Showing papers on "Aphid published in 1985"

The role of flying aphid vectors in the transmission of cucumber mosaic virus and potato virus Y to peppers in Israel

Abstract: SUMMARY More than 44 species of aphids were trapped by suction during the spring seasons of 1981, 1982 and 1983 over a pepper field at Bet Dagan, Israel. Nineteen species transmitted cucumber mosaic virus (CMV), while seven transmitted potato virus Y (PVY) at least once. Over 80% of the CMV and of the PVY infection among test plants (Capsicum annuum cv. Weindale) exposed to trapped aphids was caused by Aphis citricola and two or three other Aphis species, Myzus persicae and Macrosiphum euphorbiae. Landing rate was determined by comparing the proportion of each species found on green tiles or pepper plants with that found in suction traps. A. citricola was the most common but was found in a much lower proportion on plants than either in flight or on green tiles. Aphis spp. and M. persicae were more than 2–5 times more frequent (relative to other species) on green tiles than in flight. M. persicae and M. euphorbiae, which colonise peppers, were found on peppers at a proportion several times higher than either on green tiles or in the air. The relative importance of the different vector species was calculated by multiplying abundance by the proportion of transmitters and the landing rate. A. citricola and Aphis spp. were responsible for more than 50% of the total transmission of either CMV in 1981 and 1982 and of PVY in 1981. Peaks of CMV infection of bait plants coincided with peaks of transmitters of A. citricola and Aphis spp. caught in suction traps. The significance of these findings in primary infection of peppers with CMV and PVY is discussed.

Plant structure and the foraging success of Aphidius rhopalosiphi (Hymenoptera: Aphidiidae)

Abstract: . 1. A study of searching behaviour on wheat and host preference of Aphidius rhopalosiphi (DeStefani-Perez) is described. 2. Parasitoids divided their time equally between the leaves but spent very little time on the ear. 3. After contact with honeydew or an aphid host, parasitoids were arrested in a particular area and increased the time spent searching. 4. Aphids feeding on the ear were parasitized less successfully, since their position between the grains protected them from parasitoid attacks. 5. A.rhopalosiphi exhibited no preference for Metopolophium dirhodum (Walker) or Sitobion avenae (Fabricius), although the handling time for the latter was significantly longer; this resulted in fewer S.avenae being parasitized when it was abundant. Parasitoids did not switch between hosts in these experiments. 6. As a result of its searching behaviour, A.rhopalosiphi will encounter and parasitize M.dirhodum feeding on the leaves more frequently than S.avenae, which feeds on the ear. This will limit the parasitoid's ability to regulate populations of the cereal aphid S. avenae.

Foraging by the carabid Agonum dorsale in the field

Abstract: . 1. Small arenas in the field were used for observing adult Agonum dorsale (Pont.) foraging in a wheat crop. 2. The carabid showed no significant change in behaviour between low and high aphid density arenas. 3. Individuals foraged nocturnally and spent most of their time on the ground searching for prey. They climbed infrequently and then not high enough to reach aphid aggregations on the ears and flag leaves of wheat. 4. Gut dissection showed that more individuals had eaten aphids in the high aphid density arena than the low. Recording of aphid distribution within the arenas showed that this increase in aphid consumption could be explained by A.dorsale capturing aphids on the ground. Prey availability per unit area was in fact higher on the ground than on the wheat. 5. The contribution of ground-zone predators such as A.dorsale to the control of cereal aphids will be determined by the frequency with which aphids arrive on the ground and the proportion of these which reclimb the wheat and reproduce in the absence of predation.

Role of olfaction in host finding by aphid parasitoidAphidius nigripes (Hymenoptera: Aphidiidae).

