Showing papers on "Aphididae published in 1986"

Predator density manipulation and its effects on populations of Rhopalosiphumpadi (Horn.: Aphididae) in spring barley

Abstract: SUMMARY Experiments were carried out in 1981-83 to assess the impact of polyphagous predators (e.g. Carabidae, Staphylinidae and Araneae) on populations of cereal aphids in spring barley in Sweden. Barriers were erected around mid-field and field-edge plots at different times during the aphids' establishment phase in order to manipulate the predation pressure during the aphid pre-peak period; predators were emigrating from field boundaries. Rhopalosiphum padi was the dominant species of cereal aphid in 1981 and 1982, and was abundant in both years. Reduction of the predation pressure resulted in R. padi populations that were two to six times larger compared with those in unenclosed control plots. Aphid populations were much larger when the predation pressure was reduced earlier in June than when this was done later, in both years, since late erection of barriers excludes fewer predators because most had already entered the enclosed areas. In 1983, R. padi and Sitobion avenae were equally common but occurred in low numbers, and the effects of reducing the predation pressure were less obvious. Bembidion spp. (B. lampros and B. quadrimaculatum) and linyphiid spiders were the most abundant predators during the early establishment phase of aphid populations in each year, and significant inverse correlations were found between peak numbers of R. padi per shoot and numbers of predators from these taxa in 1981 and 1982. Similar relationships were found between total aphids and numbers of Staphylinidae, B. quadrimaculatum and Coccinella septempunctata in 1983. It was concluded that differences between the manipulated numbers of polyphagous predators caused the observed differences in peak population levels of R.padiin 1981,1982 and to a lesser extent, 1983. Apparent levels of parasitism and fungal disease were low during the pre-peak period. Aphid specific predators, abundant after the peak, were considered partly responsible for the decline of aphid populations each year. The results are compared with those from similar experiments elsewhere with S. avenae and Metopolophium dirhodum in winter wheat. Reasons why the effects of polyphagous predators are greater, and occur over a much shorter period of time in Sweden are discussed.

Control of cereal aphids in winter wheat by natural enemies: aphid-specific predators, parasitoids and pathogenic fungi

Abstract: SUMMARY Winter wheat fields on two farms in West Sussex were sampled in 1980 and 1981 for cereal aphids and their natural enemies. The grain aphid, Sitobion avenae was present in all 19 fields examined, but in no case did the populations increase to densities liable to cause economic damage. The observations strongly suggest that aphid population growth was stopped by aphid-specific predators, hymenopterous parasitoids and fungal pathogens. In two fields in 1980, S. avenae population densities approximately equalled five aphids per ear at flowering, the threshold at which insecticide application is recommended in the UK, but numbers were then reduced by natural enemies, mainly aphid-specific predators. In three fields in 1981, S. avenae would probably have exceeded the spray threshold had natural enemies not intervened in late May.

Field assessment of the relative importance of different aphid species in the transmission of potato virus Y.

Abstract: Flying aphids were trapped throughout the summer on a vertical net downwind of a plot of PVY-infected potato plants. Of 6769 individuals caught, 165 transmitted PVY to tobacco test seedlings. Of 119 species or species groups caught, 20 were found to be vectors of which nine had not been recorded previously.Brachycaudus helichrysi, Myzus persicae, Phorodon humuli andAphis species accounted for 90% of transmissions andB. helichrysi alone for 52% of transmissions. The prospects of using this information to assess the amount of virus spread in a potato crop and of forecasting the timing and abundance of the main vectors are discussed.

Morphological adaptation to host plants in uroleucon (homoptera: aphididae)

Abstract: The morphology of host-specific Old World Uroleucon (Homoptera: Aphididae) species is related to features of their host plant species (Asteraceae and Campanulaceae) by canonical correlation analysis. Aphid species on pubescent host species have longer rostra and shorter hind tarsi, adaptations for feeding and walking on hirsute surfaces. Also, aphid species on taller hosts are larger. The positive relationship between rostrum length and host trichome density is further supported by simple regression analyses on two species complexes. Regression parameters differ between groups, suggesting different responses to different trichome types. This morphological adaptation involves characters used extensively by taxonomists and could result in convergence obscuring phylogenetic relationships of herbivore taxa and, particularly, the relation of herbivore phylogeny to host phylogeny.

