Fate of photosensitizing furanocoumarins in tolerant and sensitive insects

The fate of [¹⁴C]xanthotoxin (8-methoxypsoralen) was studied in larvae of insect species that are tolerant (Papilio polyxenes Stoll) or sensitive (Spodoptera frugiperda J.E. Smith) to the phototoxic effects of photosensitizing psoralens. Both insects metabolize xanthotoxin by oxidative cleavage of the furan ring, but the detoxification occurs at a much more rapid rate inP. polyxenes in which >95% of an oral 5 g/g xanthotoxin dose is metabolized within 1.5 hr after treatment. The detoxification of psoralens byP. polyxenes appears to occur primarily in the midgut tissue prior to absorption, with the result that the intact phototoxin does not reach appreciable levels in body tissues. Studies with an angular furanocoumarin indicated that isopsoralens are metabolized byP. polyxenes at a somewhat slower rate than observed for psoralens; however, a reduced rate of metabolic detoxification of isopsoralens probably does not explain the fact that psoralen tolerance inP. polyxenes does not extend to the isopsoralen series.     

Evaluation of Synergism in the Feeding Deterrence of Some Furanocoumarins on Spodoptera littoralis

The phagodepression activity of five furanocoumarins (FC), bergapten, xanthotoxin, psoralen, imperatorin, and angelicin, has been studied against larvae of Egyptian cotton leafworm Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) using a leaf-disk choice bioassay. The dose range used was 0–10 g/cm² for linear furocoumarins and 0–30 g/cm² for angelicin, the angular furanocoumarin. Dose–feeding deterrency activity correlations were governed by various sigmoidal functions, except in the case of imperatorin and bergapten, which had dose–response curves showing irregular traces with two maxima. All five FCs induced various degrees of phagodepression in S. littoralis; at 3 g/cm², the relative feeding deterrence was bergapten = xanthotoxin > psoralen = imperatorin = angelicin. Structure–activity correlations indicated that a methoxy group on C-5 or C-8 enhanced the activity. Comparison of experimental feeding deterrence of binary mixtures of imperatorin with xanthotoxin, bergapten, or psoralen at various relative concentrations with the calculated additive activity of each combination indicated that a proportion of 40% or more of imperatorin may exert a greater antifeedant effect on S. littoralis than the sum of individual compounds. The effect of angelicin also was examined in combination with psoralen, both of which are present in Psoralea plants. Their mixtures yielded a clear synergistic effect in the 20–80% angelicin range (coactivity coefficient = 124–133). By contrast, the effect of angelicin on xanthotoxin was only additive. In the dose–response curves of imperatorin/bergapten combinations, synergism was found at >60% imperatorin relative concentration and 1 g/cm², whereas lower proportions led to antagonism. The threshold between the two opposing effects was found to depend on the total FC concentration employed. Some natural systems contain FCs in the range of synergistic proportions recorded here and, thus, may have been produced by the host to increase its defensive effect at a lower metabolic cost.     

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.     

Cardenolide content and thin-layer chromatography profiles of monarch butterflies,Danaus plexippus L., and their larval host-plant milkweed,Asclepias asperula subsp.Capricornu (woods.) woods., in north central Texas

This paper is the second in a series on cardenolide fingerprinting of monarch butterflies and their host-plant milkweeds in the eastern United States. Spectrophotometric determinations of the gross cardenolide content ofAsclepias asperula plants in north central Texas indicated wide variation ranging from 341 to 1616 g/0.1 g dry weight. The mean plant cardenolide concentration (886 g/0.1 g) is the highest for any milkweed species on which monarch cardenolide profiles have been produced. Forty-one butterflies reared individually on these plants contained a skewed distribution of cardenolide concentrations ranging from 231 to 515 g/0. 1 g dry weight with a mean of 363g/0.1 g. The uptake of cardenolide by the butterflies was independent of plant concentration, suggesting that saturation occurs in cardenolide sequestration by monarchs when feeding on cardenolide-rich host-plants. Female monarchs contained significantly greater mean cardenolide concentrations (339 g/0.1 g) than did males (320 g/0.1 g). The mean dry weight of the male butterflies (0.211 g) was significantly greater than the female mean (0.191) so that the mean total cardenolide contents of males (675 fig) and females (754 g) were not significantly different. Butterfly size was not significantly correlated to butterfly cardenolide concentration when differences due to sex and individual host-plant concentration were removed. Thin-layer chrornatograms of 24 individual plant-butterfly pairs developed in two solvent systems resolved 22 individual spots in the plants and 15 in the butterflies.A. asperula plants appear to contain several relatively nonpolar cardenolides of the calotropagenin series which are metabolized to more polar derivatives in the butterflies. Quantitative evaluation of theR _f values, spot intensities, and probabilities of occurrence in the chloroform-methanol-formamide TLC system produced a cardenolide fingerprint clearly distinct from those previously established for monarchs reared on otherAsclepias species. Our data support the use of fingerprints to make ecological predictions concerning larval host-plant utilization.A. asperula subsp.capricornu andA. viridis Walt, are the predominant early spring milkweeds throughout most of the south central United States. Cardenolide-rich monarchs reared on these two species may be instrumental in establishing and reinforcing visual avoidance of adults by naive predators throughout their spring and summer breeding cycle in eastern North America.Lepidoptera: Danaidae.Apocynales: Asclepiadaceae.     

