28 WHEELER— THE PARASITIC ACULEATA. 



was a subsequent development. Probably the predatory sanguinea 

 queen originally entered fusca nests for the purpose of devouring 

 the brood, but later came to care for the larvse and pupae till they 

 hatched. We may conceive that the number of appropriated fusca 

 young was more than was needed as food and that the queen ac- 

 quired a fostering relation towards the remainder by coming in 

 contact with the buccal secretions or fat-exudates of the larvae. In 

 other words, trophallactic relations were established between the 

 queen and the alien brood and led to a rearing of the latter (Wheeler, 

 1918). This might offer a simple explanation of dulosis, a phe- 

 nomenon which has always seemed unique and difficult of explana- 

 tion. At any rate it furnishes an hypothesis to be tested by a closer 

 study of the relation of F. sanguinea to the larval fusca. 



Among the social bees there is only one parasitic genus, Psithy- 

 rus, to which I have repeatedly alluded. Kirby was the first to dis- 

 tinguish these bees from their hosts, the species of Bomhus, as long 

 ago as 1802, but a genus was first established for them by Lepeletier 

 in 1841. The habits of Psithyriis, as described by Hoffer (1881, 

 1888), Wagner (1907) and Sladen (1912), show that it is to be 

 regarded as a permanent social parasite. Like the ants of this 

 type, it lacks the worker caste. The female hibernates alone like 

 the queen Bomhus and enters and secures adoption in a young col- 

 ony of the latter, usually after the first batch of workers has 

 emerged. The Pslthyrus female has a tougher integument and a 

 stouter, more curved sting than Bomhus, and though she visits flow- 

 ers, she does not collect pollen or nectar. After entering the Bom- 

 hus nest Sladen says : 



" Her first care is to ingratiate herself with the inhabitants, and in this 

 she succeeds so well that the workers soon cease to show any hostility to- 

 wards her. Even the queen grows accustomed to the presence of the stranger 

 and her alarm disappears, but it is succeeded by a kind of despondency. Her 

 interest and pleasure in her brood seem less, and so depressed is she that one 

 can fancy that she has a presentiment of the fate that awaits her. It is by 

 no means a cheerful family, and the gloom of impending disaster seems to 

 hang over it. But while the queen grows more dejected, the Psithynis grows 

 more lively, and takes an increasing interest in the comb, crawling about 

 over it with unwonted alacrity and examining it minutely." 



The queen is eventually killed by the parasite, which then begins to 