Abstract: The olfactory responses of the parasitoidAphidius nigripes Ashmead were investigated with a four-field airflow olfactometer. Female and male parasitoids did not respond to potato plants, the food plant of their host. However, females were strongly attracted by odors from a preferred host,Macrosiphum euphorbiae (Thomas), and also from less preferred hosts such asMyzus persicae (Sulzer) andAphis nasturtii Kalt. Moreover,A. nigripes females responded positively to odors from a nonhost aphid,Rhopalosiphum maidis Fitch. The honeydew produced by these four aphid species was also very attractive to females. Males did not respond to aphids or honeydew but were highly attracted by odors from conspecific female parasitoids.

Effects of pirimicarb, dimethoate and benomyl on natural enemies of cereal aphids in winter wheat

Abstract: SUMMARY The insecticides, pirimicarb and dimethoate are commonly applied to cereal crops in the UK and when this study was begun the fungicide benomyl was also regularly used. The effects of these chemicals on natural enemies of cereal aphids were examined in replicated plots of winter wheat. Benomyl did not affect any of the groups examined but it was applied early in the season (April/May) when most natural enemies were few or absent from the crop. Numbers of carabid beetles, staphylinid beetles and spiders, sampled using pitfall traps and a vacuum net sampler, were all reduced by dimethoate but not by pirimicarb, although these effects were only detected by pitfall traps when the small plots were surrounded by polyethylene barriers to prevent inter-plot movements. Parasitic Hymenoptera were decreased by both insecticides, partly due to direct toxicity and partly to host removal. Data on the aphid predators, Coccinellidae, Syrphidae and Chrysopidae were inconclusive because there were very few in the crop due to the scarcity of aphids. Ways in which pesticides can affect natural enemy populations other than by direct mortality and the dangers associated with routine, prophylactic pesticide applications are discussed.

The identification of an aphid juvenile hormone, and its titre in relation to photoperiod

Abstract: . Whole body extractions from larval and adult apterous forms of Megoura viciae, and from adult Aphis fabae, were analysed for the known insect juvenile hormones (JHs) by a gas chromatography-mass spectrometric method. Low levels of JH III were detected in both aphid species, the first identification of a juvenile hormone from an homopteran insect. Although the mean titre in adult M. viciae is higher in long-day than in short-day reared insects (0.12±0.03 v. 0.04±0.01 ng/g), titres were variable and measurements overlapped. The results are discussed in the context of the hormonal control of aphid polymorphism and the question of identity of homopteran and hemipteran JH.

Development of Autumn Populations of Cereal Aphids., Rhopalosiphum padi (L.) and Schizaphis graminum (Rondani) (Homoptera: Aphididae) and Their Effects on Winter Wheat in Washington State

Abstract: Planting winter wheat in early September is a common practice in much of eastern Washington. A number of agronomic benefits are associated with planting early, but there is also a higher risk of cereal aphids infesting the crop with early planting. Caged experiments were conducted in the field during two crop seasons (1979–1980, 1981–1982) to assess population development and direct feeding effects of two cereal aphids, Rhopalosiphum padi (L.) and Schizaphis graminum (Rondani), on winter wheat planted in early September and infested during the two-leaf, four-leaf, and two-tiller stages of development. Aphids were introduced at a rate of two to four per plant per species and allowed to feed uninterrupted until cold weather ended their activity in November. Data taken were: plant height, heads per plant, root and foliage weights, test weight, and grain yield. R. padi , singly or in combination with S. graminum , was generally more prolific than S. graminum . The largest aphid populations encountered were on wheats infested initially at the two-leaf stage. Injury to wheat was highest where aphid infestations started at the two-leaf stage, intermediate to none at the four-leaf stage, and none at the two-tiller stage. Mixed populations on two-leaf wheats caused the greatest damage, followed by pure populations of R. padi. S. graminum generally caused the least damage.

