INFLUENCE OF SINV ON INSECTICIDE-TREATED
RED IMPORTED FIRE ANT!
Chris M. Powell and Dr. Blake Bextine, Department of Biology, The University of Texas at Tyler, Tyler, Texas 75799!
ABSTRACT!
The Red Imported Fire Ant (Solenopsis invicta Buren) is a tenacious and costly pest to control. Multiple
chemical, physical, and biological control strategies are currently being utilized to control the S. invicta;
however, cost-effective and effective management tools are still needed. Solenopsis invicta virus (SINV) has
been shown to cause colony collapse when other biotic antagonists are present, such as fungal or bacterial
pathogens. A divergent strain of SINV-1, which exhibits 95.5% homology specific to Texas (SINV-TX5) has been
isolated and extracted. The virus can be delivered efficiently using sodium alginate pellets. Current chemical
control strategies are not selective, and indiscriminate use of insecticides can have unintentional environmental
effects. SINV is specific to the Red Imported Fire Ant, making it a viable resource in the development of species
selective control strategies. In this study, we determined the feasibility of using common-use insecticides in
concert with SINV to enhance toxicity of current-use insecticides; therefore, reducing the volume of toxic
compound needed for effective S. invicta mortality. !
INTRODUCTION!
Solenopsis invicta first appeared in Mobile Alabama in the 1920ʼs; since then, the ants have pushed through out
the southern United States, displacing and destroying native species (Drees et al 1999). Multiple chemical,
physical, and biological control strategies are currently used to manage the S. invicta; however, cost-effective
and effective management tools are still needed. Solenopsis invicta virus (SINV) causes colony collapse. SINVTX5 can be delivered with efficiently using sodium alginate pellets (Bextine et al, 2002). SINV is specific to the
Red Imported Fire Ant, making it a viable resource in the development of species selective control strategies
(Tufts et al 2009). Other forms of biological control involve the introduction of a natural predator or parasite,
though these species may become invasive in the future. In this study, we determined the feasibility of using
common use insecticides in concert with SIN-V to enhance toxicity of current-use insecticides; therefore,
reducing the volume of toxic compound needed for effective S. invicta mortality. One common use insecticide
was screened; Fipronil is a Phenylpyrazole class insecticide that targets GABA-gated chloride channels
causing overstimulation of the neuron, resulting in mortality. !
Figure 3. Amino acid comparison of SINV-1 and SINV-1 (TX5)
illustrating 95.5% homology.!
L
NTC
NEGITIVE
SAMPELS
Figure 4. Phylogenetic tree showing the association of individual
viruses within the Dicistroviridae family, accession no. shown in
parentheses !
POSITIVE
SAMPELS
500 bp
METHODS AND RESULTS!
INSECT COLONIES !
> Colonies were collected from the UT Tyler campus, and maintained in the lab (Figure 2). !
VIRUS PRESENCE ASSAY!
> Presence of virus was verified by extracting total RNA with TRIzol reagent (Invitrogen, CA), the samples were
then amplified by RTPCR using virus specific primers. Presence was assessed by gel electrophoresis
(Figure 5).!
VIRUS DELIVERY!
> Extracted virus was encapsulated in Sodium alginate pellets delivered to the ants (Bextine et al, 2002).!
ADULT INSECTICIDE TOXICITY ASSAYS!
> Adult Fire Ants were taken from colonies maintained in the Department of Biology at The University of Texas
at Tyler. Fipronil was purchased from Chem Service Inc. (West Chester, PA) (Figure 6).!
> Toxicity was assessed using dip assay. The insect were knocked down on ice for approximately 15 minutes
in a glass plate, and sorted by size. They were then dipped in the compound and placed in a three inch
culture plate. Mortality was assessed at 1 hour (Figure 7 and Table 1)!
Figure 5. 1% agarose gel of PCR product from SINV screening. !
Table 1. Effective Concentrations (EC) values for Fipronil cause
knockdown in 10% (EC10), 20% (EC20), 50% (EC50), and 85% !
of individuals.!
Virus Negative
Virus Positive
Field
Collected
Ant Colony!
Figure 7. Effective concentrations at 10%, 20%, 50%, and 85%.
95% Confidence interval shown by error bars.
PCR
Screening!
SINV
Negative!
Control
Pellets!
Toxicity
Assay!
SUMMARY AND DISCUSSION!
> Individuals from virus-positive population responded to higher concentration of Fipronil than
virus-negative populations.!
> This indicates that Fipronil is an less effective control method in populations infected with
SINV, assessment of presence could improve effectiveness of chemical treatments.!
> Future study will be focused on the physiological effects of viral infection, in regards to
detoxification pathways and immune response by assessing the activity of glutathione stransferase, general esterase, cytochrome p450, and prophenoloxidase.!
> These differences may be used to choose a directed control strategy, exploiting effects of the
SINV. !
SINV
Positive!
Colony
Split!
Figure 6. Molecular structures of Fipronil, a Phenylpyrazole
insecticide.!
Virus
Extraction!
Virus
Pellets!
Toxicity
Assay!
Figure 1. Progression of sample colonies; yellow represents
unknown infection, red represents positive, and blue shows
negative. !
Figure 2. Colony members being floated for collection (top). Typical
enclosure containing brood box, food source, and water (bottom).!
ACKNOWLEDGEMENTS!
REFERENCES!
I thank the Office of Sponsored Research at The University of Texas at Tyler for the generous awards
to support this research. I thank Danielle Tufts for her previous work with isolation and classification of
SINV TX-5, Henry Schreiber and Damon Hall for help troubleshooting molecular procedures, and Dr.
Eric Lucas for his work optimizing S. invicta cell culture. Finally I would like to thank Larry LeBeau of
the Nature Center – Wildlife Reagion 3 for allowing us to collect ants. This project has been presented
at the ESA South Western Branch meeting and the SWAN meeting.!
1.Bextine, B. R. Thorvilson, H. V.
(2002) Field Applications of Bait-Formulated Beauveria bassiana Alginate
Pellets for Biological Control of the Red Imported Fire Ant. Entomological Society of America.
Lubbock, Texas.!
2. Drees, B. M., C. L. Barr, D. R. Shanklin, D. K. Pollet, K. Flanders, and B. Sparks. (1999) Managing Red
Imported Fire Ant in Agriculture. College Station, TX: Texas Agriculture Extension Services.!
3. Grisham, Julie. (1994) Attack of The Fire Ant. BioScience 44: 587-590!
4. *Tufts, D., Hunter, W., and Bextine, B.R. 2009. Discovery of a genetically different form of the Solenopsis
invicta virus (SINV-1) in east Texas. J. Invert Path. 104: 180-185!