Host plant recognition in monophagous weevils: Specialization ofCeutorhynchus inaffectatus to glucosinolates from its host plantHesperis matronalis

Several aphid honeydews were incorporated into sucrose solutions and presented to hop aphids, Phorodon humuli (Schrank), as artificial diets in free-choice bioassays. Small additions of honeydew collected from two species of aphid feeding on hop, Humulus lupulus L., arrested the searching behavior of the hop aphid and appeared to stimulate prolonged periods of ingestion. This effect was more dependent on the host plant honeydew source than the species of aphid that produced the honeydew. Aphid honeydews collected from plants other than hop (non-hosts to P. humuli) contained hop aphid phagostimulants that were less effective. Our results indicate that analysis of aphid honeydew could help describe chemical cues involved in the recognition of appropriate host plants by aphid species.     

Behavior and Population Development of <Emphasis Type="Italic">Phorodon humuli</Emphasis> (Schrank) (Homoptera: Aphididae) on Two Hop Cultivars of Different Susceptibility

The two hop cultivars “Hallertauer Magnum” (HM) and “Spalter Select” (SE) are regarded by growers as extremely different in their susceptibility to the damson-hop aphid Phorodon humuli (Schrank). To investigate these anecdotal observations, spring migration and initial population development of P. humuli were monitored on the two cultivars in 1998 and 1999 in an experimental hop garden. Numbers of migrant aphids on SE were significantly lower, comprising 18.8 and 30.2% as compared to HM in 1998 and 1999, respectively. Population development of apterous aphids on these two cultivars differed significantly. At the end of the monitoring period numbers of aphids on SE were 7.5 and 14.2% as compared to HM in 1998 and 1999, respectively. In behavioral studies of P. humuli alates released on glasshouse plants, those on SE spent significantly more time in motile behavior patterns than aphids on HM. In the glasshouse, population development also differed significantly and the number of aphids developing on SE was 12.9% of that on HM after 28 days. It is concluded that SE exhibits a certain repellent effect on P. humuli and, compared to HM, is possibly nutritionally less suitable to the aphid.     

Effects of plant spacing and interplanting with oilseed rape on colonisation of dwarf hops by the damson-hop aphid, Phorodon humuli

The pattern of colonisation of dwarf hops (Humulus lupulus) by damson-hop aphid (Phorodon humuli (Schrank)) migrating from Prunus spp. was investigated at six plant spacings and where some of the hops were replaced by oilseed rape (Brassica napus L.), a non-host of the aphid. The number of migrant aphids that accumulated on hop stems (bines) increased with increasing bine size and density. The numbers of aphids that colonised hops interplanted with oilseed rape reflected the density of the hop plants only and not the overall plant density. As the physical size of the wind shadow within which flying aphids can manoeuvre and land was unimportant unless provided by a host plant, the finding supports the theory that flying aphids respond to olfactory stimuli associated with their hosts. Variation in bine height (as a measure of plant size) explained 29–93% of the variance in aphid counts during the 3 years' study and bine density 1–14%. Standardising the data as the numbers of aphids per metre of bine and taking a square-root transformation of these standardised counts improved the precision of the analyses and, by stabilising variances, facilitated comparisons between years as growth became more vigorous as the plants matured. Each year, the rate of increase in numbers of aphids settling on plots of hops declined curvilinearly with increasing bine density. Maximum colonisation by P. humuli occurred at a bine density of five per metre row, a density similar to that used commercially by growers of dwarf hops.     

Honeydew feeding in the solitary bee Osmia bicornis as affected by aphid species and nectar availability

