Showing papers on "Aphid published in 1979"

Studies on Polyphagous Predators of Cereal Aphids

Abstract: 1. Experiments were done in fields of winter wheat at North Farm, West Sussex, and at Rothamsted in 1978 to investigate the effect of predation by carabid beetles and other polyphagous preadtors on populations of cereal aphids. 2. Predator populations were manipulated by pitfall trapping within plot surrounded by polythene barriers and by applying an insecticide (fonofos) within such plots. Plots were set up in March, April, May and June and the development of aphid populations within them compared with aphid populations in unenclosed control areas. 3. The numbers of carabid beetles caught in the enclosed and fonofos-treated plots were much less than in 'control' plots. 4. Aphid populations were all much smaller in 'control' plots than in those with depleted predator populations both at North Farm, where beetle populations were large, and at Rothamsted where populations were small. Aphid populations were much larger in plots where numbers of polyphagous predators were decreased early in the season than where this was done later. 5. There was an inverse relationship between numbers of polyphagous predators and aphids for the North farm experiment. In contrast, there were positive relationships between aphids and aphid-specific predators and between aphids and aphid parasites. This together with the virtual absence of the pathogenic fungus Entomophtora spp, indicated that the differences in aphid density between plots were caused by polyphagous predators rather than by other natural enemies. 6. Comparison of results from the two sites suggested that amongst the carabid beetles Agonum dorsale (Pont.) was the most important aphid predator, but there was also evidence that polyphagous predators other than carabids decreased the cereal aphid populations.

A multispecies aphid–ant association: density dependence and species-specific effects

Abstract: In the central Rocky Mountains of Colorado 4 species of aphids feed on fireweed, and 10 species or ants have been observed tending 3 of these species of aphids. Local populations of aphids and their associated ants were counted nondestructively at weekly intervals for up to 11 weeks. The effects of ants upon the persistence of recently initiated populations and the growth of populations during 1-week intervals were assessed by multidimensional contingency table analysis. Macrosiphum valerianae, which is not tended by ants, was affected negatively by ants. Aphis varians and A. helianthi were affected by tending, but A. salicariae was not affected. The responses of both A. varians and A. helianthi to tending were density dependent; i.e., small populations that were untended were more likely to decrease than tended populations, but large populations that were tended were either more likely to decrease than untended populations or equivalent to them. Possible reasons for this density-dependent effect are disc...

The effect of cereal growth stages on the reproductive activity of Sitobion avenue and Metopolophium dirhodum

Abstract: SUMMARY Apterous Sitobion avenae on oats were found to have a higher reproductive rate on the ears (5–95 nymphs per day) than on young leaves (3–78 nymphs per day), mature leaves (2–17 nymphs per day) or senescent leaves (2–08 nymphs per day). At each growth stage of the the host plant large aphids gave birth to more young than small aphids, but aphids of the same weight on different growth stages of the host plant had different reproductive rates. On wheat in the field S. avenae gave birth to more young on the ears but less on the leaves than Metopolophium dirhodum on the leaves. The suitability of ears to S. avenae changed through the flowering and ripening stages. During the latter part of the milky-ripe stage the reproductive rate of S. avenae declined and its mortality increased. The consequences of the variations in reproduction and mortality are discussed in relation to the life history and population dynamics of S. avenae and the assessment of cereal varieties for aphid resistance.

The influence of predators on the movement of apterous pea aphids between plants

Abstract: SUMMARY (1) This paper examines the influence of predators on the dispersal of apterous pea aphids in the laboratory and field. (2) Individual pea aphids can be placed in one of two categories, searchers and runners, depending upon the behaviour they exhibit after dropping from their host plant. (3) In field cages, pea aphids readily disperse to new host plants in the presence of predators. Dispersal of apterous aphids is rare when active predators are absent. (4) Evidence is presented which suggests fecundity is reduced the day after an aphid disperses. (5) The distance dispersed by aphid nymphs is positively correlated with the density of aphids on the plant the aphid leaves. (6) The significance of dispersal by apterous aphids is discussed in the light of evidence presented.

