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CHEMICAL (CHLORPYRIFOS AND PERMETHRIN) TREATMENTS
AROUND STACKED BALES OF HAY
TO PREVENT FIRE ANT INFESTATIONS
Ronald D. Weeks, Jr., Michael E. Heimer, and Bastiaan M. Drees
This research evaluated the efficacy of using a chemical barrier applied to the soil area
under stacked bales of hay to prevent the red imported fire ant, Solenopsis invicta
(Hymenoptera: Formicidae), from infesting stacked hay. Specifically, we were interested in
determining if we could protect "clean" hay bales stored in fire ant infested fields for up to
several weeks. Chemicals selected as barrier treatments were Lorsban® 4E, active ingredient
chlorpyrifos, which kills ants on contact, and Astro™ Insecticide, active ingredient the
pyrethroid permethrin, which can also act as a repellent to ants. We established a series of 12ft x
12ft plots, with a 10ft buffer between plots along a fence row in a fire ant infested field. Plots
were grouped into four blocks of three stacks each. Plots within blocks were randomly assigned
to each treatment (four plots treated with Lorsban® 4E and four treated with Astro™ Insecticide,
and four control plots). Treatments included spraying a 12ftx12ft soil area with a 1-gal solution
of each chemical and water formulation. After soil treatments, we placed four square-bales of
hay, stacked two a side and interlocking in two layers, in the center of each plot. Stacked bales
were sampled for fire ant infestation using 2.5 x 2.5cm olive oil –soaked index cards; one bait
card was placed on each side of the top layer of hay in each stack. Results from ANOVA show a
significant difference in mean infestation levels among treatments. Stacks of hay sitting in the
chlorpyrifos plots had fewer ant infestations compared to the permethrin and control plots.
Results after one week showed that only one stack in the permethrin, and two in the control plots
were infested with ants, while none in the chlorpyrifos plots were infested. Results show that
after three weeks all four control stacks, three stacks in the permethrin treatment, and two stacks
in the chlorpyrifos plots were infested. These results indicate that on a short-term basis, such as
1 to 7 days, chlorpyrifos may be an effective short-term treatment option for protecting stacked
hay from fire ant infestations.
The red imported fire ant, Solenopsis invicta
frequently moves into or next to bales of hay that have been left in the field after harvesting and
their mounds can interfere with the transportation of hay. The United States Department of
Agriculture (USDA) has listed hay as a quarantined agricultural product. Currently, there are no
USDA approved quarantine chemical treatments for assuring that S. invicta
are not shipped to
new locations. Hay bales that are not removed from fields immediately after baling and stored in
an off-ground location cannot be shipped out of quarantined areas. Hay producers are in need of
quarantine treatments that provide them reasonable options for the safe storage of hay before it
can be shipped to other non-infested areas of the country. In the field, hay bales may provide a
variety of microclimates such as thermoregulation sites, flood refuges, moisture under bales
during drought, and the presence of both shady and sunny areas along the sides, which S. invicta
and other arthropods find appealing (Fig.1
). Previous research, conducted by us, has shown that
hay bales left in the field can become infested in untreated areas within a few days to weeks after
baling (http://fireant.tamu.edu/research/arr/category/site/97-01pg42/97-01pg42.pdf). Theobjective of this study was to evaluate the efficacy of using targeted soil applications ofLorsban® 4E, active ingredient chlorpyrifos, and Astro™ Insecticide, active ingredient thepyrethroid permethrin, to protect stacked bales of hay from S. invicta
Materials and Methods
Research was conducted June 2002 in Montgomery County, Texas. Three treatments
with four replicates of each treatment were used for a total of 12 sample units to compare S.
infestation levels on stacked bales of hay among treatments. Treatments were arrangedrandomly in four blocks (i.e., three stacks/block) along a fencerow in a fire ant infested field(Fig. 2). Treatments included: 1) control plots without chemical treatment, 2) 1-gal applicationof Lorsban® 4E12ft2 (chlorpyrifos) area soil treatment, and 3) 1-gal application of Astro™Insecticide (permethrin) 12ft2 area soil treatment. Four bales of hay were stacked in the center ofeach plot. Insecticide applications followed printed label directions (4.73 ml Lorsban® 4E per3.78 liter water; 2.36ml Astro™ Insecticide per 3.78 liter water).
Stacks of hay were sampled for ant infestation thorough visual inspection of stacks for
ant mound building and using 2.5 x 2.5cm index (bait) cards soaked with olive oil pinned on thesides of the top (second) layer of hay in each stack. All bait cards were placed on hay balesunder good S. invicta
foraging temperatures (25°-30° C). Ant sampling was conducted for 45min for one day each week for three consecutive weeks (June, 2002). We used analysis ofvariance (ANOVA) to test the hypothesis that our targeted bait applications around stacks of haywould significantly reduce or eliminate infested bales in treated compared to untreated stacks. We did not have enough degrees of freedom to do a repeated measures test with time ofsampling as a treatment effect. However, we able to test whether there was an overall effectamong the treatments by summing across the sampling periods, (JMP SAS, Cary N.C.). Significant differences among the means were determined using Tukey-Kramer honestsignificant difference (HSD) method (JMP statistics).
