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Sunday, July 18, 2010

The changing world of entomology:dealing with insect pests without pesticides and chemicals

 Scientists in the country of Thailand have discovered that an insect known as the cassava mealybug, is
 responsible for devastating the production of cassava in the country.


What is cassava you ask? 
The first image below is an image of a cassava plant and directly below that image is a 
photo of  a full grown root of the plant


http://www.food-info.net/uk/products/rt/cassava.htm






Source of top image: http://amber.gsc.riken.jp/cassava/
Source of bottom image: http://www.food-info.net/uk/products/rt/cassava.htm
"Cassava is a shrubby, tropical, perennial plant, from which tapioca and other foods are made.The plant 
grows tall, sometimes reaching 15 feet, with leaves varying in shape and size. 
The edible parts are the tuberous root and leaves."


"Around the world, cassava is a vital staple for about 500 million people!!! Cassava's starchy roots
 produce more food energy per unit of land than any other staple crop. Its leaves, commonly 
eaten as a vegetable in parts of Asia and Africa, provide vitamins and protein. Nutritionally,
 the cassava is comparable to potatoes, except that it has twice the fiber content and a 
higher level of potassium."


Like most crops in our world, the Cassava plant  must contend with the fact that certain insects 
have evolved and which consume the Cassava plant in order to survive. Under many situations 
scientists
might decide to use a chemical pesticide to try and reduce the population of the insect pest 
afflicting the 
plant. However, instead of using chemicals., scientists in Thailand are using a natural 
enemy of the  
 cassava mealybug,to try and control the population of this pest. Here is a photo of a 
cassava mealybug:






and here is the insect which scientists have found naturally preys on the mealybug, 
none other than
the " Anagyrus Lopezi" wasp:





" This mealybug, known to scientists as Phenacoccus manihoti. Originally from South America, 
it feeds only on cassava, sucking sap from the plants and causing them to shrivel. The mealybug
 apparently populated Thailand as a consequence of  Portuguese traders who brought it to the country
during  their business activities. Without any natural insect pests in the country, the population of  the 
mealybug skyrocketed out of control. In fact, ."The spread of cassava mealybug
 to about 200,000 hectares has been confirmed in eastern and northeastern Thailand, where the pest 
is causing yield losses as high as 50 percent. Since the country's cassava industry generates more 
than US$1.5 billion of income each year -- and the overall Thai cassava industry is worth US$ 3b!!!!
-- reductions of that magnitude could translate into hundreds of millions of dollars in economic losses, 
especially if the pest is allowed to spread further. 

Apparently this species of wasp was used successfully to deal with this same insect pest in 
Africa in the 1980's and so Thailand officials are hopeful that the wasp can once again deal
 with the mealybug, so they do not have to use other more environmentally harmful methods
 (such as pesticides) to control the mealybugs.
"Even when infestations are low, female wasps are able to detect and home-in on their prey, injecting
 their eggs into the mealybugs. The pest population is then gradually reduced, as the wasp larvae grow and as adult females feed on the host insect. The wasps pose no threat to humans, animals, or other insects.
The wasp proved so effective in sub-Saharan Africa that Hans Herren, the scientist who led the biocontrol effort there, was awarded the World Food Prize in 1995."
Let us hope that the  introduction of the Anagyrus Lopezi" wasp into the cassava fields will be able to 
control the population of mealy bugs, so that this important plant and crop can prosper and feed those
humans who have come to rely on the crop for sustenance And in doing so the wasp will make it 
unnecessary to try and control the mealy bug with potentially toxic pesticides!
Here is a video  which discusses the problem faced in Africa from the mealy bug  and also discusses entomologist  Hans Herren and his work to find a predator for
 the mealy bug, which turned out to be "Anagyrus Lopezi":


2 comments:

吳婷婷 said...

pleasure to find such a good artical! please keep update!!..................................................................

Wayne said...

Thank you for your kind words.I will try and update the information in this article as I find it becomes available.

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