Experiment Station Record, Volume 92, January-June, 1945 Page: 239
xiii, 1010 p. ; 24 cm.View a full description of this book.
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1945] ECONOMIC ZOOLOGY-ENTOMOLOGY 239
investigation of the effect of dusts on the water relations of insects. Dusts were
found not to depend for their action on any chemical reactivity, some highly inert
substances such as diamond and carborundum proving very effective; a physical
process is therefore indicated. Dusts do not penetrate into the respiratory system,
and though large amounts are ingested they seem to have little harmful effect.
Effective dusts increased the evaporation rate of water from insects to the air, and
the relative killing powers of different dusts ran parallel with their capacities for
promoting evaporation. These results harmonize with the view that inert dusts
induce death of insects by desiccation.
II. The nature of effective dusts.-As to the conditions required for an inert
dust to become effective, particle size and intrinsic hardness proved to be important
though not the only factors in killing the granary weevil. For carborundum, particles
larger than 15jx were without action, probably because they failed to adhere to
the insects; the effectiveness increased as the size was reduced from 10tt to about
21t, where a maximum was reached. The action of a large number of substances
was tested by a simple method which eliminated complications from particle size
differences; results exhibited a correlation of efficacy with hardness. Iri general,
materials softer than calcite proved ineffective; their efficacy increased with hardness,
but the method of preparation was also important. Some dry-ground powders were
inferior to those wet-ground, a result apparently due to some kind of surface change
-possibly the formation of a Beilby polish layer. The action of some dusts was
also considerably altered by superficial chemical treatment. A theory is proposedbased
on an experiment with an artificial membrane system-to explain the mechanism
by which dusts promote evaporation of water from insects. It is suggested
that clean crystalline surfaces of effective dusts can absorb, or in some way penetrate,
the water-resistant epicuticle.
III. The effect of dusts on stored products pests other than Calandra granaria,The
inert dusts used in the preceding studies against the granary weevil were also
found effective in vitro against a variety of other insects-both larvae and adultsinfesting
stored products. Both the order and the magnitude pf effectiveness of
a series of dusts differed among the insect species, but the mechanism of action
appeared to be the same, viz, promotion of evaporation of moisture, leading to death
by desiccation. In contrast to the results with the'granary weevil, highly adsorbent
dusts like charcoal were much more effective on larvae than were mineral powders.
Dusts had a particularly striking action on the yellow mealworm, which was therefore
more fully investigated; dead mealworms when dusted failed to lose water
nearly as rapidly as live dusted ones.
The mechanism of action of a contact insecticide, D. N. RoY and S. M. GHOSH
(Bul. Ent. Res., 35 (1944), No. 2, pp. 161-170, illus. 3).-These studies indicated
that rapid penetration of an insecticide into the insect body cannot be effected through
the cuticle. When a mosquito has been sprayed with a mixture of pyrethrum extract
and oleic acid the deposition of fat globules around the tracheal trunks is a characteristic
feature, suggesting that rapid diffusion of the insecticide takes place through
the tracheal wall. Experiments on flies with their spiracles closed showed that the
absorption of pyrethrum-either in liquid or powdered states-is very slow, indicating
that pyrethrum normally enters the body through the spiracles.
Insecticide diluents: Solubility of arsenicals and copper fungicides as affected
by diluents in agricultural dusts, M. W. GooDWIN, S. L. HOPPERSTEAD, and K. J.
KADOW. (Del. Expt. Sta.). (Soap and Sanit. Chem., 20 (1944), No. 8, pp. 103,
105, 107, illus. 2).-Dust mixtures were prepared with and without calcium arsenate
using different diluents, each with red cuprous oxide, tribasic copper sulfate, and
copper oxychloride. A good correlation existed between pH and water-soluble Cu
with no excessive amounts liberated about pH 5.5. The presence of calcium arsenate
in the mixture complicated the results, but usually the lower the pH, the higher
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U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc5064/m1/252/: accessed May 4, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.