The attack of the clones: tracking the movement of insecticide-resistant peach-potato aphids Myzus persicae (Hemiptera: Aphididae).

Myzus persicae (Sulzer) collected in Scotland were characterized for four microsatellite loci, intergenic spacer fingerprints and the resistance mechanisms modified acetylcholinesterase (MACE), overproduced carboxylesterase and knockdown resistance (kdr). Microsatellite polymorphisms were used to define a limited number of clones that were either fully susceptible to insecticides or possessed characteristic combinations of resistance mechanisms. Within these clones, intergenic spacer fingerprints could either be very consistent or variable, with the latter indicating ongoing evolution within lineages, most likely derived from the same zygote. Two clones (termed A and B) possessed all three resistance mechanisms and predominated at sites treated with insecticides. Their appearance on seed potatoes and oilseed rape in Scotland in 2001 coincided with extensive insecticide use and severe control failures. Clones C, I and J, with no or fewer resistance mechanisms, were found in samples from 1995 and were dominant at untreated sites in 2001. A comparison of Scottish collections with those from other UK and non-UK sites provides insight into the likely origins, distribution and dynamics of M. persicae clones in a region where asexual (anholocyclic) reproduction predominates, but is vulnerable to migration by novel genotypes from areas of Europe where sexual (holocyclic) reproduction occurs.

A comparison of the composition of epicuticular wax from red raspberry (Rubus idaeus L.) and hawthorn (Crataegus monogyna Jacq.) flowers.

Epicuticular waxes have been characterised from the flowers of raspberry and hawthorn, on both of which adult raspberry beetles (Byturus tomentosus) can feed. The flower wax from both species had similar alkane profiles and also contained long-chain alcohols, aldehydes and fatty acids. The range of the carbon numbers detected for these classes of compounds was broadly similar in both but the relative amounts of each differed between species. Raspberry flower wax also contained fatty acid methyl esters, a group of compounds that has rarely been detected in plant epicuticular waxes, however, these were not observed in hawthorn flower wax. Long-chain alcohol-fatty acid esters with carbon numbers ranging from C36 to C48 were also detected in both plant species. However, an examination of their constituent acids indicated that in hawthorn the esters based on the C16 fatty acid predominated, whilst in raspberry flower wax, esters based on the C20 fatty acid were most abundant. Both species also contained pentacyclic triterpenoids, which accounted for, on average, over 16 and 48% of the total wax extracted from raspberry and hawthorn flowers respectively. In the former, ursolic and oleanolic acids accounted for over 90% of the pentacyclic triterpenes, whilst hawthorn flower wax, in addition to containing these acids, also contained high relative concentrations of both free and esterified alpha- and beta-amyrins.

Some epidemiological approaches to the control of aphid-borne virus diseases in seed potato crops in northern Europe.

An account is given of progress during the last 30 years in knowledge of the epidemiology of diseases caused by aphid-borne viruses in seed potato production areas of northern Europe. During this period, Potato leafroll virus (PLRV) and strains of Potato virus Y (PVY(O), PVY(N)) were consistently the most prevalent and harmful. The main factors influencing spread involve the amount of initial virus inoculum in seed crops, agricultural practices in relation to seed potato production, the status of aphids as colonising or transient vectors in the crop, variation in their life cycles and behaviour, effects of environmental factors on aphid population dynamics, and the interaction between aphid phenology and mature plant resistance. Lessons have been drawn from comparisons of the causes of outbreaks of PLRV and PVY, and various comprehensive models have been designed to predict virus spread and optimise control. The accuracy and reliability of virus detection, and chemical control of aphids have been considerably improved, but use of the latter has been severely affected by the development in Myzus persicae of resistance to most types of insecticide. It is suggested that more attention should be given to breeding virus-resistant cultivars that would lead to decreased pesticide use and thus promote more integrated environment-friendly strategies for control.

Aphid Acquisition and Cellular Transport of Potato leafroll virus-like Particles Lacking P5 Readthrough Protein.

