STRAWBERRY ROOTWORM ON GREENHOUSE ROSES Dil 
NATURAL ENEMIES 
Natural enemies of the strawberry leaf beetle are apparently very 
few in the greenhouse, since no parasites have been observed attacking 
any of the ‘several stages. Among the predators, carabid beetles and 
their immature stages are occasionally found in the soil and will 
devour any adults, Narver. or pupe which they may encounter by 
chance: these insects show no preference for Paria canella, however, 
and are not plentiful enough to render any practical assistance in 
control. Aduits of Paria are often found bearing numbers of small 
mites, Uropoda sp., on their elytra. These mites are very prevalent 
in manure and soil, and it is probable that they use the beetles as 
transporting agents, since they have also been found attached to 
sowbugs and millipeds. Spiders and toads will eat adult beetles 
coming within their reach. In one packing room a large spider 
which had a web close to the sor ting bench immediately attacked and 
cilled all beetles carried in on cut flowers which were placed on a 
knife point within its reach. In the same room a large toad was 
observed to devour any of the beetles which dropped to the floor. 
None of these creatures, however, can be considered as an impor- 
tant factor in controlling this insect. 
EXPERIMENTS IN CONTROL 
Early in the progress of these investigations the futility of at- 
tempting to control the strawberry rootworm in greenhouses by 
methods normally employed against leat-feeding insects was illus- 
trated in Dietz’s report on an “infestation in Indiana, as published 
in a paper by Weigel and Chambers (30, p. 227). The roses had 
been sprayed several times with a mixture consisting of 2 pounds of 
powdered arsenate of lead and 12 teaspoonfuls of Paris green in 50 
gallons of water. This solution did not adhere well and proved in- 
effective against the beetles. A commercial brand of kerosene emul- 
sion, diluted 1 part to 16 parts of water, killed the adults by contact, 
but burned the leaves so severely that the injury was still visible five 
weeks later. Volatile nicotine at the rate of 36 teaspoonfuls to 4 
gallons of water stupefied but failed to kill the beetles. 
In 1920 the writer investigated an infestation in Cumberland, Ind., 
where he found that, as a result of the failure of all poison applica- 
tions, the growers had resorted to hand picking the adults, using the 
specially constructed pan described on page 37. 
Peterson (23, pp. 479-493), of New Jersey, and Primm and Trim- 
ble, of Pennsylvania, encountered similar difficulties, and as a last. 
resort the florists concerned turned to the laborious but certain control 
by hand picking, in some cases using the special-pan method. When 
the first control experiments were undertaken at Alexandria, Va., a 
serious infestation existed, and the ravages of the insects were pro- 
gressing at such an alarming rate that ‘the entire crop was threat- 
ened. Since the, roses at that season of the year were being forced 
because of favorable weather conditions, the control program neces- 
sarily had to be in accordance with the cultural methods in order 
not to prove deleterious to the future growth of the plants. 
