Showing papers on "Aphididae published in 1992"
TL;DR: The use of RAPD-PCR in species diagnostics, parasitoid detection, and population studies is discussed, and large amounts of genetic variation among individuals in each of these species is revealed.
Abstract: We have used a new technique to identify discrete genetic markers in aphids, a family in which biochemical and morphological genetic polymorphisms are rare. The new technique uses the polymerase chain reaction (PCR) to amplify random regions of aphid genomes (random amplified polymorphic DNA) and has been termed RAPD-PCR. We demonstrate the use of the technique in revealing genetic variation in four aphid species, the greenbug (Schizaphis graminum (Rondani)), the Russian wheat aphid (Diuraphis noxia (Mordvilko)), the pea aphid (Acyrthosiphon pisum (Harris)), and the brown ambrosia aphid (Uroleucon ambrosiae (Thomas)). In contrast with allozyme surveys, RAPD-PCR revealed large amounts of genetic variation among individuals in each of these species. Variation was detected among biotypes, populations, colour morphs and even individuals on a single plant. We also explored the utility of RAPD-PCR in the detection and identification within aphid bodies of two endoparasitic wasps, Diaeretiella rapae (McIntosh) and Lysiphlebus testaceipes (Cresson). The use of RAPD-PCR in species diagnostics, parasitoid detection, and population studies is discussed.
255 citations
TL;DR: It was established that the insect species is important in determining the sugar composition of homoptera honeydew and more than 20% of the sugar in Honeydew from the whitefly Bemisia tabaci was found to be oligomers larger than disaccharides.
Abstract: 1. 1. The sugar content of honeydew from three species of whitefly (Aleyrodidae) and four species of aphid (Aphididae) was determined by high performance liquid chromatography. 2. 2. More than 20% of the sugar in honeydew from the whitefly Bemisia tabaci was found to be oligomers larger than disaccharides. 3. 3. Honeydew from two species of the whitefly genus Trialeurodes contained more than 20% turanose. 4. 4. It was established that the insect species is important in determining the sugar composition of homoptera honeydew.
153 citations
TL;DR: Significant correlations between insect score and altitude of original collection were observed in six of thirteen species and Insect resistance was most common in the primitive and cultivated Tuberosa.
Abstract: The past 25 years, 1686 potato accessions, representing 100 species in the genus Solanum L., subgenus Potatoe, section Petota, were evaluated for field resistance to one or more of the following insect pests: green peach aphid, Myzus persicae (Sulzer); potato aphid, Macrosiphum euphorbiae (Thomas); Colorado potato beetle, Leptinotarsa decemlineata (Say); potato flea beetle, Epitrix cucumeris (Harris); and potato leafhopper, Empoasca fabae (Harris). Accessions highly resistant to green peach aphid were identified within 36 species, to potato aphid within 24 species, to Colorado potato beetle within 10 species, to potato flea beetle within 25 species, and to potato leafhopper within 39 species. Resistance levels were characteristic within Solanum species. Insect resistance appears to be a primitive trait in wild potatoes. Susceptibility was most common in the primitive and cultivated Tuberosa. Insect resistance was also characteristic of the most advanced species. The glycoalkaloid tomatine was associated with field resistance to Colorado potato beetle and potato leafhopper. Other glycoalkaloids were not associated with field resistance at the species level. Dense hairs were associated with resistance to green peach aphid, potato flea beetle, and potato leafhopper. Glandular trichomes were associated with field resistance to Colorado potato beetle, potato flea beetle, and potato leafhopper. Significant correlations between insect score and altitude of original collection were observed in six of thirteen species. Species from hot and arid areas were associated with resistance to Colorado potato beetle, potato flea beetle, and potato leafhopper. Species from cool or moist areas tended to be resistant to potato aphid.
145 citations
TL;DR: It is shown that the relative number of ants tending declined as aphid density increased, and ant tending did not reduce predator abundance at any aphid densities, suggesting that the cause of the density- dependent mutualism is probably a decline in the direct effect of ants on aphids resulting from a collapse in the Relative number of ant tending aphids at higher aphiddensity.
