8^ 



THE ENTOMOLOGIST. 



infected field during the migration period. Tlie bark was placed 

 around a tree which stood in the field, and although measuring 

 only 4|- sq. ft. in area, yielded when brought indoors over 2500 

 specimens. 



When the season is drawing to a close, liea-beetles before 

 dispersing to cover m;jnifest a habit of foregathering with one 

 another, and congregate often in considerable numbers upon one 

 or more of the plants where they have been feeding. In turnip 

 fields, for example, certain of the plants, generally isolated ones 

 in the headlands, are chosen by the beetles for their rendezvous 

 and, as the riddled condition of the foliage shows, become 

 infested to an unusual degree. When walking beside a kale 

 crop, one sometimes notices amongst the sound uninjured leaves 

 a leaf here and there eaten in one part only, generally at the 

 tip or along the margin, and, on turning it over, finds that, in 

 agreement with the limited area eaten, the beetles are not 

 scattered over the surface but are crowded together in a group. 

 In the laboratory, also, specimens have been noticed at this time 

 of year assembling at some point in the cage and " putting their 

 heads together" as though m obedience to the same habit. 



On first emerging from the pupal condition, flea- beetles 

 present a very immature and helpless appearance. The body is 

 still soft and the legs, although completely formed and dark in 

 colour, !ire too feeble to be used even for walking. In the 

 course of a day or two these defects disappear, and the beetles 

 then make their way to the surface of ttie ground. During 

 drought, when the soil becomes firmly caked together, it seems 

 probable that fresh-emerged beetles are unable to break through 

 their earthen surroundings ; and under these conditions, when 

 rain comes, numbers of young beetles may arrive above ground 

 at one and the same time, and give rise to the impression that 

 an entirely new generation has appeared, whereas they are 

 merely members of the first daughter generation that have been 

 delayed in their passage to the surface. 



Beetles that have recently emerged can be readily recognised 

 by the white colour of the stripes upon their back. As time 

 passes the colour changes to a pale straw tint, then to a brighter 

 yellow, and finally, in old age to a dull orange or even brown. 

 By examining the stripes, therefore, one can estimate to some 

 extent a flea-beetle's age, and can distinguish young beetles 

 from year-old beetles produced the previous summer. Since 

 individuals of the year-old or j)arent generation are about all 

 the summer, the production of the yoimg or daughter generation 

 is not confined to one restricted period but is continued through- 

 out the season. It is not possible, unfortunately, from mere 

 inspection to say whether all young white-striped beetles obtained 

 towards the end of the season are the offspring of year-old 

 beetles or whether some of them at least may not be the ofl'spring 



