Responses of parasiteEdovum puttleri to kairomone from eggs of colorado potato beetle,Leptinotarsa decemlineata

When females of the eulophid parasiteEdovum puttleri were exposed to ann-hexane wash of eggs of the Colorado potato beetle,Leptinotarsa decemlineata, their responses indicated that the eggs contained a kairomone which elicited host-finding and host-acceptance behaviors. The hostfinding responses included an increased amount of time searching glass beads treated with kairomone, and drumming on the beads with the flagellum of the antennae. Host-acceptance responses included grasping of the beads with the legs, raising of the abdomen, and probing the kairomone-treated surface with the ovipositor. None of these responses were noted in females on beads treated only with hexane, or in males exposed to kairomone-treated beads. When kairomone was applied to a flat surface, filter paper disks, few episodes of drumming and no episodes of probing with the ovipositor were noted. Responses ofE.puttleri to eggs of Colorado potato beetle were similar to those on kairomone-treated beads, but females normally drilled into eggs and fed on host fluids after retracting the ovipositor. The kairomone is volatile, and responsiveness was reduced in parasites exposed to beads treated several hours previously.Hymenoptera: Eulophidae.Coleoptera: Chrysomelidae.     

Leaf surface extracts ofSolanum berthaultii hawkes deter colorado potato beetle feeding

Leaf rinses ofS. berthaultii PI 473334 with methylene chloride were deterrent to feeding by the Colorado potato beetle when applied toS. tuberosum tuber and leaf disks. When the leaf rinse was separated into its nonvolatile and volatile fractions and applied to tuber disks, the nonvolatile fraction was highly deterrent, while the volatile fraction reduced consumption, but not significantly compared to the controls. A hexane leaf rinse was not deterrent to feeding, while an acetone rinse was approximately twofold more deterrent than the methylene chloride rinse when applied to leaf disks. Three cycles of bioassay-guided, reversed-phase open-column fractionation of an acetone leaf rinse yielded a relatively polar fraction with low deterrent activity, and two nonpolar fractions exhibiting higher specific activity. Reversed-phase preparative HPLC of these fractions yielded seven active fractions among the 10 assayed. Subsequent analytical HPLC indicated that two fractions each contained a single UV-absorbing compound, while another represented a mixture of at least four compounds. The remaining fractions were composed of complex mixtures of possibly ionic or polymeric compounds that were poorly resolved by HPLC.     

Seven-week persistence of an oviposition-deterrent pheromone

Cabbage leaves sprayed with a water solution of the oviposition-deterrent pheromone ofPieris brassicae remain deterrent to ovipositing females for at least 14 days. Under laboratory conditions, the pheromone, when dried on a glass surface, retains activity for a period of at least 7 weeks. After 7 days under vacuum conditions, some pheromone is still present, indicating a low volatility and / or high stability of (an active fraction of) the pheromone. After 125 eggs are slowly rinsed with 300 ml water, they still release detectable quantities of the pheromone.     

Sexual Maturation and Temporal Variation of Neural Responses in Adult Colorado Potato Beetles to Volatiles Emitted by Potato Plants

Neural responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata to volatiles emitted by potato plants, Solanum tuberosum L were investigated. Amplitudes of electroantennograms to measured amounts of a standard odorant, (Z)-3-hexenyl acetate, increased from day of emergence through at least six to eight days of adulthood. Among 20 potato volatiles examined, several constitutive compounds, e.g., the green leaf volatiles (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, and (Z)-3-hexenyl butyrate, and systemic volatiles released primarily in response to insect feeding, e.g., (±)-linalool, nonanal, methyl salicylate, and indole, were the most effective stimuli. A statistic called linear age-skew (linear orthogonal polynomial) was used to examine differences in responses to potato volatiles between young and mature CPB. Based on plots of linear age-skew and overall neural responsiveness, 10 volatiles could be identified for which responses increased at a rate similar to or greater than the standard. The results are discussed with regard to the relationship of the CPB to its host plant and developmental studies of insect sensory responses to chemical signals.     

Tasting green leaf volatiles by larvae and adults of Colorado potato beetle,Leptinotarsa decemlineata

Larvae and adults of the Colorado potato beetle,Leptinotarsa decemlineata (Say), are shown to have galeal gustatory cells that are highly sensitive to distillate of potato leaf extracts, (E)-2-hexen-1-ol, (E)-2-hexenal, and other saturated and unsaturated six-carbon alcohols. In larvae and adults, the sensory response patterns elicited by leaf homogenate, leaf distillate and a mixture of these two extracts differ in subtle ways. Beetle larvae feed most readily on Millipore disks treated with leaf homogenate and the mixture, but they did not feed on disks treated with leaf distillate. The differences in behavioral response and sensory input are used to derive a potential gustatory code that may stimulate different levels of feeding. This code may be disrupted by compounds present in nonhost leaves, thus leading to reduced feeding. Possible interactions of sapid leaf volatiles, amino acids, sugars, and potentially deterrent plant compounds are discussed.     

