MIGRATORY LARVJS 



335 



with plates, bands and spines, and the tracheal system is meta- 

 pneustic (Thompson, 1928). Such a larva moves rapidly towards 

 an earwig and, having secured itself, bores its way through the 

 neck, or between the thoracic segments, until only its caudal 

 extremity is exposed to the exterior (Altson). Certain other 

 Tachinids deposit their eggs in the soil, and the first stage larvae 

 burrow through that medium in search of 

 Scarabseid larvae which serve as their 

 hosts. Thus, both Dexia ventralis Aid. 

 and Prosena sibirita Fab. betray this type 

 of behaviour. Their first stage larvae are 

 elongate and vermiform and consequently 

 adapted for burrowing ; the tracheal 

 system is metapneustic and the body is 

 armed either with segmental setae or with 

 a caudal pair only (Fig. 78). Upon 

 meeting a host they bore their way 

 within ; the larva of the Prosena subse- 

 quently becomes attached by its spiracular 

 extremity to one of the main tracheae of 

 the host, while that of the Dexia maintains 

 its caudal end in the original perforation 

 hole and thus breathes the outside air 

 (Clausen, King and Teranischi, 1927). 



In another Dipterous family, the 

 Cyrtidae, King (1916) has shown that the 

 species Pterodontia flavipes deposits her 

 eggs on tree-trunks, and the first stage 

 larvae are strikingly planidium-like. Its 

 hard integument is armed dorsally and ventrally with segmental 

 bands of powerful spines and pectinate scales. At the caudal 

 extremity it bears a sucker flanked on either side by a long seta. 

 These active larvae bore their way into Lycosid spiders, within 

 whose bodies they transform into maggot-like endoparasites. 



An active first stage larva is also known in the parasitic families 

 Nemestrinidae and Bombyliidae. 



(c) Among the few known parasitoid Coleoptera the first stage 



Fig. 78. A, First instar 

 larva of Prosena 

 sibirita, and B, its 

 mouth-parts. C, First 

 instar larva of Centeter 

 cinerea, and D its 

 mouth-parts. (Adapted 

 from Clausen, King and 

 Teranischi, U.S. Dept. 

 Agric. Bull., 1429.) 