Escape responses of the pea aphid, Acyrthosiphon pisum (Harris) (Homoptera:Aphididae): influence of predator type and temperature.

Abstract: The escape responses exhibited by pea aphids were examined at three different temperatures, 15, 20, and 25 °C, using two different predators: syrphid larvae and coccinellid beetles. Coccinellid beetles foraged more vigorously at higher temperatures resulting in greater vibrations on the host plant as they searched for aphids. Foraging rates for syrphids were slower by comparison and did not vary with temperature. We found that most aphids dropped off the host plant when confronted by coccinellid beetles, especially at higher temperatures, and backed up when confronted by syrphid larvae regardless of temperature. We conclude that individual aphids do not have characteristic escape responses, but rather the response adopted depends in part on the foraging rate and species of predator.

Glandular trichomes of Solanum neocardenasii confer resistance to green peach aphid (Homoptera: Aphididae)

Abstract: Botanical seed of a newly described wild potato species, Solanum neocardenasii Hawkes & Hjerting, was collected in central Bolivia. Foliage of S. neocardenasii bears type A and type B glandular trichomes that entrap aphids in a manner similar to that of the highly aphid-resistant species, S. berthaultii Hawkes. Initiation of probing by the green peach aphid, Myzus persicae (Sulzer), on S. neocardenasii was delayed compared with that on S. tuberosum . Feeding rates on the two species were comparable once probing was initiated. Reduced aphid survivorship on S. neocardenasii compared with a susceptible S. tuberosum cultivar was associated with presence of extremely large droplets of adhesive type B exudate. Trichome exudate of S. neocardenasii darkened and hardened on aphid tarsi, labia, and antennae in a manner visually similar to S. berthaultii exudate. These findings indicate that S. neocardenasii is an additional source of trichome-based resistance to green peach aphid and may be of value to potato breeding programs attempting to expand the genetic base of host plant resistance to insects.

Stimulation of reproduction of the green peach aphid (Homoptera: Aphididae) by azinphosmethyl applied to potatoes

Abstract: Apterous green peach aphids, Myzus persicae (Sulzer), collected from potato plots treated with azinphosmethyl, when caged on either treated or nontreated foliage, produced 20–30% more offspring than aphids that were not exposed to the insecticide. The increase in fecundity resulted directly from the action of the insecticide on the reproduction of the aphids rather than indirectly from changes induced by the insecticide in the host potato plants. Suitability of plants to support populations of aphids varied within and between seasons. Applications of azinphosmethyl did not alter ability of the plants to support aphid populations.

Ecological genetics of host plant exploitation in the green peach aphid, Myzus persicae

Abstract: The ecological consequences of genetic variability in host plant exploitation of Myzus persicae (Hemiptera, Aphididae) were studied in several agro-ecosystems, differing in crop plant heterogeneity. An analysis of aphid populations sampled from sugar beet, potatoes, and lettuce revealed changes in the frequency distribution of aphid clones according to their respective host plant adaptations. The spatial unit of differentiation was below an average field size of 3–5 hectares and a differentiation could be found in the centre of potato and sugar beet fields but not at the edge of the fields. On a temporal scale, the differentiation of populations is transitory even on a large-scale basis of highly specialized cropping areas. The ecological parameters of differentiation are discussed with special reference to agro-ecosystems and integrated pest management. Increasing the genetic heterogeneity of crop fields may help to reduce population outbreaks. Zusammenfassung Okologische Genetik der Wirtsplanzennutzung der Grunen Pfirsichblattlaus, Myzus persicae Die okologischen Konsequenzen genetischer Variabilitat in der Wirtspflanzennutzung von Myzus persicae (Hemiptera, Aphididae) wurden in mehreren Agro-Okosystemen untersucht, die sich in der Kulturpflanzenheterogenitat unterscheiden. Eine Analyse von auf Ruben, Kartoffeln und Salat siedelnden Populationen zeigte eine genetische Differenzierung in Wirtspflanzen-angepaste Feldpopulationen. Die raumliche Einheit solcher Differenzierungen liegt unterhalb einer Feldgrose von 3–5 ha. Eine Differenzierung konnte hier in der Mitte der Felder aber nicht am Rand festgestellt werden. Aus zeitlicher Sicht ist die Differenzierung selbst in grosraumigen, spezialisierten Anbaugebieten nur vorubergehend feststellbar. Die okologischen Parameter der Differenzierung werden besonders in Hinsicht auf die integrierte Schadlingsbekampfung in Agro-Okosystemen diskutiert. Eine Erhohung der genetischen Hetero-genitat von Kulturpflanzenbestanden kann moglicherweise zu einer Verringerung von Blattlaus-Massenvermehrungen beitragen.

