THE IMPORTATION OF TIPHIA PARALLELA INTO MAURITIUS. 101 



be laid in this manner owing to their different degrees of development ; for in no 

 case could more than two eggs be found in the same stage of development, namely 

 one in the ri^ht oviduct and one in the left ; and furthermore the interval between 

 one laying and the next is explained by the marked difference in the sizes of the 

 successive eggs in the ovaries. 



The following observations will confirm this statement : 



On 21st June two female Tiphias were captured at Esperance and placed in the 

 Insectaryat Pamplemousses together with numerous Phy talus larvae and were fed 

 on honey and water. On 26th June a hundred of the larvae were examined and one 

 of them was found to be parasitised. On 10th July three other larvae were parasi- 

 tised ; on the 17th two, and on the 27th three ; or a total of 9 eggs laid by two 

 female Tiphias during a period of more than one month. On 5th August two other 

 females were submitted to the same conditions and by the 12th August had para- 

 sitised five larvae. It is quite possible that some other parasitised larvae had 

 burrowed too deep in the soil to be found, but it is clear from what precedes that 

 Tiphia and Elis lay their eggs only by twos, and exceptionally three at a time, and 

 that an interval of at least seven days takes place between one laying and the next in 

 captivity. 



It may be well to add that none of these eggs hatched out ; and furthermore Nowell 

 states that he could never obtain more than six eggs from one captured female. 



It would seem therefore that it is the longevity of the insect that is affected by 

 captivity rather than its egg-laying power, and we are then led to enquire whether 

 the food question does not play here an important role. 



Nowell has observed that in Barbados Tiphias when in a free state lived on the 

 secretions of Aphids, and that when in captivity they willingly fed on sugary liquids 

 and on honey, but that neither in the captive nor in the free state did they resort to 

 flowers for their food. The writer, who had made the same observations, was 

 therefore afraid that it would be difficult to establish them at Pamplemousses for 

 lack of proper food material, seeing that the few existing species of Aphids appear 

 only at a certain time of the year and are then rapidly destroyed by Syrphids, 

 Braconids, Coccinellids and fungi. 



Now it is a noteworthy fact that Tiphias have established themselves at Pam- 

 plemousses and have made good the scarcity of plant-lice by having recourse to the 

 sweetish content of the vesicular hairs of Cordia interrupta. This plant is a native 

 of British Guiana, which was introduced about 15 years ago ; it is now a regular 

 pest and infests all uncultivated fields. 



This unexpected change of diet might at first sight lead one to believe that the 

 quality of the food is immaterial to these insects, and it had no evil influence on the 

 captive ones. A closer observation of other facts, however, leads to a different 

 opinion ; namely, that. this change of diet was the result of a deliberate choice, most 

 probably due to the constituents of the vesicular hair content of Cordia interrupta 

 being more closely related to the secretion of Aphids than to the nectar of flowers. 

 It is indeed well known that ants are as a rule very fond of the secretions of Aphids, 

 while they are only exceptionally met with on flowers. The red ants of Pample- 

 mousses (Solenopsis sp. 1 ) show a peculiar liking for the secretions of Coccids and are 



