J.
Med. Entomol.
Vol. 14, no. 5: 589 591
10 February 1978
REPELLENCY OF SELECTED ESTERS AND AMIDES OF FOUR ALICYCLIC ACIDS AGAINST THE STABLE FLY, STOMOXYS CALC/TRANS (DIPTERA: MUSCIDAE) I By C. E. Schreck2, T. P. McGovern3 and N. Smith2
Although the major portion of the interest m repellents for the stable fly, Stomoxys calcitrans (L.), has to do with protecting livestock (Bruce & Decker 1957, Blume et a1. 1971), this insect has, on occasion, been a notable pest of humans, usually when its livestock hosts are scarce or absent. For example, the large outbreaks of S. calcitralls that occur in some coastal areas of the southeastern United States can cause much discomfort and do serious damage to the tourist industry (King & Lenert 1936). Therefore, in recent years, investigations of repellents at the Insects Affecting Man Research Laboratory at Gainesville, Florida, have given greater emphasis to studies of biting flies in an attempt to find more effective repellents than deet (N,N-diethyl-m-toluamide) for use against such species as stable flies and deer flies (Chrysops spp.). This research effort is augmented by the cooperative efforts of the ARS, USDA, Organic Chemicals Synthesis Laboratory (OCSL), Beltsville, Maryland, where a synthesis program produces many of the chemicals tested in our repellent research. Dect, the most widely used, all-purpose insect repellent, is effective for only a short period against stable flies in laboratory outdoor cage tests, whatever its formulation. Laboratory tests are the primary source of information, as it is difficult to field-test a repellent against this species because field populalThis paper reports the results of research only. Mention of a pesticide in this paper does not constitute a recommendation for use by the U.S. Department of Agriculture nor does it imply registration under FIFRA as amended. 'Insects Affecting Man Research Laboratory, Agric. Res. Serv., USDA, Gainesville, Florida 32604, U.S.A. 'Organic Chemicals Synthesis Laboratory, Agricultural Environmental Quality Institute, Agric. Res. Serv., USDA, lieltsville, Maryland 20705, U.S.A.
tions are unpredictable and occurrences are of short duration. In over 125 laboratory tests since 1972, the average protection time for an application of 250 mg of deet in ethanol on the forearm was only 199 min. It would, therefore, be desirable to find a repellent more effective than deet. It is not unexpected that a compound could show moderate or poor repellency to culicid species but still be highly effective against other families of Diptera. For example, Schreck et al. (1976) found that 2-hydroxyethyl cyclohexanecarboxylate (HECC), a moderately effective mosquito repellent, was poorly effective against Aedes taeniorhYllchus (Wiedemann), abou t equal in effectiveness against S. calcitralls and Ae. aegypti (L.), and as much as 20 times more effective than deet against the deer fly, Chrysops atlallticus Pechuman. Because of this information, a variety of unrelated and some related compounds (both esters and amides of cyclohexane-, 3-cyclohexene, 2-methylcyclohexane-, and 6methyl-3-cyclohexene carboxylic acids) were synthesized and tested against the stable fly. A total of 75 such compounds was evaluated. CHEMICAL
SYNTHESIS
AND
TEST
PROCEDURES
The esters were synthesized by a standard esterification procedure. An excess of the appropriate diol and cyclohexanecarboxylic acid were allowed to react in refluxing benzene in the presence of an acid catalyst, and the byproduct water was removed from the reaction system as it was formed by azeotropic distillation. The amides were synthesized as follows: an anhydrous ether solution of the appropriate acid chloride was slowly added with stirring to an anhydrous ether solution of the amine cooled in an ice bath. The reaction mixture was allowed to warm to room temperature and then to stand for several hours. Both esters and amides were isolated by routine extraction procedures and purified by distillation under high vacuum. First, the repellents were applied as I-ml aliquots of a 25% ethanol solution and spread evenly over the forearm of a subject from wrist to elbow. Since the ethanol solution was formulated on a weightvolume basis, 250 mg of repellent was applied to
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
AbJ/mc/: Selected esters and amides of 4 alicyclic acids were found to be significantly more effective than N,N-diethyl-mtoluamide (deet) as topical repellents against the st~b]e fly, S/omo.l:)'s calci/ralls (L.). Two compounds, 1-(3-cyclohexene-I-yl carbonyl)piperidine (AI3-35765) and 1-[ (2-methylcyclohexyl)carbonyl]piperidine (AI3-35769), were significantly more effective than deet when they were applied to skin at rates of 62.5, 125, and 250 mg/forearm. Two others, 1-[ (2-methyll'ydohexyl)carbonyl]-hexahydro-] H-azepinc (AI3-35770) and N,N-dipropylcyclohexanccarboxamide (AI3-36326), were more dfective at the 2 highest doses while the remainder were more efT('ctivt~at the highest or intermediate dose.
