Sequestration of glucosinolates by harlequin bug Murgantia histrionica

Murgantia histrionica, the harlequin bug, is an aposematic pentatomid that feeds on toxic crucifer plants. By performing predator trials, we found that the bugs are distasteful to several species of bird predators. Given this, we tested the hypothesis that the bugs sequester toxins from the crucifer plants they feed on for use in defense against predation. We used high-pressure liquid chromatography for analyses and tested if M. histrionica sequesters toxic chemicals from its crucifer diet. We found that M. histrionica sequesters mustard oil glycosides, precursors to zootoxic mephitic nitriles, and that sequestration is characteristic of the plant species fed upon. Glucosinolate titers in M. histrionica bodies were 20–30 times higher than in their guts. We found that cabbage-fed M. histrionica had higher titers of cabbage glucosinolates than bugs that were fed on a cabbage diet and then switched to a diet of garden nasturtium. This indicates that M. histrionica immediately sequesters chemicals from whichever plant it feeds upon. The study shows that M. histrionica can sequester glucosinolates from its host plants for use in defense against predation and that the bugs can retain the glucosinolates for an extended period of time.     

A long-range attractant kairomone for egg parasitoidTrissolcus basalis,isolated from defensive secretion of its host,Nezara viridula

A short-chain ,-unsaturated aldehyde, (E)-2-decenal, present in the defensive metathoracic gland ofNezara viridula (L.) (Heteroptera: Pentatomidae), stimulates a behavioral response in the egg parasitoidTrissolcus basalis (Woll.) (Hymenoptera: Scelionidae). Preliminary studies showed thatT. basalis are attracted to an area containing adultN. viridula, but we also found that femaleT. basalis would examine and probe glass beads coated with an acetone extract of the metathoracic gland from males or females. Using this bioassay, the kairomone was isolated by bioassay directed by preparative gas chromatography and identified by NMR and mass spectrometry as (E)-2-decenal. The biological activity of the identified aldehyde was compared with analogs to determine specificity. An unstable Z isomer was found to be more active but not present in detectable or behaviorly relevant levels in the host, based on the bell-shaped dose-response curve of the two isomers. An investigation was also designed to determine if theE isomer was also responsible for the egg recognition kairomone activity previously reported. However, no 2-decenal isomers were detected in host egg extracts and the chemical characteristics of the 2-decenal isomers differ from the unidentified egg recognition kairomone. The role of the (E)-2-decenal in attracting femaleT. basalts toN. viridula was demonstrated in a Y-tube olfactometer; this alk-2-enal appears to act as a long-range kairomone orientingT. basalis toNezara populations.     

Sesamia calamistis calling behavior and its role in host finding of egg parasitoids Telenomus busseolae,telenomus isis,and Lathromeris ovicida

In the Republic of Benin, the African pink stem borer Sesamia calamistis Hampson is kept under control by the two scelionid egg parasitoids Telenomus busseolae (Gahan) and T. isis (Polaszek). A third species, the trichogrammatid Lathromeris ovicida Risbec, although commonly obtained from egg batches, is of low importance. High egg and egg batch parasitism by Telenomus spp. at low host densities suggests excellent host-finding capacity. Previously it was hypothesized that pheromones produced by calling S. calamistis virgins play an important role in attracting the parasitoids to the area where oviposition is likely to occur. Thus, after determining the effect of age (1–4 days) on the calling rhythm of S. calamistis, 1-day-old virgin females were chosen to investigate the response of the parasitoids to calling and noncalling females and two empty controls, in a four-arm olfactometer. The results showed that calling started earliest and lasted longest with 1-day-old females, but was similar for 2- to 4-days-old females. The percentage of females calling was higher in early than latter scotophases. The highest percentage of active females was obtained between 8 and 9 hr after the beginning of the first scotophase. All three parasitoid species responded to calling females, while there were no differences between noncalling females and the empty controls. The response pattern was similar for the two Telenomus spp. but considerably weaker for L. ovicida, reflecting differing host specificity of the three parasitoid species.     

