ANIMALS INJURIOUS TO FARM AND GARDEN PRODUCE. 15 



Allied species found on various weeds are frequently mistaken for 

 it, as well as the Celery Fly (Acidia heraclei, Linn.). 



IV. FOOD PLANTS. 



In addition to the beet and mangel this species is found on various 

 species of Dock, the Goosefoot (Chenopodium album, L.), the Sow- 

 thistles (Sonchus arvenis, Linn., and S. oleraceus, Linn.). 



Specimens on the Dandelion (Taraxacum officinale, Web.), and 

 other weeds proved, on examination, to be distinct from P. betae. 



V. LIFE-HISTORY AND HABITS. 



The eggs are deposited by the female fly beneath the seed leaves 

 and leaves. On the seed leaves they usually occur singly or in pairs, 

 very rarely in clusters ; on the ordinary leaves, however, clusters of 

 four to ten are common. 



In colour the egg is white, elongate, oval, and characteristically 

 marked. The length is about i mm. 



From the time of deposition until hatching on the 7th gth day 

 little or no change takes place in the external appearance of the egg. 



On hatching the young larva at once commences to make its way 

 into the mesophyll of the leaf. The newly-hatched larva measured 

 1.5 mm. in length. After the first moult the larva measures 2.2 mm. 

 The second moult takes place when about 4 mm., and the third when 

 about 6 mm. long. There are probably two further moults before the 

 larva attains full growth, when it measures from 8 to 10 mm. in length. 

 The duration of the larval period is subject to some slight variation, 

 due to climatic conditions, and varies from three to four weeks. 

 When full-fed the larval skin commences to harden and forms a dark- 

 brown barrel-shaped puparium which surrounds and protects the pupa. 

 The puparium is usually found in the soil an inch or so beneath the 

 surface, but occasionally they are found within the leaf blisters. Two 

 or even three broods appear in the year. The pupae of the last brood 

 remain in the soil during the winter ; occasionally, however, they 

 develop and hybernate. 



