100 THE CANADIAN ENTOMOLOGIST 



larly of the Tachinids, it may be possible to encourage their increase by the selec 

 tion of favorable crops, and a consideration of the most advantageous dates o* 

 seeding. 



PSITHYRUS LABORIOSUS FABR. IN THE NESTS OF BUMBLEBEES 



(HYM). 

 BY 'I'liKODORK II. Prison, 



Urfbana, Illinois. 



Of the nine or possibly ten species of tiie genus Psitliynis occurring in 

 America, North of Mexico, only two have ever been recorded from the nests of 

 bumblebees. When Franklin's work on "The Bombidae of the New World" 

 appeared in 1913, there had not been recorded a single authentic instance of a 

 Psitliynts having been taken in a bumblebee's nest in this country. The fact that 

 many American writers had mentioned the inquiline habits of Psith\nis was 

 entirely due to the numerous European records on the subject. 



Mr. F. W. L. Sladen in the Canadian Entomologist for March. 1915. was 

 the first to record the finding of a species of Psithyru,^ in a Br emus [Bomhus) 

 nest in the Nearctic region. In this article he reports the discovery of Psith\rm 

 insularis Sm. in the nest of Brcuius (Boinbus) flavifrons Cress, on luly 7. 1914 

 at Agassiz, British Columbia. In April, 1916 in the lUillctin of the Brooklyn 

 Entomological Society, the writer recorded the presence of Psitliynts I'ariahilis 

 Cress, in the nests of Bremus pennsylvanicus DeGeer in the summer of 1910 

 and 1915 at Champaign. Illinois. Several times since then, both in 1917 and 1920, 

 I have taken Psiflixnis ivriahilis Cress, in the nests of Bremus pennsylvanicus 

 DeGeer; 



On July 22. 1919 I removed to the laboratory for closer study a nest of 

 Bremus (Bomhus) peinisylrauicus DeGeer. This nest was one of several start- 

 ed in domiciles I had buried in the ground for attracting searching bumblebee 

 queens. The domicile was first noted as being inhabited on June 20, when ii 

 contained a small honey-pot and eggs. As the queen was not in the nest I was 

 unable to determine the species at this time (June 20). On July ' 22, 

 when I removed the nest, it contained a queen and four small workers 

 of Bremus pennsylvanicus DeGeer., besides five egg cells containing 

 eggs, two brood masses, and fifteen pupal cocoons, fn the ne.st material near 

 the entrance were the remains of a queen of Bremus pennsylvanicus DeGeer and 

 a queen of Psithyrus laboriosus Fabr. The two dead queens were mute testi- 

 mony of the earlier history of this colony. Evidently after the nest was started 

 another queen of Bremus pennsyk'anicus DeGeer found it. and a struggle ensued 

 over the possession, of the nest. vSuch fighting over the nests is very common 

 in late spring and early summer. Which queen finally won and stung the other 

 to her death is an open question. The dead Psithyrus queen can only be account- 

 ed for in much the same manner, and all this goes to show that a Psithyrus c|ueen 

 is not always peaceably admitted into a l)umblebee nest or victorious in a battle 

 with the Bremus queen. The history of this colony was followed until Septem- 

 ber 16. and no Psithyrus were ever reared from the nest. 



In a nest of Bremus ( Bombias) auricnmus Robt.. about one and one-half 



