Field Evaluations of the Efficacy of Distance Plus on Invasive Ant Species in Northern Australia

Abstract

The efficacy of Distance Plus Ant Bait, containing the insect growth regulator pyriproxyfen, was tested in the field against two invasive ant species in northern Australia: African big-headed ant (Pheidole megacephala (F.)) and yellow crazy ant (Anoplolepis gracilipes (Fr. Smith)). Results were also gained for a third pest species, Singapore ant (Monomorium destructor (Jerdon)), from one trial focused primarily on P. megacephala. Five studies were conducted throughout northern Australia, each with different protocols, but common to all was the broad-scale dispersal of Distance Plus, coupled with long-term monitoring of ant population levels. Additionally, a laboratory trial was conducted to assess if there was a direct toxic effect by the bait on A. gracilipes workers, and ant community data were collected at some sites in the A. gracilipes trial to assess nontarget impacts and subsequent ecological recovery. All three species were greatly affected by the treatments. The abundance of P. megacephala declined dramatically in all trials, and by the final assessment for each study, very few ants remained, with those remaining being attributable to edge effects from neighboring untreated properties. At both sites that it occurred, M. destructor was initially at least codominant with P. megacephala, but by the final assessment, only three M. destructor individuals were present at one lure at one site, and only a single individual at the other site. Abundance of A. gracilipes fell, on average, to 31% of control levels by 91 d and then slowly recovered, with subsequent treatments only providing slightly greater control. No direct toxic effect on workers was found in the laboratory trial, indicating that population declines of A. gracilipes were typical bait-related declines resulting from reduced worker replacement. Nontarget impacts of the bait could not be distinguished from the negative competitive impacts ofA. gracilipes, but there was a noticeable absence of some key common ant species posttreatment, which was more likely the result of baiting rather than competitive exclusion. The species composition of treated and untreated sites was statistically indistinguishable in multivariate analysis within 2 yr posttreatment, indicating ecological recovery. Our findings indicate that Distance Plus has great potential for invasive ant management.

Previous diet affects the amount but not the type of bait consumed by an invasive ant

“…Field trials determined that a fishmeal‐based bait was attractive to yellow crazy ants, and this type of bait has been used successfully in control programs on Christmas Island . Despite the widespread use of fishmeal‐based baits for yellow crazy ant eradication and control programs, more recent studies have shown that corn grit‐based baits can be effectively used for yellow crazy ants . The Yellow Crazy Ant Eradication Program run by the Wet Tropics Management Authority in Cairns, Australia, arguably the largest eradication program for this species with about 1000 ha under treatment, has used both fishmeal‐ and corn grit‐based baits with mixed effects .…”

“…14 Despite the widespread use of fishmeal-based baits for yellow crazy ant eradication and control programs, more recent studies have shown that corn grit-based baits can be effectively used for yellow crazy ants. 20,24,25 The Yellow Crazy Ant Eradication Program run by the Wet Tropics Management Authority in Cairns, Australia, arguably the largest eradication program for this species with about 1000 ha under treatment, has used both fishmeal-and corn grit-based baits with mixed effects. 26 Given variation in both the types of baits used and the effectiveness of control for yellow crazy ants, there is interest in determining if ecological conditions affect the attractiveness and effectiveness of particular bait formulations.…”

Low reduction of invasive ant colony productivity with an insect growth regulator

“… 19 Effective suppression of ant reproduction has been achieved with just a single application, both in the laboratory 20 and against wild populations 21 . However, despite this demonstrated efficacy, some ant species, particularly from outside the subfamily Myrmicinae, have shown lower or no reduction in reproductive capacity, population, or activity levels over time 9, 22 . Numerous factors can influence the efficacy of IGRs and lead to difficulties in assessing their usefulness.…”

“…Pyriproxyfen and ( S )‐methoprene are two IGRs that are commonly used for invasive ant control, and although both have been used in A. gracilipes control programs there is little published research investigating their effects on this species 18 . A 2013 study evaluated field efficacy of a pyriproxyfen bait and showed that a single application of bait resulted in a decline in A. gracilipes workers to 31% of abundance in untreated control sites 91 days after application 22 . Up to two follow‐up treatments (approximately three month spacing) resulted in no greater effect.…”

Ecological impacts on native ant and ground-dwelling animal communities through Argentine ant (Linepithema humile) (Hymenoptera: Formicidae) management in Japan

“…The treatments had few negative non-target effects, with the abundances of native ant species and other ground-dwelling invertebrates except for cockroaches being greater in the treated areas after L. humile suppression. Thus, fipronil is an effective compound species, and the non-target impacts of the products available are only vaguely known (Hoffmann and O'Connor 2004;Hoffmann et al 2010;Marr et al 2003;Plentovich et al 2010;Webb and Hoffmann 2013). The ecological cost of control efforts with toxicants poses a considerable risk for non-target species (Plentovich et al 2010).…”