Responses of northern and western corn rootworms to semiochemical attractants in corn fields

Small plots (18 × 18 m) were treated with grids of cotton wicks that contained semiochemicals for adultDiabrotica barberi Smith and Lawrence, the northern corn rootworm (NCR). In plots treated with eugenol (350 g/hectare), NCR were attracted to point sources of the compound, but there were no significant changes in numbers of either NCR orD. virgifera virgifera LeConte, the western corn rootworm (WCR), found on plants in the plots. In plots treated with 12.5 mg/hectare of 8R-methyl-2R-decyl propanoate (2R,8R-MDP, the apparent female-produced sex pheromone of NCR and WCR), males of both species were attracted to point sources, but beetles did not congregate within treated plots. With racemic 2,8-MDP at 1.0 g/hectare, male WCR were attracted into plots, but NCR of both sexes were strongly repelled. In a separate study, capture of beetles at pheromone-baited traps declined when the surrounding area contained wicks that emitted racemic 2,8-MDP. In treated plots, male WCR were relatively inefficient at finding pheromone sources. With NCR, emigration from plots could account totally for the observed 3- to 10-fold reduction in catch at 0.01–1.0 g/hectare.Coleoptera: Chrysomelidae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Response of northern corn rootworm,Diabrotica barberi Smith and Lawrence,to stereoisomers of 8-methyl-2-decyl propanoate

The four stereoisomers of 8-methyl-2-decyl propanoate were tested in South Dakota for attractiveness to the northern corn rootworm,Diabrotica barberi Smith and Lawrence (NCR). Only the 2R,8R configuration was attractive to the NCR. Inhibition of the NCR response to 2R,8R occurred when either the 2S,8R or 2S,8S isomers were components of the pheromone source. The 2R,8S configuration elicited no behavioral activity in the NCR.Coleoptera: ChrysomelidaeMention of a commercial or proprietary product does not constitute an endorsement by the USDA.Deceased.     

Response ofDiabrotica virgifera virgifera,D. v. Zeae,andD. porracea to stereoisomers of 8-methyl-2-decyl propanoate

The four stereoisomers of 8-methyl-2-decyl propanoate were tested in the United States and Mexico for attractiveness toDiabrotica virgifera virgifera LeConte, the western corn rootworm,D. v. zeae Krysan and Smith, the Mexican corn rootworm, andD. porracea Harold. Males ofD. v. virgifera andD. v. zeae responded strongly to the (2R,8R)-isomer and secondarily to (2S,8R), whileD. ponacea responded exclusively to the (2S,8R)-isomer. The (2S,8S)- and (2R,8S)-isomers were inactive in all tests. Synergism or inhibition was not detected when various mixtures of the isomers were tested withD. v. virgifera. These phenomena were not tested withD. v. zeae andD. ponacea.Coleoptera: Chrysomelidae.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Identification of Epoxyhenicosadiene and Novel Diepoxy Derivatives as Sex Pheromone Components of the Clear-Winged Tussock Moth Perina nuda

Four EAG-active components (A–D) were found in the solvent extract of virgin females of the clear-winged tussock moth, Perina nuda. The most abundant component (B, ca. 250 ng/female) was identified as (3Z,6S,7R,9Z)-6,7-epoxyhenicosa-3,9-diene by GC-MS analyses of the extract, chemical derivatization, and comparative chiral HPLC. Minor components also elucidated were (3Z,9Z)-cis-6,7-epoxyicosa-3,9-diene, (A); (3R,4S,6S,7R,9Z)-3,4-6,7-diepoxyhenicos-9-ene, (C); and its 3S,4R,6S,7R isomer, (D); with amounts of 0.4, 5, and 8 ngt/female, respectively. Component B showed weak attractiveness to male moths in the field. The attractiveness was significantly enhanced by addition of component(s) C and/or D. No males were captured with either the antipode of component B or its mixtures with the minor components. In this field test, noctuid Hypocala rostrata males were also attracted with the synthetic P. nuda pheromone.     

Identification of a female-produced sex pheromone of the western corn rootworm

A sex pheromone has been isolated and identified from virgin females of the western corn rootworm (WCR),Diabrotica virgifera virgifera LeConte. The synthesized compound, racemic 8-methyl-2-decanol propanoate, was equal in attraction to the natural pheromone when tested in the field as a trap bait against three taxa ofDiabrotica known to respond to pheromone extracts from female WCR. Five taxa (D. virgifera virgifera; D. virgifera zeae Krysan and Smith, Mexican corn rootworm;D. longicornis barberi Smith and Lawrence, northern corn rootworm;D. longicornis longicornis (Say); andD. porracea Harold) were attracted to traps baited with 8-methyl-2-decanol propanoate. The response of male northern corn rootworms (NCR) in the field peaked at a relatively low concentration of 8-methyl-2-decanol propanoate and then was severely reduced at the higher concentrations tested. Conversely, the response of male WCR in the field continued to increase up to the highest dose tested.     

