﻿STRAWBEKRY EOOTWOEM ON GREENHOUSE ROSES 27 



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, larvse, or pupse 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. Adults 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 sorting bench immediately attacked and 

 killed 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. 

 Xone of these creatures, however, can be considered as an impor- 

 tant factor in controlling this insect. 



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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 leaf-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 (^-5, j>p. 479-Ji.93)^ 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 tlie roses at that season of tlie year were being forced 

 Ijecause of favoi-able weatlier coixlitions, the control program neces- 

 sarily had to be in accordanc<^ with the cultural methods in order 

 not to prove deleterious to the future growth of the plants. 