Abstract: Our objectives were to determine if the mutualistic effect of ant tending on aphid population growth varied with aphid density, and to consider possible mechanisms explaining such a context-dependent effect. We studied the interaction between Aphis varians and Formica cinerea on fireweed (Epilobium angustifolium) in the Rocky Mountains of Colorado. In 1988 we used two experiments to examine the interaction between ant tending and aphid density on the per capita growth of aphid populations at naturally occurring low aphid densities, and naturally occurring high aphid densities. In 1989, we conducted a similar experiment, but we manipulated aphid densities to include the full range from low to high. The results of these experiments were consistent: ant tending significantly improved the growth of small aphid populations, but the benefit from ant tending decreased or disappeared at higher aphid densities. We considered possible mech- anisms for the density-dependent mutualistic effect by examining the relationships among aphid density, the number of ants tending, and predator abundance. We show that the relative number of ants tending declined as aphid density increased, and ant tending did not reduce predator abundance at any aphid densities. Therefore, the cause of the density- dependent mutualism is probably a decline in the direct effect of ants on aphids resulting from a decline in the relative number of ants tending aphids at higher aphid densities. We discuss the implications of density-dependent mutualism for the dynamics and evolution
140 citations
TL;DR: In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphidistinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.
Abstract: . In Y-tube olfactometer tests, Aphidius ervi Hal., Trioxyssp., Praon sp., Aphelinus flavus (Nees), Lysiphlebus fabarum (Marsh.) and Aphidius rophalosiphi De Stef. responded positively to the odour of the plant on which aphid mummies containing them had been collected. The response to host plant odour was greater than the response to the odour of host aphids, their honeydew or a combination of the two. The strongest response was to a combination of plant and host aphids. A. rhopalosiphi showed a strong positive response to three wheat volatiles (cis-3-hexenyl acetate, cis-3-hexen-1-ol and trans-2-hexenal) as well as to indole-3-acetaldehyde (a breakdown product of tryptophan in aphid honeydew). In both olfactometer tests with odours and choice trials with whole plants, newly emerged A. rhopalosiphidistinguished and preferred the variety of wheat on which their development had occurred to other wheat varieties.
120 citations
TL;DR: Overall, percentage leaf chlorosis was the best criterion for detecting biotypic variation in D. noxia on cereals; however, the differing mechanisms of resistance expressed by these cereals makes it important to consider other plant and insect factors.
Abstract: Eight isolates of Russian wheat aphid, Diuraphis noxia (Mordvilko), from a worldwide collection were evaluated on resistant and susceptible barley, triticale, and wheat entries. Aphid population levels and damage ratings for leaf chlorosis, plant stunting, and leaf rolling were used to determine ifbiotypic variation occurs within this species. Overall, percentage leaf chlorosis was the best criterion for detecting biotypic variation in D. noxia on cereals; however, the differing mechanisms of resistance expressed by these cereals makes it important to consider other plant and insect factors. Each plant entry responded differently to the D. noxia isolates. Seven of the eight aphid isolates had unique virulence profiles across entries indicating a high degree ofbiotypic diversity. Moreover, isolates differed biotypically in countries where more than one isolate was collected (France and former USSR). An isolate from the former USSR was the most virulent, whereas an isolate from Turkey was the least virulent across all plant entries. Discriminant analysis showed that the U.S. isolate was most similar to a French isolate. The entries that performed best against the D. !loxia collection were the resistant triticales PI 386148 and PI 386156 and the resistant barley PI 366450. However, resistant plant germplasm will have geographical limits because of biotypic variation in D. noxia .
98 citations
TL;DR: It is concluded that a) yearly levels of R. padi infestation are mainly determined by the volume and intensity of emigrants; b) peak levels are sensitive to changes in predator density; and c) in some cases an outbreak of R . padi may be prevented by the action of spring active polyphagous predators alone.
Abstract: Predation by two carabid species, Bembidion lampros (Herbst.) and Pterostichus cupreus L., on the cereal aphid, Rhopalsiphum padi L., was described using a discrete event simulation model. The results were incorporated into an aphid population growth model. The aphid model was run using actual temperatures, R. padi emigration rates, field densities and distributions from three years with distinctly different aphid population levels. Predation was incorporated at different time periods. Predation during the arrival of emigrants and establishment of aphid populations had approximately the same effect as predation over the entire aphid period, whereas predation during the 20 days prior to peak had very little effect on resulting peak populations. We conclude that a) yearly levels of R. padi infestation are mainly determined by the volume and intensity of emigrants; b) peak levels are sensitive to changes in predator density; and c) in some cases an outbreak of R. padi may be prevented by the action of spring active polyphagous predators alone.