J.
590
Med. Entomol.
population in respect to numbers and avidity. Citrated beef blood on a cotton pad was offered for 45 min. (1530 hI' to 1615 hI') each day after the repellent tests were completed. This short-term feeding period provided a small but adequate food intake, and avidity was not reduced as a result of complete engorgement. Results obtained when an untreated forearm was inserted into the test cage before and during the tests each day gave a measure of the avidity of the flies, though it was impossible to count the attacks on the untreated arm. The effectiveness of each chemical was determined by the protection time; that is, the time between treatment and the first confirmed bite (bite followed by another within 30 min.). Therefore, 30 min. after the application of the test chemical and every 30 min. thereafter, the treated arms were inserted into the test cage for 3 min. unless bites occurred sooner. Because test subjects differ in attractiveness and
TABLE 1. Repellency to the stable fly, Stomoxp calcitralls, of candidate repellents and dcet applied to the skin at various concentrations in ethanol.'" AI3-No."'* 35765
CHEMICALNAME 1-(3-cyclohexene-I-yl carbonyl)piperidine
35766
I (3-cyclohexene-I-yl carbonyl) hexahydroIH-azepine
35768
1-[ (2-methylcyclohexyl) carbonyl]pyrrolidine
35769
1-[ (2-methylcyclohexyl)carbonyl]piperidine
35770
hexahydro-I- [ (2-methylcyelohexyl) carbonyl]IH-azepine
36326
N, N-dipropylcyelohexanecarboxamide
36328
1-[ (6-methyl-3-cyclohexenyl)carbon-lyl]pyrrolidine
36334
hexahydro-I-[ (6-methyl-3-cyclohexenyl)carbonI-y]] -I H-azepine
36343
3-hydroxypropyl cyelohexanecarboxylate
36346
4-hydroxybutyl cyclohexanecarboxylate
36347
3-hydroxybutyl cyclohexanecarboxylate
%
CONC. 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0
PROTECTION TIME(MIN.)_ RATIO Range Adj. mean TO DEET 30-120 60-240 360-390 30- 60 270-450 300-510 60-180 90-210 240-270 30-210 270-330 390-510 30- 30 2]0-375 390-510 30- 90 300-360 210-463 30- 90 120-270 150-405 30- 60 150-330 480-510 60- 90 210-270 270-420 30- 30 30-270 270-450 30- 30 90-240 150-420
"'Data compiled from II different test series each using deet as the test standard. "Not significantly different from the deet standard at the 0.05% level of confidence.
