Rhynehart — Life-History and Bionomics of the Flax Flea-lieetle. 509 



given dry, warm weather in May, after weather not conducive to the 

 thorough cultivation of the seed-bed, the prospect of a bad attaclv becomes 

 highly probable, inasmuch as such conditions retard the growth of the 

 seedlings at a time when, stimulated by the prevailing warmth, the adult 

 beetles are encouraged to come out of hibernation ; whereas if the weather 

 remains cold, although growth may be seriously checked, the beetles are not 

 encouraged to activity, and therefore the seedlings escape their attentions. 

 When, however, conditions conducive to vigorous growth are secured, the 

 dangers of serious results from attack are minimized, because the seedlings 

 are enabled by rapid growth to overcome the possible effects. 



Early sown fields often suffer considerably greater damage than those 

 sown some days later. This was very apparent in Co. Down about four 

 seasons ago, when many growers had the brairds on the early sown fields 

 completely destroyed, although later sown fields suffered much less, and the 

 latest ones were not appreciably damaged. The reason for this is not yet clear, 

 but, as already pointed out, the beetles gather in, probably attracted by a scent 

 stimulus, from surrounding hibernating places to a field in which flax is 

 brairding. Since brairding flax is not common at this early period, it is 

 highly probable that all the beetles which have hibernated in that particular 

 district will come to the young seedlings. Moreover, the beetles have a 

 greater capacity for food after coming out of hibernation, and prior to egg- 

 laying, than at a later period, so that a field of early sown flax is attacked 

 by a much greater number of beetles which, individually, possess the 

 maximum capacity for food. 



The idea that warm, dry weather favours a bad attack only holds pro- 

 vided the beetles are actually present to cause the injury. Thus, the season 

 of 1921 was an ideal one as regards suitable weather for flea-beetle depreda- 

 tions; nevertheless, as already stated, there was an uncommonly slight 

 infestation throughout the different districts. From the study of the life- 

 history and observations thereon, the writer is of opinion that the prevailing 

 weather during May and June, i.e., the months during which the earlier 

 stages are passed, determines to a lai'ge extent the infestation of the 

 following spring ; because it is the beetles which emerge during late July 

 and August as a result of eggs laid in May that are, after the hibernation 

 period, responsible for the damage which may be caused during the following 

 season. Therefore, if the weather during the months of May and June is 

 fine, dry, and otherwise conducive to the health and safety of the minute 

 and delicate larvae in the soil, the number of adults ready to attack flax 

 seedlings the following spring will be correspondingly large. Moreover, if 

 warm, sunny weather prevails during late April and early Maj', the females 



