Showing papers on "Aphid published in 1991"

Evidence for the establishment of aphid-eubacterium endosymbiosis in an ancestor of four aphid families.

Abstract: Aphids (superfamily Aphidoidea) contain eubacterial endosymbionts localized within specialized cells (mycetocytes). The endosymbionts are essential for the survival of the aphid hosts. Sequence analyses of the 16S rRNAs from endosymbionts of 11 aphid species from seven tribes and four families have indicated that the endosymbionts are monophyletic. Furthermore, phylogenetic relationships within the symbiont clade parallel the relationships of the corresponding aphid hosts. Our findings suggest that this endocytobiotic association was established in a common ancestor of the four aphid families with subsequent diversification into the present species of aphids and their endosymbionts.

Manipulation of food resources by a gall-forming aphid: the physiology of sink-source interactions

Abstract: We examined the capacity of the galling aphid, Pemphigus betae, to manipulate the sink-source translocation patterns of its host, narrowleaf cottonwood (Populus angustifolia). A series of 14C-labeling experiments and a biomass allocation experiment showed that P. betae galls functioned as physiologic sinks, drawing in resources from surrounding plant sources. Early gall development was dependent on aphid sinks increasing allocation from storage reserves of the stem, and later development of the progeny within the gall was dependent on resources from the galled leaf blade and from neighboring leaves. Regardless of gall position within a leaf, aphids intercepted 14C exported from the galled leaf (a non-mobilized source). However, only aphid galls at the most basal site of the leaf were strong sinks for 14C fixed in neighboring leaves (a mobilized source). Drawing resources from neighboring leaves represents active herbivore manipulation of normal host transport patterns. Neighboring leaves supplied 29% of the 14C accumulating in aphids in basal galls, while only supplying 7% to aphids in distal galls. This additional resource available to aphids in basal galls can account for the 65% increase in progeny produced in basal galls compared to galls located more distally on the leaf and limited to the galled leaf as a food resource. Developing furits also act as skins and compete with aphid-induced sinks for food supply. Aphid success in producing galls was increased 31% when surrounding female catkins were removed.

Imidacloprid - a new systemic insecticide

Abstract: The nitroguanidine imidacloprid, 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro-1H-imid azol-2-amine, is a systemic insecticide. It is a nitromethylene derivative synthesized in February 1985 by Nihon Bayer Agrochem K.K. The biological profile of this compound was defined on the basis of the results of exhaustive laboratory experiments and greenhouse trials. The product is extremely effective against sucking insects such as rice leafhoppers, aphids, thrips and mealybugs, and very effective against whitefly. It is also effective against some species of biting insects, such as paddy stem borers and Colorado beetle, but it has no effect on nematodes or spider mites. It has also been shown that at comparatively high dose rates it kills adult insects and has ovicidal effects. Imidacloprid is a nicotinic acetylcholine receptor stimulator. Its mechanism of action differs from that of conventional insecticides. It therefore gives excellent control of all resistant populations investigated hitherto. Imidacloprid has a positive temperature co-efficient. After foliar application it has a good residual action, it is highly photostable and it shows satisfactory resistance to the action of rain. The product is active after oral ingestion and by direct contact, but it is not active in the vapour phase. The LD95 after oral ingestion by Myzus persicae is about 2 pg/aphid. After topical application it is about 160 pg/aphid. It has not been possible to demonstrate recovery of injured aphids, or antifeeding effects. Imidacloprid has a faster action against aphids than oxydemeton-methyl. After foliar application the product shows good translaminar and acropetal translocation, so it is also likely to provide effective control of pests with a furtive lifestyle, and protect the parts of the plant which regenerate after treatment

Aphid transmission of barley yellow dwarf virus: Acquisition access periods and virus concentration requirements.

