Macrosiphum Euphorbiae Research Articles

EFFECTS OF LATE BLIGHT RESISTANT POTATO CONTAINING RB GENE ON THE SOIL MICROBES, PESTS AND PLANT DISEASES

Late blight caused by Phytophthora infestans is an important disease on potato. Several potato hybrids have been generated by crossing local varieties (Atlantic and Granola) with Katahdin SP951 which contains late blight resistance gene RB. Prior to release, these hybrids need to be evaluated for their environ-mental effects on non-target organisms and natural pests and diseases. The objectives of the study were to investigate the effect of LBR potato hybrids on beneficial soil microbes, pests and diseases. The trial was conducted in the confined field trial (CFT) in Lembang, West Java. The parental non-transgenic (NT) clones (Granola, Atlantic and Katahdin) and LBR hybrids (four clones of Atlantic x Katahdin SP951 hybrids; 10 clones of Granola x Katahdin SP951) were planted at a plant spacing of 30 cm x 70 cm. Fungicide applications were used as treat-ments (no spray, five and twenty times sprays). The experi-ment was arranged in a randomized completely block design with three replications. The parameters determined were popula-tions of N2 fixing and P solubilizing bacteria, soil C/N ratio as well as natural pests and diseases. The results showed that the transgenic LBR potato hybrids did not have negative effect on N fixing bacteria. The bacterial populations were around 1010-11 cells g-1 soil before planting, 1012 cells at 1.5 months after planting (MAP) and 108 cells after harvest. For P- solubilizing bacteria, their populations were 1010 cells before planting, 1012 cells at 1.5 MAP and 1011 cells g-1 soil after harvest. The soil C/N ratio of the transgenic plot was not statistically different compared to non-transgenic plot, i.e. 12-15 before planting, 10-11 at 1.5 MAP, and 10 after harvest in non-spray plot. Pests and diseases such as Alternaria solani, Liriomyza, potato tubber moth, aphid and mites on the transgenic and non-transgenic plots were statistically not different. The resistance score for A. solani was 7.2 (parental tansgenic) and 7.6 (parental non-transgenic); for Liriomyza it was 2.07 (parental transgenic) and 2.32 insect per plant (parental non-transgenic), the PTM was 0.63 (parental transgenic) and 0.73 insect per plant (parental non-transgenic), aphid and mites were 0.75 (parental transgenic) and 1.68 insects per plant (parental non-transgenic). The study indicated that LBR potato hybrids did not have any negative impacts on non-target organisms.

Effect of insecticide-treated potato plants on aphid behavior and potato virus Y acquisition.

The objective was to assess the effect of two contact insecticides, lambda-cyhalothrin and flonicamid, and three systemic insecticides, pymetrozine, dimethoate and imidacloprid, on the behavior and potato virus Y (PVY) acquisition of three aphid species, Macrosiphum euphorbiae (Thomas), Rhopalosiphum padi L. and Aphis fabae (Scopoli). At 1-4 days after application, contact insecticides strongly modified aphid behavior and intoxicated them. Dimethoate sprayed on potato plants did not change the behavior of the three tested aphid species, while imidacloprid slightly reduced the probing behavior of M. euphorbiae and intoxicated several R. padi. The residual effect of the insecticides (10-21 days after application) was almost non-existent. No intoxication was found, and only slight changes in the behavior of R. padi and A. fabae were observed. The acquisition of PVY by R. padi was reduced on lambda-cyhalothrin- and dimethoate-treated plants that were sprayed a few days before the test. One systemic and two contact insecticides were effective at intoxicating aphids and reducing probing behavior soon after application. Some insecticides might sporadically reduce the spread of PVY either by modifying the behavior or reducing PVY acquisition, but their action is likely limited to a short period of time after application.

