NUMBER OF ANNUAL GENERATIONS. 13 



destructive numbers is preceded by one or more scattering generations 

 in the same field. 



Other things being equal, the worm must appear earliest in the south- 

 ernmost latitudes, since extended observations on the appearance of 

 other insects show that there is retardation of from four to seven days 

 with each degree of latitude northward.^^ 



There is, in normal seasons of little injury to the crop, a similar re- 

 tardation northward in the appearance of the Cotton Worm within the 

 southern portion of the belt, corresponding in some measure with the 

 growth and development of the plant; and it is a notable fact that the 

 worm is seldom noticed* and never in great numbers before the plant be- 

 gins to bloom. What is generally under these circumstances called the 

 first brood or "crop" has been preceded by at least one and often two 

 generations sparsely distributed over the fields. Yet in years when the 

 worm abounds to a disastroys extent in the southern portion of the belt, 

 its appearance in the northern or temporary portion cannot be counted 

 on with any certainty as to time, because it is always the result of mi- 

 grations in the winged state, and these migrations may be more or less 

 extended according to circumstances. Between the first appearance of 

 the worm in the southern and northern portions of the belt there is, 

 therefore, a marked difference ordinarily observable, it being in the lat- 

 ter much later and in far greater numbers. 



NUMBER OF ANNUAL GEN^ERATIONS. 



The general impression and belief that prevails in the South is that 

 there are, in those sections where the worm is most injurious, three 

 broods or generations, or, as the planter puts it, "crops," each year. 

 This statement of the case has also been accepted as correct by most 

 previous writers on the subject.^* It is, however, essentially erroneous, 

 so far as the southern portion of tlie cotton belt is concerned, as the 

 earlier and later generations are not taken into account, but overlooked. 

 The appearance of the first generation has already been discussed, and 

 it occurs during the latter part of April and in May in the more southern 

 portions of the belt, and even in March in Florida. One generation 

 follows another continuously from that time on, just so long as there are 

 any leaves to be devoured, and we have, by protecting both plant and 

 insect from frost, kept the moths ovipositing in the city of Washington 

 all through November ; while the worms, under like conditions, have 

 hatched through the early part of December, matured, and spun up 

 about Christmas time. 



Careful observations and experiments in 1879 in South Texas show 

 that at least seven, and probably even more, annual generations are 

 produced there. The first two generations are generally well separated, 

 but, owing to the irregularity in egg-laying and in individual develop- 

 ment, the later generations so cross each other, that the insect may be 



