Maternal reproductive decisions are independent of feeding in the black bean aphid,Aphis fabae

Aphids are phloem feeders and an important assumption has been that reproduction is initiated only after phloem ingestion. Here we investigate the plant tissue location of parturition cues in winged and wingless, summer virginoparae and autumn migrants (gynoparae) of the black bean aphid, Aphis fabae. These seasonal forms have different host preferences. Using electrical penetration graph (EPG: to observe activity of the mouthparts) and video-monitoring procedures we demonstrate that the time to first parturition after host-plant contact is significantly shorter than the time to first registered phloem contact in the summer winged form. In gynoparae, the time to first parturition does not significantly differ from time to first phloem contact but is shorter than time to first phloem ingestion. Times to first parturition, first registered phloem contact and first phloem ingestion do not differ significantly in the summer wingless form. Simultaneous EPG and video recording procedures show that a high proportion of individuals of all morphs (45-70%) initiate reproduction before sustained phloem activities (salivation/ingestion). The only behaviours that all individuals demonstrate before first parturition are ‘non-penetration’ (aphid on plant surface with mouthparts outside plant) and stylet ‘pathway activity’, including secretion of gelling saliva and penetration of the non-vascular (epidermis and mesophyll) cells. A short period of penetration of the peripheral plant tissues (five cell punctures per individual) by aphids tethered and monitored by EPG decreases the time to first parturition of the winged summer form when subsequently placed on a Parafilm sachet containing 15% sucrose solution. This treatment also significantly increases the incidence of reproduction and individual reproductive output of gynoparae over a 24-h period. No detectable effects of tissue penetration on subsequent reproductive output are observed in the wingless summer form. Additionally, EPGs reveal that a number of aphids of all morphs display xylem ingestion, which occurs predominantly before initiation of phloem feeding but is not necessary to initiate parturition. It is concluded that aphids are likely to detect parturition cues during stylet punctures of cells within peripheral tissue layers, before reaching the phloem vessels.     

Chemical aspects of host‐acceptance behaviour in the bird cherry‐oat aphid Rhopalosiphum padi: host‐acceptance signals used by different morphs with the same genotype

Host acceptance by gynoparae and winged virginoparae of the bird cherry‐oat aphid Rhopalosiphum padi (L.) is investigated utilizing leaves and aqueous extracts of the primary and secondary hosts, as well as nonhost plants. Gynoparae are specialized to reproduce on bird cherry Prunus padus L., whereas virginoparae reproduce and feed on various grasses. Host acceptance is assessed using levels of reproduction and survival for adults, as well as survival for nymphs. Little is known of host acceptance by nymphs. The data show that gynoparae and winged virginoparae produce nymphs almost exclusively on their host plants, bird cherry and barley leaves, respectively, over 72 h. When tested with aqueous plant extracts, however, gynoparae produce nymphs almost exclusively on bird cherry extract and progeny numbers are found to be similar to those on plant leaves. Few nymphs are produced on artificial diet. By contrast, winged virginoparae produce nymphs on aqueous extracts of barley, bird cherry and bean, as well as on artificial diet. The numbers of nymphs deposited by gynoparae are similar on aqueous extracts of bird cherry leaves collected at different times during the growing season. When extracts from leaves of various Prunus species are tested, only leaves of P. padus and Prunus virginiana stimulate parturition. Oviparae, the sexual female nymphs of gynoparae, survive well for 96 h on both bird cherry and barley leaves but not on bean seedlings, whereas nymphs of winged virginoparae survive well only on barley leaves. They do not survive for 96 h on any plant‐leaf extracts, although they do survive on artificial diet.     

