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PHYSIOLOGICAL A.c'lD CHEMICAL ECOLOGY Structure Activity Relationships of Phenyl Alkyl Alcohols, Phenyl Alkyl Amines, and Cinnamyl Alcohol Derivatives as Attractants for Adult Corn Rootworm (Coleoptera: Chrysomelidae: Diabrotica spp.) l 2 RICHARD J. PETROSKI AND LESLIE HAMMACK Environ. Entomol. 27(3): 688-694 (1998) ABSTRACT In field trapping tests, phenyl alkyl amines and phenyl alkyl alcohols with 2-carbon side chains attracted significantly more adult females of the northern com rootworm, Diabrotica barberi Smith & Lawrence, than did phenyl alkyl amines or phenyl alkyl alcohols with 1-, 3-, or 4-carbon side chains. Both sexes ofnorthern com rootworm were attracted to 2-phenyl-l-ethylamine in greater numbers than to 2-phenyl-l-ethanol, whereas the latter was the better attractant in the case of female western com rootworm, Diabrotica virgifera virgifera LeConte. Differences in attractancy between the 2 compounds were attributed to differences in atomic charge; electrostatic charge was calculated to be -1.10 on the nitrogen atom in 2-phenyl-l-ethylamine but only -0.70 on the oxygen atom in 2-phenyl-l-ethanol. Northern com rootworms responded in Significantly greater numbers when the 2 compounds were blended than when a dose of either compound was increased 10-fold. This observation does not support the idea that 2-phenyl-l-ethylamine substitutes for 2-phenyl-l-ethanol at a phenyl alkyl alcohol recognition site. In the case of cinnamyl alcohol derivatives, cinnamyl alcohol attracted the most northern corn rootworms, but cinnamaldehyde attracted the most western corn rootworms ofboth sexes. Male western corn rootworms responded to only cinnamaldehyde. KEY WORDS northern corn rootworm, western corn rootworm, 2-phenyl-l-ethylamine, phen ethylamine, 2-phenyl-l-ethanol, phenethylalcohol NORTHERN A.c'ID WESTERN corn rootworms, Diabrotica especially cinnamyl alcohol were attractive to adult barberi Smith & Lawrence and D. virgifera virgifera northern corn rootworms (Metcalf and Lampman LeConte, respectively, are the important diabroticite 1989a, c; 1991). Northern corn rootworm beetles also pests of corn, Zea Mays L., in the U.S. corn belt. Corn found the parakairomone, 3-phenyl-1-propanol, rootworms have been estimated to cause about 81 nearly as attractive as cinnamyl alcohol and signifi billion annually in U.S. crop losses and control costs cantly more attractive than 2-phenyl-1-ethanol, (Metcalf 1986) and to account for =20% of the pes whereas phenyl alkyl alcohols with 1 or 4 carbons in ticide applied to major U.S. field crops (Suguiyama the side chain were ineffective (Metcalf and Lamp and Carlson 1985, Delvo 1993). Several types ofsernio man 1989a, 1991). chemicals show promise as tools to manage corn root Phenyl alkyl amines in a series analogous to the worm populations, including floral volatiles attractive above phenyl alkyl alcohols were all at least marginally to adult beetles (Sutter and Lance 1991, Metcalf and attractive, and those with 2- and 3-carbon side chains Metcalf 1992, Metcalf 1994) . produced captures ofnorthern corn rootworm adults Diabroticite beetles are attracted to blossoms of higher than those obtained with cinnamyl alcohol, Cucurbita spp., where feeding occurs on nectar and although not significantly so (Metcalf and Lampman pollen (Fronk and Slater 1956, Fisher et al. 1984, 1991). Cinnamyl alcohol is among the most effective Andersen and Metcalf1987). Cucurbit blossoms con tain and release a series ofvolatile alcohols including attractants described for northern corn rootworm benzyl alcohol, 2-phenyl-1-ethanol, and cinnamyl al beetles (Metcalfand Lampman 1989a) and is the most cohol (Andersen 1987, Andersen and Metcalf 1987), effective in South Dakota, where 4-methoxyphen common constituents offloral aromas (Knudsen et al. ethanol performs relatively poorly (Hesleret al.1994). 1993). In field trapping tests, 2-phenyl-1-ethanol and Efficacy ofphenyl alkyl amines has been provisionally attributed to ability of the amine moiety to interact with the OR-receptor site (Metcalf and Lampman This article reports the results of research only. Mention of a proprietary product does not constitute an endorsement or a recom 1991). This explanation has not been tested, however, mendation by USDA for its use. and the amines may represent a new class of highly I National Center for Agricultural Utilization Research, Bioactive effective corn rootworm attractants that merits fur Agents Research, USDA-ARS, 1815 N. University Street, Peoria, II. ther study. We used field trapping tests and compu 61604. 