Tobacco overexpressing β-ocimene induces direct and indirect responses against aphids in receiver tomato plants

In the last decade plant-to-plant communication has received an increasing attention, particularly for the role of Volatile Organic Compounds as possible elicitors of plant defense. The role of β-ocimene as an interspecific elicitor of plant defense has been recently assessed in multitrophic systems including different plant species (Solanaceae, Poaceae, legumes) and different pest species including chewer insects and phytophagous mites. Both chewer insects and phytophagous mites are known to elicit specific plant defensive pathways which are different (at least in part) from those elicited by sap feeders. The aim of this research was to fill this gap of knowledge and to assess the role of β-ocimene as an elicitor of plant defense against aphid pests, which are sap feeders.For this purpose we used as transgenic tobacco plant releasing an odour plume enriched in this compound as emitter and a tomato plant as receiver. We selected the aphid Macrosiphum euphorbiae and its natural enemy, the parasitoid Aphidius ervi, as the targets of plant induced defense.Tomato plant defense induced by β-ocimene was assessed by characterizing the aphid performance in terms of fixing behaviour, development and reproduction (direct plant defense) and the parasitoid performance in terms of attraction towards tomato plants (indirect plant defense). The characterization of tomato response to β-ocimene was completed by the identification of Volatile Organic Compounds as released by conditioned tomato plants.Tomato plants that were exposed to the volatiles of transgenic tobacco enriched in β-ocimene resulted in less suitable for the aphids in respect to control ones (direct defense). On tomato plants “elicited” by β-ocimene we recorded: a significant lower number of aphids settled; a significant lower number newborn nymphs; a significant lower weight of aphids feeding.In addition, tomato plants “elicited” by β-ocimene resulted became more attractive towards the parasitoid A. ervi than control ones.These results could be explained at least in part by examining the composition of the Volatile Organic Compounds released by tomato plants “elicited” by β-ocimene. Indeed, we found a significantly higher release of several compounds including methyl salicylate and cis-3-hexen-1-ol. These two compounds have been demonstrated to impair aphid development and reproduction and to be involved in the attraction of the aphid parasitoid A. ervi.By considering the ubiquity of β-ocimene and its ability to regulate the communication of plants belonging 30 to different species (if not families), we concluded that this compound is an ideal candidate for new 31 strategies of sustainable control of agricultural pests.

Trunk injection: An alternative technique for pesticide delivery in apples

Field studies, laboratory bioassays, and residue profile analysis were used to determine the seasonal effectiveness of trunk injected pesticides against key apple disease and insect pests. Insecticides formulated for trunk injection, imidacloprid (Ima-jet™), rynaxypyr (XCL-r8™), and emamectin benzoate (TREE-age™) were injected into semi-dwarf Empire apple trees Malus domestica (Borkhausen) and evaluated for a wide range of insect pests. The fungicide compounds, propiconazole (Alamo®), phosphites (Phospho-jet), and penthiopyrad (Fontelis™), were injected into semi-dwarf MacIntosh (RedMax) apple trees M.domestica (Borkhausen) for control of apple scab fungus, Venturia inaequalis (Cooke). After the original single injection, imidacloprid was highly effective in controlling piercing and sucking pests such as the potato leafhopper, Empoasca fabae (Harris), and aphids (Aphididae), and emamectin benzoate was highly effective in controlling the oblique banded leaf roller, Choristoneura rosaceana (Harris), and potato leafhopper, E. fabae (Harris), and rynaxypyr was highly effective in controlling Oriental fruit moth, Grapholita molesta (Busck), and leafrollers all for two growing seasons. The residue profiles for insecticides showed that vascular delivery was predominantly to foliage, with fruit residues far below the EPA maximum residue limits (MRLs), and low to no residues detected in apple flower parts. Phosphites provided significant levels of apple scab control over two seasons for the single injection after the foliage recovered from the phytotoxicity damage in the first season. Propiconazole and penthiopyrad showed limited effectiveness for the control of apple scab. The residue profiles for fungicides showed phosphites to be delivered primarily to foliage, but inconsistent foliar residue levels for the other two compounds suggests possible incompatibilities may be responsible for poor product performance. These incompatibilities may include molecular or chemical properties. For example, on the molecular level such as the molecular size too large to fit through vascular tissue and chemical properties such as the viscosity of the compound resulting in poor translocation or pH.