86 citations
TL;DR: The results showed that the threshold for significant yield loss under these environmental conditions was at the 10 aphid per plant level for the bird cherry oat aphid and the Russian wheat aphid, and 15 apbids per plant for greenbug.
Abstract: In most autumns on the Northern Plains of the USA, low population densities of several species of cereal aphids feed on seedling winter wheat, Triticum aestivum L., for a month or more. The objective of this research was to determine the influence of that feeding on the growth and yield of ‘Rose’ winter wheat. Experiments were conducted by confining non-viruliferous (barley yellow dwarf virus) greenbug, Schizaphis graminum (Rondani), at precisely maintained population densities of 2, 4, 6, 8, 10, and 15 aphids per plant, bird cherry oat aphids, Rhopalosiphum padi (L.), at densities of 10 or 15 aphids per plant, or Russian wheat aphids, Diuraphis noxia (Mordvilko), at 5, 10, 15, and 20 aphids per plant on seedling plants for 30 d in an environmental chamber at 10°C (to simulate mean October temperature in the field), 12 h day/night. The results showed that the threshold for significant yield loss under these environmental conditions was at the 10 aphids per plant level for the bird cherry oat aphid and the Russian wheat aphid, and 15 apbids per plant for greenbug. Yield losses caused by any of the aphid species were in the range of 35 to 40% at 15 aphids per plant. Although the visible injury to plants caused by the feeding of the greenbug and the Russian wheat aphid was striking, the bird cherry oat aphid was as damaging to yield as the other two species in this study.
86 citations
TL;DR: Honeydew contamination on egg laying by the syrphids Episyrphus balteatus and Platycheirus albimanus on ears of wheat was investigated, and females landed more frequently on ears contaminated with Honeydew than on clean ears, suggesting a response to honeydew volatiles.
Abstract: The influence of honeydew contamination on egg laying by the syrphids Episyrphus balteatus (Deg.) and Platycheirus albimanus (F.) on ears of wheat was investigated in a large laboratory flight cage. Artificially-applied honeydew elicited oviposition by E. balteatus but not by Platycheirus albimanus. Episyrphus balteatus females landed more frequently on ears contaminated with honeydew than on clean ears, suggesting a response to honeydew volatiles. Honeydew from the rose-grain aphid Metopolophium dirhodum and from the pea aphid Acyrthosiphon pisum stimulated E. balteatus to lay eggs, whereas honeydew from the nettle aphid Microlophium carnosum did not. The number of eggs laid by E. balteatus increased with increasing honeydew concentration. At low honeydew concentrations the presence of aphids increased oviposition by E. balteatus, but aphid presence had little effect on the number of eggs laid at high honeydew concentrations.
85 citations
TL;DR: There were highly significant correlations between aphid ‘preference’ and DIMBOA levels in the seedlings, and the value of these results in work leading to the production of aphid-resistant cultivars is discussed.
Abstract: Summary
In a screen of seedlings of a worldwide range of 47 cultivars of Triticum (mainly T. aestivum) the concentration of the hydroxamic acid DIMBOA ranged between 1 and 8 mmol/kg fresh wt. In a bioassay in which alatae of the aphid Sitobion avenae were released among replicated test seedlings, there were highly significant correlations between aphid ‘preference’ and DIMBOA levels in the seedlings. The value of these results in work leading to the production of aphid-resistant cultivars is discussed.
84 citations
TL;DR: The cessation of growth of wheat during infestation by the Russian wheat aphid and ability of the host to recover rapidly when the aphid was removed indicate that the duration of infestation, rather than the level of infesting, may be more important to the host.
Abstract: The effect of feeding by the Russian wheat aphid, Diuraphis noxia (Mordvilko), on growth of seedling ‘TAM W-lOl’ winter wheat ( Triticum aestivum L.) was investigated. A primary response of the wheat plant to aphid feeding involves water imbalances expressed as a loss of turgor and reduced growth. Russian wheat aphids caused substantial reductions in biomass of all plant components measured. When aphids were removed, absolute growth rates quickly recovered as relative growth rates increased. Compared with undamaged controls, recovering plants were more efficient in terms of carbon assimilation, which resulted in higher relative growth rates and compensated for lowered leaf area ratios. Reduction in leaf area ratios results from decreases in specific leaf areas (i.e., a combination of leaf stunting and the inhibition of new-leaf unfolding). As plants recovered, stem weight ratios were substantially reduced, indicating that carbon partitioning to the stem was decreased to compensate for leaf and root growth. The cessation of growth of wheat during infestation by the Russian wheat aphid and ability of the host to recover rapidly when the aphid was removed indicate that the duration of infestation, rather than the level of infestation, may be more important to the host.
