THE MONTHLY BULLETIN. 389 



POTATO CURLY LEAF. 



(Caused by Euthrips occidentalis.} 

 By D. L. Crawford, Pomona College. 



Potato plants in the San Gabriel region are being attacked by a very 

 common thrips, with considerable injury to the leaves and the crop. 

 These small insects pierce the leaves, mostly on the lower surface, and 

 suck the juice out, thereby causing the leaves to become crinkled and 

 curly and usually very much dwarfed. Curling of leaves results only 

 when the attack of the thrips has been on the very young leaves and 

 expanding leaf buds. The attack on the older leaves does not cause a 

 curling but only spotting, where the injury has been the worst. It is 

 very common to see early blight (Macrosponum solaiii) killing parts or 

 the whole of some leaves injured by these sucking insects. It is safe 

 to say that 75 per cent of the early blight in these fields is on the curly 

 plants. 



The dwai-fing of the plants is severe as sometimes they are only one- 

 tenth normal size; the leaves are much smaller and very often more 

 or less blighted. The yield of tubers is seriously reduced, averaging 

 perhaps one-fifth to one-third as many as on normal plants. The loss 

 caused is great, when it is considered that in an average field at least 

 one-eighth to one-fourth of the plants are seriously dwarfed, thus reduc- 

 ing thecrop several hundred pounds per acre. In one large field in this 

 region it was estimated that a loss of at least 12 sacks per acre had been 

 caused by curly leaf. 



DESCRIPTION OF INSECT. 



This is one of the commonest species of thrips in California and is 

 present in small or large numbers in nearly all wild flowers, as well as 



o^,"^P- 78.— Larva of EMt7»rips occidentalis, the cause of curly leaf of potatoes The 

 Very much enlare^rl'^^OH.^in?, "-.^'^P^ ^''' '^^" '^'^ P''^"'" °' ^"^^^ ^^^^de'"' ^airy wings. 



— w v,>^u UU..X*V^ ill Ol 



Very much enlarged. (Original.) 



cultivated garden flowers and the foliage of many of these same plants ; 

 it is related to the citrus thrips and pear thrips and superficially 

 resembles them very closely. This species (Euthrips occidentalis) is 

 commonly found in orange and lemon flowers and occasionally has been 

 reported as causing damage to citrus fruit, by marking the young 