Stability and variation in aphid clonal lineages

Abstract: Evidence in the literature purporting to show genetic variability within parthenogenetic lines of aphids is reviewed. The results of three experimental approaches to this problem are reported: (1) a long term study of fluctuation in alate morph production in six lines of Myzus persicae; (2) an attempt tp select for caudal hair form in Acyrthosiphon pisum; (3) a study of the inheritance of esterase variants of M. persicae in sexual and parthenogenetic reproduction. It is concluded that genetic recombination during parthenogenesis is not the general rule in diese aphids, and that aphid parthenogenesis should be regarded as of ameiotic or apomictic type. Possible alternative explanations for the different kinds of variation or apparent variation which occur within aphid clonal lineages are discussed.

Feeding and multiplication of three cereal aphid species and their effect on yield of winter wheat

Abstract: Sitobion avenae F. multiplies at a higher rate on winter wheat than Rhopalosiphum padi L. and Metopolophium dirhodum Wlk. Unlike the other two species S. avenae prefers the ear, where it multiplies twice as quickly as on the flag leaf. Infestation of the ear rather than of the leaves leads to reduction of the average grain weight. These results suggest that S. avenae is the most injurious. In 3 field trials with this aphid fungal growth on honeydew caused about half of the damage. After correction for the fungus effect, the loss in yield caused by S. avenae feeding on the ear did not differ much from that calculated from its energy budget. Therefore, it is concluded that stylet insertion and saliva injection have no important influence on the growth of grains. From results with long living and highly productive crops it seems that honeydew can cause a more serious loss in yield if the crop does not prematurely ripen under the influence of various other yield-reducing factors.

Territorial behaviour of Pemphigus gall aphids

Abstract: ALTHOUGH insects are known to defend nests, breeding sites and females1, the defence of feeding sites is less well documented. Other than the defence of egg clutches and nymphs by female treehoppers2 and the existence of a soldier caste in wooly aphids3, territoriality has not been reported in the large insect order Homoptera which includes aphids, scale insects, hoppers, cicadas and whiteflies. As the evolution of territoriality is thought to be directly correlated with competition for resources in short supply4, territorial behaviour should only be exhibited when population densities approach the carrying capacity of the environment. Because parthenogenetic reproduction and the high population growth rates of aphids seem contradictory to the notion of limited resources, aphid territorial behaviour is not expected. I report here on the settling behaviour of the aphid, Pemphigus betae Doane, which forms galls of the leaf blade of narrowleaf cottonwood, Populus angustifolia. We have quantified the existence of a defended micro-territory, the production of a floater population of individuals displaced through competitive interactions, and the differential mortality of residents and floaters which favours the evolution of territorial behaviour.

Behavioural and physiological adaptations of pea aphids (homoptera: aphididae) to high ground temperatures and predator disturbance

Abstract: Pea aphids can avoid ladybug predators by dropping from the food plant when disturbed. Once off the plant the aphid must find another food plant. If temperatures on the ground are high, the aphid may die before finding a new food plant. In Kamloops, B.C., summers are hot and dry, compared with Vancouver where the climate is warm and moist. Pea aphids from Kamloops generally exhibit back-up behaviour and rarely drop from the plant when approached by a ladybug. By contrast, Vancouver pea aphids readily drop from the plant when disturbed by a predator. Adult aphids from Kamloops are more tolerant of heat under moist conditions at 37.5 °C than Vancouver adults but under dry conditions and at 42 °C, both groups have similar survival times. First instars of both aphid biotypes die sooner at high temperatures than adults. Mortality of aphids on the ground is sufficiently high to select against dropping behaviour as a first line defense against predators in areas with hot, dry climates.

Control of aphids in glasshouses with the fungus, Verticillium lecanii

Abstract: SUMMARY In small glasshouses, aqueous sprays of spores of the entomopathogenic fungus, Verticillium lecanii, eliminated small populations of the aphid Brachycaudus helichrysi in the vegetative tips of chrysanthemum plants but not when they were in an exposed position on mature flower buds. Control of the chrysanthemum aphid, Macrosiphoniella sanborni, was however variable and usually commercially unsatisfactory. In contrast, in both small and large glasshouses, sparse populations of the major aphid pest Myzus persicae were successfully and consistently controlled, sometimes spectacularly. The inherent susceptibilities of these aphid species, measured by laboratory bioassay, did not account for the differences in control observed in the glasshouse. It is thought that a combination of species-characteristic feeding site preferences on the exposed parts of plants, where microclimate humidity was probably low, and relative immobility of M. sanborni and B. helichrysi explain why these aphids were less well-controlled than My. persicae. However, it should be possible to control satisfactorily all aphid species in large commercial glasshouses where humidity might be higher than in the small experimental glasshouses. A single spray was sufficient to introduce infection that controlled aphids for the duration of the crop.

