Saturday, May 30, 2009

Zombies and fire ants?

Earlier this month Robert Burns with AgriLife Communications published a press release regarding a project I am involved in to help establish the first fire ant parasite in East Texas. We never thought that the story would have been picked up outside of East Texas since phorid flies have been released in Texas for a number of years and are established in some parts of the state. Well we learned an important lesson. If you put the word zombie in a title people pay attention.There have been many variations of the story in the media. It is important to know that the flies will not attack humans and turn us into Zombies as some bloggers have suggested.

Here is the original version:

OVERTON – Zombie fire ants may not sound like a cool thing,Texas AgriLife Extension Service but wait a minute, said a expert.

On April 29, on the grounds of the Texas AgriLife Research and Extension Center at Overton in East Texas, Dr. Scott Ludwig released fire ants infected with a new type of phorid fly, a minuscule parasite that only preys on red imported fire ants.

The infected ants will soon exhibit some very bizarre behavior, he said.

"First they become zombies, their movements under the control of the parasite. Then their heads fall off and the parasite emerges," said Ludwig, , AgriLife Extension integrated pest management specialist.

Previously released phorid flies only preyed on ants in disturbed mounds. In contrast, the species, Pseudacteon obtusus, that Ludwig released in April is attracted to foraging red imported fire ants and not disturbed mounts. Which is even better, he said, as attacks of ants are not dependent upon the mounds being disturbed.

The "zombified," fire ant is made to wander about 55 yards away from the mound to die.

"The parasite does this so it can complete development without being detected and attacked by the fire ant colony," Ludwig said. "By making their hosts wander away, the parasite is insuring its survival."

As with the new species, the previously released phorid fly species in Texas only attacks red imported fire ants. They inject their eggs into their bodies. In response, fire ants withdraw to their underground nests and reduce their foraging range, he said.

Once established, it was hoped that earlier releases of phorid flies would spread beyond the original release sites, and there has been evidence that they have, Ludwig said.

"Pseudacteon tricuspis was first released near Austin in 1995. From 2003 to 2006, it spread over 10,000 square miles," Ludwig said. "The second species, P. curvatis, was established 2004 and is beginning its spread."

The parasite isn't attracted to native ant species, he emphasized.

"We're hoping the new parasite will reduce the foraging of fire ants, and thereby allow our native ants to regain some footing," he said.

The release was part of the Texas Imported Fire Ant Research and Management Project.

"The project was initiated in 1997 as a result of the Texas Legislature funding an exceptional item requested by Texas AgriLife Research," Ludwig said. "The project's goals are the management of imported fire ant to below economic levels on agricultural lands and to eliminate the imported fire ant as a nuisance or health threat in urban environments." The phorid flies infesting the fire ants Ludwig released were raised by Dr. Lawrence Gilbert, director of the Brackenridge Field Laboratory at the University of Texas at Austin.

"UT researchers have taken the lead on phorid fly research in the state," Ludwig said.

More information on the project and fire ant research can be found at or .

The new species was previously released in 2007 only in South Texas, where it was established but did not spread.

"It may not have spread because of the drought," he said.

Ludwig's release was the first in East Texas. In 2010, he plans to set out traps baited with live red imported fire ants to determine if and how rapidly the phorid fly has spread.

"Earlier data suggests they can spread 25 miles a year through wind-assisted dispersion," he said.

Thursday, May 7, 2009

IPM Priority Setting Meeting

The East Texas Nursery and Greenhouse IPM Program is now in its 8th year. Hopefully during this time you have benefited from one of the many activities carried out by my program. These may have included attending the East Texas Nursery and Greenhouse Conference, onsite consultations, science based pest management suggestions, or information disseminated through websites, bogs, trade journal articles, and newsletters.

In an effort to ensure that the East Texas Nursery and Greenhouse IPM Program is positioned to meet your pest management needs in the future, I will be hosting a meeting to set IPM priorities on June 11th from 1:00-4:00 at the Smith County Extension Office. The meeting will be open to all nursery and greenhouse growers from East Texas and surrounding areas. This is your opportunity to have direct impact in the areas that I will address over the next few years.

During this three-hour time period, you will identify areas that need to be addressed in weed, plant disease, and insect management. The needs assessment will be conducted for tree & shrubs, perennials, and bedding & pot plants. It is critical that we have participation from as many growers as possible to help ensure that the industries needs are met.

I am also interested in determining the best method to provide educational information to the industry. It is critical that you receive the information being produced by my program in a timely fashion.

