Shield Defense of a Larval Tortoise Beetle

Larvae of the folivorous tortoise beetle, Plagiometriona clavata, carry shields formed from feces and exuviae above their bodies. We used an ecologically relevant predatory ant, Formica subsericea, in a bioassay to determine if shields functioned as simple barriers, as previous studies indicated, or whether they were chemical defenses. Shields were necessary for larval survival; shield removal rendered larvae vulnerable. Shields produced by larvae reared on a substitute diet failed to provide protection. Solvent-leached shields also failed to deter ants, indicating the shield had a host-derived chemical component likely located in the feces, not in the exuviae. Solanum dulcamara, the larval host plant, contained free phytol, steroidal glycoalkaloids, and saponins. Shields contained partially deglycosylated metabolites of host steroidal glycoalkaloids and saponins, a suite of fatty acids, and derivatives of phytol, which together formed a deterrent barrier against ant attack. We compared the mobile shield of P. clavata to the stationary shield of another S. dulcamara-feeding leaf beetle, Lema trilinea. Both larval shield defenses were formed from a very similar array of host-derived compounds with deterrent properties. We concluded that convergent patterns of limited chemical transformation and selective incorporation of particular deterrent metabolites in shield defenses of two unrelated taxa represented responses to selection from invertebrate predators.     

The Chlorophyll Catabolite,Pheophorbide <Emphasis Type="Italic">a</Emphasis>, Confers Predation Resistance in a Larval Tortoise Beetle Shield Defense

Larval insect herbivores feeding externally on leaves are vulnerable to numerous and varied enemies. Larvae of the Neotropical herbivore, Chelymorpha alternans (Chrysomelidae:Cassidinae), possess shields made of cast skins and feces, which can be aimed and waved at attacking enemies. Prior work with C. alternans feeding on Merremia umbellata (Convolvulaceae) showed that shields offered protection from generalist predators, and polar compounds were implicated. This study used a ubiquitous ant predator, Azteca lacrymosa, in field bioassays to determine the chemical constitution of the defense. We confirmed that intact shields do protect larvae and that methanol-water leaching significantly reduced shield effectiveness. Liquid chromatography-mass spectrometry (LC-MS) of the methanolic shield extract revealed two peaks at 20.18 min and 21.97 min, both with a molecular ion at m/z 593.4, and a strong UV absorption around 409 nm, suggesting a porphyrin-type compound. LC-MS analysis of a commercial standard confirmed pheophorbide a (Pha) identity. C. alternans shields contained more than 100 μg Pha per shield. Shields leached with methanol-water did not deter ants. Methanol-water-leached shields enhanced with 3 μg of Pha were more deterrent than larvae with solvent-leached shields, while those with 5 μg additional Pha provided slightly less deterrence than larvae with intact shields. Solvent-leached shields with 10 μg added Pha were comparable to intact shields, even though the Pha concentration was less than 10% of its natural concentration. Our findings are the first to assign an ecological role for a chlorophyll catabolite as a deterrent in an insect defense.     

Chemical Defense in Larval Tortoise Beetles: Essential Oil Composition of Fecal Shields of Eurypedus nigrosignata and Foliage of its Host Plant, Cordia curassavica

Larvae of the tortoise beetle Eurypedus nigrosignata construct fecal shields using cast skins and fecal strands. Survival of larvae with intact shields was higher in the field than for larvae with shields removed. In the laboratory, E. nigrosignata feculae had a deterrent effect on feeding in the ant Myrmica rubra as did an extract of the host plant, Cordia curassavica. Three chemical types were identified in the host-plant foliage and were named -terpinene, -pinene, and sabinene, depending on their mono- and sesquiterpene composition. This is the first report of lower terpenes (essential oils) in foliage of Cordia. Fecal shields of E. nigrosignata displayed the same terpene pattern as larval host-plant leaves. The absolute concentration of mono- and sesquiterpenes in the dorsal fecal shield depended on the plant chemical type and tended to decrease with larval age. No oxidation or detoxification products of ingested terpenes were detected in the larval fecula, indicating that the chemical composition of the larval fecal shield is influenced primarily by the host-plant secondary chemistry.     

