Lychnis moth (Hadena bicruris) lays more eggs in isolated areas

The Lychnis moth (Hadena bicruris) is laying more eggs on white campion (Silene latifolia), due to the increasing fragmentation of the countryside. Dutch researcher Jelmer Elzinga studied how many white campion seeds were eaten by Lychnis moth caterpillars at various locations along the River Waal.

Elzinga discovered that at small and isolated locations, Lychnis moth caterpillars consumed more white campion seeds. This increased consumption was thought to be due to a decrease in the number of ichneumon flies, which kill the caterpillars. However, Elzinga demonstrated that this hypothesis is not correct.

Upon hatching, Lychnis caterpillars eat the seeds of the white campion on a massive scale. Half of these caterpillars die prematurely due to attacks by ichneumon flies. The increasing fragmentation of the countryside means that areas of natural habitat are becoming smaller and more isolated. Moths, such as the Lychnis, are thought to easily spread between the various fragments whereas the much smaller ichneumon flies cannot.

Based on this knowledge, Jelmer Elzinga investigated whether caterpillars more frequently attacked white campion in strongly fragmented areas. It was expected that the poor distribution of the ichneumon flies would lead to less caterpillars dying, and therefore the plants being attacked more.

Elzinga discovered that the white campion was indeed attacked more in small and isolated growing areas. He also found that in such areas, fewer caterpillars were attacked by ichneumon flies and fewer ichneumon fly species were present.

However, ichneumon flies only attack the caterpillars when they are almost fully grown. Therefore, the poor distribution of the ichneumon flies could not explain the increased consumption of the seeds. Elzinga found that this extra consumption was due to the Lychnis moth laying more eggs in isolated growing locations of the white campion.

The research was funded by the Netherlands Organisation for Scientific Research.