127 
In the examinations thus far made, I had not been able: to find 
any instance which should exactly test the hypothesis that the injury 
under examination was due to the insect only. In every case where 
two fields ‘were contrasted, there was some additional difference 
between them than that of abundance or scarcity of the plant bug; 
either a difference in variety, in location, in treatment, or in the 
amount of rust occurring. The first fields visited at Centralia, how- 
ever, gave me the example I had been seeking. 
Two large fields of Wilsons, of the same age, separated only by a 
street, upon soil of precisely the same character, mulched alike, 
and otherwise treated identically, as I was informed by Mr. Brunton, 
were found to differ to a marked degree, at least in the places ex- 
amined, with respect to the amount of buttoning apparent. In one 
field the berries were in very good condition, while in the other, 
half or more of those examined were buttoned and deformed. In 
the former, seventy-five strokes of the net gave thirty-one insects; 
and in the latter, fifty strokes gave eighty-nine. * 
I next examined a field belonging to Mr. Brunton, containing 
Crescents, Downings and Wilsons, all on new ground, and also a 
patch of Wilsons which had been in berries previously. These were 
all side by side, and of the same age and previous history. In the 
Crescents no injury was observed, nor yet in the Wilsons adjoining. 
The Downings were considerably injured, and the Wilsons in that 
part of the field which had been in strawberries previously were 
badly buttoned. In the uninjured Wilsons, twenty-five sweeps of the 
net gave but seven bugs; and in the injured Wilsons, fifty sweeps 
gave twenty. In the Downings, which were considerably buttoned, 
fifty sweeps yielded forty insects; and in the badly injured Wilsons, 
twenty-five sweeps gave sixty. Another field of Wilsons, a little 
removed from these, somewhat damaged, but not badly, yielded 
thirty bugs to twenty-five sweeps. The plants in all these fields 
were more or less affected by rust, but in about equal ratio. A 
number of other fields of Wilsons were examined, but the results 
were so strictly identical with those already given that it is not 
necessary to narrate them in detail. 
The fact has already been mentioned of the occurrence of another 
species, the dusky plant bug, Dereocoris rapidus, in the same fields 
with Lygus lineolaris. Although generally much less abundant than 
the other, in some fields at Centralia its numbers amounted to a 
third or fourth those of Lygus. Hverywhere both were in the same 
stages, and were evidently working upon the berries in precisely the 
same manner; consequently in the preceding details respecting the 
number of plant bugs present, both species have been included. A 
separate discussion of Derzocoris is, however, given elsewhere. 
Although many other plants were of course present in the straw- 
berry fields, these plant bugs were only occasionally seen upon any 
of them. In one field of Mr. Earle’s, in which the insect swarmed, 
blackberries were placed in alternate rows with the strawberries, but 
it was a very unusual thing to find the insects upon a blackberry 
bush. 
