Showing papers on "Aphididae published in 1984"

The relative efficiency of some aphid species as vectors of potato virus Yo (PVYo)

Abstract: The relative efficiency of 7 aphid species as vectors of potato virus Yo (PVYo) was investigated. Winged aphids of one species were released in a net cage containing PVYo-infected potato plants as a virus source and healthy young potato plants as test plants. After 35 hours the glasshouse chamber was fumigated and the young plants tested for PVYo by ELISA at 10-days intervals.Myzus persicae andAcyrthosiphon pisum were the most effective vectors, infecting 26 and 25% of the test plants, respectively.Aphis fabae, Aphis nasturtii andRhopalosiphum padi infected only 1–7% test plants.Sitobion avenae andBrevicoryne brassicae did not transmit PVYo. Relative ‘efficiency factors’ are suggested from these and other results.

I. Age-specific energetics models - pea aphid Acyrthosiphon pisum (Homoptera: Aphididae) as an example.

Abstract: A simple age-specific energetics (calories or biomass) model for the growth and development, reproduction, respiration, ageing, and intrinsic survivorship as a function of temperature and per capita energy availability for pea aphid (Acyrthosiphon pisum (Harris)) is reported. The ratio of energy supply–demand is used to scale all of the rates in the model. The maximum demand for energy based upon current state values is used to drive the Frazer–Gilbert functional response model (i.e. food acquisition), which is a component of the metabolic pool model used to assimilate energy to growth, reproduction, respiration, and egestion. The extensive data sets on pea aphid energetics published by Randolph et al. (1975) were used to develop the model. As the model estimates reproduction (Mx) and survivorship (Lx) values, extensive published age-specific life-data sets on pea aphids are used to test it. The results suggest:(1) the lower thermal threshold for development is raised and the upper threshold is lowered as food resources are decreased(2) the temperature-dependent rate of development is slowed with decreasing energy resources(3) the size of individuals and reproduction become smaller as temperature approaches the upper and lower thermal thresholds.A simple model for multitrophic level interactions incorporating the acquisition and assimilation functions is presented.

Demographic Statistics for the Pea Aphid (Homoptera: Aphididae) in Wisconsin and a Comparison with Other Populations

Abstract: The relationship between temperature and nymphal developmental rate for Wisconsin populations of the pea aphid, Acyrthosiphon pisum (Harris), was studied in the laboratory and the field. Laboratory studies provided estimates of both lower (2.73°C) and upper (26.02°C) thresholds for development. Age-specific life table parameters were also estimated for two apterous cohorts and one alate cohort exposed to field temperatures. Population growth statistics varied with rearing temperature but, for apterous cohorts, converged when a physiological time scale (“instar periods”) was used. Although stable stage (instar) distributions for the apterous cohorts varied on a physiological time scale, ca. 50% of the individuals in each cohort were first instars, whereas adults accounted for only 7.6 to 13.1% of the total population. Developmental thresholds and population statistics for A. pisum in Wisconsin were similar to an Ontario (Canada) population established in a climate similar to Wisconsin's, but were dissimilar to a British Columbia population established in a warm, arid region. The relevance of these results to the study of A. pisum population dynamics in the field is discussed.

Reservoirs for Aphidius ervi Haliday (Hymenoptera:Aphidiidae), a polyphagous parasitoid of cereal aphids (Hemiptera:Aphididae)

Abstract: Aphidius ervi Hal. parasitised natural populations of Acyrthosiphon pisum (Harris), Sitobion avenae (F.) and Microlophium carnosum (Buckt.) in Britain but parasitised few examples of S. avenae placed on trap plants in winter wheat, nettle-grass edge areas or lucerne-wheat strip crops. In laboratory experiments, Aphidius ervi reared from Acyrthosiphon pisum did not parasitise M. carnosum, and significantly fewer mummies were formed on S. avenae than on A. pisum. After rearing Aphidius ervi for 4–5 generations on S. avenae, similar numbers of mummies were formed on both hosts. The switch of hosts from Acyrthosiphon pisum to S. avenae was associated with the loss of certain parasitoid esterase enzyme bands revealed following electrophoretic separation of parasitoid proteins. Slow adaptation to new aphid hosts by polyphagous parasitoids such as Aphidius ervi may reduce the usefulness of reservoirs as a source of beneficial species.

