Showing papers on "Aphididae published in 1994"

Winter host component reduces colonization by Bird-cherry-oat aphid, Rhopalosiphum padi (L.) (Homoptera, Aphididae), and other aphids in cereal fields

Abstract: Methyl salicylate, a volatile component ofPrunus padus, the winter host ofRhopalosiphum padi, was found to reduce colonization of the summer host by this aphid. The compound was identified by gas chromatographic analysis coupled with recordings from cells in the primary rhinarium on the sixth antennal segment of the aphid. Methyl salicylate eliminated the attractancy of oat leaves to spring migrants in olfactometer tests. In Sweden, this compound significantly decreased colonization of field grown cereals byR. padi and in the U.K., populations ofSitobion avenae andMetopolophium dirhodum were significantly lower on treated plots.

Establishment of the Brown Citrus Aphid (Homoptera: Aphididae) in Central America and the Caribbean Basin and Transmission of Citrus Tristeza Virus

Abstract: The brown citrus aphid, Toxoptera citricida (Kirkaldy), is distributed widely on citrus but is not known to occur in the Mediterranean region or, until recently, in North America. The brown citrus aphid is an important pest of citrus because it is an efficient vector of citrus tristeza virus. Surveys have shown that the brown citrus aphid has rapidly expanded its distribution in the Caribbean Basin and Central America. In September 1991, the brown citrus aphid was found widespread on citrus in Costa Rica, Nicaragua, and Panama but was not found in Belize, El Salvador, Guatemala, Honduras, or Mexico. In 1992, it was found in the Dominican Republic, Guadeloupe, Haiti, Martinique, Puerto Rico, St. Croix, St. Thomas, Trinidad, and the U.S. Virgin Islands and, in 1993, in Cuba and Jamaica. The aphid was not found in the Bahamas or Bermuda in the survey. Enzymelinked immunosorbent assay tests from citrus trees indicated that citrus tristeza virus incidence was low (<15%) in most areas and probably was caused by the use of infected budwood, rather than by aphid vectors, because of its random pattern of a few infected fields separated by tristeza-free fields. Most citrus tristeza virus isolates detected did not react with the severe-strain discriminating monoclonal citrus tristeza virus antibody, MCA13, and, thus, are probably mild strains. Some MCA13 reactive isolates were found in Belize, Costa Rica, Panama, Bermuda, the Dominican Republic, Jamaica, Puerto Rico, and Trinidad. The brown citrus aphid was ≍6-25 times more efficient in transmitting several strains of citrus tristeza virus than the melon aphid, Aphis gossypii Glover. Incidence of decline isolates of citrus tristeza virus could increase rapidly with the advancing movement of the brown citrus aphid and could threaten ≍180 million citrus trees on citrus tristeza virus-sensitive sour orange rootstock in the Caribbean Basin, Central America, Mexico, and the United States. An additional threat exists if this aphid begins to spread grapefruit and sweet orange stem-pitting strains of citrus tristeza virus.

How an ant decides to prey on or to attend aphids

Abstract: The following results on the behavior decision making of the antLasius niger toward two species of myrmecophilous aphidsLachnus tropicalis andMyzocallis kuricola on chestnut trees have been found. (1) An individual worker consistently attended only one aphid species, even if her nestmates attended other aphid species on the same tree. (2) The ants preyed less on the aphid species which they attended than on other myrmecophilous aphid species. (3) The ants preyed less on the aphids which had been attended by their nestmates, even if both aphids were the same species. (4) The ants preyed less on aphids which had provided honeydew to their nestmates. (5) The increased aphid density per ant led to an increase in the rate of predation on the introduced aphids by the ants. These results suggest that each worker ofL. niger chooses aphid species to attend from her experience. In addition, the workers can recognize whether an aphid has been attended by their nestmates and whether an aphid has given their nestmates honeydew. Through these processes, each worker decides to attend or to prey on the aphid. As a result, they may realize efficient collective foraging dependent on aphid density per worker.

