Showing papers on "Aphid published in 1992"

The Evolution of Aphid Life Cycles

Abstract: The life cycles of aphids are among the most remarkable of any animal group. They include parthenogenetic and sexual generations, elaborate polyphen­ isms, and obligate shifting between unrelated host-plant taxa. These and other unusual life-cycle traits occur in a variety of combinations among the approx­ imately 4000 extant species within the Aphidoidea (46). Although the complexity and the diversity found in aphid life cycles are often daunting, the study of these insects repeatedly draws both entomologists and evolutionary biologists, for several reasons. First, a few aphid species are agricultural pests, and studies of life cycles can be essential to effective control measures (e.g. 71). Second, aphids, especially their life cycles, are intrinsically fascinating. Finally, aphids are good study organisms for addressing outstanding problems in evolutionary biology. For example, the partially clonal reproductive mode of aphids is useful for testing hypotheses for advantages of sexuality (18, 21, 36, 115, 124, 186) and also facilitates estimation of the genotypic component of fitness traits (e.g. 54, 102, 124, 129, 131, 148, 166, 167, 176-179). The occurrence of several other unusual phenomena, including extensive polyphenism (129), complex life cycles with seasonal alternation between two disjunct sets of hosts (29, 82, 89, 90, 109, 126, 128), soldier castes (3-5, 86), and sex-ratio control (130, 190) have

Use of the random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) to detect DNA polymorphisms in aphids (Homoptera: Aphididae)

Abstract: We have used a new technique to identify discrete genetic markers in aphids, a family in which biochemical and morphological genetic polymorphisms are rare. The new technique uses the polymerase chain reaction (PCR) to amplify random regions of aphid genomes (random amplified polymorphic DNA) and has been termed RAPD-PCR. We demonstrate the use of the technique in revealing genetic variation in four aphid species, the greenbug (Schizaphis graminum (Rondani)), the Russian wheat aphid (Diuraphis noxia (Mordvilko)), the pea aphid (Acyrthosiphon pisum (Harris)), and the brown ambrosia aphid (Uroleucon ambrosiae (Thomas)). In contrast with allozyme surveys, RAPD-PCR revealed large amounts of genetic variation among individuals in each of these species. Variation was detected among biotypes, populations, colour morphs and even individuals on a single plant. We also explored the utility of RAPD-PCR in the detection and identification within aphid bodies of two endoparasitic wasps, Diaeretiella rapae (McIntosh) and Lysiphlebus testaceipes (Cresson). The use of RAPD-PCR in species diagnostics, parasitoid detection, and population studies is discussed.

Nutritional Ecology of an Insect Host‐Parasitoid Association: The Pea Aphid‐Aphidius Ervi System

Abstract: Evolutionary host-size models assume that host quality for parasitoid growth and development is a linear function of host size. To test this assumption, we compared the growth patterns of the hymenopteran parasitoid Aphidius ervi when it developed in different nymphal instars of apterous pea aphids, Acyrthosiphon pisum. At daily intervals, unparasitized aphids and aphids that were parasitized at age 24, 48, 72, and 120 h (cor- responding to nymphal instars L,-L4) were dissected. We weighed parasitoid larvae and host remains to determine changes in their relative growth rates, based on wet mass (WM) and dry mass (DM). The growth in DM of unparasitized aphids followed a sigmoid curve. Aphids that were parasitized by A. ervi continued to grow for 5-7 d before their DM started to decline. Trajectories of the parasitoid's growth during its larval and pupal stages could be described by nonlinear equations. The maximum larval DM and the time from ovi- position to adult eclosion of parasitoids varied with host age at parasitization, and thus suggested differences in host quality. We propose that, for parasitoids developing in growing and feeding stages of the host, host quality is not a linear function of host size at parasit- ization but reflects the degree of integration of the two systems.

