Generalized aphid population growth models with immigration and cumulative-size dependent dynamics

Mechanistic models in which the per-capita death rate of a population is proportional to cumulative past size have been shown to describe adequately the population size curves for a number of aphid species. Such previous cumulative-sized based models have not included immigration. The inclusion of immigration is suggested biologically as local aphid populations are initiated by migration of winged aphids and as reproduction is temperature-dependent. This paper investigates two models with constant immigration, one with continuous immigration and the other with restricted immigration. Cases of the latter are relatively simple to fit to data. The results from these two immigration models are compared for data sets on the mustard aphid in India.     

Transmission of potato leafroll virus in relation to the honeydew excretion of Myzus persicae

Honeydew excretion of single Myzus persicae nymphs on potato leafroll virus (PLVR)-infected Physalis floridana was studied during the acquisition access period (AAP) in relation to the efficiency of virus transmission.
With increasing length of the AAP, the percentage of nymphs that transmitted the virus increased. These nymphs produced significantly more honeydew droplets during the AAP on PLRV-infected P. floridana plants than nymphs which failed to transmit the virus. However, the number of honeydew droplets excreted during the AAP by transmitting nymphs did not affect the length of the latency period. Nymphs which infected the first test plant after a short latency period produced a similar amount of honeydew during the AAP to those with a longer latency period.
Honeydew excretion recorded on plants of varied age, showed that nymphs feeding on bottom leaves of infected plants produced more honeydew droplets than on comparable leaves of healthy plants. On infected plants, nymphs produced more honeydew droplets on bottom leaves with pronounced symptoms than on top leaves that hardly showed any symptom of PLRV infection.
The concentration of viral antigen measured by ELISA was lower in top leaves than in bottom leaves of infected plants. Nevertheless, nymphs feeding on top leaves transmitted the virus more efficiently than those which used bottom leaves as virus source. When bottom leaves were used as a virus source, the percentage of viruliferous nymphs decreased with plant age. These results indicate that the availability of virus for acquisition by aphids declines with increasing plant age and symptom severity.     

Probing behavior of aposymbiotic green peach aphid (Myzus persicae) on susceptible Solanum tuberosum and resistant Solanum stoloniferum plants

The green peach aphid, Myzus persicae Sulzer (Hemiptera: Aphididae) is one of the potato important pests; it is the most efficient vector of potato viruses. Myzus persicae harbors the endosymbiotic bacteria Buchnera aphidicola which supplements their diet. There is increasing evidence that B. aphidicola is involved in plant–aphid interactions and we previously demonstrated that B. aphidicola disruption (aposymbiosis) affected the probing behavior of M. persicae on radish plants, delaying host plant acceptance. In this work, we evaluated the effect of aposymbiosis on the probing behavior of M. persicae on 2 Solanum species with different compatibility with M. persicae, Solanum tuberosum (susceptible) and Solanum stoloniferum (resistant) with the electrical penetration graph technique (EPG). To disrupt B. aphidicola, rifampicin was administered to aphids through artificial diets. Aposymbiotic aphids, on both plant species, showed increased pathway activities, mechanical problems with the stylets, and delayed salivation in the phloem. The extended time in derailed stylet mechanics affected the occurrence of most other probing activities; it delayed the time to the first phloem phase and prevented ingestion from the phloem. The effect of aposymbiosis was more evident in the compatible interaction of M. persicae–S. tuberosum, than in the incompatible interaction with S. stoloniferum, which generated the M. persicae–S. tuberosum interaction to become incompatible. These results confirm that B. aphidicola is involved in the plant–aphid interaction in relation to plant acceptance, presumably through a role in stylets penetration in the plant.     

小型昆虫DNA提取时匀浆方法的改进

应用改进的方法方便地提取了高质量的单头蚜虫基因组DNA ,有助于解决小型昆虫研究工作中单头虫体的DNA提取困难问题     

Functional divergence of three glutathione transferases in two biotypes of the English grain aphid,Sitobion avenae

The English grain aphid, Sitobion avenae (Fabricius) (Hemiptera: Aphididae), is a significant pest of cereal crops, but molecular factors and mechanisms that underpin its ability to develop differential biotypes on variable host plants are still not well understood. In this study, we investigated the interactions between two plant secondary metabolites (i.e., gramine and gallic acid) and three glutathione S-transferases (GSTs) of S. avenae. Using artificial diets complemented or not with one of these two plant compounds, we found that gramine had relatively stronger negative effects on fitness of S. avenae biotype 3 (adapted to barley), and gallic acid on that of biotype 4 (adapted to wheat). Gramine significantly induced overexpression of SaveGST1 and SaveGST2 in biotype 4, but not in biotype 3. Gramine also reduced SaveGST3 expression in biotype 4, but not in biotype 3, suggesting biotype-specific effect of GSTs’ regulation. In the treatments with gallic acid, the overexpression of SaveGST1, but not SaveGST2 or SaveGST3, was significantly induced in both biotypes, suggesting a critical role of SaveGST1 in detoxification of phenolic compounds such as gallic acid. The total constitutive GST activity was much higher in biotype 4 than in biotype 3. Significant increase in GST activity was obtained by the addition of both secondary metabolites in biotype 4, but not in biotype 3, showing significantly higher expression plasticity of GSTs in biotype 4. Thus, both constitutive and induced expression of GSTs could affect the adaptability of S. avenae on plants with variable secondary compounds, and thus contribute to the divergence of biotypes in this aphid species.     

