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PubMed2006

Effect of synthetic aphid alarm pheromone (E) -beta-farnesene on development and reproduction of Aphis gossypii (Homoptera: Aphididae).

The synthetic aphid alarm pheromone (E)-beta-farnesene (EBF) is released by aphids in response to predation or other disturbances that occur in the colony. This is presumed to benefit the population by allowing increased survival of related individuals taking successful evasive action after perception of the pheromone. The effect of pheromone perception by aphids in the absence of real threats was investigated to determine the baseline effect of this communication on aphid survival, development, and fecundity in the laboratory. All four nymphal stages of cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), were stimulated with EBF. No significant difference in survival rates was observed in the aphids stimulated with EBF compared with the untreated control. Developmental times of the aphids were significantly prolonged in first and third instars when they were stimulated with EBF. Significantly lower fecundity and lighter weight of adult aphids were observed in aphids stimulated with EBF at as first instars compared with untreated controls and other instars. Results indicate that exposure of the first instar of A. gossipii to the synthetic alarm pheromone adversely affects subsequent development and fecundity of the population. This reduces aphid fitness that must be compensated by increased survival from predation for the pheromone to confer a selective advantage to the species.

Animals↗
PubMed2006

The disruption of an ant-aphid mutualism increases the effects of birds on pine herbivores.

Predators affect herbivores directly and indirectly, by consumptive and nonconsumptive effects, and the combined influence of multiple predators is shaped by interactions among predators. I documented the individual and combined effects of birds (chickadees, nuthatches, warblers) and ants (Formica podzolica) on arthropods residing in pine (Pinus ponderosa) canopies in a factorial field experiment. Birds and ants removed herbivores but simultaneously benefited them by removing predatory arthropods. Birds and ants had net negative and positive effects, respectively, on the abundance of herbivore prey, supporting the notion that vertebrate predators have stronger negative effects on herbivores than do arthropod predators. Aphids (ant-tended and untended species) constituted three-quarters of herbivore biomass. The effect of birds on ant-tended aphids was twice that on untended aphid species or tended aphid species without ants. This was not due to there being more ant-tended aphids for birds to prey on; tended and untended aphid species were in similar abundances in the absence of birds. Instead, the effects of birds were strengthened by attributes of the mutualism that rendered tended aphids susceptible to predation. These dynamics led to nonadditive effects of birds and ants: birds only reduced tended aphid species and total herbivore abundances on trees with ants, while ants only increased tended aphid species and total herbivore abundances in the absence of birds. Consequently, top predators in this system only influenced total herbivore abundance when they disrupted an ant-aphid mutualism.

Animals↗
PubMed2003

Interaction between nutrient supplies and aphid numbers on potato (2001-2002).

We set up our experiment on 11 potato varieties with 4 treatments and 4 replications in Hungary in 2001 and 2002. The aim of the experiment was to investigate the interaction between the nutrient supplies of potato and the change in the numbers of aphids feeding on the potato plant. In our experiment we sorted 4 nutrient levels according to the recommendations of soil analyses and variety holders. During the growing period we counted the numbers of aphids feeding on the potato leaves every week and controlled the virus infestation with ELISA-method after harvesting. Using the data we concluded that there is an interaction between the nutrient supplies of the potato plant and the numbers of aphids feeding on the leaves. The numbers of aphids on the plots with good nutrient supplies exceeded the numbers of aphids counted on the control plots. In 2001 and 2002 we counted 1150 and 1205 aphids per 100 plants on plots with nutrient supplies in the peak time of swarming compared to the control plot with numbers of 799 and 978. Beside nutrient supplies weather conditions influenced the numbers of aphids, too. Different temperature and rainfall conditions in both years affected the intense and progress of swarming. This can be the reason for the appearance of the first aphids (in the last week of April in 2001 and in the first week of May in 2002) and the time of swarming (15-18 June in 2001 and 28-31 May in 2002). Summer heat and hot days lowered the numbers of aphids. In 2002 following the heat in June and July the population escalated. After harvesting we confirmed our hypothesis from the tuber samples by ELISA-method: The virus infestation was higher on plots with intensive growing practice than the virus infestation on the control plots. In 2001 the rate of PLVRV infestation on Agria variety of the control plot yielded 18.7%. At the time of the 3rd treatment it increased to 37.2%. In 2002 the control had an infestation rate of 12.6% and 40.2% at the time of the 3rd treatment. In 2001 the rates of PVY infestation were 15.2% and 23.4% respectively and in 2002 they were 14.8% and 18.2% respectively. As the interaction between nutrient supplies, changes in the numbers of aphids and the virus infestation are not yet well known, further experiments are required.