The use of visual cues in host evaluation by aphidiid wasps. I: Comparison between three Aphidius parasitoids of the pea aphid

Abstract: Host evaluation behaviour was examined in three species of aphid parasitoids, Aphidius ervi Haliday, A. pisivorus Smith, and A. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae). Parasitoids were provided under laboratory conditions with three kinds of hosts representing two aphid species: (green) pea aphid, Acyrthosiphon pisum (Harris), and green and pink colour morphs of the alfalfa aphid, Macrosiphum creelii Davis. Females of all three Aphidius species distinguished between aphids on the basis of colour, movement, and host species. Patterns of host acceptance by parasitoids were species-specific. In A. ervi, host preference was the same in light and dark conditions: pea aphid > green alfalfa aphid „ pink alfalfa aphid. In contrast, A. pisivorus attacked and accepted pea aphid and green alfalfa aphid equally in the light and preferred both of these over pink alfalfa aphid; however, it made no distinction between pea aphid and pink alfalfa aphid in the dark. Females of A. smithi attacked all three kinds of hosts (pea aphid > green alfalfa aphid „ pink alfalfa aphid) but apparently laid eggs only in pea aphid. The frequencies of attack and oviposition by all wasps were higher on ‘normal’ pea aphids than on those anaesthetized with CO2. Host recognition is confirmed by chemical cues in the aphid cuticle that are detected during antennation, and host acceptance is dependent on an assessment of host quality during ovipositor probing.

Growth Kinetics of the Endosymbiont Buchnera aphidicola in the Aphid Schizaphis graminum

Abstract: The aphid Schizaphis graminum is dependent on its prokaryotic endosymbiont, Buchnera aphidicola. As a means of determining B. aphidicola numbers during the growth cycle of the aphid we have used the quantitative PCR to measure the number of copies of rrs (the gene coding for 16S rRNA, which is present as one copy in the B. aphidicola genome). In addition we have measured the aphid wet weight and the DNA and protein content. The results indicate an approximately parallel (23- to 31-fold) increase of these properties during the period of aphid growth. A 1-day-old aphid (24 mug [wet weight]) has 0.2 x 10 copies of rrs, while a 9-day-old aphid (497 mug [wet weight]) has 5.6 x 10 copies. The coupling of endosymbiont and aphid growth is consistent with the requirement of the endosymbiont for growth and reproduction of the aphid.

Host recognition and acceptance behaviour in two aphid parasitoid species: Aphidius ervi and Aphidius microlophii (Hymenoptera: Braconidae)

Abstract: The host preference and acceptance behaviour of populations of Aphidius ervi Haliday and A. microlophii Pennacchio & Tremblay from southern Italy was investigated. In no host-choice conditions, A. ervi females showed significantly higher attack and oviposition rates on the natural host Acyrthosiphon pisum (Harris) than on the non-host aphid Microlophium carnosum (Buckton)(Homoptera: Aphididae). In contrast, A. microlophii, which specifically parasitizes M. carnosum in the field, attacked both aphid species. However, dissections showed that oviposition of A. microlophii occurred only in a few of the attacked Acyrthosiphon pisum and was significantly less frequent than in M. carnosum. These results were confirmed in experimental host-choice conditions, suggesting that Aphidius microlophii oviposition is possibly regulated by a host haemolymphatic kairomone. Hybrids obtained by crossing A. ervi females with A. microlophii males attacked and oviposited in both aphid species, suggesting that these behavioural events have a strong genetic basis. The oviposition into host or non-host aphids did not elicit an immune defence reaction. The presence of the host's food-plant had no evident close-range effects on parasitoid attack and oviposition in non-host aphids. Aphidius microlophii reared on the non-host aphid Acyrthosiphon pisum produced a significant higher number of mummies after a few generations, suggesting a possible role of larval and early adult conditioning in the host selection process. These results, together with those from previous studies, suggest that Aphidius ervi is best considered as a complex of differentiated populations, characterized by a varying degree of genetic divergence.