Chemical Ecology of the Defense of Two Nymphalid Butterfly Larvae Against Ants

We analyzed the behavioral responses of the ants Camponotus rufipes and Solenopsis geminata towards all instars of Dione junio and Abananote hylonome. We also analyzed ant behavior towards hexane extracts of larvae and extracts of the spines and neck glands of the fifth instars of both species and identified the chemical compounds present. Larvae of both species were repellent to ants from the first instar onward. Later instars survived ant attacks better than earlier instars. The spines and neck glands of the larvae influenced the behavior of C. rufipes. The chemical compounds contained in the hexane extracts of whole first and fifth instars and in the spines and neck glands of fifth instars were principally carboxylic acids and terpenes. Further bioassays confirmed the repellent effect of some of these acids toward ants.     

Sequestration, Maintenance, and Tissue Distribution of Pyrrolizidine Alkaloid N-Oxides in Larvae of Two Oreina Species

Oreina cacaliae and O. speciosissima are leaf beetles that, as larvae and adults, sequester pyrrolizidine alkaloid N-oxides (PAs) as defensive compounds from their host plants Adenostyles alliariae and Senecio nemorensis. As in most Oreina species, O. speciosissima is also defended by autogenously produced cardenolides (mixed defensive strategy), whereas O. cacaliae does not synthesize cardenolides and is exclusively dependent on host-plant-acquired PAs (host-derived defense). Adults of the two Oreina species were found to have the same PA storage capacity. The larvae, however, differ; larvae of O. speciosissima possess a significantly lower capability to store PAs than O. cacaliae. The ability of Oreina larvae to sequester PAs was studied by using tracer techniques with ¹⁴C-labeled senecionine N-oxide. Larvae of the two species efficiently take up [¹⁴C]senecionine N-oxide from their food plants and store the alkaloid as N-oxide. In O. cacaliae, there is a slow but continuous loss of labeled senecionine N-oxide. This effect may reflect the equilibrium between continuous PA uptake and excretion, resulting in a time-dependent tracer dilution. No noticeable loss of labeled alkaloid is associated with molting. Senecionine N-oxide is detectable in all tissues. The hemolymph is, with ca. 50–60% of total PAs, the major storage compartment, followed by the integument, with ca 30%. The alkaloid concentration in the hemolymph is approximately sixfold higher than in the solid tissues. The selectivity of PA sequestration in larvae is comparable to PA sequestration in the bodies of adult beetles.     

Antifungal Diketopiperazines from Symbiotic Fungus of Fungus-Growing Ant Cyphomyrmex minutus

The attine fungus Tyridiomyces formicarum, the symbiont of the fungus-growing ant Cyphomyrmex minutus, produces several antifungal diketopiperazines. This represents the first identification of antifungal compounds from an attine symbiont and contradicts previous suggestions that attine fungi do not produce metabolites with antifungal activity. T. formicarum probably produces antifungal compounds in defense (1) against other fungi that invade the gardens and escape the weeding activity of the ants, or (2) against ant-pathogenic fungi that could harm the host ants. Fungi cultivated by fungus-growing ants may represent a rich source of additional bioactive metabolites.     

Inter- and Intraspecific Comparisons of Antiherbivore Defenses in Three Species of Rainforest Understory Shrubs

Plants defend themselves against herbivores and pathogens with a suite of morphological, phenological, biochemical, and biotic defenses, each of which is presumably costly. The best studied are allocation costs that involve trade-offs in investment of resources to defense versus other plant functions. Decreases in growth or reproductive effort are the costs most often associated with antiherbivore defenses, but trade-offs among different defenses may also occur within a single plant species. We examined trade-offs among defenses in closely related tropical rain forest shrubs (Piper cenocladum, P. imperiale, and P. melanocladum) that possess different combinations of three types of defense: ant mutualists, secondary compounds, and leaf toughness. We also examined the effectiveness of different defenses and suites of defenses against the most abundant generalist and specialist Piper herbivores. For all species examined, leaf toughness was the most effective defense, with the toughest species, P. melanocladum, receiving the lowest incidence of total herbivory, and the least tough species, P. imperiale, receiving the highest incidence. Although variation in toughness within each species was substantial, there were no intraspecific relationships between toughness and herbivory. In other Piper studies, chemical and biotic defenses had strong intraspecific negative correlations with herbivory. A wide variety of defensive mechanisms was quantified in the three Piper species studied, ranging from low concentrations of chemical defenses in P. imperiale to a complex suite of defenses in P. cenocladum that includes ant mutualists, secondary metabolites, and moderate toughness. Ecological costs were evident for the array of defensive mechanisms within these Piper species, and the differences in defensive strategies among species may represent evolutionary trade-offs between costly defenses.     

