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PubMed2005

Effect of precocene II on fatty acid metabolism in the pea aphid, Acyrthosiphon pisum, under cold stress.

Pea aphids, Acyrthosiphon pisum (Harris), reared at 10 degrees C contain higher levels of fatty acids than those reared at 25 degrees C. This is primarily the result of an accumulation of triacylglycerols containing myristic acid. When aphids reared at 25 degrees C were transferred to 10 degrees C there was a gradual increase in triacylglycerol content that reached a maximum at 16 days post-transfer. Treatment of aphids with precocene II prior to transfer to 10 degrees C blocked the accumulation of fatty acids including myristic acid. A single application of 2 microg precocene II/aphid or two applications of 0.5 microg precocene II/ aphid administered on consecutive days resulted in aphids moved to 10 degrees C maintaining the same fatty acid profile as aphids maintained at 25 degrees C. Aphids that were treated with precocene II and maintained at 25 degrees C did not show changes in fatty acid profiles. Rearing aphids at 10 degrees C resulted in lower rates of reproduction and lower total numbers of progeny with longer longevity. Treatment with precocene II significantly decreased the total number of progeny produced at both temperatures. Precocene II did not reduce life span of aphids reared at 25 degrees C, however, the life span of treated aphids reared at 10 degrees C was decreased. The mechanism by which precocene II prevents the accumulation of myristic acid in aphids reared at 10 degrees C remains to be determined.

Animals↗
PubMed2005

The significance of gut sucrase activity for osmoregulation in the pea aphid, Acyrthosiphon pisum.

The osmotic pressure of the body fluids of aphids is lower than in their diet of plant phloem sap. It is hypothesised that aphids reduce the osmotic pressure of ingested food by sucrase-mediated hydrolysis of dietary sucrose to glucose and fructose, and the polymerisation of glucose into oligosaccharides of low osmotic pressure per hexose unit. To test this hypothesis, the impact of the alpha-glucosidase inhibitor acarbose on the sugar relations and osmoregulation of aphids was explored. Acarbose inhibited sucrase activity in gut homogenates and the production of monosaccharides and oligosaccharides in the honeydew of live aphids. Acarbose caused an increase in the haemolymph osmotic pressure for aphids reared on a diet (containing 0.75 M sucrose) hyperosmotic to the haemolymph and not on the isoosmotic diet containing 0.2 M sucrose. It did not affect aphid feeding rate over 2 days, except at high concentrations on 0.75 M sucrose diet, and this may have been a secondary consequence of osmotic dysfunction. Acarbose-treated aphids died prematurely. With 5 microM dietary acarbose, mean survivorship on 0.2 M sucrose diet was 4.2 days, not significantly different from starved aphids, indicating that, although these aphids fed, they were deprived of utilisable carbon; and on 0.75 M sucrose diet, mean survivorship was just 2.8 days, probably as a consequence of osmotic failure. It is concluded that the aphid gut sucrase activity is essential for osmoregulation of aphids ingesting food hyperosmotic to their body fluids.

Acarbose↗
PubMed2005

Monoclonal antibodies reveal the potential of the tetragnathid spider Pachygnatha degeeri (Araneae: Tetragnathidae) as an aphid predator.

The drive towards a more sustainable and integrated approach to pest management has engendered a renewed interest in conservation biological control, the role of natural enemy communities and their interactions with prey. Monoclonal antibodies have provided significant advances in enhancing our knowledge of trophic interactions and can be employed to help quantify predation on target species. The tetragnathid spider Pachygnatha degeeri Sundevall was collected from fields of winter wheat in the UK and assayed by ELISA for aphid proteins. It was demonstrated that this spider did not simply consume greater quantities of aphids because it was bigger. In addition, P. degeeri contained significantly greater concentrations of aphid in their guts than other spiders, showing that aphids comprised a greater proportion of their diet. Although P. degeeri constituted only 6% of the spider population numerically, females and males respectively contained 16% and 37% of total aphid proteins within all spiders screened, significantly more than their density would predict. These spiders also preyed upon aphids at a disproportionately high rate in June, during the aphid establishment phase, theoretically the best time for limiting growth in the aphid population. Although less abundant than other generalist predators, the capability of these hunting spiders to consume large numbers of aphids highlights them as a more significant component of the predator complex than had previously been realized. Limitation of aphid numbers early in the year by generalist predators provides more time for the specialist aphid predators and parasitoids to move in.