Biological control of the walnut aphid in California: Impact of the parasite, Trioxys pallidus

Abstract: The interrelationship of an Iranian ecotype of Trioxys pallidas (Hal.) (Hymenoptera: Aphidiidae) and the walnut aphid, Chromaphis juglandicola (Kale), (Homoptera: Callaphididae), was assessed over a 4-year period at two localities in California. Limited additional data were obtained from other localities. Trioxys pallidas, a highly efficient parasite, which is biologically adapted to and phenologically synchronized with C. juglandicola, has brought about substantial biological control of this pest. Trioxys pallidus substantially dampens the aphid’s vernal oscillation, and normally restrains the amplitude of the summer and autumnal oscillations. Major economic benefits have been realized by the elimination of the aphid as a pest in springtime. Trioxys pallidus is at times heavily attacked by non-specific hyperparasites, but these, at most, hinder it but slightly. Certain insecticides can disrupt T. pallidus activity, permitting aphid outbreaks. Prolonged aphid scarcity, possibly abetted by hyperparasitism, also may cause a breakdown in parasite activity and a temporary aphid resurgence in midseason. During the 4 years of investigation, this occurred on one occasion in one of the study plots. More than one-half million dollars have accrued annually to the California walnut industry as a result of the C. juglandicola biological control program.

The effect of superparasitism by Aphidius smithi (Hymenoptera: Aphidiidae) on the food budget of the pea aphid, Acyrthosiphon pisum (Homoptera: Aphididae)

Abstract: Parasitism by Aphidius smithi affected the food budget of its host, Acyrthosiphon pisum, fed on a synthetic diet. During the embryonic stage of the parasite, the weight-specific rates of feeding, food assimilation, and growth were less in parasitized aphids than in controls. In the presence of a developing parasite larva, aphids ingested more food but assimilated it less efficiently; they achieved the same or a higher relative growth rate than nonparasitized aphids as a result of having either a higher feeding rate or a higher efficiency of incorporation of assimilated food, or both. Honeydew excretion was up to 129% higher in aphids containing a parasite larva. Parasitism by A. smithi did not obviate host feeding and capacity for growth until host size was sufficient for the successful development of the parasite larva.It is suggested that the nutritional requirements of the parasite larva differ from those of the aphid. Thus parasitism affects the homeostatic regulation of aphid feeding and food assimil...

Aspects of host—parasitoid interactions of two aphid parasitoids, Aphidius urticae (Haliday) and Aphidius uzbeckistanicus (Luzhetski) (Hymenoptera, Aphidiidae)

Abstract: . 1. Various aspects were studied of two host-parasitoid interactions: Aphidius urticae parasitizing the cocksfoot aphid Hyalopteroides humilis and Aphidius uzbeckistanicus parasitizing the cereal aphid Metopolophmm dirhodum. The work formed part of a study on the population dynamics of grassland and cereal aphids in Berkshire, England. 2. A.uzbeckistanicus had a higher instantaneous attack rate but a slightly longer handling time than A.urticae. In both cases the functional response was curvilinear. 3. A.urticae was specific to H.humilis and failed to develop in M.dirhodum. A.uzbeckistanicus could develop successfully in H.humilis but the functional response was sigmoid and the progeny were less fecund than those reared on the natural host. This species showed a clear preference for M.dirhodum when supplied with mixtures of M.dirhodum and H.humilis. 4. A.uzbeckistanicus had a faster rate of development and a lower developmental threshold than A.urticae, a situation paralleled by their natural hosts. 5. The results are discussed in relation to field observations. A.uzbeckistanicus may have considerable potential for reducing cereal aphid numbers. However, its preference for M.dirhodum mitigates against a reservoir being maintained in the economically unimportant grassland aphid, H.humilis.

