COCK CHAFER

MeikeverMorphological characters
Cock chafers are 25-30 mm long and of a reddish-brown colour. Head and mesothorax are blackish. The abdomen which is partly hidden under the elytra shows laterally triangular white spots.

Distribution
The main distribution of the Cock chafer follows the light sandy soils in the central, eastern and southern part of The Netherlands. This species became quite abundant in the last decennium. In 1986 large quantities of grubs were found in a sportsfield near Eindhoven. In 1992, and especially in 1993, serious damage occurred in sandy pastures, mainly in the eastern and southern parts of the Netherlands. Damage in tree nurseries were recorded from the provinces of Brabant and Limburg. Especially in amenity grassland both adults and grubs have been found in the provinces of Drente and Utrecht and in the Eastern parts.

After the mass outbreaks of 1944-1958 the population declined strongly in NW and central Europe. Erroneously this decline was claimed to have been caused by the use of agrochemicals. At the turn of the 19th to 20th century the Swiss naturalist Decoppet discovered a 30-40 years' cycle in Cock chafer populations. He described the control of chafers by means of mass collecting of adults by schoolchildren during the past centuries. The churches payed by the basket and this was noted carefully by the church clercks. Decoppet made an inventarization of the church registers and came to the above mentioned conclusion. The last known mass flight of Cock chafers in the Netherlands occurred from the mid-forties until the late fifties. In the nineties a new Cock chafer period was to be expected. According to investigations during the flight period around 1950 it is likely to expect a ca. ten-year flight period. Predictions about the duration of the present problems and the seriousness of expected damage are difficult. Like in the Netherlands reports of Cock chafer damage has been recorded in Germany, Switzerland and Northern Italy. The cause of this cyclicity is still unknown.
A generation of Cock chafers in middle Europe lasts for three or four years whereas in Southern Scandinavia one generation occurs every five years. Presumably the second and third instar moves to deeper layers of the soil during unfavourable conditions (lack of food, low temperatures, high moisture conditions). Under these conditions the grubs stay longer in the second or third instar whereas populations developing under more favourable conditions complete a generation in three years.

Biology
After emerging from their pupae the adults feed on foliage with a preference for oak. Mass flights of chafers can damage the trees severely, causing defoliated branches at the outer edge. Mating occurs at this stage. Eggs are laid at a depth of about five to ten centimeter in the soil, as well in grassland as at the roots of trees and shrubs. The grubs have three instars and the last instar digs itself into the soil to a depth of about 50 centimeter to hibernate. The chafers appear from the end of April until the beginning of June.

Copyright Insect Consultancy 2002