OF SOME KHODESIAN' TKNfiBRIONIDiE. 8(^ 



Ufe-liistory. — Altljough no specimen has heen reared in 

 conHnenient from ovum to adnlt, the life-history of P. scro- 

 bicollis has Ijeen followed by combined observation in the 

 field and the laboratory. The adults emerge at the com- 

 mencement of the rains and lav eofps at once. Bv the 

 beginnino- of the wet season the larvfe are al)Out 20-25 nnn. 

 in length, and a year later have attained a length of 45- 

 50 mm. By the end of the last wet season the larvse are 

 practically full-grown and the adults emerge the next 

 November, giving a cycle of three years. Larvse collected 

 in the field in January, when they are usually most con- 

 spicuous for the injuries they cause, are found in two sizes, 

 namely, about 30 mm. and about 60 mm. Adults have been 

 bred from the latter the following November and from the 

 former a year later. Larv?e have been bred from ova in the 

 laboratory to a length of 50 mm., taking two years to attain 

 this size. The cycle of P. si mil is has not been elucidated. 

 A bred larva attained a length of 45 mm. in two years. 

 Growth in both species appears to take place mainly during 

 the wet season. 



Psammodes occurs mainly on sandy soils, whether on 

 sandstone or granite. The larvre have not been recorded as 

 injurious in the diorite. 



(3) DiSTRETUs. — Species studied determined as D. am- 

 plipennis, iV/.^. (Plate IV. fig. 8 ; Plate V. fig. 8 : 

 Plate YI. fig. 9). 



Ovum. — Length 3*7 to 4 mm. Breadth 1'6 to 1'8 mm. 

 Shining white : form^ sub-cylindrical, abruptly rounded at 

 ends. 



Larva. — Greatest length recorded =37 mm., but without 

 doubt they attain a greater length and probably approximate 

 50 mm. when full-grown, Colour whitish to reddish yellow. 

 General form, slightly flattened dorso-ventrally (less so than 

 preceding genera) ; strongly segmented ; a central band on 

 each segment bears numerous moderately long reddish-yellow 

 hairs, giving the larva a characteristic hairy appearance. 

 Mandibles project in front of the labrum. Anterior pair of 