103 128 387 33 306 457 80 150 266 118 320 419 30 326 459 55 315 321 63 230 264 38 306 538 70 230 296 30 181 395 28 91 323
2.5 2.4 2.39 1.00** 1.42"'* 3.78 1.6** 3.3 1.6** 2.4 4.57 2.6 1.00*'" 3.27 2.9 1.7" 4.50 2.02 1.9*'" 3.29 1.66** 1.15** 1.42** 3.02 2.2** 3.29 1.66"'''' 1.00*'" 0.84** 3.27 0.85** 0.42 2.67
No. OF TESTS 3 4 5 5 5 4 3 4 4 3 5 4 5 5 4 3 5 5 3 5 5 5 5 5 3 5 5 5 5 4 5 5 4
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
the forearm in each test. The most promlSlng compounds (those equal to or better than the deet standard at the 25% dosage) were then tested as 12.5% and 6.25% ethanol solutions. The evaluations were carried out in an outdoor cage (103 em square and 133 em high) constructed of aluminum and having a solid top and bottom and screen wire on 4 sides. Four of the sides had port openings covered with 30.5-cm (12-in.) tubular cloth stockinettes. The centers of the ports were 30 em from the bottom of the cage, which rested on a table 80 em high. One arm each of up to 4 treated subjects at a time could be inserted through the ports into the cage. Approximately 12,000 S. calcitrans pupae were placed in cups and allowed to emerge in the test cage over an 8-day period. The tests were started the 4th day, when approximately 8000 flies had emerged. The remaining 4000 that emerged over the next 4 days maintained a relatively stable
Vol. 14, no. 5
1978
591
Schreck et al. : Repellency of esters and amides
insects differ in avidity, the best measure of the effectiveness of a repellent is its ratio of protection time vs. that of a standard repellent used in similar conditions. Deet was the standard in all of the tests reported here. It was paired with each of the other candidate repellents in 10 different test series. The experimental design used was a round-robin series in which each repellent was paired concurrently against another repellent on the arms of a subject. An adjusted average protection time that allowed for individual variation between test subjects and test conditions was then computed. The method of analysis is explained by Gilbert et al. (1957). RESULTS
DISCUSSION
Structural similarities between the stable fly repellents described here and the deer fly repellent, HECC, should be noted. The acid moiety of the esters and ami des listed in TABLE 1 is comprised of an
Ackllowledgmellts: We wish to thank D. Smith, K. Posey, J. Jackson, and D. Godwin of the Insects Affecting Man Research Laboratory for their help in completing these studies. LITERATURE CITED
BIUDle,R. R., R. H. Roberts, J. L. Eschle & J. J. Matter. 1971. Tests of aerosols of deet for protection of livestock from biting flies. J. £Call. Elltomol. 64: 1193-96. Bruce, W. N. & G. C. Decker. 1957. Experiments with several
repellent
formulations
applied
to cattle
for
the
control of stable flies. J. £COil. E'ltOlllol. 50: 709-13. Gilbert, I. H., H. K. Gouck & C. N. Srn.ith. 1957. New mosquito repellent. Part 1. Soap Chelll. Spec. 33: 115-17, 129-33. King, W. V. & L. G. Lenert. 1936. Outbreaks of StOIllOXYS calcitrans L. (dog flies) along Florida's northwest coast. Fla. Entomol. 19: 33-39. Schreck, C. E., N. Srn.ith & H. K. Gouck. 1976. Repdleney of N,N-diethy1-m-to1uamide(deet) and 2-hydroxyethyl cyc1ohexanecarboxy1ateagainst the deer flies Chrysops atlanticus Pechuman and Chrysops jlavidus Wiedemann. J. Med. Entomol. 13: 115-18.
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
Of 75 varied materials tested, II were statistically equal to or better than the deet standard at 250 mgt arm. These were esters and amides of 4 alicyclic acids. Test results for these chemicals are given in TABLE 1. The data for the other 64 less effective compounds are available from the authors. At the 2S0-mg dosage, protection time for the promising repellents ranged from 4.4 hr to 9 hr; that of deet ranged from 2 hr to 3 hr, somewhat below the average protection time for deet mentioned earlier. Plainly, the repellents AI3-35765 and 35769 were significantly mOre effective than deet at all 3 dosages tested; AI3-35770 and 36326 were more effective at both 125 and 250 mg/forearm. The other 7 materials were more effective at only 1 dose (either 125 or 250 mg/forearm).
alicyclic carboxylic acid, a feature of HECC. Future efforts at synthesis of new repellents for biting flies should take these similarities into consideration. For some time, the basic assumption in repellent research has been that we are looking for a universal repellent that will protect us from all the major pests and the medically-important species of arthropods. Deet has, in part, filled this need though we have been aware for quite a while of its shortcomings against some species. On the basis of the information reported here, a more useful approach might be to identify individual chemicals or groups of chemicals that are effective against specific pests. All-purpose formulations might then be developed by using a composite of compounds. Also, a thorough study of the repellent action of these compounds against a wide range of species could provide us with a better understanding of the mode of action and the basic properties that make a repellent act as it does against various arthropods.
Med. Entomol.
