Correlation of 1-octen-3-one with antixenotic resistance in subterranean clover cotyledons to red-legged earth mite,Halotydeus destructor (Acarina: Penthaleidae)

Artificially damaged cotyledons of subterranean clover (Trifolium subterraneum L.) released several volatile metabolites, including 1-octen-3-one, arising from lipid peroxidation. The amount of 1-octen-3-one produced was negatively correlated with feeding damage caused by the red-legged earth mite (Halotydeus destructor) in nine out of 10 resistant and susceptibleT. subterraneum varieties tested. The EC₅₀ of this compound in deterring mites from feeding in a membrane bioassay was 50 ppm. Cotyledon toughness was also involved in resistance. The resistant variety, S3615D, which has the lowest toughness value among the resistant varieties, produced the highest amount of 1-octen-3-one recovered from the headspace in 1 hr. Artificially damaged cotyledons of both susceptible Dalkeith and resistant DG1007, growing in shade, showed lower toughness, but had enhanced production of C₈ volatile compounds and were avoided by mites during a 3-hr feeding test. When both 1-octen-3-one content and cotyledon toughness value were taken as cofactors in resistance, the resultant multiplication value yielded a more significantly negative correlation with mite feeding damage scores within the 10 varieties than either factor alone. We conclude that 1-octen-3-one has a role in resistance of subclover cotyledon to the mite.     

Fate of quinolizidine alkaloids through three trophic levels:Laburnum anagyroides (Leguminosae) and associated organisms

The quinolizidine alkaloids (QA) of golden rain,Laburnum anagyroides, and those of phytophagous insects associated with the plant, as well as of parasitoids of the latter, were analyzed by capillary GLC and GLC-MS. The alkaloid content in samples of vegetative plant parts was high at the beginning of the season, then decreased, while that of reproductive organs was high throughout flowering, pod formation, and maturation. The analyses showed that the QA of the plant passed through two higher trophic levels (herbivorous insects and their parasitoids) and that the alkaloid pattern changed little during the passage. The alkaloids were present in two phytophagous insect species associated with golden rain: the predispersal seed predator,Bruchidius villosus [5–13g/g fresh weight (fw)], andAphis cytisorum (182–1012g/g fw), an aphid that feeds on shoots, leaves, and inflorescences. Braconid and chalcidoid parasitoids emerging from the bruchid host also contained alkaloids (1.3–3g/g fw), as did three foraging ant species,Lasius niger, Formica rufibarbis, andF. cunicularia (45g/g fw), that visited the aphid colonies or honeydew-covered leaves of aphid-infested plants. The hypothesis that developing bruchid larvae and/or the plant manipulate QA supply to infested seeds was not supported, because QA content of leftover endosperm in seeds after bruchid development was similar to that of uninfested seeds. The frass of developing bruchid larvae was rich in QA (31g/ g dry weight). While aphids sequestered, the bruchid larvae took up and eliminated QA with the frass without chemical transformation.     

Role of Isoflavonoids in Resistance of Subterranean Clover Trifoliates to the Redlegged Earth Mite Halotydeus destructor

Mature leaves of variety SE014 of Trifolium subterraneum are resistant to the redlegged earth mite (Halotydeus destructor). Compounds with feeding deterrent activity present in the leaves were isolated and identified by using a membrane bioassay technique. The free isoflavones, formononetin, genistein, and biochanin A, their corresponding 7-O-glucosides, and biochanin A 7-O-glucoside-6-O-malonate and genistein 7-O-glucoside-6-O-malonate, were active. In addition, the biosynthetic precursors of formononetin and genistein, 2,5,7-trihydroxy-4-methoxyisoflavanol and 2,5,7,4-tetrahydroxyisoflavanol, also were deterrent to the redlegged mites. The relative activity of these compounds was determined and some structure-activity correlations are noted. The constitutive defense mechanism that contributes to the resistance of subclover trifoliates to the mite contrasts with the induced chemical mechanism previously found for subterranean clover cotyledons.     