Sequestration of Furostanol Saponins by <Emphasis Type="Italic">Monophadnus</Emphasis> Sawfly Larvae

Sawfly larvae of the tribe Phymatocerini (Hymenoptera: Tenthredinidae), which are specialized on toxic plants in the orders Liliales and Ranunculales, exude a droplet of deterrent hemolymph upon attack by a predator. We investigated whether secondary plant metabolites from Ranunculaceae leaves are sequestered by phymatocerine Monophadnus species, i.e., Monophadnus alpicola feeding upon Pulsatilla alpina and Monophadnus monticola feeding upon Ranunculus lanuginosus. Moreover, two undescribed Monophadnus species were studied: species A collected from Helleborus foetidus and species B collected from Helleborus viridis. Comparative high-performance liquid chromatographic–photodiode array detection–electrospray ionization–mass spectrometric analyses of plant leaf and insect hemolymph extracts revealed the presence of furostanol saponins in all samples. Larvae of species A and B actively sequestered (25R)-26-[(α-l-rhamnopyranosyl)oxy]-22α-methoxyfurost-5-en-3β-yl O-β-d-glucopyranosyl-(1→3)-O-[6-acetyl-β-d-glucopyranosyl-(1→3)]-O-β-d-glucopyranoside (compound 1). This compound occurred at a 65- to 200-fold higher concentration in the hemolymph of the two species (1.6 and 17.5 μmol/g FW, respectively) than in their host plant (0.008 and 0.268 μmol/g FW, respectively). In M. monticola, compound 1 was found at a concentration (1.2 μmol/g FW) similar to that in the host plant (1.36 μmol/g FW). The compound could not be detected consistently in M. alpicola larvae where, however, a related saponin may be present. Additional furostanol saponins were found in H. foetidus and H. viridis, but not in the two Monophadnus species feeding on them, indicating that sequestration of compound 1 is a highly specific process. In laboratory bioassays, crude hemolymph of three Monophadnus species showed a significant feeding deterrent activity against a potential predator, Myrmica rubra ant workers. Isolated furostanol saponins were also active against the ants, at a concentration range similar to that found in the hemolymph. Thus, these compounds seem to play a major role for chemical defense of Monophadnus larvae, although other plant secondary metabolites (glycosylated ecdysteroids) were also detected in their hemolymph. Physiological and ecological implications of the sequestered furostanol saponins are discussed. Dedicated to the memory of Professor Ivano Morelli (1940–2005)     

Microbe inhibition by Tribolium flour beetles varies with beetle species,strain, sex,and microbe group

Tribolium flour beetles produce defensive compounds, including quinones, putatively aimed at deterring predators and inhibiting microbes. Here we examine how effective the defensive secretions of Tribolium confusum and T. castaneum are at inhibiting growth of various microbes and how this varies with species, geographic strain, and sex of the beetles. We explore differences at both the kingdom and species level of common flour microbes in their susceptibility to defensive compounds. Beetle species and strains vary in their ability to inhibit microbial growth. In addition, microbes vary in their sensitivity to the beetles' defense compounds. The capability to suppress microbial growth is likely under stabilizing selection with optimum quinone production varying among populations and may be dependent on several environmental factors including temperature, humidity, and predators.     