Animal Nutritional Physiological Phenomena↗
PubMed2004

Differential susceptibility of poplar hybrids to the aphid Chaitophorus leucomelas (Homoptera: Aphididae).

After its recent introduction to Chile, the aphid Chaitophorus leucomelas Koch is becoming a serious pest affecting commercial poplar, Populus spp., plantations. The pattern of natural infestation of C. leucomelas among poplar hybrids with different pedigrees and the aphid intrinsic rate of increase (r(m)), of C. leucomelas were assessed in the field. In most of the hybrids, aphid abundance peaked in March (late summer). Among 12 types of poplar crosses, [(P. trichocarpa Torr. & Gray x P. deltoides Bartram ex Marshall) x (P. trichocarpa x P. deltoides)] and [(P. trichocarpa x P. maximowiczii Henry) x P. maximowiczii] showed the highest and lowest aphid densities, respectively. A trend to find more aphids in branch bases was apparent. The intrinsic rate of C. leucomelas increase was higher in [(P. trichocarpa x P. deltoides) x P. deltoides] hybrids, and lower in [(P. trichocarpa x P. maximowiczii) x P. trichocarpa] hybrids. Aphid density and performance were higher in hybrids with P. deltoides parentage, whereas hybrids with P. maximowiczii parentage showed lower aphid densities and performance. Hybrids with P. nigra L. parentage, namely, [P. trichocarpa x P. nigra], also had high aphid density, but aphid performance was lower compared with hybrids with P. deltoides parentage. These results suggest that among poplar hybrids studied, susceptibility to C. leucomelas is inherited through P. deltoides, whereas resistance seems to be inherited through P. maximowiczii. Thus, P. maximowiczii hybrids are recommended for commercial or ornamental planting programs in zones where there is a high risk of aphid infestation.

Animals↗
PubMed2005

The effect of predators and hymenopterous parasites on population fluctuations of alfalfa aphids.

Among alfalfa pests in Iran three aphid species, green alfalfa aphid Acyrthosiphon pisum Harris spotted alfalfa aphid Therioaphis trifolii forma maculata Buckton and blue alfalfa aphid, Acyrthosiphon kondoi Shinji are important pests. The green alfalfa aphid can be observed all along the growing season particularly from late May to mid June at Karaj climate conditions. During this period, the mean monthly maximum temperature and relative humidity were about 28 degrees C and 60-65% respectively. This aphid overwinters as nymph and viviparous female. Sexual forms and eggs could not be seen under field conditions. Spotted alfalfa aphid, Therioaphis trifolii fonna maculata is the most prevalent aphid in summer time, when the mean monthly maximum temperature and relative humidity are about 33-34 degrees C and 44-58% respectively. Sexual individuals have been observed in the laboratory but not in the field. Among predators (Coccinella septempunctata, Adonia variegata, Syrphus cinctus, S. corolae, S. grassulariae, Chrysoperla carnea and Nabis capsiformis) one coccinellid species, C. septempunctata, had greatest impact on fluctuations of population. Among hymenopterous parasitoids two species have been collected from alfalfa field they were Aphidius ervi and Praon palitans. These parasitoids destroyed a good percent of aphids and statistically proved to lower aphid populations significantly.

Animals↗
PubMed2003

The interplay between density- and trait-mediated effects in predator-prey interactions: a case study in aphid wing polymorphism.