The evolution of insecticide resistance in the peach potato aphid, Myzus persicae

The peach potato aphid, Myzus persicae is a globally distributed crop pest with a host range of over 400 species including many economically important crop plants. The intensive use of insecticides to control this species over many years has led to populations that are now resistant to several classes of insecticide. Work spanning over 40 years has shown that M. persicae has a remarkable ability to evolve mechanisms that avoid or overcome the toxic effect of insecticides with at least seven independent mechanisms of resistance described in this species to date. The array of novel resistance mechanisms, including several ‘first examples’, that have evolved in this species represents an important case study for the evolution of insecticide resistance and also rapid adaptive change in insects more generally. In this review we summarise the biochemical and molecular mechanisms underlying resistance in M. persicae and the insights study of this topic has provided on how resistance evolves, the selectivity of insecticides, and the link between resistance and host plant adaptation.

Vector activity of three aphid species (Hemiptera: Aphididae) modulated by host plant selection behaviour on potato (Solanales: Solanaceae)

SummaryViral diseases non-persistently transmitted by aphids are of great economic importance in several annual crops. Transmission efficiency of these non-persistent phytoviruses is dependant on vector efficiency (i.e. vector intrinsic ability to transmit the virus) but also on the vector activity that implies the early steps of aphid host plant selection process (i.e. brief intracellular stylet punctures after landing) and to their interplant movement ability. In Europe, Macrosiphum euphorbiae (Thomas 1878) is considered as one of the most serious virus vectors on potato (Solanum tuberosum L. 1753). Nevertheless, several alate aphid species that do not colonise potato plants are trapped in potato crops. Therefore, we investigated, through laboratory experiments, vector activity of one potato colonising aphid, M. euphorbiae, and two non-colonising potato aphids, the bird cherry-oat aphid Rhopalosiphum padi (L. 1758) and the pea aphid Acyrthosiphon pisum (Harris 1776). A settling experiment was used to evaluate dispersal activity, and the electrical penetration graph (EPG) technique was used to investigate probing activity on potato plants. Results showed that M. euphorbiae exhibited a better vector activity than other two aphid species in terms of landing and probing. By contrast, interplant movements were only recorded on non-colonising aphids, suggesting a better vector activity than M. euphorbiae in terms of locomotive behaviour. These data confirm the involvement of A. pisum and R. padi in the spread of non-persistent viruses.

Preference of Aphids (Hemiptera: Aphididae) for Lucerne, Maize, Soybean and Wheat and their Potential as Prospective Border Crops forPotato virus yManagement in seed Potatoes

Aphid landing rates, species composition and abundance on lucerne (Medicago sativa), maize (Zea mays), soybean (Glycine max), wheat (Triticum aestivum) and potato (Solanum tuberosum) were determined in a small-scale field trial to identify potential crops as prospective border plants for seed potatoes to reduce the spread of Potato virus (PVY) in South Africa. Aphids were sampled using green bucket traps to estimate aphid landing rates, whereas leaf counts and sweep-netting were used to identify colonizing species. Of the 34 species or species groups collected with green bucket traps, 18 were previously known vectors of PVY. The most abundant vector species or species groups were Acyrthosiphon pisum, Macrosiphum euphorbiae, Metopolophium dirhodum, Myzus persicae, Rhopalosiphum padi and Sitobion spp. The only other species that occurred in high numbers, but whose vector status is unknown, were Acyrthosiphon kondoi and Tetraneura fusiformis. Landing patterns suggest that A. kondoi, A. pisum and M. dirhodum may be able to discriminate between plant species and select their preferred host plant, if available within a habitat patch, in the pre-alighting phase, whereas other species such as R. padi seemed less selective. Results on aphid landing together with colonization of the crops evaluated suggest that maize and wheat show the highest potential as possible crop border plants in regions where aphids colonizing Poaceae, and lucerne in regions where aphids colonizing Fabaceae are abundant. Soybean appears to be less suitable because cultivars with a high trichome density, which reduces colonization by aphids, are preferentially planted in South Africa.