Decision trees to assess the risk of cereal aphid (Hemiptera: Aphididae) outbreaks in summer in England

Abstract: Recent studies on the ecology of two cereal aphid species, Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.), are reviewed. The most important factors affecting their abundance were used to construct decision trees to assess the risk of outbreaks of these species in the summer in England. These factors for S. avenae were crop sowing date, the size of the autumn migration, the severity of the winter, the size of the spring migration and the incidence of natural enemies in spring and early summer. For M. dirhodum, only the last two factors were considered as it does not occur on cereals until the spring in England. These decision trees were successfully tested using field data from 1983, when no outbreaks of either species occurred due to the effects of natural enemies.

Natural Enemies and Their Effects on Apple Aphid, Aphis pomi DeGeer (Homoptera: Aphididae), Colonies on Young Apple Trees in Central Washington

Abstract: Thirty-nine predators and two parasitoids were found attacking apple aphid, Aphis pomi DeGeer, in north-central Washington. Exclusion-cage experiments were conducted to determine the effectiveness of natural enemies. Early-spring control depended on aphidiid parasitoids which killed but failed to complete development in A. pomi . Poor synchrony between A. pomi and its major predators in most years resulted in a month-long “predator gap” allowing rapid aphid colony growth in June. Ground faunal predators including Forficulidae, Nabidae, Lygaeidae, and Phalangiidae helped to slow aphid population growth during this period. Terminal bud set usually occurred in July on mature trees, greatly reducing aphid populations, but young trees sometimes continued growing, allowing buildup of large aphid populations. These were preyed upon by large numbers of Coccinellidae, Chrysopidae, Miridae, Syrphidae, and Chamaemyiidae, which provided control of varying effectiveness. Important sources of effective apple aphid predators were peach orchards, riparian trees and shrubs, some urban ornamental plants, and weeds. Sage-chaparral and pear orchard habitats produced primarily ineffective apple aphid predators. Field feeding trials in single-leaf cages were used to estimate feeding rates of most of the predators.