Natural enemies not only influence prey density but they can also cause the modification of traits in their victims. While such non-lethal effects can be very important for the dynamic and structure of prey populations, little is known about their interaction with the density-mediated effects of natural enemies. We investigated the relationship between predation rate, prey density and trait modification in two aphid-aphid predator interactions. Pea aphids (Acyrthosiphon pisum, Harris) have been shown to produce winged dispersal morphs in response to the presence of ladybirds or parasitoid natural enemies. This trait modification influences the ability of aphids to disperse and to colonise new habitats, and hence has a bearing on the population dynamics of the prey. In two experiments we examined wing induction in pea aphids as a function of the rate of predation when hoverfly larvae (Episyrphus balteatus) and lacewing larvae (Chrysoperla carnea) were allowed to forage in pea aphid colonies. Both hoverfly and lacewing larvae caused a significant increase in the percentage of winged morphs among offspring compared to control treatments, emphasising that wing induction in the presence of natural enemies is a general response in pea aphids. The percentage of winged offspring was, however, dependent on the rate of predation, with a small effect of predation on aphid wing induction at very high and very low predation rates, and a strong response of aphids at medium predation rates. Aphid wing induction was influenced by the interplay between predation rate and the resultant prey density. Our results suggests that density-mediated and trait-mediated effects of natural enemies are closely connected to each other and jointly determine the effect of natural enemies on prey population dynamics.

Animals↗
PubMed2002

Pea aphid clonal resistance to the endophagous parasitoid Aphidius ervi.

The physiological mechanism of resistance to the endophagous braconid Aphidius ervi Haliday (Hymenoptera, Braconidae) by a pink clone (PC) of Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) has been investigated. Comparative data on parasitoid development and associated host biochemical changes in the resistant PC aphids and in a susceptible green clone (GC) of A. pisum are reported. When the PC aphids were attacked as early 4th instars, the developing parasitoid larvae showed a strongly reduced increase in size, compared to those synchronously developing in GC aphids, and were unable to produce a regular mummy. In contrast, parasitism of 2nd instar PC aphids, allowed completion of parasitoid development, but adults had a prolonged developmental time, due to a longer duration of parasitoid's final (3rd) instar. In all cases, teratocytes, cells deriving from the A. ervi serosal membrane, and the proteins abundantly synthesised by them, were never found in the haemolymph of parasitised PC aphids. Host castration, as demonstrated by total protein incorporation into reproductive tissues, was total in the majority of early (2nd instar) parasitised host aphids, while it was limited when later instars (4th) of PC aphids were parasitised. This is partly due to the absence of the cytolytic activity of teratocytes on host embryos, which, through their persistence, may compete for nutritional resources with the developing parasitoid larvae. In parasitised PC aphids, this competitive effect is further aggravated for the parasitoid by the absence of the regulated amino acid titre increase in the host haemolymph, which is regularly observed in GC aphids. Failure of teratocyte development in the PC clone of the pea aphid is, then, the major functional constraint accounting for the reduction/inhibition of A. ervi larval growth. The reported results allow to assess in vivo the role of teratocytes in the host physiological redirection and nutritional exploitation by the parasitoid, and to integrate and validate the proposed physiological model of host-parasitoid interactions in the system A. pisum-A.ervi.

Journal Article↗
PubMed2004

Acquired and R-gene-mediated resistance against the potato aphid in tomato.

We examined the effects of three forms of host plant resistance in tomato, Lycopersicon esculentum, on the potato aphid, Macrosiphum euphorbiae. Mi-1.2, a resistance gene (R-gene) in tomato that deters aphid feeding, reduced the population growth of both potato aphid isolates tested, although it appeared to have a greater impact on isolate WU11 than on isolate WU12. The results suggest that there may be quantitative differences in virulence between these two aphid isolates. We also examined two distinct forms of acquired resistance in tomato, jasmonic acid (JA)-dependent and salicylic acid (SA)-dependent induced defenses. Exogenous foliar application of JA triggered expression of a JA-inducible proteinase inhibitor in tomato cultivars with and without Mi-1.2, although the effects of treatment on aphid performance differed between these cultivars. JA-treatment reduced aphid population growth on a susceptible tomato cultivar that lacks Mi-1.2, but did not significantly enhance or inhibit aphid control on a near-isogenic resistant tomato cultivar that carries this gene. Foliar application of an SA analog, benzothiadiazole (BTH), was used to induce SA-dependent defenses. BTH treatment reduced the population growth of both aphid isolates on a susceptible tomato cultivar, and also enhanced aphid control on a resistant cultivar. The results indicate that both SA- and JA-dependent acquired resistance in tomato have a direct negative effect on a phloem-feeding insect. Furthermore, this study demonstrates that acquired resistance and R-gene-mediated resistance can interact for enhanced suppression of insect herbivores.

