AGRCULTURE\' b LATIOPT
THE TOXICITY OF THE NATURAL BITTER SUBSTANCES, QUASSIN, TENULIN,
HELENALIN, AND PICROTOXIN, AND SOME OF THEIR DERIVATIVES
TO CERTAIN INSECTS
By E. R. McGovran and E. L. Mayer, Division of Control Investigations,
and E. P. Clark, Division of Insecticide Investigations
A comparison was made of the insecticidal action of pyrethrum extract
or nicotine and the natural bitter substances, quassin (a natural mixture
of quassin and neoquassin), picrotoxin, helenalin, tenulin, and certain of
their derivatives, namely, isoquassin, isotenulin, and bromopicrotoxinin.
The information presented is of interest, for, while the chemical nature
of these materials is unknown, they have enough chemical similarity to
warrant the assumption that they have some common structural characteristics.
The insecticidal properties of the quassins are of special interest, since
all previous reports as to the effectiveness of quassia wood in this respect
were based on results obtained with extracts of unknown composition. The
crystalline quassins, however, are presumed to be the physiologically active
constituents of the wood.
Quassia wood extracts have been found effective against certain aphids
and not effective against other species (2) .1/ Also these extracts have been
found effective against certain sawflies but not other insects (3 and 4).
The entomological publications on quassia up to 1937 have been reviewed (1).
The insects used in the tests reported in this circular were the green
peach aphid, the Mexican bean beetle, the American cockroach, and the house-
fly. The procedures used in testing the materials are given in connection
with the various experiments.
Green d.--Nymphs and adults of the green peach aphid (My_z-
erice (Sulz.)) feeding on turnip leaves were sprayed in the laboratory
in a spray tower 2 feet in diameter and 4 feet high. Preliminary tests had
shown that when approximately 50 ml. of spray liquid were discharged in the
1/ The numbers in parenthesis refer to the litertature cited (p. 5).
spray tower one surface of the turnip leaves appeared uniformly covered with
large droplets of spray that did not coalesce and, drain to the edges of the
leaves. As most of the aphids were on the lower surface of the leaves, the
few that were found on the upper surface were removed, and the spray was
applied only to the lower surface. This procedure was therefore used. The
exact quantities used in each series of tests are given in table 1. The
sprays were prepared by adding 20 ml. of the acetone solution of the material
to 80 ml. of water that contained 0.1 percent of gum arabic.
As shown in table 1, so far as the green peach aphid is concerned
the materials under consideration have practically no aphidicidal action.
Table l.--Mortality of green peach aphids sprayed with aqueous
solutions or suspensions. Nicotine was used as the standard of
Material Number of Mortality
Series Concentration Quantity of aphids in
No. Name of solution applied tests used 24 hours
Percent Ml. Percent
1 Nicotine 0.1 50 5 260 51
2 Isoquassin 1.0 49 2 74 0
3 Quassin 1.0 49 5 515 4
4 Isotenulin 1.0 49 3 222 1
5 Tenulin 1.0 49 3 159 0.6
6 Helenalin 1.0 49 3 237 1
7 Picrotoxin 1.0 48 3 192 0.6
8 Bromopicrotoxinin 1.0 51 3 240 0
9 Check (acetone 20%,
gum arabic 0.1%) -- 50 5 480 0.2
10 Check (water) -- 52 1 57 0
Mexican bean beetle.--Five-percent acetone solutions of the various
substances were applied by means of a micropipette to the ventral surface
of adults and larvae of the Mexican bean beetle (jlacbhna varivestis
Muis.).2/ Five lambda (0.005 milliliter) were applied to each adult and
fourth instar and 2.5 lambda to each second instar. The number of dead
insects was determined after 3 days. Each mortality figure is the average
of 3 tests of 10 insects each. The second instars gave a better comparison
2/ The writers express thanks to G. L. Phillips for assisting in
making these tests.
of the toxicity of the materials used than the adults or fourth instars
(table 2), but these larvae were not sufficiently resistant to nicotine for
the data on it to be directly compared with the data on the other materials.
All the tests indicated that the experimental materials were much less toxic
than nicotine when used at the same dosage.
Table 2.--Results obtained by applying 5-percent solutions of test
materials to Mexican bean beetle larvae and adults. Nicotine was
used as the standard.