ABSTRACT Lepidopteran cells (Spodoptera frugiperda) produced isometric virus-like particles (VLP) when infected with a recombinant baculovirus Ac61 that contained the Potato leafroll virus (PLRV) coat protein gene modified with an N-terminal histidine tag (P3-6H). Cells infected with AcFL, a recombinant baculovirus that expressed cDNA copies of the PLRV genome RNA, did not produce virus-like particles (VLP). In cell lines doubly infected with Ac61 and AcFL, VLP were formed that contained PLRV-RNA packaged in P3-6H coat protein (FL). Both the P3-6H and the FL particles were morphologically indistinguishable from particles of PLRV despite the fact that they lacked the P5 readthrough protein present in wild-type PLRV. When aphids (Myzus persicae) were fed on, or injected with, purified PLRV, or VLP of either type (FL or P3-6H) and examined by electron microscopy, no differences were observed among treatments for particle endocytosis, transcellular transport, or exocytosis at the aphid midgut or accessory salivary glands. Particles were observed in the salivary canals and in the salivary duct leading out of the aphid. These results suggest that P5 readthrough protein of PLRV may not be essential for cellular transport of virus through aphid vectors.

Analysis of clonal diversity of the peach-potato aphid, Myzus persicae (Sulzer), in Scotland, UK and evidence for the existence of a predominant clone.

Clones of the peach-potato aphid, Myzus persicae (Sulzer), mostly from Scotland, UK were examined using an rDNA fingerprinting technique. Eighty patterns (genotypes) were found amongst the 276 clones. A large number of clones (30%) from all sample areas in Scotland exhibited the same simple pattern, suggesting the presence of a single M. persicae clone. There was no difference in genotype distributions between M. persicae collected from brassica or potato crops, suggesting that host-adapted genotypes have no advantage in the field. Different fingerprints were randomly distributed in the environment, although clones taken from the same leaf were more often the same fingerprint. Highly distinctive fingerprints, which were more widely distributed, suggest that this technique could be used to follow individual clones. In addition to the common clonal type, multiple fingerprint bands were found over successive years, implying that, in Scotland, local overwintering asexual populations are the most common source of M. persicae in the following year.

Ribosomal spacer length variability in the large raspberry aphid, Amphorophora idaei (Aphidinae: macrosiphini).

The large raspberry aphid, Amphorophora idaei, has several biotypes described by their abilities to overcome plant resistance genes. Bioassays of field populations showed a strong shift towards A1 resistance-breaking biotypes since the 1960s. RFLP analysis of the rDNA cistron was used to study variation found within and between standard clones of three A. idaei biotypes and twenty-nine field populations collected over 3 years. Probing genomic DNA with the ribosomal DNA probe pBG 35 produced consistent differences in RFLPs between standard clones of biotypes. However, analysis of field populations gave more complex RFLP patterns that were not biotype-specific, unlike characteristic intergenic spacer (IGS) patterns reported for Schizaphis graminum biotypes. All but one sample collected from separate fields showed considerable genetic diversity within populations, attributed to alate migrations of parthenogenetic females in summer and males in autumn.

Molecular analysis of ribosomal DNA from the aphid Amphorophora idaei and an associated fungal organism.

The ribosomal DNA cistron from the large raspberry aphid, Amphorophora idaei (Hemiptera: Aphididae), has been mapped by restriction analysis. The results showed that the map of A. idaei was similar to those of the previously characterized aphids Schizaphis graminum and Acyrthosiphon pisum. An extra Bgl II site was found in some of the ribosomal DNA intergenic spacer repeats in A. idaei. Using in-situ hybridization to aphid mitotic chromosomes it was demonstrated that probes derived from this region mapped to the pair of X chromosomes and it was therefore aphid in origin. Polymerase chain reaction using conserved rDNA primers also detected significant amounts of a fungal genome in the DNA samples. Microscopic investigation showed that the external surface of A. idaei harboured fungal propagules, hyphae and yeast-like organisms.

Impact of dietary fiber and physical form on performance of lactating dairy cows.

Two trials were conducted to study the effects of forage intake and physical form on lactating cow performance. In trial 1, four cows in a 4 X 4 Latin square were fed long alfalfa hay at 28, 36, 45, and 53% of total dry matter plus concentrate. Total dry matter intake was not affected by forage percent. Total chewing time and milk fat percentage increased linearly with increasing forage consumption. Maximum 4% fat-corrected milk production occurred when diets contained 27% neutral detergent fiber and 18% acid detergent fiber. In trial 2, four cows in a 4 X 4 Latin square were fed diets of chopped alfalfa hay and concentrate in proportions to supply 27.4% total ration neutral detergent fiber. Mean particle length measured with an oscillating screen particle separator of the chopped hay was .26, .46, .64, and .90 cm. Total dry matter and forage dry matter intakes and total chewing were not influenced by forage mean particle length. Mean particle length did not affect actual milk or 4% fat-corrected milk production. Depression of milk fat percentage was prevented when forage mean particle length was greater than or equal .64 cm. Apparent digestibility of dietary constituents and rate of passage of hay and concentrate was not influenced by forage intake or physical form.