Studies of some shot-hole borer species and their natural enemies
The biology of some shot-hole borer species is not yet fully elucidated especially with regard to voltinism. Development ofTrypodendron domesticum L. is protracted and thus multivoltism simulated. This species is, however, generally univoltine although occasionally a partial second generation may be found. The same applies forXyleborinus saxeseni Ratz.
Two parasite species have been found:Perniphora robusta Ruschka (Pteromalidae) andIpideurytoma spessivtsevi Boucek & Novicky (Eurytomidae). All investigators agree that the former is a specific primary ectoparasite of ambriosa beetles whereas the status of the latter is still disputed. The problem is discussed and phenological-, morphological-, parasitological- and geographical criteria are provided which suggest thatI. spessivtsevi is also a primary ectoparasite of shot-hole borers.
The effect of both the Chalcididae is low. Rate of parasitism is in most cases below 10 per cent and on average even below 3 per cent. Other natural enemies (predacious beetles and mites) and diseases (bacteriosis) may increase the total effect to over 50 per cent.