Antibiosis and antixenosis of chrysanthemum cultivars to the aphidAphis gossypii

An assessment was made of the antibiotic and antixenotic resistance of three cultivars of autumn flowering chrysanthemum (derived fromDendranthema morifolium (Ramat) Tzvelev andD. indicum (L.) Desmoulins) to the aphidAphis gossypii Glover. Antibiosis was also assessed at the top, middle and lower leaves of the plant. The three cultivars showed a range of resistance with Hero being the most susceptible, Surfine the most resistant and Purple Anne intermediate. There was a trend for antibiosis to improve with position down the plant, however there were cultivar by position interactions. Antixenosis was assessed at two levels, the first being under conditions where the aphid had complete access to the plant in caged choice assays and the second being under conditions where the aphid only had host odour to assess under olfactometer choice conditions. Preferences under the caged choice conditions found Hero to be the most preferred cultivar while there was no preference shown between Purple Anne and Surfine. However, olfactometer assessments showed Hero to be the least preferred of the three cultivars and, again, no preferences could be found between Purple Anne and Surfine.     

Costs and benefits of hydroxamic acids-related resistance in winter wheat against the bird cherry-oat aphid, Rhopalosiphum padi L.

Estimations of infestation by the bird cherry-oat aphid (Rhopalosiphum padi) as well as measurements of grain yield in 26 Hungarian winter wheat cultivars under field conditions were correlated with the concentration of hydroxamic acids (Hx) in seedlings of those cultivars. The significant inverse relationship between infestation ratings and Hx levels in wheat showed that Hx, despite their decreased accumulation at later plant phenological stages, may be able to confer resistance against aphid infestation in the field. Since no significant relationship was found between grain yield and Hx levels in plants it is suggested that Hx accumulation does not impose a cost to the plant in terms of yield. These findings support earlier claims stressing the potential of Hx as breeding targets for aphid resistance in wheat.     

Plant volatile-induced aphid resistance in barley cultivars is related to cultivar age

Recent studies have shown that volatile chemical interaction between certain barley (Hordeum vulgare) cultivars can cause reduced host plant acceptance by the aphid Rhopalosiphum padi, and that certain cultivars can induce this effect while others can respond. In this study, we tested whether inducing and responding capabilities are linked to year of release in Swedish two-rowed spring barley. Eighteen cultivars released between 1897 and 1992 were tested in randomly selected subsets with pairwise combinations of volatile emitters and receivers. Significantly reduced aphid acceptance as a result of exposure to volatiles from plants of a different cultivar were found in 24% of the cultivar combinations. In general, older cultivars had a higher degree of aphid resistance after barley volatile treatment than did younger cultivars. The inducing effect of the emitter was also related to date of emitter cultivar release but the time relationship was reversed. Combinations with a younger volatile emitter and an older volatile receiver gave the strongest reduction in aphid acceptance of treated plants. Linear relationships between microsatellite diversity of emitting cultivars and their efficiency as inducers indicated that younger cultivars might have a more unique odour, whereas older cultivars may be more sensitive to induction.     

Airborne interactions between undamaged plants of different cultivars affect insect herbivores and natural enemies

This study investigated the effects of airborne interaction between different barley cultivars on the behaviour of bird cherry-oat aphid Rhopalosiphum padi, the ladybird Coccinella septempunctata and the parasitoid Aphidius colemani. In certain cultivar combinations, exposure of one cultivar to air passed over a different cultivar caused barley to have reduced aphid acceptance and increased attraction of ladybirds and parasitoids. Parasitoids attacked aphids that had developed on plants under exposure more often than those from unexposed plants, leading to a higher parasitisation rate. Ladybirds, but not parasitoids, were more attracted to combined odours from certain barley cultivars than either cultivar alone. The results show that airborne interactions between undamaged plants can affect higher trophic levels, and that odour differences between different genotypes of the same plant species may be sufficient to affect natural enemy behaviour.     

