1918-19.] Life-History and Bionomics of Myzus ribis, Linn. 109 
Aphidius ribis, Haliday. Kaltenbach (16) remarks that out o£ no aphid 
did he rear so many Aphidiidse. My observations on the embryonic and 
post-embryonic development of this parasite are incomplete, and it is 
intended here to offer only a few preliminary remarks on a subject which 
I hope to investigate more fully in the future. 
Aphides struck by the Aphidius were first found on July 3rd, and were 
common until the end of August. The female Aphidius oyiposits within 
twelve hours after emerging from the pupa, but I never induced her to do 
so without a previous meal of either “ honey-dew ” from the aphides, or 
sugar syrup. If a male is present, mating then takes place and oviposition 
begins within a few minutes. If no male is at hand, she lays a number of 
eggs parthenogenetically, varying in number from four to twenty. The 
number of ovipositions after mating was difficult to determine, but seems to 
be between thirty and forty. Aphides parasitised in the second and third 
instars frequently die with the larval Braconid within them. Hence the 
number of dried and bloated aphid skins found on the leaves cannot be 
taken as representing by any means the whole control of this pest by the 
Aphidius, for there is undoubtedly a large mortality of the hosts, and 
incidentally of the parasites within them, which is not recognised as due 
to this cause. An alate Myzus was invariably ignored by the Aphidius, 
and I have never found a winged female or nymph containing the parasite ; 
but whether these forms are not attacked in the early stages, or whether 
they are unable to complete their development after parasitisation, I am 
unable to say. The apterous females of M. ribis are nearly, if not quite, 
sterile after the attack. On July 16th I isolated seven mature females 
which had been exposed to an Aphidius two days previously. After eight 
days, one which seemed healthy had produced twenty -five young, four had 
died, and three contained the-pupse of the parasite. 
The larval life of individuals from the parthenogenetic eggs is about 
fifteen days, and the pupation is between seven and fifteen days. The 
larval life of individuals from fertilised eggs is about ten days (though in 
one exceptional case it was twenty-five days), and pupation is six or seven 
days. Hence the forms from parthenogenetic eggs develop rather more 
slowly than the others. Both sexes may arise from unfertilised eggs. 
From thirty -three parthenogenetic ovipositions I was able to rear only 
five males and two females. The life of the male is three to four days ; 
that of the female is longer and she may live for a week. I have reared 
Aphidius ribis through three generations in the summer. 
The Myzus is attacked both in the red blisters and on the green leaves, 
but my observations go to show a greater number of victims on the latter. 