Analysis of Variance↗
PubMed2005

Effect of soil potassium availability on soybean aphid (Hemiptera: Aphididae) population dynamics and soybean yield.

Studies were conducted to examine the effect of potassium (K) on soybean aphid, Aphis glycines Matsumura, population growth. A laboratory feeding assay examined the effect of K-deficient foliage on life table parameters of soybean aphids, and field experiments were designed to determine the effect of three soil K treatment levels on aphid populations and their impact on soybean yields. The feeding assay found that life table parameters differed between aphids feeding on the K-deficient and nondeficient soybean leaves. Soybean aphids in the K-deficient treatment exhibited significantly greater intrinsic rate of increase (r(m)), finite rate of increase (lambda), and net reproductive rate (Ro) relative to aphids feeding on nondeficient leaves. No significant difference was observed in mean generation time (T) between the two treatments. However, the field experiment repeated over 2 yr showed no effect of K on soybean aphid populations. Soybean aphid populations were high in unsprayed plots and feeding resulted in significant yield losses in 2002 at all three K treatment levels: when averaged across 2001 and 2002, unsprayed treatments yielded 22, 18, and 19.5% less than the sprayed plots in the low, medium, and high K treatments, respectively. No significant interaction was observed between aphid abundance and K level on soybean yields in either year. This study therefore suggests that although aphids can perform better on K-deficient plants, aphid abundance in the field may be dependent on additional factors, such as dispersal, that may affect final densities within plots.

Animals↗
PubMed1996

Potyvirus transmission is not increased by pre-acquisition fasting of aphids reared on artificial diet.

Aphids (Myzus persicae), fasted after removal from healthy rearing plants, transmitted tobacco etch potyvirus (TEV) more efficiently than unfasted aphids whether virus acquisition was from infected leaves or through membranes. There was no difference in uptake of 125I-labelled TEV by fasted or unfasted aphids as measured by liquid scintillation counting. When aphids acquired 125I-labelled TEV, label was retained in the stylets (as determined by autoradiographic light microscopy) by 51 % of 272 fasted aphids, as against 7.8% of 258 unfasted aphids. There was a close correlation between virus transmission by aphids and virion retention in stylets. The effect of pre-acquisition fasting disappeared when aphids reared on an artificial diet were used in virus transmission tests. The transmission rates obtained with such aphids were similar to the rates with fasted aphids reared on healthy plants. Our results support the hypothesis that fasting eliminates plant component(s) which interfere with the retention of virions in the food canal of aphid stylets.

Animal Feed↗
PubMed2000

Cospeciation between bacterial endosymbionts (Buchnera) and a recent radiation of aphids (Uroleucon) and pitfalls of testing for phylogenetic congruence.

Previous studies of phylogenetic congruence between aphids and their symbiotic bacteria (Buchnera) supported long-term vertical transmission of symbionts. However, those studies were based on distantly related aphids and would not have revealed horizontal transfer of symbionts among closely related hosts. Aphid species of the genus Uroleucon are closely related phylogenetically and overlap in geographic ranges, habitats, and parasitoids. To examine support for congruence of phylogenies of Buchnera and Uroleucon, sequences from four mitochondrial, one nuclear, and one endosymbiont gene (trpB) were obtained. Congruence of phylogenies based on pooled aphid genes with phylogenies based on trpB was highly significant: Most nodes resolved by trpB corresponded to nodes resolved by the pooled aphid genes. Furthermore, no nodes were both inconsistent between the trees and strongly supported in both trees. Two kinds of analyses testing the null hypothesis of perfect congruence between pairwise combinations of datasets and tree topologies were performed: the Kishino-Hasegawa test and the likelihood-ratio test. Both tests indicated significant disagreement among most pairwise combinations of mitochondrial, nuclear, and symbiont datasets. Because rampant recombination among mitochondrial genomes of different aphid species is unlikely, inaccurate assumptions in the evolutionary models underlying these tests appear to be causing the hypothesis of a shared history to be incorrectly rejected. Moreover, trpB was more consistent with the aphid genes as a set than any single aphid gene was with the others, suggesting that the symbionts show the same phylogeny as the aphids. Overall, analyses support the interpretation that symbionts and aphids have undergone strict cospeciation, with no horizontal transmission of symbionts even among closely related, ecologically similar aphid hosts.

