Mites to eradicate African invader

Sunday April 10, 2016 Written by Published in Environment
The feeding of galling mites results in the production of hairy galls on the leaves and stems of the plant host. The mites then live within the galls and depend on them for survival. 16041006 The feeding of galling mites results in the production of hairy galls on the leaves and stems of the plant host. The mites then live within the galls and depend on them for survival. 16041006

The Spathodea campanulata also commonly known as the African tulip tree is a large tree that can reach around 17 metres in height.

 

Because of its beautiful red orange flowers, fast growth and relative ease of cultivation, the African tulip tree is widely used around the world as a decorative plant.

Along with its decorative features it is also commonly used as a shade tree in parks and is frequently used as living fence posts.

However looks can be deceiving when it comes to this pretty tree, as it has become a serious threat when considering the wellbeing of our indigenous biodiversity and agriculture.

It has been nominated as among 100 of the “World’s Worst” invaders.

The African tulip tree is native to Central and West Africa. However it has managed to blossom its way across to the Pacific islands including American Samoa, Fiji, Tahiti, Hawaii, Niue, Tonga, Vanuatu and the Cook Islands.

Amongst some of these islands, it has become a destructive weed, invading indigenous forests along with greatly impacting agricultural production.

Within the Cook Islands the African tulip tree can be found on Rarotonga, Atiu, Mauke, Aitutaki and on Manihiki.

It was originally introduced to the Cook Islands as an ornamental plant. Today it is viewed as a problematic invasive alien plant, and worrying evidence from neighbouring Pacific Islands suggests that the problem is likely to become much more severe if control measures are not implemented.

Controlling the spread of the African tulip tree through mechanical and herbicidal actions has proven to be very labor intensive and expensive, as experienced by our sister island countries such as Fiji.

Ringbarking has also been found to be ineffective as only the above ground parts of the plant are killed.

Although herbicide application can effectively kill the plant, this method has been found impractical for the Cook Islands as the African tulip tree already covers large areas of the land, as a result of the vast amount of seeds produced.

With methods to eradicate the African tulip tree falling short, one potential solution involves the introduction of microscopic insects, called galling mites (Colomerusspathodeae), which can cause the deformation of the stems and petioles of the African tulip tree, causing the tree to die.

The galling mite can be found throughout the native distribution of the African tulip tree, thus it is abundant in  Ghana and present in Uganda in East Africa.

The galling mite is host specific to the African tulip tree, so in other words, only feeds on this plant. There has been no record of the galling mite feeding on any other plant species, making the galling mite a potential controlling agent for the Cook Islands.

An Environmental Impact Assessment (EIA) has been produced  on behalf of the Ministry of Agriculture for the introduction of the galling mite into the Cook Islands and published in December 2015.

The environmental consequences reported within the EIA have stated some interesting points which highlight doing nothing about the tree will result in continued invasion and a range of negative impacts to native species, medicinal plants, aesthetic values and agricultural productivity.

However, permanent reductions in the number of the African tulip trees could result in       replacement by other invasive species.

The EIA then concludes that the risks of introducing the galling mite a biological control agent are minimal and the potential benefits to native biodiversity and agriculture are substantial.

A robust protocol for the introduction of the Galling mite into the Cook Islands has been designed and described within the EIA, stating the use of powerful microscopes  to be used to ensure no contaminants (i.e other mites) are mixed in with the sample  brought to the Cook Islands. Initial mass rearing will be conducted in shade house  conditions by Cook Islands Ministry of Agriculture staff along with the assistance of  Dr Iain Paterson from Rhodes University Biological Control Quarantine Facility,  Grahamstown, South Africa, (who will travel on the same flight as the shipment of  mites).

Monitoring of plots at its initial stages will also be set to assess the impacts of mite within the Cook Islands.

Currently the EIA for the “Application to introduce Colomerusspathodeae for biological control of Spathodea campanulata (African tulip tree) in the Cook Islands”  is open for submission.

The EIA for this application can view found online on the National Environment Service page, with hard copies found at Te Ipukarea Society office in Tupapa, as well as other locations.

 

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