Like honey bees (Apis mellifera), non-Apis bees could exploit honeydew as a carbohydrate source. In addition to providing carbohydrates, this may expose them to potentially harmful plant products secreted in honeydew. However, knowledge on honeydew feeding by solitary bees is very scarce. Here we determine whether the polylectic solitary bee Osmia bicornis (=O. rufa) collects honeydew under semi-field conditions, and whether this is affected by aphid species and presence of floral nectar. Bees were provided with oilseed rape plants containing flowers and/or colonies of either Myzus persicae or Brevicoryne brassicae. We used the total sugar level of the bee crop as a measure of the individual's nutritional state and the oligosaccharide erlose as indicator for honeydew consumption. Erlose was present in honeydews from both aphid species, while absent in oilseed rape nectar, nor being synthesized by O. bicornis. When bees were confined to a single honeydew type as the only carbohydrate source, consumption of M. persicae honeydew was confirmed for 47% of the bees and consumption of B. brassicae honeydew for only 3%. Increased mortality in the latter treatment provided further evidence that B. brassicae honeydew is an unsuitable food source for O. bicornis. All bees that were given the choice between honeydew and floral nectar showed significantly increased total sugar levels. However, the fact that no erlose was detected in these bees indicates that honeydew was not consumed when suitable floral nectar was available. This study demonstrates that honeydew exploitation by O. bicornis is dependent on honeydew type and the presence of floral nectar.     

Effects of elevated CO2 on five plant-aphid interactions

We investigated interactions between five species of phloem-feeding aphids (Homoptera: Aphididae) and their host plants at elevated CO₂; Acyrthosiphon pisum (Harris) on Vicia faba L., Aphis nerii Boyer de Fonscolombe on Asclepias syriaca L., Aphis oenotherae Oestlund on Oenothera biennis L., Aulacorthum solani (Kaltenbach) on Nicotiana sylvestris Speg. & Comes and Myzus persicae (Sulzer) on Solanum dulcamara L. Host plants grown at elevated CO₂ generally had greater biomass, leaf area and C:N ratios than those grown at ambient CO₂, while plants with aphids had lower biomass and leaf area than those without aphids.The responses of aphid populations to elevated CO₂ were species-specific with one species increasing (M. persicae), one decreasing (A. pisum), and the other three being unaffected. CO₂ treatment did not affect the proportion of alate individuals produced. In general, aphid abundance was not significantly related to foliar nitrogen concentration.We performed separate analyses to test whether either aphid presence or aphid abundance modified the response of host plants to elevated CO₂. In terms of aphid presence, only three of the potential 15 interactions (five aphid species x three plant traits) were significant; A. solani slightly modified the response of the plant biomass to elevated CO₂ and M. persicae affected the response of leaf area and allocation. In terms of aphid abundance, only two of the potential 15 interactions were significant with A. nerii modifying the plant response to CO₂ in terms of total leaf area and allocation.We conclude that, in contrast to other insect groups such as leaf chewers, populations of most phloem-feeders may not be negatively affected by increased CO₂ concentrations in the future. The reasons for this difference include the possibility that aphids may be able to compensate for changes in host plant quality by altering feeding behaviour or by synthesizing amino acids. In addition, there is little evidence that aphid herbivory, even at high levels, will substantially modify the response of plants to elevated CO₂.     

Genetic, biochemical, and behavioral uniformity among populations of Myzus nicotianae and Myzus persicae

Prior to designation as distinct species, an appellation presently in question, the tobacco aphid, Myzus nicotianae Blackman (Homoptera: Aphididae), was classified as a tobacco-feeding form of the green peach aphid, Myzus persicae (Sulzer). In this study, RAPD polymorphisms distinguished members of the Myzus persicae complex (M. persicae and M. nicotianae) from three outgroup Myzus species (M. cerasi (F.), M. hemerocallis Takahashi, and M. varians Davidson). Polymorphisms within the complex did not separate populations on the basis of host association (tobacco versus other host plants) or geographic origin (collections from the United States, Europe, and Japan). Similarly, while GC-MS analysis of cuticular hydrocarbon profiles revealed both developmental and inter-populational differences within the M. persicae complex, it did not separate populations of tobacco feeding aphids from those collected off non-tobacco hosts. Finally, with the exception of their responses to a choice between lettuce and collards, the host preference behavior of a green peach aphid population, a red tobacco aphid population, and a green tobacco aphid population was indistinguishable in host preference experiments. These results add to a growing body of evidence suggesting M. nicotianae and M. persicae are conspecific.     