Physiological effects of Russian wheat aphid (Homoptera: Aphididae) on resistant and susceptible barley

Abstract: A resistant barley ( Hordeum vulgare L., PI 366450) was used to compare physiological responses of a susceptible barley (‘Morex’) to the recently introduced pest, Russian wheat aphid, Diuraphis noxia (Mordvilko). As measured by chlorosis, leaf rolling, and streaking, damage by Russian wheat aphid was greater in ‘Morex’ than in PI 366450. The inhibition of growth, as measured by plant height, shoot dry weight, and number of leaves, also was greater in ‘Morex’ than in PI 366450. Relative water contents of leaves or stems showed no differences between ‘Morex’ and PI 366450 as a result of infestation. Well-watered PI 366450 showed greater stomatal closure in response to aphid infestation than ‘Morex’. However, the stomatal resistance responses of water-deprived PI 366450 and ‘Morex’ to Russian wheat aphids could not be distinguished. The two-dimensional SDS-PAGE protein profiles of uninfested ‘Morex’ and PI 366450 leaves were virtually identical. Upon infestation, a complex of proteins (≈23 kD) was altered in the PI 366450 profile and had decreased levels in ‘Morex’. Chlorophyll measurements indicated a greater relative loss of chlorophyll during infestation in ‘Morex’ than in PI 366450 when deprived of water; no differences could be distinguished when well watered. Measurements of the effectiveness of photosystem II to transfer electrons also showed no differences between well-watered resistant and susceptible barleys as a result of aphid infestation. However, the ability of the quinone pool in ‘Morex’ to recover after illumination was reduced greatly relative to that of PI 366450.

Age‐dependent foraging behaviour and host‐instar preference of the aphid parasitoid Lysiphlebus cardui

Abstract: Foraging behaviour and host-instar preference of young and old females of the solitary aphid parasitoid, Lysiphlebus cardui Marshall (Hymenoptera: Aphidiidae), were studied in the laboratory. The analysis of interactions between parasitoids and different stages of Aphis fabae cirsiiacanthoidis Scop. (Homoptera: Aphididae) revealed that encounter rates between aphids and parasitoid females and defence reactions of the aphids influenced the degree to which a particular aphid age class is parasitized. Encounter rates between hosts and parasitoid females depended on the foraging pattern of the parasitoid, which varied with age. In mixed aphid colonies patch residence time increased with parasitoid age. Furthermore, younger parasitoids (≤ 1 day old) laid more eggs into second and third instars, while older parasitoids (≥ 4 days old) did not show distinct host instar preferences. It is suggested that the oviposition behaviour of L. cardui is influenced by the physiological state, i.e. the age of the wasp.

Abundance of cotton aphids (Homoptera: Aphididae) and associated biological control agents on six cotton cultivars

Abstract: The seasonal abundance patterns of the cotton aphid, Aphis gossypii Glover, and its complex of biological control agents on six cotton cultivars differed among cultivars during much of the growing season. Differences in aphid populations among cultivars were >3-fold during the period of peak aphid abundance. Lower aphid densities were found on cultivars exhibiting the smooth-leaf character. Parasitism and predation may have reduced cotton aphid population growth early in the season. Entomopathogen infection was the primary cause of an aphid population reduction that occurred during the week after peak aphid abundance, and continued pathogen activity combined with predation maintained aphids at a low density for the remainder of the season.

