THE MARGUERITE FLY. 35 



were being placed on the leaf by artificial light, although it was endeavored 

 to keep them from doing so by keeping the leaf in constant agitation. At 

 any rate, all the eggs could not have been deposited within that short 

 time. 



However, the fact remains that absence of light or total darkness is not 

 necessarily an absolute bar to oviposition. 



Oviposition — how soon after Emergence. 

 To determine how soon after emergence egg-laying begins, virgin females 

 soon after their emergence were confined with males until they mated. 

 Immediately foUomng mating, each female was isolated on leaves on a 

 plant in the laboratory, being shifted from leaf to leaf at regular and short 

 intervals. One of these females laid her first eggs (fertile eggs) between 

 twenty-five and thirty-six hours after emergence and between seventeen 

 and twentj^-eight hours after fertiUzation; another between thirty-one 

 and forty-three hours after emergence and between two and tliree hours 

 after fertiUzation; another between thirty-one and thirty-six hours after 

 emergence and between twenty-two and twenty-five hours after fertiUza- 

 tion. The rather -wdde Umits are due to the limits of the period during 

 which each female emerged, and which necessarily has to be embraced. 

 It would seem, then, if these three females can be taken as criteria, that 

 the first eggs are deposited on the second day of adult Ufe or the second 

 day after emergence, in the laboratory, at least. 



Length of Egg-laying Period. 



To learn how long females continue ovipositing, newly emerged virgin 

 females were confined with males within cheesecloth bags on leaves on 

 plants in the laboratory. New males were introduced from time to time 

 to take the place of those dying, the females never being without males 

 for any great length of time. These fUes were shifted periodically, daily, 

 or every other day, from one leaf to another, tliroughout the Ufetime of 

 the females. After the flies were removed the leaves were examined with 

 a pocket lens, but the presence of larvse within the leaves was surest proof 

 that eggs were deposited. 



One female, in March and April, which Uved for twenty-one days, con- 

 tinued ovipositing to within three days of her death, the last eggs being 

 deposited on the eighteenth day. Another female, in March, which also 

 Uved twenty-one days, continued to oviposit to within six days of her 

 death, depositing the last eggs on the fifteenth day. Another one, also in 

 March, which was confined with males upon a plant in a cage in the 

 insectary for the purpose of ascertaining the number of eggs a female 

 deposits during her Ufetime, oviposited for the last time, as closely as 

 could be calculated, on the sixteenth day of her adult life. Just when 

 this female died is not known. StiU another female, in May (latter part), 

 which Uved seventeen days, continued ovipositing to within one day of 

 her death, depositing the last eggs on the sixteenth day. 



