Showing papers on "Aphid published in 1973"

Plant penetration by feeding aphids (Hemiptera, Aphidoidea): a review

Abstract: The factors responsible for determining the host-plants and feeding sites of aphids, and the various probing activities (the role of the labium, stylet insertion, surface saliva deposition, the behaviour of the aphid, virus transmission) are examined. There is a brief review of stylet structure and movement and the possible sensory nature of these organs, followed by a detailed review of the characteristics of aphid stylet paths in plant tissues. The penetration of epidermis and vascular tissues is treated separately while that within the intermediate tissues is covered in relation to leaves and stems, roots, trees, galls and excised tissue as well as in separate sections on Aphis fabaeScopoli and Myzus persicae (Sulzer). Stylet destinations and behaviour in the sieve tubes are discussed together with general features such as rate and depth of penetration, guidance to the feeding site, effects of tissue hardness and stylet withdrawal. The ingestion rate of plant sap is reviewed and its constitution and importance examined together with the significance of artificial diets. The salivary secretions including sheaths and tracks, their functions and their role in the transference of material between aphid and host are dealt with. The nature of the physical and internal damage resulting from aphid feeding is briefly covered, and also some plant-insect interrelations. The aphid species whose stylets have been examined in plant tissue are listed.

Aphid Alarm Pheromones: Secretion and Reception

Abstract: The aphids Aphis coreopidis (Thomas), Acyrthosiphon pisum (Harris), Acyrthosiphon soiani (Kaltenbach), and Myzus persicae (Sulzer) produce droplets at the tips of their cornicles when attacked by several species of insect predators. Alarm pheromones volatilizing from these cornicle droplets repel nearby aphids from their feeding sites. The release of cornicle droplets can also be elicited by various physical stimuli. Depending upon the type of stimulus and the aphid species involved, 50 to 90% of aphids produce droplets and 62 to 76% of droplets emit biologically active levels of pheromone. Aphids respond to the alarm pheromones at a distance of 1–3 cm from freshly secreted droplets and repellent activity is retained up to 60 minutes after secretion. Alarm pheromones are perceived by primary and secondary sensoria located on the aphids antennae.

Trans-β-farnesene, Alarm Pheromone of the Green Peach Aphid, Myzus persicae (Sulzer)

Abstract: THE chemical structure of the repellent odour found in the cornicle secretion of the aphid M. persicae1 has been identified as trans-β-farnesene.

The effectiveness of the coccinellid beetle, Adalia bipunctata (L.), as a predator of the lime aphid, Eucallipterus tiliae L.

Abstract: The two-spot coccinellid (Adalia bipunctata (L.)), will feed on a variety of aphid species but is usually associated with those living on trees or shrubs greater than 2 m in height (Putnam 1964; Iperti 1966; Hodek 1966). In Glasgow, larvae of this predator are common on lime (Tilia x vulgaris Hayne), where they feed mainly on the aphid Eucallipterus tiliae and less often on the cicadellid Alnetoidea alneti Dahlbom. A. bipunctata occurs less frequently on sycamore (Acer pseudoplatanus L.), where its effects on populations of the aphid Drepanosiphum platanoides (Schr.) were described by Dixon (1970). The numbers of the lime aphid fluctuate markedly within a season and from year to year (Dixon 1971), but the role of coccinellid predation in these changes is unknown. This paper attempts to assess the searching capacity and survival of the predator on lime, and to evaluate the role of the two-spot coccinellid in the regulation of the numbers of the lime aphid.

Biological Control of the Walnut Aphid in California: The Interrelationship of the Aphid and its Parasite

Abstract: Populations of Chromaphis juglandicola (Kaltenbach) and its natural enemies were assessed weekly during the growing season in 1969 and every 4 days in 1970. A parasite of the aphid, Trioxys pallidus (Haliday) (Aphidiidae: Hymenoptera), from Iran, was released and became established in the study area in 1969, but it did not affect the abundance of the aphid during that season. Large numbers of mummies overwintered, and the normal peak in aphid numbers in spring 1970 did not occur. Aphid numbers remained at levels about 0.01–0.001 of those in previous recorded years. An experimental release of aphids and use of a biological check method demonstrated that the parasite was responsible for the maintenance of the aphid at low numbers. The same tests showed that selective predation of parasitized aphids by the Argentine ant lridomyrmex humilis (Mayr), presents a serious threat to continued control of aphid outbreaks by the parasite where ants are present. The rapid increase in the artificially induced outbreak of aphids indicated that it was not high temperatures that previously kept aphid numbers low in summer, but leaves made unacceptable by sooty mold and debris from the spring peak of aphid numbers.

