48 Two Scoliid Parasites 



larvae. Possibly there is some check to emergence during dry weather, 

 though experiments in the insectary have not supported the supposition. 

 Of 21 laboratory-reared examples, each of which had pupated in earth 

 in a separate Petri dish, 11 which were kept air-dry averaged 35 days, 

 and 10 which were kept moist averaged 36 days in the cocoon. The 

 periods ranged between 32 and 40 days, with one exception in each 

 case : one of those kept dry emerged in 47 days, one of those kept moist 

 in 45 days. More observations are needed, but partly at any rate the 

 finding of large numbers in the wetter months must be ascribed to the 

 opportunities for collection afforded by the attraction of the honeydew. 

 No instance of their visiting flowers has been observed. Of the distri- 

 bution of Tiphia about the island little is known, and that mainly of a 

 negative character. An outbreak of Phytalus, small in area but rather 

 severe, in a cane-field at Waterford Plantation, 10 miles from Spencers, 

 was examined in May 1913, and amongst a large number of cane stools 

 dug up only one Tiphia cocoon was found. The Manager of Spencers 

 Plantation states that a similar outbreak of Phytalus took place some 

 three years back in the fields where Tiphia is now so common. It 

 would appear that we have quite sufficient room in the small area of 

 Barbados for the typical sequence of a local outbreak of a pest followed 

 by the migration and ultimate preponderance of its parasite. 



Under these circumstances the percentage of parasitism depends 

 upon the stage which has been reached in the local cycle. In the well- 

 developed example at Spencers the number of cocoons and parasitized 

 grubs found during extensive digging amounted to some thirty per cent, 

 of the total number of grubs and cocoons found. There being several 

 generations of Tiphia to each generation of Phytalus ; this figure must be 

 much below the actual one, since no account was taken of the large 

 number of empty cocoons representing recent generations of Tiphia, 

 nor does it include the number of grubs which would still have been 

 attacked before pupating. 



Information as to the life history of the parasite was first obtained 

 from discoveries of early stages in the field. Later the stocking of 

 Wardian cases for an attempt to introduce it into Mauritius afforded 

 further opportunities, especially for watching the behaviour of the adult 

 wasps, while it has recently been found possible to carry through 

 successive generations in the insectary. 



The largest number of eggs actually obtained from one female in 

 captivity is six, but an examination of the ovary tubes seems to indicate 

 an egg capacity of at least seventy. 



