Showing papers on "Aphid published in 1974"

Rate of Increase of Populations of Cabbage, Green Peach, and Turnip Aphids at Constant Temperatures

Abstract: The maximum finite rate of increase for apterous populations of the cabbage aphid, Brevicoryne brassicae (L.) was 1.14 times per day at 20°C; for the green peach aphid, Myzus persicae (Sulzer), 1.32 times at 25°C; and for the turnip aphid, Hyadaphis pseudobrassicae (Davis), 1.45 times per day at 25°C. The cabbage aphid had the smallest rate of increase at all temperatures, the green peach aphid the greatest rate between 5° and 15 °C, and the turnip aphid the greatest rate between 20° and 30°C. No aphids reproduced at 35°C, only the population of turnip aphids increased at 30°C, and only the population of the green peach aphids increased at 5°C. Other populations decreased at 5° and 30°C. The components of the rate of increase (nymphal development, age-specific survival and fecundity, length of generation, and net reproductive rate) were determined for each aphid at each temperature. Their effect on the rate of increase was examined, as was the age at which 95% of the contribution to the next generation was made. The proportion of each stage in a population with a stable age distribution was also examined. Equations for predicting the rate of increase, and models comparing the relative growth of populations of the three species with time are presented.

The ecology of Aphis craccivora Koch and Subterranean Clover Stunt Virus in south-east Australia. III. A regional perspective of the phenology and migration of the cowpea aphid.

Abstract: Many workers have studied the migration of insects (see Johnson 1969), but few have attempted to place their observations into a regional and climatic perspective. In Australia, the cowpea aphid (Aphis craccivora Koch) is the most important vector of Subterranean Clover Stunt Virus (SCSV) to crop and pasture legumes. Its long-range migratory behaviour in Australia was first reported by Johnson (1957) who observed that large populations developed during the spring of certain years on medic (Medicago spp.) on the inland plains of north-central New South Wales (N.S.W.) and were blown eastward toward the coast on north-westerly winds. The reasons for the build-up of the cowpea aphid during certain years in that area are unknown. Hughes et al. (1964, 1965) and O'Loughlin (1963) conducted aphid trapping experiments over a wide area of southeast Australia, but derived few useful generalities. This paper examines the climatic limits for the development of cowpea aphid populations in south-east Australia, relating its migration and colonization to climate. Gutierrez, Morgan & Havenstein (1971) studied the ecology of the cowpea aphid in the temperate pasture regions of south-east Australia and found that aphid populations developed only in those areas where suitable conditions occurred for both the plant and the aphid. Pastures in this area are influenced by availability of moisture, while aphids do not survive during periods of ground-frost. By using a model of the aphid's population biology, Gutierrez et al. (1974) showed that the southern pasture areas were marginal for the aphid because the season was too short for the development of large populations. When, however, the attributes of a subtropical climate and host plant were incorporated into the model, the output suggested that the cowpea aphid could be an efficient migratory species. The results conformed to the hypotheses of Dingle (1972), who used static life-table parameters to demonstrate the biological attributes required by successful migrants.

Properties and isolates of barley yellow dwarf virus

Abstract: SUMMARY Barley yellow dwarf virus is persistently transmitted by a number of aphid species of which three, Rhopalosiphum padi, Sitobion avenae and Metopolophium dirhodum, are common in most years. Other aphids may be locally important. Isolates of the virus differ in their virulence and geographical distribution and are not transmitted equally well by all aphid vectors. Isolates with similar properties are grouped into strains according to their transmission by vectors and their severity. Changes in strain and aphid occurrence from year to year alter the incidence of virus and its effect on yield. These changes emphasize the need for detailed knowledge of cereal aphid biology and epidemiology of BYDV before effective control can be used.

