Phenotypic mechanisms of host resistance against greenbug (Homoptera: Aphididae) revealed by near isogenic lines of wheat

Interactions between biotype E greenbug, Schizaphis graminum (Rondani), and wheat, Triticum aestivum L., were investigated using resistant and susceptible near isogenic lines of the greenbug resistance gene Gb3. In an antixenosis test, the greenbugs preferred susceptible plants to resistant ones when free choice of hosts was allowed. Aphid feeding resulted in quick and severe damage to susceptible plants, which seemed to follow a general pattern spatially and was affected by the position where the greenbugs were initially placed. Symptom of damage in resistant plants resembled senescence. Within-plant distribution of aphids after infestation was clearly different between the two genotypes. Significantly more greenbugs fed on the first (oldest) leaf than on the stem in resistant plants, but this preference was reversed in the susceptible one. After reaching its peak, aphid population on the susceptible plants dropped quickly. All susceptible plants were dead in 10-14 d after infestation due to greenbug feeding. Aphid population dynamics on resistant plants exhibited a multipeak curve. After the first peak, the greenbug population declined slowly. More than 70% of resistant plants were killed 47 d after infestation. Performance of both biotype E and I greenbugs on several Gb3-related wheat germplasm lines were also examined. It seems that the preference-on-stem that was characteristic of biotype E greenbugs on the susceptible plants was aphid biotype- and host genotype-dependent. Results from this study suggested that antixenosis, antibiosis, and tolerance in the resistant plants of wheat might all contribute to resistance against greenbug feeding.     

Categories of resistance at different growth stages in halt,a winter wheat resistant to the Russian wheat aphid (Homoptera: Aphididae)

This study was designed to categorize the resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko), resistant hard red winter wheat, Halt, as compared with susceptible wheat, TAM 107, at four different growth stages. Antixenosis was expressed in Halt at growth stage Zadoks 30. Antibiosis in Halt affected fecundity, number of aphids produced per reproductive day, maximum number of nymphs produced in one day, and intrinsic rate of increase. Fecundity was lower on Halt than TAM 107, and more nymphs were produced on both varieties at growth stage 20 than 10 and 40. Fewer nymphs were produced per reproductive day and on maximum production days by aphids reared on Halt than by those reared on TAM 107. The intrinsic rate of increase of Russian wheat aphids reared on Halt was lower than aphids reared on TAM 107. Differences in plant height and plant dry weight did not occur. Chlorosis ratings showed greater damage at the earlier stages in Halt and TAM 107 and significantly more damage in TAM 107 than Halt at growth stages 10, 20, and 30. Leaf rolling occurred on infested plants of TAM 107 at growth stages 10, 20, and 30, but not growth stage 40. Halt plants did not exhibit leaf rolling. The presence of a significant level of tolerance could make Halt compatible with other integrated pest management programs. However, care should be taken with cultivars containing evidence of antixenosis or antibiosis that could cause selective pressure on the Russian wheat aphid, potentially causing biotypes to be produced.     

Positive effects of an arbuscular mycorrhizal fungus on aphid life history traits

Two generations of two aphid species (Myzus ascalonicus and M. persicae) were reared on Plantago lanceolata plants, with and without root colonization by the arbuscular mycorrhizal fungus, Glomus intraradices. Life history traits of the aphids measured were nymphal development time, teneral adult weight, growth rate, total fecundity, adult longevity and duration of post-reproductive life. For both aphids in both generations, mycorrhizal colonization increased aphid weight and fecundity, while other traits were unaffected. The increases were consistent between generations. In a second experiment, M. persicae was reared on plants with and without the fungus, under varying N and P regimes. The results of N addition were inconclusive because there was high aphid mortality. However, under P supplementation, positive effects of the mycorrhiza on aphid growth were seen at low and medium P levels, while at high P levels these effects disappeared. The positive effects of mycorrhizal colonization reported here are contrary to the majority of previous studies with chewing insects, which have reported negative effects. A number of possible mechanisms for this apparent discrepancy are discussed. Received: 1 February 1999 / Accepted: 22 March 1999     