Susceptibility of hop to Phorodon humuli

A portion of the USDA World Hop (Humulus lupulus L.) Germ Plasm Collection was screened for antibiosis to the hop aphid, Phorodon humuli (Shrank). Hop aphid development and reproduction on the retained accessions 58016, 21090M, 21211, 21240, and 60038 were then compared to hop aphids reared on the commercial hop cultivars (cvs) L-8, Perle, Chinook, Galena, Eroica, Willamette, and Cascade. In general, hop aphids matured faster and reproduced more on the commercial cvs than on 21090M, 58016, 21211, or 21240. Accession 60038, of note because it supported unusually high numbers of aphids during screening, was found to be the most susceptible of any hop tested. Mortality and natality schedules were then combined to construct matrix models of aphid population growth on 60038, 58016, Cascade, and Perle (the most and least susceptible noncommercial and commercial hops, respectively). Beginning with one one-day-old nymph per leaf, the models predicted that P. humuli would require 24 days to surpass an action threshold of 100 aphids per leaf on 58016. This was seven days longer than on the susceptible Cascade and five days longer than on Perle. A commercial hop with the antibiosis of 58016 would probably require fewer insecticide applications during the growing season, thus retarding the development of insecticide resistance in P. humuli and enhancing the effectiveness of integrated management programs by protecting beneficial insects.

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Zusammenfassung Ein Teil der Genbank des USDA von Hopfen (Humulus lupulus L.) wurde auf Resistenz gegen Phorodon humuli (Shrank) getestet. Dabei wurden die besonders widerstands fähigen Klone 58016, 21090M, 21211, 21240 sowie Klon 60038, der ungewöhnlich viele Blattläuse ertrug, ausgewählt. Anschließend wurde die Entwicklung und Vermehrung der Blattläuse auf den ausgewählten Klonen und auf den Handelssorten (cvs) L-8, Perle, Chinook, Galena, Eroica, Willamette, Cascade untersucht. Im Allgemeinen entwickelten sich die Blattläuse auf den Handelssorten reascher und vermehrten sich stärker als auf den resistenten Klonen. Klon 60038 war dagegen die anfälligste Sorte. Mortalitäts- und Natlitätsdaten wurden kombiniert um Matrixmodelle des Populationswachstums der Blattläuse auf 60038, 58016, Cascade und Perle (die am meisten und am wenigsten anfälligen kommerziellen und nichtkommerziellen Sorten) zu konstruieren. Die Modelle begannen bei 1 Larve pro Blatt und sagten voraus, dass die Aktionsgrenze von 100 Tieren pro Blatt auf 58016 nach 24 Tagen erreicht wird. Das ist 7 Tage später als auf den anfälligen Sorten Cascade und 5 Tage später als auf Perle. Eine kommerzielle Sorte mit der Anfälligkeit von 58016 würde vermutlich während der Vegetationszeit weniger Insektizidspritzungen benötigen. Damit würde die Resistenzentwicklung bei Phorodon humuli verlangsamt und die Wirkung von IPM Programmen durch Schutz der natürlichen Feinde verbessert.

     

3种寄主上桃蚜的选择性及形态分化

桃蚜是一种重要的农业害虫,寄主广泛,种下分化复杂。以采自黄土高原旱作区桃树、烟草、甘蓝上的桃蚜为研究对象,通过叶片选择法、传统比较形态测定法研究了3种寄主上桃蚜的选择性及形态分化。结果表明:在3种寄主同时存在的情况下,烟草上的桃蚜嗜食烟草,表现为63.5%的桃蚜选择烟草叶,13.8%选择甘蓝叶,8.2%选择桃叶,而甘蓝和桃树上的桃蚜对原寄主没有表现出明显的嗜好性;从形态指标来看,3种寄主上的桃蚜在体长、触角末节长度、后足腿节长度、触角与体长的比例方面存在显著差异(P0.05),说明这几个特征可以作为区分这3种寄主上桃蚜的依据。综合分析可以初步认为黄土高原旱作区烟草上的桃蚜可能形成了寄主专化型-烟草型。     

Oviposition avoidance of parasitized aphid colonies by the syrphid predator Episyrphus balteatus mediated by different cues