TL;DR: Results from isoelectric polyacrylamide focusing gel techniques showed differences in carboxylesterases, both in differences in banding patterns and in expression of comigrating bands, compared with susceptible aphids.
Abstract: Laboratory assays were done to quantify proportions of phenotypes in laboratory colonies resistant to several classes of insecticides in the cotton aphid, Aphis gossypii Glover. Resistance to a carbamate (aldicarb), an organochlorine (endosulfan), an organophosphate (chlorpyrifos), and a pyrethroid (bifenthrin) was documented. Significant declines in numbers of individuals resistant to bifenthrin and endosulfan but not for chlorpyrifos occurred during a 5-mo interval after the first bioassays. Resistance ratios between clonal susceptible and resistant cotton aphid colonies for chlorpyrifos indicated a significant 4-fold difference in LC50 estimates for the two colonies. Spectrophotometric analyses indicated Significantly higher carboxylesterase activity in resistant aphids compared with susceptible aphids. Results from isoelectric polyacrylamide focusing gel techniques also showed differences in carboxylesterases, both in differences in banding patterns and in expression of comigrating bands.
TL;DR: Results indicate that any natural selection imposed by aphids and spittlebugs on goldenrod will depend on the presence or absence of branch‐causing herbivores, and selection for plant resistance may depend as much on the assemblage of insect species present as on the identity of each individual species.
Abstract: Although there is considerable evidence indicating that herbivory is detrimental to plant fitness, some recent studies of the evolution of plant resistance have concluded that insects do not impose selection on their host plants. A previously untested assumption that underlies most studies of the evolution of plant resistance is that insect distribution patterns are controlled directly by the effects of plant genotype on insect preference and performance. The experiments described here explicitly tested this assumption using the specialist herbivore Uroleucon tissoti (Homoptera: Aphididae) and its host plant Solidago altissima (Asteraceae). Measures of aphid preference and performance were used to predict aphid distribution patterns, and then the predicted distribution patterns were compared with the natural distribution pattern. Although goldenrod genotype had a strong effect on aphid distribution, aphid distribution was not controlled directly by the effect of goldenrod genotype on aphid preference and performance. Instead, a second experiment demonstrated that aphid and spittlebug (Philaenus spumarius and Lepyronia quadrangularis Homoptera: Cercopidae) distribution is controlled largely by genetic variation for resistance to a suite of "branch-causing" herbivores. These herbivores induce branching and aphids and spittlebugs are more abundant on branched plants than unbranched plants. These results indicate that any natural selection imposed by aphids and spittlebugs on goldenrod will depend on the presence or absence of branch-causing herbivores. Thus, selection for plant resistance may depend as much on the assemblage of insect species present as on the identity of each individual species.
TL;DR: Developmental rate, total numbers of aphids, and numbers of alatae and apterae decreased as the time between virus inoculation and aphid colonization increased, indicating that properties unique to the early stages of viral infection somehow stimulated wing formation.
Abstract: Zucchini yellow mosaic virus (ZYMV) and Aphis gossypii Glover are two components of a recently identified plant-parasite system that provides an excellent opportunity to study interrelations between a virus and a vector that share the same host, but have no direct physiological interaction. In a field experiment we documented numbers of alate and apterous A. gossypii on healthy Cucurbita pepo and on plants inoculated with virus 0, 7, 14, and 21 days before aphid infestation. When plants were inoculated and infested simultaneously, more than twice as many alatae were produced after 20 days of colony growth than on any other treatment. This indicates that properties unique to the early stages of viral infection somehow stimulated wing formation. Because it is spread by the activities of alatae, virus dispersal would be greater as a result of these properties. Developmental rate, total numbers of aphids, and numbers of alatae and apterae decreased as the time between virus inoculation and aphid colonization increased.
TL;DR: Aphid transmission of watermelon mosaic virus 2 and zucchini yellow mosaic virus was studied in the laboratory and field to evaluate species of probable importance in the epidemiology of each virus.
