54 THE EEPOET OF THE No. 36 



ton, on the factors operating on the Forest Caterpillar and the Fall Web Worm. 

 The elaborate studies of the parasites of the Gypsy Moth in New England, 

 and their part in the control of the pest have been summarized by H. S. Smith 

 in the "Journal of Economic Entomology," August 1919, as follows: — 



1. The reproductive capacity of available entomophagous insects must be 

 much higher than that of the host. This proposition is self-evident, and needs 

 no amplification. 



2. A complete sequence of parasites affecting the egg, larva and pupa of 

 the pest. The importance of this factor was fully shown in the campaign against 

 the gypsy moth. 



3. The entomophagous forms must be capable of being reared or obtained 

 in sufficient quantities to overcome the pest in the field. This factor is one of 

 the most difficult to bring into operation. Lady-birds are readily reared and 

 collected. 



4. The cost of producing natural enemies must remain well within the 

 bounds of profitable crop production. 



5. Secondary parasites in the local fauna should limit as little as possible, 

 much less 'entirely prevent, the action of the primary parasites. This factor 

 is also one that is most difficult to control. 



6. Agricultural practices such as spraying and fumigation which affect 

 adversely the breeding of natural enemies should be prevented. It is probable 

 that the extermination of the imported Chinese lady-bird in southern orchards 

 was due mainly to spraying operations with lime-sulphur carried on as a practice. 



7. The relative ability of the pest and its enemies to spread is an important 

 factor. If both be good fliers, the power of spreading is increased but the likeli- 

 hood of extermination of the pest is lessened. 



The citrus mealy-bug has been controlled in Southern California by the 

 Australian lady-bird Cryptolaenus mon-trouzieri which was reared in large numbers 

 at the State Insectary, and collected in orchards where they had become abundant 

 late in the season. In this instance, as in that of the cottony-cushion scale, 

 the lady-bird is an active insect while the scale insect is fixed to the plant. 

 Moreover, the lady-bird has more generations than the scale insect, and is 

 practically free from parasites. 



Dr. P. Marchal calls the gipsy and brown-tail experiments in America "a 

 gigantic biological analysis and synthesis hearing upon all the elements which 

 constitute the harmonic groupings of plant-feeding insects, their predators, para- 

 sites and hyperparasites ; the taking apart piece by piece of the whole system, 

 and its partial reconstruction in a new environment, forcing it to give the greatest 

 possible stress to the elements most favorable to man, and reducing to the minimum 

 those which oppose their action." 



2. Insects in Relation to Other Animals. 



Nature has evolved not as independent but often as closely dependent 

 organisms. The well-being of one set is frequently related in many ways to 

 other sets, and no creature can be said to live unto itself. Insects and plants, for 

 example, have been for long ages mutually adapting themselves one to the other, 

 the plant to the insect and the insect to the plant. We all know how birds keep 

 down insects and many rodents; in fact, an approximate equilibrium has been 



