The eastern 5-spined ips, Ips grandicollis (Eichhoff), is native to the eastern USA and is an invasive pest of exotic pines (Pinus spp.) in Australia. It can kill stressed trees and transmit ophiostomoid fungi that cause blue staining of wood and reduce the commercial value of timber. Ips grandicollis uses semiochemicals produced by conspecifics to locate mates, while semiochemicals from competitors and nonhosts may reduce the reaction to attractants. To investigate methods to exploit these behaviors in a management strategy, we evaluated the impact of 12 potential semiochemical inhibitors of I. grandicollis attraction using traps baited with aggregation pheromone (ipsenol and cis-verbenol) in the beetle's native (northeast Georgia and central Louisiana, USA) and invasive (southeast Queensland, Australia) ranges over 2 yr. In the first trapping experiment (2022 to 2023), 2 semiochemicals (2-phenylethanol and methyl eugenol) significantly decreased attraction to the lure by 35% to 39% in the native range and 55% to 56% in the invasive range. Camphor reduced trap catches in Louisiana (26%) and Queensland (41%) but not in Georgia. In the second experiment (2023 to 2024), the inhibitory effects of methyl eugenol, 2-phenylethanol, and camphor were tested alone and in binary and ternary combinations. The binary combination of methyl eugenol and 2-phenylethanol reduced attraction by 66% in Georgia. However, such differences were not observed in Louisiana. The ternary combination of these compounds reduced attraction by 76% in the invasive range. Further research on these inhibitors could lead to a sustainable push-pull management strategy for protecting pine trees and log stacks from I. grandicollis attacks.

The southern pine beetle, Dendroctonus frontalis Zimmermann is an important mortality agent of Pinus in the eastern United States of America where it commonly shares hosts with the black turpentine beetle, Dendroctonus terebrans (Olivier), which infrequently kills trees. Unlike D. frontalis, which must kill its hosts to become established in the bark and reproduce, D. terebrans can occupy living hosts as a parasite. Olfactory mechanisms whereby D. frontalis initially locates hosts have not been demonstrated, whereas D. terebrans responds strongly to host odors. Because D. terebrans produces frontalin, the primary aggregation pheromone component for D. frontalis, and commonly arrives on hosts prior to D. frontalis, it has been hypothesized that D. terebrans pheromone components can mediate D. frontalis location of suitable, living trees. We assessed this possibility with studies of the semiochemical interactions between D. frontalis and D. terebrans. Coupled gas chromatography-electroantennographic detection analyses indicated that D. terebrans produces nine different olfactory stimulants for D. frontalis, nearly all of them known semiochemicals for D. frontalis. A trapping experiment designed to address the potentially confounding influence of lure contamination confirmed that the D. terebrans pheromone component exo-brevicomin enhances attraction of D. frontalis and thus could be an attractive kairomone. In ambulatory bioassays, male D. frontalis were strongly attracted to odors of frass of solitary female and paired D. terebrans, indicating their attraction to the naturally occurring semiochemicals of D. terebrans. Cues from D. terebrans may influence host and mate-finding success of D. frontalis and, thereby, the latter's virulence.