Effects of a photoselective greenhouse cover on the performance and host finding ability of Aphidius ervi in a lettuce crop

In the search for a durable pest control management, biological control agents and photoselective covers are suitable candidates to be implemented in greenhouse crops. In this work, we studied the effects of a 50 mesh photoselective cover compared to a standard with similar characteristics but without UV-absorbing additives on the performance of Aphidius ervi Haliday (Hymenoptera: Braconidae), a widely used parasitoid to control aphids in vegetable crops. Four field experiments were conducted in La Poveda Experimental Farm (Central Spain) where a lettuce crop was grown during the years 2008–2010. Lettuce plants were infested by Macrosiphum euphorbiae (Thomas) (Hemiptera: Aphididae) and the parasitoid A. ervi was released and monitored throughout the crop cycle to evaluate any constraint in its performance produced by UV-absorbing nets. The ability of A. ervi to find and parasitize the host was not modified by the photoselective cover during the four seasons studied. Thus, we suggest that both strategies could be combined in the context of IPM in vegetable crops where this natural enemy is released.

The southern ladybird (<i>Cleobora mellyi</i>) as a new species association biocontrol agent of tomatopotato psyllid (<i>Bactericera cockerelli</i>)

Since its discovery in New Zealand in 2006 the tomatopotato psyllid (Bactericera cockerelli) (TPP) has emerged as a major pest of solanaceous crops In potato crops the management of TPP has predominantly relied on insecticide applications as biological control by generalist predators has been constrained by both insecticide use and temporal and spatial scales This research sought to further investigate a generalist predator already established in New Zealand the southern ladybird (Cleobora mellyi) introduced from Tasmania as a biocontrol agent for Paropsis charybdis in the 1970s and 1980s as a potential biocontrol agent of TPP The southern ladybirds prey selection ladybird longevity and ladybirdTPP predatorprey dynamics were investigated A choice test assay utilised small experimental arenas of three alternative choices between (1) TPP and green peach aphid Myzus persicae (2) TPP and potato aphid Macrosiphum euphorbiae and (3) TPP and greenhouse whitefly Trialeurodes vaporariorum Cleobora mellyi larvae and adults did not demonstrate a significant prey preference between TPP and either green peach aphid or potato aphid but did show a significant aversion to greenhouse whitefly Longevity trials consisted of a water only control and three treatments (1) a floral resource (flowering buckwheat) (2) 10 TPP/day or (3) flowering buckwheat 10 TPP/day All three treatments lived significantly longer than the water only control and southern ladybirds adults lived significantly longer when given both the floral resource and TPP compared to only being given TPP A glasshouse mesocosm study was used to investigate ladybirdTPP predatorprey dynamics Within 3 weeks the southern ladybird had significantly reduced TPP densities in the treatment in which they were present along with potato plants and TPP compared to the treatment without ladybirds a reduction that was maintained until the completion of the experiment Where there was only TPP and no ladybird no potato tubers were formed; in the presence of southern ladybird small and few potato tubers were formed while the most tubers were produced in insectfree controls This indicates a specieslevel trophic cascade This study has shown that the southern ladybird is capable of predating upon TPP and reducing densities within the controlled conditions of a glasshouse However with the current state of knowledge the southern ladybird is not likely to be a viable predator for controlling TPP in potato crops outside glasshouses in New Zealand This is due in part to the freedom to disperse in the field the economics of such large scale rearing and fundamental differences in habitat type compared to their natural environment but applications in alternative contexts cannot be ruled out