Kairomonal activities of 2-acylcyclohexane-1,3 diones produced byEphestia kuehniella zeller in eliciting searching behavior by the parasitoidBracon hebetor (say)

2-Acylcyclohexane-1,3-diones produced in the mandibular glands ofEphestia kuehniella Zeller (Lepidoptera: Pyralidae) fifth instars acted as arrestment and host-trail following kairomones for the parasitoid,Bracon hebetor (Say) (Hymenoptera: Braconidae). The behavioral response of the parasitoids to the kairomone varied with kairomone concentration and distribution. However, only small differences in activity were noted for the different mandibular gland components.B. hebetor females that encountered filter paper patches impregnated with the kairomone exhibited antennation and probing behavior. Females followed trails formed with 2-[(Z,E)12,14-hexadecadienoyl]cyclohexane-1,3-dione in the same manner exhibited with host-made trails. At concentrations of 1.0 g/mm and above, trail following was interrupted by frequent probing.     

Role of diet in host selection ofHeliothis virescens by parasitoidCampoletis sonorensis (Hymenoptera: Ichneumonidae)

Gas chromatographic analysis revealed that chemicals attractive toCampoletis sonorensis (Cameron), previously identified in cotton, were not present in wheat germ diet-rearedHeliothis virescens (F.) larvae. Diet-reared larvae fed cotton obtained the chemicals from cotton, with the consequence of enhanced kairomonal activity of the larvae and their frass toC. sonorensis. Parasitoids, presented a choice between cotton, cotton plus hosts, hosts alone, and control in an olfactometer, responded non-randomly, with the greatest number of responses to cotton plus hosts, and three times as many responses to cotton alone as to larvae alone. The role of the plant in the parasitoid-host relationship is discussed.     

Volatile infochemicals used in host and host habitat location byCotesia flavipes Cameron andCotesia sesamiae (Cameron) (Hymenoptera: Braconidae), larval parasitoids of stemborers on graminae

FemaleCotesia flavipes Cameron andCotesia sesamiae (Cameron) were attracted to odors in a Y-tube olfactometer from uninfested maize (Zea mays L.), sorghum [Sorghum bicolor (L.)], and napier grass (Pennisetum purpureum Schumach). In dual choice tests,Cotesia flavipes showed a preference for maize over sorghum, while maize and napier grass were equally attractive. In contrast,Cotesia sesamiae preferred volatiles from sorghum and napier grass over those from maize. The two parasitoids were significantly more attracted to maize infested with the stemborers,Chilo partellus (Swinhoe),Chilo orichalcociliellus Strand,Sesamia calamistis Hampson, andBusseola fusca (Fuller), than uninfested maize. In dual choice tests,Cotesia flavipes andCotesia sesamiae were unable to discriminate between odors from plants infested by the different species of stemborers.     

Host-specific recognition kairomone for the parasitoidMicroplitis croceipes (Cresson)

A water-extractable host recognition kairomone in frass of corn earworm,Helicoverpa zea Boddie (Lepidoptera: Noctuidae), host larvae stimulates antennation by females of the parasitoidMicroplitis croceipes Cresson (Braconidae: Hymenoptera). In addition, when the wasps contact water extracts of host frass they will subsequently fly in a flight tunnel to odor associated with the extract. Contact with water extracts of cowpea leaves or with water extracts of frass from larvae of nonhost beet armyworm, fall armyworm, or cabbage looper that were fed cowpea leaves does not stimulate antennation, nor do wasps fly to associated odors after contact with these substances. However, contact with the water extract of host frass in association with hexane extract of cowpea-fed nonhost frass will induce the wasps to subsequently fly to the hexane extract of the nonhost frass when it is used as an odor source in a flight tunnel. Thus the host-specific kairomone by whichM. croceipes recognizes the frass of its host is extractable with water. This substance plays a crucial role in the foraging behavior of this parasitoid by allowing it to recognize host frass and to learn to search for odors originating from plants on which the host is feeding.     