Effects of Mulching on the Spread of Aphid-Transmitted Watermelon Mosaic Virus to Summer Squash

Abstract: Alate aphid populations migrating into summer squash plantings between Feb. and May were reduced by 96 and 68% by aluminum and white plastic mulches, respectively. The green peach aphid, Myzus persicae (Sulzer), was predominant and comprised 92% of the 16 aphid species trapped. Watermelon mosaic virus was the only cucurbit virus recovered, and symptoms appeared in the field 3 weeks after peak aphid flights in Mar. Virus incidence increased rapidly and reached 90% in untreated plots by May. Aluminum and white plastic mulches reduced virus incidence by 94 and 77%, respectively, at peak fruit harvest in Apr. Mineral oil sprays significantly reduced virus spread early in the growing season, and weekly application of methyl demeton did not affect virus incidence. Aluminum and white plastic mulches increased total fruit yield by 43%. Yield responses were particularly evident during early production with 85 and 69% increases resulting from the aluminum and white plastic mulches, respectively.

Effect of precocene II on alate production in the pea aphid, Acyrthosiphon pisum

Abstract: After topical application of 1 μg precocene II, young apterous viviparous pea aphids produced alate offspring under conditions favouring the exclusive production of apterous offspring. It is sugges...

Evidence for Lack of Propagation of Potato Leaf Roll Virus in its Aphid Vector, Myzus persicae

