47 



its branches. Larva? are found most numerous in the upper portion 

 of stems, penetrating frequently as high as the diameter of the stem 

 will admit them. They also bore into the branches, and occasionally 

 a short distance into the leaf -stalks. In the upper portions the stem 

 is often completely hollowed out toward the base, the larval tunnels 

 growing much smaller. 



In many cases the leaf -stalks are killed or so injured that they part 

 from the stems when the latter are pulled up; and, again, the stems, 

 being so closely tunnelled, often part above the middle, even dropping 

 over, though not handled. 



By the end of the month no larva? could be found in any of the 

 stems of hedge mustard examined, and on removing the earth from 

 about the bases of the stems numerous cocoons were obtained. As a 

 rule, weeds seldom suffer from the attacks of injurious insects as do 

 cultivated plants; it is somewhat surprising, therefore, to find that 

 quite a number of plants of hedge mustard had been so completely 

 bored through in the upper parts of the stems that they cracked open, 

 and the plant bent over at the point of fracture, and as a consequence 

 the plants were in some cases injured so that the seed did not fully 

 mature. 



June 2 a second visit was paid to the garden at Tennallytown, D. C, 

 and although the beetles had entirely vanished from our Department 

 grounds, numerous specimens were found here upon seed turnip, as 

 also larvae in the stems of turnip and in the leaf -stalks of horse-radish. 

 Affected plants of both turnip and horse-radish could be readily detected 

 b} 7 the scars left by the puncture of the beetle and b} r the holes made 

 by the larva?, but it could not be ascertained what effect the presence 

 of the insect had upon these crops, as the plants were plowed up when 

 the place was next visited. 



June 10 beetles of the new generation were observed, though rarely, 

 on turnip at Marshall Hall, Md., this rarity being explained, at least 

 in part, by the absence of native food plants in the vicinity. 



During the next two weeks beetles were found at work on the leaves 

 of cauliflower and cabbage on our experimental plats, being more com- 

 monly met with on the former plant, and nibbling almost exclusively 

 along the edges of the leaves in much the same manner as Pkyllotreta 

 vittata. 



THE NUMBER OF GENERATIONS. 



It would scarcely seem necessary to devote any time to the subject 

 of number of generations produced annually, since with scarcely an 

 exception in the temperate climate of the United States the true weevils 

 (Rhynchophora, exclusive of the Scolvtida?) are monogoneutic. Never- 

 theless the question has been raised. To ascertain the truth, beetles of 

 the new generation were confined in a large rearing cage with healthy 



