Miscellaneo us. 357 



1 . What are the causes of the devastation, and by what means may 

 they be distinguished from one another ? 



2. What importance should be attributed to them ? 



The damage done to the rape-plants, in the fields of the " Institut 

 Agronomique" (where these observations were carried on), is due to 

 five perfect insects and three larvee. 



The former consist of four species of Haltica, and a new species 

 of weevil belonging to the genus Grypidivs of Schonherr. This 

 curious insect passes its slender curved rostrum through the walls of 

 the pod to the centre of the seed, where it gnaws a large hole. The 

 seeds thus attacked, if not ripe or nearly so, become abortive ; if ripe, 

 they lose a considerable portion of their substance ; and as, from 

 their position, the rostrum of the weevil always cuts the radicle, they 

 are rendered incapable of germinating. A very small hole in the 

 valve of the pod is the only external trace of its attacks left by this 

 insect. 



The four species of Haltica attack and destroy the young plants 

 as soon as they are above ground ; they sometimes gnaw the paren- 

 chyma of the seed-vessels, but apparently without injuring the seeds. 



Thelarvse are the most destructive enemies of the crops. The first 

 M. Focillon believes to be that of the weevil above-mentioned (Gry- 

 jridius brassicte) . It is about 3 millimetres in length and 1 \ in breadth, 

 white, footless, with a shining black scaly head. It inhabits the in- 

 terior of the pod, where it devours three or four seeds ; its presence is 

 known by the blackish colour of the seed-vessels. When mature it 

 gnaws a round hole in one of the valves of the pod, by which it passes 

 out, and no doubt goes down into the earth to undergo its metamor- 

 phosis. 



Very similar ravages are committed by the caterpillar of the Tpso- 

 lophus xylostei of Fabricius. This is about 9 millimetres in length, 

 of a pale green colour, bristled with black hairs, and with the head 

 black. Like the preceding larva it lives in the pods until the period 

 of its transformations, when it passes out through a round hole which 

 it forms in one of the valves. After leaving the pod it spins a cocoon 

 of very loose meshes, in which it remains fifteen days in the pupa 

 state. The moth appears, usually, in June. 



The third larva is about 2 millimetres in length, and during the 

 greater part of its life is of a white colour. Great numbers of them 

 are found in some pods, which soon become moist, and finally wither 

 and become mouldy, together with a larger or smaller quantity of the 

 seeds which they contain. M. Focillon has not yet ascertained the 

 perfect state of these larvae, which are known to the agriculturists by 

 the name of the " small white worm." 



The importance of these ravages will be readily understood from 

 the following statements : — Cleaned rape-seed contains 45 per cent, of 

 oil, and deducting that which is retained by the rape cake, there is a 

 return of about 34 per cent. This return will be larger if there are 

 more sound seeds, and if all were in this state, it would rise to 3G6 per 

 cent. 



The seeds eaten by the larvee of the weevil and moth give no oil. 



