The potential of three native insect predators to control the rosy apple aphid, Dysaphis plantaginea

The potential of three aphidophagous predators, Adalia bipunctata, Aphidoletes aphidimyza, and Episyrphus balteatus to control the rosy apple aphid, Dysaphis plantaginea Pass., a major pest on apple in Europe, was assessed by means of laboratory and field cage experiments in Northern Switzerland. Under laboratory conditions, all three predators efficiently preyed upon D. plantaginea on apple seedlings. The searching success of larvae of A. bipunctata for individual aphids was not dependent on the size of branches of apple trees varying in leaf surface area from 150 cm² to 960 cm². Fifty and 70% of individual aphids were found and killed 6 hours and 48 hours, respectively, after release of single second instar larva of A. bipunctata. In a first field cage experiment in 1996, A. bipunctata, and to a lesser extent E. balteatus, proved to be effective and consistent predators of D. plantaginea during spring conditions, being little affected by cool temperatures and wet weather. In a subsequent field cage experiment in 1997, larvae of A. bipunctata and E. balteatus were released singly and in combination on aphid infested apple seedlings to study interactions between these two promising control agents. Both species had a significant negative effect on aphid population increase. The two species did not significantly interact and thus, their joint effect is best explained by an additive model. Combined releases of the two predator species reduced aphid densities to 5% of the control. This indicates the potential for augmentative releases of these native aphid predators to control D. plantaginea.     

Effects of augmentative releases of the coccinellid, Adalia bipunctata, and of insecticide treatments in autumn on the spring population of aphids of the genus Dysaphis in apple orchards

The impact of augmentative releases of indigenous predators and insecticide applications to control the autumn aphid forms of the genus Dysaphis (Homoptera: Aphididae), major pest insects on apple trees, was assessed in one-year field experiments in Switzerland. Eggs and larvae of the two-spot ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) were released on 4-year old apple trees in various numbers at five different dates in autumn 1998 when sexuales of the aphids were present. Additionally, Pyrethrum HP was sprayed at the same five dates to compare the effectiveness of these augmentative releases to a commonly applied insecticide. Augmentative releases of larvae before mid-October significantly prevented the deposition of overwintering eggs by aphids of the genus Dysaphis and consequently reduced the number of hatched fundatrices in spring, 1999. There was a significant negative functional response among the number of released coccinellid larvae in autumn 1998 and the number of observed fundatrices on apple trees in spring 1999. Applications of Pyrethrum HP before mid-October were more effective than augmentative releases of larvae of A. bipunctata. The release of coccinellid eggs had no impact on the number of fundatrices of the genus Dysaphis in the next spring because they did not hatch due to bad weather conditions. The weather conditions in autumn seemed to have an impact on the autumn migration of the winged aphids back to their primary host. The prevention of egg deposition of aphids in autumn is a promising control strategy and deserves further exploration for practical use.     

The effect of ant attendance on the success of rosy apple aphid populations, natural enemy abundance and apple damage in orchards

1 The rosy apple aphid, Dysaphis plantaginea, is the most serious pest of apple in Europe and, although conventionally controlled by insecticides, alternative management measures are being sought. Colonies of D. plantaginea are commonly attended by ants, yet the effects of this relationship have received little attention. 2 An ant exclusion study was conducted in two distant orchards within the U.K. At both sites, ants were excluded from a subset of D. plantaginea infested trees at the beginning of the season and populations were monitored. The number of natural enemies observed on trees was also recorded and, before harvest, the percentage of apples damaged by D. plantaginea calculated. 3 Overall, the exclusion of ants reduced the growth and eventual size of D. plantaginea populations. On trees accessed by ants, greater numbers of natural enemies were recorded, presumably because aphid populations were often greater on such trees. However, this increased natural enemy presence was diluted by the larger aphid populations such that individual aphids on ant‐attended trees were subjected to a lower natural enemy pressure compared with those on ant‐excluded trees. 4 At harvest, apple trees that had been accessed by ants bore a greater proportion of apples damaged by D. plantaginea. There were also differences in cultivar susceptibility to D. plantaginea damage. 5 The present study highlights the importance of the ant–D. plantaginea relationship and it ia suggested that ant manipulation, whether physically or by semiochemicals that disrupt the relationship, should be considered as a more prominent component in the development of future integrated pest management strategies.     