Direct and Indirect Impacts of Infestation of Tomato Plant by Myzus persicae (Hemiptera: Aphididae) on Bemisia tabaci (Hemiptera: Aleyrodidae)

The impacts of infestation by the green peach aphid (Myzus persicae) on sweetpotato whitefly (Bemisia tabaci) settling on tomato were determined in seven separate experiments with whole plants and with detached leaves through manipulation of four factors: durations of aphid infestation, density of aphids, intervals between aphid removal after different durations of infestation and the time of whitefly release, and leaf positions on the plants. The results demonstrated that B. tabaci preferred to settle on the plant leaves that had not been infested by aphids when they had a choice. The plant leaves on which aphids were still present (direct effect) had fewer whiteflies than those previously infested by aphids (indirect effect). The whiteflies were able to settle on the plant which aphids had previously infested, and also could settle on leaves with aphids if no uninfested plants were available. Tests of direct factors revealed that duration of aphid infestation had a stronger effect on whitefly landing preference than aphid density; whitefly preference was the least when 20 aphids fed on the leaves for 72 h. Tests of indirect effects revealed that the major factor that affected whitefly preference for a host plant was the interval between the time of aphid removal after infestation and the time of whitefly release. The importance of the four factors that affected the induced plant defense against whiteflies can be arranged in the following order: time intervals between aphid removal and whitefly release > durations of aphid infestation > density of aphids > leaf positions on the plants. In conclusion, the density of aphid infestation and time for which they were feeding influenced the production of induced compounds by tomatoes, the whitefly responses to the plants, and reduced interspecific competition.     

Demographic parameters of greenbug,Schizaphis graminum (Rondani) (Hemiptera: Aphididae), on six Iranian genotypes of barley

Greenbug, Schizaphis graminum (Rondani), is one of the injurious aphids of cereals in various regions of the world. This study has measured the life table parameters of the greenbug on six barley genotypes at 25 ± 2 °C, 55 ± 10% RH and 16:8 L:D in greenhouse. According to the results, significant differences were not observed for aphids’ developmental times among the genotypes. Also, the nymphs underwent no mortality on any of the tested genotypes. The longevity of the aphids was obtained from 23.7 to 35.9 days. The least mean number of offsprings was on Raihan cultivar and the highest on line13 (Legia/CWB117-5-9-5). R₀ value was significantly higher on line 20 (Mall-4-3094-2//Alpha/Cum/3/Victoria/ICB01-1368-0AP) and line 13 than on the Raihan cultivar. However, the r_m and λ values were significantly higher on line 44 (Sls/Bda//Sararood-1) than on Raihan cultivar. T (mean generation time) and DT (doubling time) values of the Raihan cultivar were longer than the other genotypes. Results of this research indicated that among the tested genotypes, the Raihan cultivar is the most unsuitable host for greenbug aphid and lead to the decrease of greenbug population growth.     

Differential colonization of wheat cultivars by two biotypes of Russian wheat aphid （Homoptera： Aphididae）

Susceptible and resistance wheat cultivars, Triticum aestivum L, were presented to two biotypes of Russian wheat aphid, Diuraphis noxia （Mordvilko）, in multiple choice tests to assay their relative acceptability as host plants. Both apterae （third and fourth instars） and alate adults were offered plants at the two-leaf stage in different cultivar combinations at 22±1℃ and 16：8 （L： D） hour photoperiod. Apterae were released from Petri dishes in the center of a circle of test plants, whereas alatae dispersed from a mature aphid colony to settle on plants arranged in rows. Both alatae and apterous nymphs of both biotypes readily colonized all cultivars tested：‘2137＇, ‘Akron＇,‘Ankor’,‘ Halt’ ,‘ Jagger’ ,‘ Prairie Red’ , ‘Stanton＇,‘TAM 107＇,‘TAM 110＇,‘Trego＇, ‘ Yuma＇, and ‘Yumar＇. Fewer biotype I apterae responded （settled and fed） in the combination containing more resistant （Dn4- and Dny-expressing） cultivars, compared to the combinations that had fewer. The reverse was true for biotype 2 apterae; more aphids responded in the combination containing the largest number of Dn4 expressing cultivars. Differential colonization of cultivars was observed in only one combination, in which biotype 2 apterae colonized Akron and Yumar in larger numbers than they did Stanton and Yuma. A separate experiment confirmed that, 48 hours after infestation, more biotype 2 apterae abandoned plants of Yuma than plants of Yumar. This differential response was likely due to genetic differences between the two ＇ near isogenic＇ lines that include the lack of Dn4 expression in Yuma. Choice tests with alatae did not result in differential rates of cultivar colonization by either biotype in any combination tested. These results suggest that young wheat plants appear to lack any meaningful antixenosis toward D. noxia, even though the aphids appear to perceive, and sometimes respond to, certain differences in cultivar suitability.     

