Vol. L. LONDON, MARCH, 1918 No. 3 



POPULAR AND PRACTICAL ENTOMOLOGY. 

 Light Traps As a Means of Controlling 

 Insect Pests, 

 by norman criddle, dominion entomological laboratory, 



treesbank, man. 

 Collecting at light, as it is popularly termed, has been a 

 favourite method of securing certain kinds of insects, almost since 

 the time when collecting was in its infancy, and that insects were 

 so attracted was probably known before entomology, as we know 

 It, was even dreamed of. We might, in fact, suspect it of being as 

 ancient as the knowledge of fire itself. While the collector, how- 

 ever, has used this knowledge to procure specimens for his cabinet; 

 it is only within recent years that attention has been co.lled to the 

 possible use of light traps as a means of controlling certain insect 

 pests. On the face of it, what seemed easier? Moths and beetles, 

 too, were known to dash themselves against the light, at times, in 

 \"a*st numbers. All that had to he done, then, was to place light 

 tra^s at convenient distances apart and provide means for the 

 destruction of the attracted insects. Indeed, a bonfire occasionally 

 replenished would answer every purpose. The method was, in 

 fact, a repetition of the candle and the clothes moth on a large 

 scale. Yes, on the face of it there was certainly promise of suc- 

 cess, but, alas, even a casual investigation soon brought other 

 things to light. It was seen at once that the advocates of light 

 traps had overlooked several important details and one important 

 fact which in itself was sufficient to make the whole idea 

 abortive. To begin with, insects are only attracted to bright 

 light in comparatively limited numbers even under the most favour- 

 able weather conditions, among which may be mentioned warmth 

 and cloudiness. ^ A perfect night must combine these at a time 

 when the moon is below the horizon or not visible, and provide, 

 in addition, a stormy atmosphere with preferably a light rain fall- 

 ing. Such conditions occur but rarely, so much so, in fact, that 

 they have been absent during the last three years. Thus, meteor- 

 ological conditions alone, will often materially affect the value of 