Association of the root aphid parasitoids Aclitus sappaphis and Paralipsis eikoae (Hymenoptera, Aphidiidae) with the aphid-attending ants Pheidole fervida and Lasius niger (Hymenoptera, Formicidae)

Abstract: The association of two aphidiid parasitoids of a root aphid (Sappaphis piri MATSUMURA) on wormwood, Aclitus sappaphis TAKADA & SHIGA and Paralipsis eikoae (YASUMATSU), with two aphid-attending ants, Pheidole fervida FR. SMITH and Lasius niger (LINNE), was examined experimentally. The oviposition behavior of A. sappaphis was also observed. A single female parasitoid of each species was released on an aphid colony attended by workers (and soldiers) of either of the two ants, and her behavior and reactions when encountering ants and aphids were observed. A. sappaphis females were accepted by almost all P. fervida ants they encountered through mutual antennal tapping, but were attacked by L. niger ants. P. eikoae females were accepted friendly by L. niger ants if the females tested were the same in origin as the ants exposured, but were attacked if different in origin. In the interplay with L. niger ants, P. eikoae females exhibited not only antennal tapping and mouth to mouth contact but also rubbing her leg on the ant. If the female succeeded in riding on an ant of an alien colony and began rubbing, she became accepted by the colony soon after. P. eikoae females were vigorously attacked by P. fervida ants. The oviposition behavior of A. sappaphis was char­ acteristic in mounting on the host aphid and in inserting the ovipositor perpen­ dicularly. Many aphids are attended by the ants. The attendance by the ants is necessary for the true root aphids. The ants not only excavate root chambers for the aphids but also protect them, chasing away potential natural enemies. However, there are some predators and parasitoids which are not treated like strangers by the ants owing to their ant-like appearance and behavior, but rather as nest mates. Two aphidiid parasitoids: Aclitus sappaphis TAKADA & SHlGA and Paralipsis eikoae (yASUMATSU), on a root aphid of wormwood (Artemisia princeps), Sappaphis piri MATSUMURA, are such examples (TAKADA & SHIGA, 1974; TAKADA, 1976). Ac­ cording to our field survey on mountains at Kyoto and 6saka, aphids mummified by Aclitus sappaphis were found only on the plants on which the aphids were attended by colonies of the ant Pheidole fervida FR. SMITH, while the adults of Paralipsis

Spray Timing and Economic Threshold for the Pea Aphid, Acyrthosiphon pisum (Homoptera: Aphididae), on Field Peas in Manitoba

Abstract: Six insecticide regimes were tested between 1981 and 1983 in plots of field peas to determine the optimal time to control the pea aphid, Acyrthosiphon pisum (Harris), and to vary the density of the pest so that a relationship between yield and aphid density could be determined. Aphid populations rebounded rapidly after an insecticide application so that one early application did not protect the crop. Two or more sprays were uneconomical because they did not enhance yield more than a single spray applied as soon as 50% of the crop had young pods. Because the weight of 1,000 seeds provided a more precise measure of aphid damage than weight of seeds per unit area, this measurement was used to relate yield to pest density. The economic threshold was estimated to be 9–12 aphids per sweep when the crop began to flower. This threshold varied from season to season due, in part, to variation in potential seed weight caused by variation in precipitation and heat stress. A relationship between plant samples and sweep samples is presented that showsthe threshold based on sweep samples is equivalent to 2–3 aphids per tip of stem.

The Influences of Predation and Resource Subdivision on the Coexistence of Goldenrod Aphids

Abstract: Two abundant, widely co-occurring aphid species were exposed to natural or reduced predation on goldenrod transplanted as either solitary stems or small, discrete patches of plants. Local interplant movement increased colonization rates for both species, resulting in more and larger aphid colonies on patch plants than on solitary plants. Predator reduction increased aphid densities and produced evidence of increased resource limitation and interspecific competition, although the specific response differed between plant spacing treatments. On solitary plants, predator reduction resulted in a significant negative spatial association between the aphid species. Predator reduction in patches resulted in an increase in one species but a reduction in colony size of the other. In all cases, aphid abundance was negatively associated with plant health. Patterns of spatial association between the aphid species varied with experimental treatments. Aphids on solitary plants at reduced predation were spatially segregated. At reduced predation, aphids on patch plants showed no overall pattern of association. With natural predation, aphids on patch plants were positively associated, as were aphids within natural goldenrod patches in the field. The results show that predation and local interplant movement determine patterns of spatial overlap and mediate the impact of interspecific competition. Although resource limitation can influence aphid dynamics on a single goldenrod shoot, predation and interplant movement are considered to have a greater influence on community structure at a larger spatial scale. These results are discussed in terms of several recent models of predator-mediated coexistence on a subdivided resource.

