Iepenziekte, iepenspintkevers en beider bestrijding
1939
Fransen, J.J.
From the larvae and adults of the elm bark beetle Scolytus scolytus F. Ceratostomella ulmi could nearly always be isolated. The mite Pseudotarsonemo_des innumerabilis, living on the elm bark beetles, was transported by them to the newly cut egg tunnels in the tree, from where the mites transported the spores of C. ulmi through the larval tunnels to the pupal cells, where they disseminated the spores in such a way that these form a typical sward of coremia. In the absence of mites this was always lacking in the pupal cells. The dispersal of elm disease by other insects proved improbable. The exact relation between the quantity of elm bark beetles and the occurrence of new outbreaks of elm disease could be established.The different feeding techniques of S. scolytus were studied both in field and laboratory trials. The generations of these beetles were compared for different meteorological conditions. The number of generations varied greatly. Both 4 generations and (as a rule) 1 generation a year were observed. They always overlapped, so there were no periods without beetles. Breeding material had to satisfy special requirements. These requirements and the way, in which a pile of wood was attacked, were fully discussed.After explaining that control of the fungus was not possible, Fransen concluded that the only way to combat the elm disease was to destroy elm bark beetles. Control measures tested by Fransen were fully described.
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