Abstract: ESKANDARI, F., E. S. SYLVESTER, and J. RICHARDSON. 1979. Evidence for lack of propagation of potato leaf roll virus in its aphid vector, Myzus persicae. Phytopathology 69: 45-47. Two isolates of potato leaf roll virus (PLRV) were used in serial passage PLRV. Injected insects survived about 16 days and inoculated an average of tests with the green peach aphid, Myzuspersicae. Initial characterization of slightly more than one plant per insect after a median latent period of the transmission pattern indicated that at 25 C individual first instar larvae approximately 85 hr. They remained infective for approximately 5 days. In efficiently (92%) acquired and transmitted virus from infected Physalis a series of serial passage trials, infectivity of aphids was not maintained floridana. When transferred to a sequence of P. floridana test seedlings, beyond the first transfer. About 20% of larvae injected with hemolymph infective single aphids lived 18-24 days. After a 30-49 hr median latent from aphids reared on infected Physalis transmitted PLRV (first passage). period, they inoculated an average of six to eight seedlings and remained No further passage occurred, regardless of whether aphids were kept on infective for an average of 9-11 days. These estimates varied somewhat with immune or susceptible test plants. The evidence suggests that these isolates the length of the acquisition access period. Approximately 14% of late of PLRV were circulative, but not propagative, in two clones of M. instar larvae injected with hemolymph from infective aphids transmitted persicae. Additional key words: aphid transmission, propagative virus. Potato leaf roll virus (PLRV), the first of the persistent studied in our laboratory using the injection technique and in spite aphid-borne viruses to be described (13), still presents an unreof the difficulties reported with the insect injection of PLRV (10), solved problem of whether it multiplies in its aphid vectors. Until we reexamined the serial passage of PLRV in M. persicae. The the injection technique for inoculating insects with plant viruses results are reported herein. was successfully applied to aphids (6), the proponents for the propagative vector-virus relationship of PLRV used vector specificity, trans-stadial passage, a latent period, and prolonged MATERIALS AND METHODS retention of inoculativity by infective insects as evidence for multiplication (4). The inconclusive nature of these arguments is Virus. Two potato sources of PLRV were used. One, furnished apparent. by D. L. McLean, University of California, Davis, came from a Insect to insect passage of PLRV was used independently by commercial field in Tule Lake, California. The other was derived Harrison (5) and by Stegwee and Ponsen (15) in attempts to obtain from an infected potato in a home garden in Berkeley, California. decisive evidence on the question of multiplication of PLRV in a Identity of the virus was based on aphid transmission from major aphid vector, Myzus persicae (Sulzer). Insect extracts or potatoes exhibiting typical PLRV symptoms and the PLRV hemolymph were used as inocula. Stegwee and Ponsen (15) syndrome in Physalis including initial epinasty, stunting, reported 15 consecutive serial passages from aphid to aphid interveinal chlorosis, and leaf rolling. without loss of infectivity and concluded that the relationship of Vectors and test plants. Two clonal lines of green peach aphids PLRV to M. persicae was propagative. Harrison (5), however, (M. persicae) were used. Most of the experiments were done with a failed to obtain serial passage beyond one transfer, and thus his stock clonal line that was originally collected at Berkeley and has evidence did not support a propagative hypothesis. been maintained in our laboratory for approximately 15 yr. The Since these pioneering works, the injection technique has been other clonal line was derived from a stock collected at Yakima, used in other laboratories to investigate several aphid-borne Washington, and used by T. E. Mittler in his laboratory at persistent viruses. For example, the serial passage of pea enation Berkeley. All aphids were reared on PLRV-immune winter radish mosaic virus (PEMV) (3) and of barley yellow dwarf virus (9) has (Raphanus sativus) seedlings in a growth chamber set at 20 C and been reported, but only for a single passage. Thus, although the constant light of approximately 13,000 lux at plant level. multiplication of these two viruses in aphid vectors has not been The test plants were seedling Physalisfloridana, germinated in disproved, most authors view this evidence in support of a seed pans and transplanted to plastic pots about 5 cm in diameter. circulative, nonpropagative (3,9,12,16) rather than a propagative Physalis floridana plants, infected during the experiments, were vector-virus relationship. used as virus sources on which to rear the initiating donor aphids. The sowthistle yellow vein virus (SYVV) and the strawberry All aphids were confined to the plants using small cylindrical crinkle virus (SCV), on the other hand, have been transferred from cellulose nitrate cages capped with a nylon net. The acquisition and aphid to aphid by injectionfor sufficient serial passages to evidence inoculation access periods were done in growth chambers at either their propagative nature (17,19) adequately. 20 or 25 C with constant light. After removal of test aphids, all Since PEMV as well as SYVV and SCV have been successfully plants were fumigated with nicotine or sprayed with dimethioate, put in a greenhouse, and observed for symptoms for at least 4 wk. Donor aphids. Mature, wingless, female M. persicae were 00031-949X/79/000006$03.00/0 allowed to larviposit for a specified period, usually 24 hr, on @ 1979 The American Phytopathological Society infected tissue. Usually entire plants were caged, but occasionally Vol. 69, No. 1, 1979 45 detached leaves were used. After maternal females were removed, the mean weighted transmission rates indicated that vector larvae were allowed to continue feeding on the infected source for mortality was not a serious factor during the period of active virus varying periods, usually until they matured. Selected individuals transmission. then were used as donors of hemolymph. The infectivity of donor The period of time that inoculativity was retained increased aphids was assayed by transferring to Physalis test plants after they somewhat with acquisition access periods in excess of 12 hr. The were used as a donor of virus, anomalous increase in the length of the latent period, as a function Inoculum and injection. The inoculum usually was hemolymph of increasing acquisition time, probably was due to two factors. and most often this was obtained by removing an appendage, eg, a First, the age-specific transmission rate generally is less than one leg, and dipping the tip of the injection needle in the wound. In most (this results in an apparent latent period), and second, transferring of the serial passage work, the needle was inserted into the aphid at of vectors from a diseased plant to a healthy plant probably the base of a leg. This technique enabled the aphids to be tested involves a feeding adjustment period during which the rate of after serving as donors. Another variation was to insert the needle transmission is reduced. into the head of the donor, disrupt tissue by moving the tip back Hemolymph injection. The preliminary data revealed nothing and forth, and use the material drawn up by capillarity as unusual about our PLRV and M. persicae combination. The next inoculum. In one test, the head of the donor aphid was triturated in series of experiments attempted to establish infectivity in recipient 5 Mliters of distilled water and this suspension was used as aphids by injection. Longevity was somewhat shortened by the inoculum. combination of injectionand daily transfers (Table 1), but the mean Injection of the recipient aphids by inserting the needle above the weighted retention period was similar to that found with aphids siphunculi has been described previously (14). acquiring virus during an estimated 12-hr acquisition access period. Serial passage. Two procedures were used in serial transmission Three things are noteworthy in Table 1. First, the probability of trials. The first involved an immune host. Hemolymph from a obtaining an infective insect by injection (0.14) was much lower donor aphid was injected into a sample of two to five PLRV-free than with feeding (0.92), when using a 12-hr average acquisition recipient larvae. Each surviving donor was then tested for access period. Part of this discrepancy may have been because first infectivity by feeding it for 1-7 days on a healthy Physalis test instar larvae were used as recipients in the acquisition feeding trial seedling. The recipient larvae were divided into two groups. Those and late instar larvae were used in the injection test. Second, the in one group were tested for infectivity by transferring them at 24-hr latent period was noticeably extended in injected insects, compared intervals, until dead, to a series of test seedlings. The second group with that of fed insects (3.6 days versus 1.27 days). Third, the mean of recipients was put on a radish seedling for 6 days, then a sample weighted transmission rate was approximately four times lower from the surviving aphids was used as donors for the next passage. with injected infective insects than with aphids that acquired PLRV This procedure was repeated until five passages were completed. In by feeding. This sharply contrasts the results obtained with two the fifth passage, all inoculated recipient larvae were transferred to propagative aphid-borne viruses (SYVV and SCV), in which (i) Physalis and tested for infectivity, injection was more efficient than feeding in producing infective The second procedure was similar, but all recipients were insects, (ii) the latent period was shorter i

