360 REPORT ON ZOOLOGY, MDCCCXLIV. 



cularly, on account of the number and novelty of the 



observations on their economy and development. 



The only tribes injurious to the forests are the Teuthredinetse and 

 Siricites, especially the former of these, among which the genus Lophyrus 

 and a number of Lydee infest the Conifers. The Gallflies (Cyniphidse) 

 have littls influence on the woods, and accordingly the author does not go 

 into details with respect to that family. Wasps again are enumerated among 

 the injurious insects, on account of the hornet, which sometimes kills the 

 young shoots by barking them. Other kinds are named as useful on account 

 of their preying on insects. For the same reason the sand-wasps (genus 

 Sphex, L.) are placed among the kinds that arc beneficial in woodlands. 

 Particular attention has been given to the Pupivora (Ichneumonides and 

 Pteromalina), as to which the author's researches are given in greater detail 

 in a work published separately, though in substance a sequel to this. (Die 

 Ichneumonen der Forstiusekten in eutomologischer und forstlicher Bezie- 

 huug. Berlin, 1844.) As respects the economical importance of these in 

 woodcraft, the author opposes decidedly the notion that they are very 

 efficient checks on the excessive multiplication of noxious insects. He even 

 goes so far as to maintain that none but the sickly caterpillars, which would 

 have perished at all events, are stung by the ichneumon flies ; according to 

 this view, the admitted use of the parasites would consist in this, " that 

 they help to clear away quickly the diseased eggs, caterpillars, and chry- 

 salids, which are crowded together millions upon millions, in some instances 

 even to exterminate in a short time some devourer, which might otherwise 

 have left behind a scanty progeny. In this manner the animal juices in 

 course of disorganization, which are ready to infect the air with their smell 

 aud exhalations, are gradually converted into healthy living animal masses, 

 just as the diseased sap of the fir tree is formed into vigorous healthy bark- 

 beetles, Bostrichi, &c." (Ichu. Forstins. 32). It may often be the cas 

 that particular sorts of ichneumon flies touch only the sickly caterpillars, 

 and the author has done well to fix attention on this circumstance, but his 

 doctrine, in the full extent conveyed above, is not tenable, and is in contra- 

 diction to the fact known to every Lepidoptcrist of the least experience, that 

 fine specimens may be reared from caterpillars that have been pricked, if 

 the egg be carefully extracted. The Pupivora are, in fact, an important 

 agent by which Nature checks the inordinate increase of particular sorts of 

 insects, but as their own existence is dependent on that of the sorts which 

 they infest, they cannot show themselves in hosts corresponding to the 

 multiplication of the latter races, until these have existed for a certain length 

 of time, for which reason the appearance of the parasites in numbers falls 

 in with the period when diseases break out among the hosts of caterpillars, 

 which of themselves would put a stop to their ravages. 



