A. M. Pierce

Chemical communication in cucujid grain beetles

Males of five sympatric species of economically damaging cucujid grain beetles,Cryptolestes ferrugineus (Stephens),C. pusillus (Schönhen),C. turcicus (Grouvelle),Oryzaephilus mercator (Fauvel), andO. surinamensis (L.), produce macrolide aggregation pheromones especially in the presence of food. Work leading to the isolation, identification, and establishment of biological activity of these semiochemicals is reviewed. The trivial name “cucujolide” is proposed and used to identify these compounds that are characteristic of the Cucujidae. The twoOryzaephilus share species share a common cucujolide pheromone, whileCryptolestes species use cucujolides that are either enantiomeric, unique to the genus, or released in trace quantities byOryzaephilus spp. and not used as pheromones by the latter species. The major mechanisms for species specificity in chemical communication are: (1) presence of a unique pheromone (C. ferrugineus andC. pusillus); (2) use of pheromones that are inactive alone but synergize response to cucujolides unique to a species (C. pusillus, C. turcicus, andO. surinamensis); (3) response to only one enantiomer of a pheromone (C. ferrugineus, O. surinamensis, andO. mercator); and (4) synergism between enantiomers of a pheromone (C. turcicus). The only species for which cross-attraction was evident wasO. mercator toO. surinamensis. Both sexes ofOryzaephilus spp. produce (R)-1-octen-3-ol, which highly synergizes response to the cucujolide pheromones. Similar synergism occurs between hexanal, octanal, and nonanal and the cucujolide pheromones ofOryzaephilus spp. The males of a sixth cucujid species,Cathartus quadricollis (Guér) produce a different aggregation pheromone, (3R,6E)-7-methyl-6-nonen-3-yl acetate. Trapping ofCryptolestes andOryzaephilus spp. in cardboard traps baited with pheromones is efficient in environments mimicking food-storage areas. Pheromone-baited plastic probe traps are the most efficient at capturing these species in infested grain.

Fungal volatiles: Semiochemicals for stored-product beetles (Coleoptera: Cucujidae)

Responses by five species of cucujid grain beetles (mixed-sex adults) to various volatiles were assessed by means of a two-choice, pitfall olfactometer. The test volatiles were short-chain alcohols and ketones known to be produced by fungi. Both racemic and chiral 1-octen-3-ols were strong attractants forCryptolestes ferrugineus (Stephens), as had been found previously forOryzaephilus surinamensis (L.),O. mercator (Fauvel), andAhasverus advena (Waltl). 3-Methylbutanol was another good attractant for these four cucujids, and it was the only test compound to whichCathartus quadricollis (Guér.) responded positively. 1-Octen-3-one, racemic 3-octanol, and 3-octanone showed various degrees of attractiveness for the former four species of cucujids.O. surinamensis was the only species of test beetle to show much positive response to 2-phenylethanol and ethanol. ForO. mercator andO. surinamensis, 3-methylbutanol enhanced positive response to their respective cucujolide aggregation pheromones.

Chirality of macrolide pheromones of grain beetles in the generaOryzaephilusandCryptolestes and its implications for species specificity.

The chiralities of macrolide lactone aggregation pheromones of five species of economically important grain beetles have been determined by capillary gas chromatographic separation of the diastereomeric (S)-O-acetyllactate derivatives of the hydroxy methyl esters derived from boron trifluoride-catalyzed cleavage of the macrolides in methanol. Chirally pure (Z)-3-dodecen-11-olide (I) is produced in theS configuration byCryptolestes ferrugineus (Stephens) and in theR configuration byOryzaephilus mercator (Fauvel). (Z,Z)-3,6-Dodecadien-11-olide (II) is produced in theR configuration by bothO. mercator andO. surinamensis (L.). (Z,Z)-5,8-Tetradecadien-13-olide (IV) is produced in theR configuration byO. surinamensis and as a 85∶15 mixture ofR andS isomers byC. turcicus. (Z)-5-Tetradecen-13-olide (V) is produced in the S configuration byC. pusillus (Schönherr) and as a 33∶67 mixture of theR andS isomers byC. turcicus (Grouvelle). The results indicate that in these cucujids, species specificity in pheromone response is maintained at least in part by pheromone chirality.