Animals↗
PubMed2006

A dual-genome microarray for the pea aphid, Acyrthosiphon pisum, and its obligate bacterial symbiont, Buchnera aphidicola.

BACKGROUND: The best studied insect-symbiont system is that of aphids and their primary bacterial endosymbiont Buchnera aphidicola. Buchnera inhabits specialized host cells called bacteriocytes, provides nutrients to the aphid and has co-speciated with its aphid hosts for the past 150 million years. We have used a single microarray to examine gene expression in the pea aphid, Acyrthosiphon pisum, and its resident Buchnera. Very little is known of gene expression in aphids, few studies have examined gene expression in Buchnera, and no study has examined simultaneously the expression profiles of a host and its symbiont. Expression profiling of aphids, in studies such as this, will be critical for assigning newly discovered A. pisum genes to functional roles. In particular, because aphids possess many genes that are absent from Drosophila and other holometabolous insect taxa, aphid genome annotation efforts cannot rely entirely on homology to the best-studied insect systems. Development of this dual-genome array represents a first attempt to characterize gene expression in this emerging model system. RESULTS: We chose to examine heat shock response because it has been well characterized both in Buchnera and in other insect species. Our results from the Buchnera of A. pisum show responses for the same gene set as an earlier study of heat shock response in Buchnera for the host aphid Schizaphis graminum. Additionally, analyses of aphid transcripts showed the expected response for homologs of known heat shock genes as well as responses for several genes with unknown functional roles. CONCLUSION: We examined gene expression under heat shock of an insect and its bacterial symbiont in a single assay using a dual-genome microarray. Further, our results indicate that microarrays are a useful tool for inferring functional roles of genes in A. pisum and other insects and suggest that the pea aphid genome may contain many gene paralogs that are differentially regulated.

Animals↗
PubMed1999

Effects of fungal infection on the alarm response of pea aphids

Pea aphids (Acyrthosiphon pisum, Homoptera: Aphididae) infected with the fungal pathogen Erynia neoaphidis (Zygomycetes: Entomophthorales) were less sensitive to the aphid alarm pheromone (E)-beta-farnesene than uninfected aphids. Approximately 83% of the healthy aphids and 45% of the infected aphids (2 and 3 days post-inoculation) responded to the alarm pheromone. The percentage of nonresponding aphids increased as the disease progressed. When squeezed (simulated attack) healthy aphids and aphids at an advanced stage of infection elicited a response similar to that of uninfected aphids, suggesting that the alarm pheromone was produced by diseased insects. Aphids infected for 2 or 3 days did not recolonize the upper regions of bean plants after dislodgment. This showed that infected aphids are less active at late stages of infection. The implications of these results are discussed with respect to fungal transmission and biological control. Copyright 1999 Academic Press.

Journal Article↗
PubMed2026

Adaptation to Plant Defence in an Agricultural Insect Pest: Integrating Genome Scans and Gene Expression in the Soybean Aphid Reveals Multi-Genic Pathways.