Animals↗
PubMed1995

Detection of potato leafroll virus in single aphids by the reverse transcription polymerase chain reaction and its potential epidemiological application.

A reverse transcription and polymerase chain reaction (RT-PCR) system was developed using two 20-mer primers located in the potato leafroll virus (PLRV) capsid gene. A 336-bp PCR product was detected from aphids (Myzus persicae) which had been fed on PLRV-infected plants. The PCR band was specific to PLRV as determined by Southern blots and detection by a PLRV-specific probe. As little as 5 min exposure of aphids to PLRV-infected leaves resulted in the presence of PLRV-specific bands in 13% of aphids. However, the percentage of PLRV-positive aphids increased with longer exposure to infected sources and reached 90% after 3-4 days of feeding. PLRV can be detected from a single viruliferous aphid or a single viruliferous aphid combined with up to 29 non-viruliferous aphids. PLRV can be detected from freshly collected aphids, those stored at -70 degrees C, or those stored in 70% ethanol at room temperature for extended periods. This method is applicable to assess the viruliferous nature of aphids caught in yellow-pan traps during the growing season or stored for over a year.

Animals↗
PubMed2003

Probiotic effects of beta-glucuronidase on the peach-potato aphid Myzus persicae (Aphididae).

beta-glucuronidase (GUS) is a reporter protein commonly expressed in transgenic plants allowing the visualization of the transformed individuals. In our recent work, we showed that consumption of transformed potato plants expressing this GUS enzyme improves performance of the phloem feeding aphid Myzus persicae. Those results led us to the conclusion that the expression of GUS in potato plants might be responsible for the probiotic effect measured in feeding aphids. In the present paper, artificial diets were used to provide active GUS (10 and 500 microg ml(-1)), inactivated heated GUS (500 microg ml(-1)), glucuronic acid (10, 100 and 500 microg ml(-1)), and bovine serum albumin (500 microg ml(-1)) to M. persicae. Our results reveal that these chemicals provided as food intake might influence the biological parameters of this aphid. Experiments showed a probiotic effect of 500 microg ml(-1) GUS diet, resulting in reduced larval mortality, and increased adult reproduction period and fecundity, which led to an increased population growth potential (r(m)=0.17+/-0.01 versus r(m)=0.12+/-0.03 for aphids fed on control diet). A lower amount of added GUS led to fewer variations, biological parameters being only slightly altered (r(m)=0.14+/-0.03). Statistically similar alterations of the biological parameters were obtained when comparing aphids fed on the diet added with inactivated GUS or the non-structural bovine serum albumin protein (r(m)=0.15+/-0.02 and 0.14+/-0.03, respectively). Feeding assays conducted with glucuronic acid supplemented diets enhanced longevity and nymph production of the adult aphids and reduced larval mortality, resulting in r(m)=0.15+/-0.02 for the highest dose (500 microg ml(-1)). Although 100 microg ml(-1) glucuronate diet did not induce any effect on M. persicae (r(m)=0.12+/-0.03), aphids fed on 10 microg ml(-1) glucuronate diet exhibited unexpected reduced demographic parameters (r(m)=0.10+/-0.03). Immuno-histological analysis showed GUS labeling along the whole digestive epithelium of adults and in various tissues including embryos and bacteriocytes. These results suggest that GUS crosses through the digestive tract. Western blots performed with protein extracts of transformed potato plants expressing the gus gene showed a unique band of molecular weight 76 kDa. On the contrary, in extracts from aphids fed on transgenic potato plants or bred on GUS 500 microg ml(-1) artificial diet, several proteins of lower molecular weight were hybridized, revealing proteolysis of ingested GUS. It is concluded that GUS protein, and more precisely GUS activity, is responsible for the probiotic effects on aphid feeding. The possible pathways of induction of such physiological alterations by GUS are discussed.

Animal Feed↗
PubMed2003

Plant waxy bloom on peas affects infection of pea aphids by Pandora neoaphidis.

