PROC. ENT. SOC. WASH., VOL. 24, NO. 5, MAY, 1922 113 



rapidly and pupation usually takes place about the last of July, 

 the exact date varying considerably in different years according 

 to meteorological conditions. By the end of the first week in 

 August the adult stage is usually reached and the remainder of 

 the summer, fall, and winter is passed inside the cocoons as 

 adults. Occasionally adults emerge in the fall and oviposit into 

 the fall generation of the fly, but field observations indicate that 

 these ovipositions fail to mature. 



(Polygnotus) Platygaster hiemalis Forbes. 

 GEOGRAPHICAL DISTRIBUTION* 



This species occurs throughout most of the wheat growing 

 region where the fly is found. According to F. M. Webster 

 (21, 25) this parasite was introduced several years ago into 

 Washington and California and has been found in abundance in 

 Washington since that time. Mr. C. M. Packard informs me, 

 however, that this species has never been reared from rather 

 extensive collections of Hessian fly material made in California. 



LIFE HISTORY 



The egg, like that of Platygaster vernalis, is highly refractive. 

 In form it is ellipsoidal, slightly flattened along one side, and 

 with two tiny, flagellum-like processes at one extremity. 

 Freshly oviposited eggs measure approximately 0.02 mm. long 

 by 0.01 mm. wide. The size and shape of the egg undergoes no 

 appreciable change upon oviposition. 



The parasite oviposits in the host egg, or occasionally in the 

 newly hatched larva while the latter is exposed to attack. 

 From the examination of 81 ovipositions it has been found that 

 from 1 to 7 eggs with an average of 4.22, are laid at each single 

 oviposition. 



The eggs always develop in the body cavity of the host and 

 never in the mid-intestine as is the case with Platygaster vernalis. 

 The young embryos may nearly always be found as colorless, 

 spherical masses entirely separated from each other and loose 

 in the haemolymph ot the host larva. 



In the larval stage the segments are always discernible and 

 the mandibles are very small. Upon reaching the larval stage 

 development usually proceeds rapidly. The contents of the 

 host are soon almost entirely devoured, and the larvae form 

 individual cocoons which are broadly ellipsoidal, pale yellowish 

 brown in color, and made of tough, flexible material, being 

 similar to those made by Platygaster vernalis. From 1 to 2 ; 

 cocoons have been found in a single puparium, and from 100 

 puparia examined, an average of 6.52 cocoons \\eiv found. 



