Recent Developments in Chemical Attractants for Tephritid Fruit Flies

Chapter 38

Recent Developments in Chemical Attractants for Tephritid Fruit Flies R. Teranishi , R. G. Buttery , Κ. E. Matsumoto , D. J. Stern , R. T. Cunningham , and S. Gothilf 1

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Western Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture, Albany, CA 94710 Agricultural Research Service, U.S. Department of Agriculture, Hilo, HI 96720 The Volcani Center, P.O.B. 6, Bet-Dagan, 50-250, Israel

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Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 28, 2016 | http://pubs.acs.org Publication Date: January 8, 1987 | doi: 10.1021/bk-1987-0330.ch038

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Some problems presented by Tephritid fruit flies and the potential damage which these fruit flies could do to our fruit and vegetable crops on the mainland of the USA are briefly mentioned. The role of attractants in population monitoring and control is also briefly discussed. Two potential Mediterranean fruit fly attractants are presented: (+) — α-copaene, from angelica seed o i l studied both by Fornasiero and coworkers and by Jacobson and coworkers, and 2-methylnaphthalene, from our kerosene studies. Orange o i l is presented as a possible commercial source of (+)— α-copaene. Cost — effective studies must be made before these attractants can be established as being economical and practical. At the present time, trimedlure is s t i l l the only lure used for population monitoring of Medflies, and protein hydrolysates are used for baits in control methods. Fruit flies of the Diptera order, Tephritid family, damage fruit and vegetables a l l over this earth. Of the many species found, we are concerned here with only five species. The Mediterranean fruit fly, or Medfly, Ceratitis capitata (Wiedmann), the melon fly, Dacus curcurbitae (Coquillett), and the Oriental fruit fly, Dacus dorsalis. are found in the Hawaiian Islands. Efforts are being made to keep these flies from infesting the mainland of the USA. The Caribbean fruit fly, or Caribfly, Anastrepha suspensa (Leow), is now found in Florida, and efforts are being made to eradicate i t and to keep i t from spreading to other states. From Texas to California, the Mexican fruit fly, or Mexfly, Anastrepha ludens (Leow), presents a potential threat. Recently, a few Mexflies were found in the Los Angeles area. Very recently, another fruit fly has been added to this list. Dacus latifrons (Hendel), previously found in Taiwan, Malay Peninsula, Thailand, and Laos, has been discovered on the island of Oahu, Hawaii. It is sometimes referred to as the Malayasian fruit 0097-6156/87/0330-0431$06.00/0 © 1987 American Chemical Society

Waller; Allelochemicals: Role in Agriculture and Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY

f l y , and at present there i s a movement to give the common name of solanaceous f r u i t f l y to t h i s species. Unlike the small Drosophila f l i e s , commonly called vinegar or pomace f l i e s , the Tephritid f r u i t f l i e s are about the size of the common house f l i e s . Eggs are deposited under the skin of f r u i t s and vegetables, and when the eggs hatch and the insects develop to the larva stage, much damage i s done to f r u i t s and vegetables. Such damaged f r u i t s and vegetables have very l i t t l e commercial value. F r u i t s grown i n certain areas are prohibited i n the mainland of the USA to prevent the spreading of these f r u i t f l i e s . For example, mangoes grown i n Hawaii are not allowed to be shipped to the mainland. The Medfly and the Oriental f r u i t f l i e s have migrated around the world and have adapted to many f r u i t s and vegetables. As the name implies, the melon f l y predominantly attacks f r u i t s i n the melon family. D. l a t i f r o n s attacks f r u i t s i n the solanaceous family, such as eggplants, sweet and hot peppers, tomatoes, e t c . However, as t h i s species adapts i t s e l f to new surroundings, i t i s anticipated that the D. l a t i f r o n s w i l l s t a r t attacking other f r u i t s and vegetables as other species have, p a r t i c u l a r l y when urgency for food develops. Another point of interest i s that as such insects are transferred to new surroundings, t h e i r natural enemies usually do not accompany them. Therefore, the insects i n the new environment p r o l i f e r a t e and do much more damage i n the new environment because they are without the natural enemies to restrict their a c t i v i t i e s . The economic impact of an infestation of the Medfly i n C a l i f o r n i a i n 1981 serves as an example of how serious a problem these f l i e s present. The costs of eradicating the Medfly i n C a l i f o r n i a during the 1981 infestation were large. Burk and Calkins (1) reported a conservative estimate of 59 m i l l i o n d o l l a r s for chemical controls, 38 m i l l i o n dollars for quarantine and fumigation, and 260 m i l l i o n dollars i n crop losses. However these figures are small compared to the estimated 15 b i l l i o n d o l l a r s of f r u i t s and vegetables grown per year i n C a l i f o r n i a alone. Now that the importance of c o n t r o l l i n g these f r u i t f l i e s has been shown, some control methods and efforts to keep these f l i e s from spreading a r e p r e s e n t e d . Some attractants, such as hydrocarbons from kerosene and essential o i l s , are discussed. Insects often use chemical signals for finding shelter, oviposition s i t e s , mates, and food. U n t i l recently, most of chemical insect research has been focussed on how f l y i n g insects find t h e i r mates. Excellent work has been done i n the area of pheromones i n the l a s t twenty years or more. Now a c t i v i t y i s expanding to allelochemicals, chemicals which mediate i n t e r s p e c i f i c interactions. One of these important studies i s how insects find oviposition s i t e s . Another i s how they find food. Although chemists focus attention on v o l a t i l e chemical attractants, i t i s known that v i s u a l and auditory clues also play important roles i n the behavior of some insects. In order for chemists to keep a proper perspective, close cooperative research with entomologists i s necessary. In species whose larvae are s p e c i a l i s t feeders, finding suitable plants for oviposition i s of great importance. Corn earworm moths, H e l i o t h i s species, will oviposition on twine


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Attractants

for

Tephntid Fruit Flies

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impregnated with the extract of corn s i l k (2). I t does not take much imagination to see how such oviposition attractants could be used i n control of crop damage. With species which are not s p e c i a l i s t feeders, l i k e the Medfly which feeds on many f r u i t s and vegetables, i t i s much more d i f f i c u l t to find oviposition stimulants. In the 1981 Medfly i n f e s t a t i o n i n C a l i f o r n i a , an i n s e c t i c i d e was mixed with protein hydrolysates (1). Medflies are attracted to protein hydrolysates and feed on this material; hence, t h i s i s an e f f i c i e n t way to administer an i n s e c t i c i d e . Materials and Methods Sesquiterpenes were isolated from essential o i l s purchased or provided gratis by individuals or organizations. Kerosene was provided by the Chevron Chemical Corporation. Reference compounds were purchased or made by conventional synthetic methods. Isolation, separation, p u r i f i c a t i o n , and i d e n t i f i c a t i o n methods which were developed i n flavor chemistry were applied i n these experiments. Since such methods are described i n d e t a i l i n various places (3, 4), experimental d e t a i l s w i l l not be described here. Discussion Insect attractants are predominantly used for population monitoring and for control. I t i s necessary to know the degree of i n f e s t a t i o n to i n i t i a t e the most e f f e c t i v e control methods. There are two ways to prevent insecticides from entering the food chain by u t i l i z i n g e f f e c t i v e insect attractants. The f i r s t method i s to a t t r a c t the destructive insects themselves into a trap by an e f f e c t i v e lure, and the second i s by attracting t h e i r natural enemies so that the insects can be annihilated before they can cause much damage. The Animal and Plant Health Inspection Service (APHIS) i s very much aware of the tremendous potential damage which the Tephritid f r u i t f l i e s can i n f l i c t to crops. This concern has caused APHIS to e s t a b l i s h an active program of placing inspection stations at c r i t i c a l airports to monitor shipping of fresh f r u i t s and vegetables to the mainland of the USA. APHIS also has a program of setting out traps for spotting infestations of various insects, including the f r u i t f l i e s . The C a l i f o r n i a State Department of Food and Agriculture also has a program of trapping f r u i t f l i e s to detect infestations to h a l t the spread of these f l i e s into C a l i f o r n i a . For e f f e c t i v e monitoring programs, potent attractants are needed. For the C a r i b f l i e s , Mexflies, and the newly found D. l a t i f r o n s , no good chemical lures are available. Dr. Chambers has written an excellent review a r t i c l e on "Attractants for F r u i t F l y Survey and Control" (5). In t h i s review, Chambers discusses the development of parapheromones and food baits and the implementation of these attractants. Thousands of compounds were screened i n Hawaii and in Mexico during the period of 1950 to 1955 (6), and this screening process yielded some promising candidates. Methyl eugenol, proposed by Steiner i n 1952 (Z) » remains the most e f f e c t i v e lure for the Oriental f r u i t f l y . Cue lure, found by Beroza i n 1960 (8), i s a good lure for the melon