Identification of a volatile attractant forDiabrotica andAcalymma spp. from blossoms ofCucurbita maxima duchesne

Fractionation of headspace volatiles fromCucurbita maxima blossoms by high-performance liquid chromatography resulted in the isolation of a single component which was highly active in an electroantennogram bioassay onDiabrotica undecimpunctata howardi antennae. This compound was identified as indole by gas chromatography-mass spectrometry. Field-trapping bioassays were conducted which indicated that indole is a potent attractant of the western corn rootworm,D. virgifera virgifera, and the striped cucumber beetle,Acalymma vittatum. The southern corn rootworm,D. u. howardi, did not respond, despite its strong EAG response. The sex ratio ofD. v. virgifera found in indole-baited traps varied seasonally. Males were trapped in abundance in late July and later September, 1983, while females were more abundant August and early September. The effectiveness of indole as aD. v. virgifera attractant also varied seasonally. A prolonged period of depressed trap catches occurred in early August 1983, during the silking and tasseling period of the corn in the field where trapping was carried out.Coleoptera: Chrysomelidae.     

Chirality of israeli pine bast scale,Matsucoccus josephi (homoptera: Matsucoccidae) sex pheromone

The absolute configuration of the sex pheromone of the Israeli pine bast scale,Matsucoccus josephi, was determined as (2E,5R,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one, designated here asR-E with 10% (2E,5S,6E,8E)-5,7-dimethyl-2,6,8-decatrien-4-one, designated asS-E. The chirality of the quantitatively minorZ isomer was (2E,5R,6Z,8E)-5,7-dimethyl-2,6,8-decatrien-4-one (R-Z). Chiral assignments were made by comparative gas chromatographic (GC) analysis of naturalM. josephi pheromone with stereoselectively synthesized stereoisomers on a chiral Cyclodex-B column, which separated the enantiomers with baseline resolution. In gas chromatographic-electroantennographic detection (GC-EAD) analysis of the racemicZ andE isomers, the latter elicited the stronger antennal response by maleM. josephi. In GC-EAD of all four stereoisomers, employing the chiral column,R-E was the most active stereoisomer. In field testsR-E attracted 10 times more males ofM. josephi than didS-E. The racemicE/Z pheromone mixture, containing all four stereoisomers in approximately equal amounts, attracted as many maleM. josephi as did an equivalent amount ofR-E, indicating that the other stereoisomers are not inhibitory. The same keto-diene moiety with the same chiral center and configuration in all three known Matsucoccidae sex pheromones implies a common biosynthetic pathway and phylogenetic relationship.Contribution from the Agricultural Research Organization, the Volcani Center, No. 1496-E, 1994 series.Part of the work was performed during a sabbatical leave of E.D. at Simon Fraser University.     

Pheromone specificity inEriocrania semipurpurella (Stephens) andE. sangii (Wood) (Lepidoptera: Eriocraniidae) based on chirality of semiochemicals

The fifth abdominal segment of femaleEriocrania semipurpurella (Stephens) andE. sangii (Wood) contains a pair of exocrine glands. Hexane extracts of this segment were prepared from both species and analyzed by gas chromatography with simultaneous flame ionization and electroantennographic detection (EAD). For both species, the EAD active peaks were identified as nonan-2-one, (Z)-6-nonen-2-one, and (Z)-6-nonen-2-ol by means of mass spectrometry and comparison of retention indices with those of synthetic standards. Enantiomeric separation of chiral alcohols from the female extracts was achieved by gas chromatographic analysis on a cyclodextrin column. InE. semipurpurella, a mixture of (2S,6Z)-nonen-2-ol and (2R,6Z)-nonen-2-ol (2: I) was found, whereas inE. sangii (2S,6Z)-nonen-2-ol was the predominant enantiomer and only traces of theR enantiomer were indicated by the antennal response. In field tests, a blend of the three compounds was not attractive to conspecific males. A subtractive assay showed that the alcohol in various enantiomeric mixtures was the only attractive compound, whereas addition of (Z)-6-nonen-2-one to the alcohol completely inhibited the attraction of both species. A trapping experiment including a wide range of ratios between theR andS enantiomers showed that baits containing 95–100% of theS enantiomer were attractive to maleE. sangii, whereas males ofE. semipurpurella were attracted to all tested ratios of the enantiomers. However, the response profiles of maleE. semipurpurella differed between populations from southern Sweden, south Finland, and the Kola Peninsula in Russia. In south Sweden males were maximally attracted to a racemic mixture of the alcohols. At the Kola PeninsulaE. semipurpurella was attracted to baits containing 95–100% of theR enantiomer. In south Finland all tested ratios between 0 and 100%R enantiomer trappedE. semipurpurella, but the trap catches appeared to be bimodally distributed with peaks around 15 and 70%R enantiomer. The trapping results suggest the existence of pheromone races or sibling species among the specimens identified asE. semipurpurella.Dedicated to Prof. H. J. Bestmann on the occasion of his 70th birthday.     