Onion fly trap catch as affected by release rates ofn-dipropyl disulfide from polyethylene enclosures

n-Dipropyl disulfide loadings of at least 1 l and 10 l in polyethylene enclosures were required to effect significant trap catches of onion fly,Hylemya antiqua (Meigen), females and males, respectively. Corresponding release rates for this threshold for trap catch were ca. 100 g/hr. Catches increased with loadings up to 100 l/capsule but then plateaued. As determined gravimetrically, the release rate from enclosures containing a reservoir of chemical remained constant under isothermal conditions but increased exponentially as a function of temperature.Diptera: AnthomyiidaePaper No. 9422 of the Michigan State University Agricultural Experiment Station. Received for publication April 29, 1980.     

Comparative metabolism of [3H]psoralen and [3H]isopsoralen by black swallowtail (Papilio polyxenes Fabr.) caterpillars

The comparative fate of tritiated preparations of a linear furanocoumarin (psoralen) and an angular furanocoumarin (isopsoralen) was determined in last-instar caterpillars of the black swallowtail butterfly (Papilio polyxenes Fabr.). Oral administration of either furanocoumarin at 5 g/g is followed by rapid metabolism, primarily through oxidative cleavage of the furan ring, and the metabolites are rapidly excreted. Isopsoralen is, however, metabolized at a somewhat slower rate than is psoralen, and levels of unmetabolized isopsoralen in body tissues of the treated caterpillars are about three-fold higher. These data are compatible with the hypothesis that a reduced detoxification rate accounts at least in part for the susceptibility ofP. polyxenes caterpillars to the deleterious effect of isopsoralens.     

Insecticidal activity of hypericin towardsManduca sexta larvae

The toxic effect of hypericin (HYP), a photodynamic quinone that occurs in certain species of the genusHypericum, towardsManduca sexta third-instar larvae was investigated. The LD₅₀ of purified hypericin was 16 g/g larval initial fresh weight in constant light (22 W/m²). Reduced irradiance resulted in decreased mortality. Sublethal applications retarded larval growth (body fresh weight) in a dose-dependent manner. Toxicity had an absolute light dependence at the dose levels used, the active wavelengths being >500 nm. The phototoxic effect was rapidly lost when larvae were maintained in darkness (>8 hr) prior to irradiation. However, the potential for light-dependent mortality was retained if larvae were starved prior to irradiation.     

Caste-dependent pheromones in the head of the antTetramorium caespitum

The heads of maleT. caespitum contain 4-methyl-3-hexanol (1.7 g, only the erythro isomer(s) detected) and 4-methyl-3-hexanone (0.8 g). The heads of alate females contain 0.1 g of each compound, whereas only the alcohol (0.1 g) was found in the heads of workers. Both compounds act as attractants for the workers and their possible functions are discussed.'Chargé de Recherche du F.N.R.S.Chercheur qualifié du F.N.R.S.     

Effect of Trichilia americana Extract on Feeding Behavior of Asian Armyworm, Spodoptera litura

We investigated the desensitization of Asian armyworms, Spodoptera litura, to a crude methanolic extract of wood Trichilia americana. Following repeated exposures to the extract over four days, desensitization was observed under no-choice conditions at low extract concentration (0.5 g/cm²). No desensitization was observed under choice conditions or at a higher concentration (5.0 g/cm²). Repeated exposures of larvae to the extract over 7.5 hr showed that larvae increasingly tolerated the extract due to hunger, rather than showing true desensitization. When larvae were exposed to the extract in test arenas of different sizes, larvae showed reduced feeding and desensitization as arena size increased. Finally, treatment of whole cabbage plants with extract resulted in larvae abandoning the plant. The crude extract was effective at protecting the plants, although desensitization did not occur, because the larvae moved away from the plant.     