Beneficial arthropod behavior mediated by airborne semiochemicals. II. Olfactometric studies of host location by the parasitoidMicroplitis croceipes (Cresson) (Hymenoptera: Braconidae)

The response ofMicroplitis croceipes (Cresson) to odors from a plant-host complex was investigated using a four-choice olfactometer. Female, but not male, parasitoids responded in a dose-dependent fashion to volatiles from the plant-host complex and oviposition experience enhanced this response. Female age had no apparent effect on the response. Both artificially damaged leaves and frass elicited positive responses but of lower magnitude than those elicited by the plant-host complex. Volatiles collected from the plant-host complex placed on filter paper also elicited positive responses by female parasitoids.Mention of a commercial or proprietary product does not constitute an endorsement by the USDA.     

Long-chain free fatty acids: Semiochemicals for host location by western corn rootworm larvae

A bioassay-driven sequential fractionation scheme was used to isolate fractions of a crude dichloromethane maize seedling extract behaviorally active to larvae of the western corn rootworm,Diabrotica virgifera virgifera LeConte. (Z,Z)-9,12-Octadecadienoic (linoleic) acid, (Z)-9-octadecenoic (oleic) acid, and octadecanoic (stearic) acid were identified from a purified fraction of maize extract that was attractive to western corn rootworm larvae in choice tests with equal levels of carbon dioxide on both sides of the choice. When synthetic linoleic, oleic, and stearic acids were tested together in the amounts and proportions found in the attractive fraction (1000, 800, and 300 ng of linoleic, oleic, and stearic acids, respectively), significantly more western corn rootworm larvae were found on the side with synthetic free fatty acids plus carbon dioxide than on the side with carbon dioxide alone. Results of the choice-test bioassays were not significantly different when the synthetic blend of free fatty acids was substituted for the purified maize fraction. Neither the purified extract nor the synthetic blend was behaviorally active in preliminary single-choice experiments without carbon dioxide. Linoleic, oleic, and stearic acids were also tested individually in the choice test bioassay with carbon dioxide on both sides of the choice to determine a dose-response curve. Linoleic and oleic acid each had one dose that was significantly attractive in conjunction with carbon dioxide on both sides of the choice, but stearic acid was not active in the doses tested.     

Volatiles from whitefly-infested plants elicit a host-locating response in the parasitoid,Encarsia formosa

The blend of volatile compounds emitted by bean plants (Phaseolus vulgaris) infested with greenhouse whitefly (Trialeurodes vaporariorum) has been studied comparatively with undamaged plants and whiteflies themselves. Collection of the volatiles and analysis by gas chromatography revealed more than 20 compounds produced by plants infested with whitefly. Of these, 4 compounds, (Z)-3-hexen-1-ol, 4,8-dimethyl-1,3,7-nonatriene, 3-octanone, and one unidentified compound were emitted at higher levels than from the undamaged control plants. Synthetic (Z)-3-hexen-1-ol, 4,8-dimethyl-1,3,7-nonatriene, or 3-octanone all elicited a significant increase in oriented flight and landing on the source by the parasitoid, Encarsia formosa, in wind tunnel bioassays. Two-component mixtures of the compounds and the three-component mixture all elicited a similar or, in most cases, a better response by the parasitoid, the most effective being a mixture of (Z)-3-hexen-1-ol and 3-octanone. These results demonstrate that E. formosa uses volatiles from the plant-host complex as olfactory cues for host location.     

Contact chemosensory cues in egg bundles elicit male-male agonistic conflicts in the squid Loligo pealeii

Male Loligo pealeii engage in frequent agonistic bouts to gain access to female mates while aggregated at communal egg beds. Male squids are attracted to eggs in the field and in the laboratory. It was recently demonstrated that visual detection followed by physical contact with egg capsules elicited male–male aggression. We tested specific physical and chemical features of the egg capsules that may cause this strong behavioral reaction. Male squids were presented with either natural or artificial egg stimuli and scored for four selected behaviors (egg touch, egg blowing, forward-lunge grab, and fin-beating), the last two of which are highly aggressive behaviors. First, squids were presented with natural eggs versus eggs sealed in agarose-coated tubes (ESACT), which eliminated both tactile and chemical stimuli. Second, males were presented with natural eggs versus eggs sealed in agarose coated tubes containing C₁₈ Sep-Pak-purified extracts (TCPE) from squid egg capsules, which provided chemical cues from natural eggs without the physical stimulus of the egg capsules. Third, natural eggs versus heat-denatured eggs were tested to determine whether the active factor in natural eggs is heat-labile. Squids responded aggressively when contacting natural eggs and TCPE, whereas squids did not respond after touching ESACT or denatured eggs. These results suggest that aggressive behavior is elicited by a heat-labile factor that is embedded within squid egg capsules. This chemosensory cue appears to be a contact pheromone that stimulates the agonistic interactions that characterize the mating behavior of migratory squids on inshore spawning grounds.     