Quinolizidine alkaloids inGenista acanthoclada and its holoparasite,Cuscuta palaestina

About 20 quinolizidine alkaloids were identified inGenista acanthoclada by capillary GLC and GLC-MS, such as sparteine, 11,12-dehy-drosparteine, retamine,N-methylcytisine, cytisine, 17-oxosparteine, lupanine,-isolupanine, 5,6-dehydrolupanine, 10-oxosparteine,N-carbomethoxycytisine, 17-oxoretamine,N-formylcytisine,N-acetylcytisine, and anagyrine. Its phloem-feeding holoparasiteCuscuta palaestina contained alkaloids too, such as sparteine, 11,12-dehydrosparteine, retamine,N-methylcytisine, cytisine, 17-oxosparteine, lupanine,N-carbomethoxycytisine, and anagyrine. Whereas sparteine, retamine, 17-oxosparteine, and cytisine are the main alkaloids ofG. acanthoclada, lupanine, cytisine,N-methylcytisine, and anagyrine are abundant and enriched inC. palaestina. Since these alkaloids figure as antiherbivoral chemical defense compounds inGenista, it is assumed that the parasite can exploit the acquired allelochemicals for its own protection.     

Importance of quinolizidine alkaloids in the relationship between larvae ofUresiphita reversalis (Lepidoptera: Pyralidae) and a host plant,Genista monspessulana

Larvae ofUresiphita reversalis feed almost exclusively on legumes in the tribe Genisteae, which characteristically contain a variety of quinolizidine alkaloids. The larvae are aposematic, and onGenista monspessulana, a major host in California, they feed on the youngest leaves, at the periphery of the plant. These leaves, which were preferred over older foliage in choice tests, contained four to five times the level of alkaloid found in older leaves. The major alkaloids detected in these plants were dehydroaphylline andN-methylcytisine, together accounting for 74% of the total. Preliminary analyses showed the alkaloid profile of exuviae from larvae feeding on these plants was very similar to that of the plants. Two alkaloids, sparteine and cytisine, which are known components of some hosts ofU. reversalis, were phagostimulants for fifth-instar larvae when added to sucrose-impregnated glass-fiber disks. In addition, when sparteine was added to foliage ofG. monspessulana, effectively doubling the percent dry weight of alkaloid, the growth rate of late-instar larvae was positively affected. Cytisine added to plants had no discernible effect on growth of larvae. Alkaloid levels in larvae and in their frass were proportional to levels in the plants on which they fed. Although the majority of alkaloid was excreted, that which was sequestered by the insect was found entirely in the integument, possibly confering some protection from predators.     

Damage-induced alkaloids in tobacco: Pot-bound plants are not inducible

Field-grown wild tobacco plants (Nicotiana sylvestris) were subjected to a defoliation regime designed to mimic the rate and amount of leaf mass removed by one tobacco hornworm per plant. Undamaged leaves on these plants undergo a dramatic (457% for leaf position 5, 410% for leaf position 8) increase in total leaf alkaloids compared to same-age and positioned control leaves on undamaged control plants. However, potted greenhouse-grown plants fail to exhibit the same damage-induced increase in alkaloid content. The greenhouse environment differs from the field environment in factors known to influence leaf alkaloid content, particularly soil N, P, K, near-UV radiation, and relative humidity. However, altering these environmental factors does not make potted plants able to increase their leaf alkaloid levels in response to defoliation. Transplanting plants into larger pots with more soil does allow the plants to respond to defoliation. Thirty days after transplanting, the plants are again unresponsive to damage, probably as a result of becoming pot-bound. This result suggests a mechanism for the induction response, specifically that leaf damage triggers synthesis of these alkaloids in the roots, and offers a potentially valuable experimental tool for the study of induced-plant defenses in tobacco and other plants that synthesize alkaloids in their root tissues.     

Vitamin a deficiency modifies response of predatory miteAmblyseius potentillae to volatile kairomone of two-spotted spider mite,Tetranychus urticae

A volatile kairomone of the two-spotted spider mite,Tetranychus urticae, elicits a searching response of the phytoseiid predatorAmblyseius potentillae, only when the predator is reared on a carotenoid-free diet. However, after addition of crystalline -carotene or vitamin A acetate to the predator's rearing diet this searching response was absent. Because vitamin A and -carotene are indispensable nutrients for diapause induction, the carotenoid-deficient predators increase their fitness by searching for two-spotted spider mites, when other spider mites are unavailable. Two-spotted spider mites, among others, contain the carotenoids required for diapause induction, but are an inferior prey due to the dense webbing they produce. When the predators have carotenoids at their disposal, they do better by searching for other spider mites that are more profitable in terms of reproductive success. Such a prey is the European red spide mite,Panonychus ulmi. The volatile kairomone of this prey elicits a searching response of the predator whether it has a carotenoid deficiency or not.     

