Evaluation of Potential Imported Fire Ant Quarantine
Treatments
for Commercial Honey Bee Operations
Ronald D. Weeks, Jr., John G. Thomas, Charles L. Barr,
and Bastiaan "Bart" M. Drees, Department of Entomology,
Abstract. This research evaluated the efficacy of using a contact insecticide applied to the base or to the ground area around beehives in preventing red imported fire ant (Solenopsis invicta Buren) foraging on beekeeping equipment. Results from our field experiments on pallet and soil treatments shows that soil and/or support pallet applications of Lorsban 4EŽ (chlorpyrifos) are reasonable and effective techniques for preventing fire ant infestation or foraging on bee equipment for at least six weeks post insecticide application. Sampling over the six week period showed that vegetation such as grass and weeds could grow into natural "bridges" over treated pallets that ants can use to access bee equipment.
Introduction
Red imported fire ants (Solenopsis invicta Buren) can invade beehives
and feed on pollen and developing bees. Weak bee colonies are more susceptible
to ant invasions than healthy, vigorous colonies. Often, fire ants build their
nests directly against or on beekeeping equipment. They typically use structures
in contact with the ground for better colony thermoregulation and to escape
localized flooding events. Fire ants can be transported in beehives or in soil
adhering to hives and beekeeping equipment. Fire ant infestation of California's
Central Valley has been linked to intra-continental transport of beehives for
almond pollination. Consequently, beehives have recently become a regulated
item by the United States Department of Agriculture (USDA). However, there are
no currently established quarantine treatments approved for assuring that transported
hives are fire ant free.
To date, there are no insecticides registered specifically for treating bee equipment to eliminate red imported fire ant foraging. However, there are several products on the market labeled for fire ants under a variety of specific conditions. For example, Lorsban 4-EŽ (chlorpyrifos) is an agriculturally approved contact insecticide for control of various insects, including red imported fire ants, in certain field, fruit, nut, and vegetable crops (e.g. alfalfa, orchard floors, field corn, popcorn, sweet corn, cotton, cranberries, sorghum, and soybeans). The objective of this study was to evaluate the efficacy of using a contact insecticide applied to a support pallet or the soil area around beehives in preventing fire ant foraging on beekeeping equipment.
Materials and Methods
Research was conducted September - October 2000 in Royalty Pecan Orchard - Burleson
County, Texas. We used four treatments with four replicates of each treatment
for a total of 16 sample units in a randomized block design to compare fire
ant infestation levels among treatments. Treatments were randomly arranged under
pecan trees in four blocks (i.e. tree rows) in one section of the orchard. The
grass was mowed under each replicate unit before beehives and pallets were set
up in the field. For this study, we used a typical commercial beekeeping set-up
without the bees; hive pallet with clips and two hive supers with lids. In double
pallet situations we added a support pallet with no hive clips.
Treatments comprised of: 1) spraying a 10 x 10 foot area of soil with Lorsban 4EŽ directly under a single beehive pallet; 2) a double pallet with the bottom support pallet sprayed with Lorsban 4EŽ; 3) a double pallet with no insecticide application; and, 4) a single pallet with no insecticide application. Lorsban 4EŽ was applied to the soil area and pallets according to label directions. Three locations were sampled for fire ants on and around each beehive unit using 3 by 3-cm olive oil-soaked bait cards. Two bait cards were set adjacent (ca. 20 to 30 cm) to each pallet on the ground, four bait cards were placed directly on the hive pallet and two were placed on top of the beehive boxes. A ranking system was used to record the approximate number of ants per bait card (i.e. 0 = zero ants, 1= 1 to 24 ants, 2=25 to 49 ants, 3=50 to 74 ants, 4 = 75 or more ants). We compared the means and standard deviations of the ranks of fire ant infestation levels at each sampling location for each treatment.
Results
Fire ant infestation levels were not significantly different between single
and double pallet treatments in the absence of the contact insecticide (Figure
1). There were significant differences in fire ant infestation levels
between non-insecticide treatments and insecticide treated pallets and soil
applications, as indicated in non-overlapping standard deviations about the
means respectively. In the double pallet (bottom pallet treated) insecticide
treatment there were no fire ants found foraging on the pallets or the hives
after six weeks post insecticide application, except in one sampling period.
After four weeks post insecticide application a few fire ants were found on
two bee pallets that were sitting on a treated pallet. Closer inspection revealed
fire ants climbing on blades of grass, that crossed-over treated pallets, and
onto untreated bee pallets. After removing these grass "bridges" no other ants
were found on the bee equipment after subsequent sampling. Results from the
soil insecticide application showed that fire ants were prevented from foraging
on the ground area next to the bee equipment as well as on the bee equipment.
During the last sampling period, which included a week of intense rainy weather,
a few ants were found on a bait card on the ground next to one of the bee units.
This indicates that the active ingredient in the insecticide was just beginning
to degrade after six weeks post-insecticide application and several days of
heavy rains.
Discussion
We have shown that soil or pallet application of Lorsban 4EŽ, a long-residual
contact insecticide, is a reasonable and effective technique to prevent fire
ant infestation or foraging on bee equipment for at least six weeks. Our results
indicate that simply stacking beehive equipment on supporting pallets or similar
structures does not eliminate or reduce fire ant foraging on bee equipment.
Preventative barriers, such as chemical barriers, are necessary and effective
in eliminating fire ant foraging on bee equipment.
Double pallet hive set-ups appear to have several advantages over single hive pallet set-ups. Support pallets can be treated with insecticides to prevent ant foraging on bee equipment and can reduce or eliminate time spent on hive pallet sanitation (i.e. soil removal) and may even extend the life of the hive pallet. However, sampling over time indicates that it is necessary to monitor and remove any bridges that may form across treated areas between the soil surface and the bee equipment, such as over-grown vegetation or fallen tree leaves and limbs. Soil applications of contact insecticides can be used in loading yards for short-term hive storage before moving to new locations.
By applying Lorsban 4EŽ to the soil surface or on a supporting pallet foraging honey bees can be protected from direct contact with the insecticide. Thus, making the use of contact insecticides a viable option for beekeepers as a potential quarantine treatment option. Future research is aimed at evaluating the behavior of ant colonies when placed on hives above treated pallets.
Acknowledgments: We thank Paul Jackson for bee equipment procurement and Andy Sherrod at Royalty Pecan Orchard for field site use and access. Funds for this project were provided to John G. Thomas, Executive Secretary Texas Beekeepers Association thorough the Texas Department of Agriculture and the Texas Imported Fire Ant Research and Management Project.
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