United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
FIELD-PLOT TESTS OF INSECTICIDES AGAINST THE EGYPTIAN
ALFALFA WEEVIL ON ALFALFA IN SOUTHERN ARIZONA, 1950
By E. E. Russell-/ and 0. L. Barnes
Division of Cereal and Forage Insect Investigations-
In 1950 heavy infestations of the Egyptian alfalfa weevil (Hypera
brunneipennis (Boh.)), in alfalfa near Tempe, Ariz., were treated experi-
mentally with DDT, methoxychlor, toxaphene, chlordane, aldrin, lindane,
and benzene hexachloride. This species was first observed in Arizona in
1939 by Wehrle (2) and later studied and described by McDuffie (1).
Sprays were applied from March 2 to 10 against the larvae and over-
wintering adults with 3-gallon hand compression sprayers at the rate of
10 gallons per acre on 1/40-acre plots of first-crop alfalfa 10 to 14 inches
high. They were made by diluting the required quantities of emulsion
concentrates with water.
The DDT concentrate was a commercial product containing 34.3 per-
cent (3 pounds per gallon) of technical DDT, but information on the other
ingredients was not obtained.
The methoxychlor concentrate, also a commercial product, contained
25 percent (2 pounds per gallon) of technical methoxychlor, 72 percent of
petroleum hydrocarbon, and 3 percent of inert ingredients.
The toxaphene and chlordane concentrates were prepared at the lab-
oratory by adding 4 pounds of technical toxaphene or chlordane and 100 ml.
of Igepal CTA Extra High Concentration emulsifierr) to enough diesel oil
or kerosene to make 1 gallon of concentrate.
The aldrin concentrate was an experimental formulation prepared by
the manufacturer. It contained 45 percent (4 pounds per gallon) of tech-
nical aldrin, 10 percent of Atlox 1045-A emulsifierr), and 45 percent of
equal parts of kerosene and xylene.
The lindane concentrate was a commercial product containing 20 per-
cent (1.6 pounds per gallon) of the gamma isomer of benzene hexachloride
in a light-oil solvent provided with an emulsifying agent.
1/ Retired August 31, 1950.
2/ N. J. Nerney assisted with the insecticide applications.
Dusts were applied from March 24 to April 3 against the larvae and
new-generation adults with a multiple-nozzle power duster at the rate of
10 or 20 pounds per acre, depending on the concentration, on 1/4-acre
plots of second-crop alfalfa 10 to 20 inches high. The benzene hexa-
chloride dusts were made up at the laboratory from a 50-percent wettable
powder containing 6 percent of the gamma isomer. All the other dusts
were ready mixed. They were diluted with pyrophyllite and each con-
tained 5 percent of celite. The lindane dust containing 1 percent of the
gamma isomer of benzene hexachloride was obtained by mixing 4 pounds
of a 25-percent wettable powder in 96 pounds of inert diluents.
During the test period the maximum daily temperatures ranged from
63 to 95 and the minimum from 37 to 57 F., and the total rainfall
was only 0.2 inch.
Populations of larvae and adults of the weevil were sampled with a
15-inch insect net before treatment and at 2- to 6-day intervals afterward.
Control was based on the number of specimens per net stroke in collections
on treated plots as compared with the number on untreated plots in the
Data on the treatments and their effectiveness against larvae and
adults are summarized in table 1. The emulsion sprays reduced larval
populations 98 to 99 percent in 2 days and 99 to 100 percent in 4 and 6
days. Three days after treatment the dusts were as effective as the
sprays. However, after 5 days DDT at 0.5 and 1 pound and methoxychlor
at 1 pound per acre were slightly less effective than at the higher dosages
tested. The overwintering adults were highly susceptible to the sprays.
All sprays except those containing lindane gave 98 to 100 percent reduc-
tion in 2 and 4 days, and lindane gave more than 99 percent in 6 days.
The dusts were much less effective against newly emerged adults of the
1950 generation than were the sprays containing the same insecticides
against the overwintering adults of the 1949 generation.
The difference in effectiveness of the insecticides against the over-
wintering and the new-generation adults probably was not due to the form
in which the materials were applied, because in cage tests conducted from
March 31 to April 13 dusts used at dosages similar to those in the field
tests gave 94 to 100 percent kill of new-generation adults in 3 days.
Furthermore, it has already been noted that dusts and sprays were about
equally effective against weevil larvae. Most of the overwintering adults
presumably were on the plants and were hit by the sprays, whereas many
of the new-generation adults did not emerge until after treatment, by
which time the residues had lost much of their toxicity. On untreated
plots populations of overwintering adults remained fairly stable or
decreased after treatment, whereas those of spring-emerging adults
increased 100 to 600 percent within 3 to 5 days after the time of treat-
ment. It was also noted that reductions of new-generation adults were
invariably greater 3 days after the application than 5 days thereafter.
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UNIVERSTY OF FLORIDA
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