76 Annals Entomological Society of America [Vol.11, 



of four to six weeks. The wingless viviparous ? ? are more pro- 

 lific than the winged, but, of course, scatter their young less as they 

 are confined to a very limited area. It is usual to observe a wing- 

 less mother stationed on a leaf in the midst of a family of a dozen 

 or more young, varying in size from newly bom to half grown. 

 The insect moults four times. 



EFFECT OF METEOROLOGICAL CONDITIONS. 



As has already been shown, the direct effect of low temperature 

 on the insect is, in the south at least, exceedingly small. It is 

 vastly more probable that the influence of winds and humidity 

 are much more important factors, though of the latter we cannot 

 yet speak with the fullest assurance. 



As has also been shown, it may turn out that hot dry weather 

 may be found to greatly influence the time of appearance and 

 abundance of the d' and sexual 9 . 



Winds certainly do have considerable influence in the disper- 

 sion of the winged viviparous 9 9 , during the seasons of excessive 

 abundance, and as it is well known that a diminution of the food 

 supply, like the killing of the grain plants, tends to produce 

 winged instead of wingless individuals, it will be seen at once that 

 the occurrence of these winds at the time of a serious outbreak 

 may become a powerful factor in the spread of the pest. Now, 

 the prevailing winds in the Southwest during spring are from a 

 southerly direction and as there is a continually increasing food 

 supply to the northward as the season advances, these winds help 

 the insects to keep pace with this advance. This diffusion might 

 be likened to a horizontal revolving mo\'ement, the winged 9 9 

 from a destroyed field passing over others along the border and 

 settling down to breed, infest and destroy other fields more in 

 advance, and so on day after day, thus passing over miles upon 

 miles of young growing grain changing it from a luxuriant green 

 to reddish brown, as eft'ectually destro3^ing it as would be the case 

 were it to be scorched by fire. There are of course other modes 

 of dispersion, and I have observed not only winged individuals 

 but also parasites, clinging to the glass of the windows in railway 

 coaches and in this way carried long distances. 



Thus it is that an invasion of Toxoptera, originating in central 

 northern Texas in a winter temperature above the normal, yet 

 too cool to admit of its chief natural enemy becoming active, will 