Isolation of Flower-inducing and Flower-inhibitory Factors from Aphid Honeydew

Abstract: The aphid Dactynotus ambrosiae Thomas has been allowed to feed on vegetative or flowering plants of the short-day plant Xanthium strumarium L., and the honeydew which they produce is extracted and tested for an effect on flowering using the long-day plant Lemna gibba L., strain G3 for the bioassay. One zone of flower-inducing activity and at least two zones of flower-inhibitory activity are consistently obtained from the honeydew extracts. The levels of flower-inducing and flower-inhibitory activity are not demonstrably different in vegetative and flowering honeydew. The honeydew extracts are inactive on Xanthium but do give some flower induction with the short-day plant Lemna perpusilla Torr., strain 6746. The flower-inducing activity is clearly of plant origin and is present in the phloem since the same active material can be obtained from vegetative or flowering Xanthium by methanol extraction, and honeydew produced by aphids feeding on a chemically defined synthetic diet is completely without flower-inducing activity. This is the first report of successful flower induction in the long-day plant L. gibba G3 by some means other than long-day treatment.

Response of Lysiphlebus testaceipes in an Olfactometer to a Host and a Non-host Insect and to Plants

Abstract: Lysiphlebus testaceipes (Cresson) is the most abundant parasitoid of the greenbug, Schizaphis graminum (Rondani) and helps to limit infestations (Jackson et al. 1970) but often not until damage to grain sorghum has occurred. Several authors have noted different preferences of L. testaceipes for aphid hosts on different host plants (Knight 1944, Sekhar 1960, Walker et a1. 1973). We studied the response of the parasitoid in an olfactometer to a host insect (greenbug), a non-host insect ( Heliothis zea [Boddie]), an aphid host plant (sorghum), and a plant on which aphids seldom colonize (peanut cactus, Chamaecereus silvestrii [Speg.]).

Aggregation in the Birch Aphid Euceraphis punctipennis (Zett.) in Relation to Food Quality

Abstract: The concentration of soluble nitrogen in the leaves of many deciduous trees declines markedly as summer approaches and the leaves mature; there is a slight recovery at senescence (Lindemann 1948; Mittler 1958; Dixon 1963, 1971). The reproductive and growth rates of some tree-dwelling aphids such as the sycamore aphid (Drepanosiphum platanoidis (Schr.)) also decline in mid-summer and reproduction may cease or remain at a low level for up to 2 months, mainly in response to the deterioration in food quality. At this time the population consists almost entirely of adults in reproductive diapause (Dixon 1963). The reproductive rate of the birch aphid Euceraphis punctipennis also declines in mid-summer, but for a relatively short period. The extent to which this aphid, through its aggregation behaviour, overcomes the disadvantages of the variable quality of its food through the year is discussed in this paper.

Effect of amino acid concentration on diet uptake and performance by the pea aphid, acyrthosiphon pisum (homoptera: aphididae)

Abstract: The average rate of diet uptake by the 1st–3rd instar nymphs of the pea aphid, Acyrthosiphon pisum (Harris), on chemically defined diets containing 0.0–5.0% amino acids varied from 0.08 to 0.23 μl/aphid/24 h and that by 4th instar nymphs to adults varied from 0.15 to 0.74 μl/aphid/24 h. The presence of amino acids increased the acceptability of diets to a great extent, as uptake on such diets was 2–5 times more than that on amino acid free diets. Uptake was lowest on diets lacking amino acids, and highest on those containing 3.5 and 2.5% amino acids by 1st–3rd instar nymphs and 4th instar nymphs to adults respectively. It is suggested that certain amino acids, either alone or in combination, act synergistically with sucrose as phagostimulants. Methionine was slightly phagostimulatory to the pea aphid and enhanced the acceptability of a free amino acid diet and of a sucrose solution.As expected the rate of feeding increased as the aphids grew. Nymphs reached the adult stage, and reproduced on each diet, except on the one lacking amino acids. The longevity on different diets varied from 7 to 37 days. A concentration of 2–4% amino acids, with an optimum at 3.5%, appears to be essential for the growth, survival, and larviposition of the pea aphid.Due to the punctures made in the stretched parafilm by aphids during feeding the rate of evaporation from fed sachets was significantly higher than that from unfed sachets. It is therefore suggested that in experiments where rates of feeding are measured by differential weighings of the sachets, these be renewed at 24-h intervals.

