Showing papers on "Aphid published in 1996"
TL;DR: Support is provided for the hypothesis that a management strategy of providing flower borders for fields can result in more efficient biological control of aphids by syrphid larvae, thus reducing the reliance on insecticidal control.
Abstract: Hoverflies (Diopters: Syrphidae) are potentially important in arable and horticultural crops as biological control agents. Many species lay their eggs near aphid colonies, and their larvae are aphidophagous. Adult overflies need nectar for energy and the protein from pollen for sexual maturation and egg development. Phacelia tanacetifolia Bentham (Hydrophyllaceae), a North American annual species that is a good source of pollen for syrphids, was drilled in the margins of 3 winter-wheat fields on a farm in North Hampshire, southern United Kingdom in 1992 and in different fields in 1993. Numbers of hoverflies in yellow water traps, oviposition rates, and aphid densities in these fields were compared with those in control fields. In 1992 in the fields bordered with P. tanacetifolia , significantly more hoverflies were captured in the traps but differences in oviposition or aphid numbers were not significantly different between treatments. This may have been because the wheat matured early so that it was less suitable for syrphid oviposition when gravid females were in the field. In 1993, differences between numbers of adults caught in experimental and control fields were not significantly different. However, significantly more eggs were found in fields with P. tanacetifolia than in control fields and significantly fewer aphids were present in these fields than in controls during the 4th wk of the experiment when many 3rd-instar syrphid larvae were present in the crop. Our results provide support for the hypothesis that a management strategy of providing flower borders for fields can result in more efficient biological control of aphids by syrphid larvae, thus reducing the reliance on insecticidal control.
231 citations
TL;DR: The experiments demonstrate that the insecticidal effects of GNA observed in artificial diets can be reproduced in planta, both under laboratory bioassay conditions and in the glasshouse.
223 citations
TL;DR: The experiments showed that ladybird beetles prey on parasitized aphids, so over the long-term, the effectiveness of parasites is impaired by the interference of predators on ovipositing parasitoids and by the predation of parasitized Aphids.
Abstract: The question of whether multiple natural enemies often interact to produce lower host mortality than single enemies acting alone has not yet been resolved. We compared the effects of four different combinations of natural enemies-parasitoids, predators, parasitoids plus predators, and no enemies-on caged aphid populations on marsh elder, Iva frutescens, in west-central Florida. Using starting densities of natural enemies commonly found in the field, we showed that parasitoid wasps reduced aphid population densities more than predatory ladybird beetles. The addition of predators to cages containing parasites reduced the ability of parasitoids to decrease aphid population densities. Because the experiments ran only over the course of one generation, such a reduction in the effectiveness of parasites is likely caused by interference of predators with parasitoid behavior. Parasitism in the cages containing both parasitoids and predators was reduced when compared to percent parasitism in parasitoid-only cages, but this could also be due to predation. Our experiments showed that ladybird beetles prey on parasitized aphids. Thus over the long-term, the effectiveness of parasites is impaired by the interference of predators on ovipositing parasitoids and by the predation of parasitized aphids. The effects of natural enemies in this system are clearly non-additive.
169 citations
TL;DR: The previous discrimination shown by adult parasitoids emerging from aphid mummies must be determined by the chemicals contacted by a parasitoid on the skin of the mummy or while biting its way out of the dead aphid.
Abstract: . Adult female parasitoids (Aphidius rhopalosiphi De Stef.) (Hymenoptera: Aphidiidae) reared on the aphid Metopolophium dirhodum (Walk.) (Homoptera: Aphididae) changed their responses to odours of two wheat cultivars (‘Maris Huntsman’ and ‘Rapier’) when the parasitized aphids had been moved from the former to the latter cultivar at various times after parasitization. If the aphids were moved after less than 6 days, the female parasitoids emerging from mummies by then formed on ‘Rapier’ responded positively to that cultivar, whereas parasitoids emerging from mummies transferred as still living aphids after 8 days on ‘Maris Huntsman’, responded positively to that cultivar rather than to ‘Rapier’ on which they had emerged. This appeared to be evidence for Hopkins' ‘host selection principle’, which states that chemical experience acquired by the larva of an endopterygote insect can be transferred through the pupal stage to the adult. However, discrimination in favour of either cultivar disappeared when the parasitoids were reared in aphids on both cultivars, and the emerging females were tested following excision of the pupae from the aphid mummies. The previous discrimination shown by adult parasitoids emerging from aphid mummies must therefore be determined by the chemicals contacted by a parasitoid on the skin of the mummy or while biting its way out of the dead aphid.
