Dose and enantiospecific responses of white pine cone beetles,Conophthorus coniperda,to alpha-Pinene in an eastern white pine seed orchard

The white pine cone beetle, Conophthorus coniperda, exhibited dose and enantiospecific responses to -pinene in stands of mature eastern white pine, Pinus strobus, in a seed orchard near Murphy, North Carolina, USA. (–)--Pinene significantly increased catches of cone beetles to traps baited with (± )-trans-pityol. (+)--Pinene did not increase catches of beetles to pityol-baited traps and interrupted the response of beetles to traps baited with (±)-trans-pityol and (–)--pinene. Maximal attraction of cone beetles to pityol-baited traps was obtained with lures releasing (–)--pinene at a rate of 103 mg/day at 23^°C. Lures releasing (–)--pinene at rates lower or higher than 103 mg/day resulted in reduced catches to traps baited with (±)-trans-pityol. The sex ratio in all catches was heavily male biased. Attraction of the clerid predator, Thanasimus dubius, to traps baited with (±)-trans-pityol increased significantly with the presence of -pinene, irrespective of enantiomeric composition. Maximal attraction of T. dubius to pityol-baited traps occurred with devices releasing (–)--pinene at the highest rate tested, 579 mg/d at 23^°C, a sub optimal rate for cone beetles.     

Attractive and inhibitory pheromones produced in the bark beetle,Dendroctonus brevicomis,during host colonization: Regulation of inter- and intraspecific competition

Quantities of attractive (exo-brevicomin and frontalin) and inhibitory (trans-verbenol, verbenone, and ipsdienol) pheromones were monitored in both sexes ofDendroctonus brevicomis during their colonization of a ponderosa pine. Verbenone was found in males in the greatest amounts at the time of landing, and it declined more rapidly than the other pheromones in either sex. The amounts of frontalin andexo-brevicomin in males and females, respectively, increased after initial boring within the host but began to decline after mating. The quantity oftrans-verbenol in both sexes (females had significantly more) declined more gradually thanexo-brevicomin, frontalin, and verbenone. Ipsdienol was found only in males during the initial stages of attack when encountering the resin. It is suggested that along with a general decline in all pheromonal components, a sufficient change in the ratio of the attractive pheromones to an inhibitory pheromone,trans-verbenol, may play a role in termination of aggregation.trans-Verbenol may also function along with verbenone and ipsdienol in limiting the density of attack and thus intraspecific competition. These inhibitory pheromones also appear to cause several competing species of bark beetle to avoid landing in areas infested withD. brevicomis, even when their own pheromone is present.Coleoptera:Scolytidae. These studies were supported in part by the Rockefeller Foundation, USDA Forest Service, Regional research project W-110, SEA/ USDA, and the National Science Foundation and Environmental Protection Agency through a grant (NSF GB-34719/BMS 75-04223) to the University of California.     

Field response of Ips paraconfusus,Dendroctonus brevicomis,and their predators to 2-methyl-3-buten-2-ol,a novel alcohol emitted by ponderosa pine

Methylbutenol (MBO) is a major component of the aggregation pheromone of the European spruce beetle Ips typographus and also has been found to be emitted in large amounts by several species of pine native to western North America. This study investigates the influence this signal may have on the behavior of North American bark beetles and examines whether MBO functions as a defensive compound for emitting pines. The response of two North American bark beetles (Ips paraconfusus and Dendroctonus brevicomis) and their predaceous beetles (Trogositidae and Cleridae) to MBO, pheromone, and monoterpenes in varying release rates was investigated in the field using Lindgren funnel traps. MBO exhibited no repellent properties when tested alone, nor did MBO appear to have any effect on the aggregation response of these bark beetles and their predators to their pheromones. These results provide no support for a defensive function of MBO.     

Response of the clerid predatorThanasimus dubius (F.) to bark beetle pheromones and tree volatiles in a wind tunnel

Tree volatiles and pheromones produced by southern bark beetles were bioassayed for response by the clerid predatorThanasimus dubius (F.). Upwind flights in a laboratory olfactometer, modified from Visser (1976), were used to determine the attractiveness of compounds. Differences in response to a solvent control and pheromone treatment were tested for statistical significance using the Wilcoxon signed ranks test. Both sexes ofT. dubius responded to frontalin, ipsdienol, and -pinene in a dose-dependent manner with different but overlapping concentration ranges. Strong differences between the sexes were observed in response totrans-verbenol, verbenone, andl--pinene. Neither sex responded to ipsenol orendo-brevicomin.Miss. Agric. and For. Exp. Sta. Publication No. 5251.     