Infection of cereal aphids by the fungus Entomophthora

Abstract: SUMMARY Three species of Entomophthora killed many Metopolophium dirhodum, M. festucae and Sitobion avenae on wheat at Harpenden, Hertfordshire, in 1971. Rainfall was low and aphid numbers were small in May and there was no Entomophthora infection. E. planchoniana first infected M. dirhodum early in June and the percentage of each aphid species infected increased during and after heavier rain in the first 2 weeks of June. M. dirhodum and S. avenae were most often infected by E. planchoniana, and the less common M. festucae mostly by E. aphidis and E. thaxteriana. Relative frequencies of E. aphidis and E. thaxteriana were largest before, and of E. planchoniana after, mid-July. The largest percentages infected were 53% of M. dirhodum and 30% of S. avenae during the second half of July and 60% of M. festucae in late June. The percentages of old nymphs and apterous adults that were infected were similar and only about half those of infected alatae.

The effect of plant spacing on the number of aphids trapped over cocksfoot and kale crops

Abstract: SUMMARY The response to plant spacing by flying and landing aphids has been studied using cylindrical and horizontal sticky traps over cocksfoot and kale crops. Some aphid species showed a significant response to spacing, being caught more frequently over wide-than close-spaced crops; the regressions of catches over widely-spaced on those over close-spaced plants suggested that most of the species caught followed this trend irrespective of the host plant. The landing response to spacing on horizontal traps at 0.3 m was normally greater than that on cylindrical traps at 1 m. At 1 m, some species (e.g. Aphis fabae gp.) gave a different response to spacing in the two crops, whilst others (e.g. Rhopalosiphum oxyacanthae) responded similarly to both crop spacings. In contrast to previous results with other aphid species and spaced groundnuts, the landing response of Rhopalosiphum spp. was elicited both when there was a cover crop (clover) between widely-spaced drills of cocksfoot and by widely-spaced cocksfoot alone. It is suggested that one stimulus eliciting the landing response with widely-spaced plants is the electromagnetic emission from bare earth between the plants. Aphid landing behaviour was influenced by the spacing of both cocksfoot and kale plants.

Leaf size and availability of space to the sycamore aphid Drepanosiphum platanoides

Abstract: Sycamore aphids feed on the contents of sieve tubes in leaf veins. The smallest aphids prefer to settle on the minor veins of small leaves, but larger aphids select larger veins. On large leaves, however, even the adult aphids prefer to settle on the minor veins. Aphids feeding on large leaves are unable to reach the deeper sieve tubes in the thicker part of the main veins as their stylets are too short. However, the length of the aphids' stylets cannot account for the absence of aphids from the lateral veins of large leaves or the distribution of the various instars on the veins of small leaves. The preference shown by an aphid for leaf veins of a particular size is probably imposed on the aphids by the structure and physiology of leaf veins of different sizes. The outcome of this is that only a part of a leaf is suitable for colonization by aphids.

The biology ofAphelinus flavus [Hym. Aphelinidae], a parasite of the Sycamore aphidDrepanosiphum platanoides [Hemipt. Aphididae]

Abstract: Aphelinus flavusThompson is a solitary internal parasite. Males and females overwinter as free living adults and appear on sycamore in mid, May. The female consumes aphid body fluids and kills 1 aphid for food for every 1.7 eggs deposited, and parasitises 48 aphids over 27 days. Development from egg to adult requires and parasitises 48 aphids over 27 days. Development from egg to adult requires 57 days. The mortality of parasites while within the nummified host was determined: it was related to hyperparasitism and predation. Mortality due to mummies being brushed off the leaves was also determined.