Feeding and egg distribution studies of Heringia calcarata (Diptera: Syrphidae), a specialized predator of woolly apple aphid (Homoptera: Eriosomatidae) in Virginia apple orchards

Predation by the aphidophagous syrphid fly Heringia calcarata (Loew) on woolly apple aphid, Eriosoma lanigerum (Hausmann), was studied in the laboratory and in Virginia apple orchards. Feeding studies compared the prey suitability of three temporally sympatric aphid pests of apple: spirea aphid, Aphis spiraecola Patch; rosy apple aphid, Dysaphis plantaginea (Passerini); and woolly apple aphid. Significantly more H. calcarata larvae survived and completed development on a pure diet of woolly apple aphid than on rosy apple aphid, and none survived on spirea aphid. Final larval weights were significantly greater, and the larval developmental period was significantly shorter on woolly apple aphid than on rosy apple aphid, but neither the duration of pupal development nor adult weight differed between diets. H. calcarata larvae consumed an average of 105 woolly apple aphids during their development. Na?ve, neonate larvae given access to all possible pair combinations of woolly apple aphid, rosy apple aphid, and spirea aphid consumed significantly more woolly apple aphids in all pairings that included woolly apple aphid. When given a choice of rosy apple aphid and spirea aphid, significantly more rosy apple aphids were consumed. Weekly counts of syrphid eggs found in woolly apple aphid, rosy apple aphid, and spirea aphid colonies collected from apple trees showed that two generalist hover fly predators, Eupeodes americanus (Wiedemann) and Syrphus rectus Osten Sacken, were present in colonies of all three aphid species and that E. americanus was the most abundant syrphid predator in A. spiraecola and D. plantaginea colonies. H. calcarata eggs were found only in woolly apple aphid colonies and were more abundant there than E. americanus and S. rectus. These data suggest that H. calcarata is a specialized predator of woolly apple aphid in the apple ecosystem in Virginia.     

Releases of a natural flightless strain of the ladybird beetle Adalia bipunctata reduce aphid-born honeydew beneath urban lime trees

Aphids can cause major environmental problems in urban areas. One important problem is the annual outbreaks of lime aphid, Eucallipterus tiliae (L.) (Hemiptera: Aphididae), which spoil the surroundings of lime trees by depositing honeydew. To date no environmentally friendly method has been demonstrated to yield effective control of lime aphids. Attempts are made in some cities to control lime aphids by releasing larvae of the native two-spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae). However, it is known that adult ladybird beetles disperse soon after release, and there is little indication they provide control of the aphids. Here, we demonstrate experimentally that releases of a flightless strain of A. bipunctata, obtained from natural variation in wing length, can reduce the impact of honeydew from lime aphid outbreaks on two species of lime in an urban environment. Both larvae and adult beetles were released, and we discuss the contribution of the flightless adults to the decline in honeydew.     

Resistance of apple cultivars to Dysaphis plantaginea (Hemiptera: Aphididae): role of tree phenology in infestation avoidance

To test the importance of flowering phenology in damage caused to apple cultivars by rosy apple aphid, Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae), susceptibility of 16 cultivars was compared in greenhouse conditions after infestation with aptera and in the field after natural tree colonization. Flowering phenology was recorded in the field for all the cultivars. In both greenhouse and field trials, there were differences among cultivars with respect to aphid infestation and damage. However, damage in the greenhouse and field was not significantly correlated. Flowering phenology was also different among cultivars. Flowering order among cultivars was significantly negatively correlated with aphid infestation and damage in field, i.e., early leafing cultivars showed higher infestation and damage than late-leafing cultivars. If egg hatching occurs before bud bursting, neonate larvae will suffer a high mortality because they cannot feed on these late cultivars. A later recolonization of these trees is hampered because (1) winged aphids cannot live on apple but only on the secondary host, (2) apterous forms have a limited dispersal capability, and (3) aphid predators progressively increase in the orchard. Therefore, synchronization between egg hatching and bud bursting is of critical importance in the success or failure of infestation.     