Spatial and temporal distribution of induced resistance to greenbug (Homoptera: Aphididae) herbivory in preconditioned resistant and susceptible near isogenic plants of wheat

Interactions between biotype E greenbugs, Schizaphis graminum (Rodani), and two near isogenic lines of the greenbug resistance gene Gb3 of wheat, Triticum aestivum L., were examined for 62 d after infestation. By comparing aphid performance and host responses on control and greenbug-preconditioned plants, we demonstrated that systemic resistance to greenbug herbivory was inducible in the resistant genotype with varying intensities and effectiveness in different parts of the plants. Preconditioning of susceptible plants resulted in modification of within-plant aphid distribution and reduction of cumulative greenbug densities, but it showed no effect on reducing greenbug feeding damage to host plant. Preconditioning of resistant plants altered greenbug population dynamics by reducing the size and buffering the fluctuation of the aphid population. Preconditioning in the first (oldest) leaf of the resistant plant had no phenotypically detectable effect in the stem and induced susceptibility locally in the first leaf within the first 2 d after infestation. The preconditioning-induced resistance reduced greenbug density, delayed aphid density peaks and extended the life of younger leaves in resistant plants. Expression of induced resistance was spatially and temporally dynamic within the plant, which occurred more rapidly, was longer in duration, and stronger in intensity in younger leaves. Host resistance gene-mediated induced resistance was effective in lowering greenbug performance and reducing damage from greenbug herbivory in host plants. Results from this study supported the optimal defense theory regarding within-plant defense allocation.     

宁夏地区麦二叉蚜远距离迁飞的研究

通过1971-1987年的调查试验,明确了以下事实：宁夏春麦田麦二叉蚜Schizaphis graminum(Rondani)迁入高峰到来时,当地越冬蚜的春季羽化已基本结束;宁夏春麦黄矮病情与当地麦二叉蚜越冬基数相关不密切,却与东南方冬麦区的越冬基数密切相关;宁夏当地越冬麦蚜春季不带黄矮病毒,而田间却出现了带毒有翅成蚜。首次提出,在有本地蚜源的情况下,存在外来蚜源,且外来蚜源可以成为春季田间麦二叉蚜群的主体。本文分析讨论了迁入蚜的生态意义、蚜源基地、东南风作用和须进一步研究的问题。     

Transmission of Passion fruit woodiness virus by Aphis gossypii (Glover) (Hemiptera: Aphididae) and colonization of passion flower by the vector

The transmission of Passion fruit woodiness virus (PWV) by Aphis gossypii (Glover) was evaluated. In two independent experiments, A. gossypii transmitted PWV to passion fruit plants at the rates of 75% and 100%, when eight and twelve viruliferous aphids were deposited by plant, respectively. At the end of the tests, nymphs of A. gossypii were observed in some of the passion fruit plants, suggesting that the aphid species was colonizing the plants. This seems to be the first report of Passiflora edulis f. flavicarpa (Deneger) colonization by a species of aphid.     