Sugar, organic acid, phenolic acid and plant growth regulator content of extracts of honeydew of the aphid Myzus persicae and of its host plant, Raphanus sativus

Abstract: SUMMARY The honeydew of Myzus persicae feeding on radish seedlings contains glucose, fructose, trehalose, melezitose and sucrose, of which glucose and fructose are present in radish seedlings. In addition, the honeydew contains eight organic acids, of which seven are present in uninfested seedlings and six are present in infested radish seedlings: of the eighteen phenolic acids in the honeydew, five are present in uninfested radish seedlings. Auxins, gibberellins, growth inhibitors and cytokinins are present in the honeydew. The presence of carbonate and bicarbonate previously recorded in honeydew of M. persicae could not be confirmed, but ammonia is present in fresh honeydew and accounts for its high pH.

Effects of antibiotics on intracellular symbiotes in the pea aphid, Acyrthosiphon pisum

Abstract: The effects of penicillin and chlortetracyline HCl on the fine structure of the intracellular symbiotes of the pea aphid were studied in an attempt to remove the symbiote population. High penicillin concentrations, 1% and 0.1%, caused symbiote breakdown but were toxic and/or repellent to the aphids; at 0.1% specific effects were observed on the symbiotes' cell walls. After the use of 0.01% penicillin in the aphid diet, the symbiotes had abnormal cell walls and were abnormally dilated; however, symbiote division and transmission from one aphid generation to the next seemed unaffected and the aphids appeared normal. Aphids fed 0.1% chlortetracycline failed to reproduce. After 7 days, their symbiotes were found to break down at a high rate but aphid mitochondria were also adversely affected at this stage. Following 0.002% chlortetracycline, the aphids produced aposymbiotic progeny with apparently normal mitochondrial populations; these larvae failed to develop.

Supercooling and the low-temperature survival of the green spruce aphid Elatobium abietinum.

Abstract: Laboratory investigations into the low-temperature tolerance of the green spruce aphid, Elatobium abietinum, revealed that the insect was killed by freezing. Aphids and host Sitka spruce needles showed similar seasonal changes in supercooling ability. A noticeable increase in this ability occurred between June and October. Aphids were more susceptible to low temperatures when attached to the plant. It is suggested that mortality resulted from ice which formed in the sap of the host needles and spread into the feeding aphids via their mouthparts. Neither the chlorotic banding of needles, caused by aphid feeding, nor needle length affected needle supercooling. Increased duration of exposure increased the probability of freezing of supercooled needles at low temperatures. A small percentage of first-instar nymphs supercooled to much lower temperatures than the remainder of the population. These were newly born nymphs whose high supercooling ability markedly decreased when they began to feed.

Aphid-trapping glandular hairs on hybrids ofSolanum tuberosum andS. berthaultii

Abstract: The foliage of hybrids ofS. tuberosum cv. Pentland Crown andS. berthaultii bore four-lobed, glandular hairs which, when ruptured by aphid movements, released a sticky substance which glued the aphids to the plant. The transference of this property makes it more worthwhile testing as a means of decreasing the spread of aphid-borne viruses.

Spring Movement of Cereal Aphids into South Dakota

Abstract: Four species of aphids commonly colonize cereal crops in South Dakota: greenbug, Schizaphis graminum (Ron dani); English grain aphid (EGA), Macrosiphum avenae (F.); corn leaf aphid (CLA), Rhopalosiphum maidis (Fitch); and R. padi (L). However, none of these aphids seem capable of overwintering in South Dakota, though anholocyclic populations may persist until mid-December on winter grains. No sexuales of any of these species have been found in samples of populations from the field, and no sexuparae of R. padi have been taken in surveys of aphids on Prunus (Kieckhefer and Gustin 1967). The reappearance of aphids in cereal crops in South Dakota each April or May has been abrupt; initial populations consist exclusively of alate viviparae with no fundatrices or nymphs present. Appearance of alate populations on spouting grains in spring has frequently been so early as to preclude development from eggs because of insufficient time and unfavorable environment for development. Populations of alate viviparae of these species of aphids undoubtedly migrate from the south and become reestablished in South Dakota each spring. Surveys in Texas, Oklahoma, and Kansas in March and April have shown that greenbugs, EGA, and R. padi survive the winter in portions of some or all of these states and that numbers increase early in spring (Cartier 1957, Plant Pest Control Division 1965, Wallin and Loonan 1971). Jensen and Wallin (1965) and Taylor (1965) suggested low-level jets as a vehicle for long-distance transport of aphids into the North Central states and Berry and Taylor (1968) took greenbugs and EGA in collections from an airplane in low-level jet winds (3,000 ft) over Kansas. Arrival of greenbugs and EGA in Iowa has been associated with low-level jet winds (Wallin et al. 1967, Wallin and Loonan 1971). The objective of our study was to determine the dates cereal aphids reach South Dakota in spring and to analyze weather patterns that were associated with this arrival.