Occurrence and Distribution of Potato Pests and Diseases in Kenya

Potato plays an important role in food security in Kenya but yields are low (<10 t/ha), and this is partly attributed to the lack of healthy planting material. This study is the first wide-scale survey to determine the occurrence and distribution of common potato pests and diseases in Kenyan seed (certified and quality declared) and ware crops. Potato crops growing on 101 farms in 21 districts were examined. Approximately 36% of plants in farmers’ fields sampled both during the long rains (main potato-growing season) and short rains seasons displayed virus-like disease symptoms. Six viruses (potato leafroll virus (PLRV), Potato virus A (PVA), potato virus M (PVM), potato virus S (PVS), potato virus X (PVX), and potato virus Y (PVY)) were detected using double antibody sandwich enzyme-linked immunosorbent assay in potato samples. Sequencing of polymerase chain reaction products from PVY-infected plants revealed the presence of recombinant strains of PVY (NTN and Wilga). Four aphid species, Macrosiphum euphorbiae, Aphis gossypii, Myzus persicae, and Aphis fabae, colonized potato in all districts, occurring in greater numbers west of the Great Rift Valley than to the east. There was a positive correlation between virus incidence and aphid numbers in the long rains (main) potato-growing season. PLRV, PVM, PVS, PVX, and PVY were detected in solanaceous weeds. Ralstonia solanacearum was detected in soils from 13 farms in 8 of the 18 districts surveyed. Approximately 38% of soil samples were infested with Meloidogyne spp. Phytophthora infestans isolates belonging to the US 1 and 2_A1 genotypes were identified. Although many economically important diseases are present in Kenya, the lower aphid incidence in districts east of the Great Rift Valley may indicate that these districts are more suitable for seed potato production.

Relation between plant water status and Macrosiphum euphorbiae (Hemiptera: Aphididae) population dynamics on three cultivars of tomato

Deficit irrigation scheduling is used to increase the efficiency with which water is used in many crops including tomato, however a water deficit is predicted to favour phloem feeding insects. We tested if and how different cultivars of tomato grown under water deficit conditions affect the population growth of the aphid Macrosiphum euphorbiae. Three tomato cultivars (Scintilla, Beefmaster and Rio Grande) were used in the experiments. The results for three watering regimes were compared with those of a control, which was well watered every three days: stressed plants received one third of the water supplied to the control over each three-day interval (experiment 1); stressed plants received a gradually decreasing amount of water (100% at the first watering and then 80%, 60%, 50%, 40% and 20%) every three days (experiment 2); stressed plants received the same amount of water as the con- trol but at longer intervals, that is when evident signs of wilting appeared (experiment 3). The results showed that water stress either enhanced, had an adverse effect or had no effect on aphid population growth, depending on the cultivar and watering regime. No dif- ference was recorded in the population dynamics of M. euphorbiae feeding on Beefmaster tomato plants subjected to different levels of water stress. In the case of the cultivar Scintilla, live aphids were less abundant on stressed plants than on well watered ones in experiment 1 and 3 but not in experiment 2. The highest variability in aphid population dynamics on the plants grown under the dif- ferent water stress protocols was recorded on the cultivar Rio Grande. In experiment 1, the initial peak in aphid numbers was higher on the water stressed plants than on the control and then decreased to lower numbers than on the control. In experiment 2, there were no differences in the numbers of aphids infesting stressed and control plants. In experiment 3, there were fewer aphids on stressed than on control plants after six days, as in experiment 1, but there was no initial peak in aphid numbers.