Action Thresholds for Potato Leafhopper on Potatoes in Minnesota

Abstract: The appropriate action threshold for application of insecticidal sprays to control potato leafhopper, Empoasca fabae (Harris), on potatoes, Solanum tuberosum (L.), appeared to be ca. 10 nymphs/105 leaves. Applying treatments only when leafhopper populations reached 30 or more nymphs/105 leaves resulted in hopperburn and yield reductions. Treating for 10 or fewer nymphs/105 leaves necessitated additional spray applications of minimal incremental value in crop protection, but which can trigger outbreaks of green peach aphid, Myzus persicae (Sulzer). Only 2 spray applications were required when insecticidal applications were timed to coincide with peak nymphal populations in mid-July and mid-Aug. For these studies, essentially single species infestations of potato leafhopper were obtained by inter planting the potatoes with alfalfa strips.

Further studies on the effect of resistance to Amphorophora idaei in raspberry (Rubus idaeus) on the spread of aphid-borne viruses

Abstract: SUMMARY The rate of spread of viruses transmitted by the aphid Amphorophora idaei into genotypes of raspberry differing in resistance to infestation by A. idaei was studied in a field experiment which exposed plants to large numbers of infective aphids. Under these conditions, genotypes that are readily colonised by A. idaei were totally infected with virus after two to three growing seasons, whereas genotypes with a high degree of resistance were substantially free of virus after four growing seasons but 56% of plants were infected after seven seasons. Genotypes with intermediate resistance were also substantially free of virus after three seasons but 76% of plants were virus infected after seven seasons. The effectiveness of resistance to A. idaei in raspberry in restricting spread of viruses transmitted by this aphid is discussed.

Temperature-dependent model for predicting field populations of green peach aphid, myzus persicae (homoptera: Aphididae)

Abstract: A temperature-dependent model for predicting green peach aphid population development in potato fields was devised and tested. A laboratory estimate of generation time was utilized to derive expected generation number from field accumulated degree days (1975–77). Different aphid populations were produced in replicated field plots (1975–77) with various application rates of the systemic insecticide, aldicarb. Density data from these plots were regressed on the expected number of generations to derive prediction equations. These equations were coupled in a Fortran computer program with a degree day algorithm. Weather forecasts, therefore, provide input for future aphid population predictions. The model is being used to evaluate various control strategies and to decide on spray dates from weather forecasts.

Bionomics of the Turnip Aphid on Two Turnip Cultivars

Abstract: In greenhouse studies, apterous turnip aphids, Lipaphis erysimi (Kaltenbach), reared on ‘Shogoin’ turnip had a longer prereproductive period, produced fewer progeny, and were smaller than their counterparts reared on ‘Purple Top White Glob’ (PTWG) turnip. Similarly, alate aphids reared on radish and placed on turnip as prereproductive adults, produced fewer progeny on Shogoin than on PTWG. Experiments in which apterous aphids were reared on one cultivar and transferred to the other as prereproductive adults suggested that the resistance of Shogoin operates primarily against the reproductive adult turnip aphid. In 3 field plantings, turnip aphids were 3X more abundant on PTWG than on Shogoin in the one planting in which well-established aphid populations were observed. The green peach aphid, Myzus persicae (Sulzer), and the cabbage aphid, Brevicoryne brassicae (L.), were significantly more abundant on Shogoin than on PTWG in one planting, but not in 2 others. Larvae of the diamondback moth, Plutella xylostella (L.), were significantly more abundant on Shogoin than PTWG in 2 of the 3 experimental plantings.