Aphid Cornicle Secretions Ineffective Against Attack by Parasitoid Wasps

Abstract: Cornicle secretions have been reported to serve multiple functions in aphids. Of particular interest are reports that these sticky secretions serve to defend aphids against attack by predators and parasites. Dixon (1958) observed that the aphid, Microlophium evansi (Theobald) will smear its cornicle secretions on the mouthparts of the coccinellid, Adalia decempunctata (L.) allowing the aphid to escape from the temporarily immobilized predators. Edwards (1966) observed parasitoid wasps ( Aphidius ) trapped in aphid cornic1e secretions in the field.

The induction of top‐roll symptoms on potato plants by the aphid Macrosiphum euphorbiae

Abstract: SUMMARY In the field, caged potato plants of King Edward and Majestic cultivars infested with the potato aphid Macrosiphum euphorbiae developed top-roll symptoms, the proportion of affected plants increasing with the size and persistence of the aphid population. Yield of tubers from plots in which 90% of the plants had top-roll symptoms was 40% less than that from control plots; yield of saleable ware was even less. Foliage produced after the aphids had been killed was symptomless even when it arose from the axil of an affected leaf. Caged field plants treated with phorate granules to prevent aphid attack did not develop top-roll. Prolonged infestation of Pentland Crown, Majestic and King Edward plants by M. euphorbiae in a glasshouse induced rolling of upper leaves similar to top-roll of field plants. Experimental results suggest that rolling was directly attributable to heavy attack by M. euphorbiae, not to an aphid-transmitted pathogen.

Parasitoids Collected from Greenbugs and Corn Leaf Aphids in Oklahoma in 1972

Abstract: The distribution of parasitoids of the greenbug, Schizaphis graminum (Rondani), and corn leaf aphid, Rhopalosiphum maidis (Fitch), on sorghum in Oklahoma was studied during the summer, 1972. Parasitoids of the families Braconidae, Eulophidae, Pteromalidae, Encyrtidae, and Cynipidae, were collected. Predators were observed from the families Coccinellidae, Chrysopidae, and Syrphidae. Lysiphlebus testaccipes (Cresson) was the most abundant primary parasitoid collected from greenbugs. The predominant primary parasitoid emerging from parasitized corn leaf aphids was Aphelinus nigritus (Howard). A. varipes (Forester), an introduced primary parasitoid, was recovered from corn leaf aphids. The most abundant secondary parasitoid was Pachyneuron siphonophorae (Ashmead). Other secondary parasitoids were Aphidencyrtus aphidivorus (Mayr), Charips sp., and Asaphes lucens (Provancher). Both primary parasitoids and predators were active early in July. Secondary parasitoids were dominant by the latter half of July on parasitoids of the greenbug. The largest parasitoid populations were in the SW, followed by the Panhandle and north-central NE regions.

Intraspecific variation of Myzus persicae on sugar beet (Beta vulgaris).

Abstract: SUMMARY Differences in inherited resistance among seven sugar-beet stocks had similar effects on Myzus persicae clones representing the range of variation in aphid response to resistant and susceptible sugar beet observed in fifty-eight clones collected between 1969 and 1971. Three sugar-beet stocks were consistently resistant. Statistically significant interactions between beet stocks and aphid clones did not indicate the existence of biotypes with specific abilities to overcome resistance. M. persicae clones differed in their vigour of colonizing sugar beet, irrespective of the differences between beet stocks. The readiness of adult aphids to settle determined the size of aphid population produced and included a component related to the response of the aphid clone to sugar beet as a host, and a component related to the resistance ranking of the beet stock. Breeding sugar beet with resistance to aphids will be simplified, as the results indicate that, at present, differences between aphid biotypes need not be considered a problem.

