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The Wetting of Insect Cuticle*

Published online by Cambridge University Press:  10 July 2009

Rajindar Pal
Rajindar Pal
Affiliation:
Department of Entomology, London School of Hygiene and Tropical Medicine.
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Extract

The best method of assessing the wetting powers of liquids is to measure the contact angle formed with a particular solid surface. In order to study the wetting of insects by spray liquids, it was necessary to measure, as rapidly as possible, the contact angles of very small droplets on restricted surfaces (such as portions of the insects). The apparatus used projected a greatly enlarged image of the drop, the outline of which could be traced very quickly and used for subsequent calculations.

Under practical conditions, spray droplets impact on insects with some relative velocity either due to drift of the spray particles or to flight movements of the insect.Measurements were therefore made of the contact angles formed by droplets of water of known size falling on to insects (or to a beeswax surface) at a known speed. It was found that with rather large drops (5 mm. diameter) the contact angles formed were somewhat lower than the normal advancing contact angle. With small droplets (0·1-0·5 mm. diameter) there was no difference. Biological tests were made with 30 species of insects, differing widely in the nature of their integument and habitat. The resistance to wetting was found to vary greatly, not only from species to species but also on different parts of the body of a single insect. In general, most of the insects were readily wetted by oils and unwetted by water. Insects withhard cuticular lipoids, such as Tenebrio, were more hydrophobic than the Blattidswith greasy cuticular waxes. A few species were both lipophilic and hydrophilic (larvae of Mamestra, Polia, Musca). Apart from the chemical nature of the cuticle, irregularities and the presence or absence of hairs were important. Increased roughnesslowers the contact angles of liquids with good wetting powers, but has the opposite effect with liquids with poor wetting powers. Measurements were made of thecontact angles formed on individual hairs of Arctia caja larvae by spray droplets. The contact angles formed on these hairs by plain liquids were strongly correlated with the angles formed on smooth Tenebrio cuticle or on an artificial beeswax surface; but there was only very rough correlation between the three sets of data when aqueous solutions of wetting agents were tested.

The test liquids included saturated and unsaturated hydrocarbons, mineral oils with varying aromatic contents, organic esters, alcohols and aqueous solutions. Among the hydrocarbons, members of the aliphatic series wet insect cuticle more readily than the aromatic group. The aromatic contents of the oils did not, however, affect their very high wetting powers.

The effects of adding surface active agents to aqueous sprays were investigated. Of the samples tested, the most effective wetting agents were those with neutral un-ionised molecules.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 41 , Issue 1 , May 1950 , pp. 121 - 139
Copyright
Copyright © Cambridge University Press 1950

