USEFUL HYMENOPTERA. 187 



insects already diseased owing to infection by parasitic plants 

 or the weather, and the importance of ichneumons is due in 

 his opinion not to their secondary activity in attacking insects, 

 but to the fact that the approaching end of an insect-calamity 

 may be predicted from the increase in their numbers. He 

 asserts that when 50 per cent, of the caterpillars are attacked 

 by ichneumons, it is not worth while spending any more 

 money on measures for destroying the caterpillars, as the 

 calamity will then die out speedily. 



Taschenberg* and Judeich,t however, contest this opinion, 

 and consider that perfectly healthy caterpillars are attacked by 

 ichneumons ; their view is now generally and properly held. 

 It is impossible to imagine that an ichneumon, such as Pimpla, 

 which inserts its long ovipositor through the cracks of bark to 

 reach a concealed larva, can have any accurate perception of 

 the state of health of its host ; and the experiences of those 

 who breed larvae in captivity show conclusively that this is a 

 matter of indifference to the Ichneumonidae. 



The families referred to are very rich in species, 5,000, 

 of which 1,000 are parasitic on destructive forest-insects. 

 Ichneumon- wasps are either polyphagous or monophagous; 

 many are monophagous to such a degree that they attack only 

 a particular species in a certain stage of development, either as 

 larvae or pupae, etc. The greatest number of species (in all thirty- 

 nine) attack the pine-moth Gastropacha pini, L. Many are 

 found in the black-arches, the pine noctua, the pine sawfly, etc. 

 On eggs: Teleas laeviusculus, Eatz. (G. pini}, and T. terebrans, 



Eatz., are parasitic. 

 larvae : Microgaster globatus, Nees. (G. pini) ; Banchus 



compressus, Fabr. (Noctua piniper da, Panz.). 

 ,, pupae : Anomalon xantliopus, Grav. (G. pini); E. lopliy- 



rorum, Htz. (Lophyrus pini, L.). 

 ,, larvae and pupae : Anomalon circumflexum, L. (G. pini); 



Pimpla instigator, Panz. (Liparis monacha, L. dispar, 



Porthesia chrysorrhoea, etc.). I 

 ,, imagos : sp. of Braconidae (Strophosomus conjli, L., etc.). 



* Forstwirthschaftliche Insectenkunde, p. 271. 



| "SValdverderber, 7th edition, p. 14. 



| The names within brackets are those of the hosts in which the parasites live. 