Relative suitability of crested wheatgrass and other perennial grass hosts for the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), reproduces parthenogenetically in North America and must survive year-round on host plants, including in late summer when small grains are not in cultivation. During this time, cool-season perennial wheatgrasses (Poaceae: Triticeae) contribute substantially to aphid survival, crested wheatgrass (Agropyron spp.) particularly. In greenhouse studies, the number of aphids per plant was measured after four infestation periods on unvernalized and vernalized wheatgrasses. Before placement on these test plant species, aphids were reared either on winter wheat or on the grass host species on which aphid progeny were counted. On vernalized plants, aphids reared on wheat resulted in more aphids per test plant than when the aphids were reared on wheatgrasses, but on unvernalized plants the number of aphids per test plant did not differ significantly regardless of rearing host. Aphids on crested wheatgrass were similar in number to the other grasses when plants were unvernalized. However, when plants were vernalized, crested wheatgrass supported significantly more aphids than some of the other hosts. Aphid numbers increased on all test species as infestation period lengthened, and plant growth was largely unaffected by aphid feeding. These results suggest if sufficient moisture is available during summer when small grains are not in cultivation, all host species observed are capable of sustaining aphids. Crested wheatgrass is an abundant and important host of the Russian wheat aphid in its northern range of the western United States, but other less prevalent wheatgrasses also may contribute to aphid survival during late summer when small grains are not in cultivation.     

Species composition of aphid vectors (Hemiptera: Aphididae) of barley yellow dwarf virus and cereal yellow dwarf virus in Alabama and western Florida

Yellow dwarf is a major disease problem of wheat, Triticum aestivum L., in Alabama and is estimated to cause yield loss of 21-42 bu/acre. The disease is caused by a complex of viruses comprising several virus species, including Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. Several other strains have not yet been classified into a specific species. The viruses are transmitted exclusively by aphids (Hemiptera:Aphididae). Between the 2005 and 2008 winter wheat seasons, aphids were surveyed in the beginning of each planting season in several wheat plots in Alabama and western Florida Collected aphids were identified and bioassayed for their yellow dwarf virus infectivity. This survey program was designed to identify the aphid species that serve as fall vectors of yellow dwarf virus into winter wheat plantings. From 2005 to 2008, bird cherry-oat aphid, Rhopalosiphum padi (L.); rice root aphid, Rhopalosiphum rufiabdominale (Sasaki); and greenbug, Schizaphis graminum (Rondani), were found consistently between October and December. The species of aphids and their timing of appearance in wheat plots were consistent with flight data collected in North Alabama between 1996 and 1999. Both R. padi and R. rufiabdominale were found to carry and transmit Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. The number of collected aphids and proportion of viruliferous aphids were low. Although this study has shown that both aphids are involved with introduction of yellow dwarf virus to winter wheat in Alabama and western Florida, no conclusions can be made as to which species may be the most important vector of yellow dwarf virus in the region.     

Use of silicon as inductor of the resistance in potato to Myzus persicae (Sulzer) (Hemiptera: Aphididae)

The aphid Myzus persicae (Sulzer) is an important pest of potato and causes direct harm, due to the quantity of sap extracted and for being vector of important phytovirus. This work was carried out to evaluate the action of silicon as a resistance inducer of potato to M. persicae. Four treatments were tried: foliar fertilization with silicon acid at 1%; soil fertilization with 250 ml silicic acid solution at 1%; foliar fertilization with silicon acid at 1% + soil fertilization with 250 ml silicic acid solution at 1%; and a control. The treatments were applied thirty days after the explants emergence. Fifteen days after the application of the treatments, feeding preference and some biological aspects of the aphids were evaluated. After, the content of tannins and lignin present in the leaves and the activity of the enzymes peroxidase and phenylalanine ammonia-lyase were also determined. The silicon fertilization did not affect the preference of the aphids; however it reduced fecundity and the rate of population growth of the insects. The lignin percentage increased in the leaves of plants fertilized with silicon via soil and/or foliar and the percentage of tannins increased only in the leaves fertilized via soil plus foliar. The silicon acted as a resistance inducer to M. persicae in potato.     