Expression of snowdrop lectin in transgenic tobacco plants results in added protection against aphids

The range of sap-sucking insect pests to which GNA, (the mannose specific lectin from snowdrops (Galanthus nivalis) has been shown to be insecticidal in artificial diets has been extended to include the peach potato aphid (Myzus persicae). A gene construct for constitutive expression of GNA from the CaMV35S gene promoter has been introduced into tobacco plants. A transgenic tobacco line which expresses high levels of GNA has been shown to have enhanced resistance toM. persicae in leaf disc and whole plant bioassays,demonstrating the potential for extending transgenic plant technology to the control of sap-sucking insect pests.     

Attachment forces of pea aphids (Acyrthosiphon pisum) on different legume species

1. Sympatric populations of insects adapted to different host plants are good model systems not only to study how they adapt to the chemistry of their food plant, but also to investigate whether morphological modifications evolved enabling them to live successfully on a certain plant species. 2. The pea aphid, Acyrthosiphon pisum (Harris) encompasses at least 11 genetically distinct sympatric host races, each showing a preference for a certain legume species. The leaflet surfaces of these legumes differ considerably in their wax coverage. 3. It was investigated whether the attachment structures of three pea aphid genotypes from different host races are adapted to the different surface properties of their host plants and whether they show differences in their attachment ability on the respective host and non‐host plants. 4. The surface morphology of plants and aphid tarsi was examined using SEM (scanning electron microscopy). The ability of the aphids to walk on specific surfaces was tested using traction force measurements. 5. The presence of wax blooms on the leaflets lowers the aphids' attachment ability considerably and diminishes their subsequent attachment on ‘neutral’ surfaces like glass. The pea aphid host races differ in their ability to walk on certain surfaces. However, the genotype from the adapted aphid host race was not necessarily the one with the best walking performance on their host plant. All aphids, regardless of the original host plant, were most efficient on the neutral control surface glass. The general host plant Vicia faba was the plant with the most favourable surface for all aphid host races.     

Evidence for specificity in symbiont-conferred protection against parasitoids

Many insects harbour facultative symbiotic bacteria, some of which have been shown to provide resistance against natural enemies. One of the best-known protective symbionts is Hamiltonella defensa, which in pea aphid (Acyrthosiphon pisum) confers resistance against attack by parasitoid wasps in the genus Aphidius (Braconidae). We asked (i) whether this symbiont also confers protection against a phylogenetically distant group of parasitoids (Aphelinidae) and (ii) whether there are consistent differences in the effects of bacteria found in pea aphid biotypes adapted to different host plants. We found that some H. defensa strains do provide protection against an aphelinid parasitoid Aphelinus abdominalis. Hamiltonella defensa from the Lotus biotype provided high resistance to A. abdominalis and moderate to low resistance to Aphidius ervi, while the reverse was seen from Medicago biotype isolates. Aphids from Ononis showed no evidence of symbiont-mediated protection against either wasp species and were relatively vulnerable to both. Our results may reflect the different selection pressures exerted by the parasitoid community on aphids feeding on different host plants, and could help explain the maintenance of genetic diversity in bacterial symbionts.     

蚜虫基因组DNA提取方法的改进

蚜虫基因组DNA的提取是蚜虫分子生物学研究中的难点。参照动物基因组DNA的提取方法,根据蚜虫体型微小,体表有外骨骼的特点,对SDS法作了改进。改进的方法无需用组织捣碎棒破碎虫体,操作简便。与现在常用的提取方法相比,改进的SDS法能快速、有效地提取单头蚜虫的基因组DNA,适用于RAPD随机引物和测序引物的PCR扩增。     

Effect of mineral oils on host plant selection and probing behavior of Rhopalosiphum padi

Aphids that colonize and reproduce on potato are some of the most efficient vectors of Potato virus Y (PVY) (Potyviridae: Potyvirus), and hence these aphids have been the focus of the majority of studies to date. However, other non‐colonizing aphids can also function as vectors. Mineral oil is the only product available to growers that effectively prevents the spread of PVY in potato seed production. Most previous studies focused on the effect of mineral oil on the behavior of aphids on their preferential host plant, and consequently there is a lack of information for non‐colonizing aphids on potato plants. The objective of this study was to determine the effect of spraying potatoes with one of two mineral oils, Superior 70 or Vazyl‐Y, on host selection and probing behavior of the non‐colonizing aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae). The electrical penetration graph (EPG) technique, combined with ethological observations, determined that there was no difference in R. padi behavior on potato plants treated with Superior 70. However, there were few significant changes in R. padi behavior on plants sprayed with Vazyl‐Y, including a delay in the initiation of stylet penetration and an increase in the duration of xylem sap ingestion. These new data support previous results and confirm that the mode of action of mineral oil in the reduction of the spread of PVY is not solely due to the modification of the behavior of aphids.