240 



PROTECTION AOAINST INSECTS. 



The entire development lasts on an average for 10 weeks, 

 which is thus distributed over the various stages : egg, lA to 

 2 weeks ; larva, 2 weeks ; pupa, 8 weeks ; and imago, 3i to 4 

 weeks. When circumstances are very favourable they can 



reach maturity in 6 or 

 8 weeks, but in very 

 unfavourable circum- 

 stances, damp cold 

 weather, or in shady 

 places, 12 to 13 weeks 

 are required. 



The generation is 

 therefore either single 

 or double, but in moun- 

 tainous regions, such as 

 the Thuringian forest 

 and the Erzgebirge, 

 a double generation is 

 much rarer than in the 

 plains. 



In rare cases where 

 there is abundance of 

 food and a very large* 

 swarm of beetles a 

 three-fold generation 

 has been observed. 



This dangerous pest 

 has fortunately been 

 very rarely observed in 

 Britain, and has never 

 yet been recorded as a 

 destructive insect. Ob- 

 servations on the dura- 

 tion of its generation in 

 this climate are tlierefore wanting, but it is probably an annual 

 one. As other insects, such as Xi/Ichonts dispar, Hellw., which 



* Von Kujawa often found in pieces of bark 10 cm. long and broad, as many 

 as 40 to 50 beetles, and 1,000 pairs of beetles attacking one tree in the spring 

 are capable of producing as many as 800,000 by the autumn. 



Fig. 101.— Burrows of T. ti/pot/rajj/iii 



spruce-bark. {Natural size.) 



a Paiiiug-cliamber (with entraute-hole) 



b Mother-galleries (vertical aud forked). 



c Liirval-gallerics (widening outwards). 