156 citations
TL;DR: A conceptual model of host choice by aphidiid wasps is presented and host value varies dynamically with parasitoid state variables such as age, egg load, and prior experience.
Abstract: Species in the family Aphidiidae (Hymenoptera) parasitize exclusively ovoviviparous aphids. Females use a variety of information to detect and evaluate suitable hosts. Olfactory cues associated with aphids, or the aphids’ host plant, are important for host location. Visual cues including aphid colour, shape, and movement can be evaluated from a distance without physical contact; aphid movement may act as a releasing stimulus for attack. Contact chemosensory cues (gustatory cues) are evaluated by antennation of the host cuticle and during ovipositor probing. A potential host must conform to the wasp’s response profile and satisfy minimum physiological and dietary requirements for immature development and growth. Host quality is determined in part by attributes specific to each aphid species and in part by each aphid’s individual-specific growth potential. Host quality for male and female progeny may vary as a result of different patterns of resource allocation and sexual size dimorphism. For an encountered aphid to be accepted as a host, its perceived value must exceed the wasp’s response threshold for oviposition. Host value, as opposed to host quality, varies dynamically with parasitoid state variables such as age, egg load, and prior experience. A conceptual model of host choice by aphidiid wasps is presented.
137 citations
TL;DR: Direct interactions in the biological control of the alfalfa weevil and the effects of honeydew producers on other her- bivores through natural enemies fall under the general concepts of short-term apparent competition and related ecological relationships among species, and highlight the complexity with which indirect interactions can affect exploiter-victim relationships in biological control.
Abstract: The population dynamics of insect pests in agroecosystems may often be linked to those of other phytophagous species through the foraging activities of natural enemies; these indirect interactions provide both opportunities and challenges for biological control. We conducted field experiments to explore indirect interactions in the biological control of the alfalfa weevil (Hypera postica) in northern Utah. Honeydew produced by pea aphids (Acyrthosiphon pisum) in alfalfa fields may be important as a source of nutrition for adults of the wasp Bathyplectes curculionis and may thereby enhance parasitism of the wasp's host, the alfalfa weevil. The presence of aphids may also promote aggregation of lady beetles, which consume weevil larvae in alfalfa. But by feeding heavily on pea aphids as well, these predators could indirectly enhance weevil survivorship by undercutting the wasp's capacity to parasitize its host. In one field experiment, we added pea aphids and/or adults of the lady beetle Coccinella septempunctata to caged field plots of alfalfa during the first (spring) hay crop. Adding aphids increased levels of parasitism among late-maturing alfalfa weevil larvae. Adding lady beetles decreased numbers of late-maturing weevil larvae, but also decreased levels of parasitism among these larvae. In another experiment, repeated application of artificial honeydew to caged alfalfa plots during the first crop increased levels of parasitism among weevil larvae. In a third experiment, a single application of artificial honeydew to open (uncaged) alfalfa plots in mid-May also had a direct positive effect on rates of parasitism among larvae. However, this application had an indirect negative effect on parasitism as well: the presence of artificial honeydew caused aggregation of lady beetles and thus led to decreased aphid abundance. Consequently, provision of artificial honeydew as a food source for parasitoid adults was neutralized by a subsequent reduction in naturally occurring honeydew. These field experiments illustrate the complexity with which indirect interactions can affect exploiter-victim relationships in biological control. They also raise questions con- cerning the long-term consequences that may result from the purposeful introduction of the Old World lady beetle C. septempunctata to alfalfa and other crops in North America. Artificial honeydew may prove useful in enhancing parasitism of the alfalfa weevil, but frequent applications may be required to compensate for associated reductions in availability of naturally occurring aphid honeydew. The effects of honeydew producers on other her- bivores through natural enemies fall under the general concepts of short-term apparent competition and related ecological relationships among species, and highlight the impor- tance of temporal and spatial factors in indirect interactions.
127 citations
TL;DR: Plant resistance traits affect diverse species from three trophic levels supporting a “bottom-up” influence of plants on community structure.