EVALUATION OF THE SUSCEPTIBILITY OF DIFFERENT PRUNUS ROOTSTOCKS TO NATURAL INFECTION OF PLUM POX VIRUS-T

SUMMARY Plum pox virus (PPV) has been observed in Turkey since 1968, but was not widespread except in apricot and plum trees in home gardens and ornamental parks in restricted areas. Susceptibility of six different Prunus rootstocks to strain PPV-T was assessed under natural inoculum pressure in the Izmir-Aegean region during 2010-2011. Aphid populations were monitored from the first week of April to the middle of June by the stickyplant method one year after the rootstock plantation was established. Aphids collected from different rootstocks were tested individually by squash real-time RT-PCR and all rootstocks were regularly tested by DASI-ELISA. The largest aphid populations were observed at the end of May and the most abundant aphid species as averages over the two years were Myzus persicae (20.15%), Hyalopterus pruni (18.64%), Aphis craccivora (9.04%) and Aphis gossypii (8.36%). In 2011, the highest percentage of viruliferous aphids was found in M. persicae (34.78%), followed by H. pruni (32.50%), Macrosiphum euphorbiae (25.00%), A. gossypii (23.80%), A. spiraecola (12.50%) and A. craccivora (10.00%). Of the six Prunus rootstocks tested, only Nemaguard and Myrobalan 29C were infected by PPV-T, infection rate in 2010 being 6.0% (Nemaguard) and 4.0% (Myrobalan 29C). The infection rate increased to 16.0% for Nemaguard and 14.0% for Myrobalan 29C in 2011. However, the other rootstocks, Prunus marianna GF8.1, Docera6, GF677 and Garnem tested negative for PPV-T throughout 2011. PPV isolates obtained from naturally infected apricot trees (inoculum source) and from infected rootstocks in the experimental plot were characterized as PPV-T and had more than 99.5% nucleotide sequence identity.

Virus strains differentially induce plant susceptibility to aphid vectors and chewing herbivores

Plants are frequently attacked by both pathogens and insects, and an attack from one can induce plant responses that affect resistance to the other. However, we currently lack a predictive framework for understanding how pathogens, their vectors, and other herbivores interact. To address this gap, we have investigated the effects of a viral infection in the host plant on both its aphid vector and non-vector herbivores. We tested whether the infection by three different strains of Potato virus Y (PVY(NTN), PVY(NO) and PVY(O)) on tomato plants affected: (1) the induced plant defense pathways; (2) the abundance and fecundity of the aphid vector (Macrosiphum euphorbiae); and (3) the performance of two non-vector species: a caterpillar (Trichoplusia ni) and a beetle (Leptinotarsa decemlineata). While infection by all three strains of PVY induced the salicylate pathway, PVY(NTN) induced a stronger and longer response. Fecundity and density of aphids increased on all PVY-infected plants, suggesting that the aphid response is not negatively associated with salicylate induction. In contrast, the performance of non-vector herbivores positively correlated with the strength of salicylate induction. PVY(NTN) infection decreased plant resistance to both non-vector herbivores, increasing their growth rates. We also demonstrated that the impact of host plant viral infection on the caterpillar results from host plant responses and not the effects of aphid vector feeding. We propose that pathogens chemically mediate insect-plant interactions by activating the salicylate pathway and decreasing plant resistance to chewing insects, which has implications for both disease transmission and insect community structure.

Effect of irrigation regimes and artificial mycorrhization on insect pest infestations and yield in tomato crop

A 2-year field experiment was carried out to test the effect of root symbionts treatments in combination with different watering levels on tomato yield and pest infestation rates. A split-plot experimental design was followed, where the main treatments were three irrigation regimes, and the subplot factor was the mycorrhizal treatment (two mycorrhizal treatments [M1 and M2] and the control). The M1 treatment consisted in the use of a commercial preparation (Micosat F; CCS Aosta, Italy) containing a mixture of vesicular-arbuscular mycorrhizae (VAM), bacteria of the rhizosphere and saprophytic fungi, while M2 treatment used only arbuscular mycorrhizal fungi. Insect pests sampled in the field during the 2 years of experiment were all sap-feeders (Trialeurodes vaporariorum, Macrosiphum euphorbiae, Frankliniella occidentalis and an unidentified species of leafhopper). Results did not show any impact of root symbionts on pests, whereas water deficit significantly reduced plant infestation rates. Both mycorrhization treatments and water supply resulted in a significantly positive effect on crop yield.