Attack strategy of ladybird beetles (Coccinellidae): factors shaping their numerical response

Abstract: Temporal changes in aphid abundance pose a considerable challenge to ovipositing aphidophagous ladybirds, as in order to maximize their fitness they need to synchronize their reproduction with the early development of aphid populations. Field census data and laboratory experiments were used to determine how ovipositing females of the two-spot ladybird, Adalia bipunctata (L.), assess whether an aphid population is suitable for exploitation. In the field, two-spot ladybirds usually laid eggs well before aphid populations peaked in abundance. In the laboratory they showed a marked reduction in their reproductive numerical response in the presence of larvae of their own species but not of other aphidophagous ladybirds. At the highest aphid density this was not a consequence of competition for food between larvae and ovipositing females. In the presence of conspecific larvae gravid females were very active and as a consequence more likely to leave an area, and when confined with other conspecific females or larvae laid fewer eggs and later than females kept on their own. The extent of the inhibition of egg laying is negatively correlated with the rate of encounter with larvae. Thus it is proposed that gravid females appear mainly to use the presence of conspecific larvae to assess the potential of an aphid colony for supporting the development of their offspring.

Homopteran honeydew sugar composition is determined by both the insect and plant species

Abstract: 1. 1. The sugar content of honeydew from three species of whitefly (Aleyrodidae) and four species of aphid (Aphididae) was determined by high performance liquid chromatography. 2. 2. More than 20% of the sugar in honeydew from the whitefly Bemisia tabaci was found to be oligomers larger than disaccharides. 3. 3. Honeydew from two species of the whitefly genus Trialeurodes contained more than 20% turanose. 4. 4. It was established that the insect species is important in determining the sugar composition of homoptera honeydew.

Insect resistance in potatoes: sources, evolutionary relationships, morphological and chemical defenses, and ecogeographical associations

Abstract: The past 25 years, 1686 potato accessions, representing 100 species in the genus Solanum L., subgenus Potatoe, section Petota, were evaluated for field resistance to one or more of the following insect pests: green peach aphid, Myzus persicae (Sulzer); potato aphid, Macrosiphum euphorbiae (Thomas); Colorado potato beetle, Leptinotarsa decemlineata (Say); potato flea beetle, Epitrix cucumeris (Harris); and potato leafhopper, Empoasca fabae (Harris). Accessions highly resistant to green peach aphid were identified within 36 species, to potato aphid within 24 species, to Colorado potato beetle within 10 species, to potato flea beetle within 25 species, and to potato leafhopper within 39 species. Resistance levels were characteristic within Solanum species. Insect resistance appears to be a primitive trait in wild potatoes. Susceptibility was most common in the primitive and cultivated Tuberosa. Insect resistance was also characteristic of the most advanced species. The glycoalkaloid tomatine was associated with field resistance to Colorado potato beetle and potato leafhopper. Other glycoalkaloids were not associated with field resistance at the species level. Dense hairs were associated with resistance to green peach aphid, potato flea beetle, and potato leafhopper. Glandular trichomes were associated with field resistance to Colorado potato beetle, potato flea beetle, and potato leafhopper. Significant correlations between insect score and altitude of original collection were observed in six of thirteen species. Species from hot and arid areas were associated with resistance to Colorado potato beetle, potato flea beetle, and potato leafhopper. Species from cool or moist areas tended to be resistant to potato aphid.

Density‐Dependent Mutualism in an Aphid‐Ant Interaction

Abstract: Our objectives were to determine if the mutualistic effect of ant tending on aphid population growth varied with aphid density, and to consider possible mechanisms explaining such a context-dependent effect. We studied the interaction between Aphis varians and Formica cinerea on fireweed (Epilobium angustifolium) in the Rocky Mountains of Colorado. In 1988 we used two experiments to examine the interaction between ant tending and aphid density on the per capita growth of aphid populations at naturally occurring low aphid densities, and naturally occurring high aphid densities. In 1989, we conducted a similar experiment, but we manipulated aphid densities to include the full range from low to high. The results of these experiments were consistent: ant tending significantly improved the growth of small aphid populations, but the benefit from ant tending decreased or disappeared at higher aphid densities. We considered possible mech- anisms for the density-dependent mutualistic effect by examining the relationships among aphid density, the number of ants tending, and predator abundance. We show that the relative number of ants tending declined as aphid density increased, and ant tending did not reduce predator abundance at any aphid densities. Therefore, the cause of the density- dependent mutualism is probably a decline in the direct effect of ants on aphids resulting from a decline in the relative number of ants tending aphids at higher aphid densities. We discuss the implications of density-dependent mutualism for the dynamics and evolution