Parasitization of the Greenbug by Aphelinus asychis and the Effect of Feeding by the Parasitoid on Aphid Mortalitya

Abstract: Laboratory studies with an introduced parasitoid, Aphelinus asychis (Walker) (Hymenoptera: Eulophidae), and one of its hosts, Schizaphis graminum (Rondani) (Homoptera: Aphididae), were conducted during the spring and summer of 1972 to determine the number of greenbugs fed upon daily by the parasitoid, number of aphids parasitized daily, preferred mummification site, daily emergence rate of the parasitoid from the mummies, sex ratio of the emergent, and longevity for the parasitoid. A total of 608 aphids was fed upon by the 20 parasitoids. A total of 4655 mummies was formed for the 20 parasitoids of which 1967 were found on the leaves, 1200 on the stems, 121 in the whorls, 172 on the sand covering the soil, and 114 on the containers. Parasitoids emerged from approximately 81% of the mummies, and approximately 56% of these were females. Mean longevity for the 20 parasitoids was 23.4 days.

Notes on the occurrence and biology of the sorghum aphid in South Africa.

Abstract: The sorghum aphid, Melanaphis (Longiunguis) pyrarius (Passerini) forma sacchari (Zehntner), is a cosmopolitan species and is distributed widely in South Africa. Laboratory studies on the biology of this aphid indicated that young and mature grain sorghum are equally suitable as host plants. Field studies revealed no significant difference between the specific growth rates of sorghum aphid populations on young and mature grain sorghum. During early summer, grain sorghum aphid populations show an exponential growth rate.

Impact of the balsam woolly aphid (homoptera: phylloxeridae) on cones and seed produced by infested fraser fir

Abstract: Seed produced by Fraser fir, Abies fraseri (Pursh) Poir., infested by the balsam woolly aphid, Adelges piceae (Ratzeburg), was compared with that originating from uninfested trees during a cyclic year of heavy seedfall (1969) in western North Carolina. Cones were significantly shorter and seed uniformly lighter and smaller from trees infested by the aphid. X-ray examination indicated the number of full seed from uninfested trees averaged nearly 70% and 42% higher than in comparable seed samples from infested trees. Germination tests indicated viability of seed from infested trees exceeded 32% and that from uninfested trees exceeded 75%. An important factor affecting survival of seed from the two sources appeared to be the relative susceptibility of seed to attack by Megastigmus specularis Walley. Almost 28% more seed were destroyed by these seed chalcids for aphid-infested trees than for uninfested trees.

Observations on the flight periods of aphids in a Sitka spruce plantation in north-eastern Scotland

Abstract: Flight activity of aphids during 1969–71 in a Sitka spruce plantation in north-eastern Scotland was recorded by means of sticky traps. Two flight periods occurred, June–August and September–October. Fewer aphids were caught at 120 and 180 cm than at 60 cm above ground during June–August, while fewer were caught at 60 cm in September–October. After accounting for differences in wind speed at these heights, it was shown that aerial density was consistently higher at 60 cm. The first flight which comprised mostly Elatobium abietinum (Wlk.) was three weeks early in 1971; this was associated with the rapid increase in aphid population on spruce shoots, due to the preceding mild winter. Reinfestation by this species after spraying could follow under similar circumstances. Adelges laricis Vail. and A. viridis (Ratz.) sexuparae were caught in the first flight, and A. cooleyi (Gill.) gallicolae in the second; all galls on Sitka were by gallicolae of A. cooleyi. Aphis fabae Scop, was the most common species in the second flight.

Studies on aphid hyperparasites of japan, 2 - aphid hyperparasites of the pteromalidae occurring in japan (hymenoptera) -

