Pensacola News Journal

For: Saturday, July 31, 2004

By: Daniel E. Mullins

Extension Horticulture Agent

Santa Rosa County

Extrafloral Nectaries Helpful to Beneficials

Discoveries and observations in the plant world continue to fascinate. During an attack of youthful smugness many years ago, I told a health care professional that we knew more about plants than his profession knew about people. It was quickly pointed out that experiments and studies with plants are allowed more latitude than those that are acceptable when dealing with human health.

Basic and applied research and observations continue at a rapid pace. Much of the information obtained by horticulturists, botanists and others who study plants eventually finds its way and becomes useful to gardeners and commercial plant producers alike.

One example is the discovery that many plant species have extrafloral nectaries (EFN). Most everyone is aware that flowers commonly produce nectar that is important in encouraging pollination as well as providing food for hummingbirds and insects. Fewer people are aware that nectar producing glands exist that are physically apart from the flower.

EFN glands have been identified in more than 2,000 plant species in 64 families. The size, shape and secretions from these glands vary with plant species. They may be located in different places on different kinds of plants. Some are on the leaves or leaf stems, while others are found on bracts, stipules or even fruit.

The nectar from these specialized glands differs from floral nectar, varies by plant species and may or may not flow in a daily pattern. The composition of the gland secretion is about 95 per cent sugar, with the other five per cent consisting of a wide array of amino acids and other important nutrients.

Most studies of species with EFN indicate that they provide a plant defense function. They attract many beneficial organisms that help to keep plant damaging insects in check. It is easy to observe ladybird beetles and other beneficial insects feeding at these nectar producing sites.

Interestingly, many species of vines have EFN. Also, many species of ants are found in association with those having EFN and are thought to be manipulated by the host vine to defend it.

There are several Florida plants with large EFN on the leaves or stems. These include passion flower, partridge pea, Cassia spp., hairy vetch and elderberry. Most cultivars of peach, plum and nectarine have EFN on the leaves.

Other locally grown plants with EFN include beautyberry, trumpet creeper, Catalpa, Hibiscus, cotton, Osmanthus and Viburnum. The occurrence of EFN appears to be controlled by a single gene in most plant species.

EFN could be valuable if not critical components in the ecology of landscapes. Studies continue, and many opportunities exist to further our understanding of EFN.

A brand new five page University of Florida publication is available for those who would like to read up on this fascinating subject. It includes photos of nectaries on four plant species and a longer list of plants that have these nectar producing structures. Type in IFAS ENY-709 on a good internet search engine or contact your local Florida Extension office for a copy. The title of the document is: “Many Plants Have Extrafloral Nectaries Helpful to Beneficials.”

Note: This publication was written by Dr. Russ Mizell, University of Florida/IFAS Professor of Entomology. Dr. Mizell is a leader in his field and is helping to unravel some mysteries related to insect behavior and insect/plant relationships. He is also the researcher who developed the famous deer fly trap. Using a search titled “The Trolling Deer Fly Trap,” this publication can be easily found and the information contained would be useful in controlling infestations of these biting flies.