384 
On the Potato Disease. 
the common plantain, prroundsel, peas, clover, brocoli, turnips, 
gourds, cucumbers, lettuces, and many other plants and fruits 
having been attacked, and some destroyed, each by its peculiar 
parasite, after being reduced to an unhealthy condition by weather 
calculated to depress its vital energy.* 
I shall next notice the several insects with which the potato- 
plants have been infested, and to some of which the disease has 
been ascribed. Numbers of aphides which feed chiefly on the 
under side of the leaves, probably on the fluid contained in the 
glandular hairs with which they alDOund, appeared on the 13th of 
July, some of which were punctured by parasites, and from which I 
bred the Aphidius avenfe, and also Ceraphron Carpenten,t which 
destroys the larvae of the Aphidius. Perfect lady-birds and their 
larvfc were also feeding on them in considerable numbers. The 
Eupterix solani ^ appeared July 20th, and multiplied very fast, for 
I found soon after some of all sizes as well as their eggs, which 
are oval, white, and ribbed lengthwise ; but I could not breed 
them. I also found another species distinguished by black spots 
on the wings (Eupterix picta). Having watched these beautiful 
flies inserting their beaks into the leaves of the potato for a quarter 
of an hour at a time, and noted the places exactly, I can safely 
say that blotches did ensue on some of them, though not on 
others; and possibly their punctures might render the leaves more 
accessible to atmospheric injuries or even to the spores of 
botrytis. Be this as it may, if any insect which I have seen is 
accessary to the disease, I believe, from the innumerable swarms 
of ihem thrustincf their lon^ beaks into tlie leaves, it must be these. I 
afterwards found a very minute creature called Smyntliurus. He is 
rather ugly in shape, and sometimes in colour not unlike a tortoise. 
He can leap well, but is not very shy, for I watched one or two of 
them for a long time greedily devouring some loose filaments of 
botrytis; these, therefore, were doing no harm. I also fo»md tlie 
Thrips minutissima,§ but not in any quantity. This is rather 
shy, and the larvae would sometimes let themselves down by a 
thread which they spun : they seemed to feed upon the pubescence 
of tlie leaves, as a shiny patch was often observable with the hairs 
closely mown off as it were by them. 1 also found the green 
* It is well known that many plants, such as cabbages and turnips, re- 
cover from tlie effects of mildew after having been entiiely covered with 
it; and this season I had some cauliflower-plants attacked as soon as they 
were in the rough leaf, yet, having been well watered, they recovered 
entirely, and produced a crop of very fine heads ni November. 
t Agricultural Journal, by Mr. Curtis. 
% First noticed by me last year, when I sent specimens to Mr. Curtis, 
who figured it in the ' Gardener's Chronicle.' 
§ Figured by Mr. Curtis in ' Gardener's Chronicle.' 
