1918-19.] Life-History and Bionomics of Myzus ribis, Linn. Ill 
Frequently a parasitised aphis is found clinging to the edge of a leaf — a 
position it seldom chooses when alive ; but it is not known whether aphides 
who have placed themselves thus are more liable to be struck, or whether 
they crawl thither at the approach of death. The female Aphidius is very 
undiscriminating, and will not only attack the cast skins of the Myzus , but 
will also try to oviposit in a spot where an aphid has been sucking. She 
also attacks the same victim repeatedly. 
I obtained an Aphidius indistinguishable from A. ribis from P. galeop- 
sidis collected in the field in July, and these oviposited in M. ribis, both 
from currant and Labiatae. I also obtained a single example of a species 
nearly allied to, if not identical with, A. rosce, Hal. 
Summary. 
M. ribis, Linn, (red-currant aphis), on Ribes rubrum is dimorphic in 
respect of certain features of the antenna and of abdominal and wing 
dimensions. 
The nature of the food, whether healthy or blistered by the attack of 
the fundatrix, seems to be the determining factor of this dimorphism. 
The form from healthy leaves is probably identical with M. whitei, 
Theobald, and M. dispar, Patch. 
M . ribis is migratory, and in summer colonises certain Labiatee and 
other weeds ; but this migration is not obligatory, and the entire life-cycle 
may be passed on currant. 
On its summer host plant this species has been previously described as 
Phorodon galeopsidis, Kaltenbach. 
There is a decline in fertility in the later part of the summer among 
the forms remaining on currant. 
This is caused by a lower birth-rate, and not by the shortening of the 
life of the parent. 
This decline, together with the attacks of predaceous and parasitic 
enemies, accounts for the frequent disappearance of the species from 
currant in August and September. 
Both sexual forms may be produced, and eggs may be laid, on either 
host plant. Males transferred from Labiatse to Ribes can fertilise the 
females on the latter plant. 