Oviposition decisions made by members of a guild of natural enemies can have evolved to avoid intraguild predation, potentially avoiding the disruption of the extraguild prey control. We have studied the oviposition preference of the aphidophagous predator Episyrphus balteatus De Geer (Diptera: Syrphidae) within colonies of Myzus persicae Sulzer (Hemiptera: Aphididae) in the presence of two developmental stages of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae). Results from a greenhouse choice experiment showed that E. balteatus females lay significantly fewer eggs in colonies with mummified aphids than in unparasitized colonies. Colonies of parasitized, but not yet mummified did not contain significantly fewer eggs than colonies with unparasitized aphids. In three no-choice experiments, we assessed stimuli coming from aphid honeydew, from the aphids themselves and also from extracts of the aphid bodies, and all of these stimuli mediate the discrimination of mummified aphids from healthy aphids. To a lesser extent these stimuli also contribute to the discrimination against aphids that are parasitized but not yet mummified. These results suggest that the effects of these two species could be complementary for the control of M. persicae, since the species that acts as an intraguild predator, E. balteatus, avoids ovipositing on aphid colonies parasitized by the intraguild prey, A. colemani.     

Alkaloid level in narrow-leafed lupin, Lupinus angustifolius, influences green peach aphid reproductive performance

Two viviparous parthenogenetic clones of the green peach aphid, Myzus persicae (Sulzer), one collected from Rydalmere, New South Wales (NSW), and the other from South Perth (SP), Western Australia, were reared on radish, Raphanus sativus L. cv. Scarlet Globe, under controlled conditions. The NSW clone was fed on simple artificial diets containing alkaloid extracted from narrow-leafed lupin, Lupinus angustifolius L. cv. Fest., and its reproductive performance monitored over 112 h. Forty (40) h into the experiment and thereafter, aphids on the control diet (sucrose solution) produced significantly more offspring (P<0.05) than those on diets containing alkaloid. In a separate experiment, apterae of each clone were caged on three lines (cv. Yorrel, cv. Danja and 84L:441) of narrow-leafed lupin, and allowed to reproduce. The first three offspring were retained, and all developed to 3rd or 4th instar stage. Two nymphs were removed, and the remaining nymph reared through. All three lines produced adults. The number of young produced were counted over 11 days. Fecundity of the SP clone was lower on line 84L:441, but there was no difference in the fecundity of the NSW clone. Phloem exudate and green tissue was concomitantly collected from all lines, and analysed by GC-MS for the alkaloids lupanine and 13-hydroxylupanine. Line 84L:441 contained the highest level of total alkaloids in both phloem and tissue. All experiments indicate that alkaloid level may suppress fecundity of green peach aphids.     

Honeydew collection by the invasive garden ant Lasius neglectus versus the native ant L. grandis

Honeydew collection performed by the invasive ant Lasius neglectus and by the native ant L. grandis was compared. The invasive ant collected 2.09 kg of honeydew per tree while the native ant collected 0.82 kg. The aphid Lachnus roboris was visited by both ant species. In holm oaks colonized by L. neglectus, aphid abundance tended to increase and its honeydew production increased twofold. The percentage of untended aphids was lower in holm trees occupied by L. neglectus. As tending ants also prey on insects, we estimated the percentage of carried insects. The native ant workers carried more insects than the invasive ant. Both ant species preyed mainly on Psocoptera and the rarely tended aphid, Hoplocallis picta. We conclude that the higher honeydew collection achieved by L. neglectus was the consequence of (1) its greater abundance, which enabled this ant to tend more Lachnus roboris and (2) its greater level of attention towards promoting an increase of honeydew production. Handling editor: Heikki Hokkanen     

The susceptibility of Myzus persicae and Brevicoryne brassicae to 14C-phorate in artificial diets

Colonies of Myzus persicae and Brevicoryne brassicae were established on artificial diets and the honeydew produced by them collected on aluminium foils. The diets were later exchanged for others containing a range of ¹⁴C-phorate concentrations. The honey-dew produced while feeding on the treated diets was collected separately and mortalities were recorded. The diets, aphids and their honeydew were subsequently analysed. About 1.6% of the doses applied initially were found in the diets at the end of the bio-assay period. Thin-layer chromatography of diets containing LC₅₀ concentrations of insecticides showed that phorate and its metabolites were present in similar proportions. The LC₅₀ values were 15.5 nM and 277 nM phorate equivalents for B. brassicae and M. persicae respectively.     