Identification,synthesis, and bioactivity of a male-produced aggregation pheromone in assassin bug,Pristhesancus Plagipennis (Hemiptera: Reduviidae)

Pristhesancus plagipennis, a large Australian assassin bug, possesses three pairs of dorsal abdominal glands (DAGs). In the male, the anterior and posterior glands are hypertrophied and secrete an attractant pheromone. Gas chromatography-mass spectrometry (GC-MS) analyses of male DAG extracts and airborne volatiles emitted from calling males showed the pheromone signature to be dominated by a novel component. Subsequent chemical manipulations, GC-MS, and chiral-column analyses established its identity as (Z)-3-hexenyl (R)-2-hydroxy-3-methylbutyrate. Minor components included 3-methylbutanol, 2-phenylethanol, (Z)-3-hexenol, decanal, (E)-2-hexenoic acid, and three minor hexenyl esters. Bioactivity studies using laboratory olfactometers and outdoor flight cages demonstrated attraction by femaleP. plagipennis to calling males, heptane extracts of male posterior DAGs and a synthetic formulation of the (Z)R enantiomer of the major ester, alone or in combination with other components of male anterior and posterior DAGs. Males were also attracted to the major ester. The racemate andS enantiomer of the ester were not attractive. Contamination of the (Z)R enantiomer with 30–60% of theE isomer also made the compound nonattractive. This is the first report of an aggregation pheromone in the Reduviidae. The prospects for pheromonal manipulation ofP. plagipennis populations to enhance the value of this predator in horticultural ecosystems, are discussed.     

Field response of maritime pine scale,Matsucoccus feytaudi duc. (Homoptera: Margarodidae), to synthetic sex pheromone stereoisomers

The absolute configuration of the primary component of the maritime pine scale (Matsucoccus feytaudi) pheromone (i.e., (8E, 10E)-3,7,9-trimethyl-8,10-dodecadien-6-one) was determined as 3S,7R by field-trapping experiments using synthetic stereoisomers and according to previous NMR considerations. The 3R,7R isomer showed similar activity to 3S,7R, whereasM. feytaudi males responded very weakly to the two other candidates (3R,7S and 3S,7S). Further studies were conducted to optimize scale trapping for monitoring scale populations. Results of these studies showed that the trapping efficiency was related to pheromone dose, trap area, and wind speed but not to trap height.     

Attractancy and species specificity of 6-acetoxy-5-hexadecanolide,a mosquito oviposition attractant pheromone

Four stereoisomers of 6-acetoxy-5-hexadecanolide, a mosquito oviposition attractant pheromone, were bioassayed for their activity on mosquitoes. Only (–)-(5R,6S) isomer was active in attractingCulex quinquefasciatus Say females for oviposition at dosages of 0.5 g/100 ml water and above with the floating-cap method. The activity of this isomer increased 50-fold when it was applied directly to the water surface. The other three isomers, (+)-(5S,6R), (+)-(5R,6R), and (–)-(5s, 6s), were not active. The active isomer was ovipositionally attractive not only toC. quinquefasciatus but also toC. tarsalis Coquillett; however, it was 100 times more active in the former than in the latter species.Aedes aegypti (L.) andAnopheles quadrimaculatus Say were not attracted to the pheromone, thus suggesting that the pheromone is genus-specific.     

Factors influencing distribution ofDiabrotica spp. in blossoms of cultivatedCucurbita spp.

Cultivars representing three species ofCucurbita were examined for blossom preference byDiabrotica spp.C. maxima cultivars were found to be preferred byD. undecimpunctata howardi over those ofC. pepo andC. moschata.D. virgifera virgifera preferredC. maxima and the Connecticut Field cultivar ofC. pepo.C. moschata and other cultivars ofC. pepo were not preferred. Cultivars were examined for differences in floral volatile release, blossom cucurbitacin content, and pollen content of male blossoms.C. maxima male blossoms released a larger quantity of volatiles thanC. pepo orC. moschata. Also, onlyC. maxima male blossoms contained cucurbitacins. Cultivars ofC. moschata contained the largest quantities of pollen, but all three species contained relatively large quantities. The data indicate a correspondence ofD. u. howardi distribution in the field with high volatile release rates and high cucurbitacin levels that are found inC. maxima blossoms.D. v. virgifera distribution appears to be somewhat independent of these factors since this species was abundant in blossoms of aC. pepo cultivar as well as cultivars ofC. maxima.Coleoptera: Chyrsomelidae.     

