WHEELER— THE PARASITIC ACULEATA. 33 



South American stingless bees (McUpona) overpower other indi- 

 viduals of their species and bite away the propoHs with which their 

 hind legs were charged. 



The difference of sexual maturity between parasite and host 

 suggests an answer to our second question, for the time of mating 

 would of course depend on the time of sexual maturity and one 

 group of individuals may be effectually isolated so far as its further 

 phylogenetic development is concerned from another group of the 

 same species, if the mating periods fail to coincide in the two 

 groups. Thus interbreeding of the parasite with the host might be 

 avoided in a very simple manner, and parasite and host, though 

 reared on the same food and in the same environment would never- 

 theless tend to pursue divergent paths in their subsequent history. 

 It would be interesting, therefore, to collect accurate data on the 

 rate of larval development, and the time of emergence and mating 

 of parasitic Aculeates and their hosts with a view to testing the 

 strength of the hypothesis here suggested. • 



That certain Aculeates respond so readily and in such a uni- 

 form manner to simple stimuli like the urgency of oviposition and 

 dearth of food by becoming parasitic on other Aculeates may be 

 attributed to a peculiar modification of their constitution during 

 their long phylogenetic history, some of the main outlines of which 

 have been clearly revealed by morphological studies. Hymenop- 

 terists agree that the higher Aculeates are descended from primitive 

 wasps whose modern representatives constitute the families Scoliidse, 

 Thynnidse and Mutillidse and that their ancestors in turn are to be 

 sought among groups like the Ichneumonidge. The latter have been 

 called parasitic, but it is clear that their larva?, which feed on the 

 tissues of other insects and eventually kill their hosts are really 

 practicing a refined, protracted and very economical predatism. They 

 may be more properly designated as parasitoids, as Renter (1913) 

 has suggested. The Scoliidse, Thynnidse and Mutillidse, which 

 seek out the larvse of other insects in concealed places, i. c, in the 

 soil or in nest-cavities, immobilize or kill them by stinging and then 

 deposit their eggs on them, therefore occupy a position, ethologically 

 as well as structurally, midway between the higher solitary wasps 

 and the Ichneumonidae. The higher wasps in constructing nests 



PROC. AMER. PHIL. SOC, VOL. LVIII, C. JUNE 25, IQIQ. 