Females of Cotesia vestalis,a parasitoid of diamondback moth larvae,learn to recognise cues from aphid‐infested plants to exploit honeydew

1. To maximise their reproductive success, the females of most parasitoids must not only forage for hosts but must also find suitable food sources. These may be nectar and pollen from plants, heamolymph from hosts and/or honeydew from homopterous insects such as aphids. 2. Under laboratory conditions, females of Cotesia vestalis, a larval parasitoid of the diamondback moth (Plutella xylostella) which does not feed on host blood, survived significantly longer when held with cruciferous plants infested with non‐host green peach aphids (Myzus persicae) than when held with only uninfested plants. 3. Naïve parasitoids exhibited no preference between aphid‐infested and uninfested plants in a dual‐choice test, but those that had been previously fed aphid honeydew significantly preferred aphid‐infested plants to uninfested ones. 4. These results suggest that parasitoids that do not use aphids as hosts have the potential ability to learn cues from aphid‐infested plants when foraging for food. This flexible foraging behaviour could allow them to increase their lifetime reproductive success.     

Influence of Experience on the Response of Bathyplectes curculionis (Hymenoptera: Ichneumonidae), a Nonaphidophagous Parasitoid, to Aphid Odor

Bathyplectes curculionis (Thomson) is an introduced natural enemy of the alfalfa weevil in North America. The wasp requires carbohydrate foods as an adult. Adult wasps have increased longevity and fecundity when provided access to pea aphid, Acyrthosiphon pisum (Harris), honeydew in the laboratory, and adults respond positively to the presence of pea aphids in alfalfa fields. However, it is unknown how these wasps find aphid honeydew in the field. In a series of Y-tube olfactometer experiments, we evaluated the response of naïve and experienced adult female B. curculionis to odors from pea aphids, alfalfa, and pea aphids on alfalfa. Naïve adult females did not respond positively to pea aphid odor even when hungry. But adult females were able to learn aphid odor, and the mechanism of learning appears to be associative rather than by sensitization. Naïve females also showed no preference for alfalfa odor but learned alfalfa odor through sensitization. The wasps did not distinguish between alfalfa with aphids and alfalfa without aphids, even after exposure to aphids or alfalfa with aphids. However, they preferred pea aphid odor to alfalfa odor after a feeding experience in the presence of pea aphid odors. But after exposure to mixed odors of aphids and alfalfa while feeding, B. curculionis females preferred the odor of alfalfa to the odor of pea aphids. These results suggest that alfalfa odors mask or override aphid odors when aphids are associated with alfalfa (as happens naturally), thus interfering with the wasp's ability to respond to learned aphid odors. Therefore, although the wasps are capable of learning to find pea aphids and their honeydew in a simplified laboratory setting, it appears unlikely that they do so in the field.     

Isotopic enrichment in a phloem-feeding insect: influences of nutrient and water availability

The isotopic enrichment between an animal and its diet can vary among and within living systems, but the sources of variation are not yet fully understood. Some studies have found that diet quality or an animal’s nutritional status can influence the degree of trophic enrichment, while others have dismissed nutrition as a contributing factor. We evaluated the effects of nutrient and water availability on carbon and nitrogen isotopic enrichment in a specialized plant–herbivore system. Aphids are largely sedentary and rely exclusively on nitrogen-poor phloem sap of their host for nutrition. We grew potato aphids [Macrosiphum euphorbiae (Aphididae)] on an accepted host, pumpkin [Cucurbita pepo L. (Cucurbitaceae)], in a glasshouse environment. Twelve pumpkin plants growing under high- and low-watering regimes were inoculated at 4 weeks of age with aphids. During the course of the experiment we collected leaves, phloem sap, aphids and honeydew (i.e., aphid exudates). We found no trophic enrichment between aphids and their phloem sap diet, but significant carbon enrichment of honeydew relative to aphids (2.5‰) and phloem sap (2.1‰). Honeydew was also enriched in nitrogen compared to the phloem sap (1.2‰). Watering treatment had a substantial impact on trophic enrichment. Correlations among tissues, an indication of uniform trophic enrichment among samples, were significant only for the carbon isotopic composition, and then only for plants and aphids grown in the low-water treatment. Diet quality also influenced the degree of isotopic enrichment; trophic enrichment for both carbon and nitrogen isotopic composition increased as diet quality (C/N) declined. We conclude that the degree of trophic enrichment is variable due, in part, to diet quality, but that the scale of variation is small.     