Abstract: The duration of access periods and the availability of virus in source plants are two factors that influence the transmission of barley yellow dwarf virus (BYDV) by its aphid vectors. This study was conducted to quantify the relationships among acquisition access period (AAP), virus titer in infected oats, and transmission of three isolates of BYDV from New York by two aphid vector species. Thirteen AAPs, ranging from 15 min to 72 hr, were examined, and virus titer was quantified from each virus source leaf by using enzyme-linked immunosorbent assay (ELISA) (...)

Influence of aphid size, age and behaviour on host choice by the parasitoid wasp Ephedrus californicus: a test of host-size models.

Abstract: When host quality varies, parasitoid wasps are expected to oviposit selectively in high-quality hosts. We tested the assumption underlying host-size models that, for solitary species of wasps, quality is based on host size. Using Ephedrus californicus, a solitary endoparasitoid of the pea aphid, we evaluated the influence of aphid size (= mass), age and defensive behaviours on host selection. Experienced parasitoid females were given a choice among three classes of 5-day-old apterous nymphs: small aphids that had been starved daily for 4 h (S4) and 6 h (S6) respectively, and large aphids permitted to feed (F) normally. Wasps attacked more, and laid more eggs in, small than large aphids (S6>S4>F). This rank-order for attack did not change when females could choose among aphids of the same size that differed in age; however, wasps oviposited in all attacked aphids with equal probability. Host size did not influence parasitoid attack rates when aphids were anaesthetized so that they could not escape or defend themselves. As predicted by host-size models, wasp size increased with host size (F>S4; S6), but large wasps required longer to complete development than their smaller counterparts (S4

Virus spread and vector dynamics in genetically diverse plant populations

Abstract: Little is known about the influence of genetic diversity in plant populations on the dynamics of plant viruses, particularly those transmitted by insects. For these viruses, plant genetic diversity may affect virus incidence through impacts on the population dy- namics of the vector insects or through impacts on vector feeding behavior, which deter- mines transmission of the virus. This study was designed to explore the influence of plant genetic diversity on virus dispersal by aphid vectors and to examine the biological mech- anisms responsible for that influence. In a set of field experiments using the aphid-transmitted barley yellow dwarf virus, I examined the influence of genetic diversity in oat (Avena sativa L.) populations on the spread of the virus and on the population dynamics and movement behavior of aphid vectors of the virus. Only at relatively high aphid abundance were the densities of aphid vectors influenced by plant genetic diversity. In one year out of three, densities of the oat- bird cherry aphid, Rhopalosiphum padi (L.), were significantly lower in the genetically diverse stand than in the genetically homogeneous stands. In no year were densities of the English grain aphid, Sitobion avenae (F.), influenced by the host-plant population. Despite these weak or absent effects on vector abundance, the incidence of the virus was consistently lower in the genetically diverse oat populations. Disease reduction in the diverse populations appears to depend upon changes in aphid movement behavior that affect the efficiency of virus transmission. Mark-release experi- ments with S. avenae demonstrated that movement rates were significantly higher and plant tenure times were significantly lower in the genetically diverse oat populations. Be- cause the barley yellow dwarf virus requires several hours of aphid feeding for effective transmission, these reduced tenure times and increased travel time among plants led to a reduction of virus transmission. While plant genotype can clearly influence herbivorous insects dramatically, this study suggests that the effects on insects of genetic diversity per se in the host-plant population are likely to be subtle and not easily detected using standard field sampling techniques, except at high insect densities. Yet even at low vector densities, behavioral responses to plant genetic diversity can lead to significant effects on the spread of pathogens.

Intra versus interspecific interactions of ladybeetles (Coleoptera: Coccinellidae) attacking aphids

Abstract: The nature and relative strengths of intra versus interspecific interactions among foraging ladybeetle larvae were studied experimentally by measuring short-term growth rates of predators and reductions in population sizes of prey in laboratory microcosms. In these microcosms, ladybeetle larvae foraged singly or as conspecific or heterospecific pairs, for pea aphids on bean plants over a two-day period. Similarly sized third instar larvae ofHippodamia convergens andH. tredecimpunctata, H. convergens andH. sinuata, andH. convergens andCoccinella septempunctata, were tested in experiments designed to ensure that paired larvae experienced moderate competition. Interspecific competition in these experiments did not differ significantly from intraspecific competition, in that an individual's weight gain did not depend on whether its competitor was heterospecific or conspecific. Furthermore, aphid populations were reduced equally by heterospecific and conspecific pairs. These results suggest that there is little or no difference between intra and interspecific interactions among larvae of these ladybeetles when two similarly sized individuals co-occur on a host plant. Thus, the species diversityper se of assemblages of ladybeetle larvae may have little influence over the short term on the reduction of aphid populations by ladybeetle predation.