The role of lanierone in the chemical ecology ofIps pini (Coleoptera: Scolytidae) in California

Five doses of lanierone (2-hydroxy-4,4,6-trimethyl-2,5-cyclohexadien-1-one) were tested with one dose of enantiomerically pure [99.4% (4R)-(–)] ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) for activity as an aggregation pheromone ofIps pini (Say) in California. The response ofI. pini to 1 mg/day ipsdienol + 20 g/day lanierone was significantly greater than the response to ipsdienol alone, but the response pattern did not demonstrate a clear dose-response relationship. The response to the highest dose of lanierone (2 mg/day) was significantly lower than the response to ipsdienol alone. Ipsdienol attracted significantly moreI. pini than a male-infested log. Lanierone did not alter the percentage of maleI. pini responding to ipsdienol alone. Neither sex ofI. pini orDendroctonus brevicomis LeConte from California produced detectable amounts of lanierone, but myrcene-aerated maleD. brevicomis produced 97.8%-(4S)-(+)-ipsdienol. The black-bellied clerid,Enoclerus lecontei (Wolcott) (Coleoptera: Cleridae) was attracted to lanierone when released with ipsdienol. Neither compound was attractive when released alone, proving synergism for the kairomone of this predator. Lanierone did not influence the response of the predatorsTemnochila chlorodia (Mannerheim) (Coleoptera: Trogositidae) andEnoclerus sphegeus (F.) (Coleoptera: Cleridae), which were attracted to all treatments containing ipsdienol.Tomicobia tibialis Ashmead (Hymenoptera: Pteromalidae) responded in significantly greater numbers to the male-infested log than it did to ipsdienol or ipsdienol + 20 g/day lanierone.     

(R)-(+)-palasonin,a cantharidin-related plant toxin,also occurs in insect hemolymph and tissues

Gas chromatographic and mass spectroscopic analyses of extracts of cantharidin-containing meloid, clerid, and staphylinid beetles revealed the presence of minor to significant amounts of palasonin, previously only known from seeds and fruits of the Indian shrub Butea frondosa (Leguminaceae). Unlike (S)-(–)-palasonin (>99% ee) from B. frondosa, the insects produce palasonin of low ee with the (R)-(+)-enantiomer (0–50% ee) prevailing. The ee of palasonin from individual specimens of predatory insects (Trichodes apiarius), which acquire their chemical protection from cantharidin-producing insects, may vary considerably. The absolute configuration of (S)-(–)-palasonin, previously deduced from indirect chemical and spectroscopic methods, was confirmed by X-ray crystal structure analysis of a cyclic imide derived from (S)-(–)-palasonin and (S)-(–)-1-(4-nitrophenyl)-ethylamine.     

Variation in semiochemical-mediated prey-predator interaction:Ips pini (Scolytidae) andThanasimus dubius (Cleridae)

The bark beetleIps pini (Say) displays variation in its response to and production of enantiomeric blends of its pheromone ipsdienol. One of the principal predators ofIps pini isThanasimus dubius (F.), which uses ipsdienol as a kairomone for prey location. During 1988 and 1989, in Wisconsin and Michigan, the response of both species to a range of enantiomeric blends of ipsdienol was investigated. Blends tested had the following ratios of the (S)-(+) to (R)-(–) enantiomers: 3%97%, 25%75%, 50%50%, 75%25%, and 97%3%. Either75% (+) 25% (–) or 50% (+) 50% (–) ipsdienol captured the mostIps pini in both years at both sites. The 25% (+)75% (–) blend also caught moreIps pini than the control during both years at both sites. All blends tested were attractive toThanasimus dubius in both years at both locations. Blend preferences of both species were variable and labile at both sites. Response patterns of both species in Wisconsin were different from those in Michigan each year. Furthermore, response patterns of both species to the ipsdienol blends changed from 1988 to 1989 at both locations. A genetic component to this variation would permit predator-prey coevolution, as well as the development of resistance byIps pini to management strategies based on mass-trapping with single blends.     