Antipredator Defense of Biological Control Agent Oxyops vitiosa Is Mediated by Plant Volatiles Sequestered from the Host Plant Melaleuca quinquenervia

The weevil Oxyops vitiosa is an Australian species imported to Florida, USA, for the biological control of the invasive weed species Melaleuca quinquenervia. Larvae of this species feed on leaves of their host and produce a shiny orange secretion that covers the integument. When this secretion is applied at physiological concentrations to dog food bait, fire ant consumption and visitation are significantly reduced. Gas chromatographic analysis indicates that the larval secretion qualitatively and quantitatively resembles the terpenoid composition of the host foliage. When the combination of 10 major terpenoids from the O. vitiosa secretion was applied to dog food bait, fire ant consumption and visitation were reduced. When these 10 terpenoids were tested individually, the sesquiterpene viridiflorol was the most active component in decreasing fire ant consumption. Fire ant visitation was initially (15 min after initiation of the study) decreased for dog food bait treated with viridiflorol and the monoterpenes 1,8-cineole and -terpineol. Fire ants continued to avoid the bait treated with viridiflorol at 18 g/mg dog food for up to 6 hr after the initiation of the experiment. Moreover, ants avoided bait treated with 1.8 g/mg for up to 3 hr. The concentrations of viridiflorol, 1,8-cineole, and -terpineol in larval washes were about twice that of the host foliage, suggesting that the larvae sequester these plant-derived compounds for defense against generalist predators.     

Chemical Analysis of Squirt-gun Defense in Bursera and Counterdefense by Chrysomelid Beetles

The genus Bursera produces resin stored in canals in the leaf. When leaves are damaged, some, but not all, species release abundant resin. Species of Blepharida are specialized herbivores of Bursera, and they exhibit variation in their counterdefensive behavior. Species feeding on resin-releasing plants cut the leaf veins before feeding, which often makes them more prone to predation. They also adorn their backs with their feces and may regurgitate and release an anal secretion when attacked or disturbed by predators. Species that feed on Bursera species that release no fluids do not sever the leaf veins prior to feeding, and they do not carry their feces on their backs. Instead, they face their predators, raise their heads in a "boxing-like" display, and rapidly swing their abdomens from side to side. We performed a comparative chemical analysis of the compounds found in Bursera schlechtendalii, a species that releases abundant resins, and B. biflora, a species that does not. We also analyzed the frass, enteric discharges, and larvae of the two species of Blepharida that feed on each of these plants. The compounds found in the body, feces, and discharges of the Blepharida species that adorns itself with feces match the chemical mixture of its host plant, suggesting that this beetle species can compensate its higher risk of predation by using the compounds present in the plant for defense. The chemical mixture of B. biflora is more complex and does not match the compounds found in the body or frass of its beetle herbivore, suggesting that the defensive strategy of this insect is behavioral and does not rely on its host's constituents.     

Role of volatile inforchemicals emitted by feces of larvae in host-searching behavior of parasitoidCotesia rubecula (Hymenoptera: Braconidae): A behavioral and chemical study

The role of volatile infochemicals emitted by feces of larvae in the host-searching behavior of the parasitoidCotesia rubecula was evaluated during single- and dual-choice tests inside a wind tunnel. The following treatments were tested: feces produced by second and fourth instars ofPieris rapae (preferred host), second instars ofP. brassicae (inferior host), second instars ofP. napi (nonhost), and wet feces of second instars ofP. rapae. During a single-choice situation females ofC. rubecula oriented to all types of feces tested. When a preference was to be made,C. rubecula preferred feces of second instars ofP. rapae over that of fourth, feces ofP. rapae over that ofP. brassicae, feces ofP. napi over that ofP. brassicae, and wet over normal host feces. No preference was exhibited between feces of second instars ofP. napi and that of second instars ofP. rapae. The relative importance of infochemicals from host feces versus plant damage caused by host larvae to the searching behavior ofC. rubecula was also evaluated. Plant damage was more important to the searching females than host feces when feces were present in specific concentrations in relation to damage. The volatiles released by normal and wet feces of second instars ofP. rapae, wet feces of fourth instars ofP. rapae, and normal and wet feces ofP. brassicae were collected and identified. Overall, 85 chemical compounds were recorded belonging to the following chemical groups: alcohols, ketones, aldehydes, esters, isothiocyanates, sulfides, nitriles, furanoids, terpenoids and pyridines. The blend of chemicals emitted by feces of different instars ofP. rapae and different species ofPieris exhibited an instar and species specificity in both quantity and quality. Wetting of normal feces increased the amount of volatile chemicals released, and it was also responsible for the appearance of new compounds. The role of feces of larvae in the host-seeking behavior ofC. rubecula is discussed.     

