Showing papers on "Aphididae published in 1989"
TL;DR: By quantifying the per capita population growth rates for aphid colonies of differing sizes, it is found that individual aphids benefited by being clumped together, but a predator—exclusion experiment indicated that clumping was beneficial to aphids only in the presence of predators.
Abstract: It has been suggested that by clumping together, even defenseless prey may reduce their chances of being consumed by a predator. However, the advantage of clumping to prey may be negated by a strong aggregative response of predators to prey clusters. We studied the balance of forces that determine the advantage or disadvantage of clumping to prey in one particular case: the interaction between the aphid Aphis varians (Homoptera: Aphididae) and its predator Hippodamia convergens (Coleoptera:Coccinellidae). Aphid movement was congregative, i.e., aphids tended to stay within clumps of conspecifics. Furthermore, by quantifying the per capita population growth rates for aphid colonies of differing sizes, we found that individual aphids benefited by being clumped together. However, a predator—exclusion experiment indicated that clumping was beneficial to aphids only in the presence of predators. To gain a mechanistic understanding of why aphid congregation reduced predation risk to individuals, we examined the behavioral response of predators to aphid density. Predators exhibited a strong aggregating response: large colonies of aphids were attacked by more predators than were small colonies. In addition, ladybird feeding rate increased with increasing colony size. The total number of prey taken from colonies by predators, however, could not keep pace with the increase in aphid colony size, and thus the risk of predation to individual prey was "diluted" by prey numbers.
237 citations
TL;DR: It is postulated that the great abundance of the primary host of R. padi, bird cherry, and the spring planting of cereals in colder climates such as in Finland are major factors contributing to the differences in pest status of this aphid between Britain and in Scandinavia.
Abstract: The biology and pest status of Rhopalosiphum padi (L.) in Europe are critically reviewed. New data are presented and the temporal occurrence of the aphid and its host-plants considered. In Britain, R. padi is a pest mainly because of its ability to transmit virus diseases, in particular barley yellow dwarf virus. In other European countries, especially in Scandinavia, R. padi is a pest in its own right. Predator and parasite complexes in Britain and Finland are compared and contrasted. The occurrence of R. padi as a pest of cereals in Europe is compared with that of Sitobion avenae (F.) and Metopolophium dirhodum (Walker). It is postulated that the great abundance of the primary host of R. padi, bird cherry (Prunus padus), and the spring planting of cereals in colder climates such as in Finland are major factors contributing to the differences in pest status of this aphid between Britain and in Scandinavia.
112 citations
TL;DR: Resistance reactions of backcross, F2 and F3 seedlings in greenhouse tests indicated that resistance in each line is controlled by a single dominant gene and that these genes are independently inherited.
Abstract: Studies were done to determine the inheritance of resistance in two wheat ( Triticum aestivum L.) lines, PI 137739 and PI 262660, that were previously identified as resistant to Russian wheat aphid, Diuraphis noxia (Mordvilko), and to establish whether resistance was governed by the same or different genes. The resistant lines were crossed with the cultivars ‘Tugela’ and ‘Betta.’ Resistance reactions of backcross, F2 and F3 seedlings in greenhouse tests indicated that resistance in each line is controlled by a single dominant gene and that these genes are independently inherited. The gene symbols Dn 1 and Dn 2 are recommended for the resistance genes in PI 137739 and PI 262660, respectively.
110 citations
TL;DR: It should be feasible to develop a seed potato pest management program for Minnesota based on foliar sprays alone, and steep gradients of PLRV infection with distance from infector units indicated short-distance movement of vectors and suggested that apterae were of prime importance inPLRV spread.
