In the late 1970s and early 1980s, colonies of the Asian hive bee Apis cerana and the European honey bee Apis mellifera were introduced to Irian Jaya from Java. The Asian bees brought with them the parasitic mite Varroa jacobsoni, while the European honey bees introduced another parasitic bee mite, Tropilaelaps clareae.
This raised concerns that the mites would eventually spread to the main beekeeping areas of Papua New Guinea (PNG) and destroy the fledgling beekeeping industry that was based on A. mellifera and also that they could spread to Australia by 'island-hopping' through Torres Strait. The establishment of these pests in Australia would have a severe environmental impact, would result in significant losses to the local beekeeping industry and would disrupt pollination services worth over $1 billion per annum. Hence, an ACIAR project (AS2/1990/028) was initiated in 1991 to gain information about the bee and mites in PNG. That project was followed by two further projects, one in PNG (AS2/1994/018), and another that extended the research into Irian Jaya (AS2/1994/017). Each project gained valuable insights into the bee and bee mite problem, not only in Papua New Guinea, but world-wide.
However, the need for cheap and effective ways of controlling parasitic Asian bee mites remained urgent. In Indonesia and the Philippines it was a high priority, and both countries independently sought assistance from ACIAR. The recent encroachment of Asian bee mites towards Australia also highlighted the need for further information on the mites and their bee hosts in order to improve local quarantine efforts and to establish a 'state of preparedness' here should a breach in quarantine occur.
The main weapon chosen was formic acid. It had already been used for controlling bee mites in Europe and the United States, but the formulations there relied on high concentrations that can be dangerous to humans. Research had revealed that low concentrations of formic acid could be just as effective at controlling bee mites, without posing danger to human health. Accordingly, this project tested and adapted this technology for use in Indonesia and the Philippines where formic acid is readily available. Because the method was cheap, safe and effective it was ideally suited to smallholder beekeepers and stood a high chance of being be quickly adopted.
The project aimed to implement an improved method for controlling bee mites, based on a formulation containing low concentrations of formic acid.
There were four subprojects. The first tested varying concentrations of analytical and industrial grade formic acid (ranging from 10 to 20%) for controlling T. clareae in Irian Jaya and V. destructor and T. clareae in Java. The second identified and produced molecular markers for strains of the Asian bees A. cerana, A. dorsata, and the mites T. clareae and Varroa species collected throughout Asia. The third subproject undertook research for a cheap and effective control of parasitic bee mites and other diseases of bees in the Philippines. This involved trying to find out whether it was feasible to eradicate V. destructor from certain islands of the Philippines.
The fourth clarified aspects of Varroa reproduction. This included assessing hormone profiles in the blood of A. cerana, A. mellifera, V. jacobsoni and V. destructor in the lead-up to, and immediately following, bee pupation.
Initial studies in the partner countries showed that low concentrations of formic acid (FA) did not significantly reduce A. mellifera worker bee longevity, yet killed adult T. clareae and V. destructor mites, albeit more slowly than high concentrations. As well, temperatures within local hived A. mellifera colonies were found to be similar to those in temperate regions. These findings suggested that low concentrations of FA could control mites in entire hived bee colonies if acid evaporation and natural airflow within hives was improved (to increase vapour production and dispersion) and if treatments were prolonged (to allow longer contact between the vapour and mites). Removing the bottom boards from beehives and replacing them with deep wooden trays capable of holding at least 3 litres of FA solution achieved this.
Tests using hives in which bee colonies were standardised in population size, strength and mite loading (V. destructor) showed that low concentrations of formic acid were as effective as higher concentrations in ridding colonies of V. destructor, both from the bodies of adult bees and from capped bee brood cells. Moreover, the use of low concentrations of FA was more effective because bee colonies given higher concentrations showed harmful side effects. The recommended procedure for local beekeepers to control mites in bee colonies housed in single-storey hives is for two successive treatments, each with 3 litres of 15% FA in water, applied via the trays at a 2-weekly interval. This procedure provides beekeepers with a cheap and effective means of controlling mites that will reduce production costs.
Other studies in the partner countries provided information on the pest status in local A. mellifera populations. Several known pathogens were detected. This information will now allow for more targeted studies on local bee diseases to improve honey yields. Serious brood disorders were also detected in A. cerana and A. dorsata colonies in Indonesia, but their causes were not determined. However, studies confirmed that the Varroa mites indigenous to A. cerana in both partner countries are harmless to A. mellifera and that the introduced V. destructor on A. mellifera does not seek local A. cerana as a host. This new information will now allow for V. destructor to be completely eradicated from certain areas and for other areas to be kept free of V. destructor, thus lowering dependence on mite control.
The commissioned organisation undertook DNA studies that provided new insights into the complex relationships between Asian bees (A. cerana and A. dorsata) and the parasitic mites they carry (Varroa spp., and Tropilaelaps spp., respectively) and on the potential pest-status of those mites for A. mellifera.
Studies on Varroa mite reproduction (jointly supported by ACIAR and RIRDC), along with work in previous ACIAR projects, confirmed that females of most Varroa genotypes lack the ability to reproduce on A. mellifera. An understanding of this phenomenon could provide a means for developing new mite control methods. A method was also developed in this project for readily distinguishing internal tissues and organs of Varroa mites. It involved embedding entire female mites in wax blocks, obtaining ultra-thin sections from them and staining the sections so that certain tissues coloured differently. This method will be useful for constructing 3D models of entire female mites to show the layout and organisation of their internal body parts and for developing a conceptual model of their reproduction system that, when complete, will pinpoint the time when reproduction is activated. This, in turn, will assist the search for signals that trigger reproduction.
Links:
[1] http://www.aciar.gov.au/country/Indonesia
[2] http://www.aciar.gov.au/country/Philippines
[3] http://www.aciar.gov.au/programarea/Livestock Production Systems