Vol. 14, no. 5: 589 591
10 February 1978
REPELLENCY OF SELECTED ESTERS AND AMIDES OF FOUR ALICYCLIC ACIDS AGAINST THE STABLE FLY, STOMOXYS CALC/TRANS (DIPTERA: MUSCIDAE) I By C. E. Schreck2, T. P. McGovern3 and N. Smith2
Although the major portion of the interest m repellents for the stable fly, Stomoxys calcitrans (L.), has to do with protecting livestock (Bruce & Decker 1957, Blume et a1. 1971), this insect has, on occasion, been a notable pest of humans, usually when its livestock hosts are scarce or absent. For example, the large outbreaks of S. calcitralls that occur in some coastal areas of the southeastern United States can cause much discomfort and do serious damage to the tourist industry (King & Lenert 1936). Therefore, in recent years, investigations of repellents at the Insects Affecting Man Research Laboratory at Gainesville, Florida, have given greater emphasis to studies of biting flies in an attempt to find more effective repellents than deet (N,N-diethyl-m-toluamide) for use against such species as stable flies and deer flies (Chrysops spp.). This research effort is augmented by the cooperative efforts of the ARS, USDA, Organic Chemicals Synthesis Laboratory (OCSL), Beltsville, Maryland, where a synthesis program produces many of the chemicals tested in our repellent research. Dect, the most widely used, all-purpose insect repellent, is effective for only a short period against stable flies in laboratory outdoor cage tests, whatever its formulation. Laboratory tests are the primary source of information, as it is difficult to field-test a repellent against this species because field populalThis paper reports the results of research only. Mention of a pesticide in this paper does not constitute a recommendation for use by the U.S. Department of Agriculture nor does it imply registration under FIFRA as amended. 'Insects Affecting Man Research Laboratory, Agric. Res. Serv., USDA, Gainesville, Florida 32604, U.S.A. 'Organic Chemicals Synthesis Laboratory, Agricultural Environmental Quality Institute, Agric. Res. Serv., USDA, lieltsville, Maryland 20705, U.S.A.
tions are unpredictable and occurrences are of short duration. In over 125 laboratory tests since 1972, the average protection time for an application of 250 mg of deet in ethanol on the forearm was only 199 min. It would, therefore, be desirable to find a repellent more effective than deet. It is not unexpected that a compound could show moderate or poor repellency to culicid species but still be highly effective against other families of Diptera. For example, Schreck et al. (1976) found that 2-hydroxyethyl cyclohexanecarboxylate (HECC), a moderately effective mosquito repellent, was poorly effective against Aedes taeniorhYllchus (Wiedemann), abou t equal in effectiveness against S. calcitralls and Ae. aegypti (L.), and as much as 20 times more effective than deet against the deer fly, Chrysops atlallticus Pechuman. Because of this information, a variety of unrelated and some related compounds (both esters and amides of cyclohexane-, 3-cyclohexene, 2-methylcyclohexane-, and 6methyl-3-cyclohexene carboxylic acids) were synthesized and tested against the stable fly. A total of 75 such compounds was evaluated. CHEMICAL
SYNTHESIS
AND
TEST
PROCEDURES
The esters were synthesized by a standard esterification procedure. An excess of the appropriate diol and cyclohexanecarboxylic acid were allowed to react in refluxing benzene in the presence of an acid catalyst, and the byproduct water was removed from the reaction system as it was formed by azeotropic distillation. The amides were synthesized as follows: an anhydrous ether solution of the appropriate acid chloride was slowly added with stirring to an anhydrous ether solution of the amine cooled in an ice bath. The reaction mixture was allowed to warm to room temperature and then to stand for several hours. Both esters and amides were isolated by routine extraction procedures and purified by distillation under high vacuum. First, the repellents were applied as I-ml aliquots of a 25% ethanol solution and spread evenly over the forearm of a subject from wrist to elbow. Since the ethanol solution was formulated on a weightvolume basis, 250 mg of repellent was applied to
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
AbJ/mc/: Selected esters and amides of 4 alicyclic acids were found to be significantly more effective than N,N-diethyl-mtoluamide (deet) as topical repellents against the st~b]e fly, S/omo.l:)'s calci/ralls (L.). Two compounds, 1-(3-cyclohexene-I-yl carbonyl)piperidine (AI3-35765) and 1-[ (2-methylcyclohexyl)carbonyl]piperidine (AI3-35769), were significantly more effective than deet when they were applied to skin at rates of 62.5, 125, and 250 mg/forearm. Two others, 1-[ (2-methyll'ydohexyl)carbonyl]-hexahydro-] H-azepinc (AI3-35770) and N,N-dipropylcyclohexanccarboxamide (AI3-36326), were more dfective at the 2 highest doses while the remainder were more efT('ctivt~at the highest or intermediate dose.
