Journal alChemical Ecology. Vol. 13, No.4. 1987 6174 * SEMIOCHEMICAL ATTRACTANTS OF Diabrorica undecimpuncrara hOlVardi BARBER, SOUTHERN CORN ROOTWORM, AND Diabrorica virgijera virgijera LECONTE, THE WESTERN CORN ROOTWORM (COLEOPTERA: CHRYSOMELIDAE) R.L. LAMPMAN,' R.L. METCALF,' and J.F. ANDERSEN1 I D~partmem 01 Entomology Unh'ersiry ofIllinois Urbana-Champaign. Illinois 61801 2USDA-ARS North Regional Research Center Pt!oria. Illinois. 61604 (Received April 22, 1986; accepted June 9. 1986) Abstract-DUring the summers of 1984 and {98S. a variety of structurally related benzenoid compounds was evaJuated in sweet com plms as anractams for adult southern com rootworms (SCR), western com rootworms (WCR), and nonhem com rootwonns (NCR). Field response to the volatiles was mea· sured by beetle COUntS on baited cylindrical sticky traps placed inside the corn plots al a height of 1 m above ground level. SCR adults were auracled late in the season (last week of August through September. 1984 and 1985) to numerous aromatic compounds. inclUding phenylacetaldehyde. benzyl ace~ tone. phenethyJ alcohol. phenyl acetate. indole. veratrole. methyl eugenol. methyl isoeugenol. eugenol. and isoeugenol. Although many compounds at­ tracted SCR adults late in the season. only verauule. phenylacetaldehyde. and chavicol were significantly active in early and middle August 1985. WCR adul[S were attracted to a different group of compounds. namely estragole. trans-anethole. and indole. Estragole (4-methoxy-l-ailylbenzene) was an ef­ fective WCR attractant from com tasseling in earJy AugUSt 1985. until the end of the trapping period in late September and early October 1985. Indole and trans-anethole (4-methox;y-/-propenylbenzene) were less effective anrac~ tams than estragole and were most active at the beginning and/or end of the com season. Traps baited with 100 mg of estragole caught an average of 20 times more WCR adul[S [han unbaited control traps. and the females outnum­ bered the maJes in the baited lraps. Estragole dosage tests were conducted in three sweel com plots on different dates in 1985 and Ihe minimum effective dose ranged between 5 and 30 mgltrap. Field tests with stroctural anaJogs reveaJed the impormnce of the site of unsaturation in the ally lie side chain of 959 (l()q1l·onI/1l7'0J11O·oq~qSO~oom .c. 1987 Plenum Publlshln8 COrpl,lr.lUon 960 LAMPMAN ET AL. esuagole and the effect of different ring substimcnts on WCR response. The phenylpropanoids. eugenol and isoeugenol. significantly attracted NCR adults. even though these beetles were in low abundance in the test com plots. Field tests indicate there IS no cross-species response by WCR and NCR adults to their related phenylpropanoid attractants. However. in late August. SCR adults do respond to some WCR and NCR attractants (indole and several eugenol analogs). Electroantennographic analysis of SeR males reve:lIed they can perceive peripherally a wide range of benzcnoid com­ pounds. Key Words-Diabrorica. Coleoptera. ChrysomeJidat:. western com root­ wann, southern com roorwonn. nonhem com rootwonn. attractants. semi­ ochemicals. vcrturcle. esrragole. frans-anethole. indole. eugenol. phenyl~ acetaldehyde. INTRODUCTION Larvae and adults of the northern com rootworm (NCR). Diabrorica barben Smith and Lawrence, and the western com rootWorm (WCR). D. virgifera vir­ gifera LeConte, are serious root and silk pests of field and sweet com in the com belt. The univoltine NCR and WCR overwinter as diapausing eggs in North America and the oligophagous larvae develop only on the roots of grasses (Po­ aceae), primarily com (Branson and Krysan, 1981: Branson and Ortman. 1967, 1971; Smith. 1966). In contrast to these two Diabrotica species. the multivol­ tine southern com rootworm (SCR) = spotted cucumber beetle. D. undecim­ punctata howardi Barber. overwinters in southern areas as an adult. annually reinvades the Midwest. and both larvae and adults are polyphagous (Smith. 1966: Branson et al., 1978). SCR bettles are pests of cucurbits. peanuts. com. and a variery of vegetable and field crops (Campbell and Emery. (967). Although the New World diabroticites (Chrysomelidae: Galerucinae: Lu­ perini: Diabroticina) have greatly expanded their host distribution and range from their origins. they apparently retain an ancestral compulsive feeding re­ sponse to the bitter-tasting cucurbiracins found in the cotyledons. foliage. fruit. and flowers of many species of the Cucurbiraceae (Chambliss and Jones. 1966: Sharma and Hall. 1973: Howe and Rhodes. 1976: Metcalf et al.. 1982: Fer­ guson et aJ.• 1983; Andersen. 1984). Cucurbiracins are undoubtedly potent kai­ romones for the diabroticites. as well as potent allomones for many other her­ bivores and for some diabroticite predators (Metcalf, 1979; Tallamy. 1985: Ferguson and Metcalf. 1985). yet their high molecular weights and low vapor pressures make them ineffective as volatile semiochemicals (Branson and Guss. 1983). Considerable progress has been made recently in understanding Diabrorica response to volatile attractants. The sex pheromone of WCR virgin females. 