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. molecular mechanics derived initial geometrics as the starting point. Thus for each compound, rotatable Results bonds were assigned and a conformational search was performed allowing the bonds to rotate with a chosen Insect Field Trapping. 2-Phenyl-1-ethylamine cap­ 10°C stepwise increment of the dihedral angles. The tured significantly more northern corn rootworm lowest energy conformations of 2-phenyl-1-ethyl­ adults of both sexes than did any of the other com­ amine and 2-phenyl-1-ethanol that were nearly super- pounds in the 1st test (Table 1). Captures with this 690 ENVIRONMENTAL ENTOMOLOGY Vol. 27, no. 3

TahIe 1. Mean capture of corn rootworm adults by .pecie. and .ex on trap. baited "ith candidate attractants

Mean :: SE no. of com rootwonn adults captured Candidate attractant Northern com rootwonn \Vestern com rootwonn (100 mg) Female Male Female Male Benzyl amine 41.7 ::: 5.7bcd 23.2:: 4.6b 17.2:: 2.5e 6.7:: 2.1b 2-Phenyl-1-ethylamine 278.3 :: 42.3a 62.5:: 14.6a 21.0:: 3.ge 4.5:: 0.8b 3-Phenyl-1-propy!amine 31.3 :: 6.0cde 8.3:: 1.2bc 27.5 :: 3.5cde 7.8:: 1.7b 4-Pheny!-l-butylamine 2.3:: 0.8g 5.8:: 0.8c 7.2:: 1.4fg 7.8:: 1.9b Benzyl alcohol 20.3:: 3.9de 15.0:: 3Abc 45.3 :: 3.6bcd 7.8:: 1.6b 2-Phenyl-1-ethanol 84.0:: 14.ob 19.0:: 3.6b 97.5:: 12.9b 9.5:: 2.6b 3-Phenyl-1-propanol 23.2:: 1.6de 22.0:: 4.5b 24.7:: 3.3de 9.0:: lAb 4-Phenyl-1-butano! 2.5:: l.lg 5.5:: 1.2c 13.2:: 2.6ef 5.7:: 1.8b Cinnamyl amine 8.5:: 2.4f 6.8:: 2.1c 14.8:: 5.0ef 8.8:: 2.ob Cinnamyl alcohol 63.8:: 11.0bc 24.7:: 6.5b 70.3 :: 13Abc 8.0:: 2.3b Cinnamyl acetate 23.3:: 4.8de 7.8::: 2.2c 62.5::: 11.9bc 5.7:: 1.6b (E) -Cinnamaldehyde 15.8:: 2.1e 8.0:: 2.5c 212.7:: 31.4a 31.7:: 6.5a None (control) 3.0::: 1.8g 5.8:: lAc 6.3:: 1.6g 6.3:: lAb F 40.48 9.37 23.52 3.79 P (df = 12,60) <0.0001 <0.0001 <0.0001 0.0003

