74 
Mr. Theodore Pergande, who has also visited Murope recently, tells 
him that he finds, so far as Germany and middle Europe are concerned, 
the same conditions, having found both scale insects and plant lice 
very scarce as compared with eastern America. 
In America our longer summers, or rather longer Indian summers, 
with our much greater preponderance of sunshine, accompanied, how- 
ever, with an adequate amount of moisture, seem to be the disposing 
cause which leads to the serious affliction of the many scale insects 
experienced with us. We have, however, climates which parallel those 
of Europe. For instance, in California, away from the coast, the hot 
dry summers of Italy and Spain are duplicated, and with similar results 
on scale pests. The writer drew attention to this condition of affairs 
in a paper published in the Yearbook of the Department of Agriculture 
for 1896, entitled “Insect control in California.” The paragraph in 
question is as follows: 
Other influences which have an important bearing on the relations of insects to 
fruits in California are the climatic conditions, particularly the summer heat and 
the long summer drought. Heat is a most important factor, and it has been repeat- 
edly demonstrated that where the temperature remains, as it often does, at 106° F., 
or above, for two or three days, at least two-thirds of the black scale are killed. 
As an illustration of this, it may be stated that during the summer of 1896, when 
the drought was unusually severe and the temperature correspondingly excessive, it 
was the experience at Riverside that at least 90 per cent of the black scale was 
destroyed by heat, including even eggs beneath the parent scales. The benefit from 
this source obtains in greater or less degree in the case of all the important scale 
insects of both citrus and deciduous trees, and is a means of protection which is 
rarely if ever experienced in cooler or moister climates; in fact, it does not hold in 
northern California, where the rainfall is greater and the summer temperature less 
severe. The destruction of scale insects from this cause may be facilitated by the 
system of pruning which opens up the tree by the removal of interior growth, and 
such pruning is practiced and recommended by many growers in southern California. 
When considered, however, in connection with the imported ladybird enemies 
of scale insects, which will be later discussed, the dry heat and pruning are both 
inimical. These introduced parasites need a certain amount of moisture for success- 
ful multiplication; hence their usefulness is most marked in the moister coast region, 
and advocates of reliance on parasites discourage pruning, since a dense interior of 
citrus and other trees furnishes the needed shade and moisture, and also protects 
from bird and other enemies. The need of such protection is illustrated about San 
Francisco and northward, where the imported ladybirds are less successful on account 
of lack of shelter afforded by deciduous trees, particularly in winter. 
An interesting confirmation of the views there expressed comes in a 
recent letter from one of the horticultural commissioners of Riverside 
County, Mr. Felix G. Havens. Writing under date of June 8, 1899, 
he says: 
If Mr. Marlatt is in the office, please tell him that the black scale which was so 
plentiful on the orange trees at the time he was here in November, 1896, and which 
we found at that time to be about 95 per cent dead, has since entirely disappeared. 
I believe the Riverside orange district, comprising about 14,000 acres, is the largest 
citrus district in the world, and the freest from insect pests as well. 