Spread of barley yellow dwarf virus and relative importance of local aphid vectors in central Washington

Abstract: SUMMARY Data from bioassays of field collected aphids, barley indicator plants exposed to natural conditions, and various types of aphid traps were used to describe the spread of barley yellow dwarf virus (BYDV) in wheat and barley near Prosser, Washington. Bioassays were also used to assess the relative importance of local vector species. Of alate aphids collected from grain in the 1982 and 1983 fall migration seasons, 3.4–14–5% transmitted BYDV. Data from concurrent and post-migration assays of resident aphids (apterae and nymphs) reflected an increase in the proportion of infected plants in the field. Maximum increase in the percentage of viruliferous aphids occurred in late November and December of 1982 and November of 1983. The 1982 increase occurred after aphid flights had ceased for the year, suggesting active secondary spread. Collections in pitfall traps and infected trap plants from November to February confirmed aphid activity and virus spread. Rhopalosiphum padi was the most important vector in central Washington in 1982 and 1983 because of its abundance and relative BYDV transmission efficiency. Metopolophium dirhodum was more winter-hardy than R. padi and equal to R. padi in its efficiency as a vector; however, it was not as abundant as R. padi except during the mild winter of 1982–83, when it was a major contributor to secondary spread. Sitobion avenae may be important in years when it is abundant, but it was only a quarter as efficient as R. padi. Rhopalosiphum maidis was a much less efficient vector than R. padi and it only reached high populations in late autumn barley.

Effects of Single and Combined Infection of Arrowleaf Clover with Bean Yellow Mosaic Virus and a Phytophthora sp. on Reproduction and Colonization by Pea Aphids (Homoptera: Aphididae)

Abstract: Reproduction and colonizing behavior of pea aphids, Acyrthosiphon pisum (Harris), were studied on reproductive arrowleaf clover, Trifolium vesiculosum Savi, using four treatments: healthy, infected with bean yellow mosaic virus (BYMV), infected with a Phytophthora sp. that caused root rot, or infected with both BYMV and the Phytophthora sp. Reproduction of aphids in no-choice experiments was significantly lower on plants in the two treatments with the root rot disease than on healthy or BYMV-infected plants. The highest level of reproduction was observed on healthy plants. Aphid colonization also was lower on fungus-infected plants whether BYMV was present or not. Results of these studies suggest that a complex relationship exists between aphid vectors, virus disease, and fungal root disease in arrow leaf clover. Presence of fungal root rot disease may influence reproduction and movement of alate aphids and epidemiology of aphid-transmitted viruses during both fall and spring periods of alate aphid activity, when plants are in vegetative or reproductive stages, respectively.

Evaluation of aphidoletes aphidimyza (dip. : cecidomyiidae) for control of myzus persicae (hom. : aphididae) in greenhouse and field experiments in the united states

Abstract: Greenhouse and field experiments were conducted to evaluate the potential of inoculative releases of the predatory midge,Aphidoletes aphidimyza (Rondani), on aphid populations on vegetables. The predator was collected from wild and cultivated plants in upstate New York and subsequently reared in the laboratory. Midges from the rearings were released, as pupae, into greenhouses and field plots where plants were infested with aphids, predominately the green peach aphid,Myzus persicae (Sulzer).