Abstract: We compared importance of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphormae (Thomas), apterae and alatae in secondary spread of potato leafroll virus (PLRV) and the control achieved with foliar sprays alone to that of conventional practice using a soil systemic. Density gradients of apterae were produced by application of insecticidal sprays. Spread of PLRV from centrally located infector units was monitored in foliage serologically. PLRV infection ranged from 23.7 to 74% in 1985 and 12.3 to 77.2% in 1986. PLRV infection was significantly correlated with cumulative green peach aphid and with potato aphid apterae-days both years. Green peach aphid was more abundant than potato aphid and alatae were few both years. At all distances (1-5 m) from infector units, infection across rows was 38.7-60.6% of that within rows. Steep gradients of PLRV infection with distance from infector units indicated short-distance movement of vectors and suggested that apterae were of prime importance in PLRV spread. Check plots without a PLRV source and not augmented with green peach apllid (1986 only) had a final PLRV incidence of 1.5%, indicating only minor invasion of these plots by viruliferous alatae. Weekly application of methamidophos sprays reduced PLRV incidence to that in plotstreated with aldicarb at planting and weekly methamidophos sprays. It should be feasible to develop a seed potato pest management program for Minnesota based on foliar sprays alone.
101 citations
TL;DR: It is shown that ants are a Limited and Limiting resource for a tended aphid species and that fireweed aphids compete with intra-and interspecific aphid neighbors for the services of ant mutualists.
Abstract: We present two years of experimental and descriptive data which support the hypothesis that fireweed aphids (Aphis varians) compete with intra-and interspecific aphid neighbors for the services of ant mutualists (Formica fusca and F. cinerea). Specifically, we have shown that ants are a Limited and Limiting resource for a tended aphid species. First, the presence of heavily aphid-infested fireweed shoots significantly reduced the number of ants tending neighboring conspecific populations on fireweed. Second, the presence of ant-tended aphids (Cinara sp.) on Engelmann spruce significantly reduced the number of ants tending neighboring aphid populations on fireweed. Third, the number of ants, and not just the presence of ants, had a significant effect on the fitness of fireweed aphids. Aphid populations tended by three or more F. cinerea exhibited significantly higher probabilities of persisting and growing through time than colonies tended by one or two ants. Aphid populations tended by F. fusca had a significantly higher probability of growing when tended by three or more ants only if they had declined in size during the previous week.
100 citations
TL;DR: A method for determining the proportion of those aphids caught on the net that had landed and probed in the crop is suggested and the use of such information to improve a model of virus spread is discussed.
Abstract: Harrington et al. (1986) assessed the relative efficiency with which different aphid species transmitted potato virus Y (PVY), by trapping flying aphids on a net downwind of a plot of infected potatoes and transferring the aphids to tobacco seedlings. This paper reports the extension of that work over further seasons and identifies three more vector species,Aphis sambuci, Myzus cerasi andDysaphis sp. A method for determining the proportion of those aphids caught on the net that had landed and probed in the crop is suggested. The use of such information to improve a model of virus spread is discussed.
69 citations
TL;DR: Studies were done to determine the level of antibiosis and tolerance in three resistant wheat, Triticum aestivum L., lines, to Diuraphis noxia (Mordvilko), a serious pest of wheat in South Africa.
Abstract: Studies were done to determine the level of antibiosis and tolerance in three resistant wheat, Triticum aestivum L., lines, PI 262660, PI 137739, and PI 294994, to Diuraphis noxia (Mordvilko), a serious pest of wheat in South Africa. Nymphal production was lowest on PI 262660, followed by PI 137739 and PI 294994. The mean production of nymphs per adult aphid over 21 d on PI 262660, PI 137739, and PI 294994 was, respectively, 40.0, 55.1, and 66.9% of that on the susceptible cv. Betta. In the tolerance test, the plant height and dry mass of PI 262660 were significantly less affected than the other entries. PI 137739 and PI 294994 were as severely affected as the susceptible entries.
59 citations
TL;DR: In this article, a study was conducted to determine whether the wild tomato species, Lycopersicon pennellii (Corr.) D'Arcy, would be useful as a source of potato aphid resistance for tomato.