Natural Control of Cereal Aphids (Homoptera: Aphididae) by Entomopathogenic Fungi (Zygomycetes: Entomophthorales) and Parasitoids (Hymenoptera: Braconidae and Encyrtidae) on Irrigated Spring Wheat in Southwestern Idaho

Abstract: Data on the natural control of cereal aphids, Diuraphis noxia (Mordvilko), Metopolophium dirhodum (Walker), and Sitobion avenae (F.), by entomophthoralean fungi and hymenopterous parasitoids on furrow-irrigated spring wheat in southwestern Idaho are presented. The important fungi involved were Pandora neoaphidis (Remaudire & Hennebert) Humber and Conidiobolus spp., including C. obscurus (Hall and Dunn) Remaudire, C. thromboides Drechsler, and C. coronatus (Constantin) Batko. During 1986–1989, M. dirhodum and S. avenae populations usually reached or exceeded economic levels. D. noxia did not enter the region until late June 1987. It was the first aphid found infesting the crop in 1988 and reached high densities that summer but was not found in 1989, perhaps because of mortality during an extremely cold winter. Fungal infection occurred ≍2,3, and 6 wk after colonization of the crop by M. dirhodum, S. avenae , and D. noxia, respectively. Epizootics occurred each summer but usually after the crop was damaged by large aphid populations. An exception occurred during 1987 when M. dirhodum and S. avenae populations were effectively suppressed by mycoses, apparently enhanced by unusually frequent rainfall during late May and June. M. dirhodum experienced much higher mortality from fungal infection than did S. avenae and D. noxia. P. neoaphidis was the dominant fungus infecting M. dirhodum and D. noxia, whereas Conidiobolus spp. were most important on S. avenae. Entomophthora chromaphidis Burger & Swain and two Zoophthora species sporadically infected cereal aphids. Parasitoids, mainly Aphidius ervi Haliday for S. avenae and M. dirhodum and Diaeretiella rapae (M'Intosh) for D. noxia, usually attacked cereal aphids earlier than the fungi but were less influential during the decline of host populations. Multiple regression and correlation analysis indicated that mycoses and parasitoids made significant contributions to the reduction of peak populations of each aphid species compared with the influence of crop maturation. Weak correlation between fungal infection and host density and climatic factors ( r2 ranging from 0.35 to 0.53) was found. Development of fungal infection seemed to be better correlated with host density than with climatic factors. Precipitation was more associated with fungal infection of S. avenae, which inhabits upper portions of the host crop, but had little effect on that of M. dirhodum and D. noxia, which inhabit more humid microenvironments. No other climatic factors were significantly correlated with fungal infection. A hypothesis is proposed that the site on a wheat plant typically occupied by an aphid species influences the development of mycoses.

Dispersal of apterous aphids (Homoptera: Aphididae) from their host plant and its significance

Abstract: Dispersal of apterae from their natal plant was monitored for three aphid species (Myzus persicae (Sulzer), Brevicoryne brassicae (Linnaeus) and Megoura viciae Buckton), each on a different host plant. Some movement off the plant occurred even in the initial parental and second generations, when the plant appeared to be growing normally and when crowding was unlikely to be the cause. However, in most experiments the most marked increase in apterous dispersal coincided with a reduction or even cessation of plant growth. In nearly all the experiments this dispersal occurred when the population on the natal plant exceeded about 20 adults and their offspring per plant. The main emigrants were fourth instar apterae and prelarviposition adult apterae. The implications of this behaviour are discussed, and it is argued that apterous dispersal might be common in aphids, allowing a fuller utilization of the environment than would be likely by alate dispersal alone.