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fly. Trimedlure, found by McGovern, Beroza and coworkers i n 1961 (9), i s the lure presently used for the Medfly. Angelica seed o i l was indicated i n the 1950-1955 survey i n Hawaii as an attractant for the Medfly, and Fornasiero and coworkers i n 1969 (10) found that α-copaene i s the active ingredient i n this o i l which attracts the Medfly. Jacobson and coworkers (11) recently found that i t i s the (+) — rotating c h i r a l isomer of α-copaene that is effective and that the ( - ) - r o t a t i n g isomer i s much less e f f e c t i v e . It i s interesting to note that these compounds attract mainly the males of the respective species. Therefore, these compounds might be pheromone mimics. Protein hydrolysates, on the other hand, a t t r a c t both sexes of most Tephritids and are widely used as food baits. However, v o l a t i l e s from protein hydrolysates may not be simply food attractants. The c y c l i c imine, 3,4-dihydro-2H-pyrrole, has been i d e n t i f i e d i n protein hydrolysate v o l a t i l e s (12), and t h i s compound has been i d e n t i f i e d by Baker and coworkers (13) as the sex pheromone which attracts v i r g i n females to the sexually mature male Medflies. Why the protein hydrolysate v o l a t i l e s attract the males and other species remains unanswered. Figure 1 shows the chemical structures of methyl eugenol, cue lure, trimedlure, and α-copaene. Since these attractants are effective with only the respective species mentioned, i t is d i f f i c u l t to compare them quantitatively. However, i t seems that the most effective of these i s methyl eugenol. I t i s interesting that i f the acetate moiety i s taken away from cue lure, the molecule remaining i s commonly referred to as raspberry ketone, a compound that has the aroma of raspberry. As mentioned previously, trimedlure i s the material that i s currently being used as the Medfly attractant in population monitoring. McGovern and Beroza (14) have elucidated the relationship of the various isomers possible i n the structure of trimedlure to attractancy to the Medfly. Of the eight structures possible, only four need be considered because the trans configuration, with respect to the methyl and the carbobutoxy groups, i s necessary for high a c t i v i t y . The c i s isomers are not very effective as lures. The chloro group can be i n the 4- and 5-positions and can be a x i a l or equatorial, hence, the four possible isomers studied. These four isomers are found i n the commercial product called trimedlure. Leonhardt and coworkers (15) have developed a n a l y t i c a l methods for these isomers so that accurate specifications can be written for trimedlure. (+)- α-Copaene seems to be several times more potent than trimedlure; that i s , i f equal amounts of each are set out i n traps, more Medflies are caught i n traps containing α-copaene. There i s not a s u f f i c i e n t supply of angelica seed o i l to provide enough material for monitoring purposes. α-Copaene was synthesized by Heathcock (16.), but since t h i s i s a t r i c y c l i c sesquiterpene, the synthesis i s far too complicated to be economically feasible. Therefore, i f α-copaene i s to be a p r a c t i c a l lure, a p l e n t i f u l natural product supply must be found. Table I shows a survey of some essential o i l s containing α-copaene and α-ylangene. Unfortunately the rotation i s not reported i n most of the a r t i c l e s , but we have some evidence as to which are a t t r a c t i v e to the Medfly. The material from the synthesis by Heathcock (16) would be racemic because the synthesis was not a