This study examined the effects of the surface wax bloom of pea plants, Pisum sativum, on infection of pea aphids, Acyrthosiphon pisum, by the fungal pathogen Pandora neoaphidis. In prior field surveys, a higher proportion of P. neoaphidis-killed pea aphids (cadavers) had been observed on a pea line with reduced wax bloom, as compared with a sister line with normal surface wax bloom. Laboratory bioassays were conducted in order to examine the mechanisms. After plants of each line infested with aphids were exposed to similar densities of conidia, the rate of accumulation of cadavers on the reduced wax line was significantly greater than on the normal wax bloom line; at the end of the experiment (13d), the proportion of aphid cadavers on the reduced wax line was approximately four times that on the normal wax bloom line. When plants were exposed to conidia first and then infested with aphids, the rate of accumulation of cadavers was slightly but significantly greater on the reduced wax line, and infection at the end of the experiment (16d) did not differ between the lines. When aphids were exposed first and then released onto the plants, no differences in the proportion of aphid cadavers were observed between the pea lines. Greater infection of pea aphid on reduced wax peas appears to depend upon plants being exposed to inoculum while aphids are settled in typical feeding positions on the plant. Additional experiments demonstrated increased adhesion and germination by P. neoaphidis conidia to leaf surfaces of the reduced wax line as compared with normal wax line, and this could help explain the higher infection rate by P. neoaphidis on the reduced wax line. In bioassays using surface waxes extracted from the two lines, there was no effect of wax source on germination of P. neoaphidis conidia.

Animals↗
PubMed2004

Forecasting aphid outbreaks and epidemics of Cucumber mosaic virus in lupin crops in a Mediterranean-type environment.

Cucumber mosaic virus (CMV) causes a serious disease of narrow-leafed lupin (Lupinus angustifolius). It is seed-borne in lupin and seed-infected plants act as the primary virus source for secondary spread by aphid vectors within crops. Infection with CMV causes yield losses of up to 60% in epidemic years, but has little impact on yield in years when spread is limited. Aphids also cause sporadic yield losses due to direct feeding damage. A simulation model was developed to forecast aphid outbreaks and epidemics of CMV in lupin crops growing in the 'grainbelt' of south-west Australia, which has a Mediterranean-type climate. The model uses rainfall during summer and early autumn to calculate an index of aphid build-up on weeds, crop volunteers and self-regenerating annual pastures in each 'grainbelt' locality before the growing season commences in late autumn. The index is used to forecast the timing of aphid immigration into crops. The subsequent aphid build-up and movement within the crop, spread of CMV from virus-infected source plants within the crop, yield losses and percentage of harvested seed-infected are then calculated. The model evaluates the effects of different sowing dates, percentages of CMV infection in seed sown and plant population densities on virus spread. The model simulations were validated with 14 years' field data from six different sites in the 'grainbelt', representing a wide range of pre-growing season rainfall scenarios, sowing dates, percentages of infection in seed sown and plant population densities. The model was incorporated into a decision support system (DSS) for use by lupin farmers and agricultural consultants in planning CMV management and targeting sprays against aphids to prevent direct feeding damage. The inputs required from the user are lupin cultivar, anticipated emergence date, percentage CMV infection in seed sown, plant density and location. The output consists of a personalised risk forecast for the user and includes predictions for date of first aphid arrival, aphid numbers, CMV spread, final virus incidence, yield loss due to infection and percentage infection in harvested seed. Predictions from the DSS are accessible via an Internet site and from other information sources. The model can serve as a template for modelling similar virus/aphid vector pathosystems in other regions of the world, especially those with Mediterranean-type climates.

Animals↗
PubMed2004

Activity of aphids associated with lettuce and broccoli in Spain and their efficiency as vectors of Lettuce mosaic virus.

