342 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1947 



better used in some other type of control. The farmer should be edu- 

 cated to expect the economic entomologist to have the broad type of 

 training suggested above and to look confidently to the economic 

 entomologist for immediate advice and guidance in meeting his prob- 

 lems of pest control. This desirable relationship cannot materialize 

 so long as the current point of view continues to prevail. 



It may be that the danger that I have envisioned is more apparent 

 than real. Human affairs move with sufficient slowness that the un- 

 wisdom of attempts at the wholesale extermination of insects may be 

 made sufficiently clear through repercussions from early attempts that 

 efforts in this direction will be abandoned and will be replaced by 

 actions based on a saner philosophy. Certainly the usage of DDT to 

 date has revealed that such powerful insecticides, valuable as they are, 

 cannot be used indiscriminately with impunity. Nevertheless much is 

 to be gained by a concerted program of public education that is aimed 

 at balanced enlightenment in place of the present progi-am of merely 

 seeking support for more and ever more destruction of insect life. 



In the light of the reasoning thus far advanced it seems worth while 

 to review certain of the interrelations between man and insects in which 

 the insects play a beneficial role. 



As a general rule little attention is paid to the factors concerned in 

 the control of the plant population of the earth and the place that 

 insects hold among these factors. Because of man's dependence on 

 plants it is customary to label as injurious any creature aside from man 

 and his domestic animals that feeds on plant life. Yet obviously this is 

 not the case. An organism is really injurious only when it becomes 

 sufficiently abundant that its activities are genuinely detrimental to the 

 welfare of other organisms. This happens in the case of only a very 

 small proportion of insects. Moreover, it is possible for a plant as 

 well as an insect or other animal to get out of balance with the rest of 

 life ; to become, in fact, a pest. A few plants in recent decades have so 

 far escaped from normal population controls as to become veritable 

 scourges, and so far the only significant progi-ess in bringing them back 

 under control has been accomplished through the use of insects that 

 feed on them. 



The most notable example is the prickly-pear cactus in Australia 

 which, according to some authorities, by 1935 occupied some 60,000,000 

 acres of Australian soil to the extent that it was practically worthless 

 for agriculture. Cactus-feeding insects introduced from the Ameri- 

 cas have brought the cactus under control. Most of the work of con- 

 trol has been wrought by a single species, the moth C actohlastis cac- 

 tormn, whose caterpillar mines the joints of the cactus. Allan P. Dodd 

 (4) says the introduction of this insect between 1925 and 1927 "brought 

 a complete change in the outlook within a few years. Its progress 

 has been spectacular, its achievements border on the miraculous. Great 



