Post-harvest pyrethroid drench and injection treatments for quarantine control of imported fire ant (Hymenoptera: Formicidae) colonies infesting field-grown nursery plants

There is an imported fire ant (IFA) quarantine in the USA to prevent human assisted spread of the invasive, red IFA (Solenopsis invicta Buren), black IFA (Solenopsis richteri Forel), and the S. invicta × S. richteri hybrid. Quarantine regulated articles must be treated following approved protocols and must not be infested with IFA queens or reproducing colonies. Large, post-harvest field-grown nursery plants are an infestation risk because they are difficult to treat effectively with approved insecticide treatments of (i) immersing in chlorpyrifos or bifenthrin solutions, or (ii) thoroughly drenching root balls with chlorpyrifos. To improve quarantine treatments, the efficacies of drenching and injecting (D&I) large (60 cm diameter) root balls with bifenthrin or lambda-cyhalothrin to disinfest them of IFA were determined and compared with chlorpyrifos drench (standard), and water drench (control). Bifenthrin and lambda-cyhalothrin D&I treatments eliminated all IFA colonies in 2 wk, while >70% of the chlorpyrifos drench-only and control root balls were infested. Bioassays of red IFA female alates (surrogates of colony founding queens) in soil sampled from various root ball positions receiving the above treatments resulted in no survival of alates exposed to bifenthrin after 10 d. With lambda-cyhalothrin and chlorpyrifos, 10% and 11% of the soil samples had ≥1 surviving alate, respectively. The complete IFA colony disinfestation of root balls and the death of all alates in soil samples indicated bifenthrin D&I could provide additional and effective quarantine level control of IFA in large, post-harvest field-grown nursery plants.