Study on inheritance of resistance to root aphid, Pemphigus bursarius, in lettuce

Abstract: SUMMARY The inheritance of resistance to lettuce root aphid, Pemphigus bursarius, was studied in lettuce using the Wellesbourne cultivars Avondefiance and Avoncrisp as resistant parents and Borough Wonder and Webb's Wonderful as aphid-susceptible parents. All four cultivars were crossed in all possible combinations including reciprocals and the response to root aphid of plants in the P1F1F2 and BC generations was assessed using apterae of P. bursarius from the lettuce cv. Iceberg. Resistance to attack was clearly inherited and the parents appeared to be homozygous for their resistance or susceptibility. In the F1 generation, however, in all crosses between resistant and susceptible parents, segregation into susceptible, resistant and some slightly less resistant plants occurred. This and the highly significant differences in segregation between pairs of reciprocal crosses in the F1 and other generations indicate that the inheritance of resistance to root aphid is controlled by extra-nuclear factors. Modifying genes might also be involved but there appears to be no linkage of root aphid resistance with resistance to downy mildew, for which the Wellesbourne lettuces were bred.

Biology of Ephedrus plagiator on Different Aphid Hosts and at Various Temperatures

Abstract: Host preference, developmental time, fecundity, adult longevity, emergence, and sex ratio of Ephedrus plagiator (Nees) at 3 constant temperatures were studied in the laboratory. The greenbug, Schizaphis graminum (Rondani), corn leaf aphid, Rhopalosiphum maidis (Fitch), oatbird cherry aphid, R. padi (L.), and English grain aphid, Macrosiphum avenae (Fabricius) were preferred over the rusty plum aphid, Hysteroneura setariae Thomas, cotton aphid, Aphis gossypii Glover, yellow sugarcane aphid, Sipha flava (Forbes), and spotted alfalfa aphid, Therioaphis maculata (Buckton). E. plagiator was never observed probing or attempting to parasitize the latter 2 species. Developmental period of E. plagiator varied inversely with the temperature, but was approximately the same in each aphid species at each temperature. The sex ratio averaged 30% female or below on each aphid species and at each temperature. The longevity of E. plagiator (female and male) was greater at 16°C than at 21° or 27°C, and also decreased as temperature increased. The species of aphid host had no apparent effects on either adult longevity or development rate of E. plagiator .

Garden Peas Resistant to the Pea Aphid

Abstract: An attempt was made to find a race of Pisum sativum (L.) more resistant than the race ‘Onward’ to Acyrthosiphon pisum (Harris) by evaluating 1250 races. On the basis of aphid weight, progeny, and longevity, 20 pea races were Significantly more resistant than Onward. Aphids reared on one race (PI 244160) of peas were 21% lighter in weight than those reared on Onward. Reductions of 28% in number of progeny and 24% in longevity were found in other races. Two pea races (‘Konservenkonigen’ and ‘Scescio Tygodniowy.’) were significantly more susceptible than the susceptible race ‘Perfection’, and aphids on them were ca. 29% heavier.

Palm Aphid Control on `Malayan Dwarf' Coconut Palms

Abstract: Seven insecticides (Orthene (O,S-Dimethyl acetylphosphoroamidothioate), carbofuran, dimethoate, disulfoton, methomyl, monocrotophos, and oxydemethonmethyl) applied as foliar sprays provided excellent control of the palm aphid, Cerataphis variabilis H.R.L., on `Malayan Dwarf' coconut palms, Cocus nucifera L. Dialifor gave only limited control. As a soil drench only dimethoate gave satisfactory control at 2 weeks post-treatment, but by 4 weeks Orthene, monocrotophos, and oxydemetonmethyl also gave 100% control. When applied by soil drench, the insecticides translocated very slowly to the spear leaves but provided excellent control on the other leaves within 1 week. Three species of coccinellidae, Cycloneda sanguinea (L.), Hippodamia convergens Guerin, and Olla abdominalis sobrina Csy., were observed as predators of this aphid.