In agroecosystems, intense selection pressures cause species to adapt and spread, often leading to the evolution and persistence of pests. Understanding how pests rapidly adapt can help develop sustainable strategies for their management and improve agroecosystem health. Pest adaptation involves stable variations in DNA sequence, as well as dynamic shifts in gene expression, often mediated by non-coding regulatory elements. We examined adaptation to plant defences in the soybean aphid, Aphis glycines, in which virulent aphids have overcome plant defences and avirulent aphids have not. Previous data with laboratory colonies suggested that virulent aphids have higher overall gene expression, including transposable elements, some of which influence gene regulation. However, we lack information on how genetic variation in natural populations impacts adaptation and potentially gene regulation. We integrated population genome scans of field-collected, soybean aphid populations with gene expression profiles of virulent and avirulent laboratory colonies to uncover connections between genetic differentiation and gene regulation for virulence. Genome scan methods found 2144 single nucleotide polymorphisms (SNPs) with significant genetic differentiation (i.e., outliers) in field-collected populations. These SNPs were near 1004 genes, representing 5.16% of the effective number of genes. Based on previous RNA-Seq data with laboratory colonies, we found 3160 genes and 147 long non-coding RNAs (lncRNAs) with differential expression among virulent and avirulent biotypes. By integrating both data sets, we identified 16 genes and 5 long non-coding RNAs with differential expression and that were associated with an outlier SNP (within 10 kbp). We validated SNPs with additional field collected aphids and found an aphid clone with stronger virulence than our laboratory virulent colony, surviving on 2 different aphid-resistant soybean varieties. This new virulent clone had fixed allele differences at 9 SNPs compared to our avirulent and other virulent colony. Field collected soybean aphids matching the phenotype of this new virulent clone had significant genetic differentiation with 3 outlier SNPs near genes related to zinc transport and lachesin compared to field collected avirulent aphids. Our entire data reinforced the importance of a potential multi-genetic response to overcome plant defence and generates new insights into complex genetic and regulatory mechanisms involved in insect-plant interactions.

Animals↗
PubMed1999

Aphids, predators and parasitoids.

A number of studies have demonstrated the role of herbivore-induced release of plant volatiles in mediating foraging behaviour of aphid parasitoids, particularly with the parasitoid Aphidius ervi, its aphid host Acyrthosiphon pisum and the aphid food plant Vicia faba. These studies have shown that feeding by the aphid alters the composition of volatiles released by the plant and that these compounds act as synomones for the foraging parasitoid. Of particular interest is the species-specificity of the herbivore-induced synomones associated with different aphids feeding on V. faba. Aphids employ various pheromones that mediate behaviour, particularly mating and alarm responses. These pheromones play important roles in reproduction and defence against predation and parasitism. Many species of aphids reproduce sexually on their primary hosts during the autumn and the sexual females produce a pheromone that attracts males. The sex pheromones for a number of aphid species have been identified and laboratory and field studies have shown that synthetic material can act as a kairomone in attracting predators and parasitoids. The aphid alarm pheromone is released from the cornicles of aphids when they are attacked by predators or parasitoids. The activity of the main alarm pheromone component, (E)-beta-farnesene, is inhibited by the related sesquiterpene hydrocarbon beta-caryophyllene, which is reported to attract the lacewing Chrysoperla carnea. In addition, electrophysiological studies have shown that the seven-spot ladybird, Coccinella septempunctata, possesses specific olfactory receptors for (E)-beta-farnesene and beta-caryophyllene. Laboratory studies show these compounds to have behavioural activity with C. septempunctata, suggesting that they may be involved in prey location.

Animals↗
PubMed2001

Molecular systematics of aphids and their primary endosymbionts.

Aphids constitute a monophyletic group within the order Homoptera (i.e., superfamily Aphidoidea). The Aphidoidea originated in the Jurassic about 150 my ago from some aphidiform ancestor whose origin can be traced back to about 250 my ago. They exhibit a mutualistic association with intracellular bacteria (Buchnera sp.) related to Escherichia coli. Buchnera is usually considered the aphids' primary endosymbiont. The association is obligate for both partners. The 16S rDNA-based phylogeny of Buchnera from four aphid families showed complete concordance with the morphology-based phylogeny of their aphid hosts, which pointed to a single original infection in a common ancestor of aphids some 100-250 my ago followed by cospeciation of aphids and Buchnera. This study concentrated on the molecular phylogeny of both the aphids and their primary endosymbionts of five aphid families including for the first time representatives of the family Lachnidae. We discuss results based on two Buchnera genes (16S rDNA and the beta subunit of the F-ATPase complex) and on one host mitochondrial gene (the subunit 6 of the F-ATPase complex). Although our data do not allow definitive evolutionary relationships to be established among the different aphid families, some traditionally accepted groupings are put into question from both bacterial and insect data. In particular, the Lachnidae and the Aphididae, which from morphological data are considered recently evolved sister groups, do not seem to be as closely related as is usually accepted. Finally, we discuss our results in the light of the proposed parallel evolution of aphids and their endosymbionts.

