1918-19.] Life-History and Bionomics of Myzus ribis, Linn. 107 
that plant ; but he doubted whether the species is identical with M. ribis, 
because he failed to establish M. ribis upon Labiatse in the spring. 
Buckton (2, p. 172) remarks that he failed to find the oviparous female 
of P. galeopsidis, and as all observers are agreed that this form appears 
only from July to September, it seemed to me probable that the males 
and viviparous mothers of the sexual females returned to currant, and 
that the eggs were laid there. In the hope of verifying this, I tried 
repeatedly to transfer the last two viviparous generations to currant, but 
in every case they died in a day or two without reproducing. It is worth 
remarking that the males transferred from Galeopsis to Ribes lived only 
three or four days, although they fed readily, while on their birth plant 
they survived for a week or even longer. 
On October 26th, an oviparous female (A. I, 18 generation) was found upon 
Galeopsis. Unfortunately it is not certain whether the parent was winged 
or wingless. This female differed from the oviparous females on ribis only 
by a vivid green and somewhat interrupted line extending along the 
dorsum. I put her into a tube with a newly-emerged male from Galeopsis 
and copulation took place within two hours. The following day she laid 
three eggs upon Lamium leaves, and died twenty-four hours later.* 
It must not be overlooked that this female came of captive stock, and 
it is quite conceivable that her parent may have been a migrant, who, 
kept in confinement, was unable to reach the first host plant, and so of 
necessity produced her young on the second. At the same time it is clear 
that the oviparous forms of this species may be born, and can oviposit 
upon Labiatse in the laboratory, and there seems no reason why this 
should not happen in the open, if from any cause Ribes is not attainable. 
The migratory stock from currant might thus under certain circumstances 
continue indefinitely upon Labiatse. The difficulty in the way of this view 
is that Galeopsis and Lamium are both annuals, and therefore, even if 
the egg survived the winter, the fundatrix would be faced with starvation 
when she appeared in spring. Against this must be put the fact that 
Lamium at any rate is a very common weed, and in sheltered situations 
seems to flourish all the year round. On the whole, I incline to the view 
that while permanent colonisation of the second host plant is not usual, 
it is by no means impossible under certain circumstances. 
* Since the above was written, these eggs, which were kept over the winter, have 
shrivelled up without hatching. Steven (“ Biology of the Chernies of Spruce and Larch, and 
their Relation to Forestry,” Proc. Roy. Soc. Edin., vol. xxxvii, 1917, pp. 356-381) remarks 
that the eggs of Gallicolse migrantes laid on spruce, and of Gallicolse non-migrantes laid on 
larch, do not hatch. The failure of aphid eggs to hatch on certain food-plants requires 
further investigation. 