Hosts and Habitats of Parasitoids (Hymenoptera: Aphidiidae) Implicated in Biological Control of Apple Aphid (Homoptera: Aphididae)

Abstract: No parasitoids able to complete development on apple aphid, Aphis pomi De Geer, were found in north-central Washington. However, several aphidiid species oviposited in A. pomi and developed to last instars before dying. Of these, Praon unicum Smith and Lysiphlebus testaceipes (Cresson) were found attacking A. pomi in apple orchards. P. unicum was most active in spring and parasitized a high percentage of apple aphids in some orchards. L. testaceipes was more prevalent during summer and apparently contributed little to apple aphid control. Hosts and habitats of these and two other species, Praon occidentale (Baker) and Diaretiella rapae (M'Intosh), were investigated. Winter and spring generations of P. unicum were found on apple, peach, and hawthorne. The summer generation was found mainly on hawthorne, weeds, and grasses. Aphid hosts of P. unicum on apple included Dysaphis plantaginea (Passerini), Rhopalosiphum insertum (Walker), and Nearctaphis bakeri (Cowen). Myzus persicae (Sulzer) was the major host on peaches in winter and spring and on weeds during summer.

The activity of parasitoids (Hymenoptera: Braconidae) of cereal aphids (Hemiptera: Aphididae) in winter and spring in southern England

Abstract: Indirect and direct measures of parasitoid activity were taken in grassland and autumn-sown cereals in southern England between 1979 and 1981. Studies of anholocyclic aphid populations in the winter months were followed through to parasitism of the main pest species, Sitobion avenae (F.), during the period of population increase in April and May. Aphidius spp. parasitized artificially-established colonies of cereal aphids in ryegrass in every month between December and May of both seasons, but there was no Aphidius activity until March-April in winter cereals sown early enough to receive an autumn input of aphids and parasitoids, apparently due to the small amount of physiological time that accumulates before temperatures drop in the winter months. A. rhopalosiphi De Stefani Perez and A. picipes (Nees) were completely dominant over other parasitoid species in the winter and spring period. Natural populations of Aphidius adults and parasitized aphids were low (<2/m2) in both winters, and percentage parasitism of S. avenae measured by dissection in March and April did not exceed 11·7%. Rates of S. avenae parasitism in many winter wheat fields peaked in May, before the peak and rapid decline in aphid populations. The significance of winter and spring parasitoid activity to the survival of the parasitoid and effects on pest aphid peaks are discussed.

Seasonal abundance of the pea aphid, acyrthosiphon pisum (homoptera: aphididae), in manitoba field peas

Abstract: Pea aphids, Acyrthosiphon pisum (Harris), were sampled from 1980 to 1983 in field peas, Pisum sativum (L.), in Manitoba. Sweep and foliage samples were taken in commercial fields and plots. Aphids were found in late May or early June soon after the crop emerged, but populations were low throughout June. Populations increased in July, when the crop was flowering and producing pods, and peaked in the latter half of July or early August in 3 of the 4 years, when pods were maturing. Populations decreased rapidly after the peak, as the plants senesced. In 1980, a drought year, aphid densities were low and the populations peaked in the middle of August. From 1981 to 1983, densities exceeded the economic threshold in all commercial fields and all but one of the plots that were sampled.