Interactions of alkaloids with galeal chemosensory cells of colorado potato beetle

The galeal chemosensory system of the adult Colorado potato beetle was used as a model to study the effects of alkaloids on insect gustation. Nine alkaloids, representing a wide range of structural types, were used. Their ability to stimulate chemosensory cells when presented in isolation and their ability to interfere with normal chemosensory processes were emphasized. None of the alkaloids stimulated chemosensory cells in a dose-dependent manner, although a few stimulated low-level activity from some cells. There was no evidence for a general deterrent receptor in these beetles. Some of the alkaloids had a marked inhibitory effect on normal chemosensory responses. Tomatine, solanine, papaverine, and sparteine significantly inhibited responses to amino acids (represented by GABA) while quinine and papaverine inhibited responses to sucrose. An attempt was made to correlate neurophysiological action of some alkaloids with their effects on feeding behavior. It was clear from this correlation that even a dramatic inhibition of sensory input by an alkaloid does not necessarily lead to measurable effects on behavior. The results are discussed in the context of current theories on the mode of action of alkaloids and other secondary plant compounds which may be involved in host recognition by phytophagous insects.     

Piperidine Alkaloids in Nitrogen Fertilized Pinus ponderosa

We fertilized individual, pole-size ponderosa pine trees at two low-quality sites and pine saplings at a relatively high-quality site, with ammonium nitrate. Six to 12 months later, we measured total %N and 2,6-disubstituted piperidine alkaloids in the foliage. The N additions raised foliar %N above deficiency levels (i.e., from 1.0–1.1% to 1.4–1.6%) at the low-quality sites, but did not elevate foliar %N in saplings at the higher quality site, where it was already (1.9%) well above critical levels. In control trees with foliar N below a threshold of 1.1%, we detected no more than trace levels of alkaloids, indicating that alkaloid production is highly constrained by N deficiency. The N additions increased mean concentrations of the predominant alkaloid, pinidine, at all three sites. Mean total alkaloid concentrations for fertilized trees at the two low-quality sites were 12 and 155 g/g dry wt higher than controls (relative increases of 12× and 4.5×, respectively). For saplings at the high-quality site, the mean total increased by 584 g/g dry wt (1.6×) with the N additions. Allocation of foliar N to alkaloids was highest in fertilized saplings (0.81%) compared to control saplings (0.53%). These findings demonstrate that foliar alkaloid concentrations can be increased by nitrogen fertilization of forest trees growing on both low- and high-quality sites. Fertilizing for the purpose of inhibiting potential herbivores may be more successful at higher quality sites where alkaloid levels are enhanced relative to food quality (foliar %N).     

Effect of fungal metabolite peramine and analogs on feeding and development of argentine stem weevil (Listronotus bonariensis)

Peramine, a pyrrolopyrazine alkaloid produced by the fungal endophyte of perennial ryegrassAcremonium lolii, deterred the feeding of both adults and larvae of the graminacious herbivore, the Argentine stem weevil (Listronotus bonariensis), at 0.1 g/g and 10 g/g, respectively. In a no-choice test fewer stem weevil larvae fed and developed on diet containing as little as 2 g/g peramine. The proportion of larvae which did not develop beyond the first instar was higher on diet containing peramine and appeared to be due to a higher proportion of larvae which did not feed. For larvae which fed on the peramine-containing diet, feeding scores and times to pupation were not significantly different from those of controls. A number of simple peramine analogues showed feeding-deterrent activity against adult weevils, indicating the importance of the pyrrolopyrazine ring system of peramine in determining feeding-deterrent activity.     

Transfer of pyrrolizidine and quinolizidine alkaloids toCastilleja (Scrophulariaceae) hemiparasites from composite and legume host plants

Castilleja (Scrophulariaceae) species of the western United States contain pyrrolizidine and quinolizidine alkaloids. TheCastilleja obtain the alkaloids by root parasitism on host plants, withSenecio atratus andS. triangularis (Asteraceae) furnishing the pyrrolizidines, and quinolizidines being obtained fromLupinus species andThermopsis montana (Leguminosae). Individual plants within a givenCastilleja species population may be devoid of alkaloids while others have high alkaloid content. No populations have been found which are made up of both pyrrolizidine- and quinolizidine-containing individuals. These results have important implications forCastilleja ecology, for the study of insect herbivores which areCastilleja specialists, and in the development of systems for the investigation of the role of alkaloids as plant defenses.Paper 10 in the series Chemistry of the Scrophulariaceae. Paper 9: D.R. Gardner, J. Narum, D. Zook, and F.R. Stermitz.J. Nat. Prod. 50: In press.     