Abstract: We examine how the distribution of a leafgalling aphid (Pemphigus betae) affects other species associated with natural stands of hybrid cottonwoods (Populus angustifolia x P. fremontii). Aphid transfers on common-garden clones and RFLP analysis show that resistance to aphids in cottonwoods is affected by plant genotype. Because susceptible trees typically support thousands of galls, while adjacent resistant trees have few or none, plant resistance traits that affect the distribution of this abundant herbivore may directly and/or indirectly affect other species. We found that the arthropod community of aphid-susceptible trees had 31% greater species richness and 26% greater relative abundance than aphid-resistant trees. To examine direct and indirect effects of plant resistance traits on other organisms, we experimentally excluded aphids and found that abundances and/or foraging behavior of arthropods, fungi, and birds were altered. First, exclusion of gall aphids on susceptible trees resulted in a 24% decrease in species richness and a 28% decrease in relative abundance of the arthropod community. Second, exclusion of aphids also caused a 2- to 3-fold decrease in foraging and/or presence of three taxa of aphid enemies: birds, fungi, and insects. Lastly, aphidexclussion resulted in a 2-fold increase in inquilines (animals who live in abodes properly belonging to another). We also found that fungi and birds responded to variation in gall density at the branch level. We conclude plant resistance traits affect diverse species from three trophic levels supporting a "bottom-up" influence of plants on community structure.
96 citations
TL;DR: In this paper, the authors conducted laboratory experiments quantifying the behavior and effectiveness of predator species used either singly or in combination to control bean aphids, Aphis fabae Scopoli.
Abstract: An open question in biological control concerns the value of using multiple as opposed to a single species of natural enemies. To find out how the mechanisms by which multiple biocontrol agents might interact, I conducted laboratory experiments quantifying the behavior and effectiveness of predator species used either singly or in combination to control bean aphids, Aphis fabae Scopoli. The predators were larvae of a lacewing, Chrysoperla plorabunda (Fitch), and the sevenspotted lady beetle, Coccinella septempunctata L. The experiments consisted of 4 treatments tested in a 2 X 2 factorial design crossing 0 or 1 first-instar C. plorabunda with 0 or 1 first-instar C. septempunctata per fava bean plant, Vicia faba L. I also tested 2 additional treatments of 2 larvae of a single species, for a total of 6 treatments. The predators slowed the growth of aphid populations ; no evidence of interaction between the predator species could be seen in terms of their effects on the sizes of the final aphid populations. This result may be explained by the finding that larvae of C. plorabunda and C. septempunctata differed significantly in where they were most frequently found on the plant. No clear evidence for intraguild predation was found. Thus, the majority of the data indicated that C. plorabunda and C. septempunctata did not have significant interactions.
87 citations
TL;DR: Plant species which are more sensitive to elevated CO2 may show a modified response to herbivore pressure in a future atmospheric environment.
Abstract: This study investigated the effects of elevated CO2 on populations of root and/or shoot aphids and their effects on partitioning in Cardamine pratensis. Total plant biomass in elevated ( 600 ppm) CO2 of uninfested Cardamine plants was 52% higher than in ambient ( 350 ppm) concentrations but CO2 effects were not statistically significant. In elevated CO2, feeding by shoot aphids (Aphis fabae fabae) alone and in combination with root aphids (Pemphigus populitransversus), and root aphids alone had no significant effect on plant biomass. No significant effects of elevated CO2 were detected on population size of the shoot or root-feeding species. Interspecific effects were detected between the root and shoot species. Root aphid populations were significantly smaller in the presence of shoot aphids on the same plants. In this system plant growth was unaffected by an elevated CO2 environment. Plant species which are more sensitive to elevated CO2 may show a modified response to herbivore pressure in a future atmospheric environment.
84 citations
TL;DR: In aphids the olfactory receptor neurones are housed in placoid sensilla on the antennae, the so-called distal and proximal primary rhinaria on segments six and five, respectively, and, in winged aphids, the secondary rhinarius on segments three and four.
Abstract: In aphids the olfactory receptor neurones are housed in placoid sensilla on the antennae, the so-called distal and proximal primary rhinaria on segments six and five, respectively, and, in winged aphids, the secondary rhinaria on segments three and four (Shambaugh et al, 1978; Bromley et al., 1979). The overall responses of these receptors to plant odours can be studied by the electroantennogram (EAG) technique. In this way, it can be shown which plant volatiles are detected and, thus, are likely to play a role in the discrimination between the odour blends of host and non-host plant species during orientation and landing. EAGs in response to plant volatiles have been recorded in a number of aphid species, i.e., the English grain aphid Sitobion avenae (F.) and the rose-grain aphid Metopolophium dirhodum (Walk.) (Yan & Visser, 1982; Visser & Yan, 1995), the black bean aphid Aphis fabae Scop. (Hardie et al., 1995), and the vetch aphid Megoura viciae Buckton (Visser & Piron, 1994, 1995).
