ABSTRACT
Viruses have been used successfully as biocontrol agents against several insect pests but not ants. Laboratory tests have shown that Solenopsis invicta virus 3 (SINV-3) may be an effective natural control agent against its host, the red imported fire ant (Solenopsis invicta Buren). In this field trial, SINV-3 was released into 12 active S. invicta nests within a 0.088-hectare area in Florida and the impact on the ants monitored. SINV-3 was successfully transmitted, established, and multiplied within treated colonies reaching a maximum mean value of 8.71 × 108 ± 8.26 × 108 SINV-3 genome equivalents/worker ant 77 days after inoculation. SINV-3 was not detected in any of the nests in the control group. A 7-fold decrease in nests was observed in the SINV-3-treated group compared with the untreated control. A correspondingly significant decrease in S. invicta nest size also was observed over the course of the evaluation. Based on the nest rating scale, nest size among those treated with SINV-3 decreased from 3.92 ± 1.24 on day 0 to 1.67 ± 2.06 on day 77, which represents a 57.4% decrease in size. Conversely, the nest rating for the control group increased 9.3%, from 4.42 ± 1.24 on day 0 to 4.83 ± 2.12 on day 77. A follow-up survey of SINV-3-treated and -untreated plots conducted 9 months after initial treatment revealed that fire ant populations rebounded, but at a different rate. A total of 11 and 19 nests were detected in the SINV-3-treated and -untreated areas, respectively. SINV-3 was still detected in the treated area 1.8 years after the initial virus treatment and the virus had spread into the adjacent control plot. Results demonstrate that SINV-3 is an effective natural control agent against the invasive ant, S. invicta; the virus causes no known detrimental ecological impacts, is host specific, and sustained in the environment.
Subject(s)
Ants , RNA Viruses , Animals , DNA Viruses , Florida , RNA Viruses/geneticsABSTRACT
The red imported fire ant, Solenopsis invicta (Buren), is an invasive pest of agricultural, urban, and natural areas. It is also considered a public health pest due to its painful stings. While it can be efficiently controlled by commercially available fire ant baits formulated with a corn-grit carrier, rain or irrigation is thought to degrade the carrier, compromising bait effectiveness. This study assessed the effect of irrigation on the efficacy of water-resistant and standard fire ant bait formulations, by comparing worker number, brood volume, and queen survivorship after access to water-soaked baits and to irrigated, bait-treated sod. In initial testing, wetted water-resistant and standard baits reduced fire ant colonies less than dry baits, both when baits were given to colonies directly and when colonies were given access to baits broadcasted (i.e., scattered) atop sod. Comparisons of the efficacy of piled versus broadcast applications of water-resistant and standard baits revealed reductions of >88% in adults and brood and no surviving queens for all bait treatments. This result was unexpected because piled baits were hypothesized to be better protected from irrigation than broadcast bait applications. In a field study, irrigated water-resistant and standard baits caused similar and significantly higher reductions in fire ant foraging activity relative to an untreated control. These results indicated that both the water-resistant and standard fire ant bait provided significant fire ant reductions even after irrigation.
Subject(s)
Ants , Insecticides , Animals , Insecticides/pharmacology , WaterABSTRACT
The early detection and identification of the red imported fire ant Solenopsis invicta are crucial to intercepting and preventing it from becoming established in new areas. Unfortunately, the visual identification of fire ants to species is difficult and ant samples must often be couriered to an expert for positive identification, which can delay control interventions. A lateral flow immunoassay that provides a rapid and portable method for the identification of S. invicta ants was developed and commercialized, and it is available from Agdia, Inc. under the trade name InvictDetectTM. While the test was 100% accurate when using the recommended minimum sample of three ant workers, InvictDetectTM was field tested for the first time while using homogenates prepared from single S. invicta workers to determine the effectiveness of the method under these non-recommended conditions. Disregarding social form, the false negative rate was 25.5% for an initial single worker ant test and 10% after a repeat test was performed. The InvictDetectTM false negative response was independent of worker weight. Though InvictDetectTM requires a minimum of three worker ants, the test improves upon current identification methods because it can be conducted in the field, be completed in 10-30 min, and requires no special training or expertise.
ABSTRACT
Natural enemies of the imported fire ants, Solenopsis invicta Buren S. richteri Forel (Hymenoptera: Formicidae), and their hybrid, include a suite of more than 20 fire ant decapitating phorid flies from South America in the genus Pseudacteon. Over the past 12 years, many researchers and associates have cooperated in introducing several species as classical or self-sustaining biological control agents in the United States. As a result, two species of flies, Pseudacteon tricuspis Borgmeier and P. curvatus Borgmeier (Diptera: Phoridae), are well established across large areas of the southeastern United States. Whereas many researchers have published local and state information about the establishment and spread of these flies, here distribution data from both published and unpublished sources has been compiled for the entire United States with the goal of presenting confirmed and probable distributions as of the fall of 2008. Documented rates of expansion were also used to predict the distribution of these flies three years later in the fall of 2011. In the fall of 2008, eleven years after the first successful release, we estimate that P. tricuspis covered about 50% of the fire ant quarantined area and that it will occur in almost 65% of the quarantine area by 2011. Complete coverage of the fire ant quarantined area will be delayed or limited by this species' slow rate of spread and frequent failure to establish in more northerly portions of the fire ant range and also, perhaps, by its preference for red imported fire ants (S. invicta). Eight years after the first successful release of P. curvatus, two biotypes of this species (one biotype occurring predominantly in the black and hybrid imported fire ants and the other occurring in red imported fire ants) covered almost 60% of the fire ant quarantined area. We estimate these two biotypes will cover almost 90% of the quarantine area by 2011 and 100% by 2012 or 2013. Strategic selection of several distributional gaps for future releases will accelerate complete coverage of quarantine areas. However, some gaps may be best used for the release of additional species of decapitating flies because establishment rates may be higher in areas without competing species.
