74 MISCELLANEOUS RESULTS OF WORK OF BUREAU IX. 



nests. However, these ants do protect the aphides from their natural 

 enemies on the growing plants, and it is a common thing to see the 

 ants busily engaged in killing and carrying off the syrphid larvae, 

 which were doing good work in destroying the "lice." They were 

 also repeatedly observed canying away adults of the convergent lady- 

 bird (Hippodamia convergent Guer.), the nabid bug Reduviolus ferus 

 L., and a species of Chrysopa. The ladybird larvae apparently were 

 not molested, while the beneficial syrphid larvae were objects of special 

 attack, and it was not unusual to see as many as ten or twelve larvae 

 being carried away from a single vine at a time. Wherever the ants 

 were abundant the syrphid larvae were noticeably reduced in number, 

 and the aphides thus had a better chance of increasing. The ants 

 appear to use the syrphid larvae as food, as they were observed carry- 

 ing them into their nests, which, in several cases, were 12 or 15 feet 

 from the vines infested by the aphides. 



EXPERIMENTS WITH POTASSIUM CYANID AS A REMEDY. 



As frequent inquiries were made by the melon growers concerning 

 possible remedies for use against the ants it was decided to conduct 

 a series of experiments. Owing to the large number of nests which 

 occur along practically every fence and ditch, and to the large size 

 of the nests, and particularly to the fact that each nest has several 

 openings, it was obvious that carbon bisulphid would be too expen- 

 sive for practical use with this species, and it was decided to make 

 the experiments with various solutions of potassium cyanid. The 

 object of these experiments was to determine if repeated applications 

 would materially reduce the number of the ants and, if the ants were 

 thus reduced, what effect it would have on the melon-aphis problem. 



In making these experiments a strip about 80 yards in length 

 was selected along a fence at the edge of a cantaloupe field. This strip 

 was bordered along one side by a common road or highway and 

 occupied along the center by a row of elm trees which were too 

 small to cause any shade worth mentioning, as none of them was over 

 4 inches in diameter at the base. There were at least twenty-five 

 distinct nests in this strip, and the ants occurred by thousands. 

 Cantaloupes had been planted in the field along this strip for several 

 successive years, and each year the first few rows nearest the fence 

 were infested by melon "lice," while the vines which were beyond 

 the convenient range of the ants were not infested, or at least not 

 until later in the season. The owner of the cantaloupes was firmly 

 convinced that the ants were responsible for the infestation of the 

 first few rows and welcomed any attempt to destroy them. 



In order to determine the cheapest and most practical solution the 

 following preliminary tests were made: 





i 