Weather Forecasting by Insects: Modified Sexual Behaviour in Response to Atmospheric Pressure Changes

Prevailing abiotic conditions may positively or negatively impact insects at both the individual and population levels. For example while moderate rainfall and wind velocity may provide conditions that favour development, as well as movement within and between habitats, high winds and heavy rains can significantly decrease life expectancy. There is some evidence that insects adjust their behaviours associated with flight, mating and foraging in response to changes in barometric pressure. We studied changes in different mating behaviours of three taxonomically unrelated insects, the curcurbit beetle, Diabrotica speciosa (Coleoptera), the true armyworm moth, Pseudaletia unipuncta (Lepidoptera) and the potato aphid, Macrosiphum euphorbiae (Hemiptera), when subjected to natural or experimentally manipulated changes in atmospheric pressure. In response to decreasing barometric pressure, male beetles exhibited decreased locomotory activity in a Y-tube olfactometer with female pheromone extracts. However, when placed in close proximity to females, they exhibited reduced courtship sequences and the precopulatory period. Under the same situations, females of the true armyworm and the potato aphid exhibited significantly reduced calling behaviour. Neither the movement of male beetles nor the calling of armyworm females differed between stable and increasing atmospheric pressure conditions. However, in the case of the armyworm there was a significant decrease in the incidence of mating under rising atmospheric conditions, suggesting an effect on male behaviour. When atmospheric pressure rose, very few M. euphorbiae oviparae called. This was similar to the situation observed under decreasing conditions, and consequently very little mating was observed in this species except under stable conditions. All species exhibited behavioural modifications, but there were interspecific differences related to size-related flight ability and the diel periodicity of mating activity. We postulate that the observed behavioral modifications, especially under decreasing barometric pressure would reduce the probability of injury or death under adverse weather conditions.

Tomato Below Ground–Above Ground Interactions: Trichoderma longibrachiatum Affects the Performance of Macrosiphum euphorbiae and Its Natural Antagonists

Below ground and above ground plant-insect-microorganism interactions are complex and regulate most of the developmental responses of important crop plants such as tomato. We investigated the influence of root colonization by a nonmycorrhizal plant-growth-promoting fungus on direct and indirect defenses of tomato plant against aphids. The multitrophic system included the plant Solanum lycopersicum ('San Marzano nano'), the root-associated biocontrol fungus Trichoderma longibrachiatum strain MK1, the aphid Macrosiphum euphorbiae (a tomato pest), the aphid parasitoid Aphidius ervi, and the aphid predator Macrolophus pygmaeus. Laboratory bioassays were performed to assess the effect of T. longibrachiatum MK1, interacting with the tomato plant, on quantity and quality of volatile organic compounds (VOC) released by tomato plant, aphid development and reproduction, parasitoid behavior, and predator behavior and development. When compared with the uncolonized controls, plants whose roots were colonized by T. longibrachiatum MK1 showed quantitative differences in the release of specific VOC, better aphid population growth indices, a higher attractiveness toward the aphid parasitoid and the aphid predator, and a quicker development of aphid predator. These findings support the development of novel strategies of integrated control of aphid pests. The species-specific or strain-specific characteristics of these below ground-above ground interactions remain to be assessed.

OCCURRENCE AND POPULATION DENSITY OF APHIDS IN APPLE ORCHARDS OF SOUTH BULGARIA

Abstract In a 2006-2008 study, seven aphid species (Hemiptera: Aphididae) were detected on apple trees in South Bulgaria: Rhopalosiphum insertum Walk. (apple-grass aphid), Dysaphis plantaginea Pass (rosy apple aphid), Dysaphis devecta Walker (rosy leaf-curling aphid), Macrosiphum euphorbiae Thomas (potato aphid), Aphis pomi De Geer (green apple aphid), Aphis spiraecola Patch. (spiraea aphid/green citrus aphid) and Eriosoma lanigerum Nausm. (wooly apple aphid). The dominant species were D. plantaginea, found in 97.8% of the surveyed orchards. Two green aphid species from the genus Aphis were both found in 96.4% of the orchards. The rosy apple aphid was a more important pest of bearing orchards, where infestation in spring always exceeded the economic injury level (1-2% of infested shoots). The green aphids were more important in young orchards and nurseries, where they developed during the entire vegetation period and infestation sometimes exceed 50-80% of shoots. A. pomi was still more widespread, but A. spiraecola was found throughout all of South Bulgaria. As pests of apple, the other species were less common, causing lower infestations and minor economic importance.