Synthetic aphid sex pheromone lures female parasitoids.

Abstract: J. Hardie t'3, S. F. Nottingham 1, W. Powell 2 & L. J. Wadhams 2 ~ Agricultural and Food Research Council Linked Research Group in Aphid Biology, Department of Biology, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK; 2 AFRC Institute of Arable Crops Research, Rothamsted Experimental Station, Harpenden, Herts AL5 2JQ, UK; 3present address: AFRC Linked Research Group in Aphid Biology, Imperial College at Silwood Park, Ascot, Berks. SL5 7 PY, UK

Field manipulation of populations of individual staphylinid species in cereals and their impact on aphid populations

Abstract: . 1 Four species of staphylinids were caged separately on wheat and their effect on the population development of the grain aphid, Sitobion avenae (F.), was investigated over two seasons. 2 A novel field cage design was used to exclude all but the staphylinid species under investigation. 3 Predator effects were compared with total-exclusion cages in which all predators and parasitoids were kept out. 4 During a high-density phase of aphid population development only Philonthus cognutus (Stephens) significantly influenced aphid population numbers. 5 At low aphid densities, Tachyporus obtusus (L.), T.chrysomelinus (L.) and P.cognatus reduced aphid population levels. 6 The experiments showed that Tachyporus spp. can reduce the numbers of cereal aphids prior to the exponential phase of aphid population increase and that P.cognatus causes some reduction at both the stages of aphid population growth investigated.

Interactions between Solenopsis invicta (Hymenoptera : formicidae), Rhopalosiphum maidis (Homoptera : aphididae), and the parasitoid Lysiphlebus testaceipes cresson (Hymenoptera : aphidiidae)

Abstract: In the presence of the red imported fire ant, Solenopsis invicta Buren, adult emergence of the parasitoid Lysiphlebus testaceipes Cresson from laboratory colonies of the corn leaf aphid, Rhopalosiphum maidis (Fitch), was reduced. Parasitoids abandoned an attack when ants were within a few millimeters and searched elsewhere, increasing search time. However, the increased searching time in the laboratory was compensated by a reduction in parasitoids' resting time resulting in similar levels of parasitism between the controls and the ant-infested containers. A major effect of the red imported fire ant was the removal and destruction of parasitized aphids. Ants began detecting parasitized aphids 6 d after parasitization and removed them to the ant colony. Honeydew production was reduced in parasitized aphids by 6 d and they resembled starved aphids. However, in contrast to parasitized aphids, starved aphids were moved to healthy plants, when available.

Hydroxamic acids affecting barley yellow dwarf virus transmission by the aphid Rhopalosiphum padi

Abstract: 2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid (Hx) occurring in wheat, was shown to deter feeding by the aphid Rhopalosiphum padi (L.), and to reduce BYDV transmission to the plant. Dual choice tests with wheat leaves showed the preferential settlement of aphids on leaves with lower levels of DIMBOA. Electric monitoring of aphid feeding behaviour showed that in seedlings with higher DIMBOA levels fewer aphids reached the phloem and they needed longer times to contact a phloem vessel than in those with lower levels. When aphids carrying BYDV were allowed to feed on wheat cultivars with different DIMBOA levels, fewer plants were infected with BYDV in the higher DIMBOA cultivars than in the lower ones. Preliminary field experiments showed a tendency for wheat cultivars with higher Hx levels to be more tolerant to infection by BYDV than lower Hx level ones.