The “Raison D'être” of pyrrolizidine alkaloids inCynoglossum officinale: Deterrent effects against generalist herbivores

In this study we tested whether pyrrolizidine alkaloids (PAs) ofCynoglossum officinale serve as antifeedants against herbivores. Total PA N-oxide extracts of the leaves significantly deterred feeding by generalist herbivores. Specialist herbivores did not discriminate between food with high and low PA levels. Three PAs fromC. officinale, heliosupine, echinatine, and 3-acetylechinatine, equally deterred feeding by the polyphagous larvae ofSpodoptera exigua. Although the plants mainly contain PAs in their N-oxide form, reduced PAs deterred feeding byS. exigua more efficiently than PA N-oxides. On rosette plants, the monophagous weevilMogulones cruciger significantly consumed more of the youngest leaves, which had the highest PA level and the highest nitrogen percentage. Larvae ofEthmia bipunctella, which are oligophagous within the Boraginaceae, did not discriminate between leaves. All generalist herbivores tested significantly avoided the youngest leaves with the highest PA levels. In the field, the oldest leaves also were relatively more damaged by herbivores than the youngest leaves. It is hypothesized that the skewed distribution of PAs over the leaves of rosette plants reflects optimal defense distribution within the plant.     

Polymorphism in Plant Defense Against Herbivory: Constitutive and Induced Resistance in Cucumis sativus

Theory predicts that plant resistance to herbivores is determined by both genetic and environmentally induced components. In this study, we demonstrate that the phenotypic expression of plant resistance to spider mite herbivory in Cucumis sativus is determined by genetic and environmental factors and that there is an interaction between these factors. Previous feeding by spider mites induced systemic resistance to subsequent attack over several spatial scales within plants, reducing the population growth of mites compared to that on control plants. Effects of induction were effective locally over the short term, but resulted in local increased susceptibility to spider mite attack after several days. However, this local induced susceptibility on the damaged leaf was associated with induced resistance on newer leaves. Induced resistance was correlated with increases in cucurbitacin content of leaves, but was not associated with changes in the density of leaf trichomes. Induced resistance to herbivory was not detected in plants of a genotype lacking constitutive expression of cucurbitacins, which were in general highly susceptibile to mite attack. Allocation trade-offs between growth and defense are often invoked to explain the maintenance of variation in the levels of plant resistance. Contrary to current thinking, neither constitutive nor herbivore-induced plant resistance were associated with reductions in plant allocation to root and shoot growth. However, plants that had high levels of induced resistance to spider mites were the most susceptible to attack by a specialist beetle. Such ecological trade-offs between resistance to generalist herbivores and susceptibility to specialist herbivores may be important in the maintenance of variation of plant resistance traits. In summary, C. sativus exhibits strong genetic variation for constitutive and induced resistance to spider mites, and this variation in resistance is associated with ecological trade-offs.     

Influence of alkaloid concentration on acceptability of tall larkspur (Delphinium spp.) to cattle and sheep