Hiding in Plain Sight: Cuticular Compound Profile Matching Conceals a Larval Tortoise Beetle in its Host Chemical Cloud

Larvae of tortoise beetles are postulated to have fecal shields as the main defensive strategy against predators. Such a device protects beetles both physically and chemically. In order to examine how larvae Chelymorpha reimoseri are protected against predatory ants, which frequently visit extrafloral nectaries in their host plant, the morning glory Ipomoea carnea, we conducted anti-predation bioassays with live 5th instars. In the field, larvae in contact with ants had survival between 40 and 73 %, independently of shield presence. In the laboratory, when exposed to Camponotus crassus, larvae with shields had significantly higher survival (85 %) than those without shields (64 %). In both scenarios, larval survival was significantly higher when compared with palatable Spodoptera frugiperda larvae, as the latter were all consumed. We also observed that when C. reimoseri larvae showed no movement, the ants walked on them without attacking. We hypothesized that if the larval integument has a pattern of cuticular compounds (CCs) similar to that of its host plant, larvae would be rendered chemically camouflaged. In the field and laboratory, the freeze-dried palatable larvae of S. frugiperda treated with CCs of 5th instar C. reimoseri and left on I. carnea leaves were significantly less removed by ants than controls without these compounds. We also found a similarity of approximately 50 % between the CCs in C. reimoseri larvae and I. carnea host leaves. Both findings provide evidence in support of the hypothesis that chemical camouflage plays an important role in larval defense, which is reported for the first time in an ectophagous leaf beetle larva.     

Identification of Semiochemicals Associated with Jeffrey Pine Beetle, Dendroctonus jeffreyi

Analysis of frass extracts and aerations from adult beetles confirmed earlier studies identifying 1-heptanol as a principal pheromone constituent produced by female Dendroctonus jeffreyi Hopkins. The aerations also indicated that males produced 33% (+) and 67% (–)-frontalin, previously unreported for this species, and >99% (+)-exo-brevicomin. Both males and females were responsive to these compounds in electrophysiological studies. Laboratory bioassays and field trapping experiments indicated that males and females were attracted to a mixture of 1-heptanol plus the principal host resin component heptane, but females were less attracted than males. Inclusion of racemic exo-brevicomin at 0.1% concentration in the traps increased the response of females. Inclusion of racemic frontalin above a 1% concentration in the normally attractive lures blocked arrival of beetles to the traps. While the female-produced pheromone components and host synergists are very different between the sibling species D. jeffreyi and Dendroctonus ponderosae Hopkins, the principal male-produced compounds are the same, and the response of the female beetles to those compounds appears to be similar.     

Behavior and chemical disguise of cuckoo antLeptothorax kutteri in relation to its hostLeptothorax acervorum

Females of the obligately parasitic cuckoo ant,Leptothorax kutteri, a workerless inquiline, are among the only adult ants that can successfully invade ant societies and come to be accepted as a nestmate by the existing adult workers. This occurs even though the cuckoo ant is usually severely attacked by theLeptothorax acervorum workers of the colony that she is attempting to enter and parasitize. Through extensive ethogram studies of established parasites and parasitized and free-livingL. acervorum workers and queens, we show that theL. kutteri queen grooms host queens at an exceptionally high frequency. Possibly associated with this behavior, the established parasite is never attacked by theL. acervorum workers or queens she exploits. We show that there is exceptional similarity between the cuticular hydrocarbons and especially the cuticular fatty acids of the parasitic females and her nestmateL. acervorum workers, compared with nonnestmate workers and queens. We suggest that this matching of cuticular compounds may be associated with the grooming of host queens by the parasite. This in turn suggests the possibility that fatty acids have a role in colony-specific nestmate recognition in these and other ants and that grooming may serve for the dissemination of such substances throughout the colony.     