84 citations
TL;DR: As the volatile aphid alarm pheromone attracted A. uzbekistanicus females, it can be concluded that this chemical stimulus acts as a host finding kairomone for this parasitoid species, however, its effect over long distances seems to be limited due to the relatively high concentrations required for reactions.
Abstract: The present study aimed to test the possible function of the aphid alarm pheromone (E)-β-farnesene (EBF) as a host finding kairomone for aphid primary parasitoids. Extracts of volatile emissions of undisturbed aphids and of aphids under parasitoid attack were obtained by air entrainment. Extracts of cornicle secretions were gained by disturbing aphids and taking their secretions into solution. Extracts were compared by gas chromatography. Only air entrainments of aphids under attack and solvent extracts of cornicle secretions contained the alarm pheromone. In Y-tube olfactometer bioassays, femaleA. uzbekistanicus were attracted to aphid groups under attack of parasitoids, presumably by released EBF. High concentrations of synthetic EBF (1.4 µg to 5.7 µg) also attractedA. uzbekistanicus females. Females with oviposition experience reacted more readily to lower concentrations of EBF than females without experience. In experiments designed as Petri-dish bioassays, the test animals could contact filter paper discs that were treated with solutions containing EBF. Behavioural effects like antennation or stinging attack were not observed. With computer video analysis of parasitoid movements, some effects onA. uzbekistanicus behaviour were detected, again indicating attraction to EBF. As the volatile aphid alarm pheromone attractedA. uzbekistanicus females, it can be concluded that this chemical stimulus acts as a host finding kairomone for this parasitoid species. However, its effect over long distances seems to be limited due to the relatively high concentrations required for reactions. Of two other parasitoid species examined (P. volucre andL. testaceipes) onlyP. volucre was also significantly attracted to the volatile EBF in the Y-tube olfactometer.
TL;DR: One of the gut microbes belonging to the family Enterobacteriaceae was identified as Erwinia herbicola that is found mainly on plant surfaces, which may suggest that the intracellular symbiont of aphid is derived from a habitant of plant on which host insects feed.
Abstract: In an attempt to investigate the origin of the intracellular symbiont of the aphid (Buchnera), aphid gut aerobic bacteria were isolated, and their phylogenetic relations to other prokaryotes were examined based on nucleotide sequences of 16S rDNA. It turned out that there are seven aerobic bacterial groups which constitute major flora of the aphid's gut. As three of the isolated bacteria were identified as members of the family Enterobacteriaceae, and share the common ancestor with the intracellular symbiont, the nucleotide sequences of 16S rDNA were determined for 15 representative strains of the family Enterobacteriaceae. One of the gut microbes belonging to the family Enterobacteriaceae was identified as Erwinia herbicola that is found mainly on plant surfaces. This fact may suggest that the intracellular symbiont of aphid is derived from a habitant of plant on which host insects feed.
TL;DR: Exposure to δ-endotoxin of Bacillus thuringiensis tenebrionis has no statistically significant effect on survival, aphid consumption, development, or reproduction in beetles.
Abstract: We exposed larval and adult Hippodamia convergens (Guerin-Meneville), convergent lady beetle, to Myzus persicae (Sulzer), green peach aphid, reared on potatoes expressing δ-endotoxin of Bacillus thuringiensis tenebrionis . Because the toxin may be ingested by the aphid, the beetle may in turn be exposed to the toxin. However, we measured no statistically significant effect on survival, aphid consumption, development, or reproduction in beetles.
TL;DR: With the introduction of insecticide‐treated plants around the aphid‐infested plants, Parasitoids showed a greater tendency to disperse away, resulting in fewer parasitoids on plants and significantly lower rates of aphid parasitism, the implications for parasitoid foraging activity are discussed.
Abstract: The opposing effects of attraction to host-derived kairomones and repellency from the pyrethroid insecticide deltamethrin were investigated with aphid parasitoids from the genus Aphidius (Hymenoptera: Aphidiinae). The spatial distribution of female parasitoids was recorded in a series of experiments conducted in a small glasshouse containing wheat plants either infested with cereal aphids, Sitobion avenae (F.) (Homoptera: Aphididae), uninfested or treated with the recommended field concentration of deltamethrin. The number of parasitoids per plant were counted at 0.5 h, 1 h and then at one hourly intervals up to 8 h after release. Parasitoids showed a strong aggregation response to aphid-infested plants compared to adjacent uninfested plants. With the introduction of insecticide-treated plants around the aphid-infested plants, parasitoids showed a greater tendency to disperse away, resulting in fewer parasitoids on plants and significantly lower rates of aphid parasitism. The degree of aphid fall-off from plants was a good indicator of parasitoid foraging activity. In field studies, using sticky traps to measure the activity of parasitoids in plots sprayed with water, deltamethrin and/or an artificial honeydew solution, repellent properties were evident for up to 2 days after application. The attraction/arrestment stimuli associated with the honeydew solution were sufficient for parasitoids to continue searching insecticide-treated areas. The implications of these findings for parasitoids searching crops contaminated with aphid-derived kairomones and insecticides are discussed.