Abstract We conducted studies with the native woodwasp Sirex nigricornis F. (Hymenoptera: Siricidae) in Louisiana to identify host-associated olfactory stimulants that may include attractive semiochemicals for this species as well as Sirex noctilio F., an invasive species that can attack healthy trees. Loblolly pines (Pinus taeda L.) treated with a stressing agent were felled and chipped 1–2 mo after treatment, and the chips were steam–water distilled in a Clevenger apparatus to extract volatile compounds. Using coupled gas chromatography–electroantennographic detection, we analyzed the distillates with antennae of both S. nigricornis and the Sirex parasitoid Ibalia leucospoides (Hochenwarth) (Hymenoptera: Ibaliidae) to identify olfactory stimulants. In addition, we assayed S. nigricornis antennae with synthetic mixtures containing 23 volatile compounds associated with stressed and dying pines, including pheromones of bark beetles (Coleoptera: Curculionidae: Scolytinae) that also use these hosts. Antennae of both male and female S. nigricornis responded to 29 identifiable volatiles in the distillates, whereas I. leucospoides responded to 23 volatiles. Eighteen compounds in the synthetic mixtures were olfactory stimulants for S. nigricornis. Olfactory stimulants in the woodchip distillates were predominantly hydrocarbon and oxygenated monoterpenes, and the strongest antennal stimulants among compounds in the synthetic mixtures were oxygenated monoterpenes associated with pine death and early decay (e.g., verbenone, fenchone, and terpinen-4-ol). Bark beetle pheromones (frontalin, endo-brevicomin, ipsenol, and ipsdienol) also stimulated S. nigricornis antennae. The very large number of host-associated olfactory stimulants for S. nigricornis implies that our data may offer limited assistance in targeting individual compounds for investigation as possible attractants and components for a Sirex lure.

The southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae), is a major pine tree killer in North and Central America. In the southeastern USA, responses by D. frontalis to its aggregation pheromone can be substantially increased by at least three host odours: the monoterpenes alpha ‐ and beta ‐pinene, and the phenylpropanoid 4‐allylanisole. We executed three trapping experiments to assess the influence of 4‐allylanisole release rate on aggregation behaviour of D. frontalis and to evaluate the compound as an adjuvant for the operational monitoring lure for D. frontalis . Addition of devices releasing 4‐allylanisole at any of three rates (4.8, 48, and 500 mg/day measured at mean 21°C) increased D. frontalis attraction to a pheromone lure, both in the presence and in the absence of an alpha ‐pinene lure. The increase was 5‐ to 50‐fold with a positive dose response up to the highest tested release rate of 4‐allylanisole. Attraction of an associate, the black turpentine beetle, Dendroctonus terebrans (Olivier), and a major D. frontalis predator, Thanasimus dubius (F.) (Coleoptera: Cleridae), was also significantly increased by 4‐allylanisole. A device releasing 4‐allylanisole at 0.05 g/day (at mean 23°C) increased attraction of D. frontalis to the current operational monitoring lure (which uses alpha ‐ and beta ‐pinene as the host odour component) approximately 4‐fold, but it did not increase attraction to a lure with turpentine as the host odour component (used in a former operational monitoring lure). Additionally, we observed none of the attraction‐inhibiting effects that were previously reported for 4‐allylanisole with D. frontalis . It is possible that the addition of 4‐allylanisole to the D. frontalis lure might allow detection of beetles at lower population densities and, if so, aid in earlier detection of populations invading the northeastern USA in response to climate change. This possibility should receive further investigation.

The southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae) is a major destructive pest of Pinus L. In the southeastern United States, numbers of this species and a major predator, Thanasimus dubius (Fabricius) (Coleoptera: Cleridae), captured during an annual springtime trapping survey are used to make forecasts of the likelihood and severity of an outbreak during the following summer. We investigated responses by both species to six lure formulations to evaluate their suitability for the survey and allow integration of historical data sets produced with differing lure compositions. Trapping trials were performed at four locations across three states (Louisiana, Mississippi, and Alabama) during spring, and at these and one additional location (North Carolina) in fall 2016. All lures included the pheromone component frontalin. Southern pine beetle preferred lures that additionally included the pheromone component endo-brevicomin and turpentine as a source of host odors (rather than a 7:3 mixture of monoterpenes alpha- and beta-pinene). Thanasimus dubius displayed little discrimination among lure compositions. Lure preferences by southern pine beetle did not differ significantly among locations in spring but were influenced by season. Gas chromatography (GC)-electroantennographic detection analyses with southern pine beetle and GC-mass spectrometry identified numerous known and potential semiochemicals that distinguished volatiles released by the tested host odor devices. The lure combination that included endo-brevicomin and alpha/beta-pinene is recommended for the trapping survey because of its high sensitivity for southern pine beetle and potential for greater data integrity resulting from its reproducible composition.

