W
hat is Biology Good For?
Keeping Crops Insect-Free: Dipel

(This assignment is optional. Read this essay and answer the questions at the bottom for 3 extra credit points. You may only turn in one per six weeks. The assignment is due one week before the end of the six weeks. It is not necessary to visit the links in the text unless you are interested in more information.)

 


Zea mays, or corn, is one of the world's most important cereals with an annual global harvest approaching 560 million tons with main producers in the USA, China and Brazil (Novartis, 1998). However, 40 million tons of corn never reach the market because of damage by a voracious PEST of corn, in short - a Hungry Bug!.


The Culprit: The European Corn Borer, or ECB, also known as Ostrinia nubilalis. The favorite food of the ECB is corn - field corn, popcorn, seed corn, and sweet corn, plus it also likes to eat sorghum, cotton, and many vegetables. Overall, yield losses and costs associated with the European Corn Borer cost farmers in the United States billions of dollars each year.

 

The European Corn Borer is an introduced insect species that belongs to the order Lepidoptera. It probably arrived in North America during the early 1900s in broom corn imported for the manufacture of brooms. First noticed near Boston MA, in 1917, the European corn borer spread gradually from southern Michigan and northern Ohio. It reached Illinois in 1939, Iowa in 1942, Nebraska in 1944, and South Dakota in 1946. It has since spread northward into northern Minnesota, North Dakota, and the Canadian provinces of Quebec, and south along the Atlantic Coast and Missouri, Arkansas, Kansas, Oklahoma, and the Gulf states. It is now present in all but the seven most western continental states. [Source]

"Munch, munch, munch...."

Damage and yield loss of the corn plant result from:

1.Leaf feeding
2.Midrib feeding
3.Stalk tunneling
4.Leaf sheath feeding
5.Ear damage

"Munch, munch, munch...."

[Image]


I
s there No Stopping this Hungry Bug? To the rescue...Dipel, a natural insecticide manufactured by the Dragon Chemical Corporation, Roanoke, VA. (and many other companies, under many different trade names like Biobit, Cutlass, and Javelin). Dipel dust has been used for over 40 years to control the ECB and other leaf chewing worms in fields and home gardens.

What is Dipel? Dipel is a microbial insecticide - meaning that it is a bacteria that kills insects! A bag of Dipel Dust contains billions and billions of freeze-dried (dead) cells of the bacterium Bacillus thuringiensis (Bt). These bacteria live naturally in the soil and cause no harm to humans, birds, or plants.

Bt has the useful feature of producing a crystalline protein toxin as it grows. These proteins, called 'crystal proteins', are highly toxic to Lepidopteran insects. When the freeze-dried Bt cell is eaten by the insect, the toxin inside the cell is consumed as well. After the Bt crystal protein is eaten by an insect like ECB, it is activated in the insect's gut. The toxin attaches to the stomach lining of the ECB, where it paralyzes and destroys the cells of the gut wall, allowing the gut contents to leak into the insect's body cavity. Poisoned insects normally remain on plants for a day or two after treatment, but they do not continue feeding and will soon die within 2 or 3 days. Only a small amount of leaf sprinkled with Dipel needs to be eaten to provide a lethal dose...

Bt crystal protein is toxic to most Lepidopterans, like the caterpillars that attack cabbage, broccoli, cauliflower, and Brussels sprouts; bag worms and tent caterpillars on trees and shrubs; larvae of the gypsy moth and other forest caterpillars; and the Indian meal moth larvae in stored grain.

Bt is a very safe insecticide to humans, pets, and plants. Treated vegetables and plants can be picked and eaten anytime after spraying with Dipel. Pets and family members can return to the treated area as soon as the Dipel dust is dry and settled. Dipel breaks down quickly when exposed to sunlight - and Dipel is even used by many by organic gardners, since it is a product of natural origin. The Dark Side of Dipel (we will talk about this in class) is that Monarch Butterflies are also Lepidopteran insects....

Dipel in the age of the Genome: Recent advances in Agricultural Biotechnology have produced plants in which the bacterial crystal protein gene - the 'cry' gene - is inserted directly into the plant's chromosome. Such genetically modified plants (GM plants or GMOs) make the Bt crystal protein inside their cells, so that there is no need to sprinkle Dipel on plants. Since their introduction in the 1990s, a large percentage of crops in the United States have been genetically engineered with Bt to resist ECB. Products on the market genetically engineered with Bt to resist Lepidopteran pests include Monsanto's MaisGard and YieldGard Bt corn, Bollgard Bt cotton, and NewLeaf Bt potatoes. This will be the topic of our class discussion starting April 1st...!

Material for this Good For came from
The Iowa State University Entomology Site
The ECB Home Page
How corn is damaged by the ECB

The text of this "What is Biology Good For" exercise is copyrighted under the name of Dr. Kathleen A. Marrs, 1999, 2000, 2001, 2003. There are no restrictions on its use by educators or by non-profit institutions as long as its content not modified, proper copyright acknowledgement is retained, and this statement is not removed.

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Extra Credit Questions: Please answer the following questions on a piece of paper and turn it into me.


1. Why is Dipel called a 'microbial insecticide'?
2. How does Dipel kill Lepidopteran insects - in your own words?
3. How do you think the European Corn Borer got from Boston MA to the entire East Coast and Midwest of the US and Canada in just over 100 years??? (For a hint, see the photo that pops up when you click on
The ECB Home Page).

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