PRESIDEXTIAL ADDRESS SECTION D. 89 



to destroy stable manure, at the same time preventing the access 

 to manure of the necessary intermediate host, the housefly. 



Stomox^'s sp. has recently been shown by Ed. Sergent and 

 A. Donatien to be the transmitter of camel trypanosomiasis in 

 North Africa. According to these workers, the Stomoxys acts as 

 a mechanical transmitter only, and infection occurs only when 

 a fly attacks a healthy camel immediately after feeding on an 

 infected one. This fact of mechanical transmission of the 

 trypanosome of the camel has been proved experimentally, and 

 perhaps explains the relatively small numbers of infected camels 

 encountered. 



The bug, Co)iorhinus niegistus (perhaps more correctly 

 called Triatoma niegista), has been known for many years 

 as the carrier of Trypanosoma cnizi in Brazilian trypano- 

 somiasis. The disease has been reported from various parts of 

 Venezuela, where, however, Conorhinus does not occur. In 

 1919, the Venezuelan transmitter was discovered by E. Tejara 

 to be the bug, Rhodnins prolixus. 



One practical development of entomology may be briefly 

 noted. It is the use that is being made of hyperparasitism of 

 insects. jNIuch attention has been concentrated on the natural 

 enemies of injurious insects with a view to utilising natural means 

 for the extirpation of noxious pests or the prevention of their 

 undue multiplication. Recently, T. H. Johnston has been 

 working on Chalcid and other flies in Australia. He finds that 

 SpahuKjia Htuscidaruin , Nasonia hrcvicornis, Pacliycrepoideus 

 duhias and the Chalcids, Chalcis caUiphora' and Dirhinus 

 sarcopJiagu' are prevalent. He has worked out the life-histories 

 of the two first-mentioned, and their methods of parasitising bush 

 flies. He has suggested that certain hyperparasites should be 

 introduced into Australia, the chief being Alysia viauducafor and 

 Aplurrcta- ccphalofcs, for the purpose of parasitising and thereby 

 destroying noxious insects. The introduction of the Chalcid, 

 McUffobia acasta, was also suggested, but as the latter may para- 

 sitise useful insects, it would probably be unwise to introduce it. 



A new Chalcid, PmspaJangia pJatensis, jDarasitic on the larvae 

 and pupae of Miisca donicsfica and Stomoxys' calcitraus, has been 

 recently described by T3rethes, and Eroggatt has found a new 

 parasite of the flesh-fly, Sairophaga aarifrons, in Dirliiniiti 

 sarcophagcc. If it is possible to utilise these insect jjarasites, 

 they should aid in mitigating the fly nuisance. 



It is suggested that in South Africa, possibly, use could be 

 made of certain natural insect parasites to reduce the number of 

 insect pests of house and farm, especiallj^ remembering the 

 success that attended the introduction here of the Californian 

 ladybirds by Messrs. Lounsbury and Mally to combat scale 

 insects. 



Another successful application of insects to keep down pests 

 is the )ise in South Africa of a cochineal insect. Coccus indicus,'^ 

 which is a most effective destroyer of the useless prickly pear, 

 Opuntia monacantha. The insect is said not to be injurious to 

 varieties of prickly pear useful for fodder for stock. 



* Agricultural Journal of South Africa. June. 191.'). 