Flower strips increase the control of rosy apple aphids after parasitoid releases in an apple orchard

Mass releases of two parasitoid species, Aphidius matricariae and Ephedrus cerasicola, may provide an alternative measure to pesticides to control the rosy apple aphid Dysaphis plantaginea in organic apple orchards. As an exploratory study, we tested if the presence of flower strips between apple tree rows could improve the action of three early parasitoid releases––and of other naturally present aphid enemies––on the control of aphid colonies and the number of aphids per tree. Apple trees located at various distances from parasitoid release points were monitored in plots with and without flower strips in an organic apple orchard over two years, along the season of aphid infestation (March to July). Our case study demonstrated that the presence of flowering plant mixes in the alleyways of the apple orchard reduced the presence of D. plantaginea by 33.4%, compared to plots without flower strips, at the infestation peak date. We also showed a negative effect of increasing the distance to parasitoid release points on aphid control. However, our results at the infestation peak date suggest that the presence of flower strips could marginally compensate for the detrimental effect of increasing distance to the release point, probably by improving the persistence and dispersal capacities of natural enemies. Despite high variations in aphid population dynamics between years, we conclude that combining flower strips with early parasitoid releases in apple orchards is promising for biological control of the rosy apple aphid, although the method merits to be further refined.     

Aphid-ant interaction reduces chrysomelid herbivory in a cottonwood hybrid zone

In a cottonwood (Populus) hybrid zone, Chaitophorus aphids attract aphid-tending ants which subsequently reduce herbivory by the leaf-feeding beetle, Chrysomela confluens. Observations and experimental manipulations of aphids and beetle larvae on immature cottonwood trees demonstrated that: 1) via their recruitment of ants, aphids reduced numbers of beetle eggs and larvae on the host; 2) these interactions occurred within a few days of the host being colonized by aphids; and 3) although aphid colonies were ephemeral, their presence resulted in a 2-fold reduction in beetle herbivory. The aphid-ant interaction is most important in the hybrid zone where 93% of the beetle population is concentrated (for reasons unrelated to aphids and ants). Because beetle defoliation of immature trees is high (ca. 25%), the indirect effect of aphids in reducing herbivory is likely more beneficial to trees in the hybrid zone than in adjacent pure zones where beetle herbivory is virtually absent. Tree genotype likely affects the impact of the aphid-ant interaction on trees within the hybrid zone, since levels of herbivory differ between sympatric Fremont and hybrid cottonwoods.     

Effects of autumn kaolin treatments on the rosy apple aphid, Dysaphis plantaginea (Pass.) and possible modes of action

Abstract:  Autumn applications of the repellent processed-kaolin particle film (Surround® WP) might be an alternative to the insecticides commonly used in spring to control the rosy apple aphid, Dysaphis plantaginea (Pass.) (Hom., Aphididae). To assess the mode of action and the impact of kaolin on autumn forms of D. plantaginea , trials were conducted in field cages and in open-fields in autumn 2003. Choice and no-choice experiments in field cages showed that winged aphids landed in significantly lower numbers and gave birth to significantly fewer females on kaolin-treated branches compared with the untreated control. In a first open-field trial, single applications at 10 different dates and with two different concentrations of kaolin were conducted after harvest to assess the influence of the kaolin concentration on the autumn forms of D. plantaginea . No differences were found between the different concentrations and spraying dates. In a second open-field trial, single and multiple applications of kaolin were tested at different dates after harvest. Repeated applications of kaolin significantly reduced females in autumn and fundatrices in spring, whereas single kaolin treatments had no significant effect on D. plantaginea . None of the kaolin treatments reduced aphids below the economic threshold. In conclusion, kaolin showed promising results to control autumn forms of D. plantaginea. However, with a more detailed forecasting model for the autumnal flight of this aphid, treatments could be conducted more precisely and more effectively, especially in years with exceptional climatic conditions, such as in 2003.     