High variation in host adaptation among clones of the pea aphid, Acyrthosiphon pisum on peas, Pisum sativum

Abstract: The performance of one clone of the pea aphid, Acyrthosiphon pisum (Harris), was assessed on 37 different cultivars and species of Pisum L. In addition, random samples of 36 pea aphid clones collected on alfalfa and clover were tested on a selection of five Pisum sativum L. cultivars. Aphid performance was evaluated in terms of the mean relative growth rate (MRGR) during the first five days of life or other life history variables. The MRGR of the first-mentioned pea aphid clone differed little between cultivars. No significant differences in MRGR were found between wild and cultivated Pisum species or between modern and old P. sativum cultivars. There was considerable variation in host adaptation among the 36 pea aphid clones within each sampled field. The pea aphid clones showed no consistent pattern in performance on four of the five pea cultivars i.e. there was a significant pea aphid genotype — pea genotype interaction. On one of the cultivars all clones performed well. Pea aphid clones collected from red clover generally performed relatively poorly on pea cultivars, in contrast to the pea aphid clones collected on alfalfa. There was no difference in performance between the two pea aphid colour forms tested. Possible reasons for the high variation and the observed adaptation patterns are discussed. The fact that all clones were collected in two adjacent fields indicates that A. pisum shows high local intraspecific variability in terms of host adaptation.

The responses of Praon spp. parasitoids to aphid sex pheromone components in the field

Abstract: In autumn 1991, aphid parasitoids of the genus Praon (Hymenoptera; Braconidae) were caught in water traps with lures containing synthetic aphid sex pheromone components at three sites in England and one in Germany. At two of the English sites and at the German site, the traps were placed in winter cereal fields whilst the third English site was in woodland. Three species were caught, P. volucre, P. dorsale and P. abjectum. Those caught in cereal fields were almost entirely P. volucre, whilst P. dorsale dominated at the woodland site. Of the known aphid sex pheromone components, the most effective lure was the (+)-(4aS,7S,7aR)-nepetalactone. Nepetalactone traps placed at the woodland site in spring and summer caught few Praon females, and attraction may be confined to the autumn, when sexual female aphids are present in the field. Male parasitoids did not respond to the aphid pheromones at any time, although they were caught in suction traps operated at the woodland site during the autumn. At the cereal sites height had a significant influence on the efficiency of the pheromone traps, those placed just above the crop canopy being most effective. There was no evidence that any other genus of parasitoid responded to aphid sex pheromones at these sites.

Observations on the micro-organisms occurring in the gut of the pea aphid Acyrthosiphon pisum

Abstract: Most aphids possess symbiotic bacteria in specialised argans, the bacteriacytes occurring in tbeir haemocoele (Buchner, 1965). These Gramnegative bacteria, recently identified by malecular techniques as belanging to the y-3 subgraup af the Proteabacteria and named Buchnera aphidicola (Munsan et al., 1991b), are called the aphid primary symbiotes and have not been cultivated to date (Hauk, 1974; Munson et al., 1991b). They are cansidered as obligate symbiates of the insect, although viable but unfertile aposymbiotic aphids can be obtained in some species of aphids (Prosser & Douglas, 1991; Sasaki etai., 1991; Rahbe et al., 1992). Their association with Aphididae seems widespread, and is considered to be monophyletic since the origin of aphids, mare than 80 million years ago (Mun son et al., 199Ia). It is speculated that they canfer to their aphid hasts many metabolic advantages, leading to a beller adaptation to their ecolagical niche, i.e. phloem feeding (Houk & Griffiths, 1980; Campbell, 1989; Ishikawa, 1989; Douglas, 1990; Nardon & Grenier, 1993). The study of aphid primary symbiosis implies a characterisation of the micro-organisms involved, and their differentiation From ather microorganisms harboured by aphids. Actually, many aphid species also harbaur secondary symbiotic bacteria, maternally transmitted and located in sheath cells surrounding the primary bacteriomes (Houk & Griffiths, 1980). Molecular characterisation assigns them to the Enterobacteriaceae, a group which included E. coli and not Buehnera spp. (Unterman et al., 1989). Their function in aphid physiology is considered la be le" crucial since they are absent in many aphid species, such as Myzus persieae and Schizaphis graminum. Early reports also mentioned aphids with more than twa symbiotes (Buchner, 1965), and a recent paper describes an eukaryotic symbiosis in a species of gall-forming, social aphid belonging to the Hormaphidinae (Fukatsu & Ishikawa, 1992). Aside From their haemocoele symbiotes, sorne aphids have been reported to harbaur gut microorganisms (Schander! el al., 1949; Srivastava & Rouat!, 1963). Nothing is known on how widespread the infection s are, or on the function and origin of these micro-organisms. In the course of a study on the primary symbiosis of the pea aphid Acyrthosiphon pisum, we thought it useful ta further characterise the micro-organisms occurring in the aphid gut. We report here the observations and comment an their possible origin and their presence at different ages and in two biotypes currently used in our laboratory.