Light activation of Russian wheat aphid-elicited physiological responses in susceptible wheat

The impact of light and its role in Russian wheat aphid, Diuraphis noxia (Mordvilko), damage symptom formation, and photosynthetic capacity in 'Arapahoe' wheat (Triticum aestivum L.) were examined. After 72 h under continuous dark or continuous light regimes, the number of aphids (nymphs), leaf rolling and chlorosis ratings, fresh leaf weight, and chlorophyll contents were recorded. Photosynthetic rates, chlorophyll a, kinetics and chlorophyll extractions also were determined. Aphid infestation caused significant reductions in plant height, fresh weight, gas exchange, and chlorophyll fluorescence only under continuous light. Under the 72 h continuous dark regime, aphid infestation did not cause either damage symptom formation or reduction in plant growth or metabolism (photosynthesis). Furthermore, significantly more D. noxia nymphs were produced under continuous light condition than continuous dark. Our results demonstrate that the development of D. noxia feeding damage symptoms (i.e., leaf rolling and chlorotic streaks) on susceptible wheat seedlings is a light-activated process, even though the elicitor of the plant damage symptoms is aphid feeding.     

Effect of three resistant soybean genotypes on the fecundity, mortality, and maturation of soybean aphid (Homoptera: Aphididae)

The fecundity, longevity, mortality, and maturation of the soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), were characterized using three resistant soybean, Glycine max (L.) Merrill, genotypes ('Dowling', 'Jackson', and PI200538 'Sugao Zarai') and two susceptible genotypes ('Pana' and 'Loda'). Antibiosis in the resistant genotypes was demonstrated by a significant decrease in fecundity and longevity and increased mortality of A. glycines. Aphid fecundity, measured as number of offspring produced in the first 10 d by each viviparous aptera, was higher on Pana than on the resistant genotypes. Aphid longevity, the mean number of days a 1-d-old adult lived, was 7 d longer on Pana than on Dowling and Jackson. The mortality of both viviparous apterae and nymphs on resistant genotypes was significantly higher than on susceptible genotypes. A greater number of first instars survived to maturation stage (date of first reproduction) on susceptible plants than on resistant plants. None of the first instars placed on Dowling and PI200538 leaves survived to maturation. Observations of aphid behavior on leaves indicated that aphids departed from the leaves of resistant plants 8-24 h after being placed on them, whereas they remained indefinitely on leaves of susceptible cultivars and developed colonies. Reduced feeding due to ingestion of potentially toxic compounds in soybean may explain the possible mechanism of resistance to the soybean aphid.     

Evaluation of artificial diets for rearing Aphis glycines (Hemiptera: Aphididae)

Artificial aphid diets have been previously developed for the pea aphid, Acyrthosiphon pisum (Harris), and the green peach aphid, Myzus persicae (Sulzer). The ability to rear aphids on an artificial diet allows for selectively adding or subtracting compounds from an aphid's food source to determine the effect on fecundity and longevity. Five diets previously developed for the green peach aphid and the pea aphid were tested for their suitability for rearing soybean aphid, Aphis glycines Matsumura. The best diet, originally developed for the green peach aphid and based on the amino acid profile of young potato plants, allowed 12 generations of soybean aphids to develop. For all diets tested, aphid fecundity, and longevity were greatly reduced in comparison with aphids reared on soybean, Glycine max (L.) Merr., plants or on detached soybean leaves. In addition, mean developmental time was significantly longer for aphids reared on artificial diets.     

Effects of kaolin particle film on Myzus persicae (Hemiptera: Aphididae) behaviour and performance

The emergence of resistance mechanisms to, and revocation of, many insecticides used in the control of the polyphagus aphid pest, Myzus persicae (Sulzer), has increased the pressure to develop novel approaches for the control of the pest in many crops. Kaolin-based particle films provide a physical barrier against insect pests and show considerable potential for controlling M. persicae. We conducted a series of laboratory experiments to investigate the mode of action of kaolin against aphids. The material appeared to have no direct effect on M. persicae; spraying adult aphids with aqueous kaolin suspension had no significant impact on their subsequent survival or reproduction on untreated plants. Similarly, when aphids were placed on kaolin-treated host-plants (Brassica oleracea), their performance (survival, growth rate and reproduction) was not significantly different from aphids on untreated plants. However, when M. persicae were given a choice between kaolin-treated and untreated (or water solvent-treated) leaf areas, both adults and nymphs exhibited a significant preference for non-kaolin-treated host-plant material. Rejection of kaolin-treated plant material occurred very rapidly (within 20 min) and this behavioural effect may be related to the efficacy of kaolin in controlling aphids under field conditions.     

