[ 497 1 



XXXIX. 



ON THE LIFE-HISTOEY AND BIONOMICS OF THE FLAX FLEA- 

 BEETLE (ZONGITARSUS PAEVULUS, PAYK.), WITH 

 DESCEIPTIONS OF THE HITHEETO UNKNOWN LAEVAL 

 AND PUPAL STAGES. 



By J. G. EHYNEHAET, A.R.C.Sc.I., D.I.C., N.D.A., 



Entomologist in the Seeds and Plant Disease Division, Department of 



Agriculture and Technical Instruction for Ireland. 



(Plates XV-XIX.) 



[Read Fr.BuuAuv 28. Published Ai'KIL 13, 1922.] 



1. — Introduction. 



Nearly one hundred years ago the flax crop in parts of Ulster was almost 

 completely destroyed while in the seedling stage as a result of the ravages of 

 the small, black, jumping beetle, now known as the flax flea-beetle. During 

 various intervening seasons damage due to the same cause has occurred in 

 many parts of Ireland, and this beetle is now regarded as being by far the 

 most dangerous insect enemy of flax, and one capable of causing losses 

 amounting to many thousands of pounds sterling in a single season. 



Like the other members of the family Chrysomelidae, it is herbivorous, 

 feeding in the adult stage on the cotyledons and young leafy shoots of flax 

 seedlings. The destruction of the young plants gives rise to thin, uneven 

 brairds, and the ultimate production of dwarfed, branched, and uneconomic 

 crops of flax ; indeed, it is frequently the case that the young seedlings are 

 entirely destroyed and large areas are laid bare, thus necessitating re-sowing. 



Flax-growers have long been familiar with the ravages of this pest, which 

 is popularly known as the " fly " or " flea " ; but, despite this fact, little work 

 has been done regarding its biology and habits, or possible remedial measures, 

 while no details are available in entomological literature with reference to 

 the general relations of the adult beetles and their larvae with the food 

 plants and the soil in which the latter are growing. 



In July, 1920, the writer commenced, at the Department's Field 

 Laboratory for Flax Diseases, Coleraine, Co. Derry, an investigation on the 

 life-history, habits, etc., of the insect, with a view to the possibility of evolving 

 a suitable check on its ravages ; and a general account of the progress made 

 that season is incorporated in the second Report of Investigations on Flax 