2 Northern Grain Insects Research Laboratory, USDA-ARS, 2913 tional chemistry techniques to examine these alter Medary Avenue, Broo]"ings, SD 57006. natives. June 1998 PETROSKI A.'lD HAMMACK: CORe'l ROOTWORe\l ATTRACfA.'lTS 689 The first of 2 field trapping tests compared attrac imposable were kept. Geometry was further opti tiveness of cinnamyl alcohol, cinnamyl amine, and mized with a 6-31 G wavefunction and the atomic phenyl alkyl amines and alcohols with side chains charges were calculated from an electrostatic poten varying in length from 1 to 4 carbons. Cinnamyl ace tial fit. Electrostatic charge was similarly calculated for tate and (E) -cinnamaldehyde were also included in benzylamine, benzyl alcohol, 3-phenyl-1-pro the comparison. Although all ofthese compounds ex pylamine, 3-phenyl-1-propanol as well as cin cepting cinnamyl amine have been previously field namylamine, cinnamyl alcohol, and (E) -cinnamalde tested for attractiveness to northern corn rootworm hyde. beetles, simultaneously conducted comparisons are Insect Field Trapping. Attractant efficacy was de not available for all of the test compounds, including termined from the capture offeral northern and west 2-phenyl-1-ethylamine and 2-phenyl-1-ethanoI. In ern corn rootworm adults on traps baited "lith test studying structure activity relationships, simultaneous compounds and placed in field corn in Brookings testing is required for valid comparison among attract County, SD. For the 1st test, individual compounds ants for a number ofreasons, including variation in the (100 mg) were applied to cotton dental rolls (3.8 cm size ofbeetle field populations with time, in attractant long by 1 cm diameter [Patterson Dental, Minneap efficiency with crop phenology, and in trapping meth olis, MN 1) that were treated with 2.0 ml of a 1:4 odology among studies. A 2nd test examined olfactory mixture of olive oil in hexane to sustain volatilization interaction between OH and NH2 functional groups (Guss 1976). The rolls were then affixed to yellow by testing attractiveness of 2-phenyl-1-ethanol and Pherocon A.M. sticky traps (Trece, Salinas, CAl that 2-phenyl-1-ethylamine dispensed individually and in were wrapped around plants at about corn ear height. combination. The field trapping tests were designed Control traps were baited \vith dental rolls that were for the northern corn rootworm, but western corn treated only with the oil-hexane mixture. Procedures rootworms were also trapped. were modified slightly in the 2nd test when alcohol Computational chemistry techniques enable chem and amine were volatilized from the same traps. In this ists to simulate the structure and behavior of mole case, each chemical was placed on a separate half of cules. We used these techniques to examine similar a dental roll that had first been treated with 1.0 ml of ities and differences in atomic charge between the test the 1:4 mixture of olive oil in hexane. Each half was molecules to achieve a better understanding of how then fastened separately to the trap to minimize the chemical structure relates to biological activity. possibility ofchemical reactions between compounds volatilized from the same trap. Test doses were also reduced in the 2nd test; the amine and alcohol were Materials and Methods each tested at 3.0 and 30.0 mg per trap. Test Compounds. Cinnamylamine was synthesized The experiments were laid out in a randomized as described below; 3-phenyl-1-propanol was ob complete block design with 6 (1st test) or8 replicates. tained from Fluka Chemical (Ronkonkoma, NY); all Traps within blocks were placed simultaneously in othertest chemicals were obtained from Aldrich (Mil spatial proximity, generally \vithin a corn row, and waukee, WI). Purity of all compounds tested was at separated by 2:30 m. Blocks were at least 30 m from least 98%. one another and from the edge ofthe field. Traps were Cinnamyl amine was preparedbyreacting cinnamyl placed in the field on 6 September 1995 (1st test) and bromide (25 g, 0.127 mole) with hexamethylenetet 27 August 1996. Number ofnorthern and western corn ramine (19.6 g, 0.140 mole) in refluxing chloroform to rootworm beetles per corn plant and corn develop yield cinnamyl hexamethylene bromine salt (34 g, mental stage (Ritchie et aI. 1992) were determined 8 0.100 mole, 79% yield). The salt (10 g, 0.030 mole) was September 1995 and 29 August 1996 from samples of hydrolyzed with aqueous ethanolic HCL (Baumgar 40 plants situated throughout test areas at positions in ten 1973) to give the product (3.66 g, 0.28 mole, 93% trap rows about equidistant between traps. After 48 h yield). in the field, the traps were returned to the laboratory, Computational Chemistry. Molecular modeling where adult corn rootworms were counted by sex and was performed using the Spartan version 4.0 program species. (Wavefunction 1996) running on a Silicon Graphics Trap capture data were transformed [In (x + 1) 1 Indigo 2 Extreme workstation. Structures of2-phenyl to normalize variances and were then analyzed by 1-ethylamine and 2-phenyl-1-ethanol were built and analysis of variance (AJ.'\JOVA) procedure of the SAS the initial geometry was optimized with the Tripos Institute (1989). Student-Newman-Keuls test was molecular mechanics force field (Clark et aI. 1989) used to separate multiple means after a significant within Spartan. A systematic conformational search ANOVA (P < 0.05). Means and standard errors in was conducted with the AMI Hamiltonian using the tables are untransformed values.