Abstract: KAMIJO, K. & TAKADA, H. 1973. Studies on aphid hyperparasites of Japan, II. Aphid hyperparasites of the Pteromalidae occurring in Japan (Hymenoptera). Ins. matsum. n. s. 2: 39-76, 3 tabs., 31 figs. Eleven aphid-hyperparasitic species of Asaphes Walker (2 spp.), Asaphinae, and Coruna Walker (2 spp.), Pachyneuron Walker (5 spp.) and Euneura Walker (2 spp.), Pteromalinae, occurring in Japan are dealt with. Keys to the genera and to the species, descriptions, illustrations, and biological notes are given on the basis of about 1,300 specimens mainly reared. Host aphid-hyperparasite / primary parasite and primary parasite / host aphid­ hyperparasite lists are added. A. pubescens, C. laevis, P. sapporense and P. doraphis are new spp. and A. suspensus (Nees), C. clavata Walker and E. augarus Walker new to Japan. P. gifuense Ashmead is synonymized with P. aphidis (Bouche), P. umbratum Delucchi with P. mitsukurii Ashmead, and E. laeviuscula Graham with E. nawai (Ashmead), comb. n. (=Pachyneuron nawai). P. mitsukurii is recorded as an aphid hyperparasite for the first time. As hosts of these hyperparasites 50 species of aphids in 32 genera and 34 species of aphidiids in 12 genera are recorded, and 141 different host aphid-primary parasite­ hyperparasite relationships are recognized. Asaphes- and Pachyneuron-species are widely associated with various groups of Aphidoidea and Aphidiidae. Euneura-species are hyper­ parasitic exclusively on aphids of Lachnidae or Pterocomma through aphidiids of Pauesia, Diaeretus or Aphidius cingulatus, while such associations are unknown for Coruna. Habits of Pachyneuron-species, some of which have wide diversity in host and mode of para­ sitism, are discussed. Asaphes and Pachyneuron occur widely in field- to forest-type, Coruna in field- to intermediate-type, and Euneura in forest-type habitats. In any genus each species shows definite preference of habitats.

Effects of Different Foliar-applied Nitrogen Fertilizers on Balsam Woolly Aphid

Abstract: Balsam woolly aphids were reared on young grand fir trees maintained in controlled environment or outdoors. Solutions of various nitrogen fertilizers were applied repeatedly to the trees and the effects on aphids and bark amino acids were studied. On trees fertilized with ammonium nitrate or a sequence of compounds, aphid population growth was less than on trees fertilized with urea or potassium ammonium nitrate. On urea-fertilized trees, populations multiplied 16.5 times in five generations, compared with a 5.7-fold increase on unfertilized trees and a 1.4-fold increase on ammonium nitrate-fertilized trees. These differences resulted from effects of these nutrients on aphid life history. Urea promoted aphid establishment and reproduction, whereas ammonium nitrate affected these processes, as well as survival, adversely. The highest establishment and survival rates resulted from potassium ammonium nitrate.These differences may be related to fertilizer-induced changes in the amino acid diet of the aphid. T...

Control of the Green Peach Aphid and Suppression of Leaf Roll on Potatoes by Systemic Soil Insecticides and Multiple Foliar Sprays

Abstract: Systemic insecticides were applied to the soil on each side of potato seed pieces at planting time and/or were sidedressed into the soil when 75% of the plants emerged, and multiple foliar sprays were applied to obtain seasonal control of Myzus persicae (Sulzer) and the suppression of potato leaf roll virus on ‘Russet Burbank’ potatoes in eastern Washington. Aldicarb gave superior control of aphids and suppressed spread of the virus; disulfoton gave fair control of aphids, but not much suppression of potato leaf roll virus; and phorate did not give sufficient control of aphids or the disease. The 2 applications of the systemic insecticides were more effective than either single application. Endosulfan and oxydemetonmethyl as foliar sprays (2-5 applications) gave better control of aphids than demeton and disulfoton but none significantly suppressed spread of the virus. All applications of systemic insecticides in combination with multiple applications of foliar spray gave significant control of aphids, and most treatments significantly suppressed the spread of disease.

Influence of Alfalfa Resistance on a Pea Aphid Population and Its Associated Parasites, Predators, and Competitors

Abstract: From 1966 through 1969 an investigation was conducted on the influence of alfalfa resistance on populations of Acyrthosiphon pisum (Harris) and their associated parasites, predators, and competitors. One sixth as many pea aphids were found on the Kansas (‘KS 10’) variety than on the ‘Vernal’ alfalfa variety. The number of aphids on ‘DuPuits’ was about 4-fold that on the Kansas variety. The different numbers of pea aphids on the various alfalfa varieties did not affect parasitism rates or predator numbers associated with the high and low aphid numbers on the 3 alfalfa varieties. In the pea aphid, there appears also to be no direct effect of the plant host on parasitism. This finding differed from other studies with various parasite-host systems which showed that the plant host may have a significant effect upon parasitism rates. Of the pea aphid competitors, leafhoppers were most abundant on Vernal but least abundant on DuPuits. However, DuPuits had the largest number of alfalfa weevils, mirids, and other miscellaneous herbivores. No means was evident to predict how resistance to one insect species will influence the pest enemies and associated herbivores.

