Gerald N. Lanier

Chemical attractants for the smaller European elm bark beetle Scolytus multistriatus (Coleoptera: Scolytidae).

The secondary attractant for the smaller European elm bark beetleScolytus multistriatus is a mixture of three compounds: (-)4-methyl-3-heptanol(I); 2,4-dimethyl-5-ethyl-6,8-dioxabicyclo(3.2.1) octane (II); and (−)α-cubebene (III). The novel structure assigned to compound II was confirmed by synthesis. All three compounds were isolated from the volatile compounds collected on Porapak Q by aerating elm bolts infested with virgin female beetles. The GLC fractionations were monitored by two laboratory bioassays. Individually, each compound was inactive in the laboratory bioassays, but a mixture of all three showed activity nearly equivalent to that of the of the original Porapak extract. A mixture of synthetic I and II plus natural III (from cubeb oil) was highly attractive to beetles in preliminary field tests.

IPS pini: The basis for interpopulational differences in pheromone biology

Ips pini from Idaho (ID) produce (−)-ipsdienol and respond to it in the laboratory.I. pini from New York (NY) produce (+) and (−)-ipsdienol in a 65∶35 ratio and respond much more strongly to the (+) than to the (−) enantiomer. Response byI. pini-ID to (−)-ipsdienol in the laboratory was inhibited by (+)-ipsdienol, while the field response byI. pini-NY was optimal to a 50:50 mixture of (+) and (−)-ipsdienol. This differential production and response to enantiomers of ipsdienol is sufficient to account for populational specificity observed in earlier experiments and confirmed by our current work. Reciprocal hybrids of the NY and IDI. pini populations did not differ in their patterns of attraction and response; those of both types of F1 were similar to NY beetles. Thus, it appears that (+)-ipsdienol is produced by the hybrids and is necessary for their maximum response, but this supposition was not tested. The genes controlling the pheromone biology ofI. pini are not sex linked. Since previous whole-antenna and single-cell electrophysiological data show that the receptor systems of the two populations are virtually identical, response behavior seems to be governed by the central nervous system rather than by the characteristics of the olfactory receptors.

Lanierone: A new pheromone component fromIps pini (Coleoptera: Scolytidae) in New York.

A new pheromone component, lanierone, (2-hydroxy-4,4,6-trimethyl-2,5-cyclohexadien-1-one) was isolated and identified from a Porapak Q collection of volatiles from maleIps pini from New York through GC fractionation, bioassay, and spectrometry. In both the laboratory and the field, synthetic lanierone, in a 1:100 ratio with synthetic ipsdienol, is as attractive as natural pheromone sources. Synthetic ipsdienol alone is not attractive in the laboratory and only weakly attractive in the field. Varying the ratio of lanierone to ipsdienol in the field from 10−4∶1 to 1∶1 in 10-fold increments resulted in an increased number of beetles trapped at the three lower ratios, but also in an increase in the proportion of males trapped. In the field, all combinations of lanierone to ipsdienol attracted proportionately fewer males than did pheromone-producing male beetles. GC and GC-MS analyses of Porapak Q-trapped volatiles revealed that lanierone is produced in an amount equal to about 0.2% of that of ipsdienol and is produced exclusively by males. The small amount of lanierone produced, together with a GC retention time similar to that of ipsdienol on a nonpolar column, probably confounded its detection in earlier studies.

Specificity of response to pheromones in the genusIps (Coleoptera: Scolytidae)

Seventeen species ofIps were laboratory or field tested for the specificity of their response to male-produced aggregating pheromones. In the laboratory, some species appeared not to differentiate among their own pheromones and those of closely related species, whether the pheromones were bioassayed individually or in direct competition. Other species showed strong preference for their own pheromones in competition with those of closely related species, even though they had demonstrated strong attraction to pheromones of the related species. Cross-responsiveness amongI. confusus, I. montanus, andI. paraconfusus, and betweenI. mexicanus andI. concinnus, was confirmed in field tests. Moreover, wildI. paraconfusus females entered the nuptial chambers of males ofI. montanus andI. confusus but not those of the more distantly relatedI. mexicanus. It is hypothesized that specificity of response to aggregating pheromone is important in the maintenance of reproductive isolation among sympatricIps and that the lack of specificity among closely related species enforces the parapatric distributions characteristic of these species.

Collection on Porapak Q of the aggregation pheromone ofScolytus multistriatus (Coleoptera: Scolytidae)

The attractive volatiles in the air around the virgin female of the smaller European elm bark beetle,Scolytus multistriatus (Marsham), tunneling in elm logs can be collected by passing the air through a column of Porapak Q. These volatiles can be removed from the Porapak by Soxhlet extraction with hexane, yielding an extract that is attractive to in-flight beetles in the field. GLC analyses of this extract and an extract of virgin female frass indicate that the aeration extract contains active chemicals that are not in the extract of frass.