8­ methyl-2-decyl propanoate. attracts both WCR and NCR males; however, the ROOTWORM AlTRACTANTS 961 two species demonstrate temporal differences in response and high doses of the racemic synthetic mixture inhibits NCR response (Guss et al., 1982. (985). SCR females release lO-methyl-2-uidecanone and the R enantiomer is the most active anractant for male SCR and D. u. undecimpunctata. the western sponed cucumber beetle (Guss et a1., 1983). Furthermore. the nonpheromonal phen­ ylpropanoids eugenol. isoeugenol. and 2-methoxy-4-propylphenol strongly at­ tract NCR adults, whereas WCR adults do not respond to these compounds (Ladd et al.• 1983; Ladd. 1984). Andersen and Metcalf (1986) isolated the shikimic acid derivative indole from the male blossoms of Cucurbita maxima cultivars. where Diabrotlca and Acalymma adults often congregate in large numbers. and found adult WCR and striped cucumber beetles. Acalymma vlt­ tarum (Fabr.), are anracted early and late in the season to as linle as 5 mg of indole. Although indole is clearly a kairomonal attractant of WCR adults. a host-plant relationship has not been established in the literature for the attrac- tants of NCR adults (Ladd. 1984). During the summers of 1984 and 1985. we investigated the response of WCR. SCR, and NCR adults to a wide variety of benzenoid compounds using baited. one-quart (0.95-liter) white cylindrical sticky traps in sweet com plots. Chemical analogs of anractive compounds were used to determine the specific­ ity of response by the com rootworm species. This report summarizes the data obtained with more than 20 aromatic compounds. many of which have been detected in com orcucurbits (Bunety et al.. 1978. 1980. 1982; Andersen. 1984). A preliminaty electroantennographic (EAG) study with SCR males evaluates their response to several benzenoid compounds. METHODS AND MATERIALS Field Tests. During the summers of 1984 and 1985. various volatile com­ pounds were evaluated for com lOotworm attraction on the South Farms of the University of Illinois in Urbana. Illinois. In 1984. tests were conducted in a single sweet com plot which measured 52 x 22 m with eight lOWs each of cultivars. "Florida Stay Sweet" and "Gold Cup." The com plot was bordered on one side by a grass lane and on the other side by a cucurbit plot. The adjacent cucurbit plot included several common squash varieties (predominantly Cucur­ blta maxima cv. "Blue Hubbard"). as well as high cucurbitacin-containing spe­ cies and hybrids (Cucurbita andreana, C. texana. and C. andereana x C. max­ Ima hybrids) (Rhodes et al .. 1980). Large numbers of SCR adults (> 20,000 beetles) aggregated on the leaves. blossoms. and fruits of the bitter cucurbits and "Blue Hubbard" cultivar in 1984 and 1985. In both years. SCR adults were ca. 10-20 times more abundant than WCR and A. vltratum adults during the test period. The experimental design for the main plot used in 1985 was essentially the same as in 1984. except the com was a monoculture of 20 rows 962 LAMPMAN ET AL. of cultivar "lllini Xtra Sweet." Tests were also conducted in 1985 in two non­ adjacent sweet com plots located approximately 150 m and 250 m from the main plot. These auxilliary plots were not adjacent to any cucurbits and WCR adults were the predominant rootworm species present. The 1984 test plot was planted on June 12 and initial tests were conducted in late August after tasseling. Afterthe first frost (last week ofSeptember 1984). field tests were discontinued. In 1985. trapping began in mid-July. before tas­ seling. and continued until the com foliage was totally dry in late September. The two auxiliary sweet com plots were used to test WCR attractants and were planted approximately tWO and four weeks. respectively. after the main plot (June 6. 1985) and were used until the first week of October. Pretest whole­ plant counts were taken every other week in the main plot and once in the two auxiliary plots by counting beetles in the rows used for testing treatments. All compounds tested. except two. were from commercial sources and ver­ ified as being :,,95% pure by gas chromatographic analysis. Chavicol (4-hy­ droxy-I-allylbenzene) was prepared (R.L.M.) by the method of Buu-Hoi et al. (1954) and 4-methoxy-l-propylbenzene by reacting the sodium salt of 4-pro­ pylphenol with dimethyl sulfate. The products were glass distilled and purity and identiry confirmed by boiling points. infrared analysis. and gas chromatog­ raphy-mass spectrometry. Compounds were field tested for attraction of roOt­ worms by treating dental cotton wicks with 200 mg or less of each compound (see Tables). In order to prolong volatilization of the treatment compound. the wicks (ca. 15 mm long x 6 mm diameter) were soaked in polyethylene glycol and the excess squeezed out prior to treatment with each test compound. The treated wicks were attached to the tops of one-quart (0.95-liter) white paper caftons. similar to those described by Hein and Tollefson (1984).