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The southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae: Scolytinae) utilizes a multi-component aggregation pheromone to mediate mass-attacks and thereby colonize otherwise unsusceptible trees. Females produce the attractant frontalin and a synergist, trans-verbenol. We investigated trans-verbenol to determine whether enantiomeric composition, airborne concentration, and possibly other factors might affect its biological activity. Newly-emerged females from Mississippi populations produced 54-87% of the (-)-enantiomer; females initiating galleries in logs produced lower amounts and a wider range of enantiomeric ratios [12-92% (-)]. Coupled gas chromatography-electroantennographic detection (GC-EAD) studies did not suggest large differences in the concentration threshold of olfaction for the two enantiomers. We examined the effect of adding trans-verbenol to traps located outside infested areas and baited with components of the aggregation attractant. Male attraction was similarly increased by lures with 3, 81, or 98% of the (-)-enantiomer of trans-verbenol, whereas females preferred 81 over 3%. When release rate of 81% (-)-trans-verbenol in traps was varied across three orders of magnitude (0.3, 3, and 30 mg/d), the data suggested a positive dose-response trend. A high release (i.e., 2-5 g/d) device of host-odor alpha-pinene had a much stronger enhancing effect on trap catches than a trans-verbenol device (~30 mg/d), and trans-verbenol did not further enhance attraction when alpha-pinene was present. Our results suggest that the weak attraction-enhancing activity of trans-verbenol reported previously cannot be improved by adjusting the enantiomeric composition or release rate of lures, and furthermore there are no anticipated benefits of adding trans-verbenol to the D. frontalis monitoring lure.

Local outbreak risk for the southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Curculionidae), is forecast with a trapping survey conducted every spring throughout the southeastern United States. Traps baited with pine odors and components of the D. frontalis aggregation pheromone are used to obtain abundance estimates of both this species and its clerid predator Thanasimus dubius (F.) (Coleoptera: Cleridae); these data are entered into a predictive model that estimates outbreak risk. An attractant synergist for D. frontalis, endo-brevicomin, has recently been included in the survey lure, but it can have the unintended effect of attracting nontarget species Hylesinus pruinosus Eichhoff (Coleoptera: Curculionidae: Scolytinae) and Enoclerus nigripes (Say) (Coleoptera: Cleridae) which, due to their sometimes large numbers and general similarity in appearance to the target species, could complicate sorting and counting of trap catches. Analysis of bycatch data from a previously-published, 31-mo trapping study in Mississippi indicated that displacement of the endo-brevicomin releaser 6 m from the trap largely eliminated catches of the nontarget species H. pruinosus and E. nigripes while not reducing catches of the target species D. frontalis and T. dubius. Our analysis demonstrates that interspecific differences in spatial responses to attractive semiochemicals can be used to improve insect trap selectivity. Both nontarget beetle species were captured in highest numbers during late winter/early spring, coinciding with the D. frontalis survey.

Laricobius nigrinus Fender (Coleoptera: Derodontidae) is a specialist predator of the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), native to the Pacific Northwest. It has been introduced into the eastern United States for biological control of exotic hemlock woolly adelgid populations that threaten native hemlock. The possible role of olfactory cues in host finding by this predator has received little study. We used gas chromatography electroantennographic detection (GC-EAD) to test adult L. nigrinus olfactory sensitivity to volatiles from foliage of both adelgid-infested and uninfested eastern hemlock [Tsuga canadensis (L.) Corriere] and western hemlock [Tsuga heterophylla (Raf.) Sarg.], and two hemlock woolly adelgid nonhost species (eastern white pine, Pinus strobus L., and western white pine, Pinus monticola Douglas ex D. Don). Adelgid infestation did not alter L. nigrinus EAD response profiles to volatiles from either hemlock species. In total, antennal preparations detected only two compounds in samples of foliage volatiles: myrcene in all four tree species and nonanal in eastern hemlock alone. However, in GC-EAD tests with synthetic blends of common conifer volatiles presented at higher concentrations than in our foliage samples, we additionally recorded responses to (-)-limonene, terpinolene, alpha-pdimethylstyrene, linalool, (-)-bornyl acetate, 4-allylanisole, and a/pha-humulene. The apparent absence of olfactory stimulants specific to adelgid-infested foliage is consistent with published ambulatory olfactometer tests in which L. nigrinus adults were not more attracted to infested than uninfested foliage. Myrcene and nonanal should be further explored as compounds produced by hemlock woolly adelgid host trees that may influence L. nigrinus prey-finding efficiency.

