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.     

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.     

The Common Black Ant, Lasius niger (Hymenoptera: Formicidae), as a Vector of the Entomopathogen Lecanicillium longisporum to Rosy Apple Aphid, Dysaphis plantaginea (Homoptera: Aphididae)

The potential for common black ant Lasius niger workers to vector conidia of the entomopathogenic fungus Lecanicillium longisporum to colonies of the rosy apple aphid Dysaphis plantaginea was assessed in laboratory and field experiments. Scanning electron microscope studies showed that L. niger workers which were artificially contaminated with L. longisporum conidia, carried conidia primarily on their tarsae but also on antennae and mandibles. Neither L. niger workers nor larvae were susceptible to infection with L. longisporum. Workers which were artificially contaminated with conidia of L. longisporum initiated infection in colonies of healthy D. plantaginea on apple. Mortality due to L. longisporum was recorded as 68.3, 30.8 and 3.7% of aphids under laboratory, semi-field and field conditions, respectively.     

Colonization of apple orchards by predators of <Emphasis Type="Italic">Dysaphis plantaginea</Emphasis>: sequential arrival,response to prey abundance and consequences for biological control

Episyrphus balteatus (DeGeer) (Diptera: Syrphidae), Adalia bipunctata (L.) (Coleoptera: Coccinellidae) and Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) are the three most abundant natural enemies of Dysaphis plantaginea Passerini (Homoptera: Aphididae) in Asturian (NW Spain) apple orchards. They attack this aphid in sequence: E. balteatus arrived first, followed by A. bipunctata and then by A. aphidimyza. The cecidomyiids arrived too late to have a regulating effect. The syrphids laid an average of 2.3 ± 1.7 eggs per aphid colony and the coccinellids 18.4 ± 9.9 regardless of the degree of the infestation rates of the apple shoots. This value corresponds to the size of an egg batch laid by one female. Therefore, these aphid predators did not respond numerically to the abundance of the pest. The results of this study indicate that natural populations of syrphids and ladybird beetles are unable to control D. plantaginea, and therefore a more complex strategy than waiting for natural enemies is required.     

Phenology,fecundity and life table parameters of the predator Hippodamia variegata reared on Dysaphis crataegi

Phenological and some biological characteristics of Hippodamia (Adonia) variegata (Goeze) (Coleoptera: Coccinellidae), such as voltinism, hibernation, number of progeny produced by each generation, mating activity and sex ratio were studied, in order to evaluate the significance of this predator. The study of phenology was conducted in outdoor cages in Kifissia (Athens), during 1999--2001 and as prey was given Dysaphis crataegi (Kaltenbach). Hippodamia variegata completed seven generations between April and November. The hibernating population of H. variegata consisted of adults of 6th and 7th generations. The fecundity of the predator was studied under constant conditions [25 °C, 65% R.H. and 16:8(L:D)h photoperiod] in the laboratory and some population parameters were calculated: The total fecundity ranged between 789 and 1256 eggs, while the mean total fecundity was 959.6 eggs. The greatest proportion of eggs (45%) was oviposited in clutches of 11--20 eggs. The net reproductive value (R₀) was found to be 425.9 females/female, the intrinsic rate of increase (r_m) 0.178 females/female/day and the mean generation time (T) 34.0 days.     

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.     

Effects of autumn kaolin and pyrethrin treatments on the spring population of Dysaphis plantaginea in apple orchards

The impact of treatments with the pyrethrin insecticide Pyrethrum FS and the repellent kaolin product Surround^® WP to control the autumn forms of Dysaphis plantaginea Pass. (Hom., Aphididae), a major insect pest of apple, was assessed in 1‐year field experiments in Switzerland. Single and multiple applications of pyrethrin and kaolin were tested at different dates after apple harvesting in autumn 2002 when sexuales of the rosy apple aphid were present. Repeated applications of Surround^® WP in autumn significantly reduced the number of females in autumn and, consequently, the number of hatched fundatrices in spring. Single kaolin treatments were less effective. Unexpectedly, neither single nor multiple applications of the contact insecticide Pyrethrum FS had a knock‐down effect on females in autumn. However, pyrethrin significantly reduced the number of hatched fundatrices in spring. Neither pesticide completely controlled the rosy apple aphid but with a more detailed analysis of factors influencing the efficacy of autumn treatments a new approach to control this serious pest could be achieved.     

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.