Effect of trichome B exudate ofSolanum berthaultii Hawkes on consumption by the colorado potato beetle,Leptinotarsa decemlineata (Say)

The leaf extract fromS. berthaultii Hawkes (PI 473340) contains exudate from trichomes (type B). Consumption ofS. tuberosum var. Norchip foliage by the Colorado potato beetleLeptinotarsa decemlineata (Say) was reduced when treated with the leaf extract. The leaf extract from a resistantS. berthaultii clone without type B trichome had no antifeedant activity. It suggests that more than one mechanism of resistance to the Colorado potato beetle exists inS. berthaultii.     

Avoidance of antinutritive plant defense: Role of midgut pH in Colorado potato beetle

The fate of the tomato foliar phenolic, chlorogenic acid, in the digestive systems of Colorado potato beetleLeptinotarsa decemlineata (Coleoptera: Chrysomelidae) andHelicoverpa tea (Lepidoptera: Noctuidae) is compared. In larvalH. zea and other lepidopteran species previously examined, approximately 35–50% of the ingested chlorogenic acid was oxidized in the digestive system by foliar phenolic oxidases (i.e., polyphenol oxidase and peroxidase) from the tomato plant. The oxidized form of chlorogenic acid, chlorogenoquinone, is a potent alkylator of dietary protein and can exert a strong antinutritive effect upon larvae through chemical degradation of essential amino acids. In contrast, inL. decemlineata less than 4% of the ingested dose of chlorogenic acid was bound to protein. In vitro experiments to determine the influence of pH on covalent binding of chlorogenic acid to protein showed that 30–45% less chlorogenic acid bound to protein at pHs representative of the beetle midgut (pH 5.5–6.5) than at a pH representing the lepidopteran midgut (pH 8.5). At an acidic pH, considerably more of the alkylatable functional groups of amino acids (–NH₂, –SH) are in the nonreactive, protonated state. Hence, polyphenol oxidases are unlikely to have significant antinutritive effects against the Colorado potato beetle and may not be a useful biochemical source of resistance against this insect. The influence of feeding by larval Colorado potato beetle on foliar polyphenol oxidase activity in tomato foliage and its possible significance to interspecific competition is also considered.Approved by the Director of the Arkansas Agricultural Experiment Station.     

Misleading the Colorado potato beetle with an odor blend

Walking tracks of Colorado potato beetles,Leptinotarsa decemlineata Say, were recorded on a locomotion-compensator in response to wind, odors of host plantsSolanum tuberosum L. and nonhost plantsLycopersicon hirsutum f.glabratum C.H. Mull, and to mixtures of these plant species. Host-plant odor induced positive anemotactic responses in starved females, whereas odor of the nonhostL. hirsutum was neither repellent nor attractive. The attractiveness of host-plant odor, however, was neutralized in the odor blend of plant species. Masking the attractive host-plant odor will hinder the beetle's searching for host-plant patches, and this principle may be exploited in pest control by mixed cropping.The locomotion-compensator was constructed with financial support from the Foundation for Fundamental Biological Research (BION), which is subsidized by the Netherlands Organization for the Advancement of Pure Research (ZWO), grant 14-02-02. The first author was supported by a grant from the French Ministry of Industry and Research.     

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.     

Response of Colorado potato beetles,Leptinotarsa decemlineata (Say), to volatile components of tansy,Tanacetum vulgare

The responses of Colorado potato beetle,Leptinotarsa decemlineata (Say), to volatile components of tansy,Tanacetum vulgare L., were investigated in order to establish a chemical basis for observed reduction in beetle populations when potatoes,Solanum tuberosum L., were interplanted with tansy. Colorado potato beetles exhibited avoidance behavior to tansy oil, volatiles from intact tansy plants, a hydrocarbon fraction of tansy oil, obtained by fractionation on alumina, and five of the 13 known components of tansy oil that were tested. One constituent of tansy oil, -pinene, attracted beetles.     