Indole as an olfactory synergist for volatile kairomones for diabroticite beetles

Olfactory synergism, where combinations of plant volatile kairomones are quantitatively more attractive to insects than the sum of attraction of the individual components, is an important but little-studied phenomenon in host plant selection and feeding and in pollination ecology. Diabroticite beetles (Coleoptera: Chrysomelidae) are strongly attracted toCucurbita blossoms, and 2- to 3-fold olfactory synergism has been demonstrated in four species by combinations of the key blossom volatiles, 1,2,4-trimethoxybenzene, indole, and (E)-cinnamaldehyde. This TIC mixture represents an optimizedCurcurbita blossom volatile kairomone mixture useful in monitoring Diabroticite populations and in studying their behavior and ecology. Indole, which exhibits a spectrum of attraction to these beetles ranging from moderate forDiabrotica virgifera virgifera andAcalymma vittatum to very weak forD. barberi, is the primary synergistic component. Indole combined with 4-methoxycinnamaldehyde was significantly synergistic toD. v. virgifera at a ratio of 1:300 and produced 4-fold synergism at a ratio of 1:1. Indole combined with 4-methoxyphenethanol was less synergistic toD. barberi with 1.5- to 2-fold synergism at a 1:1 ratio. These consistent variations in diabroticite beetle olfactory responses presumably indicate evolutionary divergences in the numbers of relict indole antennal receptors.     

Attraction of adultDiabrotica (Coleoptera: Chrysomelidae) to corn silks and analysis of the host-finding response

Volatile chemicals from corn silks attractedDiabrotica virgifera virgifera LeConte andD. barberi (Smith and Lawrence). The behavioral response of both species of beetles to the host plant was typified by four distinct phases: perception, random movement, orientation to the source, and search with reorientation. The perception phase was composed of stationary behaviors, while the random, orientation, and search phases were composed of directed and nondirected movements. Each of the movement phases had a characteristic response pattern composed of the ratio of upwind, lateral, and downwind walking and flight movements, which affected net displacement of the beetle in the flight tunnel. The perception phase occurred within and between the other phases and was responsible for initiating changes from one movement phase to another (based on the presence or absence of volatiles from corn silks). Host finding was flexible, and the response pattern fit a flow-chart type of response, rather than a single stereotyped sequence of behaviors.     

Odors influence choice of oviposition sites byDiabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

FemaleDiabrotica virgifera virgifera LeConte were allowed to choose between oviposition substrates that were and those that were not associated with potential sources of semiochemicals. Females deposited over five times more eggs on moist towelettes that were treated with homogenates of female abdomens than on towelettes treated with distilled water. Similar results were obtained when screening separated the homogenates from the towelettes, indicating that odors alone could elicit the response. In contrast, females did not choose towelettes that had previously been used for oviposition or towelettes containing eggs over unused towelettes. Further tests with homogenates of abdomens and a bacteriostatic agent (sorbate) indicated that the females were probably responding to bacterial odors rather than an oviposition-enhancing pheromone. Four strains of bacteria were isolated from a homogenate of female abdomens; females deposited 4 to 16 times more eggs on substrates with odors of the bacteria than on substrates with odors of uninoculated nutrient agar. In no-choice tests, bacterial odors did not increase the number of eggs deposited per female beetle; however, in choice tests with dishes that tended to retain any beetles that entered, there were more eggs per female (but not more beetles) after 24 hr in dishes with bacterial odors than in those without the odors. Females also chose dishes with odors of excised maize (Zea mays L.) roots or elevated levels of carbon dioxide over control dishes.Mention of a commercial or proprietary product does not constitute an endorsement for its use by USDA.     

Pheromone-dependent species recognition mechanisms betweenNeodiprion pinetum andDiprion similis on white pine

The sex pheromones ofNeodiprion pinetum (Norton) andDiprion similis (Hartig) consist of two isomers, 2S,3S,7S and 2S,3R,7R, in either the acetate orpropionate forms of 3,7-dimethylpentadecan-2-ol, respectively. The 2S,3S,7S acetate isomer is utilized byN. pinetum as the major pheromone component and the 2S,3R,7R acetate as a Synergist. ConverselyD. similis utilizes 2S,3R,7R as propionate the major pheromone component and 2S,3S,7S propionate as a Synergist. This was confirmed in the field in both Michigan and Wisconsin. Capillary gas-liquid chromatographie analyses revealed that these two isomers are present in the natural pheromones of both species at the ratios close to those predicted by artificial blending of the two optical isomers.     

