Broadcast Baiting Research Articles

Effect of Irrigation on the Control of Red Imported Fire Ants (Hymenoptera: Formicidae) by Water-Resistant and Standard Fire Ant Baits.

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.

Efficacy of aerial broadcast baiting in reducing brown treesnake numbers

The brown treesnake (Boiga irregularis) is an invasive predator that was introduced on Guam as a stowaway in cargo after World War II. Since then, the population has exploded, attaining 50 to 100 snakes per ha in some areas. The snake has caused the extirpation of ten of the 12 native forest bird species on Guam. The U.S. Department of Agriculture, Wildlife Services, has a program to deter the spread of snakes from Guam to other islands. Hand capture from fences, trapping, toxic bait stations, and canine inspection of outbound cargo methods are used in the control program in various localized and accessible areas. We investigated aerial delivery of toxic baits as a potential method for a broader landscape control of brown treesnakes. Treated baits were deployed on 6-ha of forest at 37.5 baits per ha. Snake activity was reduced by 80 to 85% by the third application of toxicant. Nontarget bait-take was limited. Of 80 telemetered baits aerially deployed, 30 (38%) baits were taken by snakes, one was taken by a toad (Bufo marinus), and one was taken by a monitor lizard (Varanus indicus). Mortality was observed in all 30 cases of bait-take by the snakes. No evidence of ill effects was observed in the toad or the monitor lizard after bait ingestion. Aerial delivery of toxic baits holds promise as an economical, targeted method to control invasive brown treesnakes over large areas of land.

Effect of broadcast baiting on abundance patterns of red imported fire ants (Hymenoptera: Formicidae) and key local ant genera at long-term monitoring sites in Brisbane, Australia.

In 2001, the red imported fire ant (Solenopsis invicta Buren) was identified in Brisbane, Australia. An eradication program involving broadcast bait treatment with two insect growth regulators and a metabolic inhibitor began in September of that year and is currently ongoing. To gauge the impacts of these treatments on local ant populations, we examined long-term monitoring data and quantified abundance patterns of S. invicta and common local ant genera using a linear mixed-effects model. For S. invicta, presence in pitfalls reduced over time to zero on every site. Significantly higher numbers of S. invicta workers were collected on high-density polygyne sites, which took longer to disinfest compared with monogyne and low-density polygyne sites. For local ants, nine genus groups of the 10 most common genera analyzed either increased in abundance or showed no significant trend. Five of these genus groups were significantly less abundant at the start of monitoring on high-density polygyne sites compared with monogyne and low-density polygyne sites. The genus Pheidole significantly reduced in abundance over time, suggesting that it was affected by treatment efforts. These results demonstrate that the treatment regime used at the time successfully removed S. invicta from these sites in Brisbane, and that most local ant genera were not seriously impacted by the treatment. These results have important implications for current and future prophylactic treatment efforts, and suggest that native ants remain in treated areas to provide some biological resistance to S. invicta.

Longevity of rodenticide bait pellets in a tropical environment following a rat eradication program

Invasive rodents (primarily Rattus spp.) are responsible for loss of biodiversity in island ecosystems worldwide. Large-scale rodenticide applications are typically used to eradicate rats and restore ecological communities. In tropical ecosystems, environmental conditions rapidly degrade baits and competition for baits by non-target animals can result in eradication failure. Our objective was to evaluate persistence of rodenticide baits during a rat eradication program on Palmyra Atoll; a remote tropical atoll with intense competition for resources by land crabs. Following aerial application, bait condition was monitored in four terrestrial environments and in the canopy foliage of coconut palms. Ten circular PVC hoops were fixed in place in each of Palmyra's four primary terrestrial habitats and five rodenticide pellets were placed in each hoop. Five coconut palms were selected in three distinct regions of the atoll. One rodenticide pellet was placed on each of five palm fronds in each coconut palm. Fresh baits were placed in all monitoring locations after each broadcast bait application. Bait condition and survival was monitored for 7 days after the first bait application and 6 days after second application. Bait survival curves differed between applications at most monitoring sites, suggesting a decrease in overall rat activity as a result of rodenticide treatment. One terrestrial site showed near 100 % bait survival after both applications, likely due to low localized rat and crab densities. Median days to pellet disappearance were one and two days for the first and second application, respectively. Differences in survival curves were not detected in canopy sites between bait applications. Median days to pellet disappearance in canopy sites were 2 and 4 days for the first and second application, respectively. Frequent rainfall likely contributed to rapid degradation of bait pellets in coconut palm fronds.