Preference of reduviolus americoferus (hemiptera: nabidae) for potato leafhopper nymphs and pea aphids

Abstract: The preference of the nabid, Reduviolus americoferus (L.), for potato leafhopper nymphs, Empoasca fabae (Harris), and pea aphids, Acyrthosiphon pisum (Harris), was examined using functional response models. The nabid exhibited a type-II functional response to each prey. Handling time was much higher for the aphid than for the leafhopper (3.623 vs. 0.211 h). Instantaneous search rates were also higher for the aphid (0.096 vs. 0.020 h−1). A preference index was calculated using the ratio of the instantaneous search rates. The nabid exhibited strong preference for the aphid; when both prey were present in equal numbers, the nabid consumed 3 times as many aphids. The predator did not switch to leafhopper nymphs as the proportion of leafhoppers was increased.

Seasonal occurrence and relative abundance of aphid predators and parasitoids on pubescent potato plants

Abstract: During 2 field seasons, Coccinellidae (primarily Coccinella transversoguttata richardsoni , Coleomegilla maculata , Hippodamia convergens , H. tridecimpunctata , and H. glacialis ) were the most abundant predators on potato hybrids ( Solanum tuberosum × S. berthaultii , F 3 ) with various densities of glandular pubescence. Highly pubescent clones had the highest percentage of predator eggs, while clones with the lowest trichome densities had the highest percentages of immature and adult predators. By comparison, high numbers of aphid parasitoid mummies (primarily Aphidius and Praon spp.) occurred on clones with moderate to high densities of glandular pubescence. During both years, predators and parasitoids were most abundant in late July and August.

Interactions between Cycloneda sanguinea and the brown citrus aphid: adult feeding and larval mortality

Abstract: The number of Toxoptera citricida eaten per day by Cycloneda sanguinea varies in proportion to the densities of the aphid. Functional responses for the predator male and female adults corresponded to that of Holling's type II. C. sanguinea immatures failed to develop to the adult stage when fed either live brown citrus aphid or dry brown citrus aphid meal. However, successful development was achieved with larvae fed dry meal of the aphid Dactinotus ambrosiae (Thomas). This suggests that T. citricida is nutritionally inappropriate for or is toxic to C. sanguinea . Although adults and, initially, larvae of C. sanguinea were voracious predators of T. citricida , the lack of complete development of the larval stage would likely limit its use in pest management of the brown citrus aphid.

Measurement of aphid feeding rates on artificial diets using 3H‐inulin

Abstract: The radioactivity of the honeydew droplets excreted by young apterous adults of the green peach aphid, Myzus persicae, fed on an artificial diet containing 3H-inulin was a reliable measure of the volume of food ingested by the insects, since almost none of the ingested inulin was absorbed and retained by the insects. Zusammenfassung Quantitative Bestimmung der Nahrungsaufnahme von Aphiden auf kunstlicher Diat mit3H-Inulin Junge aptere Adulte von Myzus persicae wurden auf kunstlicher Diat mit oder ohne Zugabe von radioaktiv markiertem Inulin (3H, 100 μCi pro ml; 84.5 cpm pro nl) gehalten. Die Radioaktivitat der Blattlause und ihrer ausgeschiedenen Honigtautropfen wurde in Zeitintervallen nach der Futterung bestimmt. Die Ergebnisse zeigen, dass Inulin nur in geringer Menge von den Blattlausen absorbiert wird, und, dass die Radioaktivitat der ausge schiedenen Honigtautropfen nach Zugabe von 3H-Inulin zur kunstlichen Diat ein verlassliches Mass fur das Volumen der von ihnen aufgenommenen Nahrung ist.

Growth Stages of Field Peas Sensitive to Damage by the Pea Aphid, Acyrthosiphon pisum (Homoptera: Aphididae)

Abstract: Field experiments were conducted by caging groups of pea plants, Pisum sativum L., or pairs of flowers and pods and infesting them with various densities of pea aphid, Acyrthosiphon pisum (Harris). Plants infested up to time of flowering recovered from the damage and their yield was normal. Infestation of plants until flowers opened or longer reduced dry matter production, increased number of flowersand pods shed, reduced number of pods per plant and number of seeds per pod, increased percentage of empty pods, reduced weight of 1,000 seeds and yield of seeds, reduced weight of nitrogen-fixing root nodules, but did not affect protein content of seeds. All flower and pod stages were sensitive to direct feeding damage, but young pods were most susceptible. Feeding damage to flowers and pods was highly correlated with aphid density and young pods infested with four aphids for 4 days showed significant reductions in yield. We conclude that field peas must be protected from pea aphids for a 2- to 3-week period beginning when pods start to form.

