Selective and environmentally-friendly technologies for invasive ant and wasp pest management

Progress Report for June 2008 to B3 and stakeholders

Programme leader:               Dr Ashraf El-Sayed
Contract Manager:                Dr Max Suckling

Overview
This research programme aims to develop new environmentally-friendly tools, based on odorants for the management of invasive Hymenoptera. The research is focused on three invasive hymenopteran pests, the Argentine ant Linepithema humile, the German wasp Vespula germanica and the common wasp Vespula vulgaris. Here we summarise the progress up to June 2008 on the research undertaken. The report is summarised in two parts, ants and wasps as the odour management technologies differ between the groups, and there are separate objectives.  A stakeholder meeting was held in July 2007 and further meeting is planned for August 2008.

Wasps
Vespulid wasps, V. germanica, the German wasp and V. vulagris, the common wasp are pests and reach high densities in New Zealand beech forests, Nothofagus sp. in summer. Current population management techniques are based on old technologies and include the use of toxins which can be harmful to the environment. Our aim is to discover and develop new odorants that can be used as attractants for wasps in natural ecosystems, giving managers another tool to use in the population control of vespulid wasps.

We have conducted a total of 21 odour-based field trials on possible wasp attractants testing known and novel attractants and have some exciting leads. Experiments have been conducted at Mt. Thomas, Canterbury where natural wasp populations are large. A total of 13,959 wasps have been trapped in delta traps in these trials (spring 2007-autumn 2008). In addition, a number of the trials at Mt Thomas have been repeated in Hanmer. Some trapping was conducted by a local Hanmer wasp manager, who was provided with training in our methods, and funded to conduct the trials.

Further work on the individual compounds that attract worker wasps has commenced by conducting electroantennogram (EAG) work on wasps. Electroantennograms entail odours being blown past an antenna and determining which compounds are detected by the wasps. This technique will allow us to screen multiple odours for activity reducing the number of compounds that need to be trialled in the field

The premature departure of the PhD student candidate back to Europe in November (prior to degree registration at Auckland University) left the programme without a student over the summer. A US citizen has accepted the PhD fellowship, and he plans to arrive in August 2008.

Ants
One of the ways ants navigate their way around their environment is to deposit and follow small amounts of pheromone in the form of trails to find food sources and their nests. Our aim is to disrupt the trailing behaviour of Argentine ants sufficiently to reduce nest productivity in treated areas.

This work was originally funded through Better Border Biosecurity (B3, www.b3nz.org), thus had a good starting base from which to work from. The major component of the Argentine ant trail is (Z)-9-hexadecenal also known as Z9:16 Aldehyde. As an aldehyde, this compound is unstable in the environment, however, we have worked on ways to reduce the release rate, thus increasing the time that this compound is active in the environment.

Initial work was conducted in central city in Christchurch, disrupting natural ant trails on trees using pheromone-laden carnuba wax (10%) by weight. Disruption was measured by monitoring ant traffic rates before and after trail pheromone was applied during experiments in Hawaii (Suckling et al. in prep), using video analysis. This assessment and application of point source pheromone was refined and expanded by creating ant sand, consisting of sand coated with pheromone impregnated wax, and filming the trails before and after pheromone application. Ant sand provided many small point sources of pheromone rather that few large ones that were used in the initial trial. The ant sand was field trialled in collaboration with Dr Robert Peck, US Geological Survey at Volcanoes National Park, Big Island, Hawaii, in September 2007. Argentine ants dominate the landscape in open areas on Volcanoes National Park and provide a good population to work with. The USGS team shares our interest on novel approaches to invasive ants and they have provided technical support for the trials. The trials were conducted in small-large scale plots, 1m2, 4m2  (2007), 100m2  and 400m2 (2008) with foraging reduced by 90%. In addition, a novel assessment of trail disruption was trialled with success by measuring trail integrity before, during and after disruption.

This lead us to approach a US company with a microencapsulation formulation technology for similar compounds and the pheromone was encased in small balls ~10-100 μm in diameter. These microencapsulations are inert substances that break down slowly releasing the pheromone over weeks instead of days.

Trail disruption using the Suterra LLC product was tested in the field in January 2008 in Hawaii with 90% trail disruption achieved for 14 days (Fig. 2). This was repeated in May 2008 in Hawaii, increasing the application rate by three-fold, followed by a repeat application after 14 days. Experimental nests were placed in the field to assess the impact on Argentine ants at the colony level. The nests were made in such a way that the queens could not escape thus reducing the likelihood of ants abandoning the nest. Data are still being collected from this trial.  Although we don’t know what level of foraging disruption is needed to have nest-level impacts, the results are promising.

Highlights

• We were able to disrupt the foraging ability of Argentine ants in the field up for up to 14 days using a microencapsulated pheromone.

• We have used a novel approach to quantify ant trail disruption by generating R2 values from trail integrity of linear areas of natural trails. This work has been peer reviewed with reviewers suggesting that this technique may become the new standard for this area of research. The new concept of trail pheromone disruption has been well received for its potential.

• We have identified potential food sources that are more attractive to wasps than the bait currently employed by pest managers. Various compounds have been identified and will be developed further. A formulation concept has been developed and a private company has agreed to formulate our attractants in a mixture of waxes and oils readily suitable for ground or aerial application.

• A paper on the wasp research is being presented at the New Zealand Plant Protection Conference in August 2008 by Nicola White.

• A paper has been submitted to an international journal on other aspects of the new wasp attractants.

• Presentations on the ant research have been made at four international conferences, including the International Congress of Entomology in South Africa (July 2008).

• A paper on the ant research is under final revision for the Journal of Chemical Ecology.