affecting the Potato -crops. 75 



brown when dead : the apical half of the 3rd joint of the horn is 

 black as well as the pubescent seta: the abdomen is rather small : 

 wings ample, yellowish and iridescent, but transparent, nervures 

 ochreous : balancers with a large triangular club : legs whitish- 

 ochre ; at the apex of the hinder shanks, where the spur is in- 

 serted, is a brown spot ; the feet are dusky, the hinder thickened, 

 especially the basal joint : expanse of wings 5^ lines. 



The larvse of most of the Sapromyzidce are said to live in putrid 

 substances, as mushrooms, &c., but Mr. Haliday has bred S. 

 rorida from flowers. 



Thrips. 



In the summer of 1846 Mr. Barnes of Bicton* and many 

 other practical gardeners entertained so strong a conviction that 

 a little Thrips was the author of the potato epidemic, that I care- 

 fully investigated the subject, and was soon satisfied the disease 

 could not be attributed to their agency. On the 30th of July 

 Mr. Barnes sent some diseased potato-leaves with several of the 

 little Thrips upon them. Being in Oxfordshire at the time, I 

 immediately visited several allotments where I had observed the 

 leaves and stalks were spotted. On digging up some of the 

 worst, we found a diseased tuber of good size, and two more the 

 following day. After a diligent search I detected the larva and 

 pupa of the Thrips, as well as the perfect insects, amounting to 

 about twenty specimens. The Thrips was most abundant where 

 the plants were sheltered from the wind, invariably inhabiting 

 perfectly healthy leaves ; and on the following morning I could 

 find very few. In another spot, where the leaves were dead and 

 the haulm spotted, we did not find one bad potato amongst those 

 we dug up, nor a single Thrips on the green leaves of a few 

 healthy-looking plants still remaining. 



Various species of Thrips injure different crops of grain and 

 fruit, as well as greenhouse plants, by abstracting the fluids which 

 ought to sustain them, and so far the Potato-Thrips acts upon 

 the leaves, but that has nothing to do with the rot in the tubers. 

 When they congregate in countless myriads, as they often do in 

 melon and cucumber frames, their presence is soon indicated by 

 ochreous spots upon the cuticle, which end in the destruction of 

 the leaf, arising from their puncturing it with their short beaks, 

 and extracting the sap in the same manner as the Aphides ;\ but 

 their number upon the potatoes was never sufficient to effect any 

 important change on the constitution of the plants. 



These minute creatures run with activity over the surface of 



* Gardeners' Chron., vol. vi. p. 532. 



t Journal of Royal Agric. Soc, vol. vi. p. 500, Tlirips cerealium. 