Effect of Manipulations on the Host Selection Behavior of Sitobion avenae (Homoptera: Aphididae)

The study of aphid host selection and feeding behavior is difficult because aphids have to penetrate the plant to reach their feeding site, phloem tissue. The activity of the stylets, salivation or food intake, can not be observed externally and requires an indirect visualization technique such as the Electric Penetration Graph (EPG). The plant selection behavior of Sitobion avenae on potato varied depending on whether an ethological or EPG method was used to study it. A similar variation did not occur with Myzus persicae or Rhopalosiphum padi. The application of water-based silver conductive paint onto the thorax, as normally used for EPG, or onto the abdomen of Sitobion avenae alates resulted in increased duration and frequency of probing compared to results from ethological observations. Our results indicated that EPG manipulations might have different effects on different species of aphids and that a comparison of EPG and ethological data is required to confirm that the EPG method does not bias aphid feeding behavior.     

Discriminative behavioral responses by aphids to various plant matrix polysaccharides

Three species of aphids, Schizaphis graminum (Rondani) (the greenbug), Acyrthosiphon pisum (Harris) (the pea aphid) and Myzus persicae (Sulzer) (the green peach aphid), showed significantly different behavioral responses to various plant mono- or polysaccharides incorporated within thin (<200 m) films of agar overlaying artificial diets. Thirteen polysaccharides (i.e.: polygalacturonic acid, low methoxy pectin, high methoxy pectin, arabinogalactan, xylan, galactan, cellulose, starch, amylose, laminarin, dextran, 2,3-diacetyl pectin and trifluoroacetyl pectin) and 5 monosaccharides (arabinose, xylose, galactose, glucose and galacturonic acid) were tested in paired choices against a control overlay containing only agar. Glucose, dextran and laminarin were the only compounds that all three species of aphids responded to similarly (viz., glucose stimulated, dextran had no effect and laminarin deterred ingestion of underlying diets). None of the aphids exhibited negative responses to the monosaccharides tested. These monosaccharides either had no significant effect or were stimulatory. The polysaccharides tested induced a variation of unaltered, stimulatory or inhibitory behavioral responses in the 3 species of aphids. The behavioral responses of both greenbugs and pea aphids, which are oligophagous, were significantly affected by 6 out of 7 plant matrix polysaccharides tested. Feeding behavior by green peach aphids was affected by only one of these polysaccharides.Electronic monitoring of aphid probing showed that aphids salivated in and test probed the overlays prior to inserting their stylets into and ingesting from the underlying diets. Recorded responses of aphids probing overlays containing inhibitory polysaccharides resembled the recorded behavioral responses of aphids on resistant or nonhost plants (i.e., numerous short probes with either a lack of or a prolonged period prior to ingestion). The differential behavioral responses of the aphids to the various polysaccharides supports the view that plant matrix polysaccharides play a role in the chemical basis of aphid — plant interactions.