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References

Adam, N. K. (1941). The physics and chemistry of surfaces. 3rd edn. Oxford Univ. Pr.Google Scholar
Bartell, F. E. (1941). Methods for measurement of contact angle.—Chem. & Industry, 160, p. 475.Google Scholar
Beament, J. W. L. (1945). The cuticular lipoids of insects.—J. exp. Biol., 21, pp. 115–131.CrossRefGoogle Scholar
Ben-Amotz, Y. & Hoskins, W. M. (1937). Factors concerned in the deposit of sprays. III. Effects of wetting and emulsifying powers of spreaders.—J. econ. Ent., 30, pp. 879–886.CrossRefGoogle Scholar
Brown, G. T. & Hoskins, W. M. (1939). Factors concerned in the deposit of sprays. V. The effects of pH upon the deposit of the oil and water phases of oil emulsions.—J. econ. Ent., 32, pp. 57–61.CrossRefGoogle Scholar
Cassic, A. B. D. & Baxter, S. (1945). Large contact angles of plant and animal surfaces.—Nature, Lond., 155, pp. 21–22.CrossRefGoogle Scholar
David, W. A. L. (1946 a). The quantity and distribution of spray collected by insects flying through insecticidal mists.—Ann. appl. Biol., 33, pp. 133–141.CrossRefGoogle ScholarPubMed
David, W. A. L.. (1946 b). Factors influencing the interaction of insecticidal mists and flying insects. Part II. The production and behaviour of kerosene base insecticidal spray mists and their relation to flying insects.—BuIl. ent. Res., 37, pp. 1–28.CrossRefGoogle Scholar
Du Noüy, P. L. (1926). Surface equilibra of biological and organic colloids. New York, Chem. Catalog Co.Google Scholar
Ebeling, W. (1939). The rôle of surface tension and contact angle in the performance of spray liquids.—Hilgardia, 12, pp. 665–698.CrossRefGoogle Scholar
English, L. L. (1928). Some properties of oil emulsions influencing insecticidal efficiency.—Bull. Ill. nat. Hist. Surv., 17, pp. 233–259.Google Scholar
Evans, A. C. & Martin, H. (1935). The incorporation of direct with protective insecticides and fungicides. I. The laboratory evaluation of water-soluble wetting agents as constituents of combined washes.—J. Pomol. hort. Sci., 13, pp. 261–292.Google Scholar
Fogg, G. E. (1947). Quantitative studies on the wetting of leaves by water.—Proc. roy. Soc., (B) 134, pp. 503–522.Google ScholarPubMed
Hamilton, C. C. (1930). The relation of the surface tension of some spray materials to wetting and the quantity of lead arsenate deposited.—J. econ. Ent., 23, pp. 238–251.CrossRefGoogle Scholar
Hensill, G. S. & Hoskins, W. M. (1935). Factors concerned in the deposit of sprays. I. The effect of different concentrations of wetting agents.—J. econ. Ent., 28, pp. 942–950.CrossRefGoogle Scholar
Hoskins, W. M. (1940). Recent contributions of insect physiology to insect toxicology and control.—Hilgardia, 13, pp. 307–386.CrossRefGoogle Scholar
Hoskins, W. M. & Wampler, E. L. (1936). Factors concerned in the deposit of sprays. II. Effect of electrostatic charge upon the deposit of lead arsenate.—J. econ. Ent., 29, pp. 134–143.CrossRefGoogle Scholar
Lane, W. R. (1937). A microburette for producing small liquid drops of known size.—J. Sci. Instrum., 24, pp. 98–101.CrossRefGoogle Scholar
Mack, G. L. (1936). The determination of contact angles from measurements of dimension of small bubbles and drops.—J. phys. Chem., 40, pp. 159–167, 169–175.CrossRefGoogle Scholar
O'kane, W. C., Westgate, W. A., Glover, L. C. & Lowry, P. R. (1930). Studies of contact insecticides. I. Surface tension, surface activity and wetting ability as factors in the performance of contact insecticides.—Tech. Bull. N.H. agric. exp. Sta., no. 39, 42 pp.Google Scholar
O'kane, W. C., Westgate, W. A. & Glover, L. C. (1932). Studies of contact insecticides. V. The performance of certain contact agents on various insects.—Tech. Bull. N.H. Agric. exp. Sta., no. 51, 20 pp.Google Scholar
Schmidt, W. (1909). Eine unmittelbare Bestimmung der Fallgeschwindigkeit von Regentropfen.—Met. Z., 26, p. 183.Google Scholar
Stellwaag, F. (1924). Die Benetzungafähigkeit flüssiger Pflanzenschutzmittel und ihre direkte Messbarkeit nach einem neuen Verfahren.—Z. angew. Ent., 10, pp. 163–176.CrossRefGoogle Scholar
Thorpe, W. H. & Crisp, D. J. (1947). Studies on plastron respiration. I. The biology of Aphelocheirus (Hemiptera, Aphelocheiridae (Naucoridae) and the mechanism of plastron retention.—J. exp. Biol., 24, pp. 227–269.CrossRefGoogle ScholarPubMed
Wampler, E. L. & Hoskins, W. M. (1939). Factors concerned in the deposit of sprays. VI. The role of electrical charges produced during spraying.— J. econ. Ent., 32, pp. 61–69.CrossRefGoogle Scholar
Wenzel, R. N. (1936). Resistance of solid surfaces to wetting by water.—Industr. Engng Chem., 28, pp. 988–994.CrossRefGoogle Scholar
Wigglesworth, V. B. (1945). Transpiration through the cuticle of insects.—J. exp. Biol., 21, pp. 97–114.CrossRefGoogle Scholar
Wigglesworth, V. B. (1947). The epicuticle in an insect, Rhodnius prolixus (Hemiptera).—Proc. roy. Soc., (B) 134, pp. 163–181.Google Scholar
Wilcoxon, F. & Hartzell, A. (1931). Some factors affecting the efficiency of contact insecticides. I. Surface forces as related to wetting and tracheal penetration.—Contr. Boyce Thompson Inst., 3, pp. 1–12.Google Scholar