Ll. Lloyd 87 



This explanation of the spread of the pest, though difficult to prove 

 conclusively, seems to be the most reasonable one, since it presupposes 

 no modification of the instincts of the moth which cause it deliberately 

 to invade places which it apparently dislikes, and to lay its eggs on 

 foliage to which many of its larvae are unsuited. 



The species outside is checked normally by a variety of factors: un- 

 favourable weather; severe winters; the ravages of bats, birds, shrews, 

 moles, toads and other animals; the attacks of hymenopterous and 

 dipterous parasites. In the houses the climatic conditions are equable 

 from early spring to late autumn, and the pupae are protected from the 

 severity of the winter. Enemies are relatively few, the only important 

 ones being spiders, the carnivorous beetle, Carabus granulatus L. and 

 the ichneumon parasite, Pimpla instigator Fabr. The last of these, 

 though of great benefit, loses much of its importance since it fails to 

 keep pace with the rapid generations of the moth. These unnatural 

 conditions foster those larvae which find tomato foliage a suitable diet, 

 and this, together with the fact that the moth is a very prolific one, has 

 enabled it to become a very serious pest in circumstances which are 

 otherwise against it. 



The moth is therefore not a normal pest of tomatoes and is much 

 less firmly established in the houses than it at first sight appears to be. 

 There is a danger that it will become a normal pest unless it is stamped 

 out while it is still in some respects weak. If the methods adopted to 

 control it are merely sufficient to bring its ravages within small dimen- 

 sions its disappearance is not to be expected, and the cost of this partial 

 checking must be regarded as a perpetual annual tax on the tomato 

 industry. 



5. CONTROL. 



The instructions which follow have been framed with a view to the 

 complete abolition of the pest, by attacking it in all its stages in the 

 houses, and by preventing the escape of the moths to the outside, as 

 far as this is reasonably possible, so that conditions around the nurseries 

 may again become normal. If all the growers will carry out these 

 instructions for a few years it is believed that the pest will cease to 

 exist among them, but since the infection spreads in congested areas, 

 the neglect of one will neutralise the efforts of the others from this point 

 of view. 



In order to effect this it is necessary that: (i) the larvae should be 

 destroyed by spraying; (ii) larvae which appear when spraying is not 