Summer populations of the cereal aphid Metopolophium dirhodum (Walker) on winter wheat: three contrasting years

Abstract: (1) Summer populations of the rose-grain aphid, Metopolophium dirhodum (Walker), were monitored in Bedfordshire (1978-80). Population density, age structure and distribution were studied by detailed sampling, and immigration and population development in different years are compared. (2) Population growth rates (intrinsic rates of increase and multiplication rates per week) are compared and contrasted with development temperatures. (3) The rate of spread of the population (the percentage of tillers infested related to aphid density) was the same function in each year. (4) Seasonal changes in feeding site distributions are given for 1979. The highest percentage of the total population occurred on flag leaves, and adaxial (upper) leaf surfaces were favoured. (5) Dislodgement of aphids by wind gusts appeared to be an important mortality factor. Rainfall (alone) was not a factor. Parasitism was greatest in 1978, but did not appear to be a controlling factor. Coccinellid predation appeared to limit population growth in 1978, and to severely reduce population density in 1980. (6) Maximum aphid densities varied enormously. The determining factors were growth regulated by temperature, in opposition to wind gusts, predators and parasites.

Predation by Cheilomenes vicina [Coleoptera: Coccinellidae] on the cowpea aphid, Aphis craccivora [Homoptera: Aphididae] : Effect of prey stage and density

Abstract: Consumption of larvae and females ofAphis craccivora Koch by 1st and 4th larvae and adults ofCheilomenes vicina (Muls.) was studied under fluctuating temperature (24–30°C). The early aphid instars were consumed in significantly greater numbers than later instars and females. The feeding rates ofC. vicina were significantly positively correlated with the population density of prey. The number of prey consumed daily by each predator stage tested, increased more steeply at lower than at higher prey densities, exhibiting thus the type 2 functional response

The role of Diaeretiella rapae (M'cintosh) (Hymenoptera: Braconidae) in the population control of the cabbage aphid, Brevicoryne brassicae L. (Hemiptera: Aphididae) in Kenya

Abstract: Diaeretiella rapae (M'cintosh) was the only parasitoid of the cabbage aphid, Brevicoryne brassicae L., during studies reported here.Percentage parasitism of B. brassicae ranged from 27.1 to 76.1% in studies carried out around Nairobi area during 1978/79. It was highest during the month of September, when the aphid population density had reached maximum, and lowest in May when aphid numbers were low. High parasitism coincided with a decline in aphid population.Because of these high levels of parasitism and other attributes of the parasitoid, it was concluded that D. rapae played a significant role in suppressing populations of B. brassicae and should be taken into consideration in any control programme aimed at protecting brassica crops against aphid pests in Kenya.

Evaluation of Phenology Models Using Field Data: Case Study for the Pea Aphid, Acyrthosiphon pisum , and the Blue Alfalfa Aphid, Acyrthosiphon kondoi (Homoptera: Aphididae)

Abstract: Four phenology models that accumulate development based on daily temperature are evaluated for their ability to simulate and predict development of the pea aphid, Acyrthosiphon pisum (Harris), and the blue alfalfa aphid, A. kondoi Shinji, in the field. Although the most complex of these models fits the development data best, the simpler models prove to be better at prediction. This result has important implications for the use of phenology models in the field.

Relationships of yellow sugarcane aphid (Homoptera: Aphididae) density to sorghum damage

Abstract: Yield reductions, maturity delays, and stunting due to injury to seedling sorghum by yellow sugarcane aphid (YSCA), Sipha flava (Forbes), were investigated in field trials in Central Texas in 1983 and 1984. Regression analysis indicated that yield reductions were significantly related to both YSCA density and plant discoloration symptom ratings. Per panicle yield reduction of plants infested when they averaged 4–6 cm tall was 1.1 g or 2.5% per aphid and 6 g or 15% per unit increase in discoloration rating. Plant height was reduced 2.7% per aphid or 6% per unit increase in discoloration rating. Maturity was delayed 0.5 days per aphid and 1.5 days per unit increase in discoloration rating. Tolerance to YSCA injury increased greatly with very slight increases in plant height. Seedling sorghum plants 3.5, 4.5, and 5.5 cm tall infested with an average of six aphids per plant had mean yield losses of 67, 30, and 7% respectively.