Covariance of adult size and development time in the parasitoid waspAphidius ervi in relation to the size of its host,Acyrthosiphon pisum

Abstract: Adult size (in terms of dry weight; DW) and development time (Tp) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butTp did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanTp. The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andTp. When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andTp. Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified.

Reactions of adult female parasitoids, particularly Aphidius rhopalosiphi, to volatile chemical cues from the host plants of their aphid prey

Abstract: . In Y-tube olfactometer tests, Aphidius ervi Hal., Trioxyssp., Praon sp., Aphelinus flavus (Nees), Lysiphlebus fabarum (Marsh.) and Aphidius rophalosiphi De Stef. responded positively to the odour of the plant on which aphid mummies containing them had been collected. The response to host plant odour was greater than the response to the odour of host aphids, their honeydew or a combination of the two. The strongest response was to a combination of plant and host aphids. A. rhopalosiphi showed a strong positive response to three wheat volatiles (cis-3-hexenyl acetate, cis-3-hexen-1-ol and trans-2-hexenal) as well as to indole-3-acetaldehyde (a breakdown product of tryptophan in aphid honeydew). In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphidistinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.

Host behaviour modification by the endoparasitoid Aphidius nigripes: a strategy to reduce hyperparasitism

Abstract: . 1. One possible component of successful parasitism by insect parasitoids is the reduction of predation and hyperparasitism through the modification of host behaviour. 2. Just prior to death, potato aphids, Macrosiphum euphorbiae (Thomas), containing diapausing larvae of the parasitoid Aphidius nigripes Ashmead have been shown to leave the host plant to mummify in concealed sites, while those parasitized by non-diapausing individuals generally leave the aphid colony to mummify on the upper leaf surfaces. 3. The present study examines the within plant distribution of aphids and mummies containing non-diapausing A.nigripes, and compares parasitoid survival among microhabitats under field conditions. 4. On potato, Solunum tuberosum L., a significant proportion of aphids were found on lower leaf surfaces, whereas mummies were usually on the upper surfaces, particularly in the apical stratum of the plant canopy. 5. In both field surveys and experimental manipulations, parasitoid survival was higher on the upper surface of apical leaves than in other microhabitats, due to lower levels of hyperparasitism and, to a lesser extent, lower predation. This suggests that the pressure exerted by natural enemies has influenced the evolution of host behaviour modification.

Biotypic Variation in a Worldwide Collection of Russian Wheat Aphid (Homoptera: Aphididae)

Abstract: Eight isolates of Russian wheat aphid, Diuraphis noxia (Mordvilko), from a worldwide collection were evaluated on resistant and susceptible barley, triticale, and wheat entries. Aphid population levels and damage ratings for leaf chlorosis, plant stunting, and leaf rolling were used to determine ifbiotypic variation occurs within this species. Overall, percentage leaf chlorosis was the best criterion for detecting biotypic variation in D. noxia on cereals; however, the differing mechanisms of resistance expressed by these cereals makes it important to consider other plant and insect factors. Each plant entry responded differently to the D. noxia isolates. Seven of the eight aphid isolates had unique virulence profiles across entries indicating a high degree ofbiotypic diversity. Moreover, isolates differed biotypically in countries where more than one isolate was collected (France and former USSR). An isolate from the former USSR was the most virulent, whereas an isolate from Turkey was the least virulent across all plant entries. Discriminant analysis showed that the U.S. isolate was most similar to a French isolate. The entries that performed best against the D. !loxia collection were the resistant triticales PI 386148 and PI 386156 and the resistant barley PI 366450. However, resistant plant germplasm will have geographical limits because of biotypic variation in D. noxia .