J.
590
Med. Entomol.
population in respect to numbers and avidity. Citrated beef blood on a cotton pad was offered for 45 min. (1530 hI' to 1615 hI') each day after the repellent tests were completed. This short-term feeding period provided a small but adequate food intake, and avidity was not reduced as a result of complete engorgement. Results obtained when an untreated forearm was inserted into the test cage before and during the tests each day gave a measure of the avidity of the flies, though it was impossible to count the attacks on the untreated arm. The effectiveness of each chemical was determined by the protection time; that is, the time between treatment and the first confirmed bite (bite followed by another within 30 min.). Therefore, 30 min. after the application of the test chemical and every 30 min. thereafter, the treated arms were inserted into the test cage for 3 min. unless bites occurred sooner. Because test subjects differ in attractiveness and
TABLE 1. Repellency to the stable fly, Stomoxp calcitralls, of candidate repellents and dcet applied to the skin at various concentrations in ethanol.'" AI3-No."'* 35765
CHEMICALNAME 1-(3-cyclohexene-I-yl carbonyl)piperidine
35766
I (3-cyclohexene-I-yl carbonyl) hexahydroIH-azepine
35768
1-[ (2-methylcyclohexyl) carbonyl]pyrrolidine
35769
1-[ (2-methylcyclohexyl)carbonyl]piperidine
35770
hexahydro-I- [ (2-methylcyelohexyl) carbonyl]IH-azepine
36326
N, N-dipropylcyelohexanecarboxamide
36328
1-[ (6-methyl-3-cyclohexenyl)carbon-lyl]pyrrolidine
36334
hexahydro-I-[ (6-methyl-3-cyclohexenyl)carbonI-y]] -I H-azepine
36343
3-hydroxypropyl cyelohexanecarboxylate
36346
4-hydroxybutyl cyclohexanecarboxylate
36347
3-hydroxybutyl cyclohexanecarboxylate
%
CONC. 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0 6.25 12.5 25.0
PROTECTION TIME(MIN.)_ RATIO Range Adj. mean TO DEET 30-120 60-240 360-390 30- 60 270-450 300-510 60-180 90-210 240-270 30-210 270-330 390-510 30- 30 2]0-375 390-510 30- 90 300-360 210-463 30- 90 120-270 150-405 30- 60 150-330 480-510 60- 90 210-270 270-420 30- 30 30-270 270-450 30- 30 90-240 150-420
"'Data compiled from II different test series each using deet as the test standard. "Not significantly different from the deet standard at the 0.05% level of confidence.
