MIGRATORY LOCUSTS. 373 



be the barren steppes of Central Asia. It occasionally spreads 

 westwards over Germany and as far as Belgium, and even into 

 the British Isles. While, however, devouring chiefly agricul- 

 tural crops, the locust does not spare the young leaves and 

 terminal buds of broadleaved trees, though it but rarely 

 strips off all the foliage of a forest. In 1880, in Istria, chiefly 

 oak and ash were attacked by it, other broadleaved trees 

 being spared. Vineyards were also attacked. 



d. Protective Rules. 



i. Destruction of eggs. Very difficult to carry out on a 

 large scale. 



ii. Destruction of larvae which is the best method. 



They have been exterminated in Cyprus by an organised 

 system of digging trenches, into which the larvae are driven ; 

 strips of cloth on stakes lead up to the trenches, and the 

 locusts are crushed by thousands when the trenches are nearly 

 full, and then fresh trenches are dug. In South Africa, the 

 larvae, which may accumulate in masses, are killed by spraying 

 with coarse blue soap and water. The soap blocks up their 

 tracheae and kills them readily. 



iii. Destruction of the full-grown locusts may be effected 

 during wet weather, when they fly with difficulty. 



LIST OF DESTKUCTIVE INSECTS. 



A list is here given of all the destructive insects dealt with 

 in this book, arranged according to the species of tree attacked 

 and the different organs of it which suffer. 



The following details are given in the list : 



Organs of tree attacked : root, bark, cambium, wood, buds, 

 young shoots, needles, leaves, blossoms, fruits and seeds. 



Stage of the insect at the time when it is injurious : larva, 

 imago ; or sometimes, in the case of OrtJwptera, or Hemiptera, 

 all stages, including the nymph or pupa. 



Grade of injuriousness of insect. 



Age of woods attacked : seedlings, young plants, poles, or 

 trees. 



Characteristics of attack, which serve to indicate the offender. 