Relationship of Aphid (Homoptera: Aphididae) Landing Rates to the Field Spread of Soybean Mosaic Virus

Abstract: The spread of soybean mosaic virus (SMV) by aphid vectors was studied in central Illinois in 1978 and 1979 by monitoring sequentially planted plots of soybeans, Glycine max (L.) Merr. Aphids transmitted SMV from about the third week in June until early September, with maximum spread of the virus occurring at times of greatest aphid abundance. The highest disease incidence (94%) was reached between 3 and 17 August 1978 during heavy flights of Rhopalosiphum maidis (Fitch), a vector of the virus. Field observations and aphid incidence monitored with a Johnson-Taylor suction trap showed that R. maidis settled on soybean plants and remained there overnight. Twelve of the 30 aphid species collected by horizontal ermine lime traps were known vectors of SMV. Two other species collected, Aphis helianthi Monell and Capitophorus hippophaes (Walker), are reported here for the first time as vectors of the virus. Vector species composed 78.0 and 67.2% of all specimens collected in 1978 and 1979, respectively. Myzocallis punctatus (Monell), which composed 9.0% of the aphid specimens collected both years, and Lipaphis erysimi (Kaltenbach), which represented 13.8% of all aphids caught in 1979, did not transmit SMV in laboratory tests. The vector status of 16 other collected taxa is unknown. Aphids in this group represented 6.1 and 14.7% of the specimens collected in 1978 and 1979, respectively.

Hyperparasitoids from Pea Aphid Mummies, Acyrthosiphon pisum (Homoptera: Aphididae), in North America

Abstract: The pea aphid, Acyrthosiphon pisum (Harris), seems under biological control in North American alfalfa, primarily as a result of attacks by parasitoid wasps. Of the 10 known primary parasitoids, an introduced aphidiid, Aphidius ervi Haliday, seems most important in Iowa and elsewhere in the East. Mummies of A. pisum collected in central Iowa during five seasons produced four species of hymenopterous hyperparasitoids, although eight additional species are known from other studies elsewhere. The Iowa species in descending order of abundance were: Asaphes lucens (Provancher) (Pteromalidae), Dendrocerus carpenteri (Curtis) (Mesaspilidae), Alloxysta victrix (Westwood) (Alloxystidae), and Pachyneuron siphonophorae (Ashmead) (Pteromalidae). Keys and descriptive notes are presented to allow identification of all known North American A. pisum hyperparasitoid species in their adult stages, and the known primary and hyperparasitoids by means of evidence left on or in vacated aphid mummies. Hyperparasitoids constituted a smaller proportion (17.8%) of the insects successfully emerging from Iowa A. pisum mummies than expected. Speculations about the reason for the low level of hyperparasitism and its implications for biological control are provided.

Photosynthesis and assimilate transport in potato with top-roll disorder caused by the aphid Macrosiphum euphorbiae.

Abstract: SUMMARY In pot experiments in a glasshouse, top-roll symptoms were induced on potato plants after infestation with the aphid Macrosiphum euphorbiae. Leaves showing symptoms accumulated carbohydrates and tuber yields of affected plants were decreased by 44% compared with controls. Leaves grown after killing the aphids had a normal appearance and sugar contents. Infestation with aphids primarily inhibited carbohydrate transport in the stem and the accumulation of 14C-labelled assimilate in the vascular bundles of the leaves. It is suggested that photosynthesis is inhibited by impaired phloem transport and subsequent accumulation of carbohydrates in the leaves and not by direct mechanical damage caused by the feeding aphid.