Searching for wheat resistance to aphids and wheat bulb fly in the historical Watkins and Gediflux wheat collections

Insect pests can reduce wheat yield by direct feeding and transmission of plant viruses. Here we report results from laboratory and field phenotyping studies on a wide range of wheat, including landraces from the Watkins collection deriving from before the green revolution, more modern cultivars from the Gediflux collection (north‐western Europe) and modern UK Elite varieties, for resistance to the bird cherry‐oat aphid, Rhopalosiphum padi (Homoptera: Aphididae) and the English grain aphid, Sitobion avenae (Homoptera: Aphididae). A total of 338 lines were screened for R. padi and 340 lines for S. avenae. Field trials were also conducted on 122 Watkins lines to identify wheat bulb fly, Delia coarctata, preference on these landraces. Considerable variation was shown in insect performance among and within different wheat collections, with reduced susceptibility in a number of varieties, but phenotyping did not identify strong resistance to aphids or wheat bulb fly. Field trials showed within collection differences in aphid performance, with fewer aphids populating lines from the Watkins collection. This differs from development data in laboratory bioassays and suggests that there is a pre‐alighting cue deterring aphid settlement and demonstrates differences in aphid preference and performance on older plants in the field compared with seedlings in the laboratory, highlighting the need for phenotyping for aphid resistance at different plant growth stages. No association was identified between performance of the different insect species on individual varieties, potentially suggesting different nutritional requirements or resistance mechanisms.     

Fungal endosymbionts affect aphid population size by reduction of adult life span and fecundity

The symbiosis between grasses and endophytic fungi is a common phenomenon and can affect herbivore performance through acquired, chemical plant defence by fungal alkaloids. In laboratory experiments, two species of common grass aphids, Rhopalosiphum padi and Metopolophium dirhodum were tested, in a population experiment (on four plant cultivars) and individually (on one plant cultivar) for the effects of the endophyte, Neotyphodium lolii, that forms symbiotic associations with perennial ryegrass Lolium perenne. In the population experiment that lasted for four aphid generations both aphid species showed decreased population sizes when feeding on each of the four endophyte-infected cultivars. Individuals of R. padi tested individually showed reduced adult life span and fecundity when feeding on infected plants. Individuals of M. dirhodum showed no response in any of the traits measured. This suggests that R. padi individuals are more sensitive to endophyte infection than M. dirhodum individuals. However, all infected grass cultivars reduced population sizes of both aphid species over four generations. Therefore, fungal endophytes can reduce populations of aphid herbivores independent of plant cultivars.     

Influence of wheat and oat cultivars on the development of the cereal aphid parasitoid Aphidius rhopalosiphi and the generalist aphid parasitoid Ephedrus plagiator

The effects of three wheat cultivars and two oat cultivars on the development of the cereal aphid parasitoid Aphidius rhopalosiphi De Steph. and the generalist aphid parasitoid Ephedrus plagiator (Nees) (Hymenoptera: Braconidae) were evaluated in the laboratory. The level of hydroxamic acids, a family of secondary metabolites that can affect the mean relative growth rate of cereal aphids in cereals, were measured in the different cultivars. The parasitoids were reared in Sitobion avenae (F.) (Homoptera: Aphididae), using plants grown under greenhouse conditions. A. rhopalosiphi showed a longer developmental time on wheat relative to oat cultivars. This effect was accounted for by a significant increase in the time from oviposition to pupation (mummy formation), while the duration of the pupal stage remained constant between treatments. No further effects were observed in other variables evaluating A. rhopalosiphi performance, such as adult longevity, adult body weight and secondary sex ratio. The generalist E. plagiator did not show significant differences in any of the variables analysed, both between cultivars and cereal species. Hydroxamic acids levels correlated negatively with mean relative growth rates of S. avenae, but positively with the observed developmental time of A. rhopalosiphi. The results are discussed in terms of tritrophic effects and the development of breeding programmes trying to improve plant resistance to aphids.     

The use of visual cues in host evaluation by aphidiid wasps I. Comparison between threeAphidius parasitoids of the pea aphid

Host evaluation behaviour was examined in three species of aphid parasitoids,Aphidius ervi haliday,A. pisivorus Smith, andA. smithi Sharma & Subba Rao (Hymenoptera: Aphidiidae). Parasitoids were provided under laboratory conditions with three kinds of hosts representing two aphid species: (green) pea aphid,Acyrthosiphon pisum (Harris), and green and pink colour morphs of the alfalfa aphid,Macrosiphum creelii Davis. Females of all threeAphidius species distinguished between aphids on the basis of colour, movement, and host species. Patterns of host acceptance by parasitoids were species-specific. InA. ervi, host preference was the same in light and dark conditions: pea aphid>green alfalfa aphid≫pink alfalfa aphid. In contrast,A. pisivorus attacked and accepted pea aphid and green alfalfa aphid equally in the light and preferred both of these over pink alfalfa aphid; however, it made no distinction between pea aphid and pink alfalfa aphid in the dark. Females ofA. smithi attacked all three kinds of hosts (pea aphid>green alfalfa aphid≫pink alfalfa aphid) but apparently laid eggs only in pea aphid. The frequencies of attack and oviposition by all wasps were higher on ‘normal’ pea aphids than on those anaesthetized with CO₂. Host recognition is confirmed by chemical cues in the aphid cuticle that are detected during antennation, and host acceptance is dependent on an assessment of host quality during ovipositor probing.     