Effect of food sources on the longevity and fecundity of pholetesor ornigis (weed) (hymenoptera: braconidae)

Abstract: The fecundity of first-generation adult Pholetesor ornigis (Weed) increased when individuals were confined with flowers of creeping "Charlie" (Glechoma hederacea L.), dandelion (Taraxacum officinale Weber), and apple (Malus domesticus L.), but not with blossoms of chickweed [Stellaria media (L.) Cyrillo] or Shepherd’s purse [Capsella bursa-pastoris (L.) Medic]. Longevity of P. ornigis was little affected. The fecundity of second-generation P. ornigis increased when individuals were confined with terminal leaves of apple with honeydew of the aphid Aphis pomi DeGeer, but not when confined with terminal leaves without honeydew or with flowers of round-leaved mallow (Malva neglecta Wallr.) or red clover (Trifolium pratense L.). Longevity of P. ornigis adults also increased when they were provided with aphid honeydew. There were significant differences between the total number (oviposited and ovarian) of eggs produced by second-generation females given different food sources. Those given aphid honeydew oviposited a greater proportion of their eggs than those confined with apple leaves without honeydew or with flowers of M. neglecta or T. pratense, Adult P. ornigis fed an aqueous solution of honey (50:50, v/v) lived longest and produced more eggs than those provided with any other food source.

Yield Losses in Winter Wheat Caused by Low-Density Cereal Aphid Populations

Abstract: In most autumns on the Northern Plains of the USA, low population densities of several species of cereal aphids feed on seedling winter wheat, Triticum aestivum L., for a month or more. The objective of this research was to determine the influence of that feeding on the growth and yield of ‘Rose’ winter wheat. Experiments were conducted by confining non-viruliferous (barley yellow dwarf virus) greenbug, Schizaphis graminum (Rondani), at precisely maintained population densities of 2, 4, 6, 8, 10, and 15 aphids per plant, bird cherry oat aphids, Rhopalosiphum padi (L.), at densities of 10 or 15 aphids per plant, or Russian wheat aphids, Diuraphis noxia (Mordvilko), at 5, 10, 15, and 20 aphids per plant on seedling plants for 30 d in an environmental chamber at 10°C (to simulate mean October temperature in the field), 12 h day/night. The results showed that the threshold for significant yield loss under these environmental conditions was at the 10 aphids per plant level for the bird cherry oat aphid and the Russian wheat aphid, and 15 apbids per plant for greenbug. Yield losses caused by any of the aphid species were in the range of 35 to 40% at 15 aphids per plant. Although the visible injury to plants caused by the feeding of the greenbug and the Russian wheat aphid was striking, the bird cherry oat aphid was as damaging to yield as the other two species in this study.

Can polyphagous predators control the bird cherry‐oat aphid (Rhopalosiphum padi) in spring cereals?: A simulation study

Abstract: Predation by two carabid species, Bembidion lampros (Herbst.) and Pterostichus cupreus L., on the cereal aphid, Rhopalsiphum padi L., was described using a discrete event simulation model. The results were incorporated into an aphid population growth model. The aphid model was run using actual temperatures, R. padi emigration rates, field densities and distributions from three years with distinctly different aphid population levels. Predation was incorporated at different time periods. Predation during the arrival of emigrants and establishment of aphid populations had approximately the same effect as predation over the entire aphid period, whereas predation during the 20 days prior to peak had very little effect on resulting peak populations. We conclude that a) yearly levels of R. padi infestation are mainly determined by the volume and intensity of emigrants; b) peak levels are sensitive to changes in predator density; and c) in some cases an outbreak of R. padi may be prevented by the action of spring active polyphagous predators alone.

