BOOT CROPS. 67 



The Harvest Bug {Tetranychus autumnalis) be- 

 longs to the Arachnoidea, and for several reasons the 

 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 corn, especially in France. 



The Turnip Leaf Miners (DrosopMla flava and 

 Phytomyza nigricornis) are the larvae 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 larvae 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 pupae of both insects are brown 

 in colour, and, as a rule, the larvae 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 gamvia) has already been described, (ft) The 

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

 damage." The green-coloured larvas 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 spin light cocoons between the veins of the leaves 



