Développement en Laboratoire des Maladies de Melolontha Melolontha L. (Col. Scarabaeidae) dans Différents Types de Sols

SUMMARY

B. Hurpin & P.H. Robert: Laboratory studies on the development of Melolontha melolontha L. diseases (Col. Scarabaeidae) in various types of soils

Several sets containing 25 second instar cockchafer grubs were bred in individual cages at 20 °C in five different types of soils artificially infected with the six main diseases of this insect species. The infection was performed by adding a crushed diseased grub to one litre of substratum. Each of the diseases: Bacillus popilliae « melolontha » bacteriosis, Beauveria tenella mycosis, Rickettsiella melolonthae rickettsiosis, Vagoiavirus melolonthae virosis, Adelina melolonthae coccidiosis, and Nosema melolontha microsporidiosis induced the same mortality of the grubs in the five types of soil considered to represent the various soils where the larvae can live. Table I gives the characteristics of these soils.

The comparison of the germs showed that some differences appear in the proliferation of bacteria, rickettsia, virus, and the number of diseased grubs. These differences however are more a consequence of the nature and virulence of the pathogen, as well as the physiological state of the insect, than the soil characteristics, which seem to be secundary importance.

These results need confirmation in field experiments, but they already show that the soil composition, within the limits of types allowing normal development of the grubs, is not a basic factor assuring the success of the applications of the germs considered for microbial control of the cockchafer.