Effects of habitat fragmentation on the three-way interaction among ants,aphids and larvae of the giant purple emperor, <Emphasis Type="Italic">Sasakia charonda</Emphasis> (Hewitson), a near-threatened butterfly

Survival rates of both early and middle instar larvae of the nymphalid butterfly, Sasakia charonda, were estimated to be lowest on test trees planted in a meadow (site A), intermediate in a small, narrow secondary deciduous broadleaf forest (small patch, site B) and highest in a large secondary deciduous broadleaf forest (large forest, site C). The larval mortality rates due to predation by tree-climbing predators from the ground (tree climbing predator) such as ants and the larvae of carabids were estimated to be greater at sites A and B than those at site C. The number of predatory ants climbing test trees was significantly greater at sites A and B than at site C, and the ants harvested honeydew from aphids living on tree leaves at those two sites. Aphid densities were significantly higher on trees at sites A and B than at site C, and aphid densities and numbers of predatory ants were significantly and positively correlated at sites A and B. In an experiment controlling aphid density per branch on test trees, the numbers of ants and the mortality rates of S. charonda larvae were greater on branches with high aphid densities than on those with low aphid densities at both sites A and B. These results suggest that the aphid density per host tree was higher in the meadow and the small patch than in the large forest; at both sites these higher aphid densities attracted higher numbers of predatory ants to test trees, and as a result, mortality rates of S. charonda larvae were increased.     

Role of ants in structuring the aphid community on apple

1. The aphids Dysaphis plantaginea Passerini, Aphis spp. (Aphis pomi De Geer and Aphis spiraecola Patch), and Eriosoma lanigerum Hausmann are commonly found together in apple orchards. Ants establish a mutualistic relationship with the myrmecophilous aphids D. plantaginea and Aphis spp. but not with E. lanigerum. 2. Field surveys and one experiment manipulating the presence of ants and the aphid species were conducted to test the hypothesis that ants play a role in structuring the community of these aphids on apple. 3. Ants tended D. plantaginea and Aphis spp. but not E. lanigerum colonies. In the field, D. plantaginea performed better in the presence of ants while no effect was observed in Aphis spp. Contrarily, populations of Aphis spp. in the manipulative experiment performed better in the presence of ants while no differences were observed for D. plantaginea. Such differences between field and manipulative conditions could be related to thermal tolerance, phenology, and life cycles. In contrast, populations of E. lanigerum were reduced in the presence of ants. 4. Ants also had a significant negative effect on the abundance of natural enemies, which could partially explain the benefits to the tended aphids. However, while ants did not provide a benefit to Aphis spp. when it was reared alone, in the presence of other species ant attendance increased Aphis abundance by 256% and simultaneously reduced E. lanigerum abundance by 63%. Therefore, ants benefited Aphis by reducing competition with other aphid species, which involves a different mechanism, explaining the benefit of ant attendance. Considering all the aphid species together, ants had a net positive effect on aphid abundance, which was consequently considered harmful for the plant. 5. Our results highlighted the role that ants play in structuring apple aphid communities and give support to the observed pattern that ants can benefit tended aphids while simultaneously reducing the abundance of untended herbivores.     

Avoidance responses of an aphidophagous ladybird, Adalia bipunctata, to aphid-tending ants

Abstract.  1. Insect predators often aggregrate to patches of high prey density and use prey chemicals as cues for oviposition. If prey have mutualistic guardians such as ants, however, then these patches may be less suitable for predators.
2. Ants often tend aphids and defend them against predators such as ladybirds. Here, we show that ants can reduce ladybird performance by destroying eggs and physically attacking larvae and adults.
3. Unless ladybirds are able to defend against ant attacks they are likely to have adaptations to avoid ants. We show that Adalia bipunctata ladybirds not only move away from patches with Lasius niger ants, but also avoid laying eggs in these patches. Furthermore, ladybirds not only respond to ant presence, but also detect ant semiochemicals and alter oviposition strategy accordingly.
4. Ant semiochemicals may signal the extent of ant territories allowing aphid predators to effectively navigate a mosaic landscape of sub-optimal patches in search of less well-defended prey. Such avoidance probably benefits both ants and ladybirds, and the semiochemicals could be regarded as a means of cooperative communication between enemies.
5. Overall, ladybirds respond to a wide range of positive and negative oviposition cues that may trade-off with each other and internal motivation to determine the overall oviposition strategy.     