Chemoecological role of mammalian urine in host location by tsetse,Glossina spp. (Diptera: Glossinidae)

Trap catch size was used to investigate whetherGlossina pallidipes andG. longipennis could distinguish between the urine of the African buffalo, cattle, and waterbuck at Nguruman in southwest Kenya. NG2G traps baited with aged urine of these bovids caught significantly more of each tsetse than did the controls. The mean catch of either tsetse species in traps baited with aged urine of buffalo and cattle (tsetse hosts) and waterbuck (a nonhost) did not differ significantly. Aged urine from both tsetse hosts (buffalo and cattle) and the nonhost (waterbuck) was found to contain 4-cresol and 3-n-propylphenol in about the same ratio. However, the aged urine from other tsetse hosts (bushpig and warthog) lacked 3-n-propylphenol. Cattle urine had to be aged outside the soil to produce statistically significant increases in the trap catch ofG. pallidipes. Furthermore, patches of soil on which fresh urine of cattle was deposited, and in which it was aged, failed to effect a significant increase in the trap catch of eitherG. austeni, G. brevipalpis, orG. pallidipes as Gazi, southeast Kenya. The likelihood of tsetse either differentiating its hosts from nonhosts or locating favored hosts by the urine scent appears remote under natural conditions. It is more likely that the chemical signals critical for host location by the tsetse emanate from skin glands rather than volatilize from the urine of mammals.     

The haustorium and the chemistry of host recognition in parasitic angiosperms

Two parasitic angiosperms,Agalinis purpurea (Scrophulariaceae) andStriga asiatica (Scrophulariaceae), are compared as to the chemical recognition events involved in host selection.Agalinis is a hemiparasite which can mature to seed-set without a host, whereasStriga is a holoparasite and survives for only a very limited time without a host. Both parasites, however, attach to a host through a specialized organ known as the haustorium and regulate the development of this organ through the recognition of chemical factors from host plants. We now describe the discovery of 2,6-dimethoxy-p-benzoquinone (2,6-DMBQ) as an haustoria-inducing principle fromSorghum root extracts. Our investigation of this compound has led us to suggest that one level of host recognition in these parasitic plants is mediated through their enzymatic digestion of the host root surface. Degradation of surface components liberates quinonoid compounds, such as 2,6-DMBQ, which in turn trigger haustorial development.     

Identification of Volatile Synomones, Induced by Nezara viridula Feeding and Oviposition on Bean spp., That Attract the Egg Parasitoid Trissolcus basalis

Bean plants (Vicia faba L. and Phaseolus vulgaris L.) damaged by feeding activity of Nezara viridula (L.) (Heteroptera: Pentatomidae), and onto which an egg mass had been laid, produced volatiles that attracted the egg parasitoid Trissolcus basalis (Wollaston) (Hymenoptera: Scelionidae). Extracts of volatiles of broad bean and French bean plants induced by adults of N. viridula as a result of their feeding activity, oviposition activity, and feeding and oviposition activity combined were analyzed by gas chromatography-mass spectrometry (GC-MS), and tested in Y-tube olfactometer bioassays as attractants for T. basalis females. In extracts from undamaged leguminous plants, green-leaf volatiles were absent or scarcely detected, and monoterpenes and sesquiterpenes were present at trace levels. No significant differences were detected in the profiles of volatiles of undamaged plants, and undamaged plants on which bugs were allowed only to lay eggs. In contrast, feeding and oviposition by adults of N. viridula induced in both leguminous plants a significant increase in terpenoids such as linalool, (E)-beta-caryophyllene, (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene, and (3E)-4,8-dimethyl-1,3,7-nonatriene, which was induced only in French bean plants. Quantitative comparisons revealed increased levels of (E)-beta-caryophyllene in extracts from feeding-damaged plants with N. viridula egg masses compared to feeding-damaged plants without egg masses. In Y-tube olfactometer bioassays, T. basalis females were attracted by extracts of both leguminous plants only when N. viridula adults were allowed to feed and oviposit upon them. Fractionation of extracts of volatiles from broad bean plants with N. viridula feeding damage and egg masses yielded two fractions. but only the fraction containing (E)-beta-caryophyllene was attractive to the egg parasitoid. These findings indicate that N. viridula feeding and oviposition induce leguminous plants to produce blends of volatiles that are characterized by increased amounts of (E)-beta-caryophyllene, and these blends attract female T. basalis. The role of (E)-beta-caryophyllene as a potential synomone for T. basalis is discussed.     