Animals↗
PubMed2005

Effects of plant protease inhibitors, oryzacystatin I and soybean Bowman-Birk inhibitor, on the aphid Macrosiphum euphorbiae (Homoptera, Aphididae) and its parasitoid Aphelinus abdominalis (Hymenoptera, Aphelinidae).

Transgenic plants expressing protease inhibitors (PIs) have emerged in recent years as an alternative strategy for pest control. Beneficial insects such as parasitoids may therefore be exposed to these entomotoxins either via the host or by direct exposure to the plant itself. With the objective of assessing the effects of PIs towards aphid parasitoids, bioassays using soybean Bowman-Birk inhibitor (SbBBI) or oryzacystatin I (OCI) on artificial diet were performed on Macrosiphum euphorbiae-Aphelinus abdominalis system. OCI significantly reduced nymphal survival of the potato aphid M. euphorbiae and prevented aphids from reproducing. This negative effect was much more pronounced than with other aphid species. On the contrary, SbBBI did not affect nymphal viability but significantly altered adult demographic parameters. Enzymatic inhibition assays showed that digestive proteolytic activity of larvae and adults of Aphelinus abdominalis predominantly relies on serine proteases and especially on chymotrypsin-like activity. Immunoassays suggested that OCI bound to aphid proteins and accumulated in aphid tissues, whereas SbBBI remained unbound in the gut. Bioassays using M. euphorbiae reared on artificial diets supplemented with both OCI and SbBBI showed a fitness impairment of Aphelinus abdominalis that developed on intoxicated aphids. However, only SbBBI was detected in parasitoid larvae, while no PI could be detected in adult parasitoids that emerged from PI-intoxicated aphids. The potential impact of PI-expressing plants on aphid parasitoids and their combined efficiency for aphid control are discussed.

Animals↗
PubMed2005

Analysis of spatial patterns at a geographical scale over north-western Europe from point-referenced aphid count data.

The spatial analysis by distance indices (SADIE) technique was developed to evaluate the spatial pattern of point-referenced count data as well as the spatial association between two sets of data sharing the same point locations. This paper presents an analysis of spatial patterns in aphid count data and the association of these data with climate across north-west Europe. The paper tests the applicability of the technique to large geographical areas. Aggregation and cluster indices were calculated for the total annual abundance of the peach-potato aphid Myzus persicae (Sulzer) and for the annual mean rainfall and temperature at aphid monitoring sites. Association indices demonstrated the stability in time of aphid spatial structures and the correlation between aphid density and climate patterns. Groups of relatively large numbers of aphids, termed patches, and groups of relatively small numbers of aphids, termed gaps, were located and their mean size estimated. The aphid patterns were quite stable in time and the spatial patterns of temperature and rainfall were weakly associated with M. persicae annual abundance. Similarities were observed between the results of SADIE and those from the more widely used technique of spatial autocorrelation (SAC). However, the SADIE association index has the advantage of quantifying the possible associations between aphid data and the factors that determine population distribution. Thus, high temperature and low rainfall were identified as environmental factors that were positively associated with aphid abundance across north-west Europe.

Animals↗
PubMed2006

Soybean plant stage and population growth of soybean aphid.