Seasonal coincidence between rosy apple aphid fundatrices and their parasitoids: implications for an early biological control of Dysaphis plantaginea

The potential contribution of the aphid parasitoid Ephedrus persicae Froggatt (Hymenoptera: Braconidae, Aphidiinae) in regulating stem mothers of the rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae) was investigated in culture conditions using both species' phenological emergence data in spring and host stage suitability trials. In 2003, emergence of E. persicae started on April 1st, i.e., 108.2 degree-days (base: 4.5 degrees C; start date: January 1st) later than its host on March 10th. When less than 3% of parasitoids had emerged on April 12th, more than 97% of D. plantaginea stem mothers had moulted beyond their 1st instar. The latest parasitoids left their diapause mummies in late April as the majority of fundatrices had reached the adult stage. Parasitisation trials demonstrated the suitability for E. persicae of all developmental stages of rosy apple aphid fundatrices, including mature individuals. No offspring were deposited by fundatrices parasitised as Ist-instar nymphs but later instars did produce a progeny whose size was substantially reduced compared with unparasitised individuals, and scaled against their age at the time of parasitisation. Although the temperature accumulation required for emergence in spring is reached later for E. persicae than for its host aphids, thus allowing part of the stem mother population to temporarily escape parasitisation and reach maturity, the marked reduction in fecundity of individuals parasitised even as late-instar nymphs does confer to E. persicae a non-negligible role in potentially regulating D. plantaginea.     

The effect of parasitism by Aphelinus abdominalis and drought on the walking movement of aphids

The effect of simulated plant stress and parasitism by Aphelinus abdominalis (Dalman) on the mobility of four species of aphids was investigated. The aphids were placed on water stressed potted plants or on excised leaf segments on dry or moist filter-paper in Petri dishes. Winter wheat (Triticum aestivum) was infested with Metopolophium dirhodum (Walker), Sitobion avenae (F.) and Rhopalosiphum padi (L.) (segments only), aubergine (Solanum melongena) leaf segments with Macrosiphum euphorbiae (Thomas). The aphids that moved off the plants were removed and their development stage determined at 24-h (drought-stressed plants) or 3-h (leaf segments) intervals. On intact plants, aphid larvae were reluctant to move, and only moved after moulting into adults. On cut leaves, young 1st and 2nd instar larvae were more reluctant to move than 3rd and 4th instar larvae and adults. The numbers moving were initially positively correlated with aphid population density, and in M. euphorbiae occurred mainly during the night. Depending on aphid species and parasitoid age, parasitism by A. abdominalis retarded or accelerated movement, but the differences between young and old larvae and adults persisted after parasitism. A. abdominalis lays male eggs in small hosts and female eggs in large hosts. Consequently, its sex ratio was affected by differential movement of the host aphids of the male and female parasitoids. Old larvae and adult aphids readily moved and carried off female parasitoids, while the small aphids were more likely to remain and give rise to male-biased sex ratios.     

Temporal and spatial variability of rosy apple aphid Dysaphis plantaginea populations: is there a role of the alternate host plant Plantago major?

