508 Scientific Proceedings^ Royal t)ubUn Society. 



same regions of the plants, the most favoured one being between two of the 

 newly developed leaves just behind the growing point. The effects of the 

 feeding beetles become less obvious as the plants increase in size, and little 

 anxiety is felt regarding damage. The newly emerged adults in August 

 attack old flax stalks, and liave been observed to " bark " them completely in 

 the attempt to secure sufficient preferred food. 



(&) By the Larva. — The feeding larvae live on the flax roots, tunnelling 

 into and feeding upon their soft parenchymatous tissues. The youngest parts 

 of the roots seem to be preferred. Whilst plants growing in restricted 

 amounts of soil in pots in laboratory cages suffered as a result of the larvae 

 feeding upon their roots, no damage which could be ascribed to the activities 

 of feeding larvae was observed in seedlings growing in field cages, or in plots 

 in the open field. This is probably due to the fact that about three weeks 

 must elapse from the time the eggs are laid until the larvae are capable of 

 doing appreciable damage, and during this time the flax plants will have 

 formed an extensive root system, and thereby become proof against serious 

 injury. The fact, however, must not be overlooked, that where the growth 

 of seedlings has been delayed, owing to unsuitable conditions, or otherwise, 

 the inherent possibility of these larvae feeding in the roots, and thus further 

 retarding growth, always remains. 



It is interesting to note that in the case of the larvae of the Chrysomelid 

 genus Donacia, which live upon the roots and stems of aquatic plants, 

 Boving (4) concludes that the plants rarely suffer from the effects of the 

 feeding larvae. Howard (35), referring to the larvae of the tobacco flea- 

 beetle {Epitrix parvula F.), which feed upon the roots of the tobacco plant, is 

 of opinion that " the damage done to the roots . . . must affect the health 

 of the plant to a certain extent, but it is not appreciable in comparison with 

 the damage which the adult beetles do to the leaves." Chittenden and 

 Marsh (14) state that the injury done to cruciferous plants by the root- 

 feeding larvae of the Western Cabbage Flea-beetle {Phyllotrcta punllaHova.) 

 is negligible, but the larvae of the Desert Corn Flea-beetle {Chaetocnema 

 ectypa Horn.) are, according to Wildermuth (63), highly destructive to alfalfa 

 and maize by reason of the damage done to the roots on which they feed. 



9. — Conditions avhich Favour Attacks. 



The opinion is generally held by farmers that attacks by flea-beetles are 

 largely governed by the time of sowing, tilth of soil in the seed-bed, and the 

 prevailing weather conditions at and for weeks after brairding— all factors 

 which tend to exert considerable influence on the rate of growth. Thus, 