Effects of brief exposures to low temperature on the development, longevity and fecundity of the grain aphid Sitobion auenae (Hemiptera: Aphididae)

First instar nymphs and adults of the grain aphid Sirobion auenae that had been reared at 10°C and 20°C over a number of generations, were cooled to -5°C and -10°C for 1 h and 6 h and returned to 20°C to assess the effects of brief exposures to low temperatures (cold-pulses) on their survival. rate of development, longevity and fecundity. A strong acclimation response was observed in first instar nymphs, with significantly less mortality in groups reared to 10°C compared to 20°C. Mean development time from first instar to adult was not significantly affected by low temperature exposure at the first nymphal stage. Longevity in all groups cooled as first instars was reduced by the sub-zero cold-pulses, and was also dependent on temperature and exposure time. Acclimated aphids survived longer than non-acclimated individuals. Reproductive rate, in terms of the number of nymphs born per aphid per day, was unaffected by cold stress applied at the first instar stage. Total fecundity was however reduced, being a function of the number and longevity of the survivors. Adult aphids were less cold hardy than nymphs; mortality was higher at -10°C than -5°C increasing with duration of exposure from 1 h to 6 h. Mean fecundity was reduced significantly in aphids cooled at the adult stage, the number of aphids born per day decreasing as the exposure period of the cold-pulse increased, suggesting that low temperature had affected embryogenesis. All the nymphs born to adults surviving exposure to -5°C for 6 h died within 48 h of birth, indicating that low temperature has a pre-natal effect on mortality.     

Host-stage preference and functional response of aphid parasitoid Diaeretiella rapae (McIntosh) (Hym.: Braconidae) on greenbug,Schizaphis graminum (Rondani) (Hem: Aphididae)

Searching capacity is of great importance in the efficiency of natural enemies. In this research, the host-stage preference and functional response of Diaeretiella rapae (McIntosh) to different densities of greenbug, Schizaphis graminum (Rondani) were determined on Pishtaz wheat leaves at 25 ± 1°C, 60–70% relative humidity, and a photoperiod of 16:8 h (L:D). The host-stage preference was investigated by exposing 60 number of all nymphal instars and adults of greenbug to individual parasitoid females at eight replicates. Results indicated significant preference of D. rapae to second instar nymphs of S. graminum to perform functional response experiment. Densities of 2, 4, 8, 16, 32, 50, 64, 90 and 130 second instar nymphs of greenbugs were exposed to individual mated female wasps at 10 replicates for 24 h. Type of functional response was determined by logistic regression and its parameters, searching efficiency (a) and handling time (T _h), were estimated by non linear regression. The results indicated that the functional response of D. rapae was type III and values of searching efficiency, handling time and maximum rate of parasitism were calculated by two models as 0.1364 ± 0.084, 0.5761 ± 0.0179, 41.6594; 0.06489 ± 0.00652 (h^?1), 0.5628 ± 0.0173 (h) and 42.6439 (aphids/parasitoid/day), respectively.     

Intraguild Predation by Anthocoris nemorum (Heteroptera: Anthocoridae) on the Aphid Parasitoid Aphidius colemani (Hymenoptera: Braconidae)

The magnitude of intraguild predation by adult females of the predator Anthocoris nemorum on immature larvae of the aphid parasitoid Aphidius colemani inside mummies of peach-potato aphids Myzus persicae was investigated under laboratory conditions in a preference experiment. Each predator consumed a mean (95% confidence limits) of 2.8 (2.1; 3.8) immature parasitoids within mummies and 3.6 (2.7; 4.6) unparasitised aphid nymphs. Thereby A. nemorum engaged in intraguild predation with A. colemani and did not exhibit prey preference between mummies and unparasitised aphids.