April
2017

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

Download the audio files or subscribe to our podcast.

 

Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

4-27-17

Download the audio of On Six Legs: MP3
Follow us online at Purdue Agriculture News Columns

Red dye from insects


Like it or not, insects show up everywhere, even in some unexpected places. One of those places is in products needing red coloration. I’m talking about a variety of things including paint, food coloring, medications, and cosmetics. Yep, that rouge or bright red lipstick just might get its color from insects.

We are talking about a red color known by several names including carmine, natural red 4, and cochineal. That last name refers to the fact that an insect is the source for this bright-red pigment. Cochineal insects contain a chemical called carminic acid from which carmine is produced. The carminic acid functions as a defensive chemical to help protect the insect from predators.

Cochineal insects belong to a group of insects generally known as scales. These small insects are so named because the wingless females of some species encase themselves in a protective covering that resembles a fish scale. Some scale insects are called armored scales because they have a hard protective covering. In others, the covering is soft, and they are known as soft-shelled scales. Scale insects feed on plant sap, and many species are considered pests because their feeding can damage plants.

The cochineal scale, Dactylopius coccus, feeds on cactus plants and is commonly found on the well-known prickly pear cacti. The fact that the cochineal scale can be used to produce a red dye was probably discovered well over 1,500 years ago by native peoples of Central and North America. Aztecs and Mayans actually used cochineal dye as a currency. European settlers to the New World quickly discovered cochineal, and it became a valued product for export to Europe in the 17th century.

To be sure, some red dyes had been available to people way back in ancient Greek and Roman times. One Old World red dye was known as kermes. This dye was also produced from bodies of a scale insect (genus Kermes) that is found in the Mediterranean region. Like its New World counterpart, this dye was used as a type of currency in the Middle Ages and some people even paid their rent with this insect product. The kermes dye – often called grain because of the seed-like look of the insects – was inferior to the cochineal dye and was quickly replaced by the New World product.

The production of cochineal dye is a laborious process. First, the insects have to be collected from the cactus plants by brushing them by hand into a basket. And that is a lot of brushing, because it takes some 70,000 insects to produce a pound of dye.

Today, Peru is the largest producer of carmine in the world, exporting some 850 tons each year. Rural family members gather most of the cochineal insects for the industry from wild prickly pear cacti. However, a few farms in Peru specialize in cochineal production.

Cochineal insects are removed from the host plant and dried either in sunlight or in an oven to preserve them. The dried insects are then sold to traders, who in turn supply the processing plants where carmine is produced.

Historically, several methods have been used to extract the carmine from the insects. One method is to make a powder of the dried insects, and then boil the powder in ammonia or sodium carbonate solution. Alum is added to the mixture to precipitate the red aluminum salt. Sometimes, the dried insects are just boiled in water, and the resulting clear solution is treated with alum. Either way, red carmine dye is produced.

In addition to adding red color to consumer products, carmine can also be used as a stain to identify glycogen in animal tissues. This technique is widely used in diagnostic laboratory procedures associated with human health. I remember using what was called Best’s carmine to stain tissue as part of a college histology course I took years ago. I don’t recall that the teacher pointed out that the carmine stain was an insect product.

But then, I am willing to wager a dollar or two that many folks who encounter bright red lipstick either first or second hand probably don’t know that the color comes from an insect. Maybe it is just as well. After all, knowing that your lipstick is “essence of smashed scale insects” might not appeal to everyone!

 

Writer: Tom Turpin
Editor: Cindie Gosnell