Odor learning and foraging success in the parasitoid,Leptopilina heterotoma

A brief 2-hr experience with hostDrosophila larvae in artificial apple-yeast or mushroom microhabitats had three effects on the foraging behavior of femaleLeptopilina heterotoma (Hymenoptera: Eucoilidae) parasitoids under field conditions. First, experienced females released at the center of circular arrays of apple-yeast and mushroom baits were more likely to find a microhabitat over the course of a daily census than naive ones. Second, for those females that found a microhabitat, experienced ones found it faster than naive ones (i.e., experience reduced travel times). Third, females experienced with a particular microhabitat were more likely to find that micro-habitat than an alternative one. Learned preferences were retained for at least one day and possibly as many as seven. Results generally did not depend on the host species (D. melanogaster orD. simulans) with which females were given experience. Females tended to arrive at baits upwind of the point of release, suggesting that odor is involved in finding host microhabitats and, in particular, in learning to find them more effectively. The implications of these results for the application of semiochemicals in biological control are discussed briefly.     

Relative importance of semiochemicals from first and second trophic levels in host foraging behavior ofAphidius ervi

The responses of femaleAphidius ervi to odors from a host food plant (Vicia faba), host aphids (Acyrthosiphon pisum), nonhost aphids (Aphis fabae), and aphid-plant complexes were investigated in a specially designed wind tunnel and a Y-tube olfactometer. In single-target (no-choice) and two-target (dual-choice) experiments, plant volatiles played a crucial role in the host foraging behavior ofA. ervi. The odor from theA. pisum-plant complex elicited the strongest responses byA. ervi females, followed by the odor from plants previously damaged by the feeding ofA. pisum. There was a significantly weaker response to odor fromA. pisum in the absence of the plant and to undamaged plants. Similarly, mechanically damaged plants and plants infested with the nonhost aphidA. fabae did not elicit strong responses. A plant that had been damaged byA. pisum and subsequently washed with distilled water was as attractive as an unwashed, previously infested plant.Aphidius ervi probably overcomes the reliability-detectability problem by selectively responding to herbivore-induced, volatile, semiochemical cues emitted by the first trophic level and by distinguishing between the volatiles induced by host and nonhost aphids.     

Effect of kairomones from egg and female adult stages ofOstrinia nubilalis (Hübner) (Lepidoptera,Pyralidae) onTrichogramma brassicae Bezdenko (Hymenoptera,Trichogrammatidae) female kinesis

Volatile chemicals emanating from the different developmental stages ofOstrinia nubilalis Hübner (Lepidoptera, Pyralidae) increase the mobility ofTrichogramma brassicae Bezdenko (Hymenoptera, Trichogrammatidae) in a linear airflow olfactometer. In this paper, we have demonstrated that airborne chemicals from egg masses and virgin females during calling activity stimulate an intensive search behavior byTrichogramma females. On the other hand, emanations from mated females with extruded abdominal tips do not incite the parasitoid's movement. For the moment we cannot elucidate, with these bioassays, the real role of these kairomones as attractants, guides, stimulants, or retainers.     