Semiochemicals produced by western balsam bark beetle,Dryocoetes confusus Swaine (Coleoptera: Scolytidae).

The most prominent beetle-produced volatiles identified in the abdominal extracts of maleDryocoetes confusus Swaine after they had bored for 24 hr in logs of subalpine fir,Abies lasiocarpa (Hook.) Nutt. were:exo andendo-brevicomin,trans-verbenol, verbenone, myrtenol,trans-pinocarveol,cis- andtrans-p-menthen-7-ol, 3-caren-10-ol, and several monoterpenes and sesquiterpenes. Myrtenol was the only conspicuous compound in extracts from males that had been exposed toA.lasiocarpa resin volatiles for 24 hr. Laboratory bioassays indicated that both (−)- and (+)-exo-brevicomin were attractive to femaleD. confusus, and that the (−) enantiomer did not inhibit response to its antipode. Results from field trapping experiments indicated that bothero-brevicomin and myrtenol are aggregation pheromones forD. confusus.exo-Brevicomin baits were effective in causing attack byD. confusus on baited and surrounding trees, suggesting that this pheromone may have utility in manipulating populations of the beetle.

Aggregation pheromones of the grain beetle,cryptolestes turcicus (Coleoptera: Cucujidae).

Two biologically active macrolides were isolated from Porapak Q-captured beetle and frass volatiles ofCryptolestes turcicus (Grouvelle) and identified spectroscopically as (Z,Z)-5,8-tetradecadien-13-olide (I) and (Z)-5-tetradecen-13-olide (II). Natural I was active alone and was synergized by inactive II. The pheromones were male-produced but attractive to both sexes. Pheromone production increased dramatically when insects were aerated on a food source. Pure (R)- and (S)-I were inactive, but mixtures of (R)- and (S)-I were active, the first reported instance of enantiomeric synergism in the Cucujidae.

1-Octen-3-ol, attractive semiochemical for foreign grain beetle,Ahasverus advena (Waltl) (Coleoptera: Cucujidae)

Volatiles were captured on Porapak Q from foreign grain beetles,Ahasverus advena (Waltl), feeding on rolled oats at various population densities. At low population density, males, females, and mixed-sex beetles four to six weeks posteclosion and older produced 1-octen-3-ol. Mixed-sex beetles emitted almost pure (R)-(−) enantiomer. Weekly production rates of 1-octen-3-ol by males were at least four times greater than those of females. Production of 1-octen-3-ol was barely detectable in volatiles from mixed-sex adults maintained at the highest population density. Laboratory bioassays in a two-choice, pitfall olfactometer modified to retain responding beetles revealed that 1-octen-3-ol serves as an aggregation pheromone forA. advena. Both racemic and chiral 1-octen-3-ols were good attractants for mixed-sex adults in the pitfall olfactometer.

Azasterol inhibitors in yeast: Inhibition of the 24-methylene sterol Δ24(28)-reductase and Δ24-sterol methyltransferase of saccharomyces cerevisiae by 23-azacholesterol

The effects of 23-azacholesterol on sterol biosynthesis and growth of Saccharomyces cervisiae were examined. In the presence of 0.2, 0.5, and 1 micron 23-azacholesterol, aerobically-growing yeast produced a nearly constant amount of ergosta-5,7,22,24(28)-tetraenol (approx. 36% of total sterol) and slowly accumulated zymosterol with a concommitant decline in ergosterol synthesis. Growth and total sterol content of yeast cultures treated with 0.2-1 micron 23-azacholesterol were similar to that of the control culture. Yeast cultures treated with 5 and 10 micron 23-azacholesterol produced mostly zymosterol (58-61% of total sterol), while ergosta-5,7,22,24(28)-tetraenol production declined to less than 10% of total sterol. The observed changes in the distribution of sterols in treated cultures are consistent with inhibition of 24-methylene sterol 24(28)-sterol reductase (total inhibition at 1 micron 23-azacholesterol) and of 24-sterol methyltransferase (71% inhibition at 10 micron 23-azacholesterol). Yeast cultures treated with 10 micron 23-azacholesterol were found to contain 4,4-dimethylcholesta-8,14,24-trienol and 4alpha-methylcholesta-8,14,24-trienol, which were isolated and characterized for the first time.

