Showing papers on "Aphididae published in 1996"

Hopkins' 'host selection principle', another nail in its coffin.

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.

A consideration about the origin of aphid intracellular symbiont in connection with gut bacterial flora

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.

Biological Parameters of Convergent Lady Beetle (Coleoptera: Coccinellidae) Feeding on Aphids (Homoptera: Aphididae) on Transgenic Potato

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.

Effects of honeydew and insecticide residues on the distribution of foraging aphid parasitoids under glasshouse and field conditions

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.

Ant‐attendance as a critical factor in the biological control of the banana aphid Pentalonia nigronervosa Coq. (Hom. Aphididae) in Oceania

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.

Role of cuticular hydrocarbons of aphid parasitoids in their relationship to aphid-attending ants.

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.

RFLP mapping of an aphid resistance gene in cowpea (Vigna unguiculata L. Walp)

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.

Melon Aphid (Homoptera: Aphididae) Control by Inundative Convergent Lady Beetle (Coleoptera: Coccinellidae) Release on Chrysanthemum

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.

Effect of pirimicarb on the foraging behaviour of Diaeretiella rapae (Hymenoptera: Braconidae) on host-free and infested oilseed rape plants

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.

Effects of Temperature on Development, Longevity and Reproduction of the Soybean Aphid, Aphis glycines (Homoptera: Aphididae)

Abstract: The soybean aphid, AphisgijcinesMATsuMuRA, is distributedin tropical and subtropical regions such as SoutheastAsia and partsof Africaas wcll as temperate zones such as nomhern China andJapzn CWANG et al., 1962; KoBAyAsHI et al., 1972; SINGH and van EMDEN, 1979; HILL, 1987; HIRANo and Ftull,1993), A. glycinesisan important pestof the soybean plant CWANGct al., 1962; KoGAN und TuRN]?sEEn, 1987), causing not only dircctdamagc by feeding but also indircctdamage from itsheavy secretion of honcydew on the plants,which scrvcs as a growing medium forsoety mold fungus.A. glyct'nes isalso an important vector ot' viraldiseasesCIwAKI,1979;TAKAHAsHI et aL, 1980). Although A.glycineshaslongbcenknown as a soybean pest,fewstudics have beencarried out on the mechanism involvedinitspopulation flu¢ tuations. It isncccssary to clarify thc demographicparameters and ecological characteristics ofA. gipcines as a first step toward undcrstanding the populationdynamics of thisspecies. The presentrcport fbcuseson the dcvclopmental thresholds and ratcs, intrinsicrates of incrcasc,and other pertinentdemographic parametcrs forA.glycines

Positive effects of endophyte infection on sycamore aphids

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.

Influence of plant quality on interactions between the aphid parasitoid ephedrus californicus baker (hymenoptera: aphidiidae) and its host, acyrthosiphon pisum (harris) (homoptera: aphididae)

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.

Resistance to Brevicoryne brassicae in horticultural brassicas

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.

Inhibition of Aphid (Homoptera: Aphididae) Reproduction by Neem Seed Oil and Azadirachtin

Abstract: Exposure of adult green peach aphid, Myzus persicae (Sulzer), and lettuce aphid, Nasonovia ribisnigri (Mosley), for 3 d to a 1.0% solution of neem seed oil applied to leaf disks reduced the number of live offspring by 82 and 66%, respectively, compared with controls. Fourth-instar N. ribisnigri were more sensitive than adults to the sterilizing activity of neem, because they produced 87% fewer offspring than controls following exposure to 1.0% neem seed oil. Exposure to azadirachtin, considered to be the most active component of neem, reduced the fertility (live offspring per aphid per day) and the fecundity (live + dead offspring per aphid per day) of adult M. persicae, N. ribisnigri , and strawberry aphid, Chaetosiphon fragaefolii (Cockerell), in a linear, concentration-dependant manner. Dissections of treated N. ribisnigri indicate that exposure to neem seed oil or azadirachtin results in higher mortality rates for embryos just before parturition, but increased mortality during this stage does not account for the recorded decrease in fecundity.

Interaction Between Russian Wheat Aphid (Homoptera: Aphididae) and Resistant and Susceptible Genotypes of Wheat

Abstract: Interaction between the Russian wheat aphid, Diuraphis noxia (Mordvilko), and the resistant wheat, Triticum aestivum L., plant introduction lines PI 137739, PI 140207, and PI 262660 and the susceptible wheat cultivar ‘Stephens’ were studied. D. noxia reproductive rate and population development were higher when fed on Stephens compared with the resistant genotypes. Reproductive rate of D. noxia decreased as aphid density and length of aphid time on plant increased. Whereas, D. noxia populations increased with increasing aphid densities and length of aphid time on plant. Although the populations of D. noxia were lower when fed resistant genotypes. total chlorophyll content was reduced compared with the susceptible genotype. This could have been caused by increased aphid probing activity on resistant genotypes. There was no significant difference between the antibiotic line PI 140207 and the tolerant line PI 262660 in aphid reproductive rate, population density or reduction in leaf chlorophyll content. Expression of several polypeptides were altered by D. noxia feeding on PI 137739 and Stephens. Three polypeptides of sizes ≈32, 33, and 35 k were enhanced in PI 137739 but not in Stephens. Involvement of these proteins in plant defense is discussed.