An investigation of the resistance to cabbage aphid in brassica species

Abstract: Summary Fifteen Brassica species and subspecies, as well as accessions of Arabidopsis thaliana and Eruca sativa, were evaluated for their resistance to the cabbage aphid, Brevicoryne brassicae, in the field and laboratory at Horticulture Research International (HRI) Wellesbourne in 1992. In the laboratory, aphid performance was measured in terms of pre-reproductive period, reproductive period, population increase and insect survival. Using these parameters it was possible to identify brassicas possessing antibiosis resistance. In the field B. brassicae attack was assessed in terms of numbers of insects and it was possible to determine aphid preferences for alighting on different species. High levels of antixenosis and antibiosis resistance were discovered in accessions of Brassica fruticulosa and B. spinescens, in a Brassica juncea breeding line and in Eruca sativa. Partial resistance was found in several other Brassica species. The potential of these various sources as donors of resistance genes to be bred into cultivated brassicas is discussed.

Pest Status of Aphids and Other Insects in Winter Canola in Georgia

Abstract: Canola, Brassica napus L., is being evaluated as a winter grain crop in the southeastern United States. The damage potential of insect pests was studied during three growing seasons in the Piedmont and coastal plain regions of Georgia by controlling insects with insecticides at the rosette, beginning bloom, or pod-fill stages of plant development. Canola pod infestations by the cabbage seedpod weevil, Ceutorhynchus assimilis Paykull, reached 60% at some sites in northern Georgia indicating that this insect will be an important pest of canola in this area. However, C. assimilis was not collected in any year in southern Georgia. Yield responses to insecticide treatments were associated with a complex of aphids, primarily the turnip aphid, Lipaphis erysimi (Kaltenbach), and green peach aphid, Myzus persicae (Sulzer), which caused direct injury to leaves and stems. Aphid injury reduced plant height and winter survival and delayed plant development. Comparison of untreated and season-long treated plots indicated that aphid injury reduced yield by 9.9, 30.4, and 34.8% in 3 yr in the coastal plain region. In northern Georgia, yield losses caused by aphids were ≤2.0% in three of four trials, but aphid injury reduced yield by 32.7% in one trial. Insecticidal control of aphids had the greatest effect on yield during the rosette stage with treatments at first bloom also enhancing yield in some trials. Insecticide treatments at pod-fill stage did not affect canola growth and yield in any trial. Aphids most likely will be a limiting factor in canola production in the southern United States, particularly in the coastal plain region. Aphid management activities should be directed at seedling and rosette stages of plant development.

Falling aphids enhance impact of biological control by parasitoids on partially aphid-resistant plant varieties

Abstract: Summary Cage experiments, in which the population increase of Metopolophium dirhodum was measured either in the absence or presence of the parasitoid Aphidius rhopalosiphi, showed reductions of peak populations in the presence of the parasitoid of 30% on the susceptible wheat cultivar Armada, but of 57% on the partially resistant Rapier. On both cultivars, aphid population curves in the presence and absence of the parasitoid diverged before the first mummies were formed. The number of aphids leaving plants was measured, and was found to increase in the presence of the parasitoid, particularly with Rapier (almost double). Most aphids (about 75%) which left plants fell, and a smaller proportion regained plants when parasitoids were present than when they were absent. A field experiment with Brevicoryne brassicae and natural predation on Brussels sprouts also showed an increase in aphids leaving a less susceptible compared with a more susceptible cultivar.

