Sorting the Collection
Sorting the Collection

 

Classical biological control, or biocontrol in short, is the use of a host-specific natural organism to manage the population of another, the target species. The target species being managed is a pest or weed which is causing economic damage to crops, negatively affecting animal or human health, causing nuisance to people, or negatively affecting native or endemic species.

The principle of biocontrol is to achieve a sustainable balance by introducing a natural enemy from the target pests’ native range. Islands have proven very suitable for biocontrol due to their isolation and ecological simplicity, and St Helena is no exception.

The St Helena biocontrol Facility

Biocontrol has a long and successful history on St Helena and this is summarized here. In addition, there are also a number of parasitic wasps present of unknown date of introduction which are presumed to have arrived via infested produce or plants. These include the very useful species Encarsia formosa, and Aphidius spp.

In addition, there are also a number of parasitic wasps present of unknown date of introduction which are presumed to have arrived via infested produce or plants. These include the very useful species Encarsia formosa, and Aphidius spp.

 

A large number of the early introductions consisted of a single release of a few individuals which didn’t survive to establish themselves on the island. Experience around the world has indicated that success of biocontrol agents is directly related to the number introduced, with higher numbers leading to a higher likelihood of establishment and success.  The biocontrol unit addressed this from 1995 onwards by breeding up new biocontrol agents in a programme of repeated releases of as high numbers as possible. Those achieved in the early phases of mass breeding and release for each of the 8 species is shown in the table below:

 

Target pest

Biocontrol agent

Numbers released at a range of sites around the island

Diamondback moth Diadromus collaris

16,031

Cotesia plutella

13,401

Cabbage leafminer Diglyphus begini

3,022

Citrus woolly whitefly Cales noaki

2,047

Citrus psyllid Tamarixia dryi

137

Medfly Fopius ceratitivorous

11,572

Psytallia concolour

31,326

Pumpkin fly Psytallia phaeostigma

9,806

 

Key factors on St Helena which have contributed to the success of the introductions from 1995 onwards are therefore the presence of dedicated and experienced staff, mass-production and multiple release of the biocontrol agent on-island in a dedicated facility to ensure establishment through large scale and repeated introductions, and collaboration with farmers to avoid killing biocontrol agents through extensive use of broad-spectrum pesticides.

 

 

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