The influence of host plant species on parasitism of pollen beetles (Meligethes spp.) by Phradis morionellus

We investigated the response of the specialist insect predator Oligota kashmirica benefica (Coleoptera: Staphylinidae) to volatiles from lima bean leaves infested with the spider mite Tetranychus urticae (Acari: Tetranychidae), both in a Y-tube olfactometer and in a field in Kyoto, Japan. Adult male and female predators were significantly more attracted to T. urticae-infested leaves than to clean air. Adult male and female predators were not more attracted to uninfested leaves, artificially damaged leaves, or the spider mites and their visible products when compared to clean air. In a field trap experiment, 12 adult predators were caught in three traps containing T. urticae-infested lima bean plants over 13 days, whereas no adult predators were trapped in three traps containing uninfested lima bean plants during the same period. These results showed that O. kashmirica benefica adults responded to herbivore-induced plant volatiles from T. urticae-infested lima bean leaves under both laboratory and field conditions.     

Hydroxamic acids affecting barley yellow dwarf virus transmission by the aphid Rhopalosiphum padi

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid (Hx) occurring in wheat, was shown to deter feeding by the aphid Rhopalosiphum padi (L.), and to reduce BYDV transmission to the plant. Dual choice tests with wheat leaves showed the preferential settlement of aphids on leaves with lower levels of DIMBOA. Electric monitoring of aphid feeding behaviour showed that in seedlings with higher DIMBOA levels fewer aphids reached the phloem and they needed longer times to contact a phloem vessel than in those with lower levels. When aphids carrying BYDV were allowed to feed on wheat cultivars with different DIMBOA levels, fewer plants were infected with BYDV in the higher DIMBOA cultivars than in the lower ones. Preliminary field experiments showed a tendency for wheat cultivars with higher Hx levels to be more tolerant to infection by BYDV than lower Hx level ones.     

High variation in host adaptation among clones of the pea aphid,Acyrthosiphon pisum on peas,Pisum sativum

The performance of one clone of the pea aphid,Acyrthosiphon pisum (Harris), was assessed on 37 different cultivars and species ofPisum L. In addition, random samples of 36 pea aphid clones collected on alfalfa and clover were tested on a selection of fivePisum sativum L. cultivars. Aphid performance was evaluated in terms of the mean relative growth rate (MRGR) during the first five days of life or other life history variables. The MRGR of the first-mentioned pea aphid clone differed little between cultivars. No significant differences in MRGR were found between wild and cultivatedPisum species or between modern and oldP. sativum cultivars. There was considerable variation in host adaptation among the 36 pea aphid clones within each sampled field. The pea aphid clones showed no consistent pattern in performance on four of the five pea cultivars i.e. there was a significant pea aphid genotype —pea genotype interaction. On one of the cultivars all clones performed well. Pea aphid clones collected from red clover generally performed relatively poorly on pea cultivars, in contrast to the pea aphid clones collected on alfalfa. There was no difference in performance between the two pea aphid colour forms tested. Possible reasons for the high variation and the observed adaptation patterns are discussed. The fact that all clones were collected in two adjacent fields indicates thatA. pisum shows high local intraspecific variability in terms of host adaptation.     

Effect of various cauliflower cultivars on population density fluctuations of the cabbage aphid,Brevicoryne brassicae (L.) (Hom.: Aphididae) and its parasitoid Diaeretiella rapae (McIntosh) (Hymenoptera: Braconidae)

In this study, population density changes of the cabbage aphid, Brevicoryne brassica (L.), were tested in the field during 2011 under natural infestation at research field of the Shahed University (South of Tehran). This investigation was conducted on the eight cauliflower cultivars including Smilla, Snow mystique, White cloud, Buris, Galiblanka, Snow crown, SG and Tokita in randomised complete block design with five replications. Sampling was done after starting of aphid activity in the field every week and the total number of adult aphids and nymphs were counted in three leaves of the upper, middle and lower parts of the plant. In addition, the percentage of parasitism of the cabbage aphid by Diaeretiella rapae was evaluated. Results of the sampling showed that peak of the aphid population were at the first half of November. The parasitism percent of the cabbage aphid by D. rapae was significantly different among studied cultivars (p?<?0.05). Therefore, it can be concluded that using of Smilla, Buris and SG cultivars probably increases the efficiency of D. rapae in the control of the B. brassica (L.).     