The Russian wheat aphid; Diuraphis noxia (Mordvilko); Population dynamics and effect on grain yield in the western Orange Free State

Abstract: The newly emerged crop was colonized primarily by D. noxia apterae from volunteer wheat. The infestation was spread by apterae migrating from plant to plant. There were indications that wind assisted the process. More persistent infestations caused significant loss in grain yield, particularly if colonization of the flag and second leaf occurred. There was no evidence to suggest that an aphid transmitted pathogen was associated with reductions in yield.

The use of incidence counts for estimation of cereal aphid populations. 3. Population development and the incidence-density relation.

Abstract: The relation between the population density of the cereal aphid,Sitobion avenae, and the proportion of wheat tillers infested is examined. Three of the six models considered require the assumption that the aphids' spatial configuration can be described by a single statistical distribution; as this is not true forS. avenae these models are unsuitable. When the other three models were applied to field sample data, only that of Nachman (1981) yielded a regression equation that remained constant throughout the development of the aphid population.

Fall and early spring aphid (Homoptera: Aphididae) populations affecting wheat and barley production in Virginia

Abstract: Effects of fall and early spring populations of the grain aphids Schizaphis Graminum (Rondani), Rhopalosiphum padi (L.), R. maidis (Fitch), and Microsiphum avenae (F.) on winter wheat and winter barley production were evaluated in field trials and in state cultivar trials in eastern Virginia. Data collected in field tests where aphids were controlled with systemic insecticides (disulfoton, carbofuran, or dimethoate) revealed significant yield increases compared with the untreated plots in 1980 and 1983 when aphid populations at time of application were >20 per 0.3 m of row. Barley yellow dwarf virus (BYDV) infection was>10% of total untreated plot area in 1980 and 1983. No reductions in grain yields were noted in 1981, 1982, and 1984, years when aphid populations were very low (<1.3 per 0.3 m of row) and no BYDV symptoms were present. Yield increases were observed in the wheat and barley cultivar trials in 1980 and 1983 when early spring applications of disulfoton 15 G were made; no differences were noted in 1981 and 1982 when the same insecticide application was made. ‘Tyler’ wheat had relatively high yield increases in the treated plots during all four seasons, even when aphid populations were very low. ‘Massey’ had lower yield increases in the treated plots than most of the 30 cultivar entries each year. ‘Barsoy’ and ‘Maury’ barley also had lower yield increases in the treated plots than the other 20 cultivars being evaluated in 3 of the 4 years tested.

Host-plant oligosaccharins in the honeydew ofSchizaphis graminum (Rondani) (Insecta, Aphididae)

Abstract: The honeydew of the aphidSchizaphis graminum (Rondani) contains hetero-oligosaccharides (mol. wt>2200 D) having neutral sugar and uronic acid compositions similar to the pectic substances of the host plant,Sorghum biocolor (L.) Moench. These oligosaccharides are pectic fragments which result from the depolymerization of pectic substances in the phloem by aphid salivary polysaccharases.

Interactions between aphid infestation and plant growth and uptake of nitrogen and phosphorus by three leguminous host plants

Abstract: The effects of cowpea aphids (Aphis craccivora Koch) and pea aphids (Acyrthosiphon pisum (Harris)), both Homptera: Aphididae, on nitrogen (N) and phosphorus (P) uptake by and growth of cowpea (Vigna unguiculata (L.) Walp. cv. Caloona), broad bean (Vicia faba L. cv. Aquadulce), and garden pea (Pisum sativum L. cv. Victory Freezer) seedlings were investigated. After 10 days of aphid infestation, all leaf areas were significantly lower in infested plants, and plant dry weight, mean relative growth rate, and unit leaf rate were significantly lower in all plant–aphid combinations except for pea – pea aphids. The mean leaf area ratio was the same for infested and control plants indicating that infested plants did not reallocate their assimilate resources in response to aphid feeding. The accumulation of N and P as a percentage of plant dry weight did not differ between control and infested plants and was specific to the species examined. However, control plants all had greater absolute amounts of N and P after ...