Molecular analysis of ribosomal DNA from the aphid Amphorophora idaei and an associated fungal organism

Abstract: The ribosomal DNA cistron from the large raspberry aphid, Amphorophora idaei (Hemiptera: Aphididae), has been mapped by restriction analysis. The results showed that the map of A. idaei was similar to those of the previously characterized aphids Schizaphis graminum and Acyrthosiphon pisum. An extra Bgl II site was found in some of the ribosomal DNA intergenic spacer repeats in A. idaei. Using in-situ hybridization to aphid mitotic chromosomes it was demonstrated that probes derived from this region mapped to the pair of X chromosomes and it was therefore aphid in origin. Polymerase chain reaction using conserved rDNA primers also detected significant amounts of a fungal genome in the DNA samples. Microscopic investigation showed that the external surface of A. idaei harboured fungal propagules, hyphae and yeast-like organisms.

Leaf Pubescence Effects in Wheat on Yellow Sugarcane Aphids and Greenbugs (Homoptera: Aphididae)

Abstract: Observations during previous wheat germ plasm evaluation tests indicated that wheat lines with high levels of leaf pubescence are resistant to the yellow sugarcane aphid, Sipha flava (Forbes). Earlier work also suggested the same relationship for the green bug, Schizo phis germanium (Ronni), but the evidence was not as strong. This research studied the effects of leaf pubescence on the two aphid species in greater detail. Trix home length and density measurements were made on second and third leaves from seedlings of six pubescent wheat entries and two nearly glabrous wheat cultivars. Yellow sugarcane aphid and greenbug antibiosis and antixenosis tests were conducted using standard methods for the antibiosis test and new techniques for the antixenosis test. The results showed that leaf surface pubescence is of questionable value in a greenbug; plant resistance program, but it is an effective resistance mechanism against the yellow sugarcane aphid.

Seasonal ecology of Aphidius nigripes (Hymenoptera: Aphidiidae), a parasitoid of Macrosiphum euphorbiae (Homoptera: Aphididae).

Abstract: Aphidius nigripes Ashmead is the most common parasitoid attacking the potato aphid Macrosiphum euphorbiae (Thomas) in eastern North America. In field and insectary experiments, >87% of A. nigripes prepupae successfully overwintered. Spring emergence occurred from mid-April to mid-May, the period during which diapausing M. euphorbiae eggs are hatching on primary hosts. Data obtained from sticky traps indicate that both aphid and parasitoid enter the potato agroecosystem in early June, suggesting that one or several generations occur on primary host plants in the spring. The number of males captured in sticky traps containing virgin females indicated that the parasitoid is present in high numbers throughout the potato growing season. Diapause in A. nigripes was observed from mid-August, when aphids had migrated back to their primary host plants. Our results do not support the hypotheses that inability of the parasitoid to overwinter or host-parasitoid asyncrony explain why A. nigripes does not appear to have any major regulating effect on M. euphorbiae in the potato agroecosystem.

The effect of ant-attendance on the foraging behaviour of the aphid parasitoid Lysiphlebus cardui

Abstract: Ant-attended and unattended colonies of the aphid Aphis fabae cirsiiacanthoidis differ in their quaIity for the aphid parasitoid Lysiphlebus cardui, with ant-attended colonies being of higher quality due to a reduced aphid defence behaviour and a reduced offspring mortality. L. cardui-females responded to this difference in patch quality by an alteration of their foraging behaviour in medium-sized and large colonies but not in small ones. In small colonies, neither patch time allocation, oviposition numbers nor oviposition rate (= number of ovipositions per unit time) differed significantly between unattended and ant-attended colonies

Effect of imidacloprid on nonflight movement of Rhopalosiphum padi and the subsequent spread of barley yellow dwarf virus.