Insect predator-prey coevolution via enantiomeric specificity in a kairomone-pheromone system

Insect predators can be guided to their prey by a kairomonal response to the prey pheromone. We found this phenomenon to be highly specific in the bark beetle predatorThanasimus dubius. Olfactory responses and behavioral tests revealed that the predator is guided to its major preyDendroctonusfrontalis by the primary enantiomer of the pheromone of the prey, (1S, 5R)-(–)-frontalin. These and other findings suggest the co-evolution of a kairomone system of the predator and the pheromone system of its prey.Texas Agricultural Experiment Station paper No.TA17770. The work was funded in part by McIntire-Stennis project 1525 (TAES) and the USDA program entitled The Expanded Southern Pine Beetle Research and Applications Program through TAES-CSRS grant 680-15-10. The findings, opinions, and recommendations reported herein are those of the authors and not necessarily those of the United States Department of Agriculture.     

Chemically Mediated Predator-free Space: Herbivores Can Synergize Intraspecific Communication Without Increasing Risk of Predation

Natural enemies of herbivores often locate cryptic insects by responding to volatiles associated with the prey's feeding and mating. For example, predators of bark beetles (Coleoptera: Scolytidae) exploit the aggregation pheromones that their prey use to attract mates and secure hosts. Bark beetles are cryptic insects that feed and develop in the subcortical tissues of trees and spend all but a portion of their life history within this habitat. The pine engraver, Ips pini, produces the pheromone ipsdienol throughout its transcontinental range. Predators of I. pini exploit this chemical as a kairomonal cue. Eastern and Midwestern I. pini populations also produce lanierone, which synergizes their attraction to ipsdienol. We evaluated the effects of varying amounts of lanierone, in combination with a constant amount of racemic ipsdienol, on the relative attraction of I. pini and its major predators in Wisconsin. Higher numbers of I. pini were captured with increasing release rates of lanierone. In contrast, the numbers of the major predators, such as Thanasimus dubius, Enoclerus nigrifrons, Platysoma cylindrica, and P. parallelum, did not differ among different lanierone release rates. The response of I. pini but not their predators to lanierone at ecologically realistic release rates may be part of a coevolving interaction between predators and prey and offers new strategies for semiochemically based pest management by selectively removing pests and leaving predators.     

Reduced offspring production in bark beetleTomicus piniperda in pine bolts baited with ethanol and α-pinene,which attract antagonistic insects

Bolts of Scots pine,Pinus sylvestris L., attacked by the bark beetleTomicus piniperda (L.) were baited with ethanol and -pinene to attract antagonistic insects and thereby enhance their detrimental effects on the production of bark beetle progeny. Unbaited and caged bolts were included in the experiments as controls. Attraction of beetles to the bolts and subsequent emergence were estimated using traps. Six phloem-feeding species (potential competitors ofT. piniperda) and four predatory species were caught in significantly higher numbers at the baited bolts than at the unbaited ones. The number of offspring and the productivity ofT. piniperda were four to seven times higher in unbaited bolts than in baited bolts. Exclusion of other insects, by using cages, resulted in a nine-fold increase in the number ofT. piniperda offspring per square meter and productivity (offspring per egg gallery) compared with unbaited, exposed bolts.Hylurgops palliatus (Gyll.) (Scolytidae) andRhagium inquisitor (L.) (Cerambycidae) attacked both the baited and unbaited bolts, whereasAcanthocinus aedilis (L.) (Cerambycidae) andPytho depressus (L.) (Pythidae) reproduced almost exclusively in the baited ones. Large numbers of larvae ofThanasimus (Cleridae) andRhizophagus (Rhizophagidae) emerged from both the baited and unbaited bolts. Adults ofPlegaderus vulneratus (Panzer) andCylister linearis (Er.) (Histeridae) emerged almost exclusively from the baited bolts. The low progeny production ofT. piniperda in the baited bolts was attributed largely to the influence of adults ofRhizophagus andEpuraea (Nitidulidae), and larvae ofThanasimus andA. aedilis.