Abstract: The potato aphid, Macrosiphum euphorbiae Thomas, is an important pest of tomato, Lycopersicon esculentum Mill., because it transmits tomato viruses and directly reduces crop yields by its feeding. This study was conducted to determine whether the wild tomato species, Lycopersicon pennellii (Corr.) D'Arcy, would be useful as a source of potato aphid resistance for tomato. Type IV trichome density and aphid resistance were assessed in six generations (P1, P2, F1, F2, BC1P1, and BC1P2) from crosses between L. pennellii (LA 716) and two tomato cultivars, New Yorker and VF Vendor. Weighted leastsquares were used in joint scaling tests to estimate the relative importance of gene effects on type IV trichome density and potato aphid resistance of the hybrids. A simple additive-dominance model adequately explained the variation in type IV trichome density. Models which included digenic epistatic effects were required to explain the variation in aphid resistance. Standard unit heritability estimates of aphid resistance in the backcross to L. esculentum were obtained by regression of BC1F2 off-spring families on BC1F1 parents. Regression coefficients and heritability estimates varied between years with the level and uniformity of the aphid infestation. In the 1985-1986 growing seasons, when aphid infestations were uniform, aphid resistance exhibited a moderate level of heritability (29.8% ± 14.1% and 47.1% ± 11.5% in New Yorker and VF Vendor backcross populations, respectively). The non-uniform aphid infestation of 1984 resulted in lower heritability estimates in the 1984-1985 growing seasons (16.1% ± 15.7% and 21.9% ± 14.8% in the New Yorker and VF Vendor backcross populations, respectively). Selection for potato aphid resistance would probably be most efficient if it were delayed until gene combinations are fixed in later generations, because of the large epistatic effects and the low heritability of this trait in seasons with variable aphid infestations.
45 citations
TL;DR: In this article, a Rubiaceae-feeding aphid, Acyrthosiphon nipponicus, is seldom attacked by the ladybird beetle Harmonia axyridis, and a potent deterrent against the beetle was isolated from the aphid and identified as paederoside, an iridoid glycoside originating in the host,Paederia scandens.
Abstract: A Rubiaceae-feeding aphid,Acyrthosiphon nipponicus, is seldom attacked by the ladybird beetle,Harmonia axyridis. A potent deterrent against the beetle was isolated from the aphid and identified as paederoside, an iridoid glycoside originating in the aphid's host,Paederia scandens. The iridoid content was as high as 2% of the intact body weight, and a large portion was found in the cornicle secretion.
45 citations
TL;DR: Results with these and other compounds are discussed in terms of antifeedant activity against Myzus persicae, their effects on resistant aphids and the evidence for decŕease in virus spread by aphids in laboratory and field is discussed.
Abstract: The probing and feeding behaviour of aphids can result in uptake of viruses from infected plants and subsequent transmission to healthy plants. It is possible to interfere with virus acquisition and transmission by influencing aphid host-selection and feeding behaviour with antifeedant chemicals. Published work is reviewed and new work is presented in this paper. The two most successful classes of antifeedants against aphids are (a) compounds derived from the aphid alarm pheromone and (b) plant-derived antifeedants such as the sesquiterpene (-)-polygodial. Results with these and other compounds are discussed in terms of antifeedant activity against Myzus persicae, their effects on resistant aphids and the evidence for decŕease in virus spread by aphids in laboratory and field.
44 citations
TL;DR: Release of the chrysopid, Chrysoperla cornea Stephens, reduced significantly the numbers of apterous adults and nymphs of the green apple aphid, Aphis pomi DeGeer, on dwarf apple trees.
Abstract: Release of the chrysopid, Chrysoperla cornea Stephens, at a rate of ca. 335 000 eggs per hectare, reduced significantly the numbers of apterous adults and nymphs of the green apple aphid, Aphis pomi DeGeer, on dwarf apple trees. Greater reduction in aphid numbers occurred in 1984 than in 1985, and the efficiency of the predator might have been influenced by the predator:prey ratios (1:10 and 1:19) used and by the mean daily temperature that occurred during the test periods. Application of azinphosmethyl (Guthion 50% wp, 0.105 and 0.075 kg AI/100 L) did not adversely affect predation of apterous A. pomi by larvae of C. carnea.
