90 [ DISEASES OF CITRUS TREES 



Walk, B. lugens, and B. cognata, Loew., are three 

 Syrphus flies which perform good service in the Citrus 

 groves of North America. 



Among the Hymenoptera there are many valuable 

 though minute enemies of the scale insects. Thus a large 

 percentage of Lecanium Oleae and L. hesperidum, some- 

 times as much as 75 per cent, if examined late in autumn, 

 will be found to have a minute hole on the summit of the 

 scale or covering, and sometimes near its margin. On 

 removal, the scale is found to be a mere shell, the insect 

 and eggs having disappeared. They have been eaten by 

 the grub of Scutellista cyanea which is often quite 

 common in our groves, and also by the grubs of Cocco- 

 phagus Lecanii Fitch, Coccophagus cognatus How., and 

 Encyrtus flavus, How. The grub of Corny s bicolor How., 

 and Tomocera calif or nica How., are the equivalents of 

 these beneficial insects in North America. In the body 

 of Mytilaspis citricola and M. Gloveri have been found 

 Aphelinus aspidioticola Ash, Signiphora flavo-palliata 

 Ash, Aphelinus fuscipennis How., and Aphycus flavus 

 How., these last two being present in Malta. Encyrtus 

 inquisitor How., Leptomastix Daetylopii How., and 

 Chiloneurus Dactylopii, How., have been found feeding 

 upon the mealy bug in America. A species of Encyrtus 

 somewhat larger than E. inquisitor, has been found 

 feeding on Dactylopius in Malta. Whole colonies of 

 Aspidiotus Hederae were found in our gardens with the 

 scales perforated by a species of Aphelinus, probably 

 Aphelinus aspidioticola. A fungous disease is common on 

 Lecanium Oleae in local groves, particularly early in 

 winter, and probably has an important share in keeping 

 this scale in check. 



Aleyrodes citri Riley and Howard, the white fly 

 of North America, is nearly allied to the scale insects. 

 It infests the Citrus groves, as well as certain 

 ornamental slirubs, and is now fairly common on green- 

 house plants in Europe, but so far has not found its 