This research sought to identify the aphid virus vector species associated with lettuce and broccoli crops in Spain, and to determine their population dynamics and ability to transmit Lettuce mosaic virus (LMV). Green tile traps and Moericke yellow water-pan traps were used to monitor aphid flights during the spring and autumn growing seasons of 2001. Aphid species feeding on lettuce were counted weekly. The transmission efficiencies of LMV were determined for the aphid species caught most frequently. The Moericke traps generally caught more aphid species than the tile trap, but the latter was the most suitable to estimate flight activity of species involved in virus spread. Spring aphid catches indicated that the main aphid species landing on lettuce in the regions of Madrid and Murcia was Hyperomyzus lactucae, but Brachycaudus helichrysi was also abundant in both regions. In broccoli in the Navarra region, the most abundant species in spring were Aphis fabae, B. helichrysi and H. lactucae. In autumn-sown crops, the main species landing on lettuce in the Madrid region were Hyadaphis coriandri and Aphis spiraecola. In Murcia, A. spiraecola and Myzus persicae were the most abundant, while in Navarra, Therioaphis trifolii, and various Aphis spp. were the most numerous landing on broccoli. The main aphid species colonising lettuce was Nasonovia ribisnigri, but other less abundant colonising species were Aulacorthum solani and Macrosiphum euphorbiae. The most efficient vectors of LMV were M. persicae, Aphis gossypii and M. euphorbiae, while A. fabae and H. lactucae transmitted with low efficiency, and Rhopalosiphum padi and N. ribisnigri did not transmit. Occurrence of LMV epidemics in central Spain in relation to aphid flights and the role of weeds as virus reservoirs is discussed.

Animals↗
PubMed2006

Protecting crops from non-persistently aphid-transmitted viruses: a review on the use of barrier plants as a management tool.

Barrier plants are a management tool based on secondary plants used within or bordering a primary crop for the purpose of disease control. Aphid-transmitted viruses account for approximately 50% of the 600 known viruses with an invertebrate vector. Barrier plants may act as real natural sinks for non-persistent aphid-transmitted viruses and have proved in the past to be an effective crop management strategy to protect against virus infection. Increasing the knowledge on aphid host seeking and flying behaviour, and on how barrier plants may affect the behaviour of aphids and their natural enemies will allow further development of this environmentally-friendly habitat manipulation strategy. An ideal plant barrier should be a non-host for the virus and the vector, but appealing to aphid landing and attractive to their natural enemies and should allow sufficient residence time to allow aphid probing before taking-off occurs. In this review, we have addressed why aphids are manageable by barrier cropping, the mechanisms by which barrier plants affect the occurrence of non-persistently aphid-transmitted viruses and the limitations of using barrier plants as a virus control strategy. Finally, we have pointed out future directions of research that should be conducted to integrate barrier cropping with other disease management strategies, and optimise and extend the use of barrier plants as a strategy for managing aphid-transmitted virus diseases.

Agriculture↗
PubMed2002

Transgenic potatoes with enhanced levels of nematode resistance do not have altered susceptibility to nontarget aphids.

Cysteine proteinase inhibitors (cystatins) confer resistance to plant-parasitic nematodes when expressed in transgenic plants. The survival and growth of nymphs of the peach-potato aphid, Myzus persicae, were adversely affected when cystatins were added to artificial diets. When aphids were clip-caged onto transgenic plants expressing chicken egg white cystatin (CEWc) there was no adverse effect on aphid fitness. Field populations of aphids on transgenic Desiree potatoes, expressing CEWc or a modified version of oryzacystatin I, were not significantly different from populations on control Desiree plants. The effect of other nematode management options on aphid numbers was also studied. A conventionally bred cultivar, with partial nematode resistance, supported higher populations of aphids than the transgenic lines at the beginning of the sampling period. Peak aphid densities on the untreated control and untreated transgenic lines were 7 and 5.2 aphids per plant. Aldicarb, commonly used to control nematodes on potatoes, reduced the value to less than 0.2 aphids per plant. The results demonstrate that levels of expression in the plant tissue actually consumed are important in determining the risk of cystatins to nontarget invertebrates. The study also highlights the importance of including currently used management options in any assessment of the impact of transgenic plants on nontarget organisms.

Aldicarb↗
PubMed2004

Multitrophic interactions involving genetically modified potatoes, nontarget aphids, natural enemies and hyperparasitoids.