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Methyl

Chemical

Attractants

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Tephritid

Fruit

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Flies

Cue lure

eugenol

Cl CHU

Χ α-Copaene

Trimedlure Figure 1. trimedlure,

Chemical structures and α - c o p a e n e .

of

methyl

eugenol,

cue


lure,

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Table I.

Sources of

a-Copaene

a-Copaene

a-Ylangene

Source

Synthetic

Synthetic

Heathcock Fornasiero


Angelica Copaiba

—

Fritzsche

Cubeb

—

Fritzsche Sunkist

Grapefruit Hop

(20% of a-eopaene)

Buttery

Orange

....

Sunkist

—

Schizandra chinensis

Sorm

Ylang ylang

--

Fritzsche

stereospecif i c one. The α-copaene from angelica seed o i l has been shown to be a t t r a c t i v e by Fornasiero and coworkers (10) and by Jacobson and coworkers (11). Jacobson (11) has reported that the α-copaene from copaiba o i l has a (-) rotation and has been shown to be not very effective as a Medfly attractant. Our work has shown that α-copaene from cubeb o i l has a (-) rotation and i s not very effective. Sufficient supplies of α-copaene from grapefruit, hop, and ylang ylang o i l s were not available to take rotations or to test with Medflies. Of the e s s e n t i a l o i l s l i s t e d i n Table I, i t seems that only orange o i l i s promising as a p r a c t i c a l source. Even though the α-copaene i s present at about 0.01% of the t o t a l o i l , orange o i l is produced i n such large quantities that i t may be a p r a c t i c a l source. Orange o i l was investigated because the Medfly i s attracted to oranges. When a sesquiterpene cut from orange o i l was tested, i t was indeed a c t i v e . It was hoped that valencene would be the active material because i t i s the major sesquiterpene i n orange o i l , and i t i s commercially available. However, valencene i s not a c t i v e . It was found that ( + ) - α - c o p a e n e , a contaminant in the valencene cut, i s the active material. Because α-copaene is a sesquiterpene, a hydrocarbon, and because of very early reports that kerosene i s a Medfly attractant (17), hydrocarbons i n kerosene were re-investigated. Also, i n the Hawaiian 1950-1955 survey (6), 2-methylnaphthalene was indicated as active. This compound was found i n kerosene and was tested for a c t i v i t y again. The p o s i t i o n a l isomer, 1-methylnaphthalene, has very l i t t l e a c t i v i t y , but 2-methylnaphthalene did exhibit a c t i v i t y i n olfactometer tests by G o t h i l f and i n f i e l d t r i a l s by Cunningham. Although the a c t i v i t y of 2-methylnaphthalene i s somewhat less than