Effects of infestations by the corn leaf aphid, rhopalosiphum maidis (homoptera: aphididae), on field corn in southwestern ontario

Abstract: The effects of various levels of infestation of the corn leaf aphid, Rhopalosiphum maidis (Fitch), on yield of field corn were examined from 1965 to 1970 inclusive when all plants whose yield might have been influenced by factors other than aphid feeding were excluded from the data. A possible relationship between moisture stress in plants and degree of aphid injury was also investigated.A light infestation (maximum of 400 aphids on the tassel) caused average yield reductions up to 8.3% when plants were under moisture stress, but nil to negligible losses when moisture was adequate. Moderate infestations (many hundreds of aphids on part of the tassel) produced average losses up to 34.8% under drought conditions and up to 11.8% when moisture was abundant. Severe infestations (many hundreds of aphids on most of the tassel) caused average yield reductions ranging from 43.2 to 91.8% when plants were under water stress and up to 58.9% even with abundant moisture. Very severely infested plants (many hundreds on all of the tassel and whorl leaves) were usually barren or had ears with just a few kernels regardless of moisture conditions.Most injury from aphid feeding appeared to occur before and during pollination. No particular combination of temperature and rainfall favored aphid buildup.

Seasonal changes in abundance of the pea aphid and its associated parasites in the southern interior of British Columbia

Abstract: The s tudy e s t i m a t e s t h e r e l a t i v e abundance and d i s t r i b u t i o n of f o u r hymenopterous p a r a s i t e s of t h e pea aph id , Acyrthosiphon piswn, i n sou the rn B r i t i s h Columbia. The f o u r p a r a s i t e s a r e : Aphidius ervi ervi and A. smi th i , which were in t roduced i n t o North America from Europe and I n d i a , r e s p e c t i v e l y , and t h e n a t i v e A . e. pu l ehe r and Praon pequodomun. The e f f e c t i v e n e s s of t h e p a r a s i t e s , i n p a r t i c u l a r t h a t of t h e e x o t i c A. s m i t h i , i n c o n t r o l l i n g t h e pea aphid i s eva lua ted . L i f e t a b l e c h a r a c t e r i s t i c s , such a s t h e developmental and r ep roduc t ive r a t e s , of t h e pea aphid and i t s a s s o c i a t e d p a r a s i t e s were determined under l a b o r a t o r y cond i t i ons . I n t h e f i e l d , pea aphid popu la t i ons i nc reased r a p i d l y du r ing e a r l y a l f a l f a growth, b u t aphid d e n s i t i e s g e n e r a l l y l e v e l l e d o f f and sometimes dec l ined b e f o r e each c rop was c u t . Weather c o n d i t i o n s subsequent t o hay h a r v e s t i n g in f luenced aphid recovery. Mild weather a f t e r t h e f i r s t crop allowed r ap id aphid popula t ion recovery , wh i l e ho t and d r y weather a f t e r t h e second c rop decimated aphid and p a r a s i t e popu la t i ons . The numbers of p a r a s i t i z e d and u n p a r a s i t i z e d aphids su rv iv ing from t h e p rev ious c rop and t h e numbers of immigrant a l a t a e were important f a c t o r s i n determining t h e peak d e n s i t y of aphid popu la t i ons i n a l f a l f a f i e l d s . Aphidi id p a r a s i t e s appeared t o be t h e most impor tan t n a t u r a l enemies of t h e pea aphid i n t h e Kamloops a r e a . Aphidius s m i t h i was t h e numer ica l ly dominant p a r a s i t e under h o t , d r y c l i m a t i c cond i t i ons i n t h e I n t e r i o r of B r i t i s h Columbia, wh i l e A. e. ervi was numer ica l ly dominant under t h e r e l a t i v e l y wet and mild c l i m a t i c cond i t i ons of t h e lower F r a s e r Val ley. A l l p a r a s i t e s p e c i e s showed a d e n s i t y dependent response t o changes i n aphid abundance. On occas ion , t h e d e n s i t y dependent response was masked by t h e e a r l y s p r i n g emergence of p a r a s i t e s from d i apause , by t h e immigr,.;ion of

Changes in growth regulator content of radish seedlings, Raphanus sativus, infested with the aphid Myzus persicae

Abstract: SUMMARY Following 10 days of infestation by the aphid Myzus persicae there was an increase in the amount of growth inhibiting substances and a decrease in cytokinins, gibberellins and auxins in infested as compared with similar uninfested radish seedlings. Even after previously infested seedlings have been freed of aphids for 10 days, differences in the hormone balance remained. The possible relationships between the changes in hormonal balance and the effect of the aphid infestation on growth, translocation and wilting are discussed.