The influence of host food plants on host recognition by four aphidiine parasitoids (Hymenoptera: Braconidae)

Abstract: The attack rate of four parasitoids against different aphid species was investigated in the absence and presence of leaves from aphid food plants. The parasitoids used, Aphidius ervi Haliday, A. rhopalosiphi De Stefani, A. picipes (Nees) and Ephedrus plagiator Nees, varied in the extent of their host ranges. The presence of plant leaves significantly influenced the attack rate of A. ervi and A. rhopalosiphi , the two parasitoids with the most restricted host ranges, but did not appear to affect attack rates by the more polyphagous A. picipes and E. plagiator. Consideration of these results together with those from previous studies on the host preferences of laboratory populations of A. ervi and A. rhopalosiphi leads to the conclusion that genotype is probably determining the responses of individual parasitoids to semiochemicals involved in host recognition. It is proposed that field populations of oligophagous aphid parasitoids consist of a mixture of specialist and generalist individuals.

Evidence that heteroencapsidation between two potyviruses is involved in aphid transmission of a non-aphid-transmissible isolate from mixed infections

Abstract: A non-aphid-transmissible isolate of zucchini yellow mosaic virus, ZYMV-NAT, which possesses a transmission-deficient capsid protein, was regularly transmitted by aphids from plants infected concomitantly by this virus and a transmissible isolate of papaya ringspot virus type W (PRSV-E2). This phenomenon was reproduced in in vitro acquisition experiments by mixing virions purified from plants co-infected by ZYMV-NAT and PRSV-E2, with PRSV-E2 helper component (HC) preparations (...)

Aphid transmission of barley yellow dwarf virus : inoculation access periods and epidemiological implications

Abstract: In this study, we examined the efficiency of transmission of three isolates of barley yellow dwarf virus (BYDV) from New York by two aphid species for the purpose of assessing the relative importance of these species as vectors. The influence of the duration of the aphid inoculation access period (IAP) on transmission was investigated for RPV and PAV isolates of BYDV transmitted by Rhopalosiphum padi and for MAV and PAV isolates transmitted by Sitobion avenae. For each aphid-isolate combination, 15 IAPs, ranging from 30 min to 72 hr, were tested (...)

Fate of quinolizidine alkaloids through three trophic levels:Laburnum anagyroides (Leguminosae) and associated organisms.

Abstract: The quinolizidine alkaloids (QA) of golden rain,Laburnum anagyroides, and those of phytophagous insects associated with the plant, as well as of parasitoids of the latter, were analyzed by capillary GLC and GLC-MS. The alkaloid content in samples of vegetative plant parts was high at the beginning of the season, then decreased, while that of reproductive organs was high throughout flowering, pod formation, and maturation. The analyses showed that the QA of the plant passed through two higher trophic levels (herbivorous insects and their parasitoids) and that the alkaloid pattern changed little during the passage. The alkaloids were present in two phytophagous insect species associated with golden rain: the predispersal seed predator,Bruchidius villosus [5–13μg/g fresh weight (fw)], andAphis cytisorum (182–1012μg/g fw), an aphid that feeds on shoots, leaves, and inflorescences. Braconid and chalcidoid parasitoids emerging from the bruchid host also contained alkaloids (1.3–3μg/g fw), as did three foraging ant species,Lasius niger, Formica rufibarbis, andF. cunicularia (45μg/g fw), that visited the aphid colonies or honeydew-covered leaves of aphid-infested plants. The hypothesis that developing bruchid larvae and/or the plant “manipulate” QA supply to infested seeds was not supported, because QA content of leftover endosperm in seeds after bruchid development was similar to that of uninfested seeds. The frass of developing bruchid larvae was rich in QA (31μg/ g dry weight). While aphids sequestered, the bruchid larvae took up and eliminated QA with the frass without chemical transformation.