TL;DR: M Monitoring of the aphid and natural enemy populations, and caging aphids onto the crop, revealed that the principal cause of the population decline around G.S. 59 was predation by syrphids.
Abstract: Summary
Sitobion avenae was introduced into areas within a field of winter wheat in Norfolk in mid-May 1985, when the indigenous population was negligible. Aphid numbers in these areas increased for the first 3 wk and declined for the next 4. A second S. avenue introduction into the same areas and into previously uninfested areas was carried out 5 wk after the first introduction, when the crop was at ear emergence complete (G.S. 59). This increased aphid numbers in the previously uninfested areas, but numbers in the previously infested areas continued to decline to below the level in control areas during the subsequent 2 wk. Populations in all areas then increased rapidly to a maximum, followed by a rapid final decline. Monitoring of the aphid and natural enemy populations, and caging aphids onto the crop, revealed that the principal cause of the population decline around G.S. 59 was predation by syrphids. The relevance of these findings to the problem of forecasting S. avenae outbreaks is discussed, and a general explanation for cereal aphid outbreaks is put forward.
TL;DR: In this paper, the relative accuracy of sweep net sampling was compared with D-vac (Dvac, Riverside, Calif.) and absolute sampling methods for determining population densities of pea aphid, Acyrthosiphon pisum (Harris), Nabi s spp, Hippodamia spp., and Chrysopa spp. in lentils.
Abstract: Relative accuracy of sweep net sampling was compared with D-vac (D-vac, Riverside, Calif.) and absolute sampling methods for determining population densities of pea aphid, Acyrthosiphon pisum (Harris), Nabi. s spp., Hippodamia spp., and Chrysopa spp. in lentils ( Lens culinaris Medikus). Relative effects of the a biotic environment, predators, and time of sampling on population estimates also were determined during 2 yr. Original counts, area, and volume adjustments were used to evaluate accuracy of the sampling method. Volume adjustment was most accurate and was used in all subsequent evaluations. Sweep net estimates of pea aphid, Nabis spp., and Hippodamia spp. densities were similar to those obtained with absolute and D-vac sampling methods, although sweep net sampling consistently gave lower population estimates than those found for absolute sampling. In these experiments, the sweep net did not adequately sample the Chrysopa spp. in lentils. The time of sampling was significant when sampling for pea aphid; however, it was not as important for sampling of the three insect predators. Each year, sweep net samples were taken randomly at two locations in two fields every hour for 72 consecutive hours. The a biotic factors studied were light intensity, temperature, relative humidity, and wind velocity; Nabis spp., Hippodamia spp., and Chrysopa spp. were the predator groups studied. Light intensity was the only a biotic factor that was significantly correlated with pea aphid numbers over both years, whereas all four a biotic factors had significant correlations at low aphid densities in 1983. The diurnal sine of hour was significantly and positively correlated with number of aphids collected by sweep net each hour, whereas predator densities were significantly and negatively correlated with aphid densities over both years. Optimum sampling time for pea aphids in lentils can depend on the dominant predator group being sampled; however, for pea aphids and all predator groups, a sample taken in late morning is preferable when sweep net samples are taken.
TL;DR: Significant differences in nymphal development and total lifespan were observed among species within a temperature regime and among temperature regimes for a species.
Abstract: The effects of constant (1O°C) and fluctuating (5-15°C and I-19°C) temperature regimes on the reproduction, development, and intrinsic rate of increase of the Russian wheat aphid, Diuraphis noxia (Mordvilko), greenbug, Schizaphis graminum Rondani, and the bird cherry-oat aphid, Rhopalosiphum padi Fitch, were studied in the laboratory at an average-temperature regime (1O°C) that is common in the spring when all three of these aphids are found in small grain fields in the Texas Panhandle. Significant differences in nymphal development and total lifespan were observed among species within a temperature regime and among temperature regimes for a species. Natality was highest for D. noxia and R. padi at 5-15°C; S. graminum natality was highest at I-19°C. Estimates of the intrinsic rate of increase (rm,) for the three aphid species were highest at I-19°C (0.188 for D. noxia , 0.144 for S. graminum , and 0.200 and for R. padi) .