• 1 The rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae) is a pest of economic importance to the apple industry worldwide, particularly in organic apple orchards where no acceptable controls are available. In the Similkameen Valley of British Columbia, Canada, the rosy apple aphid population size varies widely between orchards and between years. To explain this variation, potential environmental correlates of aphid density were evaluated. The architecture of the alternate host was also evaluated for its effect on rosy apple aphid summer survival and reproduction.
• 2 The percentage of trees infested by rosy apple aphids among orchards was in the range 8–94% for trees having at least one cluster with more than ten aphids in 2007 and in the range 0–39% in 2008.
• 3 A general linear model correlating aphid densities to the environmental variables of abundance of the alternate host (plantain Plantago spp.), foliar nitrogen, tree age and planting density, and reduced by stepwise regression, indicated that foliar nitrogen and tree age explained 33% of the variation. Abundance of the summer, alternate food plant, plantain, was not related to later aphid densities on apple trees.
• 4 Plantain architecture, however, influenced aphid numbers and 25‐fold more aphids were found on low‐lying plantain leaves than on more upright leaves. Experimental manipulation of leaf angle and leaf size showed that significantly more aphids occurred on low angle, large leaves. Finally, mowing that encouraged low lying plants prior to spring aphid migration was associated with a four‐fold greater number of both winged and wingless aphids on the plantain.

     

Conservation biological control of rosy apple aphid, Dysaphis plantaginea (Passerini), in eastern North America

Because of the potentially serious damage rosy apple aphid, Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), can cause to apple fruit and branch development, prophylactic insecticides are often used for control. If biological control could be relied on, the amount of pesticide applied in orchards could be reduced. This study examined biological control of rosy apple aphid in eastern West Virginia and the potential for enhancement through conservation biological control, in particular, the effect of interplanting extrafloral nectar-bearing peach trees. By 20 d after first bloom, only 2% of fundatrices initially present survived to form colonies based on regression of data from 687 colonies. Exclusion studies showed that many of the early colonies were probably destroyed by predation; the major predator responsible seemed to be adult Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Mortality before apple bloom was most important in controlling rosy apple aphid population growth but by itself is not sufficiently reliable to prevent economic injury. Interplanting of extrafloral nectar-bearing trees did not increase biological control, and interplanting with 50% trees with extrafloral nectar glands reduced biological control. The number of leaf curl colonies in the 50% interplanted orchards was lower than in monoculture orchards, suggesting a preference of alate oviparae for more diverse habitats, supporting the resource concentration hypothesis but not at a level sufficient to prevent injury. Predation and parasitism after the formation of leaf curl colonies was not adequate to control rosy apple aphid populations.     

Oviposition preferences of Maculinea alcon as influenced by aphid (Aphis gentianae) and fungal (Puccinia gentianae) infestation of larval host plants

Abstract 1. The influence of infestation of the larval host plant Gentiana cruciata on the egg‐laying preferences of the xerophilous ecotype of Alcon Blue butterfly (Maculinea alcon) was studied in a semi‐dry grassland area (Aggtelek Karst Region, Northern Hungary). 2. We examined whether oviposition patterns of females differed when G. cruciata stems were uninfested compared with when they were infested by an aphid (Aphis gentianae) or a rust (Puccinia gentianae) species. 3. Females laid more than 90% of their eggs on fertile, uninfested G. cruciata stems, although these stems comprised only ～ 50% of the total stems available. Stems infested by aphids were similar to uninfested ones in properties that had a strong correlation with egg numbers, and yet there were significantly fewer eggs on infested stems than on intact ones. 4. Females never laid eggs on parts of Gentiana stems infested by aphids, and the presence of Lasius paralienus ants, which have a mutualistic interaction with Aphis gentianae, did not increase the repulsive effect of aphids. Infection of Gentiana by Puccinia did not influence the egg‐laying behaviour of females, even though the flowers and buds of infested stems exhibited a delayed development. 5. Aphid infestation can influence butterfly oviposition patterns through both direct and indirect effects. The presence of aphids directly excluded oviposition, but our data also indicated the possibility of an indirect effect of aphid infestation. Stems that had no aphids at the last egg counting, but were infested prior to it, had significantly fewer eggs than those that were never infested.     

