BIONOMICS AND DEVELOPMENT OF LYGOCERUS sP. 125 
dius ervi, and the nearly related species A. avenae, are 
parasites of such pests as Macrosiphum granarium, 
the grain aphis, and according to Marshall (19) are polyphagous, 
preying indiscriminately on various species of aphides. If 
their parasites follow them to other hosts, their efficiency 
as controls of plant-lice must be seriously impaired. For 
instance, two collections of A. ervi from M. urticae, made 
from different places round Cambridge in August, gave the 
following results : 
Number Parasitised by Parasitised by Total % eis 
examined. other families. Lygocerus. parasitised. Ly; aul 
ygocerus. 
I 50 12 16 56 32 
Other collections, of which exact records were not kept, 
likewise showed a high percentage of hyperparasitisation by 
these Proctotrypids. 
Aphidius is at least twice as prolific as its parasite, 
and each female destroyed by the latter means the loss of 
thirty or forty ovipositions, which would kill, or at least impair 
the fertility of, the same number of aphides. If this high 
rate of hyperparasitisation should occur in a grain crop infested 
by Macrosiphum granarium, attacked by Aphi- 
dius, the efficiency of this natural control might be lowered 
by 50 per cent. 
SUMMARY. 
1. Lygocerus testaceimanus, Kieff. is a hyper- 
parasite of Aphis saliceti, Kalt., through the primary 
parasite, Aphidius salicis, Hal.; and L. cameroni, 
Kieff. is similarly a hyperparasite of Macrosiphum 
urticae, Kalt., through the primary parasite, A phidius 
ervi, Hal. 
2. The Aphidius is attacked immediately before or 
after metamorphosis, when lying within the empty skin of the 
aphis within which it is reared. 
3. The egg is laid, and post-embryonic development takes 
place, outside the body of the host. 