Biological and chemical characteristics of a genetic resistance of melon to the melon aphid

Abstract: Host plant resistance to pests is an important component of integrated control strategies. Due to the specialised phloem-feeding of aphids and many other hemipteran insect pests, which necessitates specific chemical treatments and control of virus transmission, this genetic strategy seems particularly attractive for this insect group. In the melon Cucumis melo L., a gene labelled vat, for virus aphid transmission (Pitrat & Lecoq, 1982), brings both a resistance to the melon aphid Aphis gossypii Glover and a resistance to the transmission by this vector of many non-persistent viruses. This gene induces both an antixenotic response to adults and an apparent antibiosis towards A. gossypii larvae. The purpose of the experiments reported here was to investigate the mechanisms of this resistance (mechanical, chemical, tissue localisation...) and to characterize any chemical difference between genotypes differing by the presence/absence of the vat gene.

Dwarf Phenotype of the Cotton Aphid, Aphis gossypii Glover (Hemiptera: Aphididae)

Abstract: The cotton aphid, Aphis gossypii Glover, is a polyphagous aphid that is a pest on a wide range of commercially important crops. It sometimes gives birth to small yellow offspring that grow to be only about 1/2 to 1/3 of the typicaladult weight. These “yellow dwarfs” differ from the typical form in their small size, by having 5 instead of 6 antennal segments, and by never attaining dark greedblack coloration; they are considered to be a separate developmentally-programmed morph. A morphometric description of the yellow dwarf form is provided. Yellow dwarfs develop at a slower rate than typical aphids and have a lower intrinsic rate of increase. An orthogonal experiment demonstrated that production of yellow dwarfs can be induced by presumed less-suitable host-plant species at temperatures of 15 ° and 25 °, but not 20 °C. Crowding may also induce birth of yellow dwarfs. Possible advantages of the yellow dwarf developmental pathway are discussed.

Influence of wheat and oat cultivars on the development of the cereal aphid parasitoid Aphidius rhopalosiphi and the generalist aphid parasitoid Ephedrus plagiator

Abstract: Summary. The effects of three wheat cultivars and two oat cultivars on the development of the cereal aphid parasitoid Aphidius rhopalosiphi De Steph. and the generalist aphid parasitoid Ephedrus plagiator (Nees) (Hymenoptera: Braconidae) were evaluated in the laboratory. The level of hydroxamic acids, a family of secondary metabolites that can affect the mean relative growth rate of cereal aphids in cereals, were measured in the different cultivars. The parasitoids were reared in Sitobion avenae (F.) (Homoptera: Aphididae), using plants grown under greenhouse conditions. A. rhopalosiphi showed a longer developmental time on wheat relative to oat cultivars. This effect was accounted for by a significant increase in the time from oviposition to pupation (mummy formation), while the duration of the pupal stage remained constant between treatments. No further effects were observed in other variables evaluating A. rhopalosiphi performance, such as adult longevity, adult body weight and secondary sex ratio. The generalist E. plagiator did not show significant differences in any of the variables analysed, both between cultivars and cereal species. Hydroxamic acids levels correlated negatively with mean relative growth rates of S. avenae, but positively with the observed developmental time of A. rhopalosiphi. The results are discussed in terms of tritrophic effects and the development of breeding programmes trying to improve plant resistance to aphids.

Costs and benefits of hydroxamic acids-related resistance in winter wheat against the bird cherry-oat aphid, Rhopalosiphum padi L.

Abstract: Summary. Estimations of infestation by the bird cherry-oat aphid (Rhopalosiphum padi) as well as measurements of grain yield in 26 Hungarian winter wheat cultivars under field conditions were correlated with the concentration of hydroxamic acids (Hx) in seedlings of those cultivars. The significant inverse relationship between infestation ratings and Hx levels in wheat showed that Hx, despite their decreased accumulation at later plant phenological stages, may be able to confer resistance against aphid infestation in the field. Since no significant relationship was found between grain yield and Hx levels in plants it is suggested that Hx accumulation does not impose a cost to the plant in terms of yield. These findings support earlier claims stressing the potential of Hx as breeding targets for aphid resistance in wheat.