Abstract: The bird cherry-oat aphid (Rhopalosiphum padi) is an important vector of the barley yellow dwarf luteovirus, BYDV-PAV-IL. Insecticides used to reduce the abundance of the vector on small grains can result in an increase in aphid activity and a subsequent increase in disease incidence. The transmission characteristics of viruliferous wingless (nymphs and apterous adults) R. padi after access to oats treated with different rates of imidacloprid, a seed-treatment insecticide, were compared. After access to treated plants, aphid fecundity was reduced and aphids walked and fed atypically and often abandoned the host plant

Influence of predators on population development of Phorodon humuli (Homoptera: Aphididae) on hops

Abstract: Population development of the hop aphid, Phorodon humuli (Schrank), was studied on insecticide-free field-grown hops Humulus lupulus L. in 1992. The influence of predators was assessed using large sleeve cages installed 2 July after aphid immigration ended. Aphid immigration numbers increased geometrically throughout July in cages that excluded predators but increased more slowly and then fell in cages with access by predators. Aphid numbers remained much lower on uncaged plants. Hop cone yields were 97, 381, and 598 g per plant from exclusion-caged, open-caged and uncaged plants, respectively. The main predators were Coccinellidae, Coccinella transversoguttata Faldermann and Hippodamia convergens Guerin-Meneville; Chrysopidae, Chrysoperla carnea (Stephens), C. rufilabris (Burmeister) and Chrysopa spp.; Hemerobiidae, Hemerobius sp.; Anthocoridae, Orius tristicolor (White); Geocoridae, Geocoris sp.; Nabidae, Nabis sp. Predatory Diptera were scarce as were hymenopterous parasitoids. Hops are dioecious, perennial, climbing plants that are grown on a 6-m trellis. They grow best where day length increases rapidly in the spring (45–51°N or S) and do not grow well where days are <14 h long. The hop cones (female flowers) contain pollen-like, lupulin glands. The commercial value of hops lies in the lupulin glands, which contain resins and oils. The resins are used for bittering beer, and the essential oils contribute to beer flavor.

Insecticidal effect of some plant extracts on the cowpea aphid Aphis craccivora Koch (Homoptera: Aphididae)

Abstract: The insecticidal activity of acetone extracts ofCymbopogon citratus (DC) Stapf.,Momordica charantia L.,Zingiber officinale (Ros.),Xylopia aethiopica (Dunal) A. Rich.,Ocimum gratissimum L. andAframomum melegueta (Ros.) K. Schum against the cowpea aphid,Aphis craccivora Koch was investigated.Z. officinale andA. melegueta extracts had the greatest effect in causing mortality ofA. craccivora and inhibiting its reproduction. Extract fromM. charantia caused high nymphal mortality whilst extract fromC. citratus also caused significant nymphal mortality, reduction of life span of adult aphids and inhibition of aphid reproduction.

Intrinsic rate of increase of Lysiphlebus testaceipes Cresson (Hym.; Braconidae), a parasitoid of Aphis gossypii Glover (Hom., Aphididae) at different temperatures

Abstract: Lysiphlebus testaceipes Cresson is one of the candidates for use in a programme for biological control of cotton aphid, Aphis gossypii Glover. Longevity, reproduction, development, and intrinsic rate of increase of L. testaceipes were determined in the laboratory at two different temperatures with cotton aphids as host. The average life-time fecundity of one parasitoid was 128.2 eggs at 20°C and 180.0 eggs at 25°C. Immature mortality was 9.5 and 29.6% at 20 and 25°C respectively. Development from egg to female adult was completed in 12.9 days at 20°C and 9.5 days at 25°C. The lifespan of the females was very short (2.7 and 2.6 days at 20 and 25°C respectively). At 20°C the rm value of L. testaceipes was slightly lower than for cotton aphid. At 25°C the rm values of L. testaceipes and A. gossypii were equal. Lysiphlebus testaceipes might be a suitable natural enemy although rm values are probably too low to be able to overtake an established aphid population.