Means within a column followed by the same letter do not differ at P = 0.05 by Student-Newman-Keuls test. Com was in the dough to dent stage (R4-R5) and beetle numberperplant (mean :: SE) wasOA:: 0.1 and 1.2:: 0.2 for northern and western com rootwonn, respectively. amine were about 3 times those with 2-phenyl-l-eth­ 2-Phenyl-l-ethanol captured only about one-third anol, the 2nd most attractive compound. In no other as many western corn rootworm females as did (E)­ instance did a phenyl alkyl amine perform significantly cinnamaldehyde. However, this alcohol was almost 5 better than its corresponding alcohol. In contrast to times more effective than 2-phenyl-l-ethylamine, the phenyl propyl compounds, which showed no sta­ which is just the opposite ofthe pattern displayed by tistically Significant varation in attractancy with amine northern corn rootworms. Benzyl alcohol also cap­ substitution for the alcohol moiety, cinnamyl amine tured significantly more western corn rootworm fe­ (with a double bond in a 3-carbon side chain) at­ males than did benzylamine. None ofthe amines was tracted significantly fewer northern corn rootworms more than marginally attractive to western corn root­ than did cinnamyl alcohol. This latter difference oc­ worm females. curred in both sexes. Although cinnamyl amine at­ Blends of 2-phenyl-l-ethanol and 2-phenyl-l-eth­ tracted significantly more northern corn rootworm ylamine captured at least 100 more northern corn females than did the control, the response difference rootworm beetles than did either component alone, an was only just detectable. increase that was statistically significant for 3 of 4 (E) -Cinnamaldehyde and cinnamyl acetate were dosage combinations (Table 2). In contrast, although intermediate between cinnamyl alcohol and cinnamyl captures showed a tendency to increase with a lO-fold amine in their attractiveness to northern corn root­ increase in dose ofalcohol or amine, the increase was worm females. Ofthese 4 compounds, only cinnamyl fewer than 30 beetles, at most, and not statistically alcohol attracted significantly more northern corn significant for either compound (Table 2, within col­ rootworm males than did the control. umn comparisons). Response of western corn root­ In both the phenyl alkyl alcohol and amine series, worm females to the blends of2-phenyl-l-ethanol and compounds with a 2-carbon side chain were clearly 2-phenyl-l-ethylamine compared with individual more attractive to northern corn rootworm females compounds followed a pattern that was similar to that than were those with shorter or longer chains. Those shown by northern corn rootworms, although cap­ with 4-carbon side chains performed no better than tures were muchlowerfor western than northern corn the control. Northern corn rootworm males tended rootworm (Table 3). Western corn rootworm males toward a similar pattern, but showed differences with were excluded from the analyses because they failed length of the side chain that were less striking than to respond to any treatment in numbers significantly those manifested by the female. exceeding the control. Response patterns of northern and western corn Computational Chemistry. The electrostatic charge rootworms showed little similarity. They shared only was calculated to be -1.10 on the nitrogen atom in the superiority of cinnamyl alcohol over cinnamyl 2-phenyl-l-ethylamine but only -0.70 on the oxygen amine and the tendency for 2-phenyl-l-ethanol to atom in 2-phenyl-l-ethanol. Electrostatic charge was perform better than alcohols with shorter or longer calculated for the benzylamine nitrogen (-1.07) and side chains. Thesefew similarities between the species benzyl alcohol oxygen (-0.69) as well as the3-phenyl­ held only for western corn rootworm females. Males I-propylamine nitrogen (-1.07) and 3-phenyl-l-pro­ showed significant attraction only to (E) -cinnamal­ panol oxygen (-0.73). Electrostatic charge was also dehyde, which also captured significantly more west­ calculated for the cinnamylamine nitrogen (-1.12), ern corn rootworm females than did any of the other the cinnamyl alcohol oxygen (-0.70), and the (E)­ test compounds. cinnamaldehyde oxygen (-0.33). June 1998 PErnOSKI Ac'lD HAMMACK: COR.'I ROOTWOR.\I ATI'RACfAc'lTS 691

Table 2. Respon;;e of northern corn rootworm adul18 to 2-phenyl-I-ethanol (OH), 2-phenyl-I-ethylamine (NH), hoth componnds dispen;;ed separately from the same trap, and nnhaited control

Dose (mg) / trap Capture/trap (mean :: SE) F OH NH OH NH OH+NH Control 3.0 3.0 33.6:: 7.6b 155.6 :: 28.9a 257.5 =52.5a 25.1 :: 9.ob 17.06*** 3.0 30.0 27.9:: 3.1c 16304 :: 30.1b 298.1 :: 39Aa 14.6:: 2.9d 90.12*** 30.0 3.0 30.9:: 3.0c 176.6 :: 25Ab 307.6 :: 20.3a 18.8:: 2.7d 157.78*** 30.0 30.0 44.9:: 8.2c 18204 :: 26.6b 323.9 :: 45.1a 15.0:: 2.8d 153.13*** F 0.64NS O.45NS 1.49NS 0.90NS Pooled Pooled 34.3:: 3.1c 169.5 :: 13.3b 296.8 :: 20.0a 18.4:: 2.5d 206.86***

Means "~thin rows followed by different letters differ at P = 0.05 by Student-Newman-Keuls test after data transformation [In(x + 1) ] and a significant A..c'lOVA (df = 3, 21 or 3,117 before and after pooling, respectively; ***p :$ 0.0001; NS, P > 0.05). Untransformed means and SE are shown. Com was in late milk to dough stage (R3-R4) and mean number of beetles per plant (::SE) was 2.8 :: 0.4.