Susceptibility of selected apple cultivars to the Mediterranean fruit fly

Ceratitis capitata (Wiedemann), the Mediterranean fruit fly, is one of the key pest species affecting deciduous fruit orchards along the Mediterranean coasts. Because of global warming, C. capitata is gradually spreading north and is becoming a major pest of apples. Determining the susceptibility of the main apple varieties grown in the region will serve as a cornerstone to the management of this pest. In this study, we show the results of a field and laboratory no‐choice test conducted to determine the Medfly preferences on different apple cultivars. The seven main varieties of apples (Gala, Red Delicious, Golden Delicious, Granny Smith, Kanzi, Morgen Dallago and Fuji) were tested. The results demonstrate that C. capitata lays eggs on all apple cultivars in both field and laboratory conditions. The Granny Smith, Red Delicious and Morgen Dallago varieties showed the lowest susceptibility in laboratory conditions, (0.75, 1.55, 2 oviposition punctures/fruit, respectively), with significant differences in oviposition compared to the Golden Delicious, Kanzi and Fuji (3.27, 3.31, 3.1 oviposition punctures/fruit, respectively) varieties, which were shown to be the most susceptible to Medfly attack in laboratory conditions. On the other hand, only slight and not statistically significant differences emerged from the field trials. In relation to the physico‐chemical characteristics, the apple cultivars showing the lowest susceptibility (Granny Smith, Red Delicious and Morgen Dallago) had harder peels and pulps and lower sugar contents than the most susceptible cultivars (Golden Delicious, Fuji and Kanzi). These results were also confirmed through evaluation of larval development on different varieties. In fact, Granny Smith, Red Delicious and Morgen Dallago were the three varieties that did not allow adequate larval and adult development and reduced the possibility of the emergence of a new generation.     

Ant attendance of the cotton aphid is beneficial for okra plants: deciphering multitrophic interactions

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Intraspecific heritable variation in life-history traits can alter the outcome of interspecific competition among insect herbivores

Competition is one of the most important biotic factors determining the structure of ecological communities. In this study, we show that there is variation in competitive ability between two clones of the pea aphid, Acyrthosiphon pisum, both of which out-compete a clone of the vetch aphid, Megoura viciae, in the laboratory. We tested whether this variation in competitive ability would alter the outcome of interspecific competition in the field. While one pea aphid clone followed the pattern set in the laboratory, out-competing the Megoura viciae clone, another showed the reverse effect with Megoura viciae dominating. These differences appear to be the result of variation in early population growth rate between the pea aphid clones, rather than predation, although predation did lead to the eventual extinction of colonies. We also questioned whether intra- and interspecific differences in predator escape behaviour could affect the outcome of competition in the field. All three clones responded similarly to the presence of foraging hoverfly larvae (Episyrphus balteatus), but the Megoura viciae clone dropped from the plant significantly less often in response to the presence of a foraging two-spot ladybird (Adalia bipunctata). This work provides evidence that intraspecific variation in competitive ability can alter the outcome of interspecific competitive interactions in nature and suggests that species–specific behavioural traits may have the potential to modify the outcome of these interactions.     

Effect of wheat resistance, the parasitoid Aphidius rhopalosiphi, and the entomopathogenic fungus Pandora neoaphidis, on population dynamics of the cereal aphid Sitobion avenae

The influence of wheat (Triticum aestivumL.) resistance, the parasitoid Aphidius rhopalosiphiDe Stephani-Perez (Hymenoptera: Braconidae) and the entomopathogenic fungus Pandora neoaphidis(Remaudière et Hennebert) Humber (Zygomycetes: Entomophthorales) on the density and population growth rate of the cereal aphid Sitobion avenae(F.) (Hemiptera: Aphididae) was studied under laboratory conditions. Partial wheat resistance was based on hydroxamic acids, a family of secondary metabolites characteristic of several cultivated cereals. The partial resistance of wheat cultivar Naofén, the action of the parasitoid and the joint action of the parasitoid and fungus, reduced aphid density. The lowest aphid densities were obtained with the combination of the parasitoid and the fungus, but wheat resistance under these circumstances did not improve aphid control. Significant reductions of population growth rate (PGR) of aphids were obtained with the joint action of wheat resistance and natural enemies. In particular, the combined effects of parasitoids and fungi showed significantly lower PGR than the control without natural enemies in both wheat cultivars. Our results support the hypothesis that wheat resistance and the utilization of biological control agents could be complementary strategies in an integrated pest management program against cereal aphids.     