Transmission of Citrus Tristeza Virus by Aphids (Homoptera, Aphididae) in Spain

Abstract: Transmission of citrus tristeza virus (CTV) by aphids was tried with two Spanish CTV isolates, T-300 and T-308. Isolate T-300 causes mild symptoms on Mexican Lime and is very widespread, while T-308 is very severe on Mexican Lime and has a limited distribution. Transmission of the two isolates was tried using 200 aphidstplant of the most important aphid species found on citrus in Spain: Aphis citricola, Toxoptera aurantii, Myxus persicae, Aphis gossypii, Aphis fabae and Aphis craccivora. Two other aphid species, Aphis nerii and Hyalopterus pruni were tested, only with the T-300 isolate. Isolate T-308 was transmitted only by A. gossypii with an efficiency of 28%, whereas the isolate T-300 was transmitted by A. gossypii (78%), by A. citricola (6%) and by T. aurantii (6%). Tristeza was first detected in Spain a t the Ribera Alta area in Valencia in 1957. Subsequently it spread to various citrus growing areas, and thus far, about 8 million trees have been killed by the disease and many thousands more are in different stages of decline. At present, the following seven insect species from the Aphididae (Homoptera), have been established as CTV vectors in different counties : Toxoptera citricidus (Kirk.) (9 ) , Aphis gossypii Glover (6) , Aphis citricola Van der Goot (11) , Toxoptera aurantii (Boyer de Fonsicolombe) (12), Myxus (Nectarosiphon) persicne (Lube.) (16), and Aphis craccivora Koch and Uroleucon (Uromelan) jaceae (Linnaeus) (15). Differences of transmission efficiency have been observed among the various aphid species and virus isolates used by different authors (1, 2, 4, 5, 12, 13, 14,15,16). In previous work, the composition of the aphid fauna feeding on citrus was studied in areas where natural spread of CTV occurred (8) . The following species were found: A. citricola, T. aurantii, M. persicae, A. gossypii, Aphis fabae Scopoli, A. craccivora, Macrosiphum euphorbiae (Thomas) and Brachycaudus helichrysi (Kalteabach) . Nevertheless, the species responsible for CTV spread in Spain remained undetermined with transmission experiments with this objective were begun. The relative frequency of the different species was evaluated by means of yellow water traps (unpublished results) and since M. euphorbiae and B. helichrysi appeared in negligible quantities they were not included in this study. However, two other species were included: Aphis nerii Boyer de Fonscolombe and Hyaloptems pruni (Geoffroy) . Neither have been found on citrus in Spain, and moreover the second one has never been reported on citrus. However, CTV could be detected in both of them by the immunoenzymatic ELISA method after feeding on CTV infected plants (3). In this paper we report the first results of the transmission experiments carried out with several aphid species and some Spanish isolates of CTV. MATERIALS AND METHODS Transmissibility of CTV isolates was tested with the following aphid species : A. citricola, T. aurantii, M. persicae, A. gossypii, A. fabae, A. craccivora, A. nerii, and H. pruni. Two CTV isolates Ninth IOCV Conference coded as T-300 and T-308, from citrus growing areas of Spain were used. Isolate T-300 induces mild symptoms on Mexican lime and it was obtained by exposing healthy Mexican lime seedlings to natural infection in the field. This isolate was representative of the commonest type of CTV in Spain and it was suspected to be highly transmissible in the field. In contrast, isolate T-308 induces very severe symptoms on Mexican lime including stunting, vein clearing, leaf yellowing, vein corking and severe stem pitting. This isolate was obtained from a calamondin tree that was known to be infected for many years. Since none of the trees around became infected i t was suspected to be a poorly transmissible isolate. Virus source plants were prepared by graft-inoculating each CTV isolate on several potted Madame Vinous sweet orange seedlings. Plants were pruned periodically to produce young shoots for aphid feeding. Some of the aphid species used in transmission experiments were collected from field trees and some others were reared in controlled environment growth chambers a t 22 + 1.5 C, 70 t 10% relative humidity and a 15-hour photoperiod a t 700 lux. A. citricola and T. aurantii were collected from field citrus trees, A. nerii from oleander plants (Nerium oleander L.) and H. pruni from peach trees (Prunus persicae L.) . A. gossypii was reared on cotton and A. craccivora, A. fabae and M. persicae on broad bean plants in a controlled environment chamber. Usually, 50 Mexican lime plants, about 30 cm high were used for each aphid species and virus isolate in transmission experiments. A. nerii and H. pruni were tested only with isolate T-300 using 40 and 17 Mexican lime plants, respectively. Negative controls consisted of three plants (six for A. citricola) in which aphids of the different species were fed without a previous acquisition feeding on virus-infected plants. Transmission experiments with each aphid species were carried out in the following way: leaf pieces carrying about 200 aphids were caged in transparent rigid plastic tubes 8 cm long and 3 cm in diameter with one end closed by a screen of tergal or silk cloth. A young shoot or a leaf of the virus source plant was introduced into the cage and a strip of foam was wound around the shoot or leaf petiole to close the cage and to keep i t attached to the source plant. The aphids moved from the leaf pieces to the young shoot or leaf of the source plant inside the cage. After 48 hours the shoot or leaf was cut off the plant, the cage with aphids inside was attached to a healthy Mexican lime plant as previously described and i t was kept there for another 48 hours. During that time aphids moved from the source plant shoot to the Mexican lime receptors. Finally, the cages were removed and the aphids were killed by spraying with nicotine. All these operations were carried out in the controlled environment chambers used for aphid rearing. After aphid inoculation feeding, Mexican lime plants were transferred to a greenhouse with temperatures ranging from 18 C to 25 C. Plants were checked for foliar symptoms periodically over a 6 month period and after that period lime plants were cut, the bark was removed and the trunks were checked for stem pitting.