Seasonal variability in response ofIps pini (Coleoptera: Scolytidae) to ipsdienol in New York

In May,Ips pini in New York did not respond in the field to 50–98.5% (R)-(−)-ipsdienol (synthetic). In September, beetles responded strongly to 50–60% (R)-(−)-ipsdienol (synthetic). In May and June, New York beetles showed marked preference for their own males over Arizona males, which produce an average of 94.1% (R)-(−)-ipsdienol. This suggested that ipsdienol stereochemistry alone does not ensure activity and that an additional compound is necessary for attraction in May. In the second year of field tests, attraction to synthetic ipsdienol and male beetles was tested in the spring, summer, and fall. There was response only to males in the spring and mid-summer and to both males and synthetic ipsdienol in the late summer and fall, causing a significant treatment x sampling period (date) interaction. Laboratory-reared beetles were not significantly more attracted to ipsdienol than to a blank airstream in laboratory assays, while male volatiles were significantly more attractive than ipsdienol and the blank. These data demonstrate that there is one or more unknown semiochemicals necessary for pheromonal response and that the behavioral activity of synthetic ipsdienol varies seasonally.

Pheromone receptor cell specificity in interpopulational hybrids ofIps pini (Coleoptera: Scolytidae).

Electrophysiological studies of pheromone receptor cells keyed to ispdienol were performed in laboratory-raised hybrids of the eastern and western populations of the pine engraver,Ips pini. As previously shown in the parental beetles, the receptor cells keyed to ipsdienol could be classified as two distinct types: one keyed to (+)- and one to (−)-ipsdienol. None of the 20 ipsdienol cells recorded from F1 hybrids were of an intermediate type. Recordings of the summated receptor responses (EAGs) showed no significant difference between parental beetles and hybrids. Similar results were obtained in reciprocal crosses, eastern females with western males and the reverse. Thus, there was no indication that sex-linked alleles determined the specificity of the ipsdienol receptor cell. The ratio between (+) and (−) cells was 14∶6 in the hybrids compared to 1∶12 in the western and 9∶12 in the eastern populations.

Interspecific activity of semiochemicals among sibling species ofPissodes (Coleoptera: Curculionidae).

Pissodes strobi, P. approximatus, andP. nemorensis are sibling species of pine weevils that can hybridize in the laboratory but are presumed to be reproductively isolated in nature. Males of all three species produce the terpenoids grandisol and grandisal; these compounds serve as an aggregation pheromone forP. approximatus andP. nemorensis when deployed with odors from pine bolts. A series of field experiments examined the possibility of cross-attraction among the three species. Tests in New York and Florida found that parapatrically distributedP. approximatus andP. nemorensis were cross-attractive, but different photoperiodic conditioning was required for pheromone production in males of the two species. Long-day pheromone production (P. approximatus-type.) was inherited in interspecific hybrids. Other tests showed thatP. strobi males, or hybrid males from crosses ofP. strobi withP. approximatus, were not attractive to sympatricP. approximatus. When the response ofP. strobi was assessed to males of eitherP. strobi orP. approximatus confined on white pine leaders (the breeding site ofP. strobi), no evidence of cross-attraction or pheromone activity was found;P. strobi were caught in equal numbers onP. strobi-baited leaders,P. approximatus-baited leaders, and unbaited leaders. Tests of interspecific interactions found that maleP. strobi produce an allelochemical signal that interrupts the response ofP. approximatus to its natural or synthetic aggregation pheromone. This interspecific response is apparently adaptive for members of both species (classified as an allomone-kairomone or synomone) because it may ultimately serve to prevent interspecific matings that would lower the fitness of the parents.

Deployment of Traps in a Barrier Strategy to Reduce Populations of the European Elm Bark Beetle, and the Incidence of Dutch Elm Disease

Dutch elm disease (DED) is caused by a fungus, Ceratocystis ulmi (Buisman) C. Moreau, that infests the vascular systems of elms and forms sticky masses of conidial spores (coremia) in cavities under the bark of the diseased portions of the tree. These spores have been detected on many arthropods that are found beneath the bark of diseased elms, but only bark beetles are an efficient vector because only they frequently visit or inflict wounds in healthy elms deposition of spores in wounds is necessary for infection.

Laboratory and field tests with the synthetic sex pheromone of threeMatsucoccus (1) pine bast scales.

Matsunone, (2E,4E)-4.6,10,12-tetramethyl-2,4-tridecadien-7-one, is the primary sex pheromone ofMatsucoccus resinosae, M. thunbergianae, andM. matsumurae. The synthetic compound was tested in the laboratory and in field tests with all three species, and significantly more males responded to synthetic matsuone than to controls. The attraction of synthetic matsuone to males in field tests was not significantly different from that of virgin females at the same matsuone release rate. An analog of matsuone previously shown to be biologically active was also tested in the laboratory withM. resinosae andM. thunbergianae, and field tested withM. resinosae. The active analog required a dose approximately 100 times greater than matsuone to yield maximum laboratory bioassay response, and in field tests, attraction was not significantly different from controls at doses at which matsuone was significantly attractive.