DISTRIBUTION OF INJURIOUS INSECTS 65 



did not hatch out. Should it appear in this country, it would 

 prove another serious enemy in our already much-smitten 

 orchards, and we have no law to prevent any such incursion. 



Scale Insects, or Coccidcv, are also largely distributed on 

 fruit, the majority on citrus fruits, but many on other kinds. 

 We find amongst these the Red Scale {Aspidiotus aurantice), the 

 San Jose Scale {Aspidiotus pemiciosus), and the Mussel Scale 

 {Mytilaspis pomorum). 



The Mussel Scale occurs most abundantly on apple and 

 pear, but also on many other plants, both cultivated and wild, 

 such as thorns, in this country. By means of imported stock 

 and fruits this insect has become almost world-wide in dis- 

 tribution. It is now found in Cape Colony, Natal, Egypt, 

 all over America, Australia, and New Zealand, as well as in 

 Europe, which is probably its original home. This Coccid is 

 found on trunks, boughs, leaves, and fruit. It is not so often 

 seen on the fruit in this country, but it comes over from 

 abroad in large numbers in this way on apples, pears, etc. 

 The great difficulty of keeping the Mussel Scale in check is 

 well known, as it lives on wild as well as cultivated plants. 

 Moreover, it is difficult to kill, except with strong paraffin 

 emulsion ; hence it is very important to keep it from entering 

 a country or district where it does not occur. This can only 

 be done by absolutely prohibiting any plants infested with it. 

 Fumigation with hydrocyanic acid gas, I have found, has no 

 effect upon the egg stage. When trees are lifted for removal or 

 export, the scale is usually found in this condition. I do not 

 think it is yet found in Central, Eastern, or Western Africa, so 

 these areas should guard against its introduction in no uncertain 

 manner. 



The danger of introducing a scale insect is best seen in the 

 case of the White Cushion Scale {Icerya purchasi, Comstock). 

 This insect was imported into America from Australia. Its 

 rapid increase, with such disastrous results to fruit-growers, is 

 now a matter of history ; and also its subsequent check by 

 bringing over its natural enemy from Australia — the Lady-bird 

 {Vcdalia cardinalis). We now have this Icerya working in other 

 places, notably in Egypt, in company with an allied species 

 {Icerya cegyptica), and also in Portugal. 



The San Jose Scale {Aspidiotus pemiciosus, Comstock) is 

 perhaps most feared of all Coccidae. Its original home cannot 



5 