The role of honeydew as an ovipositional stimulant for two species of syrphids

Abstract: The influence of honeydew contamination on egg laying by the syrphids Episyrphus balteatus (Deg.) and Platycheirus albimanus (F.) on ears of wheat was investigated in a large laboratory flight cage. Artificially-applied honeydew elicited oviposition by E. balteatus but not by Platycheirus albimanus. Episyrphus balteatus females landed more frequently on ears contaminated with honeydew than on clean ears, suggesting a response to honeydew volatiles. Honeydew from the rose-grain aphid Metopolophium dirhodum and from the pea aphid Acyrthosiphon pisum stimulated E. balteatus to lay eggs, whereas honeydew from the nettle aphid Microlophium carnosum did not. The number of eggs laid by E. balteatus increased with increasing honeydew concentration. At low honeydew concentrations the presence of aphids increased oviposition by E. balteatus, but aphid presence had little effect on the number of eggs laid at high honeydew concentrations.

A screen of worldwide wheat cultivars for hydroxamic acid levels and aphid antixenosis

Abstract: Summary In a screen of seedlings of a worldwide range of 47 cultivars of Triticum (mainly T. aestivum) the concentration of the hydroxamic acid DIMBOA ranged between 1 and 8 mmol/kg fresh wt. In a bioassay in which alatae of the aphid Sitobion avenae were released among replicated test seedlings, there were highly significant correlations between aphid ‘preference’ and DIMBOA levels in the seedlings. The value of these results in work leading to the production of aphid-resistant cultivars is discussed.

Effects of leaf and sap feeding insects on photosynthetic rates of goldenrod.

Abstract: Herbivory can alter the balance between sources and sinks within a plant, and changes in the source-sink ratio often lead to changes in plant photosynthetic rates. We investigated how feeding by three insect herbivores affected photosynthetic rates and growth of goldenrod (Solidago altissima). One, a phloem-sap feeding aphid (Uroleucon caligatum), creates an additional sink, and the other two, a leaf-chewing beetle (Trirhabda sp.) and a xylem-sap feeding spittlebug (Philaenus spumarius) both reduce source supply by decreasing leaf area. Plants were grown outside in large pots and insects were placed on them at predetermined densities, with undamaged plants included as controls. All insects were removed after a 12-day feeding period. We measured photosynthetic rates both of damaged leaves and of undamaged leaves that were produced after insect removal. Photosynthetic rates per unit area of damaged leaves were reduced by spittlebug feeding, but not by beetle or aphid feeding. Conductance of spittlebugdamaged leaves did not differ from controls, but internal carbon dioxide concentrations were increased. These results indicate that spittlebug feeding does not cause stomatal closure, but impairs fixation within the leaf. Effects of spittlebug feeding on photosynthetic rates persisted after the insects were removed from the plants. Photosynthetic rates per unit area of leaves produced after insect removal on spittlegug-damaged plants were lower than control levels, even though the measurements were taken 12 days after insect removal. The measurement leaf on spittlebugdamaged plants was reduced in area by 27% relative to the controls, but specific leaf area (leaf area/leaf weight) was increased by 18%. Because of the shift in specific leaf area, photosynthetic rates were also examined per unit leaf weight, and when this was done there were no significant differences between control and spittlebug-damaged plants. Beetle and aphid feeding had no effects on the photosynthetic rate of the leaves produced after insect removal. Plant relative growth rates (in terms of height) were reduced by spittlebugs during the period that the insects were feeding on the plants. Relative growth rates of spittlebug-damaged plants were increased above control levels after insect removal, but these plants were still shorter than controls 17 days after insect removal. Beetles and aphids did not affect plant relative growth rates or plant height. Feeding by both spittlebugs and beetles reduced leaf area, and the effect of the spittlebug was more severe than that of the beetle. These results show that effects of herbivory on photosynthetic rates cannot be predicted simply by considering changes in the source-sink ratio, and that spittlebug feeding is more damaging to the host plant than beetle or aphid feeding.