Relative feeding rates of Brevicoryne brassicae and Myzus persicae on brussels sprout plants in relation to their susceptibility to systemic insecticides

Abstract: SUMMARY Brevicoryne brassicae and Myzus persicae removed similar quantities of 32P-labelled material from Brussels sprout leaves whether they fed for 24 or 48 h periods. They also removed similar quantities from untreated leaf disks as from leaf disks treated with a sub-lethal dose of menazon. When a lethal dose was used, the uptake of 32P by B. brassicae was significantly less than by M. persicae. M. persicae excreted a greater proportion of 32P label in the honeydew than B. brassicae and a greater proportion of the amount absorbed was lost in the progeny of this aphid than in B. brassicae. B. brassicae was 6.2 times more susceptible than M. persicae to dimethoate acting systemically. When it was applied topically the aphids were equally susceptible. Considerable variation in uptake of 32P occurred between replicates and the factors that could influence this are discussed.

Effects of Metopolophium dirhodum on Spring Wheat in the Glasshouse

Abstract: SUMMARY Pot-grown plants of spring wheat, cultivar Maris Dove, Were subjected, commencing at ear emergence, to different, constant levelsof infestation hy Metopolophium dirhodum (Wlk.) in a glasshouse. Infestation with six aphids per stem over 11 days had no significant effect on yield. Infestations with either six or 50 adult aphids or their equivalents, when maintained until ripening, resulted in lower yields of both grain and straw dry matter. Loss of grain was due to reduction in both 1,000 grain weight and the average number of grains per fiertile spikelet. Harvested dry matter content of leaf blades was unaffected by infestation, but the dry matter, content of stems was reduced in infested plants. In breeding aphid-resistant cereals for Britain, resistance characters restricting aphid multiplication are most likely to reduce yield losses due to aphid attack.

Biology and host specificity of two aphids Dactynotus chondrillae (Nevsk.) and Chondrillobium blattnyi (Pintera) (Hemiptera) living on Chondrilla juncea.

Abstract: The biology and host specificity of Dactynotus chondrillae (Nevsk.) and Chondrillobium blattnyi (Pintera) living on the weed Chondrilla juncea (Compositae, Cichoriaceae) have been studied in the Mediterranean region as part of the biological control programme against this weed for Australia. Both are recorded from south-eastern Russia to the western Mediterranean region. The two species are monoecious. D. chondrillae has a facultative sexual reproductive phase every year but Chondrillobium blattnyi reproduces indefinitely by parthenogenesis in the Mediterranean region. D. chondrillae feeds mostly on young shoots, has population peaks in the spring and in the autumn, and can damage Chondrilla in the field. Chondrillobium blattnyi is a leaf feeder capable of seriously injuring the rosettes, but it never occurs in large enough populations in nature to be damaging. To demonstrate specificity, both aphids were tested against various Cichoriaceae and other Compositae and also against 61 cultivated plant species belonging to 20 families. The two aphids were shown to be specific to the genus Chondrilla. In the laboratory D. chondrillae was less host restricted than the other aphid and it reproduced on Sonchus asper and Taraxacum officinale. Comparative testing with strains of the two aphids from various sources against various forms of C. juncea showed that each strain was adapted to the form of C. juncea occurring in its own geographic area. The southern French strain of these aphids was ill-adapted to the main Australian form of C. juncea, but a strain of D. chondrillae originating from the Italian Adriatic coast heavily infested this form. D. chondrillae was not considered to be specific enough to permit its introduction into Australia and the introduction of Chondrillobium blattnyi has been delayed until it can be shown that it cannot transmit virus diseases that affect lettuce.