TL;DR: The presence of honeydew significantly increased the growth of bacteria, yeast and filamentous fungi on the surface of needles and there was a pronounced seasonal trend, with the highest abundance in midsummer correlating with the period of peak aphid abundance.
Abstract: Aphids of the genus Cinara, feeding on Norway spruce, excrete copious amounts of honeydew, a carbon-rich waste product, which accumulates locally on needles and twigs. We investigated the role of honeydew as a potential source of energy which might promote the growth of micro-organisms in the phyllosphere of conifer trees. To approach this question, we followed the population dynamics of Cinara spp. in a natural forest stand over two seasons. We also studied the amounts of honeydew produced by individual aphids and identified potential parameters which might influence honeydew production. Finally, we determined the growth of micro-organisms on infested and uninfested needles of Norway spruce during the growing season. Confined to Picea abies, the investigated Cinara species only became abundant in midsummer, when needles and shoots were expanding. The populations showed only a single peak in abundance, the timing and magnitude of which may vary from year to year due to weather conditions, changes in plant quality in a yearly cycle or the impact of natural enemies. The amount of honeydew produced by individual aphids was dependent on the developmental stage of the aphid, the nutritional supply of its host plant and on the developmental state of the Norway spruce (e.g. bud burst, end of shoot extension). The presence of honeydew significantly increased the growth of bacteria, yeast and filamentous fungi on the surface of needles and there was a pronounced seasonal trend, with the highest abundance in midsummer correlating with the period of peak aphid abundance. Taken together, these findings indicate that aphids have an influence on microbial ecology in the phyllosphere of trees. The implication of our study, from interactions at the population level to effects and potential consequences for C and N fluxes at the level of forest ecosystems, is discussed.
TL;DR: Investigation of within-plant variation in the concentrations of chemicals in the phloem sap of black mustard using the green peach aphid uses honeydew from aphids fed on artificial diets with known concentrations of amino acids, sucrose, and sinigrin to call into question the prevailing opinion that phloems sap contains only low concentrations of allelochemicals.
Abstract: Although within-plant variation in the nutrient and allelochemical composition of phloem sap has been invoked to explain patterns of host use by phloem-feeding insects, little is known about within-plant variation in phloem chemistry. Here I describe a new technique in which I use the green peach aphid,Myzus persicae Sulz., to investigate within-plant variation in the concentrations of chemicals in the phloem sap of black mustard,Brassica nigra (L.) Koch (Cruciferae). Relationships between the concentrations of chemicals in aphid diets and honeydew were established using honeydew from aphids fed on artificial diets with known concentrations of amino acids, sucrose, and sinigrin. These relationships were applied to honeydew from aphids fed on different aged leaves of black mustard to estimate the concentrations of the chemicals in phloem sap. Sinigrin concentration was estimated to be high (>10 mM) in phloem sap in young leaves, calling into question the prevailing opinion that phloem sap contains only low concentrations of allelochemicals. High concentrations may function as defenses against sap-feeding herbivores. Within-plant variation in phloem sap composition was high: (1) young leaves had high concentrations of nutrients (216 mM amino acids, 26% sugar) and sinigrin (>10 mM); (2) mature and presenescent leaves had lower concentrations of nutrients (77-83 mM amino acids, 19-20% sugar) and low concentrations of sinigrin (1-2 mM); and (3) senescing leaves had high concentrations of nutrients (199 mM amino acids, 25% sugar) and low concentrations of sinigrin (3 mM).
TL;DR: It is concluded that ant‐attendance may limit the economic impact of this successfully introduced parasitoid species of aphid P. nigronervosa.
Abstract: Colonies of the banana aphid Pentalonia nigronervosa Coq. were heavily attended by ants in banana plantations on Tongatapu Island, Kingdom of Tonga. Ant-attendance reduced the density of indigenous predators of P. nigronervosa considerably. Most important was the reduction by ants of the parasitism of Aphis gossypii by the aphelinid wasp Aphelinus gossypii. The introduced aphid parasitoid Aphidius colemani was also heavily attacked by various ant species, and we conclude that ant-attendance may limit the economic impact of this successfully introduced parasitoid species.