Effects of soil nitrogen level on ferulic acid inhibition of cucumber leaf expansion

It has been suggested that the allelopathic activity of phenolic acids should be primarily important in soils of low fertility. If this is true, then plant growth inhibition by phenolic acids may be unimportant in managed agricultural soils. The objective of this study was to determine how soil nitrogen (N) level might modify phenolic acid inhibition of growth. Cucumber seedlings (Cucumis sativus cv Early Green Cluster) grown in containers in growth chambers under varying N levels (5, 10, 15, 20, and 25 g N/g soil) in Portsmouth B,-horizon soil material were treated with ferulic acid (0 or 10 g/g soil). Nitrogen and ferulic acid (FA) were applied every other day to the soil surface. The amount of FA in the soil solution declined with depth in the containers. A more rapid disappearance of FA from the soil solution was observed for the last FA treatment (0% recovered after 10 hr on day 23) than the first treatment (44% recovered after 10 hr on day 13). Both low N (5 g N/g soil) and FA treatments reduced shoot dry weight, the mean absolute (AGR) and the mean relative (RGR) rates of leaf expansion, and increased the root-shoot ratio. High N treatments reduced shoot dry weight and the AGR. Ferulic acid inhibited cucumber seedling growth over a range of N concentrations, suggesting that the allelopathic activity of phenolic acids may be important in both nutrient limiting and nonlimiting soils for some species.Paper No. 12219 of the journal series of the North Carolina Agricultural Research Service, Raleigh, North Carolina 27695-7601. The use of tradenames in this publication does not imply endorsement by the North Carolina Agricultural Research Service of products named, nor criticism of similar ones not mentioned.     

Distribution of the carcinogenic terpene ptaquiloside in bracken fronds,rhizomes (Pteridium aquilinum), and litter in Denmark

The distribution of ptaquiloside (PTA) was studied in four Danish bracken populations in order to evaluate the transfer of PTA from ferns to soil. Populations showed statistically significant differences in PTA contents of fronds and rhizomes despite large in-site variations. The highest concentrations were encountered in fronds with concentrations ranging between 213 and 2145 g/g, while rhizomes had concentrations between 11 and 902 g/g. PTA was present in soil materials in amounts of 0.22–8.49 g/g but apparently with no correlation with PTA contents of fronds or rhizomes. Laboratory tests showed that water could leach PTA from bracken fronds, which is in support of the high soil contents observed at sites exposed to heavy showers just before sampling. The observed soil contents correspond to estimated soil solution concentrations of 200–8500 g/liter, demonstrating a substantial risk of PTA contamination of surface water and groundwater.     

Defensive secretions of three species ofAcilius (Coleoptera: Dytiscidae) and their seasonal variations as determined by high-pressure liquid chromatography

A rapid, sensitive, stable, and quantitative high-pressure liquid chromatographic technique was developed for the analysis of defensive secretions obtained from the pygidial and prothoracic glands of dytiscids. Methods were developed for both normal phase (Porasil) and reverse phase (Bondapak C₁₈) columns. The applicability of this technique was demonstrated when defensive compounds ofAcilius semiculcatus, A. sylvanus andA. mediatus were isolated, identified, and quantitated. No major differences were found in the composition of the defensive secretions between the three species. The seasonal defensive titer ofA. semisulcatus was determined from June through October 1977. The pygidial defensive agents (benzoic acid,p-hydroxybenzaldehyde, and methylp-hydroxybenzoate varied from 9.0 to 67.8 g and exhibited a maximum in July, and a steroid from the prothoracic gland varied from 7.1 to 33.2 g and was maximum in October.     

Sequestration of host plant-derived compounds by geometrid moth, Milionia basalis, toxic to a predatory stink bug, Eocanthecona furcellata

A predatory stink bug, Eocanthecona furcellata, died after feeding on Milionia basalis larvae. The compounds toxic to E. furcellata were isolated from the hemolymph of M. basalis larvae and identified as inumakilactone A, nagilactone C, and nagilactone C glucoside. The concentrations of inumakilactone A, nagilactone C, and nagilactone C glucoside in the hemolymph of the final instar larvae were 130, 50, and 770 g/ml, respectively. Nagilactone C showed the highest insecticidal activity against second-instar nymphs of E. furcellata, while nagilactone C glucoside showed the lowest, one twentieth of that of nagilactone C. When mixed compounds were given at the same concentrations as those in hemolymph of M. basalis, all nymphs of E. furcellata died with in three days. Inumakilactone A and nagilactone C were found to be in the leaves of podocarp, Podocarpus macrophyllus, the only host plant of M. basalis, at concentrations of 13 and 175 g/g fresh weight, respectively. However, no nagilactone C glucoside was detected in the leaves of this species. These results suggested that M. basalis may transform nagilactone C to its glucoside.     