Abstract: Aphid transmission of watermelon mosaic virus 2 (WMV 2) and zucchini yellow mosaic virus (ZYMV) was studied in the laboratory and field to evaluate species of probable importance in the epidemiology of each virus. Relative transmission efficiencies among species were compared using alates obtained from laboratory-maintained colonies as well as from natural populations collected with an aerial net. In laboratory studies, Myzus persicae, Aphis gossypii, and Acyrthosiphon pisum transmitted WMV 2 with 18, 16, and 16% efficiencies, respectively (...)
TL;DR: The secondary metabolise DIBOA was found in seedlings of wild Hordeum species, but not of cultivated barley, and correlated negatively with performance of the aphid Rhopalosiphum padi on seedlings.
TL;DR: Wheat cultivars previously identified as resistant to the Russian wheat aphid, Diumphis noxia (Mordvilko), in South Africa and in Idaho were evaluated in the greenhouse to determine the categories of resistance in operation, and none of the test entries reduced overall fecundity during the total reproductive period of the experiment.
Abstract: Wheat cultivars previously identified as resistant to the Russian wheat aphid, Diumphis noxia (Mordvilko), in South Africa and in Idaho were evaluated in the greenhouse to determine the categories of resistance in operation. All test entries tested possessed a significant level of tolerance to D. noxia feeding, based on percentage reductions in plant height. Twenty-one days after infestation, D. noxia maintained on the three plant introductions from South Africa displayed reduced reproductive rates indicative of low-level antibiosis. However, none of the test entries reduced overall fecundity during the total (84-d) reproductive period of the experiment. None of the test entries displayed antixenosis.
TL;DR: The electrophoretic mobility of the enzyme glutamate oxaloacetate transaminase on cellulose acetate plates was compared among sibling species of the Myzus persicae (Sulzer) group and can provide a means of distinguishing most individual specimens, including trapped alatae, of M. nicotianae.
Abstract: The electrophoretic mobility of the enzyme glutamate oxaloacetate transaminase (GOT) on cellulose acetate plates was compared among sibling species of the Myzus persicae (Sulzer) group ( M. persicae, M. nicotianae Blackman, M. antirrhinii (Macchiati)). M. persicae itself is monomorphic for GOT-1 (genotype ff ), whereas European populations of M. nicotianae are polymorphic for this enzyme, with two forms of slightly different mobility (alleles s, f ). In the samples of M. nicotianae examined, M. persicae-like ff genotypes were rare and heterozygotes ( sf ) were in large excess, even in samples from Greece where M. nicotianae has a regular holocycle (i.e., annual sexual reproduction). In North America, where M. nicotianae is probably entirely anholocyclic, samples of both red and green colour morphs of this species were found to be heterozygous for GOT-1. The enzyme difference can thus provide a means of distinguishing most individual specimens, including trapped alatae, of M. persicae and M. nicotianae . The anholocyclic taxon M. antirrhinii appears to be a fixed heterozygote for GOT-1 and thus resembles most M. nicotianae , but can be distinguished electrophoretically from both M. persicae and M. nicotianae by its distinctive pattern of esterases.
TL;DR: Experiments indicated that for offspring of apterous Rhopalosiphum padi (L.) (Hemiptera: Aphididae), photoperiod and crowding were the most important determinants of wing development whereas crowding and plant quality were more significant for the next generation.
Abstract: Experiments indicated that for offspring of apterous Rhopalosiphum padi (L.) (Hemiptera: Aphididae), photoperiod and crowding were the most important determinants of wing development whereas crowding and plant quality were more significant for the next generation. Plant quality became increasingly important as temperature increased while crowding became less so. More alates developed on plants previously infested with aphids, indicating that aphid feeding reduced plant quality. High temperature suppressed alatoid production, but could be overcome by crowding. Temperature appeared to influence wing development indirectly rather than directly by acting on the aphid through the plant. Adult weight and potential fecundity were also reduced for aphids which fed on previously infested plants.
TL;DR: Greenhouse experiments were conducted to determine effects of spirea aphid, Aphis spiraecola Patch, feeding and nitrogen fertilization on net photosynthesis (Pn), total chlorophyll content (Tchl), and greenness (Gn) of apple leaves.