Mycophagy as a factor limiting predation of aphids (Hemiptera: Aphididae) by staphylinid beetles (Coleoptera: Staphylinidae) in cereals

Abstract: Previous work demonstrated the potential of the staphylinids Tachyporus hypnorum (Fabricius), T. chrysomelinus (Linnaeus), T. obtusus (Linnaeus) and Philonthus cognatus (Stephens) to feed on the grain aphid, Sitobion avenae (Fabricius). However, gut dissection and observations of foraging behaviour showed that mycophagy could be a factor influencing the potential of Tachyporus spp. to control aphids. The main fungal material detected in the guts of Tachyporus spp. was spores (conidia) of Erysiphe spp. (powdery mildews). In the present study, numbers of conidia (pustules of mildew on leaf-sections) were offered with aphids in food-choice experiments to test how fungal food affected feeding on aphids by these staphylinids. An index of food preference was calculated for each species, sex and for two age classes of larvae, based on the number of conidia and aphids remaining after feeding. Results showed a preference for mildew conidia by T. hypnorum, no preference by T. chrysomelinus and Tachyporus spp. larvae and a preference for aphids by T. obtusus and P. cognatus (adults and larvae). Food-preferences compared well with dietary composition in recent studies of field collected staphylinids. Futhermore, a functional response was detected to increasing numbers of mildew conidia presented (in mildew only consumption-rate experiments) and to the increase in total food density in food-choice experiments. Mycophagy limited aphid predation and explained the numerical response of staphylinid beetles to areas of cereals with high aphid densities, whilst, in other studies, the proportion of aphids eaten by those beetles did not increase.

Patterns of host selection by four species of aphidiid (Hymenoptera) parasitoids: influence of host switching

Abstract: . 1 We tested switching behaviour in four species of aphidiid parasitoids, using a two-aphid experimental system consisting of second-instar nymphs of pea aphid (Acyrthosiphon pisum (Harris)) and alfalfa aphid (Macrosiphum creelii Davis) feeding on broad beans in the laboratory. 2 Aphidius ervi Haliday, A.pisivorus Smith, A.smithi Sharma & Subba Rao, and Pram pequodorum Viereck showed an innate preference for pea aphid when both host species were provided in equal numbers. 3 Wasps encountered both aphid species equally but differed in their acceptance of alfalfa aphid. Females of A.pisivorus and P.pequodorum accepted alfalfa aphids when few pea aphids were available, but A. smithi always concentrated attacks on pea aphid. Aphidius ervi super-parasitized an increasing proportion of pea aphids as their availability declined. 4 Switching to the alfalfa aphid occurred in A.ervi and P.pequodorum (but not in A.pisivorus and A.smithi) under the condition of a 1:3 ratio of pea aphids:alfalfa aphids. Wasps did not switch when more pea aphids than alfalfa aphids were provided (3:1 ratio). 5 Alfalfa aphids were more likely than pea aphids to escape from parasitoid attack. 6 Switching to the most abundant host may not be adaptive in these four species of aphid parasitoids. A foraging wasp incurs a potentially higher cost in lost opportunity time when attacking (and failing to oviposit in) alfalfa aphids. In addition, alfalfa aphids may have lower host quality than pea aphids, a difference that could influence offspring fitness.

Are ant-aphid associations a tritrophic interaction? Oleander aphids and Argentine ants.

Abstract: Oleander aphids, (Aphis nerii), which are sporadically tended by ants, were used as a moded system to examine whether host plant factors associated with feeding site influenced the formation of ant-aphid associations. Seasonal patterns of host plant utilization and association with attendant ants were examined through bi-weekly censuses of the aphid population feeding on thirty ornamental oleander plands (Nerium oleander) in northern California in 1985 and 1986. Colonies occurred on both developing and senescing plant terminals, including leaf tips, floral structures, and pods. Aphids preferentially colonized leaf terminals early in the season, but showed no preference for feeding site during later periods. Argentine ants (Iridomyrmex humilis) occasionally tended aphid colonies. Colonies on floral tips were three to four times more likely to attract ants than colonies on leaf tips, even though the latter frequently contained more aphids. Ants showed a positive recruitment response to colonies on floral tips, with a significant correlation between colony size and number of ants. There was no recruitment response to colonies on leaf tips. These patterns were reproducible over two years despite large fluctuations in both aphid population density and ant activity. In a laboratory bioassay of aphid palatability, the generalist predator,Hippodamia convergens, took significantly more aphids reared on floral tips compared to those reared on leaf tips. The patterns reported here support the hypothesis that tritrophic factors may be important in modifying higher level arthropod mutualisms.