Robber bees (Lestrimelitta limao) and their host chemical and visual cues in nest defense byTrigona (Tetragonisca) angustula (Apidae: Meliponinae)

The nest of the stingless bee,Trigona (Tetragonisca) angustula, is guarded by bees positioned in the nest entrance and others hovering in front of it. Hovering guard bees track returning foragers sideways along the last 10 cm in front of the nest, but intercept and incapacitate nest intruders by clinging with mandibles to wings and legs. When attacked by the cleptobiotic stingless beeLestrimelitta limao, the colony strengthens its aerial defense with hundreds of additional hoverers. To test our hypothesis that this reaction is due to interspecific chemical communication based on kairomone effects, we presented synthetic cephalic volatiles of both species at the nest entrance and counted the number of bees leaving the nest and taking up hovering positions. We conclude that guard bees recognizeL. limao by the major terpenoids of their volatile cephalic secretions, geranial, neral (=citral) and 6-methyl-5-hepten-2-one; other components may fine-tune this recognition. The effect of chemical stimuli is not significantly enhanced by combination with a dummy ofL. limao. Guard bees, we hypothesize, respond to this kairomone by secreting a species specific alarm pheromone; a major component of this pheromone, benzaldehyde, recruits additional bees to defend the nest.     

The Egg Parasitoid <Emphasis Type="Italic">Trissolcus basalis</Emphasis> uses <Emphasis Type="Italic">n</Emphasis>-nonadecane,a Cuticular Hydrocarbon from its Stink Bug Host <Emphasis Type="Italic">Nezara viridula</Emphasis>, to Discriminate Between Female and Male Hosts

Contact kairomones from adult southern green stink bugs, Nezara viridula (L.) (Heteroptera: Pentatomidae) that elicit foraging behavior of the egg parasitoid Trissolcus basalis (Wollaston) were investigated in laboratory experiments. Chemical residues from tarsi and scutella of N. viridula induced foraging by gravid female T. basalis. Residues from body parts of female N. viridula elicited stronger responses than those from the corresponding body parts of males. Deproteinized tarsi still elicited searching responses from wasps, indicating that the kairomone was not proteinaceous. Hexane extracts of host cuticular lipids induced searching responses from T. basalis, with a strong preference for extracts from female hosts. Extracts consisted primarily of linear alkanes from nC₁₉ to nC₃₄, with quantitative and qualitative differences between the sexes. Extracts of female N. viridula contained more nC₂₃, nC₂₄, and nC₂₅ than the corresponding extracts from males, whereas nC₁₉ was detected only in extracts from males. Direct-contact solid phase microextraction (DC-SPME) of N. viridula cuticle and of residues left by adult bugs walking on a glass plate confirmed gender-specific differences in nC₁₉. Trissolcus basalis females responded weakly to a reconstructed blend of the straight-chain hydrocarbons, suggesting that minor components other than linear alkanes must be part of the kairomone. Addition of nC₁₉ to hexane extracts of female N. viridula significantly reduced the wasps’ arrestment responses, similar to wasps’ responses to hexane extracts of male hosts. Overall, our results suggest that a contact kairomone that elicits foraging by T. basalis females is present in the cuticular lipids of N. viridula, and that the presence or absence of nC₁₉ allows T. basalis females to distinguish between residues left by male or female hosts. The ecological significance of these results in the host location behavior of scelionid egg parasitoids is discussed.     

Chemical mediation of behavior in hermit crabs: Alarm and aggregation cues

Field studies with three common local species of hermit crabs,Clibanarius vittatus, Pagurus longicarpus, andPagurus pollicaris, showed that these crabs responded behaviorally to chemicals originating from crushed conspecifics. Hermit crabs are attracted specifically and in a manner similar to previously reported crab responses to odors from dead gastropods. Responses byC. vittatus to both kinds of odor are of three types: (1) aggregation/shell investigation responses (previously reported for odors from dead gastropods), characterized by increased locomotor activity, investigation of shells in the vicinity, and switching into empty shells; (2) alarm responses, in which crabs flee the area; and (3) withdrawal responses, in which crabs pull into their shells and do not come out. Studies withC. vittatus showed that the stimulatory chemicals originate from hemolymph, are less than 500 D, adsorb to octadecyl silica, and are recovered by elution with 20% methanol. Responses ofC. vittatus are dependent upon crab size, type of shell occupied, and shell fit. Chemicals originating from dead conspecifics provide a forum for shell acquisition by crabs in relatively small shells and alarm by crabs in relatively large shells.