Relationship of Green Peach Aphid Numbers to Spread of Potato Leaf Roll Virus in Southern Idaho

Abstract: During a period from 1973 to 1975, 90 commercial potato fields in southern Idaho were sampled to measure the relationship between spread of potato leaf roll virus (PLRV) and numbers of Myzus persicae (Sulzer). From these data, mathematical models were constructed to predict whether or not economic levels of PLRV would be present at harvest. Simple word models were prepared for growers’ use. The model for southwestern Idaho stated that control measures should be initiated when more than 40 green peach aphids were found/50 leaf samples in 2 consecutive weeks before Aug. 1. In southcentral Idaho, aphids should be controlled when more than 10 were found/50 leaf samples in 2 consecutive weeks before Aug. 1.

Shifts in host plant resistance to the cabbage aphid (Brevicoryne brassicae) exhibited by Brussels sprout plants

Abstract: SUMMARY Seven cultivars of Brussels sprouts from different sources were tested for their relative degrees of resistance to the cabbage aphid (Brevicoryne brassicae) by estimating the Potential Increase Rate of aphid infestations. The cultivars Winter Harvest and Early Half Tall were selected as susceptible and resistant respectively and tested further. Glasshouse experiments indicated that the resistance of Winter Harvest to the aphids increased with age. These relative levels of resistance were confirmed by population counts in the field. Aphid numbers were initially significantly higher on Winter Harvest than on Early Half Tall although significance was lost as the season progressed at a time when the characteristics responsible for the resistance mechanism ceased to be distinguishable between the two cultivars. Analysis of the amino acid content of leaf tissues collected at monthly intervals through the aphid season enabled ‘risk rating’ predictions of aphid resistance to be made. These conformed with the shifts towards greater resistance as the plants aged noted in the glasshouse trials and endorsed the part played by amino acids in the mechanism of resistance. Total amino acid concentrations reached a peak during September and October then declined with generally lower levels of amino acids in Early Half Tall than Winter Harvest. This cultivar also possessed a greater concentration of those amino acids known to be favourable to B. brassicae although the difference between the two had diminished considerably by the end of September. Analyses of the mustard oil glycoside levels in mature glasshouse-grown plants did not indicate a difference between the cultivars.

Yellow Sugarcane Aphid: Plant Resistance in Cereal Crops

Abstract: In greenhouse studies, corn (maize) was the least preferred host for the yellow sugarcane aphid, Sipha flava (Forbes) and had little damage and supported few and small nymphs. Oats had extremely low nymphal production and survival but was moderately preferred and damaged. Rye had intermediate antibiosis but high nonpreference and tolerance. Triticale was intermediate between the parental rye and wheat. Pearl millet was non preferred but had poor antibiosis and tolerance. Feed barley was relatively susceptible, but low levels of resistance were found. All tested entries of common wheat and Sorghum bicolor (L.) were susceptible. The yellow sugarcane aphid on sorghum and barley takes ca. a week longer than the green-bug, Schizaphis graminum (Rondani), to mature sexually, and it reproduces at slower rates. However, it causes even greater plant necrosis and must be considered a serious outbreak pest of sorghum, wheat, and barley.

Action Thresholds for Green Peach Aphid on Potatoes in Minnesota

Abstract: The appropriate action threshold for application of insecticidal sprays to control green peach aphid, Myzus persicae (Sulzer), on potatoes, Solanum tuberosum (L.), appeared to be ca. 30 apterae/105 leaves. For seed production, assuming a soil systemic was used at planting, an action threshold of ca. 10 apterae/105 leaves was indicated. Spraying on a schedule, even with effective aphicides, can result in late-season green peach aphid control problems more severe than occur on untreated potatoes. Serious outbreaks resulted when an insecticide to which the aphid is resistant was applied on a schedule. During this study, 2 insecticides, pirimicarb and fenvalerate, lost much of their original effectiveness against green peach aphid.