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Zusammenfassung Drei Blattlausarten, Schizaphis graminum, Acyrthosiphon pisum and Myzus persicae, zeigten deutliche Unterschiede in ihrem Probeverhalten auf künstlichen Nährmedien, die mit dünnen (<200 m), verschiedene Mono- und Polysaccharide enthaltenden Agarschichten bedeckt waren.Die in den Agarschichten enthaltenen Monosaccharide bewirkten bei allen drei Arten eine deutliche Steigerung des Probeverhaltens. Im Gegensatz dazu war der Einfluss der Polysaccharide von Art zu Art verschieden. Sechs von sieben getesteten pflanzlichen Matrixpolysacchariden beeinflussten deutlich das Probeverhalten von Schizaphis graminum und Acyrthosiphon pisum. Im Gegensatz dazu wurde das Probeverhalten von Myzus persicae nur von einem der untersuchten Polysaccharide beeinflusst. Die Zahl der Wirtspflanzen für Schizaphis graminum und Acyrthosiphon pisum ist relativ klein im Vergleich zu der von Myzus persicae. Dies ist möglicherweise darauf zurückzuführen, daß die Fähigkeit, chemosensorisch zwischen pflanzlichen Matrixpolysacchariden zu unterscheiden, bei Myzus persicae weniger stark ausgeprägt ist.Elektronische Registrierung des Probeverhaltens zeigte, daß Schizaphis graminum vor der Aufnahme der künstlichen Nährmedien zunächst die darüber liegenden Agarschichten testete. Dies geschah durch Einstechen des Stiletts in die Agarschicht, Absonderung von Speichel, Aufsaugen der verflüssigten Matrix und auschliessendes Wiederausstoßen.Das Probeverhalten von Schizaphis graminum auf Trifluoroacetylpektin, welches eine Aufnahme der darunter liegenden Nährstoffe verhinderte, war vergleichbar zu dem Probeverhalten von Schizaphis Graminum auf resistenten oder Nichtwirtspflanzen. Andererseits glich das Probeverhalten von Schizaphis graminum stark methyliertem Pektin, welche die Nährstoffaufnahme steigerte, dem auf natürlichen Wirtspflanzen. Die Ergebnisse dieser Untersuchung zeigen, daß pflanzliche Matrixpolysaccharide für die Wechselwirkung zwischen Blattläusen und Pflanzen keine chemisch inerten Komponenten darstellen. Der unterschiedliche Einfluss der pflanzlichen Matrixpolysaccharide auf die verschiedenen Blattlausarten zeigt, daß diese pflanzlichen Biopolymere eine entscheidene Rolle bei der Erkennung von Wirtspflanzen durch Blattläuse spielen könnten.Darüberhinaus zeigt das extrem unterschiedliche Probeverhalten von Schizaphis graminum auf Trifluoroacetyl- bzw. stark methyliertem Pektin, daß selbst geringe Änderungen in den chemischen Eigenschaften dieser Komponenten das Probeverhalten von Blattläusen deutlich beeinflussen können.

     

Insect growth regulating effects of neem extract and azadirachtin on aphids

Neem,Azadirachta indica (A. Juss.), seed oil (NSO) applied to leaf discs at a concentration of 1.0% resulted in 94% to 100% mortality of second instar nymphs of currant-lettuce aphid,Nasonovia ribis-nigri (Mosley), and green peach aphid,Myzus persicae (Sulzer), after nine days. The equivalent amount of pure azadirachtin (AZA) (≈40 ppm), the principle active ingredient of neem, was as effective as NSO. The survival of adult aphids was unaffected by NSO or AZA, but the survival of offspring from treated adultM. persicae andN. ribis-nigri was reduced significantly. The lethal concentration of AZA resulting in 50% mortality of second instar nymphs of nine species of aphids ranged from 2.4 ppm forM. persicae on pepper to 635.0 ppm for the strawberry aphid,Chaetosiphon fragaefolii (Cockerell), on strawberry. ForM. persicae, the growth regulating effect of AZA was influenced by the host plant and the nymphal instar treated.     

Effects of dietary sucrose concentration on aphid honeydew carbohydrate levels and rates of excretion

Honeydew droplets freshly excreted by two aphid species, Myzus persicae (Sulz.) and Acyrthosiphon pisum (Harr.), feeding on nutritionally adequate, artificial diets containing 10–40% w/v sucrose, were collected in oil. The volume, frequency of excretion, and carbohydrate content of the droplets were determined by measuring the diameter of the droplets in the oil, by recording the number of droplets excreted per aphid per hour, and by using a quantitative colorimetric method for estimating carbohydrates. Rates for the intake or excretion of fluid, the intake and absorption of sucrose, and the excretion of carbohydrate were consequently calculated for the two species on each dietary sucrose concentration. The percentage of dietary sucrose absorbed by the aphids ranged from 36% on diet with 40% sucrose to 97% on diet with 10% sucrose. Such honeydew/diet relationships may allow one to use honeydew carbohydrate concentrations to estimate the sucrose concentrations of the phloem sap ingested by aphids feeding on host plants.