TL;DR: Chemical analysis of the cuticular extracts revealed that both L. cardui and Afc exclusively possess saturated hydrocarbons:n-alkanes, monomethyl (MMA), dimethyl (DMA), and trimethyl alkanes (TMA), while comparison of the hydrocarbon profiles of parasitoid and aphid showed great qualitative resemblance between parasitoids and host.
Abstract: Lysiphlebus cardui, the dominant aphidiid parasitoid of the black bean aphid,Aphis fabae cirsiiacanthoidis (Afc), on creeping thistle, is able to forage in ant-attended aphid colonies without being attacked by ants. Several behavioral observations and experimental studies led to the hypothesis thatL. cardui mimics the cuticular hydrocarbon profile of its host aphid. Chemical analysis of the cuticular extracts revealed that bothL. cardui and Afc exclusively possess saturated hydrocarbons:n-alkanes, monomethyl (MMA), dimethyl (DMA), and trimethyl alkanes (TMA). Comparison of the hydrocarbon profiles of parasitoid and aphid showed great qualitative resemblance between parasitoid and host:L. cardui possesses almost all host-specific compounds in addition to species-specific hydrocarbons of mainly higher molecular weight (>C30). However, there is a lesser quantitative correspondence between parasitoid and host aphid. Furthermore, we analyzed the cuticular hydrocarbon profile of another parasitoid of Afc,Trioxys angelicae. This aphidiid species is vigorously attacked and finally killed by honeydewcollecting ants when encountered in aphid colonies. Its cuticular hydrocarbon profile is characterized by the presence of large amounts of (Z)-11-alkenes of chain lenghts C27, C29, C31, and C33, in addition to alkanes and presumably trienes. The role of the unsaturated hydrocarbons onT. angelicae as recognition cues for aphid-attending ants is discussed.
TL;DR: One RFLP marker was found to be tightly linked to the aphid resistance gene (Rac1) and several flanking markers in the same linkage group (linkage group 1) were also identified.
Abstract: Restriction fragment length polymorphism (RFLP) analysis has several advantages over traditional methods of genetic linkage mapping, one of these being the starting point for map-based cloning. The recent development of an RFLP map of cowpea (Vigna unguiculata L. Walp) has allowed the investigation of associations between genes of interest and RFLP markers. A cross between an aphid (Aphis craccivora Koch) resistant cultivated cowpea, TT84S-2246-4, and an aphid susceptible wild cowpea, NI 963, was screened for both aphid phenotype and RFLP marker segregation. One RFLP marker, bg4D9b, was found to be tightly linked to the aphid resistance gene (Rac
1) and several flanking markers in the same linkage group (linkage group 1) were also identified. The close association of Rac
1 and RFLP bg4D9b presents a real potential for cloning this insect resistance gene.
TL;DR: Release of commercially available convergent lady beetles can provide augmentative control of relatively high aphid densities on small potted plants and there was a density-dependent functional response in predation; beetles consumed more aphids when released on plants with higher aphid density.
Abstract: Convergent lady beetles, Hippodamia convergens Guerin-Meneville, collected from aggregations in California were released for control of melon aphids, Aphis gossypii Clover, infesting potted chrysanthemum, Dendranthema grandiflora (Tzvelev) ‘Hurricane’, outdoors. Most beetles dispersed from plants within 1-3 d after a single release during May 1993 and July and September 1993 and 1994. Most dispersing beetles left the study area, although some moved within release plots to adjoining plants or dispersed to nearby plots within ≈40 m. Aggregation-collected beetles that were allowed to drink and fly in a screen tent for 7–10 d before release and insectary-reared beetles dispersed more slowly than aggregation-collected beetles that were stored at 4–10°C until the day of release. Although beetles dispersed within days, releases significantly reduced aphid densities during all trials. A single release of 34–42 adult H. convergens per pot provided 25–84% aphid control, calculated according to the Abbott method. Each beetle consumed ≈25–170 melon aphids per day. There was a density-dependent functional response in predation; beetles consumed more aphids when released on plants with higher aphid densities. Release of commercially available convergent lady beetles can provide augmentative control of relatively high aphid densities on small potted plants.
TL;DR: The effectiveness of the compound at reducing the fecundity or reproductive rate of several aphid species may be advantageous in controlling secondary spread of viruses and the contact properties of the compounds, important in repelling aphids or preventing phloem feeding, may be short-lived.
TL;DR: The effects of the pirimicarb on the foraging behavior of the aphid parasitoid Diaeretiella rapae were investigated in the laboratory, using aphid-infested and uninfested, young oilseed rape plants as mentioned in this paper.
