OF WASHINGTON. 25 



of parasites. Then, too, though hyperparasites may not be a 

 considerable factor, the various predatory enemies undoubtedly 

 are, as it is certain that at times they will attack parasite and 

 host with like freedom. When any species becomes as numer- 

 ous as Thanasimus duhius Fab. occasionally does, in trees 

 infested with Dendroctonus, not only a great m.any of the 

 barkbeetles, but also an almost equal percentage of their para- 

 sites are destroyed. 



A few very striking instances have come to my attention of 

 parasites eminently capable of continuing indefinitely on one 

 host only. Such a one is an apparently undescribed Spathius, 

 a parasite of Hylesinus in ash. The host is single-brooded, 

 for the most part entering branches and trunks of dying trees 

 in the spring, and emerging in June and July. The parasite 

 oviposits upon the larvae in May and June, and its larvfe, after 

 development, spin cocoons in which all or a large proportion 

 remain until the May or June of the following season, when 

 they emerge at the best possible time to attack the next suc- 

 ceeding brood of Hylesinus. Another species attacks the com- 

 mon Phloeosinus in Taxodium, and remains in its cocoon for 

 the better portion of the year. As our knowledge increases, 

 more and more species are added to this list, but the limita- 

 tions of hymenopterous parasites as factors in the control of 

 forest insects are probably narrow. 



Another striking point of difference between the parasites 

 of external feeders and of the wood-boring Coleoptera lies in 

 the relative importance of predatory enemies. Among the in- 

 sect enemies of the latter, predation is developed to a remark- 

 able extent, at times approaching so closely to true parasitism 

 as to render it practically impossible to draw a distinction be- 

 tween the two. That it is of relatively more importance than 

 parasitism, becomes more and more evident as the habits, 

 hitherto unknown, are revealed of one after another of numer- 

 ous species of Coleoptera commonly found about dead and 

 dying trees. The list of important predatory forms now in- 

 cludes many of the Elateridse, Cucujidse, Trogositidss, Coly- 

 diidae, Cleridse, etc., among them species never before enumer- 

 ated as such, and at the same time there is good reason to be- 

 lieve that the list is far from being complete. Many of these 

 are predaceous as adults as well as in their larval stages, and 

 by actively destroying the adults of the same destructive species 

 upon which their larvae prey are enabled to do double service. 



As an illustration the clerid Thanasimus diibins may be 

 mentioned, which among insects of a predatory nature unques- 

 tionably ranks among the most important. It is the particular 

 enemy of the destructive pine barkbeetle (Dendroctonus fron- 