Attraction ofOryzaephilus surinamensis (L.) andOryzaephilus mercator (Fauvel) (Coleoptera: Cucujidae) to some common volatiles of food.

Responses by adultOryzaephilus surinamensis (L.) andOryzaephilus mercator (Fauvel) to various food volatiles were assessed by means of a two-choice, pitfall olfactometer. The individual experimental stimuli, all potential products of lipid oxidation, had a range of attractive doses of ≤ 1000-fold over the test dose ranges of 0.001–100 gmg, or 0.01–1000 gmg. Of 13 aliphatic C3-C14 aldehydes and benzaldehyde tested forOryzaephilus spp., 10 C3-C10 aliphatic aldehydes and benzaldehyde showed some attractiveness for both species. ForO. mercator, nonanal had the lowest lower threshold for positive response at 0.01 μg. The addition of small amounts of nonanal or of a 1∶1∶1 mixture of hexanal, octanal, and nonanal to small amounts of cucujolide aggregation pheromones enhanced response by mixed-sexO. mercator to the pheromones. Eleven aliphatic C2-C9 free fatty acids showed some attractiveness for bothOryzaephilus spp. Isovaleric acid and valeric acid had the lowest lower thresholds for positive response at 0.1 μg forO. mercator andO. surinamensis, respectively. Four olefinic oat volatiles were found to possess various degrees of attractiveness for bothOryzaephilus spp. The data suggest that food volatiles in this study might be used byOryzaephilus spp. as host-finding kairomones in nature.

Aggregation pheromone of square-necked grain beetle,Cathartus quadricollis (Guér.)

When feeding on rolled oats, male square-necked grain beetles,Cathartus quadricollis (Guér.), produced the aggregation pheromone (3R,6E)-7-methyl-6-nonen-3-yl acetate, for which the trival name “quadrilure” is proposed. The pheromone was highly attractive to both sexes in a two-choice, pitfall olfactometer modified to retain responding beetles by placing a food stimulus (an oat flake) in the glass vials containing the experimental and control stimuli. TheS enantiomer of the pheromone was inactive. Males also produced small amounts of (E)-7-methyl-6-nonen-3-one, (E)-7-methyl-6-nonen-3-ol, and (6E)-7-methyl-3-propyl-2,6-nonadienyl acetate, but these compounds were inactive in the laboratory bioassay. Segregated males and females both produced (R)-(−)-1-octen-3-ol, which by itself was repellent to both sexes but did not diminish beetle response to the aggregation pheromone.

Influence of pheromone chirality on response byOryzaephilus surinamensis andOryzaephilus mercator (Coleoptera: Cucujidae)

The response of the sawtoothed grain beetle,Oryzaephilus surinamensis (L.), and the merchant grain beetle,O. mercator (Fauvel), to synthetic racemic and chiral macrolide aggregation pheromones was assessed in pitfall olfactometers.O.mercator utilizes theR enantiomers of (Z)-3-dodecen-11-olide and (Z,Z)-3,6-dodecadien-11-olide.O. surinamensis utilizes theR enantiomers of (Z,Z)-3,6-dodecadien-11-olide and the Synergist (Z,Z)-5,8-tetradecadien-13-olide in combination with achiral (Z,Z)-3,6-dodecadienolide. For both species, the racemates of the respective chiral pheromones were effective attractants. The respectiveS enantiomers were inactive for both species and had no effect on the biological activity of the active antipodes. No diel periodicity in responsiveness to pheromones was detected inOryzaephilus spp. reared either on a 12∶12 light-dark photoperiod or in darkness. Nonpheromone macrolides, naturally released in trace amounts byOryzaephilus spp., did not affect the aggregation response of either species to its pheromones when these additional macrolides were combined with the pheromone mixtures.