Potato leafroll virus spread in relation to densities of green peach aphid (Homoptera : Aphididae) : implications for management thresholds for Minnesota seed potatoes

Abstract: Tolerances for potato leafroll virus in potato, Solanum tuberosum L., seed are low in Minnesota, necessitating intensive insecticide use to control the vector, green peach aphid, Myzus persicae (Sulzer). We sought to determine the relation between low green peach aphid densities and potato leafroll spread, and to learn if insecticide use in seed potatoes could be reduced using green peach aphid apterae action thresholds. Plots containing leafroll infected plants were sprayed with methamidophos on thresholds of 0, 10, 30, and 100 apterae per 100 leaves in 1987 and 0, 3, 10, and 30 per 100 leaves in 1988. Percent potato leafroll infection was related to cumulative green peach aphid apterae-days (number of aphids per 100 leaves × number days present) and time of leafroll source introduction (R2 = 0.79). Leafroll infected sample units were more often adjacent than would be expected if occurrence were random in 17 of 18 apterae action threshold plots. The pattern of leafroll spread and the relation with green peach aphid apterae-days suggested that apterae were primarily responsible for spread of the virus. Percent potato leafroll infection in potato, cv. Russet Burbank, was related to the green peach aphid apterae thresholds at which insecticidal sprays were applied, although variation was large within a threshold. Data from these studies suggest that the threshold concept might be employed, but that the threshold for treatment would be very low, perhaps in the range of 3-10 green peach aphid apterae per 100 leaves. Experiments in 1988 showed little spread early in the season, even though aphids and leafroll infected plants were present.

Survey and detection of endophytic fungi in Lolium germ plasm by direct staining and aphid assays

Abstract: Wilson, A. D., Clement, S. L., and Kaiser, W. J. 1991. Survey and detection of endophytic fungi in Lolium germ plasm by direct staining and aphid assays. Plant Dis. 75:169-173. Clavicipitaceous anamorphic endophytes were detected in 28 of 85 accessions from five of eight species in a collection of Lolium germ plasm. Comparative descriptions of endophytic mycelium in seeds of L. multiflorum, L. perenne, L. persicum, L. rigidum, and L. temulentum revealed morphological characteristics distinguishing endophytes in each host species. Most endophyte-infected accessions originated from Eurasia, particularly from Middle Eastern countries. Endophyte incidence and infection percentages varied widely with host species and geographic origin. Feeding tests with Diuruphis noxia were useful in detecting endophyte-infected accessions of perennial ryegrass. Additional keywords: Acremonium, bioassay, biological control, Clavicipitaceae, Russian wheat aphid

Consumption of aphid honeydew, a wheat yield reduction factor, by phyllosphere yeasts under field conditions

Abstract: Aphid honeydew on wheat leaves can affect host physiology directly and can stimulate infection by necrotrophic pathogens. The role of naturally occurring saprophytes on wheat flag leaves in removing aphid honeydew was examined in five field experiments at different locations in the Netherlands in 1987 and 1988. Aphid populations, saprophyte populations and aphid honeydew were measured weekly. Diseases were monitored at 1–4 week intervals. In the control treatment, sprayed with water, the naturally occurring saprophytes consumed the honeydew almost completely, except in one experiment in which the aphid population increased very rapidly. In the treatments in which the saprophytes were reduced by the broad-spectrum fungicide maneb in 1987 and with maneb alternated with anilazin in 1988, honeydew accumulated. The observed honeydew consumption by the naturally occurring saprophytic population is ascribed mainly to pink and white yeasts (Sporobolomyces spp. andCryptococcus spp., respectively). Additional treatments showed, that in the presence of the naturally occurring saprophytes the yield loss per aphid-infestation-day was lower than when the saprophytes were inhibited by fungicides, showing that yeasts can reduce the detrimental effect of aphid honeydew in wheat.