insp:cts attacking weeds in Minnesota. 137 



eat the leaves and deposit eg'i^s on the Intckwheat, it will probably 

 never be a serious pest, since buckwheat is such a fast-growing 

 plant. Under favorable conditions, however, it is easy to see that 

 it may be a pest. 



Furthermore, the spinach leaf miner maintains itself on lamb's 

 quarters, while the cabbage maggot lives over on wild mustard. 

 While such insects are useful, in that they help to destroy these 

 weeds, they are also very injurious because they are not conhned 

 to one host plant. Furthermore, an insect that appears quite harm- 

 less, and conhned to a certain weed may, if a near relative of its 

 host plant is cultixated, l)ecome very injurious. Such possil)ilities 

 are becoming more in evidence, especially since hundreds of foreign 

 plants are being tried out by the United States Department of Agri- 

 culture, with a view to adapting them to our needs and conditions. 



The subject is also interesting from an ecological point of view. 

 According to Shelford, the original habitat of our native pests and 

 the places that support the majority of them, are the forest edges 

 and thickets, made up largely of rank w^eeds. The above situations 

 oflfer ideal conditions for the breeding of many of our native pests 

 and with the destruction of the forests, the liuilding of roads, rail- 

 roads, and the presence of the farm woodlot, the thicket formation 

 is greatly increased. In fact, the author was in the habit of visiting 

 just such places for this study l:)ecause weeds w^ere there found 

 in abundance. 



In this connection it might be well to mention that a knowledge 

 of our weed insects wovild be Aery useful to the teacher. Often 

 it happens that even in midsummer it is difficult to get illustrative 

 material for class use, because the insects have been controlled in 

 the cultivated plants or are not present for some other reason. 

 Weeds, however, are always present, together with their insect 

 fauna, and if one knows where to look, he is sure to be rewarded. 

 The little purslane saw-fly^ for example, is generally abundant all 

 summer. 



Finally, a knowledge of our w^eed insects will help to make 

 the natural history of our state better known. In his classic re- 

 ports, Riley devoted a portion of them to what he calls innoxious 

 insects, many of wdiich attack weeds. 



In this paper I have confined myself only to the insects of the 

 herbaceous weeds, although the wild cherry could be considered a 

 weed, since it harbors many orchard pests. An attempt w^as made 

 to get the breeding habits, and especially the location of the larva, 