Oviposition response of green lacewings (Neuroptera: Chrysopidae) to aphids (Hemiptera: Aphididae) and potential attractants on pecan

Pecan foliage is attacked by three species of aphids [Monellia caryella (Fitch), Melanocallis caryaefoliae (Davis), and Monelliopsis pecanis Bissell], resulting in damage that can reduce tree nut yield. In this study, we assayed the ovipositional response of the green lacewing Chrysoperla rufilabris (Burmeister) to M. caryella and M. caryaefoliae at high and low aphid densities and the development of C. rufilabris larvae when fed solely on each of the three pecan aphid species. During 2004 and 2005, combinations of attractants and food sprays were applied to pecan trees in an orchard to monitor green lacewing ovipositional response. We found that C. rufilabris laid more eggs on seedling trees infested with the M. caryella (at both high and low densities) than on seedlings infested with M. caryaefoliae. Development of C. rufilabris was unaffected by aphid species. At least one attractant/food spray treatment applied to trees in an orchard significantly increased green lacewing oviposition for three of the five treatment dates over both years. These results show that larvae of C. rufilabris will consume all aphid species attacking pecan, even though female ovipositional response can differ for aphid species. It is likely that combinations of attractants and food sprays can be used to enhance green lacewing populations in orchards.     

Molecular interactions between rosy apple aphids, Dysaphis plantaginea, and resistant and susceptible cultivars of its primary host Malus domestica

The use of crop varieties resistant or tolerant to insect pests or other stress factors is one approach in non‐chemical crop‐protection. Knowledge of the biochemical and molecular background of insect–plant interactions is a prerequisite for optimizing breeding for resistance. However, the resistance genes involved in plant–aphid interactions have so far only been identified and characterized in very few plant species. Our work aims to elucidate the molecular and biochemical mechanisms involved in resistance of apple trees, Malus domestica L. (Rosaceae), against its primary aphid pest, the rosy apple aphid, Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), which is considered a serious economic pest of apple. Gene expression in both resistant and susceptible apple cultivars after infestation with rosy apple aphids was investigated by employing the cDNA‐AFLP method (cDNA–Amplified Fragment Length Polymorphism). From approximately 12 500 cDNA fragments detected on polyacrylamide gels, 21 bands were apparently up‐ or down‐regulated only in the resistant cultivar ‘Florina’ after aphid infestation compared to the susceptible cultivar ‘Topaz’ and/or mechanically wounded or non‐infested leaves. These fragments were cloned, sequenced, and the pattern of gene expression for six fragments was subsequently verified by virtual Northern blots. Sequence comparisons of these fragments to GenBank accessions revealed homologies to already known genes, most of them isolated from Arabidopsis thaliana L. Among them, a putative RNase‐L‐inhibitor‐like protein, a pectinacetylesterase, an inositol‐phosphatase‐like protein, a precursor of the large chain of the ribulose‐1,5‐biphosphate‐carboxylase, and defence‐related genes such as a vacuolar H(+)‐ATPase subunit‐like protein and an ADP‐ribosylating enzyme were identified. The results are discussed in relation to a putative role of these genes in conferring aphid resistance in apple trees.     

In-field production of parasitoids of Dysaphis plantaginea by using the rowan aphid Dysaphis sorbi as substitute host

A system was developed to provide the parasitic wasp Ephedrus persicae Froggatt (Hymenoptera: Braconidae: Aphidiinae), which attacks the rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), with the alternative host Dysaphis sorbi Kaltenbach (Homoptera: Aphididae) in apple orchards. Rowan trees (Sorbus aucuparia L.) arranged along the side of an unsprayed orchard were artificially infested in late February 2002 with eggs of D. sorbi. Colonies of D. sorbi successfully developed from the introduced eggs and persisted on several trees until the end of June. The only primary parasitoid species emerging from a sample of mummified aphids collected in spring from the infested rowan trees was the braconid wasp species E. persicae. In a host-switching experiment, nymphs of D. plantaginea proved suitable for female parasitoids originating from mummified D. sorbi. A series of mummies collected from the rowan trees in early summer contained diapausing parasitoids and hyperparasitoids that only hatched in April of the following spring. These observations suggest the possibility of establishing a local population of E. persicae in apple orchards, so that D. plantaginea can be readily attacked by diapause-emerging parasitoids in early spring.