TL;DR: Differences between lettuce lines in aphid reproduction increased with increasing aggressiveness of the aphid clone, which means that aggressive clones are most effective for selection purposes.
Abstract: Six lettuce lines, representing two types of resistance to the green peach aphid, Myzus persicae, and a control line with high susceptibility to M. persicae were tested for resistance to six different clones of Myzus persicae and two clones of the potato aphid, Macrosiphum euphorbiae.
TL;DR: The photoperiodic responses of two clones of pea aphid, Acyrthosiphon pisum (Harris), collected on the same day in the same field are compared to emphasize the need to observe a sample of clones when attempting to describe any aspect of the species characteristics of aphids.
Abstract: The photoperiodic responses of two clones of pea aphid, Acyrthosiphon pisum (Harris), collected on the same day in the same field are compared. The clones differ not only in the photoperiods at which sexuals first appear, but also in the rate of transition from production of one morph to another. When these clones are compared with other pea aphid clones for which data on production of sexuals are available in the literature, further differences in pattern of production of sexuals become apparent. These comparisons further emphasize the need to observe a sample of clones when attempting to describe any aspect of the species characteristics of aphids.
TL;DR: The findings indicate that there are important genetic differences within Russian wheat aphid, and it is suggested that TXGH2290 could be used as a susceptible standard in future host plant resistant studies, and this breeding line has been recommended for release.
Abstract: The Russian wheat aphid, Diuraphis noxia (Mordvilko), was discovered in Texas on wheat, Triticum aestivum L., in 1986, and 17 collections from 11 Texas counties were made that same year. Two Russian wheat aphid collections, designated as the Randall 2290 colony and the Swisher colony, were tested on four wheat varieties with three infestation levels to differentiate susceptible and resistant plants. Two aphids per plant were the best initial infestation level because higher levels caused too much damage and masked differences between the wheat varieties. Plant height, expressed as a percentage of an uninfested check, was a nonsubjective measure of plant response to Russian wheat aphid. In a second test, all 17 collections were tested on TX78V2290-36-1(TXGH2290) and ‘TAM 107’ with an initial infestation level of two aphids per plant. The results from the second test indicated that there were significant variations in damage between aphid cultures, and differences between colonies occurred within counties and between counties. Reproductive capacity of Russian wheat aphid was affected by variety and was highest overall on TXGH2290. We suggest that TXGH2290 could be used as a susceptible standard in future host plant resistant studies, and this breeding line has been recommended for release. These findings indicate that there are important genetic differences within Russian wheat aphid.
TL;DR: Spirea aphid, Aphis spiraecola Patch, greatly outnumbered, in apple orchards sampled in spring of 1986 in Virginia, West Virginia and...
Abstract: Spirea aphid, Aphis spiraecola Patch, greatly outnumbered [87% A. spiraecola (S.D. ± 3.4)] apple aphid, Aphis pomi DeGeer, in apple orchards sampled in spring of 1986 in Virginia, West Virginia and...
TL;DR: The wide distribution of wild hosts in late summer affects the numbers of autumn migrants, and the regional variation in abundance of E. europaeus affects the success of the aphid in finding sites for overwintering eggs.
