Mar. 1, 1925 
Distribution of the Alfalfa Weevil 
481 
One of the first successful control 
measures was based upon the maximum 
fatal temperature. In connection with a 
discussion of harrowing after removing 
the first crop Reeves (8 , p. 128) states: 
“ ... Under such circumstances the 
insects can be destroyed and the crop 
protected by taking advantage of the 
fact that a temperature of 120° F. is 
fatal to the insects. This temperature 
is best produced by covering the sur¬ 
face of the field with something ap¬ 
proaching a dust mulch, unshaded by 
clods and vegetation. On a bright, 
warm day such a surface is heated by 
the sun enough to kill all stages of the 
weevil, and the dust kills many of those 
which escape the heat.” 
The very high temperature obtained 
at the soil surface in direct sunlight has 
rarely been utilized to control insects. 
HUMIDITY 
In addition to those passages quoted 
above, in which reference is made to 
humidity in connection with tempera¬ 
ture, there are a few places in which 
humidity seems to be more important 
than temperature. 
Titus (12, p. 49) says: “During the 
period when they are going into hiber¬ 
nation they are quite susceptible to 
climatic conditions; even the passing 
of the sun behind a cloud will drive 
them to shelter, and a cold rain follow¬ 
ing a very hot day will so chill those that 
have not been able to get into proper 
shelter that many will not survive the 
night.” 
Indirect Influences of Climatic 
Factors 
The parasites of the alfalfa weevil 
are of two kinds—insect parasites and 
fungi. The parasitic insects which have 
proven of importance in the control of 
Phytonomus posticus have been secured 
from Italy, a region of nearly optimum 
conditions for the weevil. On the other 
hand, fungi have been of importance 
in the Old World near the distribu¬ 
tional limits. No information of value 
has been published regarding the cli¬ 
matic relations of insect parasites, but 
there are several statements concerning 
the fungi. 
There are two entomophagous fungi 
reported as attacking the weevil. One 
of these, Empusa sphaerosperma, is an 
important enemy of a closely related 
species, the clover leaf-weevil ( Hypera 
punctata ), in the eastern United States 
and has killed as high as 44 per cent of 
the mature larvae of Phytonomus posti¬ 
cus at Salt Lake City. (18, p. 41.) Web¬ 
ster reports a mortality of about one- 
fifth on June 13, 1911, at Salt Lake City. 
The meteorological records show that 
the spring of 1911 at that place was 
nearly normal (see table on p. 480), 
which proves that this fungus is capable 
of destroying large numbers of the 
weevils under average Utah conditions 
and may prove of great importance 
near the limits of the range, where the 
spring conditions are cooler and wetter. 
A second species (Sporotrichum globulif- 
erum) has been reported by Rockwood 
(10, p. 499) to be working on the adult 
beetles in Utah. Some of his conclu¬ 
sions are quoted below: 
“The entomogenous fungus Sporo¬ 
trichum globuliferum Speg. develops 
spontaneously as an infectious disease 
of the alfalfa weevil, Hypera variabilis 
(posticus), on the bench lands of the 
Salt Lake Valley in the early spring. 
Infection experiments show the weevil 
to be very susceptible to fungus infec¬ 
tion at this season, a complete mortality 
from the fungus being secured in breed¬ 
ing cages in usually two weeks time. 
The ground-frequenting habits of the 
alfalfa weevil at this season render it 
particularly liable to infection from 
contact with fungus-covered insects. 
“The new generation of weevils is 
less susceptible to the fungus during 
the periods of aestivation and hiberna¬ 
tion in the summer and fall. Moreover, 
favorable conditions for the growth and 
spread of the fungus are unlikely to 
occur in Utah at this time. 
“The period of greatest mortality 
from the fungous disease, coinciding 
as it does with a period of great poten¬ 
tial injury from the pest, namely, the 
oviposition period, makes the fungus 
worthy of record as a natural enemy of 
the alfalfa weevil.” 
Some further remarks by Rockwood 
(10, p. 493-494) on the relations of 
climate to the abundance of Sporo¬ 
trichum are relevant: “The fungus 
Sporotrichum globuliferum Speg. was 
first found on the alfalfa weevil near 
Salt Lake City, Utah, on March 14, 
1914. It was frequently met with and 
could easily be found on weevils and 
other insects under alfalfa plants from 
that time until May. This was a time 
of considerable precipitation and the 
ground in alfalfa fields was moist to 
wet most of the time. The time of 
greatest abundance of the fungus was 
April 21 to 29. At this time at least 
one weevil killed by the fungus could 
be found under almost every plant 
examined.In the early spring, 
the optimum conditions for the growth 
of the fungus are likely to be found in 
all the alfalfa fields on the East Bench 
or old Lake Bonneville regardless of the 
irrigation practice. 