Genetically modified (GM) potatoes expressing a cysteine proteinase inhibitor (cystatin) have been developed as an option for the management of plant parasitic nematodes. The relative impact of such plants on predators and parasitoids (natural enemies) of nontarget insects was determined in a field trial. The trial consisted of GM plants, control plants grown in soil treated with a nematicide and untreated control plants. The quantity of nontarget aphids and their quality as hosts for natural enemies were studied. Aphid density was significantly reduced by nematicide treatment and few natural enemies were recorded from treated potatoes during the study. In contrast, similar numbers of aphids and their more abundant predators were recorded from the untreated control and the GM potatoes. The size of aphids on GM and control plants was recorded twice during the study. During the first sampling period (2-9 July) aphids clip-caged on GM plants were smaller than those on control plants. During the second sampling period (23-30 July) there was no difference in aphid size between those from the GM and control plants. Host size is an important component of host quality. It can affect the size and fecundity of parasitoid females and the sex ratio of their offspring. However, neither the fitness of females of Aphidius ervi, the most prevalent primary parasitoid, nor the sex ratio of their progeny, were affected when the parasitoids developed on aphids feeding on GM plants. Two guilds of secondary parasitoid were also recorded during the study. The fitness of the most abundant species, Aspahes vulgaris, was not affected when it developed on hosts from GM plants. The transgene product, OC I Delta D86, was not detected in aphids that had fed on GM plants in the field, suggesting that there is minimal secondary exposure of natural enemies to the inhibitor. The results indicate that transgenic nematode resistance is potentially more compatible with aphid biological control than is current nematicide use.

Aldicarb↗
PubMed2003

The causes and processes of the mid-summer population crash of the potato aphids Macrosiphum euphorbiae and Myzus persicae (Hemiptera: Aphididae).

Populations of many phloem-feeding aphid species in temperate regions increase exponentially in early summer and then 'disappear', usually over a time-scale of a few days, in July. To understand these dynamics, empirical investigation of the causes and modelling of the processes underlying population change are required. Numbers of the aphids Myzus persicae(Sulzer) and Macrosiphum euphorbiae (Thomas), monitored over three years in commercial potato fields in the UK, increased to a maximum of 2-2.5 per leaflet on 16 July in 1999 and 2001, and then declined to < 0.25 per leaflet by 26 July. In 2000, aphid numbers remained very low (< 0.25 per leaflet) throughout the season. The onset of the crash in aphid numbers (16-19 July in 1999 and 2001) was consistently associated with changes in the phloem amino acid composition of potato leaflets. Natural enemies, including syrphids, parasitoids, coccinellids, chrysopids and entomopathogenic fungi, increased in abundance throughout the sampling period. The incidence of winged emigrant aphids prior to the crash was low (< 10%). Experimental manipulation during 2001 demonstrated that, during the crash period, the fecundity of aphids (caged on leaves to exclude natural enemies) was depressed by 25-45% relative to earlier in the season, and that presence of natural enemies reduced aphid numbers by up to 68%. Using these data, an excitable medium model was constructed, which provided a robust description of aphid population dynamics in terms of plant development-induced changes in aphid fecundity and temporal change in natural enemy pressure.

Amino Acids↗
PubMed2006

Comparing growth patterns among field populations of cereal aphids reveals factors limiting their maximum abundance.

Cereal stands in central Europe are commonly infested with three species of aphids that may become serious pests. With increasing abundance, the proportion of a particular species in the total aphid population may remain constant, suggesting a density-independent exponential growth, or the proportion can change, suggesting density-dependent constraints on growth. The constraints that affect particular species, and thus their relative abundance, were studied. The proportionality between maximum abundances of the cereal aphids was studied using a 10-year census of the numbers of aphids infesting 268 winter wheat plots. For two species their abundance on leaves and ears was compared. With increasing aphid density the maximum abundance of Rhopalosiphum padi (Linnaeus) remained proportional, but not that of Sitobion avenae (Fabricius), which was constrained by the smaller surface area of ears compared to leaves. There was no evidence of inter-specific competition. Maximum abundance of R. padi and Metopolophium dirhodum (Walker) on leaves did not change proportionally as the proportion of M. dirhodum decreased with increasing overall aphid density. This decrease was probably caused by the restricted distribution of M. dirhodum, which is confined to leaves, where space is limiting. No change in proportion between populations was detected when the average densities were below 0.54 aphids per leaf or ear. Non-proportional relationships between aphid populations appeared to be due to spatial constraints, acting upon the more abundant population. Detecting the limitation of population growth can help with the assessment of when density-independent exponential growth is limited by density-dependent factors. This information may help in the development of models of cereal aphid population dynamics.

Animals↗