Cockchafer

The cockchafer (genus Melolontha) belongs to the order Coleoptera and the family Scarabaeidae. It is a major agricultural and forestry pest widely distributed throughout Europe and parts of Asia. While the adult beetles are known for feeding on tree leaves, it is the larvae, commonly referred to as white grubs, that are responsible for significant subterranean damage to a wide range of plant species.

The biological cycle of this insect is remarkably long, typically spanning 3 to 5 years depending on local climatic conditions. Most of this period is spent in the larval stage underground. The larvae go through several instars, with their size and appetite increasing drastically over the years. By the third or fourth year, a single larva can consume the root systems of large plants, leading to their collapse and subsequent death.

The larvae are polyphagous, meaning they feed on a variety of crops, including strawberries, potatoes, cereals, and the roots of young fruit trees. The adult beetles, on the other hand, emerge in late spring and feed on the foliage of deciduous trees such as oak, birch, and apple. Intense feeding by large swarms of beetles can cause severe defoliation, weakening the trees and making them susceptible to disease.

The damage caused by larvae is often difficult to detect until the plant starts to show signs of wilting or dies entirely. Because they sever the roots, the plant loses its ability to absorb water and nutrients. In field crops, this results in patchy growth, while in ornamental nurseries, it can lead to total loss of stock. Understanding the larval density in the soil is crucial for planning effective management strategies.

Control measures are multifaceted and focus on both life stages. Agronomic practices like deep soil cultivation during the pupation stage can physically destroy the larvae. Biological control agents, such as entomopathogenic fungi (e.g., Beauveria spp.), provide a sustainable alternative for soil treatment. In severe cases, targeted insecticide applications or soil drenching at the time of planting are used to protect high-value crops from these damaging pests.