APRIL
2008

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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Check out these books by Tom Turpin:

Flies in the face of fashion

What's Buggin You Now?

 

 

 

04-24-08

Download the audio of On Six Legs: MP3, WMV.

How Beneficial are Birds in Battles with Bugs?


It is well known that many species of birds eat insects. Birds, like any other animals that chow down on insects, are called insectivores. Some insectivorous birds are entirely dependent on the insect world for food while other bird species use insects for a portion of their diet. Either way, it has always been a matter of speculation as to whether or not bird predation helps keep insect populations in check.

C. N. Ainslie with the U.S. Bureau of Entomology wrote an article in 1930 titled, "The Economic Importance of Birds as Insect Predators." In this article Ainslie writes, "The great army of insect-eating birds are entitled to full credit for their efforts in our behalf."

In spite of this accolade for insect-devouring birds, Ainslie argues that there is another side to the story. While birds consume a lot of insects, such predation is probably of little value in keeping insect populations at low levels. Or for that matter, in reducing insect populations that reach very high levels.

According to Ainslie, birds can generally find enough insect food for themselves and their offspring. However, when a bird's craw is full it won't eat more insects, even if additional insects are available for consumption. So when insect populations are at very high levels, the only way for birds to keep up would be to increase their populations. That can't be done rapidly; so Ainslie argues that birds really don't regulate insect populations in the same way as other environmental factors do. But as the quote above expresses, we humans appreciative any help in our age-old battle to kill insects.

Birds might not play a major role in regulation of insect populations in ecological systems, but it might be a different matter down on the farm. Indeed, prior to the advent of widespread use of insecticides and before farms became less diversified, poultry played a major role in insect control in agriculture.

For instance, the large bird that is native to North America and was Ben Franklin's nominee for the U.S. national symbol. We're talking turkey here. Before World War II, the turkey was more than Thanksgiving dinner to many farmers. In the south, turkeys were used to control hornworms in tobacco fields.

Turkeys will eat any kind of insect. According to turkey farmers, the only insects that turkeys will not eat are the ones they can't catch. The food habits of turkeys, and the fact they can be trained to follow a farmer, allowed this living insect-control detail to be easily moved from one field to another as the need for insect control dictated.

Chickens also played a role in insect control on many farms. In general, chickens had the run of the farmstead, where they scratched up and consumed fly maggots and pupae in the animal barns.

One chicken-based insect-control approach was for that infamous orchard pest the plum curculio. These are the little worms that are found in cherries, peaches, plums and apples and generally cause infested fruit to fall. The plum curculio pupates in the soil beneath the fruit trees that it infests. Chickens are happy to scratch up and devour plum curculio from the orchard soil where the insect spends the winter. So allowing chickens to run in the orchard helped reduce the population of these insects prior to the time they laid eggs in the young fruit.

Some farmers embellished this chicken-scratching system a bit by introducing a few calves into the orchard. It seems that plum curculio drop to the ground when infested trees are vibrated. Modern pest managers use a stick to strike the tree in order to see if any curculio dropped into a sheet on the ground. The calves would rub on the tree, dislodging the insects that were then consumed by the waiting hungry chickens. That, folks, is an environmentally safe way to kill insects and cut down on chicken feed costs at the same time.

 

 

Writer: Tom Turpin
Editor: Olivia Maddox