1922.] 



Spring-Tails Attacking Mangolds. 



829 



during a high wind the top portion of the plant becomes sepa- 

 rated from the lower. 



To avoid confusion it is also necessary to mention a not 

 dissimilar type of damage where the root heloiv ground becomes 

 threadlike, the portion above remaining intact. The cause of 

 this damage is well known, however, being due to the attack 

 of a minute beetle, Atomaria linearis. 



As a result of an investigation in a field of attacked plants 

 exhibiting the type of damage first mentioned — a threadlike 

 condition of the root above ground — very large numbers of a 

 minute Spring-tail (Collemhola) were found to be present upon 

 the plants and surrounding soil, while many of the insects were 

 seen to be feeding upon the mangolds at the affected parts and 

 causing quite a conspicuous bleeding. 



Collemhola are primitive insects without wings, and the par- 

 ticular members of the Order {Bourletiella hortensis, Fitch = 

 pruinosus, Tulb.) in question are very small slate -coloured 

 globular creatures capable of leaping considerable distances. 

 They immediately scatter when the plants are approached. This, 

 in conjunction with their small size, probably accounts for their 

 not having been hitherto associated (according to the literature 

 so far consulted) with the particular form of damage done, as no 

 plant on being handled for examination would reveal a specimen. 



It should be added that, although it is extremely probable that 

 these insects are the first and only cause of the threadlike con- 

 dition of young mangold plants above ground, this has not been 

 definitely proved. These observations are made rather as giving 

 a possible clue and to promote further investigation by those 

 interested, than to suggest that a final settlement of the problem 

 has been arrived at. 



Bourletiella {Smynthurus) hortensis has previously been 

 reported as injuring various crops, including mangolds, in this 

 country and abroad, but does not appear to have been associated 

 with the particular form of damage under consideration. 



As the insects never feed on a root below ground level, it is 

 probable that, when feasible, earthing up the seedling plants so 

 that no roots are exposed would tend to ward off an attack. It 

 is noteworthy that varieties of mangolds are susceptible according 

 to the amount of exposed root exhibited above ground in the early 

 stages of growth, which appeared on the fields examined to be a 

 characteristic of yellow rather than red mangolds. 



Mft * * * * * 



