INFLUENCE OF WINDS ON DIFFUSION. 



81 



FECUNDITY OF OVIPAROUS FORMS. 



The oviparous forms are far less prolific than the viviparous. They 

 produce, under favorable circumstances, from 1 to 10 eggs, or an 

 average of 5.4 eggs per individual. This average was made up from 

 observations on 27 individuals. 



ABERRANT INDIVIDUALS. 



During our studies of Toxoptera we have found some rather inter- 

 esting abnormalities. In December, 1907, 1 while dissecting some 

 individuals in the laboraton T , two were found that contained both 

 living embryos and true eggs. In April, 1908, Mr. C. N. Ainslie found 

 the same phenomenon occurring in 

 individuals here in Washington. 

 These latter resembled the wingless 

 viviparous forms externally (see fig. 

 16). Mr. S. J. Hunter, in "The 

 Green Bug and Its Enemies," finds, 

 besides this form, what he terms 

 "winged intermediate females, re- 

 sembling the winged agamic females 

 in antennal characteristics." Other 

 writers mention the same phenom- 

 enon as occurring among other species 

 of plant-lice, and no doubt these abnor- 

 malities occur much of tener than any 

 of us are aware. At present, however, 

 there appears to be no satisfactory 

 explanation of such occurrences. 



One single instance came under our observation where a puparium 

 produced 6 young and then died. The cauda of this individual 

 resembled that of an adult insect and the wing-pads were aborted, 

 the abdomen being much broader than that of the normal pupa. 

 (See fig. 17.) 



INFLUENCE OF WINDS ON DIFFUSION. 



By referring to the maps (fig. 5) showing the area covered by the 

 different outbreaks of Toxoptera in the United States, west of the 

 Mississippi River, it will be observed that they have all had their 

 origin in central Texas, with a single exception, extending broadly to 

 the north and northeast. This was especially true of two most des- 

 tructive invasions of 1890 and 1907, and was also implied by that of 

 1901, the case of 1903 having been too incipient. This strongly indicates 



i Proc. Ent. Soc. Wash., vol. 10, pp. 11-13, January, 1908. 

 26675°— Bull. 110—12 — -6 



Kprr 



Fig. 17.— The spring grain-aphis: Aberrant 

 female pupa which produced young. En- 

 larged. (Original.) 