Electroantennogram and behavioural responses of different forms of the bird cherry-oat aphid,Rhopalosiphum padi,to sex pheromone and a plant volatile

Winged (alate) virginoparae were induced in the laboratory by crowding the bird cherry-oat aphid, Rhopalosiphum padi (L.) under long-day conditions. Males and gynoparae (the winged female form that produces sexual females) were induced by short days. Electroantennogram (EAG) and behavioural responses were investigated in each of the three forms to two aphid sex pheromone components, (-)-(4aS,7S,7aR)-nepetalactol and (+)-(4aS,7S,7aR)-nepetalactone, and benzaldehyde, a volatile which is released by the winter host plant. All three compounds elicited EAG responses with the males showing the highest sensitivity to each compound. Both the nepetalactol and the nepetalactone elicited larger EAG responses in gynoparae than in the winged virginoparae but antennae from virginoparae were more responsive to benzaldehyde. Although the nepetalactone is not a sex pheromone component in R. padi the EAG responses were similar to those evoked by the nepetalactol, the sex pheromone, in all three aphid forms. In a linear-track olfactometer, significantly more male R. padi moved into air containing nepetalactol, nepetalactone or benzaldehyde than into a simultaneous choice of clean air (i.e. attraction) but nepetalactol was more attractive than nepetalactone. Males, however, showed no response to a mixture of nepetalactol and nepetalactone. Gynoparae were attracted only to the nepetalactol but were less sensitive than the males and showed no response to the nepetalactone or benzaldehyde. In contrast, alate virginoparae showed no behavioural responses to any of the compounds. The present study supports the idea that the male R. padi utilise both sex pheromone and benzaldehyde for mate/host-plant location in autumn. It also demonstrates, for the first time, polyphenic differences in the olfactory responses at the peripheral level between the two female forms. Such differences impact on the life-cycle strategy where winged virginoparae move between graminaceous summer host plants while gynoparae move from the summer hosts to the bird cherry, winter host. The latter move appears to be assisted by the sex pheromone released by sexual females, already present on that host, acting as an aggregation pheromone.     

A potent, morph-specific parturition stimulant in the overwintering host plant of the black bean aphid, Aphis fabae

Abstract. The black bean aphid, Aphis fabae Scopoli, has a host‐alternating life cycle. Winged female autumn migrants (gynoparae) develop on numerous summer host plants but as adults will only colonize the winter host (spindle, Euonymus europaeus L.). When stylet activities of gynoparae were electrically recorded during access to a spindle leaf, the insects spent the majority (75%) of the 6‐h experimental period penetrating the plant surface and a large proportion of it (44%) ingesting from either phloem or xylem vessels. Most (95%) gynoparae initiated reproduction on spindle, producing 4.15 ± 0.59 offspring per adult by the end of the experiment (mean ± SEM). By contrast, gynoparae placed on a seedling of their natal, summer host (broad bean, Vicia faba L.) penetrated the plant for only 39% of the available time, rarely ingested plant sap and never reproduced. The number of nymphs deposited on spindle leaves was not correlated with the occurrence or duration of ingestion from vascular tissues, suggesting that parturition stimulants are detected before feeding, probably during penetration of nonvascular cells. Presentation of an aqueous spindle extract to the aphids in artificial feeding chambers showed that water‐soluble spindle factors evoke stimulation of parturition by gynoparae in 72‐h bioassays. The stimulant was extremely potent, remaining active until the total extracted material was diluted to less than 10 p.p.m. Stylet activities and reproductive responses were also evaluated for summer winged females (alate virginoparae), which have a broad host range, and will colonize both bean and spindle under laboratory conditions. On both of these plant species, virginoparae often ingested plant sap and deposited nymphs during the 6‐h electrical recording experiment (producing 4.60 ± 0.48 offspring on bean; 2.70 ± 0.35 on spindle: mean ± SEM), but no significant correlations were found between reproduction and the occurrence or duration of particular stylet activities. Aqueous host‐plant extracts had no effect on the numbers of offspring deposited by virginoparae in artificial feeding chambers, showing that this form of the aphid is not responsive to the spindle‐derived parturition stimulant. The results highlight the need for more information on the factors determining host acceptance and parturition by polyphagous aphid phenotypes.     