Abstract: Greenhouse experiments were conducted to determine effects of spirea aphid, Aphis spiraecola Patch, feeding and nitrogen fertilization on net photosynthesis (Pn), total chlorophyll content (Tchl), and greenness (Gn) of apple leaves. One-year-old apple trees grown in pots were infested with spirea aphid. Spirea aphid reduced Pn at various levels of infestation, and the reduction persisted after aphid removal. Pn rates decreased with increasing accumulation of sooty mold. Gn and Tchl were reduced by spirea aphid feeding. Chlorophyll concentrations obtained by methanol extraction technique were linearly related to Gn values obtained with a SP AD leaf greenness meter for both infested and control leaves and for sooty mold and control leaves. Four nitrogen (N) rates were applied to trees in the second year. Pn and Gn were correlated with aphid-day accumulations at each N rate. Pn increased linearly with increasing Gn. Pn and Gn were positively related to N rates. Decrease in Tchl helps to explain the reduction in Pn. Pn may be related to Tchl, but leaf age, nutritional status, and other parameters may influence the results. Callose accumulation at the phloem sieve plates in response to aphid feeding was observed but to a lesser degree than for other aphids reported on apple and pecan leaves.
TL;DR: The hypothesis that variation in the quality of the host plant mediated the mutualistic interaction between a phloem-feeding homopteran (Aphis varians) and the ant (Formica cinerea) tending it was investigated and population growth of A. varians was positively correlated with plant height.
Abstract: We investigated the hypothesis that variation in the quality of the host plant (Epilobium angustifolium) mediated the mutualistic interaction between a phloem-feeding homopteran (Aphis varians) and the ant (Formica cinerea) tending it. First, we used a bioassay to define the quality of Epilobium for A. varians. We established cohorts of first-instar A. varians on fireweed shoots of different heights. Development time, size at maturity, and the number and size of embryos per adult were significantly correlated with plant height. Therefore, plant height provided an indirect measure of plant quality. Second, we experimentally tested the effects of plant height and tending by ants on the growth of aphid populations. We conducted this experiment in the absence of natural enemies of A. varians in order to examine the direct link between plants, aphids and ants, rather than the indirect links involving the natural enemies of aphids. As expected, population growth of A. varians on individual Epilobium ramets was positively correlated with plant height. However, in the absence of natural enemies, the effect of ants on the growth of aphid populations did not vary
TL;DR: The linyphiid spider E. atra (♀) was the most intrinsically susceptible species and had the narrowest tolerance distribution of the predators tested, whereas the small carabid beetle D. atricapillus was the least intrinsically susceptible predator species.
Abstract: The intrinsic toxicity of deltamethrin to the grain aphid Sitobion avenae (F.) (Hemiptera: Aphididae) and a range of its important natural enemies was determined by laboratory topical bioassay. The natural enemies included polyphagous predators such as Pterostichus melanarius (Illiger), Harpalus rufipes (Degeer), Nebria brevicollis (F.), Agonum dorsale (Pont.), Demetrias atricapillus (L.), Trechus quadristriatus (Schrank), Bembidion obtusum (Serville), and B. lampros (Herbst.) (Coleoptera: Carabidae), Tachyporus hypnorum (F.) (Coleoptera: Staphylinidae) and Erigone atra (Blackwall) (Araneae: Linyphiidae), as well as the aphid-specific ladybird Coccinella septempunctata (L.) (Coleoptera: Coccinellidae). Dose–response relationships were compared between species by probit analysis and maximum likelihood procedures to determine trends of susceptibility, measured in terms of ng a.i. arthropod−1 and μg a.i. g−1 body weight. The range of LD50 values varied between 0.8 and 232 ng arthropod−1 and 0.76 and 66.17 μg g−1 body weight for the species tested. The linyphiid spider E. atra (♀) was the most intrinsically susceptible species and had the narrowest tolerance distribution of the predators tested, whereas the small carabid beetle D. atricapillus was the least intrinsically susceptible predator species. There were significant differences in susceptibility between species of different orders, i.e. the Araneae, Hemiptera and Coleoptera. Differences within the Coleoptera were closely related to body weight, with the exception of the carabid beetle D. atricapillus, which seemed to be tolerant to deltamethrin. Knockdown time studies indicated that D. atricapillus had a higher survival rate after being knocked down than other species of predator. Aphid susceptibility per unit body weight was not significantly different from that of the predators. The aphid did, however, demonstrate a broader tolerance distribution than most of the predators, which may be related to its herbivorous nature. The use of laboratory susceptibility data to determine selectivity and to predict pesticide hazard is discussed.
TL;DR: In laboratory bioassays, whole-body homogenates and fresh cornicle wax of Rhopalosiphum padi(L.) elicited antennal examination and attack behavior in naive females of the polyphagous aphidiid parasitoid, Lysiphlebus testaceipes (Cresson).