Characterization of Plant Damage Caused by Russian Wheat Aphid (Homoptera: Aphididae)

Abstract: The effect of feeding by the Russian wheat aphid, Diuraphis noxia (Mordvilko), on growth of seedling ‘TAM W-lOl’ winter wheat ( Triticum aestivum L.) was investigated. A primary response of the wheat plant to aphid feeding involves water imbalances expressed as a loss of turgor and reduced growth. Russian wheat aphids caused substantial reductions in biomass of all plant components measured. When aphids were removed, absolute growth rates quickly recovered as relative growth rates increased. Compared with undamaged controls, recovering plants were more efficient in terms of carbon assimilation, which resulted in higher relative growth rates and compensated for lowered leaf area ratios. Reduction in leaf area ratios results from decreases in specific leaf areas (i.e., a combination of leaf stunting and the inhibition of new-leaf unfolding). As plants recovered, stem weight ratios were substantially reduced, indicating that carbon partitioning to the stem was decreased to compensate for leaf and root growth. The cessation of growth of wheat during infestation by the Russian wheat aphid and ability of the host to recover rapidly when the aphid was removed indicate that the duration of infestation, rather than the level of infestation, may be more important to the host.

Relationship of insecticide resistance to carboxylesterases in Aphis gossypii (Homoptera: Aphididae) from midsouth cotton.

Abstract: Laboratory assays were done to quantify proportions of phenotypes in laboratory colonies resistant to several classes of insecticides in the cotton aphid, Aphis gossypii Glover. Resistance to a carbamate (aldicarb), an organochlorine (endosulfan), an organophosphate (chlorpyrifos), and a pyrethroid (bifenthrin) was documented. Significant declines in numbers of individuals resistant to bifenthrin and endosulfan but not for chlorpyrifos occurred during a 5-mo interval after the first bioassays. Resistance ratios between clonal susceptible and resistant cotton aphid colonies for chlorpyrifos indicated a significant 4-fold difference in LC50 estimates for the two colonies. Spectrophotometric analyses indicated Significantly higher carboxylesterase activity in resistant aphids compared with susceptible aphids. Results from isoelectric polyacrylamide focusing gel techniques also showed differences in carboxylesterases, both in differences in banding patterns and in expression of comigrating bands.

Aphid distribution and the evolution of goldenrod resistance

Abstract: Although there is considerable evidence indicating that herbivory is detrimental to plant fitness, some recent studies of the evolution of plant resistance have concluded that insects do not impose selection on their host plants. A previously untested assumption that underlies most studies of the evolution of plant resistance is that insect distribution patterns are controlled directly by the effects of plant genotype on insect preference and performance. The experiments described here explicitly tested this assumption using the specialist herbivore Uroleucon tissoti (Homoptera: Aphididae) and its host plant Solidago altissima (Asteraceae). Measures of aphid preference and performance were used to predict aphid distribution patterns, and then the predicted distribution patterns were compared with the natural distribution pattern. Although goldenrod genotype had a strong effect on aphid distribution, aphid distribution was not controlled directly by the effect of goldenrod genotype on aphid preference and performance. Instead, a second experiment demonstrated that aphid and spittlebug (Philaenus spumarius and Lepyronia quadrangularis Homoptera: Cercopidae) distribution is controlled largely by genetic variation for resistance to a suite of "branch-causing" herbivores. These herbivores induce branching and aphids and spittlebugs are more abundant on branched plants than unbranched plants. These results indicate that any natural selection imposed by aphids and spittlebugs on goldenrod will depend on the presence or absence of branch-causing herbivores. Thus, selection for plant resistance may depend as much on the assemblage of insect species present as on the identity of each individual species.

Alatae production and population increase of aphid vectors on virus-infected host plants

Abstract: Zucchini yellow mosaic virus (ZYMV) and Aphis gossypii Glover are two components of a recently identified plant-parasite system that provides an excellent opportunity to study interrelations between a virus and a vector that share the same host, but have no direct physiological interaction. In a field experiment we documented numbers of alate and apterous A. gossypii on healthy Cucurbita pepo and on plants inoculated with virus 0, 7, 14, and 21 days before aphid infestation. When plants were inoculated and infested simultaneously, more than twice as many alatae were produced after 20 days of colony growth than on any other treatment. This indicates that properties unique to the early stages of viral infection somehow stimulated wing formation. Because it is spread by the activities of alatae, virus dispersal would be greater as a result of these properties. Developmental rate, total numbers of aphids, and numbers of alatae and apterae decreased as the time between virus inoculation and aphid colonization increased.