Antifungal leaf-surface metabolites correlate with fungal abundance in sagebrush populations

A central component in understanding plant–enemy interactions is to determine whether plant enemies, such as herbivores and pathogens, mediate the evolution of plant secondary metabolites. Using 26 populations of a broadly distributed plant species, sagebrush (Artemisia tridentata), we examined whether sagebrush populations in habitats with a greater prevalence of fungi contained antifungal secondary metabolites on leaf surfaces that were more active and diverse than sagebrush populations in habitats less favorable to fungi. Because moisture and temperature play a key role in the epidemiology of most plant–pathogen interactions, we also examined the relationship between the antifungal activity of secondary metabolites and the climate of a site. We evaluated the antifungal activity of sagebrush secondary metabolites against two fungi, a wild Penicillium sp. and a laboratory yeast, Saccharomyces cerevisiae, using a filter-paper disk assay and bioautography. Comparing the 26 sagebrush populations, we found that fungal abundance was a good predictor of both the activity (r ² = 0.36 for Saccharomyces, r ² = 0.37 for Penicillium) and number (r ² = 0.34 for Saccharomyces) of antifungal secondary metabolites. This suggests that selection imposed by fungal pathogens has led to more effective antifungal secondary metabolites. We found that the antifungal activity of sagebrush secondary metabolites was negatively related to average vapor pressure deficit of the habitat (r ² = 0.60 for Saccharomyces, r ² = 0.61 for Penicillium). Differences in antifungal activity among populations were not due to the amount of secondary metabolites, but rather to qualitative differences in the composition of antifungal compounds. Although all populations in habitats with high fungal prevalence had secondary metabolites with high antifungal activity, different suites of compounds were responsible for this activity, suggesting independent outcomes of selection on plants by fungal pathogens. The location of antifungal secondary metabolites on the leaf surface is consistent with their putative defense role, and we found no evidence supporting other functions, such as protection from ultraviolet light or oxidation. That the antifungal activity of sagebrush secondary metabolites was similar for two different fungi provides support for broad antifungal defenses. The incidence and severity of fungal disease in the field (caused by Puccinia tanaceti) were similar in moist and dry habitats, possibly reflecting an equilibrium between plant defense and fungal attack, as sites with greater fungal abundance compensated with more effective secondary metabolites. The geographic correlation between fungal abundance and antifungal secondary metabolites of sagebrush, coupled with our other data showing heritable variation in these metabolites, suggests that pathogenic fungi have selected for antifungal secondary metabolites in sagebrush.     

Differences in attraction to semiochemicals present in sympatric pine shoot beetles,Tomicus minor andT. piniperda

The chemical ecology of host- and mate-finding in the pine shoot beetles,Tomicus minor andT. piniperda, was studied in southern Sweden. Beetles were collected in the field from defined attack phases on Scots pine. Using gas chromatography-mass spectroscopy, a number of oxygen-containing monoterpenes, e.g., 3-carene-10-ol, myrtenol,trans-verbenol, and verbenone, were identified from hindgut extracts of both sexes of both species. Compared toT. minor,T. piniperda contained additional compounds and in larger amounts. The amounts were highest in both species at the time when the beetles had bored into contact with the resin-producing xylem-phloem tissue. The synthesis of (1S,6R)-3-carene-10-ol by photooxidatipn of (+)-(1S,6R)-3-carene is described. In comparative electroantennogram (EAG) measurements on males and females of both species, the most active of the tested compounds wastrans-verbenol. Laboratory bioassays of walking beetles showed thatT. piniperda was attracted to uninfestèd pine logs.T. minor was more strongly attracted to pine logs infested with females than to uninfested pine logs, indicating a female-produced aggregation pheromone. Field tests confirmed thatT. piniperda was strongly attracted to pine logs. The attraction ofT. minor to logs was significant only when logs were combined with racemictrans-verbenol and (1S,6R)-3-carene-10-ol.T. minor was also attracted to a combination of these monoterpene alcohols alone. We suggest that host and mate location inT. piniperda is achieved by means of a kairomone composed of host monoterpenes, whileT. minor utilizes a primitive pheromone synergized by host odors. Evolution of host colonization strategies of the two beetles are discussed.Coleoptera: Scolytidae.This study was made within the project Odour signals for control of pest insects.     