Components of resistance to Aphis fabae in faba bean cultivars

An aphid rate of increase index was used as a comparative measure of antibiotic resistance to Aphis fabae Scopoli (Homoptera: Aphididae) in five faba bean cultivars. The index was measured over a range of bioassays in laboratory and field, with seedlings and older plants, with three different previous aphid hosts and with two different aphid clones. Antixenotic resistance was measured by recording host selection and acceptance of the same cultivars by alate aphids. Cultivars which were antibiotically resistant were also antixenotically resistant. Antibiotic, but not antixenotic resistance, was less effective in the field than in the laboratory. The resistance of cv. Herra was influenced by previous aphid host, aphid clone and plant age but the resistance of Line 14 was more stable. Honeydew production was measured; aphids on resistant cultivars produced less honeydew of lower amino acid concentration than those on susceptible cultivars.

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Résumé L'importance des composantes antibiotique et antixénotique de la résistance de la fève à A. fabae a été évaluée dans différentes conditions au champ et au laboratoire.Un indice de performance du puceron sur des cultivars témoins très voisins du taux intrinsèque d'accroissement naturel a été utilisé pour les mesures comparant la résistance antibiotique. La lignée 14 et le cv. Herra ont été les plus résistants des 5 cultivars examinés. La résistance antibiotique de 14 par comparaison avec les cultivars sensibles n'a pas été modifiée par l'âge de la plante, le clone de puceron ou les cultivars qu'avaient eu précédemment les pucerons dans des expériences de laboiratoire. La résistance de Herra était moins stable. Les différences entre résistances antibiotiques des cultivars était plus faible en champ où aucune différence significative dans les taux de multiplication des pucerons n'a été observée.L'antixénose a été évaluée au laboratoire en mesurant les taux d'installation des ailés sur les cultivars et les taux d'acceptation des ailés quand ils avaient été placés sur les cultivars. La résistance antixénotique a refleté la résistance antibiotique. L'antixénose reste efficace quand aucun cultivar sensible alternatif était disponible. Des observations sur des infestations précoces de pucerons sur parcelles ont laissé penser que l'antixénose était effective aux mêmes niveaux au champ et au laboratoire.Les pucerons s'alimentant sur des cultivars résistants ont produit moins de miellat avec une plus faible concentration en acides aminés.Ces résultats font penser que les efforts dans la sélection pour la résistance à A. fabae devraient être orientés vers l'antixénose pour laquelle un screening rapide en laboratoire pourrait être efficace.

     

Identification and characterisation of antixenosis and antibiosis to pea aphid (Acyrthosiphon pisum) in Pisum spp. germplasm

Acyrthosiphon pisum is a polyphagous aphid of major importance on the pea crop to which few resistant cultivars are available. In this study, we screened a germplasm collection of Pisum spp. under field conditions over two seasons yielding the identification of a number of accessions with intermediate levels of resistance. Selected accessions were further studied under semi‐controlled and controlled conditions in no choice and choice assays to validate the responses, and to further characterise the mechanisms of resistance operative. Results elucidated the valuable resistance of accession P40 (Pisum sativum ssp. sativum) and P665 (P. sativum ssp. syriacum), with the combination of both antixenosis, by reducing aphid preference, and antibiosis, by diminishing aphid proliferation.     

Inheritance of resistance to lettuce root aphid in the lettuce cultivars 'Avoncrisp' and 'Lakeland"

The inheritance of resistance in two lettuce cultivars to lettuce root aphid, Pemphigus bursarius, was studied in a series of laboratory and field experiments at Wellesbourne between 1989 and 1992. A source of total resistance in the cv. ‘Avoncrisp’ which is linked to the downy mildew resistance gene Dm6, was shown to be governed by a single dominant gene. There were no maternal effects evident in the inheritance of this resistance. The basis of the high level of resistance which exists in the cv. ‘Lakeland’ (formerly known as ‘Jubilee’) was also shown to be controlled by the same dominant gene. The linkage between Dm6 and root aphid resistance was broken in ‘Lakeland’ as this cultivar does not possess the Dm6 gene. The linkage was presumably broken when the original cross between the parents of cv. ‘Lakeland’, ‘Calmar’ and ‘Avoncrisp’ was made. Under laboratory conditions small numbers of aphids commence development on cv. ‘Lakeland’ but colonies fail to develop and under field conditions the resistance provides adequate Protectión against the pest. The resistance in both ‘Avoncrisp’ and ‘Lakeland’ was effective against a population of lettuce root aphid collected from an endive crop in southern France as well as being effective against the Wellesbourne population of this aphid.     

Adaptations to water gradient in three Rorippa plant species correspond with plant resistance against insect herbivory under drought and waterlogged conditions

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