Improving the efficacy of aerial poisoning of brushtail possums (Trichosurus vulpecula) through reduced fragmentation of bait

In New Zealand, aerial delivery of sodium fluoroacetate (1080) baits to poison introduced brushtail possums (Trichosurus vulpecula) is a key pest management tool. GPS-guided broadcast baiting systems should expose all possums to large amounts of toxic bait, but some possums still survive despite being poisoned. This sub-lethal poisoning might reflect bait fragmentation, so we measured bait size before and after broadcast sowing from helicopter-slung buckets with spinners used to fling bait laterally. Mean bait size was smaller after sowing than before. The amount of fragmentation differed between operations and between buckets. Small fragments were concentrated under the flight path suggesting that they were caused by the spinner. Fragmentation increased with spinner speed. Removing the spinner resulted in less fragmentation. Use of spinners may therefore adversely affect poisoning efficacy by producing sub-lethal bait fragments. Solutions to this bait fragmenation problem include reducing spinner speed, removing the spinner, or development of shatterproof baits. A reduction in the amount of fragmentation is likely to reduce the need to sow large numbers of baits, so our findings could enable major reductions in toxin use.

Field Suppression of the Invasive Ant <I>Wasmannia auropunctata</I> (Hymenoptera: Formicidae) in a Tropical Fruit Orchard in Hawaii

The little fire ant, Wasmannia auropunctata (Roger) (Hymenoptera: Formicidae), is an invasive ant that forms supercolonies when it successfully invades new areas. W. auropunctata was first reported in Hawaii in 1999, and it has since invaded a variety of agricultural sites, including nurseries, orchards, and pastures. Amdro (hydramethylnon; in bait stations), Esteem (pyriproxyfen; broadcast bait), and Conserve (spinosad; ground spray) were tested for their efficacy against W. auropunctata in a rambutan, Nephelium lappaceum L. and mangosteen, Garcinia mangostana L., orchard by making treatments every 2 wk for 16 wk. Relative estimates of ant numbers in plots was determined by transect sampling using peanut butter-baited sticks. Significant treatment effects were observed on weeks 13-17, with reductions in ant counts occurring in the Amdro and Esteem treatments. During this period, the reduction in ant numbers from pretreatment counts averaged 47.1 and 92.5% in the Amdro and Esteem plots, respectively, whereas ant numbers in the untreated control plots increased by 185.9% compared with pretreatment counts. Conserve did not cause a reduction in ant counts as applied in our experiment. No plots for any of the treatments achieved 100% reduction. Pseudococcidae were counted on branch terminals at 4-wk intervals. The two predominant species, Nipaecoccus nipae (Maskell) and Nipaecoccus viridis (Newstead) were significantly lower in the Amdro and Esteem treatments on week 16 compared with controls. Many W. auropunctata were found nesting in protected sites in the orchard trees, which may have compromised the ground-based control methods. Absolute density estimates from shallow core samples taken from the orchard floor indicated the W. auropunctata supercolony exceeded 244 million ants and 22.7 kg wet weight per ha.

Vole Damage Control in Forest Plantations

Abstract The effects of five treatments (mowing with broadcast baiting, mowing with hand baiting, hand baiting with no mowing, herbicide, and untreated control) on vole population and damage to forest plantations were evaluated. All treatments caused reductions in vole feeding, as well as reduced seedling damage and potential seedling mortality. This study shows the practical importance of monitoring planting sites for vole populations in the fall prior to and after planting and suggests an immediate control of high and severe vole population ratings with rodenticide with or without mowing to minimize potential seedling mortality. North. J. Appl. For. 23(4):297–300.