Mammalian Safety of the Aphid-Attacking Fungus Entomophthora nr. thaxteriana

Abstract: A strain of the entomogenous fungus, Entomophthoza nr. thaxteriana (Petch), isolated from the green peach aphid, Myzus persicae (Sulzer) shows promise as a biological control agent for aphids. This isolate is intermediate in its morphology between E. thaxteriana and E. virulenta Hall and Dunn. The spore sizes, i.e. conidia 24 × 19μ, resting spores 22μ, more closely approximate E. virulenta . Lack of rhizoid production, however, has caused us to call this strain E. thaxteriana . The resting spores produced by this isolate can be stored for long periods of time and when properly treated will give up to 98% germination. Greenhouse and field studies have shown this species to be both pathogenic and virulent, giving 100% control in 3 days. The resting spores of this fungus are currently under production in the laboratory and will be field tested against the potato aphid complex in Northern Maine. Effectiveness, however, is not the only criteria which determines an insect pathogen as a good candidate for biological control. It must also be demonstrated that it is safe for man.

The influence of host plant on the production of sexuparae in the aphid Pemphigus bursarius

Abstract: In his review of factors controlling polymorphism in aphids, Lees (1966) pointed out that most work on this subject had been done with species in the most specialised family, the Aphididae, and future work with the mo~'e primitive families might show \"considerable difference in the mechanism of form determination\". As with Megoura viciae Buck. fLees, 1961) and Aphis craccivora Koch (Johnson, 1965), ho~vever, the results of Judge (1968) with lettuce root aphid, Pemphigus bursarius (L.), emphasised that in Pemphigidae also, crowding was an important form-determining factor. Nevertheless f rom the description of the technique used by Judge to assess the effects of crowding, photopefiod and temperature on form determinat ion in P. bursarius, the influence of host plant condition may not always have been dissociated f rom the results he obtained. Tha t nutr i t ion may play a part in form determination in subterranean aphids was suggested by Lees (1966) and confirmed by Sethi & Swenson (1967), who found that the format ion of sexuparae irt Eriosoma pyricola Baker & Davidson feeding oa pear roots was associated with the cessation o~ gro~vth of the host plant. Fur ther evidence of the influence of the host plant on form determination in Pemphigidae recently came to light while the present author was do,ing certain host range work with P. bursarius. Details of the biology of P. bursarius given by Dunn (1959) show that all winged forms of the aphid produced among the salbterranean colonies of virginoparae on lettuce roots are sexuparae, which are unable to eolonise lettuce fur ther and are obliged to re turn Go their pr imary host, Populus nigra especially vat. italica. To rear root colonies of P. bursarius continuously on lettuce, therefore, conditions must be provided that do not promote the format ion o~ sexuparae. Thus for some years cultures of this aphid have been reared on lettuce at Wellesbourne at 19 ~ --0.5~ and a photoperiod of 16 hours in 24. Stock plants of lettuce cv. Webb ' s Wonderful are grown individually in 5-era plastic pots in \"Alexpeat\". The pots are sunk to r im level in a tray of peat kept moist enough to enable good plant growth without saturating the contents of the pots. One newly mature virginopara is put onto the roots of each plant in its two-true-leaf-stage and the colony she establishes there is allo~ved to develop for 21 days. The roots are then teased and discarded after suitable virglnoparae for fur ther culturing and experimental work h~ve been removed. In this way virginoparous reproduction is maintained and sexuparae seemingly occur only if the culture is retained longer, or a eolonised plant is less vigorous and healthy, than usual. When testing plants as potential hosts of the lettuce root aphid, fuadatrigeniae of P. bursarius straight f rom poplar galls have normally been used (Dunn, 1959 & 1960) but in a recent test of plants of Lactuca serriola Torner use was made of P. bursarius virginoparae from the WeUesbourne cultures. The plants were f rom seed f rom three different eountries and their response to lettuce root aphid was compared with that o,f cv. Webb's Wonderful lettuce plants. The plants were grown, and each was inoculated with a virginopara of P. bursarius, as with the root aphid culture, but within the tray of peat a plant of every kind occurred at random once in each of ten sets of pots. Three weeks later vigorous colonies of root aphid which had produced much fi lamentous wax were present on all plants of Webb 's Wonderful and a population of at least 100 P. bursarius irt their 3rd instar or older was estimated for each root system. Of these all were virginoparae. Only five plants of L. serriola f rom Afghanistan