INSECTS AFFECTING I'ARK AND WOODLAND TREES 21 



this leaf feeder for their sustenance. 1 hi- relations eNistiny between this 

 insect ami its parasites were further complicated b)- the presence of 14 

 species of hyperparasites, some of which lixc on iheir associates, and were 

 therefore parasites of hyperparasites. 



This study also resulted in the breedinu- of i 1 species of flies from 

 cocoon masses of this pest. Insect enemies of this species were so abun- 

 dant in Washington in the autumn of 1895 ^^^'^^ they destroyed about go/v 

 of the larvae, as estimated l)y l)r Howard. 



The etficiencv of the parasites of the forest tent caterpillar, M a 1 a c o- 

 soma disstria Hiibn. has been brought to the writer's attention on 

 several occasions in recent years. In one instance he found that from 

 90 to Q5'^f' of the caterpillars in one locality had been killed by insect ene- 

 mies. These two illustrations, and others might be cited, give some idea of 

 the importance of these forms. Insect enemies are also noticed in the fol- 

 lowing accounts in connection with the species on which they prey, and 

 the reader, by consulting them, may easily note the number of species prey- 

 ing on an injurious form, and in most cases gain some idea of their habits. 

 The great value of insect enemies makes it very desirable to become some- 

 what familiar with the general characteristics of the more important of 

 these groups. 



J'ara.u'h-s. True parasites are distinguished from the predaceous insect 

 by differences in habits. The parasites, in many instances, work internally 

 and are comparatively easy to breed from their hosts, while our evidence 

 regarding the value of predaceous forms rests very largely on their being 

 found in association with a species, or on their being observed depredating 

 on the pest. The true j^arasites belong to several families of Hymenop- 

 tera and to one in the Diptera. Many of our largest and most important 

 true parasites, such for example as species of Pimpla, Ojjhion, '1 halessa, 

 and others, belong to the Ichn^umonidae, a ver\- large family, the mem- 

 bers of which are distinguished by their wasplike appearance and by their 

 having the abdomen usually flattened as though by pressure from above, 

 and with the first abdominal seement bent at nearlv right angles. 