Russian Wheat Aphid (Homoptera: Aphididae) Population Development and Plant Damage on Resistant and Susceptible Wheat

Abstract: The resistant wheat plant introductions PI 137739 and PI 262660 and the susceptible wheat ( Triticum aestivum L.) cultivar ‘Stephens’ were used to determine the effects of varying Russian wheat aphid, Diuraphis noxia (Kuvdjumov), population densities (0, 10, and 40 aphids per plant) on plant growth and aphid population development. Aphid population development and plant growth were evaluated by destructively sampling plants and aphids at 1, 5, 10, and 15 d after infestation. Plant parameters measured included height, dry weight, and damage. D. noxia feeding damage was determined by counting the number of leaves that were rolled and were chlorotic. The numbers oflive and dead aphids were counted to measure D. noxia population development. D. noxia densities on susceptible ‘Stephens’ wheat were greater than on the resistant accessions at 5, 10, and 15 dafter infestation. The impact of aphid feeding was less on PI 137739 and PI 262660 than on ‘Stephens’ wheat. When the initial D. noxia density was 40 aphids per plant, the total number of aphids produced was higher at days 5 and 10 than the other aphid density, and the reproductive rates were lower on all dates. Plants intially infested with 10 aphids supported larger populations on day 15, because of lower mortality, higher aphid reproductive rates, and fewer dying plants.

Population Dynamics of Woolly Apple Aphid (Homoptera: Aphididae) in West Virginia Apple Orchards

Abstract: Woolly apple aphid, Eriosoma lanigerum (Hausmann), populations were studied in eastern West Virginia from 1985 to 1989. In an unsprayed orchard, peak abundance of arboreal populations was 22-24 colonies per tree in early June each year. Spraying the orchard with a pyrethroid three times during 1989 had little effect on the population behavior, demonstrating the resilience of the woolly apple aphid and its natural enemy guild. Nearly 20% of the aphid colonies in June had syrphid larvae present and parasitism by Aphelinus mali (Haldeman) was > 50% in July. Age structure of arboreal woolly apple aphid colonies varied through the summer with a significant reduction in first instars in July, signaling a return of aphids to the edaphic from the arboreal environment at that time. Samples of arboreal populations were not useful for predicting year-to-year population abundance or the extent of root infestations in a managed orchard. Microhabitat preference of arboreal colonies during the spring was for wound sites and other protected feeding sites on the tree branches and trunk. Leaf axils were the predominant microhabitat (51% of the colonies observed) from the end of May through August. Cicada oviposition sites were also highly preferred, with one orchard having 98% of the colonies in cicada oviposition scars. Woolly apple aphid colonies were observed more often in wounds and protected sites on branches in sprayed orchards and in high density populations than in unsprayed or low density populations. We suggest that these protected sites act as refugia for woolly apple aphid populations in apple orchards.

Effect of trap color on species composition of alate aphids (Homoptera: Aphididae) caught over watermelon plants

Abstract: The species composition and abundance of alate aphids caught in water traps containing green or yellow tiles were compared. Traps were operated in a watermelon field during the spring and autumn growing seasons of 1992. Aphis spiraecola Patch, a vector of watermelon mosaic virus 2 (WMV-2), accounted for 79% of the aphids caught in the spring and 91% of those caught in the autumn in yellow traps. However, this species accounted for only 6% and 11% of aphids caught in green traps in the spring and autumn, respectively. Uroleucon pseudambrosiae (Olive), also a vector of WMV-2, was the most abundant aphid in green traps in the spring but was absent in the autumn. Aphis gossypii Glover (16% of aphids in green traps) and Aphis craccivora Koch (31%) were more common in the autumn than in the spring and may be important vectors of cucurbit potyviruses at that time.