Abstract: (1) Populations of Aphisfabae Scop. were monitored in Britain on its primary winter host, Euonymus europaeus L., on the two principal secondary summer crop hosts, springsown Viciafaba L. and sugar beet, and during the spring, summer and autumn migrations. This unique year-round monitoring was used to examine the spatial dynamics of the aphid in 1969-86. (2) Changes in the mean spatial pattern of abundance of the aphid during a single annual cycle reflect a sequence of changing host plants. (3) The longer-term dynamics and survival of the aphid depend on the spatial pattern of abundance in the non-crop environment. Thus, the wide distribution of wild hosts in late summer affects the numbers of autumn migrants, and the regional variation in abundance of E. europaeus affects the success of the aphid in finding sites for overwintering eggs. (4) Spatial patterns of abundance of other aphid pest species are compared with that of A. fabae. (5) The implications of varying spatial patterns of abundance are discussed in relation to pest forecasting.
TL;DR: Cowpea, Vigna unguiculata was infested at the young, mid-fill and mature pod growth stages with, respectively, one, two and three pre-reproductive adult apterae of Aphis craccivora per pod in a screen house.
Abstract: Summary
Cowpea, Vigna unguiculata was infested at the young, mid-fill and mature pod growth stages with, respectively, one, two and three pre-reproductive adult apterae of Aphis craccivora per pod in a screen house. A. craccivora caused pod shrivelling at the young and mid-fill pod stages, on which the aphid was more fecund. All levels of infestation caused significant reduction in seed yield irrespective of age of pod.
TL;DR: The future of dichlorvos, malathion, and more in detail are revealed.
Abstract: 静岡県におけるワタアブラムシの薬剤感受性低下の実態を明らかにするため,各種の植物から採集した個体群について薬剤感受性の検定を実施し,あわせて個体別のエステラーゼ活性を測定した。1) 有機リン剤(dichlorvos, malathion),カーバメート剤(carbaryl),合成ピレスロイド混合剤(fenvalerate・malathion)のうち,合成ピレスロイド混合剤に対する感受性低下はほとんどみられなかったが,有機リン剤に対しては顕著な感受性低下が認められた。2) Dichlorvosの抵抗性比は最大でも30倍強にとどまったのに対し,malathionのそれでは100倍に達する個体群も認められ,有機リン剤のなかでも薬剤の種類によって抵抗性の発達程度が異なった。3) 有機リン剤に対する感受性低下の程度は,ウリ科作物,キク,イチゴから採集した個体群で大きく,ナス科作物,ムクゲ,ツルウメモドキから採集した個体群では小さい傾向がみられたが,感受性低下の程度と殺虫剤の使用回数には明確な関連が認められなかった。4) エステラーゼ活性の個体頻度分布は寄主植物によって大きく異なり,ウリ科作物,キクおよびイチゴでは高活性個体の頻度が高く,ナス科作物,ムクゲ,ツルウメモドキでは低活性個体の頻度が高かった。5) 薬剤感受性の検定およびエステラーゼ活性の測定結果から,本虫の薬剤抵抗性には寄主植物との関連が示唆された。6) DichlorvosあるいはmalathionのLC50値は個体別に測定したエステラーゼ活性の平均値と正の相関を示した。
TL;DR: The cabbage root fly, Delia radicum, was deterred from laying eggs on brassica plants with >250 cabbage aphid, Brevicoryne brassicae, or peach‐potato aphids, Myzuspersicae (Sulz.).
Abstract: . 1. The cabbage root fly, Delia radicum (L.), was deterred from laying eggs on brassica plants with >250 cabbage aphid, Brevicoryne brassicae (L.), or peach-potato aphid, Myzuspersicae (Sulz.).
2. Flies did not lay on plants infested with >250 aphids.
3. Preparations of (E)-β-farnesene, the aphid alarm pheromone, deterred the flies from laying only at the extremely high dose of 32 mg/plant.
4. Although M. persicae secreted large (1 ng/insect) amounts of alarm pheromone and B. brassicae extremely small (<0.01 ng/insect) amounts, both aphids equally deterred D. radicum from laying.
5. The deterrent effect appeared to result from the aphids physically disturbing the flies during host-plant selection.
TL;DR: Aphis chloris shows a high level of host-discrimination and does not transmit persistent viruses between non-host plants and would contribute only marginally to the risk of virus transfer posed by the Australian aphid fauna as a whole.
