildlife with Native Plants by Douglas W. Tallamy points out: “All plants are not created equal, particularly in their ability to support wildlife.”  Tallamy, an entomologist, noticed that many showy alien plants do not have insect damage compared to natives. Our native insects have adapted to our native plants for food, but unfortunately most native insects are not able to eat or to survive on alien plant species.  Alien plants have different chemicals that are unrecognizable, poisonous or can’t be digested by our native insects.  With the continued habitat destruction on our planet and the resulting loss of species, this book redefines what gardens need to be like to preserve our native flora and fauna and maintain biodiversity. Most plant eating insects (90%) are specialists feeding only on one species of plant, and10% are generalist feeding on more than one, thus we need a variety of plants to support numerous insects to support varied wildlife.  Yards with large areas of grass are thus what are termed a “monoculture” meaning there is one plant species instead of a variety needed to support diverse insects.

Tallamy suggests that we fundamentally need to change the way we think about our gardens and their role in the larger landscape.  Moreover, gardens with natives could be extremely important in preserving our ecosystems.  He points out:  “Like it or not, gardeners have become important players in the management of our nation’s wildlife.”  They can provide the biodiversity needed to support our native plants and animals and the ecosystems that sustain them.  “Gardening with natives is no longer just a peripheral …It is an important part of a paradigm shift in our shaky relationship with the planet that sustains us.” 

In one study, native plants produced over 4 times more herbivore biomass than did alien species and supported 3.2 times as many herbivore species.  Native plants in the study supported a whopping 35 times more caterpillar biomass than the aliens: moths, butterflies, and sawfly caterpillars were the largest diet component of insectivorous birds. Alien plants occupy space and use resources (light, water, and soil nutrients) that would otherwise have been available for a native plant, but do not pass the energy it harnesses from the sun up the food web as the insects will not be feeding on them. Interestingly, the alien buddleias or butterfly bush attract nectar-seeking butterflies and are common in many butterfly gardens, but no larvae can live on the plant!  Thus adults do not lay their eggs on such plants, but only come for the nectar.

Today over 5,000 species of alien species have invaded the natural areas of North America. They become pests themselves, and they can bring in as hitchhikers, serious pests and diseases into the country.  In Indian River County we have 3 recent examples:

  • Laurel wilt, a new disease of redbay (Persea borbonia) and other plant species in the family Lauraceae, is causing widespread mortality in the coastal regions of South Carolina, Georgia and Florida. The disease is caused by an exotic fungus (Raffaelea species) that was is introduced  n 2002 by an exotic insect, the redbay ambrosia beetle (Xyleborus glabratus), which is native to Asia and is the 12th new species of ambrosia beetle introduced into the U.S. since 1990.
  •  A weevil, (Metamasius callizona), a native to southern Mexico and Central America, was detected in Broward County in 1989 attacks and kills our large native Tillandsia bromeliads and also Catopsis and Guzmania genera.
  • In Florida, we have a bacterium (Candidatus liberibacter) that causes greening disease in citrus also an alien, considered to be the worst citrus disease in the world. First seen in August 2005, it has spread to all citrus producing counties in Florida by the Asian citrus psyllid (Diaphorina citri), a tiny homopteran insect that arrived on infested orange jasmine, an ornamental plant that is shipped by the thousands throughout the state by discount stores.  Robert Adair, Director of the Florida Research Center, states that our famous citrus groves will be dramatically reduced in Indian River County and the State of Florida in the next 3 to 5 years due to this deadly disease unless a cure is found. Some ‘alien’ plants like avocado or mangoes feed people, squirrels, raccoons, … and are pecked upon by birds.

There is no debate that we should close our borders to carriers of human diseases like SARS, mad cow disease, and avian flu virus.  Why are the native plants that sustain us and our native animals less worthy of protection?  We can all do a better job supporting the natural world, which is both beautiful and full of life.  Why can’t our yards reflect this? What if every homeowner with a yard, began planting more diverse native plants, replacing our monocultures? Native plants are more likely to survive frosts, use less water, pesticides, and fertilizer thus saving us money and reducing pollution.  However, native plants put in the wrong habitat may require water or fertilizer, and therefore the ‘right’ native plant needs to be put in the right place.

Life began in Florida with native plants, but may end with aliens…unless we act together now.

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