380 



tion per year, and since as many as 150 eggs may be laid on the aver- 

 age by one female, there would seem to be ample provision for its propa- 

 gation. Nevertheless the insect has been in many localities so rare, 

 that in 50 years in one district hardly a specimen for collection could 

 be found, where now millions suddenly have made their appearance. 

 The reason for its sudden multiplication is sought in climatic conditions 

 (rains), which were unfavorable to the Tachinse, Ichneumonidse, and 

 other parasites without impeding the development of Liparis. 



As reasons for the rapid spread from a center of first development 

 and the infesting of areas formerly unoccupied by the insect were cited 

 voluntary and involuntary migration of both imago and larva. Invol- 

 untary migration, or drifting by wind over large distances, has been 

 definitely observed, while the larva is wafted by the winds when sus- 

 pended by its threads in the early and also later periods of its life. 

 Rains also bring it to the ground. There are also observations extant 

 which would prove voluntary immigration of the imago and a normal 

 progress of the exceedingly mobile larv.ne from thinned out fields of 

 attack to the unattacked shadier surroundings ; the observation of 

 Altum, however, that ''the insect rarely feeds in the same district two 

 years in succession, and that hardly any eggs are found in the thinned- 

 out parts, the insect seeking the shadier outskirts for oviposition," does 

 not seem to hold for spruce forest. For oviposition it seeks the scaly 

 bark of pine and spruce, under which the eggs are inserted; the smooth 

 bark of beech, on which the insect seems to develop better than on coni- 

 fers, does not offer a good place for oviposition. Three hundred larvfe, 

 3,000 pupfB, and up to 140,000 eggs could be counted on a tree. The 

 insect is polyphagous, almost omnivorous, but it is considered danger- 

 ous only on spruces, which are apt to die from its attacks. One addi- 

 tional reason for the rapidity of defoliation is that the larva bites off 

 the needle half way up, so that the upper half falls to the ground and 

 is wasted. 



Of interest entomologically is the appearance of a black variety (var. 

 eremita) in certain locations, and also that at first the males are in pre- 

 ponderance, and remain so in proportion of 70 per cent to 30 per cent 

 of females. 



The most important biological feature of economic interest is the tend- 

 ency to migration and great mobility of the larva, which gives indica- 

 tions for the methods of coping with the pest. 



Various methods of checking the ravages have been proposed and 

 practiced. The sweeping and collecting of larvae are found ineffectiv^e 

 on account of numbers, and undesirable because enemies are destroyed 

 at the same time ; gathering of eggs, because all over the tree, high 

 up, and difficult to get at; collecting pupjie, too few on the ground j 

 breeding of TacMna monachce, too diflQcult and uncertain. Ditches have 

 been found a good aid to check migration of the larvie and confine it. 

 One of the most ingenious but costly and ineffective propositions has 



