58 NATURAL CONTROL OF WHITE FLIES IX FLORIDA. 
RELATION BETWEEN ABUNDANCE OF WHITE FLIES AXD RESULTS IN 
SPREADING FUNGOUS INFECTIONS. 
While theoretically introduction of fungi should begin as soon as 
the presence of the white fly is discovered in a grove, the authors 
have met with such poor success with all attempts at such introduc- 
tions that they have recommended the waiting until the white fly 
becomes abundant enough to cause a very slight blackening of foliage. 
Attempted earlier introductions have proved practical failures. It 
is contrary to natural laws governing the relation between host and 
parasite to expect to keep the fungus abreast of the fly all the time, 
and all experiments and observations during the past three years have 
failed to bring out a single instance where the fungus has spread, 
art ific ally or naturally, in a newly infested grove soon enough or fast 
enough to prevent the blackening of foliage. One can reasonably 
hope for success in holding down the fly in slightly infested groves 
only by careful attention to the direct remedial measures. 
SUSCEPTIBHITT OF DIFFERENT STAGES OF HOST INSECTS. 
Experiments have shown that the presence of no one instar of 
either species of white fly is essential to successful infections, or that 
any one larval stage is more susceptible to fungous attack than 
another, or than the pupal stage. Considering the large number of 
larvse that hatch and the high rate of mortality that greatly reduces 
the number of forms in each successive instar, it is only natural that 
such leaves sprayed with spore solutions when the larvre are very 
young should develop a large percentage of pustules on young larvse. 
It has been found equally true that a much larger percentage of 
pustules develops on advanced larvse and pupse when introductions 
are made when the fly is largely in these later stages. A count of 40 
leaves of various ages, picked promiscuously and with the citrus 
white fly in all stages, gave the percentages of red and yellow Ascher- 
sonia pustules developed on the first, second, and third larval, and 
on the pupal stage as 33, 32.1, 22.2, and 12.7, respectively. Another 
count following introduction of the fungus in experimental work gave 
in percentages of the total number of pustules developed: Pupal stage 
36.5 per cent, third larval stage 34.5 per cent, and first and second 
larval stages 29 per cent. Examination showed that the various 
stages of fly were present in about this proportion at the time of the 
application of the fungous spores. 
COST OF IXTRODUCIXG AND SPREADING PARASITIC FUNGI. 
The very low cost of introducing fungi into white-fly infested groves 
has influenced many to resort to this method of control, hoping to 
get much for little. Men who have taken up the matter in a commer- 
cial way furnish the supply of fungus and spray trees with water 