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that of trimedlure, because the naphthalene compound i s cheaper, i t may be cost-effective to use the naphthalene compound. Some alkylbenzene fractions from kerosene showed some a c t i v i t y . Gas chromatographic-mass spectral analyses showed a considerable amount of alkylated toluene compounds. Dreiding models were made, and 2-methyl-3-(3-methylphenyl)heptane was selected to be synthesized on the basis that the shape of this molecule i s s i m i l a r to that of α-copaene. Unfortunately, this compound showed no a c t i v i t y . Also, no f r a c t i o n for this alkylbenzene cut from kerosene had much higher a c t i v i t y than the starting material. Therefore, i t was assumed that only l o w - a c t i v i t y compounds are i n t h i s f r a c t i o n . So far, 2-methylnaphthalene i s the only compound isolated from kerosene that has shown any promise as a p r a c t i c a l Medfly attractant. Dreiding models of trimedlure and α-copaene were compared, and the models of these compounds looked s u r p r i s i n g l y s i m i l a r , as well as the 2-methyl-3< 3-me thy lphenyl) heptane compound. If the dotted bonds of the cyclobutane ring of α-copaene are broken, and the cyclohexane ring containing the double bond i s made aromatic, the phenylheptane compound i s obtained. However, i t has been stated already that this compound has no a c t i v i t y . Thus, i t seems that s i m i l a r shape may be necessary, but shape alone does not seem to be s u f f i c i e n t . I t must be kept i n mind that (+)-α-copaene i s active, whereas (-)-α-copaene i s not. Fornasiero (10) has stated that α-ylangene i s a c t i v e , but because copaene and ylangene are so d i f f i c u l t to separate, the a c t i v i t y of the ylangene cut may be due to some copaene contamination. However, i n view of trimedlure, with chloro and carbobutoxy moieties, and α-copaene, a hydrocarbon with one double bond, being a c t i v e , i t may be possible that there are other compounds which w i l l s a t i s f y shape and polarity requirements to be Medfly attractants. Also, good attractants for C a r i b f l i e s , Mexflies, and Dacus l a t i f r o n s must be found for effective population monitoring and control of these fruit flies. Acknowledgments The authors thank Ed Aoyagi, Chevron Chemical Company, for kerosene samples, and James A. Rogers, Fritzsche D & 0 Company, for essential o i l samples.

Literature Cited 1. Burk, T.; Calkins, C. O. Florida Ent. 1983, 66, 3-18. 2. Metcalf, R. L.; Metcalf, R. A. In "Introduction to Insect Pest Management"; Metcalf, R. L.; Luckman, W. Η., Eds.; John Wiley and Sons: New York, 1975; p. 283. 3. Teranishi, R.; Flath, R. A.; Sugisawa, Η., Eds.; "Flavor Research: Recent Advances"; Marcel Dekker, Inc.: New York, 1981; pp. 11-123. 4. Schreier, P., Ed.; "Analysis of Volatiles"; Walter de Gruyter: Berlin, 1984; 469 pp. 5. Chambers, D. L. In "Chemical Control of Insect Behavior"; Shorey, H. H.; McKelvey, J. J., Jr., Eds.; John Wiley and Sons: New York, 1977; pp. 327-344.



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6. Beroza, M.; Green, Ν., Eds.; "Materials Tested as Insect Attractants"; USDA Agricultural Handbook No. 239: Washington, D.C., 1963; 148 pp. 7. Steiner, L. F. J. Econ. Entomol. 1952, 45, 241-248. 8. Beroza, M.; Alexander, Β. H.; Steiner, L. F.; Mitchell, W. C.; Miyashita, D. H. Science 1960, 131, 1044-1045. 9. McGovern, T. P.; Beroza, M.; Ohinata, K.; Miyashita, D.; Steiner, L. F. J. Econ. Entomol. 1966, 59, 1450-1455. 10. Fornasiero, U.; Guitto, Α.; Caporale, G.; Baccichetti, F.; Musajo, L. Gazetta Chmica Italiana 1969, 99, 700-710. 11. Jacobson, M.; Uebel, E. C.; Lusby, W. R.; Cunningham, R. T. Chemical and Engineering News 1984, Dec. 17, 24. 12. Flath, R. A. Private communication. 13. Baker, R.; Herbert, R. H.; Grant, G. G. J. Chem. Soc. Chem. Commun. 1985, 824-825. 14. McGovern, T. P.; Beroza, M. J. Org. Chem. 1966, 1472-1477. 15. Leonhardt, Β. Α.; McGovern, T. P.; Plimmer, J. R. J. HCR & CC 1982, 5, 430-431. 16. Heathcock, C. H. J. Am. Chem. Soc. 1966, 88, 4110-4112. 17. Severin, H. H. P.; Severin, H. C. J. Econ. Ent. 1913, 6, 347-351. RECEIVED December 9, 1985


Recent Developments in Chemical Attractants for Tephritid Fruit Flies

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