362 
Parasites of Common Flies 
Experiments with M. acasta. 
From M. acasta which emerged in 1916 several generations were reared 
on healthy puparia of several species of flies, and some observations made 
on their habits under these conditions. In most of these experiments the 
chalcids and the puparia were kept in small corked glass tubes, the contents 
of which could be examined easily under a binocular dissecting microscope. 
Oviposition. 
When a $ is placed in a tube with a fly puparium she soon begins 
to walk over it, stopping at frequent intervals and apparently examining 
the surface. Eventually a place is chosen and the ovipositor applied. During 
the process of inserting the ovipositor the position of the legs is not changed, 
but the whole body is raised and lowered rhythmically by movements of the 
tarsi. At each movement of the body the ovipositor seems to be rotated 
through a quarter of a circle. Eventually the ovipositor is completely buried. 
The whole process frequently occupied 2 hours. 
Fig. 12. Melittobia acasta ovipositing in a puparium. 
One $ was seen ovipositing over a period of 48 days and another over a 
period of 37 days. Fly larvae, whether large or small, did not attract the 
chalcids, and no attempt was ever made to oviposit in them. 
On carefully dissecting a healthy fly puparium a few days after oviposition 
the eggs of the chalcid, which measure 0*275 x *0875 mm. and are sticky, 
are found in groups up to the number of 12, though single scattered eggs are 
also seen, on the surface of the nymph. The larvae, which emerge from these 
eggs, remain on the surface of the fly nymph, but become partly imbedded in 
shallow grooves. Where a puparium already infected by a braconid was 
attacked only small numbers of chalcid eggs were found lying on the surface 
of the braconid larva. 
The development of M. acasta larvae. 
The events, which occur during the later stages of the larval life of M. acasta, 
may be followed by opening the infected fly puparia and keeping them in 
glass topped boxes in the dark. Such opened puparia with M. acasta larvae 
within them have been illustrated previously (Graham-Smith, vm. 1916, PI. 
