NOTES ON NOXIOUS INSECTS. 449 



NOTES ON NOXIOUS INSECTS.* 



BY PROF. A. J. COOK, AGRICULTURAL COLLEGE, MICH. 



There are few, if any insects which cause more serious anxiety to our 

 gardeners than do the Anthoinyia. From some peculiarity of these insects, 

 possibly scent, unsavory taste, or perhaps their protected position in the 

 earth, and in the tunnels which they form in the roots which are burrowed 

 by them ; they seem quite free from attaclc of parasitic or predaceous insect. 

 So, unlike most of our injurious species, each year, whether dry or wet, 

 warm or cold, finds the cabbages, onions and radishes well stocked with these 

 destructive maggots. 



In our works on practical entomology, we find these insects mentioned, 

 and described as three sepai'ate species: Aiithomyia ceparum, which works, 

 on the onion, A. hrassicce, which attacks the cabbage, and A. raphani, 

 which furrows the radish. It will be remembered, that in a paper which I 

 read before this society at its last meeting, I questioned this classification 

 and suggested that all might belong to one species. After another year's 

 study, observation and experience, I am fully confirmed in the opinion 

 expressed a year ago. I believe they are trimorphic. True, the flies reared 

 from maggots on the radish are usually darker and more hairy than those 

 reared on the cabbage, while those from the onion are larger and quite yel- 

 lowish. Yet we find in rearing a large number of forms that these characters 

 are not constant. It is utterly impossible to distinguish many of the radish 

 and cabbage flies. The flies from onions are generally more characteristic ; 

 but we have secured several that are good examples of the radish or cabbage 

 type. 



Again, we find th?,t we can easily rear maggots from eggs laid on the cab- 

 bage, by transferring them to the radish, and vice versa. Eggs transferred 

 from radish and cabbage to the onion did not fully develop, although some 

 reached the puparium. These coarctate pupse were very small. In all these 

 cases the plants fed upon were transplanted in pots and taken to the 

 laboratory. The onions did not bear transplanting well, and it is more than 

 possible that the feeble plants caused the ill success. A few eggs from 

 onions were removed to cabbages and radishes, but none developed. 



For some years, previous to last year, our cabbage bed at the Michigan 

 Agricultural College had suffered seriously from the ravages of the 

 Anthomyia. This bed had been planted year after year in nearly the same 

 place, and close alongside a large onion bed. Close inspection each year, 

 however, failed to find any maggots on the onions. Last year the cabbage 

 bed was removed about ninety rods from its previous location, to the opposite 

 side of a large apple orchard ; and the place where the cabbages were planted 

 the previous year was occupied with onions. The cabbages in this case were 

 entirely free from attack, while the onions were almost a total failure. The 

 closest observation could detect no essential difference in the maggots work- 

 ing on these onions and those found on cabbages hard by. Of the adult flies 

 reared from these onion maggots, while most were larger, and a little lighter 



* This paper was read before the American Association of Agricultnrists, at the August, 1887» 

 meeting in New York. 



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