8 HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA. 



THE PURPLE SCALE. 



(Lepidosaphes beckii Newm.) 



The purple scale appears to prefer the more moist regions in the 

 vicinity of the ocean, as its distribution is confined largely to this 

 part of the citrus belt. This insect confines its attacks to citrus trees, 

 infesting not only the leaves and branches but also the fruit. Much 

 injury results. The young purple scale insects hatch from eggs 

 deposited by the adult. The number of broods of this insect in 

 southern California has never been exactly determined. Prof. H. J. 

 Quayle, of the University of California, is at present investigating the 

 life history of this, as well as the other injurious citrus scale pests. In a 

 climate like that of southern California, which is never severe at any 

 time of the year, there is much overlapping of broods, so that scales in 

 all stages of development can be found at almost any time of the year. 

 The writer's own observations in the field have shown that there are 

 two very noticeable general broods, one appearing in the early spring 

 during March or April, the other in the fall, usually about October. 

 These broods are much earlier some years than others, depending on 

 the nature of the weather. The fall brood of the scale is the most 

 injurious, as shown by the fact that trees which at a distance may 

 appear entirely healthy one month may have the leaves of a large 

 area, or even an entire side, turn yellow and drop off the next month. 

 The orchardists speak of this as " firing. " It is due to the attacks of 

 the enormous number of young insects which, on hatching, have 

 spread about and settled down on those branches immediately 

 adjoining the ones previously infested. Trees infested with the 

 purple scale seldom present a diseased appearance on all sides. The 

 habit of this insect is to frequent the inner and shadier portions of 

 the tree, so that sometimes severely infested trees may present no 

 visible appearance of this condition on the outside. In the majority 

 of cases where the infestation appears on the outside of the tree it 

 will be found that it is at or near the northwest corner, which is the 

 shadiest part during the day. The attacks are also confined largely to 

 the lower part rather than the top of the tree. In long and seriously 

 infested trees the insects may spread throughout. 



THE BLACK SCALE. 



(Saissetia olex Bern.) 



The black scale is found more or less throughout southern Cali- 

 fornia, yet matures more freely and causes more injury in the region 

 adjacent to the ocean than in the hot interior valleys. It occurs on 

 a wide range of hosts, including trees, shrubs, and herbaceous plants. 

 The commercial importance of the black scale arises largely from 