Abstract: In laboratory bioassays, whole-body homogenates and fresh cornicle wax of Rhopalosiphum padi(L.) (the bird-cherry oat aphid) elicited antennal examination and attack behavior in naive females of the polyphagous aphidiid parasitoid, Lysiphlebus testaceipes (Cresson). No such response was elicited by either homogenates or cornicle wax of Aphis nerii(Boyer de Fonscolombe) (another known host of the parasitoid) or by preparations of the aphid alarm pheromone, (E)-β-farnesene. The response to R. padiproducts was independent of rearing host and appears to be innate. Application of R. padicornicle wax to the dorsum of a nonhost aphid [Acythosiphum pisum(Harris)] increased the frequency with which this species was attacked by L. testaceipes.There was a tendency for the kairomonal activity of the cornicle secretion to decline as the wax dried, although parasitoid attack behavior was still elicited by wax which had been allowed to dry for up to 30 min before testing.
TL;DR: Taylor’s power law was used to model relationships between Mean densities (per tiller) and variances for four cereal aphids-Diuraphis noxia (Mordvilko), Metopolophium Dirhoclum (Walker), Sitobion avenae (F.), and Schizaphis graminum (Rondani)- infesting spring wheat in southwestern Idaho.
Abstract: Taylor’s power law was used to model relationships between Mean densities (per tiller) and variances for four cereal aphids-Diuraphis noxia (Mordvilko), Metopolophium Dirhoclum (Walker), Sitobion avenae (F.), and Schizaphis graminum (Rondani)- infesting spring wheat in southwestern Idaho. Model slopes were > 1.0 for all species, which indicated that the aphid species all showed aggregated spatial patterns. The spatial pattern of D. noxia was significantly more dumped than those of the other three species. No differences among years were found in the aphid species’ degree of aggregation. Taylor’s power law parameters were used to generate numerical (complete count) sample size curves for each aphid species. Parameters from the regression of In(mean density) on In[-In(proportion of wheat tillers with no aphids)] were used to develop a functional relationship between mean density and proportion of empty sample units, and binomial (presence-absence) sample size curves for each aphid species.
TL;DR: For the Russian wheat aphid, the supercooling point and the ability to survive cold temperatures are notclosely related; although extremely cold temperatures result in extinction of exposed populations, most winter mortality occurs at temperatures above the super cooling point.
Abstract: Russian wheat aphid, Diuraphis noxiu (Mordvilko), is a new pest of winter wheat, Triticum uestivum L., in western Canada. Studies were conducted to compare the cold hardiness of Russian wheat aphid, as expressed by the supercooling point, with overwintering mortality in the field, Mean supercooling points ranged from -26.8°C for first ins tars to -24.9°C for adults. These differences were not reflected in the winter survival of each stage in the field. Generally, aphid numbers declined steadily at surface temperatures between 0 and -10°C. In 1988-1989, temperatures at 1 cm above the soil surface dropped lower than -25°C for 4 d on one occasion, resulting in 100% mortality of Russian wheat aphid. In 1989-1990, when temperatures did not drop below -25°C, a low number of Russian wheat aphids were able to overwinter successfully. For the Russian wheat aphid, the supercooling point and the ability to survive cold temperatures are notclosely related. Although extremely cold temperatures result in extinction of exposed populations, most winter mortality occurs at temperatures above the supercooling point.
TL;DR: This research was designed to determine the economic injury level for Russian wheat aphid, Diuraphis noxia (Mordvilko), on dryland winter wheat, and the best sampling unit was tillers, based on high R2, low root mean square error, and ease of sampling.
Abstract: This research was designed to determine the economic injury level for Russian wheat aphid, Diuraphis noxia (Mordvilko), on dryland winter wheat, Triticum Aestivum L. Two sample units were evaluated: whole plants and individual tillers. Russian wheat aphid densities were low in the fall but increased rapidly from late February to May. The percentage of the plants infested or damaged by Russian wheat aphid feeding exceeded 90% by March 1987. The same proportion of infested or damaged tillers was not recorded in 1988until late April. There were ≤ 80% and 60%yield reductions from Russian wheat aphid feeding in 1987 and 1988, respectively. Although 27% of the plants were damaged in the fall, there were too few aphids (≤ 2 aphids per plant, 32 aphid-days, by December) to cause a yield loss. Regression analysis was used to compare several independent variables (aphid densities, aphid-days, percentage infested, percentage damaged, and percentage infested + damaged) with yield, number of seeds per spike, tiller length, number of tillers, and plant dry weight for plant and tiller samples. Yield was the only dependent variable that correlated with the independent variables. The best sampling unit was tillers, based on a high R2, low root mean square error, and ease of sampling. There were 0.46 and 0.48% yield losses for each 1% increase in damaged and infested tillers, respectively.