The effect of aphid-resistance in cowpea on infestation and development of Aphis craccivora and the transmission of cowpea aphid-borne mosaic virus

Abstract: SUMMARY The virus-vector-host relationships of cowpea aphid-borne mosaic virus (CAMV) and its vector, Aphis craccivora, were studied in cowpea lines differing in resistance to aphid infestation. CAMV was acquired and inoculated by its vector during brief probes, confirming that it is non-persistently transmitted. On aphid-resistant cowpea lines, the abundance and the relative sizes of aphids was less than in aphid-tolerant and aphid-susceptible lines. However, aphids were observed to make more numerous probes and probes of shorter duration on aphid-resistant lines than on aphid-susceptible lines. Resistance to aphid infestation in cowpea did not provide resistance to infection with CAMV.

Host preferences of Aphidius (Hymenoptera: Aphidiidae) populations parasitising pea and cereal aphids (Hemiptera: Aphididae)

Abstract: Laboratory studies were carried out on different populations of Aphidius ervi Hal., A. picipes (Nees) and A. rhopalosiphi De Stef. collected in England from Acyrthosiphon pisum (Harris), Sitobion spp., Microlophium carnosum (Buckt.) and Metopolophium dirhodum (Wlk.). When mated females from each population were confined separately with 4–5 other species of these and other genera, each population varied in their host preferences, even though individual populations of each species were electrophoretically and morphometrically homogeneous. These host preferences differed in terms of fecundity. Different populations of Aphidius ervi exhibited markedly different host ranges. This behaviour is probably conditioned rather than inherited, and its significance to biological control is discussed. The results suggest a need to assess quantitatively the effect of temperature, host size and host species on the parasitoids' ability to control pest aphids.

Feeding Response of the Green Peach Aphid (Homoptera: Aphididae) to Potato Glandular Trichomes

Abstract: Green peach aphid, Myzus persicae (Sulzer), feeding behavior on the resistant potato species Solanum berthaultii Hawkes is characterized by a delay in probing, probes of shorter duration, and a decrease in total feeding time compared with the susceptible S. tuberosum cultivar ‘Hudson,’ The causal factor is associated with type B glandular trichomes. Removal of type B droplets resulted in a decrease in preprobe time compared with that on intact S. berthraultii leaves. Foliage of an F3 inter specific hybrid lacking type B trichomes did not deter feeding, Transfer of type B exudate to leaves of cv. Hudson produced a delay in probing compared with untreated leaves. The deterrence of type B exudate may reduce vector efficiency of the green peach aphid by delaying probing beyond the retention period of nonpersistent viruses such as potato virus y.

Detection of aphid remains in predatory insects and spiders by ELISA

Abstract: SUMMARY An ELISA was developed which would detect and quantify ingested aphids in predators found in and around cereal crops. The detection limit of the assay was less than one hundredth of an homogenised adult aphid. Tests with 13 species of aphid showed that those which had been used as the principal immunogens reacted most strongly in the assay. Nearly a hundred species of invertebrates, both predators and alternative prey, have been tested in the assay and no evidence of significant cross-reaction was found with any of these species or with a number of samples of plant material on which aphids may be found. Aphid material could still be detected in predators which had been stored for up to 7 days in 4% formalin or 70% ethanol.

The potential host ranges in Australia of some imported aphid parasites [Hym: Ichneumonoidea: Aphidiidae]