A sex attractant for the scarab beetle Anomala solida Er

(R,Z)-5-(-)-(Oct-1-enyl)oxacyclopentan-2-one (R-buibuilactone) attracted male Anomala solida Er. (Coleoptera: Scarabaeidae, Rutelinae), a vineyard and orchard pest in Southeastern Europe. The presence of the corresponding (S) enantiomer or of 2-(E)-nonen-1-ol (a frequently found pheromone component in other Anomala spp.) in the bait did not influence catches. Traps baited with (R,Z)-5-(-)-(oct-1-enyl)oxacyclopentan-2-one were successfully used for monitoring the flight of A. solida, and may have practical applications for detection, monitoring, and mass trapping of the pest.     

Field response and gas-liquid chromatograph separation of optically active synthetic and natural pheromones in two sympatric diprionid sawflies,Neodiprion nanulus nanulus andNeodiprion sertifer (Hymenoptera: Diprionidae)

The male red pine sawflyNeodiprion nanulus nanulus Schedl responds mainly to the (2S,3S,7S)-3,7-dimethylpentadecan-2-yl acetate (2S,3S,7S-A) in the field. No other isomer is as effective by itself or syner-gizes 2S,3S, 7S-A in this species. ForNeodiprion sertifer (Geoffroy), however, we confirmed our earlier report that males responded significantly to a 50.003 mixture of 2S,3S,7S-A and either 2S,3R,7R-A or 2S,3R,7R/S-A. The 2S,3S,7S-A isomer was separated from 2S,3R,7R-A by capillary gas-liquid chromatographic (GLC) analysis using Carbowax 20 M and DB-5 columns. The latter column also separated 2S,3S,7S-A from 2S,3R,7S-A. Only 2S,3S,7S-A was found in the natural pheromones ofN. n. nanulus andN. sertifer by GLC analysis.     

Sex phermone components of mulberry looper,Hemerophila atrilineata butler (lepidoptera: Geometridae)

(6Z-9S, 10R)-Epoxy-octadecene (SR-1) and (3Z, 6Z-9S, 10R)-epoxy-octadecadiene (SR-2) are sex pheromone components of the mulberry looper (MBL),Hemerophila atrilineata Butler. Compounds extracted from female MBL pheromone glands were identified by coupled gas chromatographic-electroantennographic detection (GC-EAD) and GC-mass spectrometry. In field experiments in China,SR-2,RS-2, or both combined were hardly attractive, butSR-2 in combination withSR-1 attracted significant numbers of MBL males. Synergistic behavioral activity ofSR-1 plusSR-2, but not of corresponding antipode mixtures, indicates enantiospecificity of MBL pheromone communication. Because blends of racemic and enantiospecific (SR)1 plus2 were similarly attractive, racemic1 plus2 may have potential for mass trapping or confusion of MBL males in commercial mulberry plantations.     

Structure-activity studies on aggregation pheromone components ofPityogenes chalcographus (Coleoptera: Scolytidae)

Syntheses of all four Stereoisomers (2S,5S; 2S,5R;2R,5R; and2R,5S) of chalcogran, a major component of the aggregation pheromone ofPityogenes chalcographus, and of all four isomers (2Z,4Z; 2Z,4E; 2E,4E; and 2E,4Z) of methyl 2,4-decadienoate (MD), the second major pheromone component, are briefly described. Attraction responses of walking beetles of both sexes were tested to mixtures of the synergistic pheromone components or analogs. These bioassays showed that theE,Z isomer of MD is the most active when tested with chalcogran. When tested with (E,Z)-MD, (2S,5R)-chalcogran was the most active stereoisomer, while 2R,5R and 2R,5S isomers had intermediate activities, and the 2S,5S isomer was inactive. There was no evidence that the relatively less active Stereoisomers of chalcogran inhibited or promoted attraction to (2S,5R)-chalcogran with (E,Z)-MD. Male beetles only produce the activeE,Z isomer of MD (inactive alone) and their hindguts contain the most active (2S,5R)- and least active (2S,5S)-chalcogran. A mixture of all MD isomers with racemic chalcogran was not significantly different in attractivity compared to (E,Z)-MD with racemic chalcogran, indicating no synergistic or inhibitory effects of the inactive isomers of MD.