Mortaly in days
Series Fourth-instar Second-instar
No. Material Adults larvae larvae
Percent Percent Percent
1 Nicotine 67 77 100
2 Picrotoxin 9 13 80
3 Quassin 9 13 80
4 Isoquassin 18 13 63
5 Helenalin 34 17 67
6 Tenulin 9 3 50
7 Isotenulin 3 0 57
8 Check (acetone) 0 0 13
Cockroaches.--Adult American cockroaches (PEripRaneta americana (L.))
were treated individually at the rate of 5 lambda of 5-percent acetone
solution of the material per gram of insect. The solution was applied by
means of a micropipette to the dorsal surface of the integument of the
thorax and abdomen. After treatment the roaches were placed in cages with
food and water, and the knockdown and mortality were observed for 4 days.
The results given in table 3 are the average of three tests of 5 female
roaches in each test.
As shown in table 3, quassin and tenulin caused neither knockdown nor
mortality. Picrotoxin showed some toxicity to the roaches and caused the
highest mortality of the materials of unknown toxicity, but it was con-
siderably lower than that for pyrethrins used at a greater dilution The
male roaches were less resistant than the females.
Table 3.--Knockdown and mortality of American cockroaches treated
individually. Pyrethrum extract was used as the standard.
Material Knockdown Mortality
Series in acetone sclution in 1 day_ in a ds
No. Name Concentration Male Female Male Female
Percent Percent Percent Percent Percent
1 Pyrethrins 0.1 93 60 93 66
2 Tenulin 5.0 0 0 0 0
3 Isotenulin 2.5 7 0 7 7
4 Helenalin 5.0 0 0 7 0
5 Picrotoxin 5.0 14 7 40 7
6 Quassin 5.0 0 0 0 0
Houseflies.--Reared adult houseflies3/ (Musca domestic L.) that were
3 to 5 day; old were treated individually with 2 lambda of acetone solutions
of the materials listed in table 4. The liquids were applied to the ventral
surface of the abdomen by means of a micropipette after the flies were
rendered motionless by chilling them for about 3 1/2 minutes. The untreated
check flies (series 10. table 4) were also chilled. After treatment the
flies were placed in 6-inch petri dishes with screen covers and supplied
with sugar and water. The dead flies were counted for 4 days and are
recorded (table 4) under percent of mortality. The figures are the average
of 5 tests of 10 flies each.
The results show that none of the materials under consideration showed
appreciable toxicity to the flies under the conditions of the experiment.
3/ The authors thank W. N. Sullivan and J. H. Fales for supplying
the houseflies used in these experiments.
Table 4.--Results obtained by treating adult houseflies individually
with 2 lambda of acetone solutions of the materials indicated.
Pyrethrum extract was used as the standard of comparison.
Series Material Mortality
No. Name Concentration after 4 days
1* Pyrethrins 0.2 40
2 Pyrethrins 0.4 77
3 Quassin 5.0 0
4 Isoquassin 5.0 4
5 Tenulin 5.0 2
6 Isotenulin 2.5 2
7 Helenalin 5.0 10
8 Picrotoxin 5.0 6
9 Check (acetone) -- 2
10 Check (untreated) 2
*These pyrethrin solutions were made by dissolving a pyrethrum oleo-
resin, which contained 12.7 percent of pyrethrin I and 12.6 percent of
pyrethrin II, in acetone.
Laboratory insecticidal tests of quassin, isoquassin, picrotoxin,
helenalin, tenulin, and isotenulin on the green peach aphid on turnip, the
housefly, and the Mexican bean beetle showed that these materials had little
if any toxicity to these insects. Second instars of the Mexican bean beetle
were susceptible to these materials, but adults and fourth instars were
much more resistant. These same materials, with the exception of isoquassin,
which was not tested, were relatively nontoxic to the American cockroach.
Bromopicrotoxinin was nontoxic to the green peach aphid, While the insects
used in these tests were resistant to quassin, a survey of the literature
shows that quassia wood extract is effective against certain sawflies and
aphids which were not included in these tests.
(1) Busbey, R. L. 1939. A bibliography of quassia. U. S. Dept. Agr.,
Bur. Ent. and Pl. Quar. E-483, 56 pp. (Mimeographed.)
(2) McIndoo, N. E., and Sievers, A. F. 1917. Quassia extract,as a contact
insecticide. Jour. Agr. Res. 10 (10): 497-531.
(3) Petherbridge, F. R., and Thomas, I. 1937. Spraying for plum sawfly;
with notes on red spider and thrips. Jour. Min. Agr. (Great Britain)
44 (9): 858-865.
(4) Thiem, H. 1937. Successful combat of the plum sawfly with quassia.
Kranke Pflanze 14: 59-65.
NITED STATES DEPARTMENT OF AGRICULTURE
OFFICE OF THE SECRETARY
WASHINGTON, D. C.
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