ROOT CROPS. 67 



The Harvest Bug {Tetranychus autumnalis) be- 

 longs to the Arachnoidea, and for several reasons tlie 

 members of this class are looked upon as modified insects. 

 The so-called " harvest bug " is a spinning mite, and on 

 the authority of M. Megnin {L'Insectologie Agricole) 

 possibly injures the leaves of turnips as well as those of 

 grass and corn crops. 



According to Curtis, another arachnoid {Trombidium 

 trigonum) injures the spikes of com, especially in France. 



The Turnip Leaf Miners {Drosopliila flava and 

 Phytomysa nigricornis) are the larvse of two dipterous 

 flies which feed upon the parenchyma (soft parts) of tur- 

 nip leaves. D. flava is about one-tenth of an inch long, of 

 a yellow colour. The larvaB of this two-winged fly are 

 of a green colour, and live beneath the cuticle on the 

 upper side of the leaves. P. nigricornis is the same size 

 as the " yellow leaf miner," but has a black body and 

 slate-coloured wings. The larvae burrow beneath the 

 cuticle on the under side of turnip leaves, and there feed 

 upon the soft parts. The pupee of both insects are brown 

 in colour, and, as a rule, the larvse turn to the pupal stage 

 within the leaves. 



Prevention. — ^Burn all infested leaves. 



The Turnip Moths {Plusia gamma, Cerostoma 

 xylostella, Noctua [Agrotis] exclamationis, and Noctua 

 [Agrotis] segetum) are four in number, and their methods 

 of attack are somewhat dissimilar, (a) The Silver Y Moth 

 {Plusia gamma) has already been described. (^) The 

 Diamond-back Moth (C. xylostella) " seldom does much 

 damage." The green-coloured larvse feed on the foliage 

 of turnips and swedes. They are about half an inch long, 

 and taper towards both ends. When mature, the cater- 

 pillars spiu Hght cocoons between the veins of the leaves 