Discussion formed as well or better than the corresponding al­ cohol. Superiority of the amine over the alcohol was Metcalfand Lampman (1991) were the 1st to show 2-phenyl-l-ethylamine highly attractive to northern obvious only when the side chain was 2 carbons long. corn rootworm beetles. It captured almost 4 times as Large differences in attractiveness between 2-phe­ manv beetles in their tests as did benzvl amine or nyl-l-ethylamine and 2-phenyl-l-ethanol cannot be 4-ph~nyl-l-butylamineand almost twice' as many as explained by differences in lipophilicity or volatility. did 3-phenyl-l-propylamine or cinnamyl alcohol, al­ The octanol!water paction coefficient (Log P) for though the differences were not statistically signifi­ 2-phenyl-l-ethylamine is 1.36 and for 2-phenyl-l-eth­ cantin the latter 2 instances. Ourtest also showed that anol is 1.41 (Hansch et al. 1995). The boiling point phenyl alkyl amines performed best when the side range for 2-phenyl-l-ethylamine is 197-200°C, chain was 2 carbons long. However, our study de­ whereas the boiling point range for 2-phenyl-l-etha­ tected larger differences between responses to the 2­ nol is 219-225°C (Aldrich 1996); however, the mea­ and 3-carbon phenyl alkyl amines; 2-phenyl-l-ethyl­ sured release rate for 2-phenyl-l-ethanol is 30 mole­ amine captured nearly 9 times as many northern corn cules per second, whereas the measured release rate rootworm beetles as did 3-phenyl-l-propylamine. This for 2-phenyl-l-ethylamine is 8.8 molecules per second disparity might arise from regional variation in north­ (Metcalf and Lampman 1991). Western corn root­ ern corn rootworm responsiveness to non-phero­ worm females responded betterto 2-phenyl-l-ethanol monal attractants, as discussed below, or simply from than to 2-phenyl-l-ethylamine (Table 1). differences in the time relative to crop phenology The reason for the difference in attractancy be­ when the tests were conducted. Captures tend to tween 2-phenyl-l-ethylamine and 2-phenyl-l-ethanol increase as corn matures after silking (Hesler et al. might be explained by large differences in electro­ 1994, Hammack and Hesler 1995), and it becomes static charge ofthefunctional moieties. The calculated easier to differentiate among attractants late in the season when our field trapping test was conducted. electrostatic charge on the nitrogen atom in 2-phenyl­ Substitution of an alcohol for an amine moiety had l-ethylamine is -1.10 whereas the calculated electro­ an effect on attractiveness ofphenyl alkyl and aIkenyl static charge on the oxygen atom in 2-phenyl-l-eth­ compounds that varied markedly with both length of anol is only -0.70. These values are in accord with a the side chain and its degree of saturation. Thus, cin­ calculated electrostatic charge of -0.997 on the ni­ namyl amine captured fewer than one-fifth as many trogen atom in methylamine and an electrostatic northern corn rootworms as did cinnamyl alcohol, charge of -0.643 on the oxygen atom in methanol whereas amines having a saturated side chain per- (Tannor et al. 1994). Northern corn rootworms are

Table 3. Respon;;e of western eorn rootworm females to 2-phenyl-1-ethanol (OH), 2-phenyl-I-ethylamine (NH), hoth componnds dispen;;ed separately from the same trap, and nnhaited control

Dose (mg)/trap Capture/trap (mean :: SE) F OH NH OH NH OH+NH Control 3.0 3.0 8.0:: 3.1a 10.3:: 4.3a 18.0:: 8.8a 2.1 0.5b 7.46** 3.0 30.0 3.6:: 1Aab 4.1:: 1.3ab 9.5:: 3.8a 2.5:: 0.8b 3.07* 30.0 3.0 6.6:: 2.2b 7.0:: 2Ab 19.0:: 4.8a 2.0:: 0.8c 14.92*** 30.0 30.0 9.3:: 4.3b 6.1:: 2.3b 14.8 5.8a 2.5:: 0.9b 6.36** F 1.38NS l.42NS 2.93NS 0.21NS Pooled Pooled 6.9:: lAb 6.9:: lAb 15.3:: 3.0a 2.3:: OAc 25.69***