The soybean aphid, Aphis glycines Matsumura, is a newly invasive species of aphid in North America. Previous studies disagree as to whether soybean, Glycine max (L.) Merr., plant stage has an impact on aphid intrinsic rate of increase. Therefore, the growth rate of soybean aphids on soybean plants of different stages was examined at two different scales in the field. A planting date experiment was used to measure the population growth of soybean aphids on plants of different stages. Clip-cages were used to measure life history characteristics of individual aphids on plants of different stages. No differences were found in the population growth or dynamics of soybean aphids in the planting date experiment. The life history characteristics of individual aphids also showed no significant difference when feeding on different growth stages of soybean plants. The impact of these findings on soybean aphid management is discussed and the possible reasons why the results differ from previous estimates of the aphid growth-plant stage relationship are considered.

Analysis of Variance↗
PubMed2006

Sweet problems: insect traits defining the limits to dietary sugar utilisation by the pea aphid, Acyrthosiphon pisum.

Plant phloem sap is an extreme diet for animals, partly because of its high and variable sugar content. The physiological and feeding traits of the pea aphid Acyrthosiphon pisum that define the upper and lower limits to the range of dietary sucrose concentrations utilised by this insect were determined principally using chemically defined diets containing 0.125-1.5 mol l(-1) sucrose. On the diets with 0.125 mol l(-1) and 1.5 mol l(-1) sucrose, the aphids died as larvae within 8 and 14 days of birth, respectively. On the other diets, 60-96% of aphids developed to adulthood, and the 0.5 mol l(-1) and 0.75 mol l(-1) diets supported the highest fecundity. The diet with 0.125 mol l(-1) sucrose was ingested at 36% of the rate of the 0.25 mol l(-1) sucrose diet, but >90% of ingested sucrose-carbon was assimilated on both diets. This suggests that the lower limit is dictated by the aphid feeding response, specifically, a requirement for a minimal concentration of sucrose for sustained feeding. The haemolymph osmotic pressure of aphids on diets with 0.125-1.5 mol l(-1) sucrose was up to 68% higher than on 0.125-1.0 mol l(-1) sucrose diets, but diet consumption and sucrose-carbon assimilation was not reduced on the very high sucrose diets relative to 1.0 mol l(-1) sucrose. This suggests that failure of the osmoregulatory capacity of the insects on high sucrose diets may define the upper limit to the range of dietary sucrose utilised by the aphids. The mean haemolymph osmotic pressure of aphids on plants with phloem sap containing 0.37-0.97 mol l(-1) sucrose was 1.61+/-0.063 MPa (mean +/- s.e.m.), not significantly different from that (1.47+/-0.059 MPa) on diets with 0.25-1.0 mol l(-1) sucrose. It is concluded that the osmoregulatory response of aphids to diets and plants are comparable, and, more generally, that the feeding and osmoregulatory capabilities of the aphids are compatible with the phloem sugar levels commonly encountered by aphids feeding on plants.

Animals↗
PubMed2001

Seasonal abundance of aphids (Homoptera: Aphididae) in wheat and their role as barley yellow dwarf virus vectors in the South Carolina coastal plain.

Aphid (Homoptera: Aphididae) seasonal flight activity and abundance in wheat, Triticum aestivum L., and the significance of aphid species as vectors of barley yellow dwarf virus were studied over a nine-year period in the South Carolina coastal plain. Four aphid species colonized wheat in a consistent seasonal pattern. Greenbug, Schizaphis graminum (Rondani), and rice root aphid, Rhopalosiphum rufiabdominalis (Sasaki), colonized seedlingwheat immediately after crop emergence, with apterous colonies usually peaking in December or January and then declining for the remainder of the season. These two aphid species are unlikely to cause economic loss on wheat in South Carolina, thus crop managers should not have to sample for the subterranean R. rufiabdominalis colonies. Bird cherry-oat aphid, Rhopalosiphum padi (L.), was the second most abundant species and the most economically important. Rhopalosiphum padi colonies usually remained below 10/row-meter until peaking in February or March. Barley yellow dwarf incidence and wheat yield loss were significantly correlated with R. padi peak abundance and aphid-day accumulation on the crop. Based on transmission assays, R. padi was primarily responsible for vectoring the predominant virus serotype (PAV) we found in wheat. Pest management efforts should focus on sampling for and suppressing this aphid species. December planting reduced aphid-day accumulation and barley yellow dwarf incidence, but delayed planting is not a practical management option. English grain aphid, Sitobion avenae (F.), was the last species to colonize wheat each season, and the most abundant. Sitobion avenae was responsible for late-season virus transmission and caused direct yield loss by feeding on heads and flag leaves during an outbreak year.