Field and laboratory transmission of watermelon mosaic virus 2 and zucchini yellow mosaic virus by various aphid species.

Abstract: Aphid transmission of watermelon mosaic virus 2 (WMV 2) and zucchini yellow mosaic virus (ZYMV) was studied in the laboratory and field to evaluate species of probable importance in the epidemiology of each virus. Relative transmission efficiencies among species were compared using alates obtained from laboratory-maintained colonies as well as from natural populations collected with an aerial net. In laboratory studies, Myzus persicae, Aphis gossypii, and Acyrthosiphon pisum transmitted WMV 2 with 18, 16, and 16% efficiencies, respectively (...)

Influence of Superparasitism on Development Rate and Adult Size in a Solitary Parasitoid Wasp, Aphidius ervi

Abstract: We tested the assumption that superparasitism by solitary species of parasitoid wasps has no fitness consequences For the surviving larva. Using Aphidius ervi and its aphid host, Acyrthosiphon pisum, as an experimental system, we compared adult dry mass and development time from oviposition to adult eclosion between male wasps that developed in single- and in superparasitized aphids. Parasitoids gained 14% more dry mass (with no increase in development time) in superparasitized hosts. It is suggested that superparasitized aphids have higher growth potential for the surviving parasitoid larva because they ingest more food than single-parasitized and unparasitized aphids, in that order

Partial antibiosis to Rhopalosiphum padi in wheat and some phytochemical correlations

Abstract: Summary The fecundity of the aphid Rhopalosiphum padi during the first ten days of reproduction was measured on five wheats at three growth stages. The wheats were of UK and Iranian origin, but also involved both spring and winter wheats as well as hexaploid and tetraploid types. Aphids which had already been reared on the respective variety for at least one generation were transferred to the experimental plants. The tetraploid Emmer showed some resistance in comparison with the hexaploid UK varieties at later growth stages, whereas the Iranian variety Moghan 2 appeared relatively resistant only at the tillering stage. The other Iranian variety, Ommid, was resistant at all growth stages, and appears to be the most resistant hexaploid wheat variety to R. padi so far identified. Correlations of aphid fecundity with plant chemistry were attempted with total phenolic compounds, hydroxamic acids and amino acids. All three of these chemical groups have previously been reported as correlated with plant resistance to cereal aphids. Even just for the results at the tillering stage, no correlation could be found for phenolics or hydroxamic acids, but a multiple regression based on the levels of alanine, histidine and threonine accounted for over 95% of the variation in aphid fecundity at all 15 data points (5 wheats × 3 growth stages). No cause or effect relationship is necessarily implied.

Inducing the sexual forms and hatching the eggs of pea aphids.

Abstract: In temperate climates, pea aphids (Acyrthosiphon pisum) produce a single sexual generation each year in response to declining photoperiod and temperature. Mating occurs in the fall and the eggs have an obligatory winter diapause. Genetic recombination during the sexual phase is thought to be an important source of genetic variability within cyclically parthenogenetic aphid populations. Methods for reliably producing sexual forms and hatching the eggs of aphids are therefore central not only to the study of evolutionary change in aphid populations, but also for a general understanding of the origin of agriculturally important variation in destructiveness within pest species. Here, sexual forms of six pea aphid clones were induced in the laboratory and eggs were successfully hatched by creating conditions that closely mimicked those found in field situations. A declining photoperiod was produced by controlling artificial lighting using a timer with variable cycle length. Using these conditions, sexual forms were successfully produced for all six clones tested, which were then mated in all combinations. Eggs were exposed to a daily cycle of freezing and thawing in an incubator under a short-day photoperiod. Egg hatch averaged 60%, but was as high as 89% for some crosses. These methods will permit testing of evolutionary hypotheses and execution of detailed genetic studies of sources of variability within pea aphid populations. They are thus important tools for both evolutionary and agricultural studies.