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Résumé Des gouttelettes de miellat fraîchement excrétées par deux espèces de pucerons, Myzus persicae (Sulz.) et Acyrthosiphon pisum (Harr.), pucerons nourris sur des régimes nutritifs synthétiques contenant 10–40% de saccharose, ont été récupérées dans de l'huile. Le volume des gouttelettes a été déterminé en mesurant leur diamètre individuel dans l'huile, la fréquence d'excrétion établie par le nombre de gouttelettes excrétées par puceron par heure, et la teneur en glucides par une méthode d'analyse colorimétrique quantitative. Les taux d'ingestion et d'excrétion de liquide, d'ingestion et d'absorption de saccharose ainsi que les taux d'excrétion de glucides ont été par la suite calculés pour les deux espèces d'aphides nourris sur les différentes concentrations de saccharose. Le pourcentage de saccharose alimentaire absorbé par les aphides a été de 36% sur le régime contenant 40% de ce glucide, mais s'est élevé à 97% sur le régime ne contenant que 10% de saccharose. D'après ces relations miellat/régime nutritif, et en connaissant la teneur du miellat en glucides, on peut faire une approximation de la concentration du saccharose dans la sève élaborée du phloème ingérée par les aphides.

     

Negative dietary effects of Colorado potato beetle eggs for the larvae of native and introduced ladybird beetles

Aphidophagous ladybird beetles (Coleoptera: Coccinellidae) are attracted to and feed heavily on aphids, but many species will also feed opportunistically on other prey that they encounter. In potatoes (Solanum tuberosum L.) in Washington State, USA, coccinellids feed on both green peach aphids (“GPA,” Myzus persicae Sulzer) and eggs of the Colorado potato beetle (“CPB,” Leptinotarsa decemlineata Say). The guild of aphidophagous ladybirds includes two native species, Hippodamia convergens Guérin-Méneville and Coccinella transversoguttata Brown. Recently, an introduced species, Coccinella septempunctata L., has invaded and apparently displaced its native congener. A second exotic, Harmonia axyridis Pallas, has colonized the area and is becoming more abundant. We compared larval development of each species on a monotypic diet of GPA, a monotypic diet of CPB eggs, or a mixed diet of both GPA and CPB eggs. Our goal was to answer two questions: (1) do larvae of the four ladybird species benefit from including CPB eggs in their diet and (2) do the four ladybird species differ in their ability to utilize CPB eggs as prey? No larva of any species completed development on a pure diet of CPB eggs, and survivorship was highest for all species when they fed on a pure diet of GPA. One native species, H. convergens, and one exotic species, H. axyridis, exhibited significantly lower survivorship on a mixed diet of both CPB eggs and GPA, compared to a pure GPA diet; H. axyridis also took longer to develop from egg to adult when both prey were provided. Survivorship of the two Coccinella spp. was not altered by the inclusion of CPB eggs with GPA, although CPB eggs lengthened the development time of C. transversoguttata. Adult size was not consistently affected by diet for any of the coccinellids. Overall, no ladybird species benefited from the inclusion of potato beetle eggs in its diet. The two Coccinella species responded similarly to the inclusion of CPB eggs, and so we would not expect any difference in the success of coccinellid larval development in potato fields following the replacement of C. transversoguttata by C. septempunctata. Hippodamia convergens and H. axyridis, the two species whose survivorship was depressed by combining CPB egg and aphid prey, were also the two species that consumed the greatest number of CPB eggs during successful larval development. A comparison of total egg consumption by each species cohort suggested that displacement of the other species by H. axyridis would not alter CPB biological control, because the higher per capita feeding rate by H. axyridis larvae compensated for individuals’ greater mortality risk on a diet including CPB eggs.