Investigating nicotinic acetylcholine receptor expression in neonicotinoid resistant Myzus persicae FRC

The peach–potato aphid Myzus persicae is a pest of many commercial crops due to its polyphagous nature of feeding and has a well-documented history of acquiring resistance to insecticides. In 2009 a strain (M. persicae FRC) emerged in southern France with a point mutation (R81T) at the nicotinic acetylcholine receptor (nAChR), the target site for neonicotinoids such as imidacloprid. This point mutation was associated with the loss of the high affinity imidacloprid binding site (pM Kd), with the single remaining binding site (low nM Kd) highly overexpressed compared to laboratory controls (Bass et al., 2011 [1]). Here we report that after 2years of continuous selection in the glass house environment with neonicotinoids, the total level of IMD-sensitive nAChRs (low nM Kd) in M. persicae FRC is now comparable to laboratory controls (pM and low nM Kd). Interestingly, despite this large reduction in IMD-sensitive nAChRs, this was not associated with any significant alteration in NNIC-lethality. Additionally, sustained absence of neonicotinoid-selection did not alter nAChR protein levels. We suggest that alterations in nAChR protein expression level described in the original characterisation of the field-isolated M. persicae FRC is unlikely to have been a direct consequence of the R81T mutation. Rather, we speculate that nAChR expression in aphids is likely influenced by as yet unknown conditions in the natural field environment that are absent in the laboratory setting.

Plant-mediated RNAi of a gap gene-enhanced tobacco tolerance against the Myzus persicae

Plant-mediated RNAi has been developed as a powerful weapon in the fight against agricultural insect pests. The gap gene hunchback (hb) is of crucial importance in insect axial patterning and knockdown of hb is deforming and lethal to the next generation. The peach potato aphid, Myzus persicae (Sulzer), has many host plants and can be found throughout the world. To investigate the effect of plant-mediated RNAi on control of this insect, the hb gene in M. persicae was cloned, plant RNAi vector was constructed, and transgenic tobacco expressing Mphb dsRNA was developed. Transgenic tobacco had a different integration pattern of the transgene. Bioassays were performed by applying neonate aphids to homozygous transgenic plants in the T2 generation. Results revealed that continuous feeding of transgenic diet reduced Mphb mRNA level in the fed aphids and inhibited insect reproduction, indicating successful knockdown of the target gene in M. persicae by plant-mediated RNAi.

Expression of α-DIOXYGENASE 1 in Tomato and Arabidopsis Contributes to Plant Defenses Against Aphids

Plant α-dioxygenases (α-DOX) are fatty acid-hydroperoxidases that contribute to the synthesis of oxylipins, a diverse group of compounds primarily generated through oxidation of linoleic (LA) and linolenic acid (LNA). Oxylipins are implicated in plant signaling against biotic and abiotic stresses. We report here that the potato aphid (Macrosiphum euphorbiae) induces Slα-DOX1 but not Slα-DOX2 expression in tomato (Solanum lycopersicum). Slα-DOX1 upregulation by aphids does not require either jasmonic acid (JA) or salicylic acid (SA) accumulation, since tomato mutants deficient in JA (spr2, acx1) or SA accumulation (NahG) still show Slα-DOX1 induction. Virus-induced gene silencing of Slα-DOX1 enhanced aphid population growth in wild-type (WT) plants, revealing that Slα-DOX1 contributes to basal resistance to aphids. Moreover, an even higher percent increase in aphid numbers occurred when Slα-DOX1 was silenced in spr2, a mutant line characterized by elevated LA levels, decreased LNA, and enhanced aphid resistance as compared with WT. These results suggest that aphid reproduction is influenced by oxylipins synthesized from LA by Slα-DOX1. In agreement with our experiments in tomato, two independent α-dox1 T-DNA insertion mutant lines in Arabidopsis thaliana also showed increased susceptibility to the green peach aphid (Myzus persicae), indicating that the role α-DOX is conserved in other plant-aphid interactions.