The baldcypress leafroller, Archips goyerana Kruse (Lepidoptera: Tortricidae), is a specialist on Taxodium distichum (L.) Richard and has caused serious defoliation in swamps of southeastern Louisiana, accelerating decline of baldcypress forests concurrently suffering from nutrient depletion, prolonged flooding, and saltwater intrusion. We investigated the composition of the sex pheromone of this species. Coupled gas chromatography-electroantennographic detection (GC-EAD) analyses indicated that male antennae were sensitive to four compounds [(Z)-11-tetradecenyl acetate (Z11-14:OAc), (E)-11-tetradecenyl acetate (E11-14:OAc), (Z)-9-tetradecenyl acetate (Z9-14:OAc), and (Z)-11-tetradecen-1-ol (Z11-14:OH)] present in female abdominal tip extracts in an approximately 100:1.5:0.6:10 ratio. In trapping trials performed in a cypress-tupelo swamp in southeastern Louisiana, moths were attracted to blends of these four components presented in approximately the female-produced ratios. Elimination of Z11-14:OH had no impact on moth response, whereas elimination of any of the three acetates strongly reduced or eliminated attraction. A blend in which the E11:Z11 ratio of 14:OAc was 5:100 was much less attractive than the same blend with the female produced ratio of 1.5:100. A. goyerana is closely related to the sympatric species Archips argyrospilus (Walker) with which it was previously synonymous. Our data revealed differences between the pheromone composition of A. goyerana and that reported for A. argyrospilus, which could account for the apparent absence of cross-attraction between these species. We conclude that a lure containing a 100:1.5:0.6 ratio of Z11-14:OAc, E11-14:OAc, and Z9-14:OAc has the potential to be used in traps to detect and measure A. goyerana populations and thereby monitor an important biotic factor contributing to the loss of coastal baldcypress forests.

A method for determining the sex of live adult Laricobius nigrinus Fender (Coleoptera: Derodontidae) is described. Beetles were briefly chilled and positioned ventral-side-up under a dissecting microscope. Two forceps with blunted ends were used to gently brace the beetle and press on the centre of the abdomen to extrude its terminal segments. Male beetles were distinguished by a sclerotised, reticulate ninth abdominal sternite. In females, the distinct ovipositor (tergite, valvifers (ninth sternite), and laterotergites of the ninth abdominal segment) was visible. The procedure was rapid and harmed only a small number of individuals (fewer than 5%).

