426 



Journal of Agricultural Research 



Vol. XX, No. 6 



in the first instar, and each puparium contained a well-formed pupa of 

 O. jletcheri. C. capitata larvae into which O. jletcheri had deposited eggs 

 on June 12 were examined on June 24. Each of 7 which were still in 

 the larval stage contained a strong, living, first-instar larva of O. fletcheri; 



while 7 of the host larvae, which 

 had formed puparia, each con- 

 tained a mature pupa of 0. 

 fletcheri about to emerge. Eggs 

 that were deposited on June 13 

 produced, on June 27, ro adult 

 male O. jletcheri, and on June 28, 

 4 males and 2 females. On June 

 28, also, 2 of the host larvae that 

 had not yet pupated each con- 

 tained a living first-instar larva 

 of O. jletcheri. On June 14 eggs 

 of O. jletcheri were deposited in 

 fruit-fly larvae. On June 27, 1 

 adult male O. jletcheri had de- 

 veloped from this lot, while 4 

 of the host larvae, that had not 

 formed puparia, each contained 

 a living first-instar larva of 0. 

 jletcheri. 



These results indicate that the 

 first instar of Opius jletcheri is 

 controlled to a great extent by 

 the development of its host, since 

 it never molts into the second 

 instar until the host has formed 

 its puparium, and that the first 

 instar may extend over a period 

 of 10 to 12 days. When the host 

 forms a puparium shortly after 

 being parasitized, the first instar 

 may be as short as 1^ days. 



The second-instar larva (fig. 5) 

 is very much without distinctive 

 characters. The mandibles (fig. 

 6) are very small, soft, and indis- 

 tinguishable even under high magnification, except upon occasions where 

 the position and lighting are most favorable. They are 0.045 mm - m 

 length and so far as can be seen serve no purpose. No tracheal system is 

 present. None can be detected under the best of lighting and the highest 

 of magnification. No part of the head or body is chitinized. The entire 



Fig. 4.— Opius jletcheri: .Molted skin of first-instar larva, 

 showing the absence of egg serosal cells. Length 

 0.8 mm. 