Toxic Effects of Synthetic Juvenile Hormones on Several Aphid Species

Abstract: Nine synthetic juvenile hormone mimics were screened as toxicants against the pea aphid, Acyrthosiphun pisum (Harris), and the raspberry aphid, Amphorophora agathonica (Hottes). First- and second-instar and adult aphids exposed to plant material dipped in 0.1% hormone solutions indicated that certain structures were most toxic to the pea aphid (Hoffman-LaRoche RO 8-4314 and Stauffer R 20458) while others were essentially nontoxic (Hoffman-La Roche RO 20-3600) or almost equitoxic (Zoecon ZR-512) to both species. Feeding eight different aphid species on plant material dipped in 0.1% Zoecon ZR-512 gave a mortality range of 18% for the turnip aphid, Hyadaphis psendobrassicae (Davis), to 73% for the pea aphid. Exposure to lower levels of hormone did not always produce direct toxic results but did yield a wide range of morphological abnormalities and considerably altered reproduction.

A new corn leaf aphid biotype and its effect on some cereal and small grains

Abstract: The reproduction on, and damage to, seedlings of several varieties of sorghum by a strain of Rhopalosiphum maidis (Fitch) reared in the laboratory in Kansas from a single alate collected from sorghum of the variety R.S. 671 near Manhattan in September 1971 was investigated in the laboratory. As the strain proved able to attack varieties previously considered resistant and to reproduce well at high temperatures, it was given the status of a new biotype (KS-5) [cf. RAE/A 51, P.297]

Inundative Releases of Aphidius smithi Against Acyrthosiphon pisum

Abstract: In 1965, 1966, 1967, and 1969, field tests were conducted in the Walla Walla, Washington, area with an estimated 100–300 million cage-reared Aphidius smithi Sharma & Subba Rao (inundative releases) in an effort to control populations of the pea aphid, Acyrthosiphon pisum (Harris) on alfalfa. The objective was to prevent migration of the aphids from their overwintering site in the alfalfa to about 100,000 acres of peas grown for processing. Parasites from 14 pairs of cages effectively controlled pea aphids on 2500 acres of seed alfalfa in 1967, until the area was sprayed for Lygus spp. When parasitic, natural, and chemical control systems were compared in 1967, averages of 13, 56, and 82 aphids/100 sweeps, respectively, were obtained. The population in the field exposed to chemical control oscillated wildly, but the population in the field exposed to parasitic control remained uniformly low. Use of aphid parasites in this manner appears impractical at present because of production and distribution requirements.

Metabolic acclimatization to seasonal changes in temperature in the sycamore aphid, Drepanosiphum platanoides (Schr.), and lime aphid, Eucallipterus tiliae L.

Abstract: Both sycamore and lime aphids live on the leaves of their respective host trees. The sycamore aphid unlike the lime aphid has the ability to adapt metabolically to changes in temperature. The difference in ability of these two tree-dwelling aphids to adapt metabolically to changes in temperature can be related to their mode of life. The sycamore aphid lives on sycamore which is native to the mountainous areas of southern and central Europe where conditions are cool. Sycamore also has a longer growth period than lime as its buds burst earlier and it sheds its leaves later. Sycamore aphids are therefore naturally exposed to a wider range of temperatures than lime aphids.

Spring Populations of the Green Peach Aphid on Peach Trees and the Role of Natural Enemies in Their Control

Abstract: A 2-year study of the spring population of Myzus persicae (Sulzer) on peach trees showed that the number of surviving fundatrices reaching reproductive maturity represented less than 2% of the overwintering eggs. Colonies established from surviving fundatrices protected from natural enemies by slecve cages displayed a tremendous numerical recovery. For example, in a protected environment (cage) the average number of alate aphids per stem mother was 3596 in 1970, and 1080 in 1971. In contrast, on unprotected twigs the natural enemies, primarily coccinellid and syrphid predators, played a major role in reducing the production of alate aphids by an estimated 95% in both years (based on counts of immature aphids).