A growing body of evidence suggests that bark beetles detect and avoid release points of volatile compounds associated with nonhost species, and thus such nonhost volatiles may have potential utility in the management of bark beetles. We used a coupled gas chromatograph-electroantennographic detector (GC-EAD) to assay the olfactory sensitivity of the southern pine beetle, Dendroctonus frontalis Zimmermann, to volatiles from leaves and bark of eight species of nonhost angiosperm trees that are common in the range of D. frontalis. Tree species sampled were red maple (Acer rubrum L.), mockernut hickory [Carya alba (L.) Nutt. ex Ell.], sweetgum (Liquidambar styraciflua L.), black tupelo (Nyssa sylvatica Marsh.), black cherry (Prunus serotina Ehrh.), southern red oak (Quercus falcata Michx.), blackjack oak [Quercus marilandica (L.) Muenchh.], and water oak (Quercus nigra L.). Beetle antennae responded to a total of 28 identifiable compounds in these samples. The relative olfactory responsiveness to 14 of these, as well as to nonanoic acid and four additional volatiles reported to be associated with nonhost angiosperms, was assessed in GC-EAD analyses of synthetic dilutions spanning six orders of magnitude. The largest response voltage amplitudes were obtained with trans-conophthorin, nonanoic acid, terpinen-4-ol, phenylethyl alcohol, and eucalyptol, whereas the lowest response thresholds were to nonanoic acid, nonanal, linalool, (E)-2-hexen-1-ol, and phenylethyl alcohol. Funnel traps baited with various combinations of eleven antennally-active angiosperm volatiles along with a standard attractant captured significantly fewer male and female D. frontalis than traps baited with the standard attractant alone. Our data suggest that a diversity of semiochemicals may be involved in host species discrimination by D. frontalis, and several may have utility in their management.

We conducted laboratory and field bioassays to characterize the pheromone system of an ash bark beetle, Hylesinus pruinosus Eichhoff (Coleoptera: Curculionidae: Scolytinae). Solitary females in newly initiated galleries in ash logs produced (+)-exo-brevicomin, whereas male beetles paired with females produced (+)-endo-brevicomin, lesser quantities of (+)-exo-brevicomin, and a third compound that could not be identified. Beetles produced these compounds also after exposure to juvenile hormone III, and they were the sole volatile chemicals isolated from beetles or aerations of infested logs that elicited electrophysiological responses from antennae of either sex. In the field, both sexes were strongly attracted to traps baited solely with either racemic or pure (+)-endo-brevicomin. Racemic exo-brevicomin was much less attractive to both sexes than racemic endo-brevicomin, and it did not increase attraction of endo-brevicomin when released in combination. Host odors (volatiles from mechanically damaged ash branches) failed to attract beetles or increase attractiveness of racemic exo-brevicomin. Our evidence suggests that male-produced (+)-endo-brevicomin is the major component of an aggregation pheromone for H. pruinosus, with (+)-exo-brevicomin and the unidentified male compound playing an indeterminate role in the chemical ecology of this species. Our data thus show an instance in which the major aggregation pheromone component of a bark beetle is produced by the secondarily arriving sex, a rare occurrence in bark beetles but one which has been reported previously for the Hylesini.

Stem volatile extracts from ten trees that are sympatric with the western pine beetle, Dendroctonus brevicomis LeConte (Coleoptera: Curculionidae) were assayed by gas chromatographic-electroantennographic detection analysis (GC-EAD). The extracts were from the primary host, ponderosa pine, Pinus ponderosa Dougl. ex Laws. (Pinaceae); two nonhost angiosperms, California black oak, Quercus kelloggii Newb. (Fagaceae), and quaking aspen, Populus tremuloides Michx. (Salicaceae); and seven nonhost conifers, white fir, Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (Pinaceae), incense cedar, Calocedrus decurrens (Torr.) Florin (Cupressaceae), Sierra lodgepole pine, P. contorta murrayana Grev. & Balf. (Pinaceae), Jeffrey pine, P. jeffreyi Grev. & Balf. (Pinaceae), sugar pine, P. lambertiana Dougl. (Pinaceae), Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco (Pinaceae), and mountain hemlock, Tsuga mertensiana (Bong.) Carr. (Pinaceae). Sixty-four compounds were identified from the ten trees, 42 of which elicited antennal responses in D. brevicomis, usually in both sexes. In addition, several synthetic compounds, including a number of the antennally-active compounds from the extracted trees and some bark beetle pheromone components, elicited antennal responses in a manner similar to that observed with the extracts. Of the antennally-active compounds known to be present in trees sympatric with D. brevicomis, only geraniol was unique to its host. Four antennally-active compounds were found in the host and in other conifers; five compounds were found only in nonhost conifers; eight compounds were found in either or both of the nonhost angiosperms; eight compounds were found in either or both of the angiosperms and in nonhost conifers, but not in the host; and 19 were found in both the host and in angiosperms and/or nonhost conifers. Several bark beetle pheromone components were found in the stem volatile extracts. Conophthorin was identified from both nonhost angiosperms; exo-brevicomin was identified in A. concolor; verbenone was identified from a number of nonhost conifers; and chalcogran was identified from P. tremuloides. The number of nonhost volatile chemicals that D. brevicomis encounters and is capable of detecting, and the diversity of sources from which they emanate, highlight the complexity of the olfactory environment in which D. brevicomis forages. This provides a basis for further work related to chemically-mediated aspects of foraging in this insect and perhaps other coniferophagous bark beetles, and highlights the need to consider foraging context in the design and implementation of semiochemical-based management tactics for tree protection.

