350 



PARASITISM 



intestine discharged. The waste matter usually assumes the form 

 of a chain of faecal pellets which is commonly found in close 

 proximity to the pupa. 



A new type of respiratory inter-relationship between a 

 Hymenopterous parasite and its host has been recently described 

 by Thorpe (1936). The parasite, Encyrtus infelix (Chalcidoidea), 

 utilises the Coccid SaiseUia hemisphcrrica as its host. In its first 

 three larval instars the Encyrtus is metapneustic, the spiracles 

 being in communication with the atmospheric air by means of the 

 protruding pedicel of the egg in the manner already described in 



the case of certain other 

 Chalcids. In the fourth and 

 fifth instars the mode of 

 respiration of the parasite 

 becomes completely altered. 

 The parasite now becomes 

 dependent upon a special 

 structural development of its 

 host. It turns round within 

 the body of the latter and 

 ^/ " becomes invested with a 



Fig. 87. A, diagram of anal extremity closely fitting membranous 

 of young larva of Apanteles. B The j^ ^j j^- j^ • ^ ^ . 

 same of fully grown larva. e, Blmd -^ 



extremity of gut. m, Mid-intestine, the phagocytes and tracheal 

 m.^. Malpighian tubes. v, Caudal branches of the host. The 

 vesicle. 



sheath becomes attached to 



the main lateral tracheal trunks of the host in four or six places 

 in the vicinity of the spiracles of the parasite (Fig. 86). An 

 actual continuity becomes developed between the lumen of the 

 host trachea at these points and the narrow space between the 

 sheath and the parasite. In this manner the larval parasite is 

 able to breathe air from the tracheal system of its host. 



Another peculiar type of host relationship, of a different nature, 

 has been recorded by Flanders (1936) with reference to the 

 Chalcid Coccophagus. In the species studied the progeny of 

 parthenogenetic females consists, as is often the case, of males 

 only. Fertilised females produce females only, and these develop 