Ecological Risk Assessment for Use of Agricultural Rodenticides in California

The California Department of Food and Agriculture holds registrations for four grain-based anticoagulant rodenticides used in agricultural areas in California to control the California ground squirrel. These rodenticides contain either chlorophacinone or diphacinone as the active ingredient at 0.005% or 0.01% by weight, and are applied by either broadcast or spot baiting techniques. Using residue data from recent field studies, an ecological risk assessment was performed for non-target species potentially receiving secondary exposure through consumption of squirrel carcasses. The species of concern included five birds (American kestrel, burrowing owl, common raven, golden eagle, red-tailed hawk) and one highly sensitive mammal, the coyote. Risks to nontarget species were estimated using a risk quotient (RQ) approach, with RQ values calculated using species-specific daily exposure estimates and levels of concern derived from subchronic toxicity studies. Exposure estimates for the birds of concern ranged from 0.05-0.21 mg/kg bw/day for chlorophacinone and from 0.04-0.16 mg/kg bw/day for diphacinone. For chlorophacinone uses, RQs for birds ranged from 0.172-0.724. RQ values for diphacinone were 16-18 times lower. Based on the methodology used and using EPA risk criteria, the RQ data indicate de minimus risks for all avian receptors of concern. Exposure estimates for adult and subadult coyotes spanned a range from 0.009-0.028 mg a.i./kg bw/day depending on the use pattern. RQs for mortality and blood coagulation were generally near, or slightly above, a value of 1.0 for all of the use patterns evaluated; however, because of the conservative exposure assumptions and other factors, it is highly unlikely that ecologically significant effects on coyotes does or could occur due to use of CDFA’s anticoagulant baits. Wildlife incidence data and population modeling studies corroborate this. Based on the weight of evidence, it is concluded that use of CDFA’s rodenticides for spot and broadcast baiting will not cause “unreasonable adverse effects” on coyote populations or those of other predators/scavengers that feed on squirrel carcasses.

Timing bait applications for control of imported fire ants (Hymenoptera: Formicidae) in Mississippi: Efficacy and effects on non-target ants*

An experiment was conducted to assess the efficacy of mid-day (11:00 – 13:00 h) and late evening (18:00 – 20:00 h) broadcast bait (Seige Pro®, 0.73% hydramethylnon) applications against black and hybrid imported fire ants (Solenopsis richteri Forel and S. richteri × invicta, respectively) and their impact on native ant species. It was hypothesized that evening bait applications would have less impact on native ant species that slow or cease foraging at night relative to mid-day applications. Bait was applied to a series of plots in northeastern Mississippi, USA, in summer of 2002 and 2003. Population densities and foraging activity of imported fire ants and native ants were compared between treated and control plots. Population density and foraging activity of imported fire ants were equally suppressed in plots receiving mid-day and evening broadcast bait applications. Population density of Monomorium minimum (Buckley), the little black ant, approached zero in treated plots during 2003 but remained relatively high in untreated control plots. Species richness declined in treated plots with no difference between mid-day and evening bait application. These data indicate that evening bait application offers no advantage over mid-day application in terms of preserving some native ant species.

Reduced risk anticoagulant baiting strategies for California ground squirrels

Author(s): Whisson, Desley A.; Gorenzel, W. Paul; Salmon, Terrell P. | Abstract: The anticoagulants diphacinone and chlorophacinone (0.01% and 0.005% concentrations) are used extensively for control of California ground squirrels (Spermophilus beecheyi). Because of concerns of risks to nontarget wildlife, there is a need to develop baiting strategies that minimize the amount of bait applied, while still providing a high level of control. In 1997 and 1998, we conducted laboratory studies to determine the effect of timing and number of bait applications, and amount of bait given per application on the efficacy of 0.01% diphacinone for California ground squirrels. Results suggest that only two applications with 4 or 5 d between applications are necessary to achieve control. This is in contrast to the label recommendation of three to four applications with 48 h between applications (spot baiting), and two applications with 2 or 3 d between them (mechanical broadcast baiting). Furthermore, in our study, squirrels only required a small amount (less than 4 g of bait) per application to receive a lethal dose. Field studies are underway to test this baiting strategy and various bait application methods in the field.

Efficacy of Zinc Phosphide Broadcast Baiting for Controlling Richardson's Ground Squirrels on Rangeland

Efficacy of Zinc Phosphide Broadcast Baiting for Controlling Richardson's Ground Squirrels on Rangeland