1^ PEESIDKNTIAL ADDRESS SECTIOX D. 



Olive Insects. 



In view of tlie highly favourable natural conditions, South 

 Africa should have the finest olive groves in the world, but 

 there are two little insects that serve as effectual deterrents — 

 the Ulive Tingid'id, Teleonemia australis Dist., and the 

 Chrysomelid, Fseudococcinella sewvittata Chevr. When it bas 

 been demonstrated that the control of these two species by 

 either spraying- or fumigation falls within practical limits, 

 olive culture should go ahead by leaps and bounds. 



Other Species of Importance. 



To continue with even a brief survey of outstanding 

 problems, would recjuire an undue amount of time; but even 

 so, attention must be called to the fact that the vine has its 

 mealybug, every tree and busli its scale insects, the wattle its 

 bagv.-orm, and the veld its termites. All are replete with 

 scientific as Avell as economic interest, 



Fluctnotions in Relative Abundance of Insects. 



Xo insect species is uniformly abundant from year to year. 

 Some fluctuate far more than others. The American Army 

 Worm, Leucania unipuncta, and the South African Mystery 

 Worm, Laphijgma exempta, are species in which extreme 

 fluctuations occur, a season or two of extraordinary abundance 

 being followed by a series of seasons of almost total absence 

 and then a sudden increase to excessive abundance again. With 

 other species the fluctuations are not so violent, but they are 

 fairly well marked. Unfortunately there is no really satisfac- 

 tory way of explaining them. One thinks at once of natural 

 enemies in the form of parasitic insects, diseases and unseason- 

 able weather. Climatic conditions coupled with excessi^^e 

 abundance may possibly affect the vitality of any given species, 

 which after a time resumes full vitality and makes its influence 

 felt accordingly. Variations in farm practice may help or 

 hinder a species. It is highly desirable to determine the exact 

 causes of these fluctuations, for through the knowledge we may 

 find a clue to easy coiitrol measure. 



Beneficial Insects. 



Beneficial insects are important factors in human welfare. 

 Whether concerned in the production of human food in the 

 form of honey and the distribution of pollen to ensure the 

 cross fertilisation of flowers, or whether they are acting as 

 internal parasites or external enemies of injurious insects, they 

 are all contributing their share towards making and keeping 

 the earth a fit place for human beings. Although a few species 

 are fairly well understood, the great majority of named species 

 mean little more than names to us. In fact, we have scarcely 

 touched the fringe of the great problem of parasitism and the 

 possibility of controlling injurious species by means of their 

 natural enemies. This phase of entomological work will 

 increase in importance as the increase in population necessitates 

 the utmost economy in the production of food. The study of 