Abstract: The effects of the aphicide pirimicarb on the foraging behaviour of the aphid parasitoid Diaeretiella rapae were investigated in the laboratory, using aphid-infested and uninfested, young oilseed rape plants. Female parasitoids spent significantly less time foraging on plants sprayed with pirimicarb within the previous 24 h than on untreated plants, regardless of the presence of aphid hosts. Whilst foraging on sprayed plants, parasitoids spent relatively more time walking than they did when foraging on untreated plants. On sprayed plants foraging parasitoids tended to avoid leaf surfaces, thereby reducing the chances of encountering aphid hosts whilst on the plant. These sublethal effects of the aphicide on foraging parasitoids would considerably reduce their impact on aphid populations which survived in a crop after spraying. This has important implications for the control of aphids, such as Myzus persicae, which have developed pesticide resistant strains.
TL;DR: Support is provided for the hypothesis that endophyte presence may determine seasonal patterns of herbivory in sycamore aphids and that increased numbers of aphids, resulting from endophytic infection, may alter the between- as well as the within-year population dynamics of the species.
Abstract: In this study, I examined the effects of infection of leaves by an endophytic fungus (Rhytisma acerinum) on the populations and individual performance of two species of aphid (Drepanosiphum platanoidis and Periphyllus acericola), living on Acer pseudoplatanus. Populations of aphids were followed through one season and numbers compared on infected and uninfected leaves. Both species of aphid aestivated during the summer. D. platanoidis aestivated as non-reproducing adults, while P. acericola did so as nymphs. Fungal abundance, as measured by stromata number, was very low compared with previous studies in the UK. Nevertheless, in contrast to other studies of arboreal endophytes and insects, fungal presence affected aphid numbers in a positive manner, and in late summer, aphid numbers were higher on infected leaves. In D. platanoidis, higher aphid numbers resulted from an increased nymphal production by adults, but in P. acericola there was an accumulation of dispersing nymphs on infected leaves. Field rearing experiments with both aphid species demonstrated an increase in adult weight and potential fecundity in two autumnal generations. The infected leaves had higher soluble and total nitrogen and total carbon contents and the increases in aphid performance are attributed to the increase in soluble nitrogen. The numbers of sycamore aphids in one year can influence the dynamics of the population in the following season. It is suggested that increased numbers of aphids, resulting from endophytic infection, may therefore alter the between- as well as the within-year population dynamics of the species. In addition, the data appear to provide support for the hypothesis that endophyte presence may determine seasonal patterns of herbivory. The hypothesis may be interpreted with an endophyte-induced change in food quality, but other possibilities are discussed.
TL;DR: Numbers of midge larvae per ear were the same in control and enclosed areas where polyphagous predators had been reduced, but were 17% lower in the IFS compared with CFP plots, and there was a trend towards poorer grain quality in enclosed areas.
TL;DR: In this paper, variations in selected life-history parameters in a tritrophic system that consisted of a plant (broad bean, Vicia faba L.), an aphid (pea aphid, Acyrthosiphon pisum), and an Aphid parasitoid (Ephedras californicus).
Abstract: We determined variations in selected life-history parameters in a tritrophic system that consisted of a plant (broad bean, Vicia faba L.), an aphid (pea aphid, Acyrthosiphon pisum), and an aphid parasitoid (Ephedras californicus). We manipulated plant and aphid quality by growing bean plants in a high- and a low-quality nutrient solution for three generations. Pea aphids adapted to reduced nutrient availability by differentially allocating resources to somatic and gonadal growth across generations. On low-quality plants, time from birth to adult increased and dry mass decreased. The number of sclerotized embryos was correlated with adult dry mass. By contrast, in E. californicus, variations in dry mass, rate of development, and number of ovarial eggs did not suggest transgenerational adaptations to resource quality as measured by aphid size. The number of mature eggs was dependent on female age. Development time varied with parasitoid sex and was independent of aphid stage at the time of death. In the low-quality treatment, males survived on average longer than females eclosing from the same kinds of hosts.Aphids and their parasitoids have evolved flexible life-history strategies in response to variations in plant quality. Pea aphids adapted to qualitatively variable resources by optimizing the balance between somatic and gonadal investment across successive generations. But E. californicus responded to low host quality at the level of the individual, rather than across generations; the trade-off pattern was influenced by the host’s growth potential after parasitization.
TL;DR: It is concluded that aphid interference with the phloem sealing system of the plant is a likely mechanism of rejection of T. monococcum lines Tm44 and Tm46 as hosts by S. avenae.