Reproduction and probing behaviour of the bird cherry‐oat aphid Rhopalosiphum padi on detached leaves and leaves on intact seedlings of the winter host,bird cherry Prunus padus

Video recording and electrical penetration graph techniques are used simultaneously to investigate host acceptance (in terms of reproduction) and probing activities of autumn migrants (gynoparae) of the bird cherry‐oat aphid Rhopalosiphum padi (L.) on detached leaves and on leaves on intact plants of the winter host, bird cherry Prunus padus. There are no significant differences between the times taken to first parturition or the number of nymphs produced over a 6‐ or 18‐h period on intact plants or detached leaves. Stylet probing activities (i.e. total probe duration, xylem ingestion, the time to first phloem contact and phloem salivation) are also similar in the two situations.     

Behavioural differences during host selection between alate virginoparae of generalist and tobacco-specialist Myzus persicae

Host plant selection and acceptance by aphids involves four consecutive steps: (1) prealighting behaviour, (2) leaf surface exploration and probing of subepidermal tissues, (3) deep probing of plant tissues, and (4) evaluation of the phloem sap. Host specialisation in aphids may involve not only different performances on potential hosts, but also different strategies for host selection and acceptance. Myzus persicae s.s. (Sulzer) (Homoptera: Aphididae) is one of the most polyphagous aphid species, although a tobacco‐adapted subspecies, M. persicae nicotianae, has been described. These two taxa constitute a good system for studying the effect of host range on host selection strategies. We studied the first two steps in the host selection process by alate virginoparae of M. persicae s.s. and M. persicae nicotianae on host and non‐host plants, using three types of behavioural assays: wind tunnel, olfactometry, and video‐recording. Alate virginoparae of M. persicae nicotianae recognised and chose their host plant more efficiently than M. persicae s.s., on the basis of olfactory and visual cues, and factors residing at cuticular and subcuticular levels. Host recognition was evident before phloem tissues were contacted. Olfactory cues were apparently not involved in host selection by M. persicae s.s.     

Host-selection behaviour by genetically identical aphids with different plant preferences

The behaviour of summer and autumn winged forms of the black bean aphid, Aphis fabae Scopoli (Homoptera: Aphididae), was compared on two plants utilized at different stages of the insect’s life cycle. Adult autumn migrants (gynoparae) are monophagous, colonizing spindle (Euonymus europaeus), whereas polyphagous summer winged aphids (alate virginoparae) are associated with a variety of herbaceous plants, including broad bean (Vicia faba). When aphids from a single clone were given access to a spindle leaf and a bean seedling in choice tests, many virginoparae settled and larviposited on both plant species over 24 h. By contrast, gynoparae showed a clear preference for spindle, with 93.5% of settled adults and 98.3% of larvae on this plant species. Close‐up video monitoring showed that gynoparae discriminated beans from spindle within a 5‐min period, whereas virginoparae behaved similarly on both plant species. For gynoparae, the major behavioural difference on the two plants appeared after a brief (epidermal) stylet penetration, with many insects taking flight within a few seconds of stylet withdrawal from bean. Factors detected during stylet insertion by gynoparae must therefore inhibit take‐off on spindle. Electrical recording experiments showed that aphids often punctured a cell membrane during brief probes on both plant species, and intracellular stylet activities always included a waveform associated with ingestion. When gynoparae puncture spindle cells their behaviour is probably modified by intracellular metabolites detected via gustation of ingested epidermal cell sap. These cues may inhibit the take‐off reflex which otherwise follows probing.     

