PART IV. 
There remains the utilisation of the indigenous enemies of a pest, 
which presumably controlled it effectively before the time when, with 
the growing of a crop on an extensive scale, it had the opportunity to 
become a pest; and which may well be hoped to control it again, 
provided that the complicated inter-relations of these beneficial insects 
with their enemies, and of these latter with their parasites and 
predators to a third and even fourth degree, can be satisfactorily 
understood. 
The problem of the Common Coffee Mealy-bug in this country 
affords a good example of what may be possible in this direction. 
Tae Common Corree MEaLy-Bua. 
At least five species of true Mealy-bugs of the genus Pseudococcus 
occur on coffee in this Colony. Only one of these, the most abundant 
and the most dangerous, will be dealt with here. 
This is a species which has been identified as Pseudococcus citri, 
Risso, a species which is almost cosmopolitan, and has been recorded 
from coffee in other countries, but is more usually known as a pest of 
citrus. In this country not only is it never found on citrus trees, even 
when these are growing actually among infested coffee, but it is 
unable to survive when artificially transferred to citrus. It would 
therefore appear that even if it is anatomically indistinguishable from 
the true P. citri, it is at least a distinct biological species. At first 
sight this might seem to be a point of scientific interest only, but in 
reality it is of the utmost practical importance. For instance it is 
now just as necessary to guard against the introduction into the Colony 
of the citrus-feeding form of P. citri, as if no form of this species 
were already present. Again it is more than likely—though one 
cannot be certain on this point—that it would be useless to attempt 
to introduce any internal parasite of the citrus-feeding form in the 
hope that it would control the coffee-feeding race. It may be 
mentioned in this connection that a species of Pseudococcus very 
similar to the coffee-feeding one, has been found in the Ruiru district 
of Kenya living on a wild shrub; this mealy-bug is very heavily 
attacked by a parasite which can not be induced to parasitise the coffee 
mealy-bug. 
The Common Coffee Mealy-bug has been known to exist in the 
Colony since 1909 (1, p. 98)+ and is probably indigenous. It breeds on 
a number of other plants, both cultivated and wild, in addition to 
coffee; but it is a matter of some difficulty to make a complete list of 
its host-plants, as not only must miscroscopical preparations be made 
of a mealy-bug found living on some other plant, to find out if it is the 
same systematic species, but it is also’ necessary to determine by 
experiments whether or not it is capable of living on coffee, to 
ascertain whether it is the same biological species. 
It is only within the last three years or so that the species has 
spread to an alarming extent, and it is now to be found widely 
distributed over the coffee growing area east of Nairobi as far as the 
Kakusi hills; being most prevalent in the neighbourhoods of Ruiru 
and Thika. The altitude of infected areas lies as a rule between 5,000 
and 5,700 feet; it has however been found on one farm, the altitude 
of which was as much as 6,500 feet. It appears useless to speculate 
t See list of references on page 194. 
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