Abstract: Under laboratory conditionsAphis chloris Koch has been demonstrated to be specific to plants belonging to the genusHypericum. It can effect severe damage to its principal host,H. perforatum L., and shows good potential for contributing to the control of this noxious weed. Other species ofHypericum are less favoured hosts ofA. chloris and would not be endangered by it.
TL;DR: Adults of Aphidius smithi, a parasite of the pea aphid, were exposed for various periods to carbaryl residues on broad bean leaves and it is suggested that insect behaviour influences the degree of insecticide hazard.
TL;DR: It is proposed that chronic, high susceptibility of trees to aphids could reduce concomitant susceptibility to budworm through direct (competition) and indirect (host and communitylevel) effects.
Abstract: The balsam twig aphid, Mindarus abietinus Koch, infested nearly all trees in a range-wide provenance plantation of balsam fir, Abies balsamea (L.) Mill., in Michigan. Infestation levels were highest on eastern and lowest on western seed sources of fir. Large populations of the aphid were correlated with low survival and reduced developmental rates of the spruce budworm, Choristoneura fumiferana (Clemens). We propose that chronic, high susceptibility of trees to aphids could reduce concomitant susceptibility to budworm through direct (competition) and indirect (host and community-level) effects.
TL;DR: A biotype ofTrioxys pallidus Haliday was found to parasitize the aphid throughout western Europe and successfully attacked and completed its development on Oregon populations of the filbert aphid.
Abstract: Hazelnut orchards in Spain, France, and Italy were searched for parasitoids of the filbert aphid,Myzocallis coryli (Goetze). A biotype ofTrioxys pallidus Haliday was found to parasitize the aphid throughout western Europe. Wasps were imported, quarantined, mass-reared, and released in Oregon orchards. The wasp successfully attacked and completed its development on Oregon populations of the filbert aphid. A greenhouse culture of the parasitoid was maintained continuously for over 50 generations, and approximately 30,000 adult wasps were released in western Oregon. Overwintering survival has been documented in at least 12 different locations. In 3 commercial hazelnut orchards, the parasitoids proved capable of reducing aphid population peaks by 33–48%.
TL;DR: Results from a three-year field trial of the effectiveness of insecticides applied at various growth stages of winter wheat used to test the accuracy of the predictions of the Entwistle and Dixon (1986, 1987) models for forecasting aphid damage and population growth.
Abstract: Summary
Aphid counts and yield results from a three-year field trial of the effectiveness of insecticides applied at various growth stages of winter wheat, were used to test the accuracy of the predictions of the Entwistle and Dixon (1986, 1987) models for forecasting aphid damage and population growth. In general, the peak aphid populations of Sitobion avenae and damage were not accurately predicted but the spray recommendations, which would have resulted from the predictions, would have been correct in each of the three years; one outbreak and two non-outbreak years. In particular the effectiveness of early spraying was over-estimated because the persistence of the effect of insecticides was over-estimated. It is recommended that further work be done on the rate of development of aphid populations following application of insecticides.
TL;DR: Development time of nymphs and adults, daily fecundity and survival rate of adults were determined for the apterous and alate viviparae of Toxoptera citricidus reared on Gitrus natsudaidai HAYATA.
Abstract: Development time of nymphs and adults, daily fecundity and survival rate of adults were determined for the apterous and alate viviparae of Toxoptera citricidus (KIRKIALDY) reared on Gitrus natsudaidai HAYATA, at 20 and 25°C under 16L-8D photo-period regime. The nymphal and pre-reproductive periods of apterae were significantly shorter than those of alatae. The age specific fecundity of apterae was consistently higher than that of alatae. The net reproductive rate (R0) and capacity for increase (rc) of apterae were higher than those of alatae. The capacity for increase of each morph was higher at 25°C than that at 20°C.