103 128 387 33 306 457 80 150 266 118 320 419 30 326 459 55 315 321 63 230 264 38 306 538 70 230 296 30 181 395 28 91 323
2.5 2.4 2.39 1.00** 1.42"'* 3.78 1.6** 3.3 1.6** 2.4 4.57 2.6 1.00*'" 3.27 2.9 1.7" 4.50 2.02 1.9*'" 3.29 1.66** 1.15** 1.42** 3.02 2.2** 3.29 1.66"'''' 1.00*'" 0.84** 3.27 0.85** 0.42 2.67
No. OF TESTS 3 4 5 5 5 4 3 4 4 3 5 4 5 5 4 3 5 5 3 5 5 5 5 5 3 5 5 5 5 4 5 5 4
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
the forearm in each test. The most promlSlng compounds (those equal to or better than the deet standard at the 25% dosage) were then tested as 12.5% and 6.25% ethanol solutions. The evaluations were carried out in an outdoor cage (103 em square and 133 em high) constructed of aluminum and having a solid top and bottom and screen wire on 4 sides. Four of the sides had port openings covered with 30.5-cm (12-in.) tubular cloth stockinettes. The centers of the ports were 30 em from the bottom of the cage, which rested on a table 80 em high. One arm each of up to 4 treated subjects at a time could be inserted through the ports into the cage. Approximately 12,000 S. calcitrans pupae were placed in cups and allowed to emerge in the test cage over an 8-day period. The tests were started the 4th day, when approximately 8000 flies had emerged. The remaining 4000 that emerged over the next 4 days maintained a relatively stable
Vol. 14, no. 5
1978
591
Schreck et al. : Repellency of esters and amides
insects differ in avidity, the best measure of the effectiveness of a repellent is its ratio of protection time vs. that of a standard repellent used in similar conditions. Deet was the standard in all of the tests reported here. It was paired with each of the other candidate repellents in 10 different test series. The experimental design used was a round-robin series in which each repellent was paired concurrently against another repellent on the arms of a subject. An adjusted average protection time that allowed for individual variation between test subjects and test conditions was then computed. The method of analysis is explained by Gilbert et al. (1957). RESULTS
DISCUSSION
Structural similarities between the stable fly repellents described here and the deer fly repellent, HECC, should be noted. The acid moiety of the esters and ami des listed in TABLE 1 is comprised of an
Ackllowledgmellts: We wish to thank D. Smith, K. Posey, J. Jackson, and D. Godwin of the Insects Affecting Man Research Laboratory for their help in completing these studies. LITERATURE CITED
BIUDle,R. R., R. H. Roberts, J. L. Eschle & J. J. Matter. 1971. Tests of aerosols of deet for protection of livestock from biting flies. J. £Call. Elltomol. 64: 1193-96. Bruce, W. N. & G. C. Decker. 1957. Experiments with several
repellent
formulations
applied
to cattle
for
the
control of stable flies. J. £COil. E'ltOlllol. 50: 709-13. Gilbert, I. H., H. K. Gouck & C. N. Srn.ith. 1957. New mosquito repellent. Part 1. Soap Chelll. Spec. 33: 115-17, 129-33. King, W. V. & L. G. Lenert. 1936. Outbreaks of StOIllOXYS calcitrans L. (dog flies) along Florida's northwest coast. Fla. Entomol. 19: 33-39. Schreck, C. E., N. Srn.ith & H. K. Gouck. 1976. Repdleney of N,N-diethy1-m-to1uamide(deet) and 2-hydroxyethyl cyc1ohexanecarboxy1ateagainst the deer flies Chrysops atlanticus Pechuman and Chrysops jlavidus Wiedemann. J. Med. Entomol. 13: 115-18.
Downloaded from http://jme.oxfordjournals.org/ by guest on June 8, 2016
Of 75 varied materials tested, II were statistically equal to or better than the deet standard at 250 mgt arm. These were esters and amides of 4 alicyclic acids. Test results for these chemicals are given in TABLE 1. The data for the other 64 less effective compounds are available from the authors. At the 2S0-mg dosage, protection time for the promising repellents ranged from 4.4 hr to 9 hr; that of deet ranged from 2 hr to 3 hr, somewhat below the average protection time for deet mentioned earlier. Plainly, the repellents AI3-35765 and 35769 were significantly mOre effective than deet at all 3 dosages tested; AI3-35770 and 36326 were more effective at both 125 and 250 mg/forearm. The other 7 materials were more effective at only 1 dose (either 125 or 250 mg/forearm).
alicyclic carboxylic acid, a feature of HECC. Future efforts at synthesis of new repellents for biting flies should take these similarities into consideration. For some time, the basic assumption in repellent research has been that we are looking for a universal repellent that will protect us from all the major pests and the medically-important species of arthropods. Deet has, in part, filled this need though we have been aware for quite a while of its shortcomings against some species. On the basis of the information reported here, a more useful approach might be to identify individual chemicals or groups of chemicals that are effective against specific pests. All-purpose formulations might then be developed by using a composite of compounds. Also, a thorough study of the repellent action of these compounds against a wide range of species could provide us with a better understanding of the mode of action and the basic properties that make a repellent act as it does against various arthropods.