Previous research indicated that the aggregation pheromone of the southern pine beetle, Dendroctonus frontalis, is produced only by females, the sex that initiates attacks. We provide evidence indicating that secondarily arriving males augment mass aggregation by releasing the attractive synergist (+)-endo-brevicomin. Healthy pines artificially infested with both sexes of D. frontalis were significantly more attractive to conspecifics than trees infested solely with females. Coupled gas chromatography-electroantennographic detection (GC-EAD) analyses of volatiles isolated from male beetles revealed substantially greater olfactory sensitivity by D. frontalis to endo-brevicomin than to any other component. The threshold of detection of both sexes for (+)-endo-brevicomin was four orders of magnitude lower than for its antipode and at least one order of magnitude lower than for either enantiomer of frontalin, the major female-produced aggregation pheromone component. Pairing with a female in a gallery stimulated individual male beetles to produce hundreds of nanograms of (+)-endo-brevicomin. (+)-endo-Brevicomin was detected in a small percentage of female D. frontalis, whereas (−)-endo-brevicomin was never detected in either sex. In field trapping bioassays, we confirmed that (+)-endo-brevicomin is a potent synergist for attractive combinations of frontalin and pine turpentine. However, (+)-endo-brevicomin failed to attract D. frontalis either when presented alone or in combination with turpentine. We postulate that mass colonization of host trees by D. frontalis is mediated by distinct semiochemicals from both sexes rather than females alone. Our discovery of a key aggregation pheromone component in such an apparently well-studied species implies that the pheromone models of other bark beetles could benefit from systematic reexamination using newer technologies. Additionally, baits fortified with (+)-endo-brevicomin may enhance pest management strategies that exploit attractants for D. frontalis.

We measured electrophysiological responses in the antennae of two predaceous hister beetles, Platysoma parallelum and Plegaderus transversus, exposed to racemic mixtures of primary aggregation pheromones of scolytid bark beetle prey, ipsenol, ipsdienol, and frontalin. No significant differences were found for either histerid species between male and female antennal responses to any of the three pheromones. Measurement of antennal threshold responses indicated that Pla. parallelum has increasing antennal sensitivity to ipsdienol, ipsenol, and frontalin. In contrast, Ple. transversus exhibited similar detection thresholds to all three pheromones. Pla. parallelum antennae exhibited different response amplitudes to the three pheromones at quantities above the detection threshold, while Ple. transversus had similar responses to each. Behavioral responses to the same three pheromones were evaluated for both histerid species using pedestrian olfactometer bioassays. Both species were attracted to frontalin and ipsenol, but not ipsdienol. Pla. parallelum was significantly more attracted to frontalin than ipsenol, while Ple. transversus showed no significant preference for either compound. Our results suggest that histerids that prey upon pine bark beetles may have different host or host habitat preferences, which could reduce interspecific competition.