Please RSVP to Kim Cushman at 903-834-6191 or by June 10th so we can assure adequate resource for all the meeting attendants.

Friday, May 1, 2009

Managing Insecticide Resistance

A resistance management plan is a critical component of any integrated pest management (IPM) program. In order to develop a resistance management program you need to understand the mode of action of the products available and the biology of your target pests.

For years entomologists have been telling growers to rotate insecticides by mode of action. The mode of action is the mechanism by which the pesticide kills the pest. Determining the mode of action of an insecticide has become easier over the last few years. Newer insecticide labels have the mode of action group listed on the top of the first page. You can also find a complete listing of the mode of action groups in a number of locations. These include OHP’s Chemical Class Chart ( and BASF’s Pest Management Guide (

There is still debate over how many times a product can be used before you need to rotate to another product and how different products should be in the rotation program. Your first step should be to read the label and see if there are any label restrictions regarding resistance management. Most products will limit the total number of applications per year. One extreme is the Pedestal® label which states “Do not make more than two (2) applications of Pedestal per crop per year.” In addition to a limit of the total number of applications that can be made, a products label may also have other use restrictions.

A general rule of thumb is that you want to rotate to a different mode of action for each insect generation. Products that kill by desiccation or smothering, such as soaps and oils, can be used anytime in a pesticide rotation scheme without negatively impacting resistance management programs.

There are a few instances where products in different mode of action groups have the same or similar modes of action, examples include 1) cross-resistance between organophosphates and carbamates and 2) pymetrozine (Endeavour®) has been shown to be cross-resistant to neonicotinoids in Bemisia tabaci. It is also important to take note if there is a letter after the mode of action group number, such as 4A with the neonicotinoids. Products with different letters within the groups have different modes of killing the insect, although the end result appears similar or the active ingredients have very similar chemical structures. One example is MOA Class 9. Although Endeavor (9B) and Aria (9C) are both selective feeding blockers, they can be rotated with each other since each product has a different target site on the insect.

Unfortunately, many people do not understand how resistance develops. Insecticide resistance is the genetically based, inherited ability of an individual to survive exposure to an insecticide that is lethal to other individuals in the population. That is a nice scientific definition. Here is a very simplistic way to visualize resistance. You have 1000 aphids on an oleander and because you have not been rotating insecticides 10 individuals or 1% of them are resistant to your favorites insecticide. After you spray there are 100 aphids left on the plant. Assuming the resistant individuals were not impacted by any other mortality factor they now comprise 10% of the population. You decide that a second insecticide application is need a month later. The there are now 2000 aphids on the plant and 200 are resistant to our favorite insecticide (2000 x 10% = 200). Your spay tech does a phenomenal job spraying and kills all the susceptible aphids, but the 200 aphids not impacted by the spray are still on the plant. A week later you decide you want to sell the plants without any aphids and have the plants sprayed again with your favorite insecticide and to your surprise you are unable to detect any decrease in the population. This is a very simplistic hypothetical situation, but hopefully give you a way of visualizing how resistance can develop.

As illustrated above, it takes a number of generations for an insect species to develop resistance to an insecticide. Generally, the shorter the generation time the faster the species can develop resistance. According to the Insecticide Resistance Action Committee ( there are four mechanisms that may cause an insect population to become resistant to insecticides. Some insects may actually exhibit more than one of the mechanisms at a time.

Metabolic resistance. This is the most common mechanism of insecticide resistance. Resistant insects use internal enzymes to detoxifying or destroy the insecticide’s toxin more rapidly than a susceptible insect. The resistant insect may also be able to rid its bodies of the toxic molecules.

Altered target-site resistance.
The second most common mechanism of resistance is a result of the target site where the insecticide toxin binds becoming altered. This modification reduces the ability of the insecticide to kill the insect.

Behavioral resistance.
Resistant insects detect or recognize the insecticide and avoid the toxin. The insect may stop feeding or move to an area where there is no insecticide.

Penetration resistance.
The resistant insect’s outer cuticle develops barriers that slow an insecticides ability to penetrate into the insect.

The first evidence of resistance is usually reduced efficacy against the target pest even when the pesticide was properly applied at the recommended rate. If you suspect a pest population is developing tolerance to a particular chemical, continued use or increasing the rate of the product will only accelerate the rate of resistance selection, eventually leading to complete control failure. If you are applying an insecticide that is not longer effective you are wasting money on labor and insecticides that will have no impact on the pest population.

If you suspect insecticide resistance or need further information, please do not hesitate to contact me, the insecticide company, or your local extension specialist.