Tall larkspur (Delphinium spp.) is a serious toxic plant problem on western U.S. ranges. The major toxins in tall larkspur are methyllycaconitine (MLA) and 14-deacetylnudicauline (14-DAN); the sum of both is termed the toxic alkaloid concentration. Toxic alkaloids comprise about 20–50% of the total alkaloid concentration in tall larkspur. Toxic and total alkaloid concentration generally declines with maturity, whereas cattle and sheep consumption of larkspur typically increases with plant maturity. We hypothesized that cattle and sheep consumption of tall larkspur was negatively related to higher concentrations of total or toxic alkaloid. We compared consumption of several collections of dried, ground larkspur and fresh larkspur in a series of trials. In another trial, a crude alkaloid fraction was extracted with ethanol, added to alfalfa hay, and consumption compared to untreated alfalfa hay, alcohol-treated hay, and the essentially alkaloid-free plant residue. In all cases we correlated amounts eaten with total and toxic alkaloid concentration. A grazing trial was also conducted to relate larkspur consumption over time to alkaloid concentrations. Total alkaloid concentrations in dried, whole-plant collections ranged from 9.3 to 38.8 mg/g of dry weight, whereas toxic alkaloid concentrations varied from 0.0 to 7.1 mg/g. In one pen trial, cattle preferred a larkspur collection (P<0.01) that contained no toxic alkaloids but had a high total alkaloid concentration (39 mg/g). There was no correlation (P>0.05), however, between concentrations of total or toxic alkaloids and amount of dry plant consumed in this or any other trial. Conversely, sheep consumption tended to be negatively influenced by total and toxic alkaloid concentration (P0.08). In the trials with extract, cattle preferred the alcohol-treated hay and rejected the alkaloid-free residue (P<0.01), whereas the alkaloid-treated hay was of intermediate acceptability. Cattle preferred the alkaloid-treated hay over the alkaloid-free residue, indicating that alkaloids did not deter consumption. Conversely, the alkaloid-treated hay was less preferred than either untreated or alcohol-treated hay, suggesting a negative effect on acceptability. There was no correlation between alkaloid concentration and amount of treated feed eaten. In field trials, the amount of composited, fresh leaves or flowers eaten by cattle was influenced by plant part (P=0.04), but was not related (P>0.05) to alkaloid concentration. Cattle preferred leaves over flowers when offered individual plants differing in phenological stage and/or amount of shade, but alkaloid concentration was not related to consumption. We conclude that knowledge of the concentration of total or toxic alkaloid in tall larkspur will give little or no indication of plant acceptability to cattle. Even though accurate predictions can be made about the potential toxicity of larkspur based on the concentration of toxic alkaloids, predictions about consumption must be based primarily on plant phenology.     

Does mowing height influence alkaloid production in endophytic tall fescue and perennial ryegrass?

The mutualistic symbiosis following infection of tall fescue, Festuca arundinacea, and perennial ryegrass, Lolium perenne, by fungal endophyte (Neotyphodium spp.) results in the production of alkaloids that are feeding deterrents or toxic to insects and livestock. If the levels of the alkaloids can be manipulated by cultural practices in the grasses that are used for home lawns and golf courses, this could alleviate the need for pesticide applications in urban environments. We evaluated the influence of mowing height on the levels of some alkaloids in a greenhouse experiment for two consecutive months. In tall fescue, levels of four of the nine alkaloids, including one presumptive alkaloid, showed increased levels with increasing the mowing height from 2.5 to 7.5 cm. The alkaloids were ergonovine, ergocryptine, perloline methyl ether, and an unidentified alkaloid designated as unknown C. In perennial ryegrass, three out of six alkaloids, perloline methyl ether, chanoclavine, and unknown A, showed similar increases. The alkaloid levels in perennial ryegrass showed more variability than those in tall fescue between the two sampling dates. It was clear in both grasses that the relative levels of the alkaloids varied with mowing height, as well as over time.     

Influence of monoterpene vapors on spruce spider mite,Oligonychus ununguis,adult females

Adult female spruce spider mite,Oligonychus ununguis (Jacobi), were exposed to various concentrations of four host conifer monoterpene vapors (limonene,-pinene,-pinene, and ³-carene) for 24 hr to determine the lethal and sublethal effects. All four compounds were toxic to the mites. Further, at concentrations below the calculated LC₅₀s, all four compounds decreased oviposition by the mites and three of the compounds (limonene,-pinene, and-pinene) influenced movement. WhereasO. ununguis populations may not normally be exposed to high concentrations of host monoterpenes, trees continuously emit some monoterpene vapors, and when trees are damaged or under stress, oleoresin may accumulate at points on the external surface of tree tissues thereby exposing mites to the influence of monoterpene vapors.     

Visualizing a Plant Defense and Insect Counterploy: Alkaloid Distribution in <Emphasis Type="Italic">Lobelia</Emphasis> Leaves Trenched by a Plusiine Caterpillar

Insects that feed on plants protected by latex canals often sever leaf veins or cut trenches across leaves before feeding distal to the cuts. The insects thereby depressurize the canals and reduce latex exudation at their prospective feeding site. How the cuts affect the distribution and concentration of latex chemicals was not known. We modified a microwave-assisted extraction technique to analyze the spatial distribution of alkaloids in leaves of Lobelia cardinalis (Campanulaceae) that have been trenched by a plusiine caterpillar, Enigmogramma basigera (Lepidoptera: Noctuidae). We produced sharp two dimensional maps of alkaloid distribution by microwaving leaves to transfer alkaloids to TLC plates that were then sprayed with Dragendorff’s reagent to visualize the alkaloids. The leaf prints were photographed and analyzed with image processing software for quantifying alkaloid levels. A comparison of control and trenched leaves documented that trenching reduces alkaloid levels by approximately 50% both distal and proximal to the trench. The trench becomes greatly enriched in alkaloids due to latex draining from surrounding areas. Measurements of exudation from trenched leaves demonstrate that latex pressures are rapidly restored proximal, but not distal to the trench. Thus, the trench serves not only to drain latex with alkaloids from the caterpillar’s prospective feeding site, but also to isolate this section, thereby preventing an influx of latex from an extensive area that likely extends beyond the leaf. Microwave-assisted extraction of leaves has potential for diverse applications that include visualizing the impact of pathogens, leaf miners, sap-sucking insects, and other herbivores on the distribution and abundance of alkaloids and other important defensive compounds.     

