1P22.] 



63 



split appears on the dorsum of the old skin and the larva slowly frees 

 itself, leaving the old skin attached to the leaf. Frequently the larva is 

 seen eating aphides before it has left the old skin. Prior to pupating 

 the larva attaches itself very firmly to the leaf in a horizontal position 

 by means of a sticky black fluid ; the pupal case is formed of the old 

 larval skin. The adult escapes by pushing off the lid of the pupal case, 



Econo7nic importance. — This small fly undoubtedly assists mate- 

 rially in the control of the aphides affecting the two main crops of the 

 Sudan, its short life-cycle compensating for the relatively small numbers 

 of eggs produced by each female. The number of Leucopis eggs — • 

 exclusive of other stages — found on twelve aphid-infested dura leaves, 

 picked at random, varied from 7 to 153, with an average of 93. 



Descriptions of stages. — Adult. Length 2*25 mm., general colour 

 silvery-grey. Head, thorax, and abdomen silvery-grey, sparsely clothed 

 with black bristles. Head large, almost as broad as the thorax and with 

 thi'ee ocelli ; compound eyes dark brown and widely separated in both 

 sexes ; antennae greyish-brown, arista bare. Thorax \v\l\\ four longi- 

 tudinal dorsal stripes, the inner pair grey, the outer pair greyish-black ; 

 halteres ivory-white. Abdomen with two conspicuous black spots on 

 the dorsum of the second segment, 



Egg. — Length "SS mm,, colour ivory-Avhite when newly deposited, 

 darkening to leaden as the embrj^o develops. In shape elongate-oval, 

 tapering towards either end. Surface marked with shallow longitudinal 

 striae. 



Larva. — Length when mature 3 mm. First-stage larva ivory-white 

 in colour, spiny, Avith two prominent anal processes — the spiracles — 

 resembling the eye-stalks of a snail and pro jecting from either side of the 

 anal segment ; body flattened dorso-ventrally, narrow anteriorly, and 

 abruptly truncated jjosteriorly. Second-stage larva transparent glossy 

 white with a girdle of spiny tubercles of the same colour on each 

 segment; a series of longitudinal ivory-white stripes visible through 

 the skin on the dorsum. Mature larva glossy transparent creamy- 

 Avhite, much flattened dorso-ventrally ; spiny tubercles arranged in 

 girdles, those situated laterally being larger than those on the dorsum ; 

 lateral tubercles arranged in three longitudinal rows ; white lines 

 showing through the skin of the dorsum each in the form of a V. three 

 in number, situated parallel to each other and with their apices directed 

 posteriorly ; apices of spiracles black. 



Pupa. — Length 2-5 mm, to 3*5 mm,, colour light to dark brown. 

 In shape elongate-oval, flattened dorso-ventrally; two prominent pro- 

 cesses on the anal segment. 