Animals↗
PubMed2003

Development of a sampling plan in winter wheat that estimates cereal aphid parasitism levels and predicts population suppression.

From 1998 to 2001, the relationship between the proportion of tillers with >0 mummified aphids (Ptm) and the proportion of cereal aphids parasitized (Pp) was estimated on 57 occasions in fields of hard red winter wheat located in central and western Oklahoma. Both original (57 fields) and validation data (34 fields; 2001-2002) revealed weak relationships between Ptm and Pp, however, when Ptm > 0.1, Pp always exceeded the recommended parasitism natural enemy threshold of 0.2. Based on the relationship between Ptm and Pp, upper (Ptm1) and lower (Ptm0) decision threshold proportions were set at 0.1 and 0.02, respectively. We monitored cereal aphid populations in 16-25 winter wheat fields over time, and based on the upper and lower decision threshold proportions (Ptm1 = 0.1, Ptm0 = 0.02), predicted whether aphid intensities (# per tiller) would increase above or be maintained below selected economic thresholds (3, 9, and 15 aphids per tiller). Results of this validation study revealed that aphid intensity exceeded an economic threshold in only one field when predicted to remain below Ptm > 0.1, but aphid intensity reached a maximum of only four aphids per tiller. The sampling plan developed during this study allowed us to quickly classify Ptm, and independent of initial cereal aphid intensities, very accurately predict suppression of populations by parasitoids. Sequential sampling stop lines based on sequential probability ratio tests for classifying proportions were calculated for Ptm1 = 0.1 and Ptm0 = 0.02. A minimum of 26 tiller samples are required to classify Ptm as above 0.1 or below 0.02. Based on the results of this study, we believe that simultaneous use of aphid and parasitoid sampling plans will be efficient and useful tools for consultants and producers in the southern plains and decrease the number of unnecessary insecticide applications.

Animals↗
PubMed2005

Variation for resistance to aphids (Homoptera: Aphididae) among tomato inbred backcross lines derived from wild Lycopersicon species.

Two tomato inbred backcross line (IBL) populations, derived from crosses between aphid-susceptible Lycopersicon esculentum Mill. 'Peto 95-43' X resistant wild L. pennellii Corr (D'arcy) accession LA716, and Peto 95-43 X resistant wild L. hirsutum f. glabratum Mull accession LA407, were evaluated in replicated field experiments for resistance to potato aphid, Macrosiphum euphorbiae (Thomas), and green peach aphid, Myzus persicae (Sulzer). Aphid infestation scores for each IBL and control (LA716, LA407, Peto 95-43, and susceptible 'Alta') plot were recorded weekly for 5 and 9 wk during the summers of 2000 and 2001, respectively. Aphid infestation scores from leaflets were used to calculate area under the infestation pressure curve (AUIPC), a measure of aphid infestation throughout the growing season, for each IBL and control. Score AUIPC was highly correlated with actual aphid count AUIPC, indicating that scores accurately reflected aphid infestation. Score AUIPC was also highly correlated across both years (2000 and 2001) and locations. Low score AUIPC was significantly correlated with larger plant size and sprawling, indeterminate plant growth habit. Seven IBLs, LA716, and LA407 were significantly more resistant to aphids (lower score AUIPC) than susceptible parent Peto 95-43 in both years. Two IBLs, 1034 and 1051, were not significantly different from resistant LA407 for score AUIPC in both years. The seven aphid-resistant IBLs identified here can be useful as donor parent material for resistance breeding efforts in cultivated tomato.

Animals↗