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Redheaded Pine Sawfly Is Destructive

July 4, 2019

Looks, as the old saying goes, can be deceiving. This useful advice is certainly applicable to all the nocturnal visitors in the past weeks who are showing up in the home landscape and garden plots.

Those small nondescript moths which flit around the porch light are busy doing more than decorating car grills under the cover of darkness. They are also leaving tiny eggs which hatch into a plethora of caterpillars.

These writhing, larval-state insects arrive in a variety of colors, sizes and textures.  This fact has caused a longstanding problem for those who are attempting to recognize a specific insect group, beneficial or destructive, based on its immature state.

Mistaken identity

Sometimes the wiggling defoliators are not caterpillars. The sawfly’s larvae are frequently mistaken for a caterpillar and sawflies in Wakulla County are native insects with a well-deserved reputation for destructive behavior.

Sawfly WN 7-4-19 insert Photo by Les Harrison

Blackheaded Pine Sawfly larvae may appear as caterpillars, but eat pines and cedars. Left uncheck, they can kill these common Wakulla County trees.

To entomologist, those people who spend their careers studying insects and other crawly creatures, the term caterpillar has a very specific meaning.  Popular culture has converted this term into a brand, cartoons, and most tubular shaped bugs located on shrubs.

Technically speaking only butterflies and moths, Lepidoptera, larvae are correctly classified as caterpillars. Among the more obvious characteristics are five or fewer pairs of pro-legs, those appendages extending from the base of its body.

Other traits include Y or V shaped cleavage lines on the head and a complex eye with six stemmata, for those who wish to look closers. There are other even smaller and specific identifiers, but these are often left to be assessed by professionals.

Numerous sawfly species found in North America

There are numerous sawfly species found in North America. The redheaded pine sawfly, Neodiprion lecontei,  and the blackheaded pine sawfly, Neodiprion excitans, are found in Wakulla County and are native to the United States being found primarily east of the Great Plains and north into Canada.

Though similar in appearance to caterpillars, sawfly larvae have six pro-legs and simple eyes with only two stemmata. As their name implies, they do have a red or black head and they are commonly found on pine trees.

These pine sawfly species are two of many sawfly species worldwide, including 35 in its specific genus.  The term sawfly comes from the saw-like ovipositor which females use to deposit its eggs.

For the timber and landscape industry, this species is an economically important defoliator of commercially grown pines. Unfortunately, it feeding and reproductive environment are enhanced in monocultures of shortleaf, loblolly, and slash pine, all of which are commonly cultivated in the southern United States.

Emerging larvae

Adults are easily overlooked, being less than half an inch in length.  The emerging larvae are usually the first sign a problem exist.

An adult female creates slits in a pine needle and lays one egg per slit. Needles which have eggs laid in them look spotted or banded with alternating green and yellow patches.

In approximately four weeks, larvae emerge and feed on the pine needles in large gregarious groups. In approximately four more weeks, larvae drop to the ground below the tree they were feeding on and begin to spin cocoons in the leaf litter or top layer of soil.

Pine trees are preferred

Young, open-growing pine trees less than 15 feet tall are especially vulnerable. While pines are preferred, larvae will feed on a cedar if the favored food source is exhausted.

A large infestation is capable of completely stripping small pine trees of foliage. Younger larvae eat the outer edges of pine needles leaving behind the central tissue which wilts and dies to creating the appearance of dried straw, making sawfly damage distinctive.

Older larvae eat the entire needle, and if complete defoliation occurs, groups of larvae will move to the nearest acceptable food source and continue feeding. When foliage becomes scarce, larvae will even feed on the soft bark tissue of defoliated trees.

Control methods are available, but an early start is the key to minimizing damage.

These larval mimics are active now in Wakulla and can cause problems for caterpillar proof pines. Seems nothing is really safe.

To learn more about sawflies in Wakulla County, contact your UF/IFAS Wakulla Extension Office at 850-926-3931 or http://wakulla.ifas.ufl.edu/

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information, and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions, or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A&M University Cooperative Extension Program, and Boards of County Commissioners Cooperating

2 Comments on “Redheaded Pine Sawfly Is Destructive

  1. Les, just saw your site. Thanks for your efforts. I’ve become obsessed with the destructive impact of the muscadine vine across the state of FLORIDA. Its pulling down all of the grand old Oak trees and as one who was born and raised in Florida it is disheartening. I’ve just reached out to IFAS and UF sources, but do not expect any real support.

    Please walk any Wakulla trail or drive any FL Hwy and see the impact of the destructive nature of this vine. Makes kudzu look like a ….

    What can be done before it is too late and how can I participate?

    • Here is advice from the extension service in Prince George County, Maryland:
      Wild grape vines are native and good for wildlife, but they are rampant growers! (‘Invasive’ usually means a foreign invading plant these days.) So they can be a real problem in home landscapes.

      The easiest way to handle them is to cut them down at the base and IMMEDIATELY treat the freshly cut stump with an herbicide with glyphosate or triclopyr. Do not let the herbicide get on the trunks of your trees (or anything but the vine). You can use a shield of cardboard or plastic to keep the spray off your desirable plants.

      You don’t have to remove the vine from the tree. It will decompose in place, but it is heavy, so you may want to remove it at least as high as you can easily reach.

      This is a plant with a big root system with lots of energy reserves. It will probably start sending up new shoots quickly or next spring. Spray them immediately with the herbicide. (Do not get any spray on the trees or other desirable plants) The leaves absorb more of the herbicide, so they are actually helpful in getting the herbicide to the root system. Both the herbicides are systemic, which means they will be absorbed into the system of the plant and translocated down to the root system. Spraying shoots in the fall is especially effective.

      It may take a while to exhaust the energy reserves and get enough herbicide down to the roots, but just be persistent. It will happen.

      If you have any questions or suggestions for future articles please email to wakullamg@ifas.ufl.edu

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