Abstract: Host selection trials on restricted populations of the aphidiid parasites,Lysiphlebus fabarum (Marshall) andL. testaceipes (Cresson), imported into Australia as biological control agents ofAphis craccivora Koch, the cowpea aphid, have shown that these imported parasites are not widely polyphagous, and thus support a view that the 2 species, as presently recognized, each represent a complex of host-restricted biotypes or of sibling species. Whereas both of the importedLysiphlebus readily oviposited in species ofAphis andToxoptera, and developed successfully to adulthood inA. craccivora, A. gossypii Glover andT. aurantii (Boyer de Fonscolombe), they failed to complete development inA. citricola van der Goot, one of the most common aphid species in Australia, and only a small number completed development inT. citricidus (Kirkaldy). Both of these hosts, then, act as “egg traps” for theLysiphlebus. A. nerii Boyer de Fonscolombe was a suitable host forL. testaceipes but not forL. fabarum. NeitherL. fabarum notL. testaceipes oviposited inCavariella aegopodii (Scopoli),Brevicoryne brassicae (L.),Brachycaudus helichrysi (Kaltenbach),B. persicae (Passerini),Hyperomyzus lactucae (L.),Acyrthosiphon kondoi Shinji,A. pisum (Harris),Macrosiphum euphorbiae (Thomas) orM. rosae (L.); andL. fabarum did not oviposit inRhopalosiphum padi (L.) orMyzus persicae (Sulzer). The prognosis for the effective establishment in Australia of these 2 parasites is therefore not good

A field study of the predators of the grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), in winter wheat in Britain.

Abstract: In a field study of Sitobion avenae (F.) in winter wheat at Cranfield in southern England, the main predators were found to be the larvae of the staphylinid Tachyporus sp. and syrphids. Most predation occurred overnight. These predators were active during the period when the wheat crop was most suitable for aphid population increase, and in 1982 were apparently responsible for preventing an outbreak at Cranfield.

Reproduction and longevity of cabbage aphid, brevicoryne brassicae (homoptera: aphididae), parasitized by diaeretiella rapae (hymenoptera: aphidiidae)

Abstract: Parasitized cabbage aphids, Brevicoryne brassicae (Linnaeus), produced fewer offspring than unparasitized aphids. Aphids parasitized by Diaeretiella rapae (M'Intosh) during the first, second, or third instar died before producing any offspring; those parasitized during the fourth instar or the adult stage produced a variable number of offspring. The aphid's survival time was correlated with the rate of development, as measured by the length of the pre-reproductive period. A multiple-linear-regression equation is provided for predicting the mean total fecundity of parasitized cabbage aphids from the host age at the beginning of parasitism and the pre-reproductive period.

Taxonomy, evolution and domestication of Vicia in relation to aphid resistance

Abstract: SUMMARY Thirty Vicia species and 28 V. faba cultivars were evaluated for Aphis fabae resistance by measuring rates of aphid population increase (rm) on the host plants. A subset of these species (22) and cultivars (five) were evaluated for resistance to Acyrthosiphon pisum and Megoura viciae. For the same subset of 22 Vicia species and all three aphid species, positive correlations were observed between the concentration and numbers of leaf and stem non-protein amino acids and the level of aphid resistance. Correlations were also observed between trichome density, on some organs of the host, and both nymphal survival and development time. Aphid resistance, together with these possible physical and chemical resistance mechanisms, showed a pattern which was described in relation to the taxonomy of the genus Vicia and the degree of domestication of the host. The least advanced Vicia species were most resistant whilst the more specialised species and those most closely related to V. faba and V. faba itself were most susceptible. Within each taxonomic group (subgenus or section), the most domesticated species were least resistant. The merits of utilising the resistance found in some V. faba cultivars and in other wild Vicia species were considered.

Population dynamics of the cabbage aphid, Brevicoryne brassicae (Homoptera: Aphididae) at Vancouver, British Columbia. I. Sampling methods and population trends.

Abstract: Maris Kestrel kale, Brassica oleracea L., was planted and sampled in two locations during 1977–78. The aphids Brevicoryne brassicae (L.) and Myzus persicae (Sulzer), syrphids in the genera Syrphus and Scaeva, the cecidomyiid Aphidoletes aphidimyza (Rond.), the parasite Diaeretiella rapae (M'Intosh), and the fungus Entomophthora aphidis Hoffman were observed in the samples. A volumetric technique for assessing aphid numbers was developed and evaluated. Peak numbers of B. brassicae differed by an order of magnitude between plots, but the pattern of monotonic increase in the spring, followed by an abrupt decline in the rate of increase, a mid-summer peak, and an autumn population decline was consistent throughout. The first major decline in the rate of increase of B. brassicae was correlated with the appearance of A. aphidimyza and syrphid larvae. Declining adult aphid weight, which suggested declining fecundity, increased alate production at high aphid densities, parasite pressure, and leaf fall added to the damping effect of predators. In autumn, cool temperatures and production of sexuals further reduced the rate of increase of B. brassicae.

