506 Scientific Proceedings^ Royal Dublin Society. 



the favoured food plant, attracted thereto by tropisms as yet unexplained. 

 Apart from these slight attacks — bothof wliich occurred on early sown flax — 

 the brairds of 1921 suffered little, if at all, from flax flea-beetle depredations. 

 Some probable factors in the origin of this freedom from attack are discussed 

 in section 9. 



Outside of Ireland there are few, if any, authentic records of damage to 

 flax by this species. Heikertinger (28) records parvidus as the only species 

 of the genus Zongitarsus known to injure flax ; but there is nothing to 

 indicate that the injury referred to occurred in Germany. More recently, 

 Blunck (3) includes L. parvuhis Payk. in his list of the insect and other 

 animal enemies of flax ; but here again the country is not specified. 

 Kuhnert (43) does not make any mention of L. 2Mrvuhis, but records 

 Phyllotreta nemorum, our turnip flea-beetle, as destructive to flax seedlings. 



7. — Eange of Food Plants. 



Cultivated flax, Linum usitatissimum L. is, undoubtedly, the favoured 

 food plant, and is eaten in preference to all others, with the possible 

 exception of narrow-leaved flax, Linum angustifolium (Huds.). The latter is 

 a dwarf spreading species, found growing wild in the south and east of Ireland, 

 but not in the north. A small plot grown from seed at Coleraine in 1920 

 became badly infested with beetles, and was eaten simultaneously with 

 cultivated flax growing alongside. The preference for flax is well seen in 

 spring if a small plot be sown early. The beetles, if the weather be suitable, 

 will gather to it rapidly and feed voraciously, showing no desire for other 

 plants. Purging flax, Linum catharticum L., is eaten if supplied to beetles 

 in captivity ; no definite proof, however, of its having been eaten in the open 

 could be seen. 



Other alternative food plants are clovers and grasses. These have 

 been observed to be eaten both in the field and in laboratory cages ; but in 

 the open are only attacked late in the year after the flax has been pulled, 

 and possibly in spring, if there is a spell of dry warm weather before the 

 flax brairds are ready. Twenty beetles lived happily on a plant of white 

 clover ( Tri/olium repens) in one of the laboratory cages. The leaflets were 

 not notched or perforated, but were eaten from the under surface, usually 

 near the insertion of their stalks, the upper epidermis being left intact. In 

 the field, however, leaflets with notches eaten out have been observed late in 

 the season. Of the grasses, the younger leaves seem to be preferred. 



Some experiments were made to determine if the beetles showed a 

 preference for any of the common weeds when flax is not available. 



