320 Studies in Forestry [CHAP. xiv. 



neumonidae that the suppression of the occasional enormous 

 plagues of devastating insects raised in the pure coniferous 

 forests of Germany, Russia, and Austria is ascribable. 



Of about 5,000 species of ichneumon-flies nearly 1,000 are 

 parasitic on noxious insects 1 . The female is provided with 

 a long ovi-depositor by means of which her eggs can be laid 

 either singly in the case of large species, or in considerable 

 numbers for smaller genera (290 larvae of Microgaster globatus 

 have been counted in a single caterpillar of the Pine moth, 

 Gastropacha pini]. The eggs are more frequently deposited on 

 the ova or the larvae than on the pupae or the mature insects. 

 The tiny larvae subsist on the vital fluids of the hosts they are 

 parasitic on, and then work their way out to the surface, where 

 their cocoons may be seen thickly studding the dying cater- 

 pillars. As the generation of the Ichneumonidae is only partly 

 simple, and in other cases manifold, they increase with 

 enormous rapidity when the number of hosts is large. The 

 larvae attacked become even more voracious than previously in 

 order to maintain supplies of nourishment for their parasites, 

 but perish during the pupal state when they succeed in 

 passing through the larval stage of development. 



The Tachininae are chiefly parasitic on the larvae and pupae 

 of moths and saw-flies. The principal species are Tachina 

 monachae on the caterpillars of the Spruce moth (Liparis 

 monachd], and Echinomyia fera on those of the Spruce moth 

 and the Pine Owlet or Pine Beauty (Trachea piniperdd). They 

 are easily distinguishable from other flies by the rough, brush- 

 like hairs on their abdomen. 



It would perhaps be asserting far too much to say that 

 enormous swarms of insects might quite well be suppressed by 

 Ichneumonidae and Tachininae unaided ; for there can be little 

 doubt that, in addition to killing larvae outright, the fungoid 

 diseases predispose caterpillars to attacks from these parasitic 



1 Hess, Der Forstschutz, vol. i. 1887, p. 213. 