Antifeedant and toxic effects of sesquiterpenes fromSenecio palmensis to colorado potato beetle

A bioassay-guided fractionation of the aerial parts ofSenecio palmensis resulted in the isolation of two sesquiterpenes, 2,10-bisaboladien-1-one and 11-acetoxy-5-angeloyloxy-silphinen-3-one. The bisabolene and the silphinene represented 0.012% and 0.024% of the plant dry weight, respectively. Both compounds showed antifeedant activity againstLeptinotarsa decemlineata larvae and adults in short-term choice and no-choice bioassays. Both compounds were also tested against different species of phytopathogenic fungi. The beetles were more sensitive to these compounds in choice than in no-choice assays, with a gradient of increasing sensitivity from second instars to adults. Bisabolene was 45 times less active as an antifeedant than juglone, which was tested as a positive control. The silphinen was more active than the bisabolene, with a range of activity similar to juglone. Furthermore, exposure of fourth instars to these compounds over a 24-hr period resulted in reduced feeding and growth rates. To distinguish between antifeedant and toxic effects, growth efficiencies were calculated as the slope of the regression of relative growth rate on relative consumption rate. The comparison of these results with those of antifeedant simulation and contact toxicity bioassays indicates that feeding inhibition is the primary mode of action of the bisabolene, while the silphinene shows both antifeedant and toxic effects.     

Host-plant acceptance by geographic populations of the colorado potato beetle,Leptinotarsa decemlineata

We used a detailed analysis of feeding behavior to investigate the role of solanaceous alkaloids as sensory-based feeding deterrents for the Colorado potato beetle,Leptinotarsa decemlineata (Say). Experiments were conducted on three geographic, host-adapted populations of beetles to determine whether evolutionary changes in host use have been accompanied by behavioral adaptations to alkaloids. Solanine and tomatine, steroidal glycoalkaloids found in two regional host plants, did not reduce leaf consumption or significantly alter behavior patterns of newly emerged beetles, including those from populations that normally will not feed on plants containing the compounds. Atropine, a tropane alkaloid found in several taxonomically related nonhost species, caused a significant increase in sampling behavior (indicating direct action on the sensory system) and reduced acceptance of treated potato leaves. We propose that variable acceptance of host plants among regional populations ofL. decemlineata has evolved independently of adaptations to alkaloids at the sensory level. To establish that secondary compounds such as atropine influence host choice in nature, field observations are needed to confirm that beetles routinely encounter, and sample, nonhost species.     

Effects ofSolanum glycoalkaloids on chemosensilla in the Colorado potato beetle

Steroidal glycoalkaloids, found in species of the Solanaceae, elicit bursting activity in galeal and tarsal chemosensilla of adult Colorado potato beetles. The effect has an average latency of 6–12 sec, depending on the sensillum/alkaloid combination. A 20-sec alkaloid treatment is often suffficient to render galeal sensilla unresponsive to gamma-aminobutyric acid, normally an effective stimulant. The alkaloids have similar effects on galeal sensilla of larval Colorado potato beetles and on labellar chemosensilla of the blowfly. It is concluded that these compounds act independently of any specialized chemoreceptor in the Colorado potato beetle, and that association of the Colorado potato beetle with solanaceous plants has not led to evolution of a specific receptor forSolanum glycoalkaloids.     

Identification of branched alkanes in lipids ofLeptinotarsa decemlineata say andTribolium destructor by GC-MS: A comparison of main-beam and link-scanned spectra

Branched hydrocarbons were identified in the lipids ofLeptinotarsa decemlineata Say andTribolium destructor by gas chromatography, ordinary electron impact mass spectrometry, and linked, scanned, daughterion monitoring. This methodology allowed us to revise our earlier results based only on GC-MS data confirming the existence of only monomethyl-, dimethyl-, and trimethylalkanes in the hydrocarbons ofL. decemlineata Say. The hydrocarbons fromTribolium destructor consist ofn-alkanes, 3-methylalkanes, internally branched monomethylalkanes and dimethylalkanes. Daughter-ion monitoring can be particularly important for distinguishing between incidentally overlapped GC peaks of hydrocarbons from different series. A trace, for example, of dimethylalkane coeluating withn-alkane was easily identified in GC peak of hydrocarbon mixture ofT. destructor. Link scans confirmed also molecular weights for the compounds without molecular ions in the mass spectra. Structural assignment of the compounds were verified by comparison of the experimental and calculated values of the GC retention Kovats indexes (KI).     

Isolation and identification of volatiles in the foliage of potato,Solanum tuberosum,a host plant of the colorado beetle,Leptinotarsa decemlineata

The volatile compounds ofSolanum tuberosum L., a host plant of the Colorado beetle,Leptinotarsa decemlineata Say, were isolated by successive vacuum steam distillation, freeze concentration, and extraction. The main components aretrans-2-hexen-1-ol, 1-hexanol,cis-3-hexen-1-ol,trans-2-hexenal, and linalool. The distribution of these compounds in a variety of plant families and their biosyntheses are reviewed. These leaf volatiles constitute a general green leaf volatile complex, being active in the olfactory orientation of the Colorado beetle and as such are probably of importance to various phytophagous insects.     

