hunger” [40]. Bergman then described the most notorious species of butterflies that
attack apple- and pear trees.
Bergman had studied the subject thoroughly and described many methods that
had been suggested to him, and explained why they would not work. Fortunately,
he could also deliver several suggestions on how to get rid of the butterflies and
their caterpillars. First, the species had to be identified as it determined the remedy.
Some species could be caught by fires by night: they were attracted by the light but
had to pay with their lives. Others could be killed with swatters, a proper work for
children according to Bergman. Other species could be caught by catching the
females and attaching them to the trees with needles. The males could then be
caught when they came for mating with the immobilised females.
To kill the caterpillars, Bergman had two solutions depending on the species.
Those who spent the winter nestled in the trees could be picked manually. Another
solution was to release beetles of the gender Carabus, especially the blue ground
beetle, which eat caterpillars. The beetles themselves were harmless since “as little
as a wolf can learn to eat apples, as impossible is it for these small predators to eat
vegetables”. After criticism from an anonymous author, claiming that the caterpillars of the butterfly Aporia crataegi were the main problem, Bergman had to
deliver a defence of his ideas in a public letter to the Secretary of the Academy [41].
Apparently, the solutions Bergman provided were not effective enough, and
caterpillars continued to eat the leaves from the Swedish fruit trees. Therefore, the
Academy renewed the question in 1768. This time four answers were delivered, and
after opening the sealed author tickets it turned out that Bergman, now professor of
chemistry, once again was the winner. The second prize went to Carl Fredric Lund
(1716–1776), the Mayor of Linköping, who suggested planting spruce between the
fruit trees and Adolph Modéer (1739–1799), who frequently delivered answers to
the Academy’s competitions. The fourth answer came from an unidentified person
with initials C. F. H. [42].
Since 1762, Bergman had gained much additional knowledge, and in his second
essay he focused on two insects. The first, the winter moth, he had found
responsible for most of the damaged during the past years. He had collected the
caterpillars and placed them in a bell jar with suitable food and soil. After some
time, the caterpillars buried themselves in the soil, and Bergman buried the bell jar
outside. In October, moths appeared, some with wings (males) and some without
(females). The wingless females climbed the tree in order to mate with the males.
Bergman could observe the mating and how the small eggs were laid close to the
buds of the fruit trees. With this knowledge the solution was simple: in September
1767 he attached birch bark around the trunk of the apple trees in a small garden
and painted it with sticky tar. In October the female moths, attempting to climb the
trees, got stuck in the tar. The other insect was a weevil Curculio pomorum, for
which there was no better treatment than to cut off and burn infected twigs. After a
few years, the problems would be under control, Bergman promised. Bergman’s
method of capturing the climbing insects was successfully tried by count Cronstedt
and Mine Councillor (bergsrådet) Adlerheim, who caught 28,716 females the following year [43].
5.3 Bergman’s Research in Entomology
69
attack apple- and pear trees.
Bergman had studied the subject thoroughly and described many methods that
had been suggested to him, and explained why they would not work. Fortunately,
he could also deliver several suggestions on how to get rid of the butterflies and
their caterpillars. First, the species had to be identified as it determined the remedy.
Some species could be caught by fires by night: they were attracted by the light but
had to pay with their lives. Others could be killed with swatters, a proper work for
children according to Bergman. Other species could be caught by catching the
females and attaching them to the trees with needles. The males could then be
caught when they came for mating with the immobilised females.
To kill the caterpillars, Bergman had two solutions depending on the species.
Those who spent the winter nestled in the trees could be picked manually. Another
solution was to release beetles of the gender Carabus, especially the blue ground
beetle, which eat caterpillars. The beetles themselves were harmless since “as little
as a wolf can learn to eat apples, as impossible is it for these small predators to eat
vegetables”. After criticism from an anonymous author, claiming that the caterpillars of the butterfly Aporia crataegi were the main problem, Bergman had to
deliver a defence of his ideas in a public letter to the Secretary of the Academy [41].
Apparently, the solutions Bergman provided were not effective enough, and
caterpillars continued to eat the leaves from the Swedish fruit trees. Therefore, the
Academy renewed the question in 1768. This time four answers were delivered, and
after opening the sealed author tickets it turned out that Bergman, now professor of
chemistry, once again was the winner. The second prize went to Carl Fredric Lund
(1716–1776), the Mayor of Linköping, who suggested planting spruce between the
fruit trees and Adolph Modéer (1739–1799), who frequently delivered answers to
the Academy’s competitions. The fourth answer came from an unidentified person
with initials C. F. H. [42].
Since 1762, Bergman had gained much additional knowledge, and in his second
essay he focused on two insects. The first, the winter moth, he had found
responsible for most of the damaged during the past years. He had collected the
caterpillars and placed them in a bell jar with suitable food and soil. After some
time, the caterpillars buried themselves in the soil, and Bergman buried the bell jar
outside. In October, moths appeared, some with wings (males) and some without
(females). The wingless females climbed the tree in order to mate with the males.
Bergman could observe the mating and how the small eggs were laid close to the
buds of the fruit trees. With this knowledge the solution was simple: in September
1767 he attached birch bark around the trunk of the apple trees in a small garden
and painted it with sticky tar. In October the female moths, attempting to climb the
trees, got stuck in the tar. The other insect was a weevil Curculio pomorum, for
which there was no better treatment than to cut off and burn infected twigs. After a
few years, the problems would be under control, Bergman promised. Bergman’s
method of capturing the climbing insects was successfully tried by count Cronstedt
and Mine Councillor (bergsrådet) Adlerheim, who caught 28,716 females the following year [43].
5.3 Bergman’s Research in Entomology
69