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.     

What defense doesSchouwia purpurea (Cruciferae) have against the desert locust?

A field study of the food eaten by solitary desert locusts was carried out in a winter breeding area in Mauritania. The food eaten, determined by the plant epidermis found in fecal pellets, was compared to the plant's availability in the habitat.Schouwia purpurea, well represented in the diets, was dominant at the study site. Adults had a preference forTribulus terrester. Growth and feeding on these two plants were compared. The high water content ofS. purpurea leaves limited the dry matter eaten and slowed down growth. Glucosinolates were separated and quantified by gas chromatography. There are 132mol/g dry matter in green leaves. In multiple choice tests, with paper disks, glucosinolate extracts were phagostimulant at a low concentration (21mol/g dry matter) and repulsive at a higher one (214mol/ g dry matter). Biting behavior onS. purpurea was recorded and analyzed on video. The importance ofSchouwia purpurea in desert locust habitats and its defenses is discussed.     

Systemic effects of Heterobasidion annosum on ferulic acid glucoside and lignin of presymptomatic ponderosa pine phloem,and potential effects on bark-beetle-associated fungi

Concentrations of soluble phenolics and lignin in the phloem of ponderosa pines inoculated with the pathogen Heterobasidion annosum were assessed over a period of 2 years in a 35-year-old plantation in northern California, USA. The major effect of the pathogen on phloem-soluble phenolics consisted of a significant accumulation of ferulicacid glucoside: 503 ± 27 g/g fresh weight (FW), compared with 366 ± 26 g/g FW for mock-treated and 386 ± 27 g/g FW for control trees. Lignin content was negatively correlated with ferulic acid glucoside concentration, and there was an indication of lignin reduction in the cell walls of inoculated trees. Lignin had a negative effect on the in vitro growth of two common bark beetle fungal associates, Ceratocystiopsis brevicomi and Ophiostoma minus. For this reason it, is hypothesized that lower lignification may facilitate the growth of beetle-associated fungi, resulting in greater susceptibility of the presymptomatic host to bark beetle colonization.     

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.     

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.     

Attraction ofOryzaephilus surinamensis (L.) andOryzaephilus mercator (Fauvel) (Coleoptera: Cucujidae) to some common volatiles of food

Responses by adultOryzaephilus surinamensis (L.) andOryzaephilus mercator (Fauvel) to various food volatiles were assessed by means of a two-choice, pitfall olfactometer. The individual experimental stimuli, all potential products of lipid oxidation, had a range of attractive doses of 1000-fold over the test dose ranges of 0.001–100 gmg, or 0.01–1000 gmg. Of 13 aliphatic C₃-C₁₄ aldehydes and benzaldehyde tested forOryzaephilus spp., 10 C₃-C₁₀ aliphatic aldehydes and benzaldehyde showed some attractiveness for both species. ForO. mercator, nonanal had the lowest lower threshold for positive response at 0.01 g. The addition of small amounts of nonanal or of a 111 mixture of hexanal, octanal, and nonanal to small amounts of cucujolide aggregation pheromones enhanced response by mixed-sexO. mercator to the pheromones. Eleven aliphatic C₂-C₉ free fatty acids showed some attractiveness for bothOryzaephilus spp. Isovaleric acid and valeric acid had the lowest lower thresholds for positive response at 0.1 g forO. mercator andO. surinamensis, respectively. Four olefinic oat volatiles were found to possess various degrees of attractiveness for bothOryzaephilus spp. The data suggest that food volatiles in this study might be used byOryzaephilus spp. as host-finding kairomones in nature.Research supported by the Natural Sciences and Engineering Research Council of Canada, Strategic Grant G0958 and Operating Grants A3881 and A3785.     

Defense Secretion of Prorhinotermes simplex: Toxicity to Insecticide Susceptible and Resistant House Fly

(E)-1-Nitropentadec-1-ene (NPE), the main component of the defense secretion of Prorhinotermes simplex soldiers, is toxic to both insecticide-susceptible (S) as well as to insecticide-resistant (R) strains of the house fly, Musca domestica. The LD₅₀ is 11.7 g/female fly for the S strain and 9.7 g for the R strain. The same efficacy of NPE on R and S strains indicates a different mechanism of action compared to conventional chlorinated, organophosphorus, and pyrethroid insecticides. Termite nestmates are protected against NPE by a specific detoxification mechanism. 1-Nitropentadecane, the detoxification product of NPE is nearly nontoxic to house flies, and doses up to 160 g/fly caused only very low mortality.