Insecticide-stimulated reproduction of myzus persicae, the green peach aphid (homoptera: aphididae)

Abstract: Many instances of pest populations increasing following the application of pesticides to crops have been reported, with natural enemy destruction by the pesticide often cited as the cause (Putman and Heme 1959). Other explanations include a greater food supply available due to the death of competing pest species (Root and Gowan 1978), and direct stimulation of the enhanced species by sublethal doses of a pesticide, evidenced as increased fecundity (Leigh and Wynholds 1980; Boykin and Campbell 1982; Coombes 1983). In Ontario the use of the insecticide azinphosmethyl has been followed by population increases of the green peach aphid (Myzus persicae (Sulzer)) (Founk and McClanahan 1970; Ritcey et al. 1982). Our study was undertaken to determine the causes.

Effects of aphid alarm pheromone derivatives and related compounds on non- and semi-persistent plant virus transmission by Myzus persicae

Abstract: SUMMARY A derivative, prepared from the aphid alarm pheromone (E)-β-farnesene and the saturated straight 14-carbon chain dialkyl ester of acetylene dicarboxylic acid, was the most active compound tested for inhibiting acquisition by the aphid Myzus persicae of the non-persistently transmitted potato virus Y (PVY). Derivatives lacking, or with shorter, or branched or partially-unsaturated carbon side-chains were less active. The one derivative tested also inhibited inoculation of PVY, and acquisition of beet mosaic virus (also non-persistent) and the semi-persistent beet yellows virus. However, it had no obvious effect on aphid probing behaviour; related compounds lacking the (E)-β-farnesene moiety also inhibited acquisition of PVY.

Population dynamics of the cabbage aphid, Brevicoryne brassicae (Homoptera: Aphididae) at Vancouver, British Columbia. V. A simulation model.

Abstract: A computer model was written to simulate the population dynamics of the cabbage aphid, Brevicoryne brassicae (L.), on the host Maris Kestrel kale, Brassica oleracea L., at Vancouver, British Columbia. The model incorporated the effects of temperature, morph determination, plant quality, predators, parasites, and leaf fall. Comparisons of simulated results with field observations indicated that although B. brassicae, Aphidoletes aphidimyza (Rond.), and Diaeretiella rapae (M'Intosh) were reasonably well understood, syrphid predation was not, and appropriate feed-back mechanisms which could prevent monotonic increase or decrease in the simulated population were lacking. A detailed study in which the population dynamics of the prey is accounted for in terms of the numerical and functional responses of syrphid predators is necessary to understand the population dynamics of B. brassicae on Maris Kestrel kale at Vancouver. Comparisons with other aphid systems suggest that a major change in one component of the system can be compensated for by changes in other components. An overview of the cabbage aphid system at Vancouver is given.

The effect of temperature and host species on the population growth potential of the cowpea aphid, Aphis craccivora Koch (Homoptera: Aphididae)

Abstract: Age-specific life and fecundity tables were compiled to determine the effect of temperature and host plant on the population growth potential of Aphis craccivora Koch. The intrinsic rate of natural increase (r*m) increased from zero at 5° to a maximum at 30°C, and then declined rapidly to zero at 35°C for aphids reared on all the host species tested. At 25°C aphids on Vicia faba showed a greater population growth potential than those on Capsella bursa-pastoris, followed by those on two Trifolium subterraneum cultivars and finally those on Medicago minima. An increase of temperature resulted in an earlier onset of mortality, irrespective of host-plant species. At higher temperatures the reproductive period began earlier and was shorter than at lower temperatures. The rate of reproduction appeared to be the key determinant in the aphid's population growth rate. The estimated lower temperature threshold of development of the aphid was 8.1°C.

