Agricultural Science Digest
Vol. 12 Jan. - Feb., 1970	PURDUE UNIVERSITY

CEREAL LEAF BEETLE DAMAGE STUDIED

The cereal leaf beetle, a relatively new
crop pest in the state, has been the target of
continuing research at Purdue University
since it was first reported in 1963.

The first crop losses, based on data from
field research plots, were reported the fol	lowing year and researchers initiated an in-
tensive study program to determine the im-
pact of the beetle on oats, wheat and corn.

Using both laboratory and field research
methods, Purdue and Ohio entomologists and
agronomists began work to learn the relative
damage to various crops by the four stages of
beetle development to pupation. Research
reported in this paper was conducted on Newton
oats in 1966 and Jaycee oats in 1968.
The beetle population levels were controlled in field plots by applying various
rates of malathion sprays. Population counts
were made weekly and damage estimates
were made by calculating the percentage of
the leaf surface consumed by the beetle.

The researchers concluded that a cereal
leaf beetle larva completing development to
pupation will normally consume 20 percent
of the leaf surface on one stem, regardless
of the vigor of the plant. They also determined
that the loss in grain yield will be dependent
	upon the condition of the crop, its vigor, the
amount of available soil nutrients and moisture,
and the availability of the crop to recover.

All other factors being equal, they pre-
dicted a loss of two to four bushels of grain
per acre for each increase of one larva per
average stem infestation. Further, the
earlier the infestation occurs after the
emergence of the seedling crop, the greater
the rate of loss per larva per stem. Highest
losses occurred with the oats in the 2 to
3-inch seedling stage. Least losses occurred
where the crop achieved 6 inches of vigor-
ous growth before infestation.

Journal paper 3646, M. Curtis Wilson,
R. E. Treece, R. E. Shade, K. M. Day,
and R. K. Stivers.

PARASITE ATTACKS ALFALFA WEEVIL
Unexpected findings, the sometimes
happy results of a research project, may
have given Purdue entomologists another
non-pesticidal weapon in the battle against
alfalfa weevils.

In 1967 a joint Illinois--Indiana alfalfa
weevil research program was initiated in
Knox County, Indiana, where a large alfalfa
acreage offered an opportunity to attempt
massive control programs and to study the
effects on weevil populations.

At the heart of the area is the Charles
Schenk and Sons Farms, Inc., site of nearly
2, 000 acres of alfalfa each year. A con-
tinuing intensive weevil control program
there includes several insecticide sprays
each year.

In 1968 the researchers found a large
buildup of Bathyplectes curculionis, a natural
enemy of the weevil. A tiny beneficial wasp
brought from the old world to help control
the pest, the parasite lays eggs in larvae of
the weevil. The eggs hatch into larvae
which feed on and eventually kill the weevil.,
The buildup of this beneficial natural enemy
gave the researchers an opportunity to
assess its potential in an integrated control
program.

To determine the effect of the insecti-
cides on the weevil and the parasite, the
researchers marked off endo and exo
circles. The endo, or inner, circle included
about 28 square miles with the Schenk Farms
at the center. The outer circle included an

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