72 Belladonna Leaf -Miner 



top shoots are most heavily infested early in the season, but later the 

 radical leaves are most attacked. 



Hibernation occurs in the pupal condition about two inches below 

 the surface of the soil near the food plants. 



The number of broods vary. There are at least three in latitude. 

 The broods are not separated sharply off- from each other. There is a 

 good deal of overlapping so that all stages occur in the field during the 

 greater part of the season. 



The eggs are deposited superficially on the back of the leaf in groups 

 consisting of parallel series varying in number. The incubation period 

 is about 5 days. 



The larvae feed uninterruptedly and complete their metamorphosis 

 in 10 days under the most favourable circumstances. The larvae of 

 the first two broods sometimes pupate in the leaf, generally making 

 their way to the margin to do so. The pupal period of the first two 

 broods is about 17 days. 



The average period for one complete life-cycle is about 36 days. 



Two closely related species, P. bicolor and P. nigrilarsis, attack com- 

 mon weeds such as dock. Their life-histories are, in all details, almost 

 similar to that of P. hyoscyami. Structurally, there are some interesting 

 differences, especially in the larval stages. 



According to the different food plants which it affects, hyoscyami 

 may be divided up into at least two " biologic " species, one of which 

 would seem to confine its energies to a few members of the Cheno- 

 podiaceae, the other to Solanaceae, and within these two families 

 preferences to different species are shown. But in the absence of the 

 one favoured food plant, another, not ordinarily so attractive, may be 

 selected. 



Species of the Chenopodiaceae and Solanaceae have in common 

 certain specific organic substances belonging to the group known as the 

 alkaloid bases. They probably serve as an attraction to the fertilised 

 females to oviposit on the leaves of the plants which contain the active 

 principles concerned. 



Experiments showed that mangold-reared adults would not oviposit 

 on belladonna and vice versa. This restriction to one kind of plant is 

 indirectly advantageous to the agriculturist in that strains of flies reared 

 on belladonna confine themselves probably to this species or one closely 

 related, such as henbane, and do not attack mangolds. 



The young plants are more easily killed than the more advanced 

 ones. 