Biology of Aphelinus spiraecolae (Hymenoptera: Aphelinidae), a parasitoid of the spirea aphid (Homoptera: Aphididae)

Abstract: The biology of nonindigenous Aphelinus spiraecolae Evans & Schauff on spirea aphid, Aphis spiraecola Patch, was investigated in Florida. Reproduction, fecundity, longevity, oviposition, and host feeding behavior were examined in the laboratory. A. spiraecolae showed a distinct preference for 1st- and 2nd-instar spirea aphids for both oviposition and host feeding, although all aphid life stages were acceptable. Longevity of A. spiraecolae was 17.8 ± 1.6 (mean ± SEM) d, fecundity was 138.2 ± 16.2 eggs, and the parasitoid consumed 27.1 ± 4.0 aphids per lifetime. Ovipositor insertion time of ≤30 s indicated nonacceptance for host feeding and oviposition, whereas insertion time of 31–120 s was correlated with oviposition, and >120 s indicated host acceptance for feeding but not for oviposition. A. spiraecolae was confirmed to be arrhenotokous. The intrinsic rate of increase was 0.33 female offspring per female per day, the net reproductive rate was 67.3 female progeny, and population doubling time was 1.8 d. These data indicated that A. spiraecolae has a high intrinsic rate of increase, good host discrimination and preference for young life stages of spirea aphid, and suggests that A. spiraecolae has potential as a natural enemy of spirea aphid.

Aphids (Homoptera: Aphididae) Colonizing Cott on in the United States

Abstract: Eight aphid species known to colonize cotton in the United States are described and illustrated. A brief summary of taxonomic characteristics, usual hosts, and distribution within the United States are given for each species. Pictorial and dichotomous keys are included to aid personnel charged with detection, identification, and control of aphids associated with cotton in the United States.

Aphids (Homoptera: Aphididae) colonizing cotton in the United States.

Abstract: Eight aphid species known to colonize cotton in the United States are described and illustrated. A brief summary of taxonomic characteristics, usual hosts, and distribution within the United States are given for each species. Pictorial and dichotomous keys are included to aid personnel charged with detection, identification, and control of aphids associated with cotton in the United States.

Variability among aphid clones of rhopalosiphum padi l. and sitobion avenae fabr. (homoptera: aphididae) in transmission of three pav isolates of barley yellow dwarf viruses

Abstract: Variability in vectoring efficiency among six clones of Rhopalosiphum padi L. and five clones of Sitobion avenae Fabr. in transmission of three French PAV isolates (PAV-RG, PAV-2t, and PAV-13t) of barley yellow dwarf viruses (BYDVs) on seedlings of barley (Hordeum vulgare L.) cv. Plaisant was determined. All the clones could transmit these three isolates, but their vectoring efficiency was significantly different: 91% and 56% transmission efficiencies were obtained from the most efficient clones (Rp-M and Sa-R1) but only 21% and 9% from the least efficient clones (Rp-R26 and Sa-V) with 5-day acquisition and inoculation access periods (AAP, IAP). A significant difference in overall transmission between apterous adults and winged aphids of the tested clones was also found. In most cases, apterous adults were more efficient than were winged aphids. The overall transmission efficiency of apterous adults was 1.5 and 1.7 times that of winged ones for R. padi and S. avenae, respectively. The transmissibility of PAV-RG and PAV-2t isolates was similar within each of the tested aphid clones, but that of the PAV-13t isolate differed, particularly for the poorly efficient vector clones of S. avenae. Temperature could significantly influence the vectoring efficiency of the tested clones of R. padi, but the influence was greater on Rp-R26. High temperature (25 °C) facilitated more transmission than did low temperature (14 °C), and high temperature for AAP played a more important role than it did for IAP.

Variation in aphid alarm pheromone content among glandular and eglandular-hairedMedicago accessions.

Abstract: Pea (Acyrthosiphon pisum Harris) and blue alfalfa aphid (A. kondoi Shinji) deterrency in alfalfa (Medicago saliva L.) may result from incorporating higher levels of the aphid alarm pheromone,(E)-β-farnesene relative to(E)-β-caryophyllene. We evaluated five eglandular and two glandular-haired alfalfa accessions for differences in(E)-β-farnesene and(E)-β-caryophyllene content under glasshouse conditions using supercritical fluid extraction and gas chromatography. In addition, pea and blue alfalfa aphid olfactory behavioral tests were conducted uponMedicago species containing different ratios of(E)-β-famesene relative to(E)-β-caryophyllene. No differences in(E)-β-caryophyllene content were observed among the seven entries (μ=0.42 ng/g plant material). Significant differences (P ≤ 0.05) among entries were observed for(E)-β-famesene content, with KS94GH6 exhibiting the highest (1.18 ng/g), and CUF 101 the lowest levels (0.35 ng/g). Elite tetraploid sources possessed significantly lower levels (μ=0.42 ng/g) of(E)-β-farnesene than did wild and cultivated diploid accessions (μ=0.83 ng/g). Olfactory behavioral tests for both the pea and blue alfalfa aphids demonstrated KS94GH6 repelled aphids while cultivated alfalfa types attracted aphids in each case. Previously demonstrated aphid resistance in diploid KS94GH6 may result from superior(E)-β- farnesene levels, but(E)-β-farnesene is probably not a factor in cultivated alfalfa resistance. Finally, accession KS94GH6 could act as an excellent germplasm resource for the incorporation of higher(E)-β-farnesene levels into cultivated alfalfa.