Means within rows followed by different letters differ at P = 0.05 by Student-Newman-Keuls test after data transformation [1n(x + 1)] and a significant A..c'lOVA (df = 3,21 or 3,117 before and after pooling, respectively; *p = 0.05; **p :$ 0.01; ***p :$ 0.0001; NS, P > 0.05). Untransformed means and SE are shown. Com was in late milk to dough stage (R3-R4) and mean number of western com rootworms per plant (=SE) was 0.5 :: 0.1. 692 ENVffiONMENTAL ENTOMOLOGY Vol. 27, no. 3

more attracted to the more alkaline compound, 2-phe­ northern corn rootworms because it substitutes for nyl-1-ethylamine. 2-phenyl-1-ethanol at an OH receptor site. If the Attractant recognition sites have electrostatic and amine and alcohol shared such a similar action and steric preferences for the molecules that fit those sites. differed only in potency, then dispensing blends ofthe Although benzylamine, 2-phenyl-1-ethylamine, and 2 compounds from the same trap should be no more 3-phenyl-1-propylamine have similar charge on the efficacious than doubling the dose of the most effec­ nitrogen atom (-1.07, -1.10, and -1.07respectively), tive single compound. That was not the case for north­ benzylamine has a side chain that is 1 carbon too short ern corn rootworms, which responded in significantly and 3-phenyl-1-propylamine has a side chain that is 1 greater numbers when compounds were blended but carbon too long to optimally fit the hypothetical at­ not when the dose ofeither compound was increased tractant recognition site. Only 2-phenyl-1-ethylamine lO-fold (Table 2, within column comparisons). West­ has the correct size and charge on the heteroatom. ern corn rootworm females showed a similar, although Varying the length of the side chain had a similar less striking, pattern. Our results are more consistent effect on attractancy ofthe phenyl alkyl alcohols as on with a synergistic interaction between alcohol and that ofthe corresponding amines; that is, 2-phenyl-1­ amine, assuming a predictableincrease in capturewith ethanol captured significantly more northern corn increasing dose of the alcohol or amine. The capture rootworms in our test than did alcohols with shorter of diabroticicte beetles on traps baited with volatile or longer side chains. This pattern contrasts with the kairomonal or parakairomal attractants does generally significantly and often sizably higher captures re­ increase linearly with dose plotted logarithically, and ported previously for 3-phenyl-1-propanol compared the response ofboth northern and western corn root­ with 2-phenyl-1-ethanol (Metcalf and Lampman worms to 2-phenyl-1-ethanol is no exception over a 1989a). The major discrepancy appears to be the rel­ range oftest doses from 1.0 to 100 mg pertrap (Metcalf atively greater efficacy of 2-phenyl-1-ethanol in our and Lampman 1989a, 1991; Hammack 1996; L. H. un­ test as compared with those ofMetcalfand Lampman published data). (1989a, 1991). The reason for this difference is un­ Relative attractiveness of (E) -cinnamaldehyde, clear. However, the tests were done in different re­ cinnamyl acetate, and cinnamyl alcohol to northern gions ofthe United States, and geographic variation in corn rootworm adults (Table 1) matched that re­ northern corn rootworm responsiveness to nonphero­ ported in an earlier study. Thus, Metcalf and Lamp­ monal attractants, including phenyl compounds with man (1989) found the alcohol significantly more at­ 2- and 3- carbon side chains, has been suggested (Hes­ tractive than the aldehyde or acetate. They also ler et al. 1994). For example, 4-methoxyphenethanol reported captures with the latter 2 compounds that was about 4 times more attractive than cinnamyl al­ were twice those ofthe control, but neitherdifference cohol or else only half as attractive as the alcohol, was statistically significant in their study in contrast to depending on whethertests were conductedin Illinois our study. (Metcalfand Lampman 1991) or South Dakota (Hes­ Differences in attractancy between cinnamyl alco­ ler et al. 1994), respectively. Differences in trap design hol and (E) -cinnamaldehyde cannot be attributed to orplacement between regions, as well as geographical differences in either lipophilicity or volatility. The variation between northern corn rootworm popula­ octanollwater partition coefficient (log P) for cin­ tions, could also contribute to inconsistencies among namyl alcohol is 1.95 and for (E) -cinnamaldehyde is the studies. 