36 



MISCELLANEOUS PAPERS. 



These six experiments with six unfertihzed females gave a total of 

 135 parasitized forms, and from these were reared 104 parasite adults. 



In many other species of parasitic insects where adults have been 

 reared from eggs deposited by unfertilized females, the offspring 

 have all been males.^ However, in so far as we have progressed in 

 the rearing of tliis parasite artificially, the offspring of unfertilized 

 females have been females, for in every case these insects, when 

 placed separately in vials with thrips larvae, began to oviposit in 

 their host. In one case at least the prepupa of the thrips developed 

 signs of parasitism from the unfertilized egg of the second generation. 



Table II shows results of 9 experiments to show effect of partheno- 

 genesis in offspring of the first generation. 



Table II. — Effect of parthenogenesis on offspring of first generation of Thripoctenus 



russelli. 



METHOD AND PERIOD OF OVIPOSITION. 



Oviposition was observed under laboratory conditions in many 

 cases, and in nearly all the operation was identical. The females of 

 this insect, within a few hours after emerging from the pupa, and in 

 all cases under observation, without being fertilized by the males, 

 when placed on a leaf with thrips larvae began to oviposit as soon as 

 they had located their hosts. The time required for this, of course, 

 varied, as some species of thrips were not as active as others, nor as 

 easily disturbed, so that the parasite had little trouble in finding 

 them. The process is probably best described by the author's notes 

 on oviposition in Heliothrips fasciatus taken at the time of observation. 



The female, in ovipositing, crawled very slowly over the leaf with her antennte 

 diverging but horizontal and constantly moving from side to side. In this manner 

 she moved over the leaf more or less in a circle until she came in contact with the 

 larva of Heliothrips fasciatus. At this point the antennae were drawn closely together 

 and moved carefully and slowly over the larva from one end to the other; then, if she 



» See pp. 257-258, Bui. 91, Bur. Ent., U. S. Dept. Agr. The Importation into the United States of the 

 Parasites of the Gipsy Moth and the Brown-tail Moth. By L. O. Howard and W. F, Fisfce. 