There was a significant treatment effect (Table 1
). Stacks of hay in the Lorsban® 4E
(chlorpyrifos) plots had significantly fewer mean occurrences (mean = 1.00) of ant infestationcompared to stacks in the Astro™ Insecticide (permethrin) treated (mean = 2.00) or control plots(mean = 3.66) during the three-week sampling period (Tukey's HSD = 0.46).
Examination of the timing of infestation show that after one week of chemical application
only one stack in the permethrin, and two in the control plots were infested with ants, while zero
in the chlorpyrifos plots were infested (Table 2
). Results after three weeks show that all four
control stacks, three stacks in the permethrin treatment, and two stacks in the chlorpyrifos plots
were infested. These results indicate that on a short-term basis, such as 1 to 7 days, chlorpyrifos
may be an effective short-term treatment option for protecting stacked hay from fire ant
Results of analysis of variance (ANOVA) test comparing the mean number of hay
bale stacks, per treatment, infested with red imported fire ants after three weeks in plots where
either Lorsban® 4E(chlorpyrifos) or Astro™ Insecticide (permethrin) were applied to the soil
under treatment stacks; N = 12 stacks of hay sampled with four treated with chlorpyrifos, four
treated with permethrin, and four untreated control stacks. Ants were sampled with oil-soaked
bait cards for 45-minutes on the second tier of hay in each stack.
Sum of Squares
Number of stacks of hay infested with S. invicta
and the number days until
infestation. Hay infestation evaluation was conducted three weeks after plots where treated
with either Lorsban® 4E (chlorpyrifos) or Astro™ Insecticide (permethrin) to the soil under
treatment stacks; N = 12 stacks of hay sampled, with four treated with chlorpyrifos, four
treated with permethrin, and four untreated control stacks. Ants were sampled with oil-soaked
bait cards for 45-minutes on the second tier of hay in each stack.Treatment
Ants quickly infested all of the unprotected hay bales. Yet, we were able to prevent ant
infestation of stacked hay bales for a one-week period in the Lorsban® 4E (chlorpyrifos) soiltreatment plots. We were not able to get the same level of protection using the Astro™Insecticide (permethrin) treatments as we did with the chlorpyrifos treatment. Considering thehigh number of infested hay stacks and the relatively fast invasion rate of ants in the permethrintreated plots compared to the chlorpyrifos plots it appears that our pyrethroid barrier was not asuitable barrier in our situation.
Our initial results using the chlorpyrifos soil treatment may provide hay producers a
small (e.g. 7 day) window in which hay destined for travel outside of a quarantined county canbe stored on the ground before shipment. However, our results with this application ofchlorpyrifos were not as long-lived as expected. In previous studies using chlorpyrifos sensitivequarantine regulated articles were protected from fire ant infestation for up to 6 weeks(http://fireant.tamu.edu/research/arr/category/site/97-01pg39/97-01pg39.pdf). In our study, antswere able to breach this protective barrier within a few weeks. It is unlikely that the activeingredient had degraded enough to allow ants to cross it. One possible explanation for the shortperiod of protection afforded by treatments, based on limited observation data, may lie in the fact
that some ant colonies may have occurred underneath or near the stacks of bales deeper in thesoil than what was treated with the soil surface spray of the contact insecticides. After a shorttime (> 7 days) foraging ants tunneling up from these colonies may have been able to "cover-up"the chemical through excavation of uncontaminated dirt from deep within their colonies, therebyavoiding contact with treated soil particles and insecticide residues. Results suggest the need foranother experiment where, larger areas in and around areas designated as hay storage locationsmay be selected for broadcast applications, to reduce ant populations, in addition to targetedapplication of chemically treated barriers.
One important finding from this study is the presence of foraging worker ants attracted to
hay bales on the second layer of stacked bales. The presence of live worker ants on regulateditems constitutes an infestation according to USDA fire ant quarantine regulations and thesesecond-layer bales would, therefore, be considered infested and not allowed to be transportedoutside of quarantined areas. The practice of allowing producers to move bales from untreatedstacks not directly in contact with the ground (i.e., second layer and up), is therefore brought intoquestion by these results.
Funding for this research was provided to Michael Heimer, County Extension Agent,
Agriculture, Montgomery County, Texas through the Texas Department of Agriculture and theTexas Imported Fire Ant Research and Management Project. Thanks to Mr. Berkeley, for hayand field sites and to Mr. Kyle Miller at American Cyanamid for the Amdro® donation. Thanksto Dr. Charles Barr for bait application support and equipment use.
Figure 1. A large fire ant colony moved
Figure 2. Stacks of hay in Montgomery
against stack of hay.
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