When playing around with insects, a single mistake can cost you dearly. Étienne Léopold Trouvelot wanted to interbreed a European moth species, the gypsy moth (Lymantria dispar), with native US silk-producing moths to make them more resistant to disease. Unfortunately, his moths escaped and spread quickly, causing millions of dollars in damages every year. To counter the spread of this very expensive all-consuming moth, a 3 cm large monster beetle, the forest caterpillar hunter (Calosoma sycophanta), has been called to aid.
The great escape
The year is 1869, Massachusetts, USA. Étienne had been raising gypsy moths in the forest behind his house since the mid-1860’s. He had taken them from France as egg masses, from which he fled after the coup. Raising them was easy enough, they are able to consume leaves from hundreds of species of plants, trees and shrubs, so finding food for them is easy. He aimed to cross-breed them with native silk moths to create more resistant silk moths in the USA. Unfortunately, some larvae escaped. Whether he warned the officials or not about the escape is debated. What is not debated, however, is the quick spread of the escapees across USA territory. The first years after their release, they were considered a mere nuisance. However, in 1889, the first major outbreak occurred leading to massive tree defoliation, houses and sidewalks covered with caterpillars and caterpillars raining down upon residents. The first eradication program began in 1890 and the struggle has been so intense that it has been dubbed, the Great Gypsy Moth War (1).
Release the Titan
To help them in the struggle against this voracious caterpillar, a titan of a beetle was imported from Europe to the USA. This beetle reaches sizes up to 3 cm and has an appetite for caterpillars and pupae, amongst which the ones from the gypsy moth. The beetle in question is the forest caterpillar hunter (Calosoma sycophanta).
In order to handle the caterpillars of the gypsy moth, large jaws are needed. And boy o boy does this beetle have jaws!
Not only the adults of this beetle attack caterpillars and pupae of the gypsy moth, also their larvae munch away at them! Therefore, between 1905 and 1910, 35,830 beetles and 19,930 larvae of this beetle were released in New England to help control gypsy moth numbers (2). Currently, steady populations of this beetles exist in large parts of New England. The abundance and general distribution of these beetles in the areas heavily infested by the gypsy moth warrants the belief that it is one of the most important of the imported natural enemies of this pest. A study on their efficiency indicated that the larvae of this beetle kill up to 70% of the pupae of the gypsy moth (3).
Restore the balance
This beetle is good in what it does, eating caterpillars and pupae. But as with any “predator – prey” relation, a balance needs to be found. If there are many caterpillars, the number of beetles will increase. The increase of the number of beetles will decrease the number of caterpillars, taking away food for the beetles again. This causes the number of beetles to decrease. This in turn will give the caterpillars the opportunity to increase in number again.
In this way, a balance between the gypsy moth numbers and the beetle numbers is kept. This also means that getting rid of the caterpillar completely in the USA will not be reached in this way. Although complete eradication is not reached, the beetle helps to significantly reduce the number of gypsy moths and thereby reduces damage. So, we are lucky that this monster of a beetle is happy to lend us a jaw!
- The Great Gypsy Moth War: A History of the First Campaign in Massachusetts to Eradicate the Gypsy Moth, 1890-1901. (2005) Robert J. Spear – University of Massachusetts Press; ISBN: 978-1-55849-479-4
2) Biological control of insect pests in the continental United States (1956) Curtis Paul Clausen, U.S. Dept. of Agriculture, Washington.
3) PREDATION BY CALOSOMA SYCOPHANTA L. (COLEOPTERA: CARABIDAE): EVIDENCE FOR A LARGE IMPACT ON GYPSY MOTH, LYMANTRIA DISPAR L. (LEPIDOPTERA: LY MANTRIIDAE), PUPAE (1985) Ronald M. Weseloh – The Canadian Entomologist 117: 11 17-1 126.