Sequestration of Host Plant Glucosinolates in the Defensive Hemolymph of the Sawfly Athalia rosae

Interactions between insects and glucosinolate-containing plant species have been investigated for a long time. Although the glucosinolate–myrosinase system is believed to act as a defense mechanism against generalist herbivores and fungi, several specialist insects use these secondary metabolites for host plant finding and acceptance and can handle them physiologically. However, sequestration of glucosinolates in specialist herbivores has been less well studied. Larvae of the turnip sawfly Athalia rosae feed on several glucosinolate-containing plant species. When larvae are disturbed by antagonists, they release one or more small droplets of hemolymph from their integument. This reflex bleeding is used as a defense mechanism. Specific glucosinolate analysis, by conversion to desulfoglucosinolates and analysis of these by high-performance liquid chromatography coupled to diode array UV spectroscopy and mass spectrometry, revealed that larvae incorporate and concentrate the plant's characteristic glucosinolates from their hosts. Extracts of larvae that were reared on Sinapis alba contained sinalbin, even when the larvae were first starved for 22 hr and, thus, had empty guts. Hemolymph was analyzed from larvae that were reared on either S. alba, Brassica nigra, or Barbarea stricta. Leaves were analyzed from the same plants the larvae had fed on. Sinalbin (from S. alba), sinigrin (B. nigra), or glucobarbarin and glucobrassicin (B. stricta) were present in leaves in concentrations less than 1 mol/g fresh weight, while the same glucosinolates could be detected in the larvae's hemolymph in concentrations between 10 and 31 mol/g fresh weight, except that glucobrassicin was present only as a trace. In larval feces, only trace amounts of glucosinolates (sinalbin and sinigrin) could be detected. The glucosinolates were likewise found in freshly emerged adults, showing that the sequestered phytochemicals were transferred through the pupal stage.     

Primary Attraction of the Fir Engraver, Scolytus ventralis

In laboratory bioassays, Porapak Q-captured and steam-distilled volatiles from the bark of host trees, Abies grandis, particularly from root-rot-infected trees, attracted 50–70% of male and female fir engravers, Scolytus ventralis. Gas chromatographic–electroantennographic detection (GC-EAD) analyses of Porapak Q-captured bark volatiles revealed 19 EAD-active compounds of which 13 (mostly monoterpenes) were identified by GC–mass spectrometry (GC-MS). In separate field experiments, multiple-funnel traps baited with two blends of these 13 synthetic volatiles released at 280 and 340 mg/ 24 hr attracted 66 and 93% of the total S. ventralis captured, respectively. The clerid predator, Thanasimus undulatus, also responded strongly to the kairomonal volatiles. Additional experiments produced no evidence for aggregation pheromones in S. ventralis. These included laboratory bioassays and GC and GC-EAD analyses of Porapak Q-captured volatiles from male- and female-infested logs or trees undergoing mass attack in the field, GC analyses and/or bioassays of extracts from female accessory glands, extracted volatiles from emerged, attacking and juvenile hormone-treated beetles of both sexes, and videotape analysis of the behavior of attacking beetles on the bark surface. We argue against the hypothesis of pheromone-mediated secondary attraction in S. ventralis and conclude that the attack dynamics of this species can be explained solely by its sensitive primary attraction response to host volatiles.     

Effects of Host Tree Species on Attractiveness of Tunneling Pine Engravers, Ips pini, to Conspecifics and Insect Predators

The effect of host tree species on the attractiveness of tunneling Ips pini to flying beetles and their insect predators in Wisconsin was investigated. Tree species influenced the flight response of both predators and prey in the same rank order. Ips pini and its major predators, Thanasimus dubius and Platysoma cylindrica, were more attracted to I. pini males boring into bark–phloem disks of Pinus strobus L. than Pinus banksiana Lamb, and least attracted to I. pini males boring into bark–phloem disks of Pinus resinosa. Sources of within-tree, between-tree, and between-species variation in the degree of attraction elicited by tunneling beetles were quantified. A bioassay for evaluating host tree effects on pheromone based communication among bark beetles under conditions of controlled beetle entry was developed. Possible mechanisms of host species effects on the dynamics of predator and prey interactions in bark beetle ecology are discussed.