Behavior ofTetranychus urticae toward essential oil mixtures from strawberry foliage

A standard essential oil mixture (SEOM) was formulated containing volatile compounds in the relative proportions found in the essential oil of the foliage of Citation, a strawberry cultivar relatively resistant toTetranychus urticae. Other mixtures contained varied levels, relative to the SEOM, oftrans-2-hexen-1-ol, nonanal, -terpineol, and methyl salicylate. The behavior ofT. urticae females in response to these mixtures at several concentrations in propylene glycol was studied in choice tube (preference) tests. Feeding effects were measured by incorporating the mixtures and individual components into sucrose with³²P. In the choice tube tests, mites were generally attracted by mixtures at concentrations of 0.1% or below unless the level of methyl salicylate was below 0.5 × that in the SEOM, or the level of nonanal was above that of the SEOM. When mixtures were incorporated into food, methyl-salicylate-stimulated feeding and nonanal levels were inversely related to the amount of food ingested.     

Honeydew analysis for detecting phloem transport of plant natural products

Analysis of honeydew excreted by various sap-sucking insects indicated the presence of certain plant secondary constituents in the phloem of their host plants. Honeydew excreted by mealybugs (Pseudococcus longispinus), living onCastanospermum australe, contained the indolizidine alkaloid castanospermine, a potent -glucosidase inhibitor. Similarly, honeydew from green peach aphids (Myzus persicae), feeding onSenecio vulgaris flower buds, contained the pyrrolizidine alkaloid senecionine, itsN-oxide, and hydrolytic products including retronecine. Cardenolides were detected in the honeydew of oleander aphids (Aphis nerii) feeding on oleander (Nerium oleander), indicating that these compounds are translocated in the phloem. On the other hand, honeydew from greenbugs (Schizaphis graminum), feeding on barley, lacked gramine or related indole metabolites. Similarly MBOA, the breakdown product of DIMBOA, was not detected in the honeydew of greenbugs living on DIMBOA-containing wheat.     

Scheloribatid Mites as the Source of Pumiliotoxins in Dendrobatid Frogs<Superscript>†</Superscript>

The strawberry poison frog Dendrobates pumilio (Anura: Dendrobatidae) and related poison frogs contain a variety of dendrobatid alkaloids that are considered to be sequestered through the consumption of alkaloid-containing arthropods microsympatrically distributed in the habitat. In addition to ants, beetles, and millipedes, we found that adults of two species of oribatid mites belonging to the cohort Brachypylina, trophically a lower level of animal than ants and beetles, contain dendrobatid alkaloids. Gas chromatography/mass spectrometry (GC/MS) of hexane extracts of adult Scheloribates azumaensis (Oribatida: Acari) revealed the presence of not only pumiliotoxin 251D (8-hydroxy-8-methyl-6-(2′-methylhexylidene)-1-azabicyclo[4.3.0]nonane), but also precoccinelline 193C and another coccinelline-type alkaloid. From the corresponding extracts of an unidentified Scheloribates sp., pumiliotoxin 237A (8-hydroxy-8-methyl-6-(2′-methylpentylidene)-1-azabicyclo[4.3.0]nonane) was detected as a minor component, and identified by synthesis. The presence of related alkaloids, namely deoxypumiliotoxin 193H, a 6,8-diethyl-5-propenylindolizidine, and tentatively, a 1-ethyl-4-pentenynylquinolizidine, were indicated by the GC/MS fragmentation patterns, along with at least another six unidentified alkaloid components. Thus, one possible origin of pumiliotoxins, coccinellid alkaloids, and certain izidines found in poison frogs may be mites of the genus Scheloribates and perhaps related genera in the suborder Oribatida. Chemical Ecology of Oribatid Mites IV.