6 CALIFORNIA STATE HORTICULTURAL COMMISSION. 



work in or on the body of their host. These latter are often microscopic, 

 or very nearly microscopic, in size, but are among the most effective of 

 our insect friends. 



Usually each predaceous or parasitic insect attacks but one kind of 

 insect ; each has its own particular form of food and will touch no other. 

 The Vedalia, for instance, lives wholly upon the cottony cushion scale, 

 and if it can not get this, it will starve before it will touch any other 

 form of food; so that, in searching for the enemies of onr destructive 

 insects, it is necessary to find just the right one. 



It is a fact well known to all entomologists, that in their native homes, 

 while insects are sometimes very troublesome, and in some sections exist 

 in unusual numbers, they never become the serious pests that they do 

 when they are removed to a new country where their checks do not exist. 

 Usually in their native homes they are rather rare than otherwise. So 

 when it is known that any pest is especially severe in any section, as, for 

 instance, the San Jose scale (Aspidiotus perniciosus) over a great part 

 of the Eastern States, it is very certain that it has been introduced there, 

 and in order to find its check, we must find its native home, where it is 

 scarce, and then we must find what agency is keeping it down. Some- 

 times our native parasites will adapt themselves to the introduced 

 species, as has been the case in California with the San Jose scale. This 

 pest was as great a terror to our growers some twenty years ago as it now 

 is over a great part of the Eastern States ; but one of our native parasites, 

 the Aphelinus fuscipennis, adapted its taste to it, and finding in the San 

 Jose scale a suitable food supply, it increased with almost unprecedented 

 rapidity until it overtook the scale, and to-day this scale is no longer a 

 pest in the California orchards. It is true that it occasionally makes its 

 appearance in remote sections, but never to any dangerous extent, and 

 the little parasite soon overtakes it and reduces it below the danger line. 

 So little regard is paid to the San Jose scale in California now, that we 

 never recommend any action against it. Spraying is still carried on, 

 but this is more for the purpose of keeping the trees clean and healthy 

 'than for the purpose of getting rid of the San Jose scale. Before this 

 parasite did such effective work, California orchardists were having very 

 much the same experience that their Eastern brethren are having now, 

 and trees by thousands were dug out and destroyed in order to get rid 

 of the scale. It is to be hoped that the days of this terrible pest in the 

 Eastern orchards are numbered, for it has been discovered that the same 

 parasite which has freed the California orchards is now at work there, 

 and in a report made by Prof. W. G. Johnson, when entomologist of 

 Maryland, he says: 



Since we assumed charge of the State work in Maryland, we have collected the S:m 

 JosA 'scale on various food plants and inclosed infested twigs, about four inches in 

 length, in glass cylinder tubes, open at both ends ; the ends were closed with cotton, and 

 if any parasites existed upon the scale, they were easily detected and mounted for 



