EXPERIMENT STATION BULLETINS. 321 



THE BEAN MAGGOT IN 1915. 



Circular No. 28. 



BY DOX B. WHELAN. 



The "bean maggot'' has appeared in Michigan from time to time, but 

 visits heretofore have been scattered over quite a large area and the 

 damage has been comparatively slight up to the present season. This 

 pest also bears the name ''seed corn maggot," having long been known 

 as being destructive to seed corn. It is recorded in connection with 

 quite a variety of host-plants, including beans, peas, corn, cabbage, tur- 

 nips, potatoes and some weeds besides other cultivated plants. Its work 

 in the past has often been confused with both that of the "onion 

 maggot" and "cabbage maggot." 



As in the case of the last two species, the adult of the bean-maggot is 

 a fly, in form and color very similar to the house-fly but differing in that 

 it is somewhat smaller. This winged fly usually lays its eggs on the 

 stems of plants just coming through the soil or on decaying vegetable 

 matter, which appears to be its favorite breeding place. The eggs hatch 

 into maggots which scrape channels and tunnels in growing plants and 

 ruin them. There is every reason to believe that two or more genera- 

 tions develop during the growing season. 



It has long been known that decaying vegetation furnishes a breeding 

 place for this pest, although the opportunity has never before presented 

 itself to bring this fact out so favorably. During the year 1915, serious 

 damage from the bean-maggot was reported from Huron, Sanilac, Tus- 

 cola, Saginaw, Gratiot. Eaton and Berrien counties. The beginning of 

 the trouble occurred near Charlotte when a farmer first noticed the 

 work of this insect on a large field of beans, on June 14th, four days 

 after the seed was planted and before the beans had pushed their way 

 above the ground. The samples brought to the Entomological labora- 

 tory, including both beans and growing stems, were perforated and 

 badly injured by dirty-Avhite maggots, about a quarter of an inch in 

 length. About sixty per cent, of the plants were killed before appear- 

 ing above ground. This case showed clearly that the maggots were in 

 the soil before the beans were planted and that they merely transferred 

 their attention from the fresh manure which had recently been plowed 

 under, to the beans, (the land having previously been a vineyard). This 

 explanation appealed immediately to Professor Pettit, who turned the 

 problem over to the writer for thorough investigation. Examination of 

 a series of bean fields, beginning on July 1st, revealed many cases of 

 a quite similar nature, from which it appears that the maggots are 

 sometimes found in fresh manure and also in clover sod and in the rot- 

 ting stems of clover. Furthermore, it appears that while beans were 

 apt to suffer when planted on freshly turned clover sod, especially if 

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