Lethal and Sublethal Effects of Aldicarh on Two Potato Aphids (Homoptera: Aphidae): Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas)

Abstract: Field tests conducted in 1982 and 1983 indicated that a minimum of 30 h was required to reach a 50% mortality level when winged green peach aphids, Myzus persicae (Sulzer), are exposed to aldicarb-treated potato plants. Surviving aphids are not expected to be efficient vectors of persistent viruses because of a significantly reduced ability to fly and to probe. Tests done with the common potato aphid, Macrosiphum euphorbiae (Thomas), yielded similar results.

Sampling for adult coccinellids and their numerical response to strawberry aphids (coleoptera:coccinellidae: homoptera:aphididae)

Abstract: Searching for adult coccinellids in large cages placed over sections of strawberry fields produced an average of 10 times as many coccinellids per metre of row as a relative method of sampling. Methods of converting relative indices to absolute indices of abundance were found. Results suggest that the frequently observed slow increase in abundance of aphid predators in response to increasing aphid abundance may be an artifact resulting from using relative indices of abundance that make no correction for the effects of hunger on predator activity. Calibrating the samples shows that numbers of adult coccinellids follow the trend of aphid abundance closely enough that coccinellid numbers may be predictable.

European Earwigs (Dermaptera: Forficulidae) Fail to Control Apple Aphids on Bearing Apple Trees and Woolly Apple Aphids (Homoptera: Aphididae) in Apple Rootstock Stool Beds

Abstract: Insectary-reared and wild European earwigs, Forficula auricularia L., provided with artificial daytime retreats on bearing apple trees infested with apple aphids, Aphis pomi DeGeer, failed to slow aphid population growth. The difference between this result and earlier success on nonbearing apple trees is not explained. Caged earwigs damaged a few apple fruits by feeding at the calyx end, but no damage to fruit and only minimal damage to leaves was observed when earwigs were allowed free movement. Earwigs released and caged on apple rootstock stool beds after suppression of apple aphids by insecticide treatment prevented resurgence of apple aphids but had no apparent effect on infestations of woolly apple aphids, Eriosoma lanigerum (Hausmann).

Impact of Natural Enemies on the Blackmargined Pecan Aphid, Monellia caryella (Homoptera: Aphidae)

Abstract: Populations of the blackmargined pecan aphid, Monellia caryella (Fitch), were studied in the field, using sleeve cages to manipulate aphid populations and their natural enemies. Each cage enclosed 10 compound pecan leaves. M. caryella populations were observed to increase rapidly within closed cages from 1 aphid per leaf to 50 aphids per leaf at any time throughout the summer. Opening sleeve cages to allow natural enemies access to the increasing aphid populations always resulted in the decline of aphid numbers compared to their activity in adjacent closed cages. Release of 1 chrysopid or 1 coccinellid larvae per 10 leaves when aphid populations were increasing in closed cages always resulted in the prevention of an aphid outbreak. Laboratory feeding studies of selected chrysopid and coccinellid predators showed average feeding rates of between 25 and 60 aphids per day. Results indicate that natural enemies, particularly predators, play an important role in maintaining M. caryella populations at low levels in the field.

Seasonal changes in the within-crown distribution of the aphid Cinara pini on Scots pine

Abstract: The within-tree distribution of Cinara pini L. was studied on five, 18-yr-old Scots pine trees at about weekly intervals throughout the growing season. Aphid emigration and mortality from natural enemies were reduced by placing cages around the trees. Aphids were aggregated on the young internodes in the top parts of the crown during early summer, and on the older internodes in the lower parts of the crown during late summer. Seasonal changes in the within-tree distribution of the aphids are discussed in relation to the phenology of translocation streams in the tree. Both quantitative and qualitative changes take place in the phloem sap of Scots pine during the course of the growing season which correlate well with changes in aphid distribution patterns.