1.90 (Hansch et al. 1995). The boiling point for cin­ Although our study was designed to examine struc­ namyl alcohol is 250°C whereas the boiling point for ture-activity relationships in northern corn root­ (E) -cinnamaldehyde is 248°C (Aldrich 1996). The worms, data for western corn rootworms were also measured release rates for both compounds are 2.5 X included because ofthe difference between species in 1014 molecules per second (Metcalf and Lampman efficacy ofthe phenyl alkyl alcohols and amines. In no 1991). case was the amine superiority characteristic ofnorth­ The reason for the differences in attractancy be­ ern corn rootworms evident amongwestern corn root­ tween cinnamyl alcohol and (E) -cinnamaldehyde worms. Instead, cinnamaldehyde was the most effec­ might also be explained by large differences in elec­ tive ofourtest compounds for western corn rootworm trostatic charge. The calculated electrostatic charge beetles, although it is considered to be only a mod­ on the nitrogen atom in cinnamyl alcohol is -0.70, erately effective attractant for this species when used whereas the calculated electrostatic charge on the alone (Metcalfand Lampman 1989a). 2-Phenyl-1-eth­ oxygen atom in (E) -cinnamaldehyde is only -0.33. anol, which captured 15 times more females than did Cinnamyl acetate has an acetate function making the the control in our study, was a distant 2nd to cinna­ molecule larger than cinnamyl alcohol. The size dif­ maldehyde and statistically no better than cinnamyl ference could account for the difference in attracta­ alcohol, which is only a very weak western corn root­ ncy between these 2 compounds. worm attractant (Metcalf and Lampman 1989c, Ham­ Although cinnamylarnine has an electrostatic mack 1996). 2-Phenyl-1-ethanol was not previously charge of - 1.12, the compound has only slight activity found attractive to western corn rootworm adults as an attractant in the field bioassay (Table 1). Our (Metcalf and Lampman 1989a, c, 1991). dataconcerning2-phenyl-1-ethylamine and 2-phenyl­ Our field trapping results did not support the sup­ I-ethanol suggest different recognition sites for the 2 position that 2-phenyl-1-ethylamine is attractive to compounds (Table 2). It is therefore possible that a June 1998 PETROSKI fu'ln HAMMACK: CORN ROOTWORM ATTRACffu'lTS 693 similar situation exists in the case of cinnamylamine Hammack, L. 1996. Corn volatiles as attractants for north­ and cinnamyl alcohol and that cinnamylamine is ern and western corn rootworm beetles (Coleoptera: poorly recognized. Chrysomelidae: Diabrotica spp.). J. Chern. Ecol. 22: 1237­ 2-Phenyl-l-ethylamine has not been reported 1253. among corn or squash (Cucurbita spp.) volatiles, and Hammack, L., and L. S. Hesler. 1995. Seasonal response to phenylpropanoid attractants by northern corn rootworm the biological significance ofthe strong northern corn beetles (Coleoptera: Chrysomelidae). J. Kans. Entomol. rootworm response to this compound remains un­ Soc. 68: 169 -177. clear. Indole, another nitrogen-containing compound Hansch, C., A. Leo, and D. Hoekman. 1995. Exploring more attractive to western than northern corn root­ QSAR: hydrophobic, electronic, and sterlc constants, p. worms, has been reported from corn (Turlings et al. 45. ACS Professional Reference Book. American Chem­ 1991, Thompson et al. 1974) and squash blossoms ical Society, Washington, DC. (Andersen and MetcalfI986). In thelattercase, indole Hesler, L. S., D. R Lance, and G. R Sutter. 1994. Attrac­ acts as a strong olfactory synergist when blended with tancy of volatile non-pheromonal semiochemicals to other floral attractants (Metcalf et al. 1995). Cinna­ northern corn rootworm beetles (Coleoptera: Chry­ monitrile and especially 4-methoxycinnamonitrile somelidae) in eastern South Dakota. J. Kans. Entomol. also attract western corn rootworms buthave notbeen Soc. 67: 186 -192. Kaiser, R 1991. Trapping, investigation and reconstitution reported from host plants (Metcalf and Lampman of flower scents, pp. 213-250. In P. M. Miiller and D. 1989b, Lance 1990), although smaller nitriles and Larnparsky [eds.], Perfumes: art, science and technology. oximes are released by corn seedlings after herbivore Elsevier, London. damage (Takabayashi et al. 1995). Similar small Knudsen, J. T., L. 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