Abstract: Possible reasons for the rejection of some lines ofTriticum monococcum (Tm44 and Tm46) by the aphidSitobion avenae were explored. In allT. monococcum lines studied, whether unfavourable (non-host/resistant plant) or favourable (host/susceptible plant), the concentrations of hydroxamic acids, a family of aphid-resistance factors in cereals, were significantly lower than the levels in the favourable host-plantTriticum aestivum cv. Therefore, hydroxamic acids did not account for the host/non-host patterns observed. Phloem sap was collected by stylectomy from young seedlings of favourable and unfavourable plants. In non-aphid-resistant genotypes, the success in stylectomy, the proportion of amputated stylets resulting in long (>1 min) exudations, the average duration of exudation, and the final volume of sap exuded, were higher than in the aphid-resistant genotypes. It is concluded that aphid interference with the phloem sealing system of the plant is a likely mechanism of rejection ofT. monococcum lines Tm44 and Tm46 as hosts byS. avenae.
Journal Article•
TL;DR: A wide range of cultivated brassica accessions including broccoli, Brussels sprouts, Chinese cabbage, cauliflower, collard, kale and swede material was tested against the cabbage aphid, Brevicoryne brassicae, at HRI, Wellesbourne in the field and laboratory in both 1992 and 1993.
Abstract: A wide range of cultivated brassica accessions including broccoli, Brussels sprouts, Chinese cabbage, cauliflower, collard, kale and swede material was tested against the cabbage aphid, Brevicoryne brassicae, at HRI, Wellesbourne in the field and laboratory in both 1992 and 1993. In the field, B. brassicae attack was assessed as the proportion of infested plants and the numbers of aphid colonies present. In the laboratory, aphid performance was measured in terms of the pre-reproductive and reproductive period, population increase, and insect mortality. Interpretation of the data was facilitated by plotting sorted accession means against normal order statistics. This statistical approach indicated the spread of variation amongst the accessions and permitted identification of extremes. Partial levels of antixenosis resistance were discovered in red brassicas. Glossy accessions of cabbage and cauliflower possessed antixenosis and antibiosis resistance that lasted throughout the season of crop growth in the field. Other accessions were shown to withstand aphid attack and therefore possessed tolerance. The laboratory studies provided information on mechanisms of antibiosis resistance. The potential value of the different sources of resistance is discussed.
Journal Article•
TL;DR: Population dynamics of the soybean aphid, Aphis glycines and its effects on soybean growth and yield were surveyed in 1989-1990 and experiments were conducted using 10% enhanced Dimethoate to treat naturally infested and treated plots.
Abstract: Population dynamics of the soybean aphid, Aphis glycines and its effects on soybean growth and yield were surveyed in 1989-1990. Experiments were conducted in the naturally infested plots and in the treated plots using 10% enhanced Dimethoate. In 1989, soybean aphids in the untreated plots developed earlier and increased rapidly. Aphid density per 100 plants on June 15th was over 10,000, and the rapid development period was over 40 d. But aphids in 1990 developed slightly later with a shorter development period. Soybeans in the untreated plots significantly displayed the symptoms of distorted leaves, shorter stems and stunted plants. Plants in the treated plots were higher (20.2 cm in 1989) than those in the untreated plots. Soybean aphids significantly affected soybean yields. Yields in the untreated plots reduced 27.8% compared to that in the treated plots in 1989.
TL;DR: The relative attractiveness of tobacco etch virus infected versus healthy flue-cured tobacco plants to alighting aphids under field conditions was evaluated in 1985 and 1986 and in 1987, and the effect of plant age and time of inoculation on aphid alighting was also evaluated.
Abstract: The relative attractiveness of tobacco etch virus (TEV) infected versus healthy flue-cured tobacco plants to alighting aphids under field conditions was evaluated in 1985 and 1986. In 1987, the effect of plant age and time of inoculation on aphid alighting was also evaluated. Many more aphids (4 species, 2 genera) were attracted to TEV-infected plants than to healthy plants in the 1st half of the growing season. However, no significant trends were detected for the 2nd half of the growing season. The relative attractiveness of TEV-infected plants compared with healthy plants was greater in 1985 than 1986 or 1987. The tobacco cultivar used in 1985, 'NC 2326', showed much inure pronounced TEV-induced chlorotic mottling of young leaves compared with 'Coker 176', which was used in 1986 and 1987 and exhibited more subtle symptoms of TEV infection. Younger plants were more attractive to alighting aphids early in the growing mason.