As a group, arthropod natural enemies have been shown to substantially reduce within-tree pine bark beetle populations. However, little is known about the impacts of individual species on bark beetle mortality. In a controlled laboratory study, we measured the effects of two predaceous histerid species, Platysoma parallelum (Say) and Plegaderus transversus (Say), on Ips calligraphus (Germar) and Ips grandicollis (Eichhoff) brood mortality. Platysoma parallelum was found to have a greater impact on I. grandicollis mortality than Ple. transversus when only one histerid and prey species were present. No significant differences in I. calligraphus mortality were observed for either of the two histerid species. More I. grandicollis brood was killed per introduced Pla. parallelum adult than per introduced Ple. transversus adult likely as a result of the larger size and biomass requirements of Pla. parallelum. The results of this experiment indicate that histerids, by themselves, have the ability to lower within-tree bark beetle populations and could have potential use in a bark beetle biological control program.

The most common predaceous hister beetles (Coleoptera: Histeridae) found associated with Ips engraver beetles (Coleoptera: Scolytidae) in southern Louisiana were Platysoma attenuata LeConte, P. cylindrica (Paykull), P. parallelum (Say), and Plegaderus transversus (Say). The seasonal abundance of histerids caught in flight traps coincided with Ips spp. activity in the area. Histerid adults were initially caught in sticky traps on Ips-infested loblolly pine logs 1 wk after Ips spp. attacks had begun. As a group, histerids emerged from logs in a bimodal pattern with the first peak occurring during Ips spp. emergence and a second 4 wks later. The abundance of P. parallelum and P. transversus indicates that they likely fed on bark beetles and organisms arriving later in the colonization sequence. Visual orientation appeared to play a role in attraction of histerids to logs colonized by bark beetles. Platysoma attenuata preferred vertically-positioned logs to horizontal logs, while P. parallelum was the opposite. These results suggest that some histerids may be visually attracted to horizontal silhouettes, such as pine trees that have been blown down or felled and often are infested by Ips spp. Other hister beetles may prefer vertical silhouettes, such as standing pines, which tend to be colonized by the southern pine beetle, Dendroctonus frontalis Zimmermann.

The most common predaceous Histeridae (Coleoptera) found associated with Ips engraver beetles (Coleoptera: Scolytidae) in Louisiana were Platysoma attenuata LeConte, Pla. cylindrica (Paykull), Pla. parallelum (Say), and Plegaderus transversus (Say). Seasonal abundance of histerids in flight traps coincided with Ips spp. activity in the area. Histerid adults arrived at loblolly pine (Pinus taeda L.) logs one wk after Ips attacks had begun. As a group, histerids exhibited a bimodal emergence pattern with the first peak occurring during Ips emergence and a second four wks later, indicating that they fed on bark beetles and associated organisms arriving later in the colonization sequence. Visual orientation appeared to affect host tree location by histerids and may facilitate niche partitioning among species. Platysoma parallelum was attracted to horizontally positioned logs, representing trees more likely to be infested by Ips spp., while Pla. attenuata preferred vertical logs, representing standing pines, which tend to be colonized by the southern pine beetle, Dendroctonus frontalis Zimmermann. Histerid predators also utilized bark beetle pheromones as kairomonal odor cues to locate their prey. Histerid species had differential electrophysiological (antennal) and behavioral responses to three prey aggregation pheromones: ipsenol (produced by Ips grandicollis (Eichhoff)), ipsdienol (Ips avulsus (Eichhoff) and Ips calligraphus (Germar)), and frontalin (D. frontalis). Histerids may use various strategies of long-range host habitat finding and short-range host finding, which could reduce interspecific competition. Measurement of antennal threshold responses indicated that Pla. parallelum could perceive frontalin at lower quantities than Ple. transversus and, thus, may have the ability to locate D. frontalis attacks earlier. In a controlled study, Pla. parallelum was found to have a greater impact on I. grandicollis mortality than Ple. transversus when only one histerid and one prey species were present. More I. grandicollis brood was killed per introduced Pla. parallelum adult likely as a result of Pla. parallelum’s larger size and biomass requirements. In a separate experiment, Pla. parallelum adults consumed I. calligraphus larvae until satiation (up to four per day). Collectively, these experiments provide evidence that augmentative releases of histerids have potential use for biological control of bark beetles.