Parasitism of Aphids (Homoptera: Aphididae) Associated with Texas Sorghum

Abstract: More than 7,700 greenbug and nearly 2,200 corn leaf aphid mummies were collected from sorghum grown in the six vegetational regions of Texas. Adult parasites emerged from 5,635 of the collected greenbug mummies and 1,468 of the collected corn leaf aphid mummies. Of the mummies producing adult parasites, 4,040 resulted in three species of hymenopterous primary parasites, Lysiphlebus testaceipes (Cresson) and Diaeretiella rapae (M'Intosh) (Braconidae), and Aphelinus varipes (Foerster) ( =A. nigritus Howard) (Aphelinidae). The remaining 3,064 emerged adults represented five species of hymenopterous hyperparasites, Pachyneuron siphonophorae (Ashmead) and Asaphes lucens (Provancher) (Pteromalidae), Alloxysta sp. ( megourae complex) (Cynipidae), Aphidencyrtus aphidivorus (Mayr) (Encyrtidae), and Tetrastichus minutus (Howard) (Eulophidae). About 43% of the 7,103 aphid mummies produced hyperparasite species, or ca. 45% of the greenbug mummies and 35% of the corn leaf aphid mummies. Alloxysta sp. was always most common from L. testaceipes-produced mummies, and A. aphidivorus was usually most common from A. varipes -produced mummies. P. siphonophorae was nearly always the most common hyperparasite regardless of region or host aphid, Alloxysta sp. was usually second most common, and A. aphidivorus third most common. The survey did not recover any of the six species of exotic greenbug parasites previously imported from Europe and released in Texas or Oklahoma. These exotic parasite species are either not established or not yet exerting a significant influence on the greenbug.

Developmental stages of Praon pequodorum Viereck (Hymenoptera: Aphidiidae), a pea aphid parasitoid

Abstract: Praon pequodorum Viereck, a parasitoid of the pea aphid, has four larval instars. At 21.1°C, eclosion of the egg occurs 3 days after oviposition. The 1st and 4th instars are mandibulate, while the 2nd and 3rd are amandibulate. Supernumerary larvae are eliminated during the 1st instar, probably by physical combat. The host aphid is killed on day 6. The 4th-instar larva spins a skirtlike cocoon underneath the mummified aphid, in which prepupal and pupal development occurs. Adult emergence begins 13 days after oviposition. In certain cases, aberrant internal pupation followed by successful adult emergence was observed.

The distribution of the sea-lavender aphid Staticobium staticis on a marine saltmarsh and its effect on host plant fitness

Abstract: 1) On marine saltmarshes, the sea lavenders Limonium vulgare Mill. and L. humile Mill. can suffer very heavy infestations (>50000 m-2) of the aphid Staticobium staticis (Theobald). 2) There is a clear and consistent pattern of aphid distribution on the marsh. Dense populations occur on plants in the middle zones of the marsh, but at the upper and lower zones, aphid populations are low. 3) Where aphid populations are dense, the sea lavenders fail to produce seed. As a result, in peak aphid years over the majority of the marsh virtually no seed is produced by the sea lavenders. Field experiments established that the aphid can greatly reduce the fitness of its host plant. 4) Thus, although the sea lavender and its aphid are an ideal natural system in which to study Owen and Wiegert's hypothesis that plants can benefit from aphid attack, the present observations provide no support for their hypothesis.

Systematic differences in the population density of green spruce aphid, Elatobium abietinum in a provenance trial of Sitka spruce Picea sitchensis

Abstract: SUMMARY Aphid populations were evaluated on foliage samples within an experimental forest area. There were marked differences in aphid density between three areas within the experiment and between individual trees. Significant differences between provenances of Sitka spruce were of particular interest since aphid density appeared to be related to the latitudinal origin of the seed. The more southerly provenances were especially susceptible. The accumulated evidence suggests that no single physiological difference between trees will account for all observed variations in aphid density although the later growth cessation of susceptible provenances deserves further study.