TL;DR: The results show that the mitochondrial DNA methodology is a very promising tool for analyzing aphid population structure and for studying its relationships with the epidemiology of aphid-transmitted disease agents such as barley yellow dwarf virus.
Abstract: In total, 35 clones of the bird cherry-oat aphid, Rhopalosiphum padi (L.) established from samples collected in four distant localities of Spain during fall 1989 and spring 1990 were examined for mitochondrial DNA variation using 20 restriction endonucleases. Individual parthenogenetic adults were used to establish clonal lines on wheat (‘Talento’) seedlings. Restriction site polymorphism was detected only with endonuclease Rsa I, but no statistical treatment of data could be done until more polymorphic endonucleases are found. Length variation of the mitochondrial DNA molecule, however, was extensive among R. padi clones. Distribution among populations of this size polymorphism was used to estimate total and within-population diversity indexes. The population structure index was estimated to be 0.28. This value was compared with the corresponding diversity index obtained by allozyme analysis for the less migratory (more structured) aphid Macrosiphum rosae (L.). Our results show that the mitochondrial DNA methodology is a very promising tool for analyzing aphid population structure and for studying its relationships with the epidemiology of aphid-transmitted disease agents such as barley yellow dwarf virus.
TL;DR: Population growth rates and within-plant distributions of Aphis gossypii Glover and Myzus persicae (Sulzer) were studied on potted chrysanthemums, Dendranthema Grandiflora Tzvelev and findings are discussed with respect to intra- and interspecific competition, host plant suitability, and pest management.
Abstract: Population growth rates and within-plant distributions of Aphis gossypii Glover and Myzus persicae (Sulzer) were studied on potted chrysanthemums, Dendranthema Grandiflora Tzvelev. Three groups of plants were studied: plants infested with A. gossypii , plants infested with M. persicae , and plants infested with both species. Both species exhibited similar population growth rates ( rm = 0.16-0.17) for the first 16 dafter plants were inoculated with 20 aphids per plant (40 aphids per plant in the mixed species treatment). A. gossypii continued to increase at this same rate until termination of the experiment (day 28); however, after day 16, M. persicae reached the carrying capacity of the chrysanthemum plants (≈200 aphids per plant on young plants with an average of 19 leaves per plant) and began to decline in both the single and mixed species treatments. This decline was probably due, at least in part, to emigration of M. persicae . In both the single and mixed species populations, A. gossypii individuals remained on the leaves where they were initially placed or moved to lower leaves on the plant, whereas M. persicae remained on the upper leaves where they were initially placed and moved upward as the plants grew. These findings are discussed with respect to intra- and interspecific competition, host plant suitability, and pest management of these aphids on chrysanthemums.
TL;DR: Higher DIMBOA levels in the plant appear to reduce aphid feeding rates (and rates of DIM BOA ingestion), decreasing aphid survival and minimizing the effect of the toxin on the predator.
Abstract: DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), a secondary metabolite found in cereal extracts, confers resistance in wheat to aphids. Its effect on beneficial organisms was tested on larvae of the aphid predatorEriopis connexa Germar. Larvae were fed until pupation on artificial diets to which different concentrations of DIMBOA (2–200μg/g diet) were added, as well as on aphids that had been feeding on wheat seedlings with different DIMBOA levels (140–440 μg/g fresh tissue). In diets, the effect of DIMBOA was greatest on survival of third-instar larvae and on the duration of the second and fourth instars. When aphids were provided as food, those that had fed on a wheat cultivar with an intermediate DIMBOA level led to a significantly longer larval duration in the predator than did those that fed on either low or high DIMBOA cultivars. Shortest predator development times were obtained with aphid prey that had fed on high DIMBOA seedlings. Higher DIMBOA levels in the plant appear to reduce aphid feeding rates (and rates of DIMBOA ingestion), decreasing aphid survival and minimizing the effect of the toxin on the predator.
TL;DR: The results show that maize spacing and size are vital factors influencing A. fabae infestation on beans in bean/maize intercrops.