Biological performance of Colorado potato beetle larvae on potato genotypes with differing levels of polyphenol oxidase

Two potato genotypes resistant to the Colorado potato beetle (CPB) and three susceptible genotypes were used to investigate the role of total foliar polyphenol oxidase (PPO) on the performance of CPB larvae in long-term feeding assays. A significant positive correlation was found between larval mortality and PPO content in potato foliage. Moreover, a significant negative correlation was also observed between PPO content and larval weight, fecundity, and relative larval growth rate. These results suggest a significant role of PPO in conferring potato resistance to the Colorado potato beetle at least in those clones where the PPO levels were above a certain threshold.     

Plant response to eggs vs. Host marking pheromone as factors inhibiting oviposition byPieris brassicae

Pieris brassicae L. butterflies secrete miriamides onto their eggs. These avenanthramide alkaloids are strong oviposition deterrents when sprayed onto a cabbage leaf. However, these compounds could not be detected in cabbage leaves from which egg batches had been removed two days after deposition and that still showed oviposition deterrency. It was concluded that the miriamides were not directly responsible for the avoidance by females of occupied leaves while searching for an oviposition site. Evidence was obtained that cabbage leaves themselves produce oviposition deterrents in response to egg batches. Fractions containing potent oviposition deterrents could be isolated from surface extracts of leaves from which previously laid egg batches had been removed. The term host marking pheromone that was used previously is not applicable in this case.     

Host-marking pheromones in lepidoptera,with special reference to twoPieris spp

Adult females of several lepidopteran species avoid oviposition near conspecific eggs. Laboratory and field studies indicate that visual factors as well as chemical host markers may be involved in egg avoidance behavior. The oviposition-deterring pheromones (ODP) of two pierids,P. brassicae andP. rapae have been studied in considerable detail. The ODPs are probably produced in the female accessory glands and contain volatile and nonvolatile components. They are perceived by nonspecialized antennal or tarsal receptors, respectively. The ODP ofP. brassicae affects oviposition ofP. rapae females and vice versa. ODPs show promise for insect control programs, but more information on oviposition behavior in the presence of ODP under field conditions is required.     

Cardenolides as oviposition deterrents to twoPieris species: Structure-activity relationships

Oviposition responses ofPieris rapae andP. napi oleracea to 18 cardenolides were compared under the same conditions. Effects of different concentrations of selected cardenolides were also tested. Most of the compounds were deterrent to oviposition by both insects, but to significantly different degrees.P. rapae were strongly deterred by K-strophanthoside, K-strophanthin-, cymarin, convallatoxin, oleandrin, erysimoside, erychroside, and gitoxigenin. The most deterrent compounds forP. napi oleracea were erychroside, cymarin, erysimoside, convallatoxin, and K-strophanthoside. Strophanthidin-based glycosides were more deterrent than digitoxigenin-based ones, and the number and type of sugar substitutions can have profound effects on activity. Both similarities and contrasts were found in responses ofP. rapae andP. napi oleracea to these cardenolides. Cymarin was equally deterrent to bothPieris species at all concentrations tested. However, when compared withP. rapae, P. napi oleracea was less sensitive to most of the cardenolides.P. napi oleracea was insensitive to K-strophanthin- and oleandrin at 0.5 × 10^–4 M, which were highly deterrent toP. rapae.     

Relative activities of glucosinolates as oviposition stimulants forPieris rapae andP. napi oleracea

The relative activities of 10 glucosinolates in stimulating oviposition byP. rapae andP. napi oleracea were compared under the same conditions. When tested at the same concentration, the structurally different glucosinolates stimulated both butterfly species to widely varying degrees. In most cases,P. rapae was more sensitive to aromatic and indole glucosinolates than to aliphatic representatives. This species responded even less to alkyl thio and sulfinyl glucosinolates. However,P. napi oleracea responded strongly to these aliphatic and sulfur-containing members of the group, and the relative activities of aromatic and aliphatic glucosinolates did not show a clear pattern for this species.P. napi oleracea was much more sensitive to low concentrations of sinigrin than wasP. rapae. The threshold concentration for response ofP. napi oleracea to sinigrin was 10^–8 M, which was 100 times lower than forP. rapae, butP. rapae was more sensitive thanP. napi oleracea to changes in glucosinolate concentrations. For bothPieris species, an optimal concentration was reached, above which the response remained constant or tended to decrease.