Proceedings, 1920. 95 



one to fifteen (2) and are laid at the base of the young plants or in the soil 

 close to a plant. Later broods may lay them in the axil of the leaves when 

 the plants are well grown. The incubation period of the eggs may vary 

 from three to ten days (2 and 3), according to climatic conditions. The 

 larval period (2) is completed in two to three weeks in green onions, onion- 

 sets, and small-seeded onions, but in onions stored from the previous year 

 may require from four to five weeks to complete their larval period. The 

 pupal period (2) of the summer broods is from nine to sixteen days, with 

 an average of eleven to twelve days. There are probably three broods of 

 flies each season. 



When the eggs are hatched the young larvje immediately work their 

 way down the plants and commence feeding, and as at this time, the end of 

 May or early June, the onions are quite small, one larva may destroy a large 

 number of plants, with the result that long stretches in each row of onions 

 may be completely destroyed, making it unprofitable to continue cultivation. 

 Later when the bulbs are forming a number of larvae may be found in one 

 bulb. The top of the onion in this case may be completely killed, but the 

 lower part of the bulb may still continue to grow owing to the roots being 

 uninjured. 



The losses to the onion-growers occasioned by the maggot during the 

 years 1917 and 1918 in the Okanagan Valley were very heavy, amounting 

 to thousands of dollars. Li some instances the crops were so badly injured 

 during the earl)' summer that it was unprofitable to continue cultivation and 

 the crops were consequently ploughed under. It is well to state, however, 

 that yields were also greatly interfered with by other conditions, such as 

 wireworm -attack and poor quality of imported seeds. So far as is known, 

 this insect has no other host-plant, but to determine if this insect was able 

 to complete its life-cycle on other food, Messrs. Severin & Severin (2) 

 conducted a number of experiments. Freshly laid eggs were placed in 

 contact with growing radishes, and it was found that the onion-maggot 

 completed its life-cycle in twenty-nine to thirty-five days. A second experi- 

 ment was tried by placing the eggs on fresh horse-droppings, with the result 

 that the maggots completed their life-cycle in twenty-nine to thirty-one days; 

 one maggot taking fifty-two days to complete its life-cycle. It is therefore 

 evident that the fly can adapt itself to other food than the onion, but in a 

 general way, under strictly natural conditions, most investigators agree that 

 the onion-maggot attacks onions and no other crop. 



Control. — A large and varied number of methods of control for the 

 onion-maggot have been advocated at different times. Few of these appear 

 to have been tested on a commercial scale. Many of them are too expen- 

 sive to be considered, and a few of them, such as carbolic-acid emulsion, 

 kerosene emulsion, and hellebore, are only useful in the kitchen-garden. 



Professor Sanders (4), having determined that the pre-oviposition period 

 of the female fly covered a period of ten to fourteen days, thought it feasible 

 to prepare a poison bait that would attract the adult fly during the pre- 

 oviposition period. Accordingly, experiments on a commercial scale were 



