OBSERVATIONS ON HABITS OF THE TURNIP FLEA- BEETLE. 85 



of the daughter generation itself. It is beh'eved, however, that 

 the beetles which emerge each season are produced by the year- 

 old generation, and that they on their part do not reproduce 

 themselves until the following year. This view, it may be added, 

 is supported by an examination of the soft parts which shows 

 that even in beetles several months old the ovaries are still 

 immature. 



The figures given below tend to show how variable these 

 insects are in their life-history when they are bred in the 

 laborator3\ At present it is not possible to say what are the 

 precise causes of this variation, nor what in each species is 

 the normal duration of the early stages. It seems pretty certain, 

 however, when development is unduly prolonged, the reason 

 should be assigned to something unfavourable in the conditions 

 of the experiment. 



Life-ldstorii of Phyllotreta nemorum, L. 



The eggs have hitherto been sought in vain on leaves of the 

 turnip and allied plants. On the other hand, a cluster of four 

 or five nemorum eggs was obtained from the soil in which a row 

 of turnips was growing. It has been noticed, also, that when 

 the beetles are imprisoned in a cage they deposit their eggs 

 preferably in moist places. For instance, when cotton-wool is 

 used for the purpose of holding the food-plant in position, eggs 

 are laid freely amongst the fibres, provided the fibres are wet. 

 The egg-stage appears to last about nine days, but the evidence 

 on this point is at present very meagre. Tlie larvae, on hatching, 

 quit the soil and establish themselves in the leaves of turnip, 

 garden radish, charlock, sometimes of swede and wild radish. 

 Their having to crawl up the stalks for this purpose perhaps 

 explains why nemoriuii iarvffi are often found in the basal 

 segments of affected leaves, and they would no doubt be feund 

 tliere more often were it not that they can pass directly from the 

 soil to the blade itself when they meet one touching the ground. 

 When burrowing into a leaf a nemoriLm larva doubles under itself 

 in such a way that the body, when half-m, instead of being 

 stretched out straight is bent like a horse- shoe, the effect being 

 that when the larva enters it keeps the ventral surface turned to 

 the cuticle as before but travels in the oj)posite direction. From 

 the few records at present available, the larval period appears 

 to last twenty-five to thirty days. In one instance, indeed, 

 thirty-nine days passed after hatching before pupation took 

 place, but a period of this length is probably very unusual. 

 The last six to ten days are spent by the larva in burying itself 

 in the soil and preparing to pupate. During this non-feeding 

 transitional stage the body, becoming shorter and broader, bends 

 at the same time into the shape of the letter C — a shape which 

 the larva perhaps finds useful in preparing the pupal cell. When 



