114 
PACIFIC SCIENCE, Vol, III, April, 1949 
Baermann method extracted 209 males, females, 
and larvae per gram. To retain the soil while 
allowing small nematodes to crawl through, we 
have used a fine-textured grade of paper towel 
that retains its strength when wet. 
Soil from under pineapple plants in old 
fields frequently contains 100 or more paraty- 
lenchs per gram. Two samples from separate 
fields have yielded over 900 per gram. These 
nematodes are particularly numerous in imme- 
diate association with roots. Four composite 
samples of unwashed roots from each of two 
fields were held in extraction funnels for 48 
hours, then the heaviest nematode population 
from each field was selected for closer study. 
The extracted roots were washed free of soil, 
blotted, weighed, and measured. From one sam- 
ple, paratylenchs were obtained at rates of 
23,800 per gram of root or 570 per centimeter 
of length. Soil from this source yielded 266 per 
gram. From the other field, paratylenchs num- 
bered 23,500 per gram of root or 600 per centi- 
meter of root length, and 258 per gram of soil. 
These and the remaining six samples contained 
much smaller numbers of other plant parasites 
in addition to predaceous species of Aphelen- 
choides and Dorylaimus (see Linford, 1937^- 
42-44, and Christie, 1939). 
Within fields, populations sometimes are 
highly variable, even from plant to plant, but 
if this nematode is pathogenic to pineapple its 
effects are overshadowed by other injurious fac- 
tors, for no apparent correlation exists between 
populations of paratylenchs and growth vigor 
of the plants. Very heavy populations are some- 
times found around the roots of strong plants. 
TOLERANCE TO ADVERSE CONDITIONS 
Extraction of numerous paratylenchs from 
dry, loose soil in September in a field that was 
almost ready for planting after having been 
plowed several times suggested that this nema- 
tode was tolerant to desiccation. Naturally in- 
fested soil selected for laboratory tests was of 
fine texture, with a wilting point in the vicinity 
of 27 per cent moisture. When first sampled, at 
30.7 per cent moisture, it contained numerous 
females, males, and larvae. After drying to 20 
per cent moisture in 5 days these were only 
slightly less abundant. At 16. 3 per cent moisture, 
males and larvae were more reduced in numbers 
than were the females. No living males were 
recovered at 10.0 per cent, the next drier sam- 
ple tested. A few larvae were recovered at 9.4 
per cent but not at 7.5 per cent. Females revived 
sparingly after the soil had dried to 7.5 per cent 
and 7.2 per cent but not to 6.3 per cent moisture. 
There is no assurance that drying was suffici- 
ently gradual in these tests to measure the max- 
imal degree of tolerance to desiccation. The data 
are adequate, however, to demonstrate that nat- 
ural desiccation in the field is not likely to 
eradicate this nematode, for it occurs in subsoil 
to a depth of 18 inches or more where drying 
is much less extreme than near the surface. 
Limited information on the sensitivity of P. 
minutus to soil fumigants has been obtained 
from experiments concerned chiefly with the 
root-knot and reniform nematodes. Roots of 
cowpea or tomato grown as indicator plants 
were washed rapidly from their pots and then 
held in dishes of shallow water 18 hours or 
longer before being examined for galls and egg 
masses. Microscopic examination of the sedi- 
ment in such dishes frequently detected suf- 
ficient paratylenchs for comparative scoring, al- 
though the method seriously underestimates 
populations of this species. 
Data collected in this way from laboratory 
fumigation tests have indicated P. minutus to 
be almost equal to Heterodera marioni in sensi- 
tivity to various samples of D-D mixture, chloro- 
picrin, and ethylene dibromide. It sometimes has 
appeared slightly more tolerant. In field tests, 
following injection of 200 pounds of D-D mix- 
ture per acre under mulch paper, this nematode, 
like other species, has not been recovered from 
soil samples taken before planting. After 2 years 
of pineapple growth, however, it has been found 
even where the soil had been fumigated with 
400 pounds per acre or, in one test, with 600 
