INDIGENOUS PARASITES 405 



progeny are relatively few in number. The efficiency of Scolia 

 manilice in Hawaii is largely attributed by Muir to its highly 

 developed faculty for discovering its host. Furthermore, a 

 fragile and minute parasite with restricted powers of locomotion 

 may prove highly effective when hosts are abundant, but play 

 an insignificant part in control when they are scarce. The converse 

 would appear to be the case with certain of the more robust 

 parasites of low fecundity. 



III. The Utilisation of Indigenous Parasites 



The relationship between a given indigenous insect and its 

 parasites is one involving a complex condition of ecological 

 equilibrium which, moreover, is subject to seasonal fluctuation. 

 The component factors, together with their individual and 

 collective effects, which govern these fluctuations, have not so far 

 been subjected to other than the most elementary analysis, and 

 we are hardly in a position to assert whether adequate analysis is 

 at all possible. In the absence of fundamental information of this 

 kind the feasibility of the utilisation of indigenous parasites can 

 only be answered by actual experiment. It needs to be recollected 

 that the subject involves somewhat different principles from 

 those concerned with parasite introductions. In the latter case 

 the building up of a condition of natural equilibrium is aimed at, 

 whereas the utilisation of indigenous parasites is largely concerned 

 with efforts to modify a condition of equilibrium usually already 

 highly adjusted. In order to secure practical results it is necessary 

 to maintain a permanently readjusted equilibrium against 

 tendencies which are constantly operating in the opposite 

 direction. 



Suggestions have been frequently made and, in certain cases, 

 actual attempts carried out, with a view to making use of 

 indigenous parasites as auxiliary agents in pest control. Such 

 operations consist either of conserving or increasing the numbers 

 of a parasite or predator in a given area with the idea of obtaining 

 a higher degree of control over some individual species of pests, 

 or of attempting to colonise such enemies in an area of a country 

 where they did not previously exist. 