Induced resistance by Myzus persicae in the peach cultivar `Rubira'

The effect of a previous infestation by the green peach aphid Myzus persicae (Sulzer) on the settling behaviour and reproduction of the same aphid species was investigated in the resistant peach cultivar Rubira, and compared with that observed in the susceptible control cultivar GF305. A previous infestation of 48 h triggered induced resistance in Rubira. There were significantly fewer aphids settling on preinfested than on uninfested plants, indicating an increased rejection of Rubira as a host plant. The level of induced resistance in preinfested plants was positively related to the duration of the first infestation. In GF305, previous infestation had no detrimental effect on aphid settlement and even slightly enhanced larviposition by adult females. The aphid probing behaviour after a 48-h preinfestation was also monitored for 8 h with the electrical peneration graph (EPG) technique. On preinfested GF305, most EPG parameters indicated an enhanced host plant acceptance. On preinfested GF305, aphids produced less sieve element salivation and more continuous sap ingestion than on uninfested GF305, indicating that the previous aphids provoked changes in plant properties beneficial to the test aphids. In Rubira, a major induced factor of resistance was thought to be expressed in the sieve element as phloem sap ingestion was 4-fold shorter on preinfested than on uninfested plants. The time taken by the aphid stylets to reach a sieve element was also significantly increased on preinfested Rubira, suggesting the induction of resistance factors outside the phloem. The originality of the Rubira/M. persicae interaction is discussed in the perspective of a better understanding of plant induced responses to aphids.     

The role of sinigrin in host plant recognition by aphids during initial plant penetration

Plant penetration behaviour (probing) of the cabbage aphid, Brevicoryne brassicae, and the pea aphid, Acyrthosiphon pisum, was studied on excised leaves of broad beans, Vicia faba, kept in water or in a 1% aqueous solution of sinigrin. Using the DC EPG (Electrical Penetration Graph) technique it was shown that the cabbage aphid on sinigrin-untreated bean leaves showed numerous short probes into epidermis and mesophyll. None of these aphids showed either phloem salivation or ingestion waveforms on untreated leaves. In contrast, on sinigrin-treated bean leaves, 35% of the probing time was spent on phloem sap ingestion (E2) and almost all aphids reached phloem vessels and started feeding. The duration of phloem salivation before phloem ingestion and the mean duration of phloem ingestion periods were similar on a host and a sinigrin-treated non-host plant. However, the total probing time by B. brassicae was 10% longer, the total phloem sap ingestion time was twice as long, and the time to the first phloem phase within a probe was three times shorter on the host plant compared to sinigrin-treated broad beans. Acyrthosiphon pisum also responded to the addition of sinigrin to broad beans, but in this case sinigrin acted as a deterrent. On sinigrin-treated leaves, A. pisum terminated probes before ingestion from phloem vessels, and none of these aphids showed phloem salivation and ingestion on treated leaves. Glucosinolates were detected in the mesophyll cells of the brassicaceous plant, Sinapis alba. Based on this finding and in addition to the foregoing EPG analysis of aphid probing on these plants and broad beans, our hypothesis is that aphids may recognise their host plants as soon as they probe the mesophyll tissue and before they start ingestion from phloem vessels.     

Behavior of bird cherry-oat aphid and green peach aphid in relation to potato virus Y transmission

Potato virus Y is transmitted to potato in a nonpersistent manner by many aphid species, some of which do not colonize this crop. The behavior of bird cherry-oat aphid, Rhopalosiphum padi (L.) on potato, Solanum tuberosum L., a plant species that is not colonized by this aphid, was described and compared with that of the potato-colonizing green peach aphid, Myzuspersicae (Sulzer). A higher proportion of winged morph of R. padi than M. persicae left the plant, but aphids that stayed in contact with the plant took the same mean time to initiate the first probe and it lasted the same mean time compared with M. persicae. Electronic penetration graph technique was used to study the probing behavior of the aphids during Potato virus Y (family Potyviridae, genus Potyvirus, PVY) transmission tests. Transmission rate decreased from 29 to 8% when the acquisition time increased from 5 min of continuous probing to 1 h with M. persicae, but it remained low (2 and 1%) with R. padi. Most of the difference in transmission rate between acquisition time with M. persicae and between aphid species was related to the change in the time and behavior taking place between the last cell puncture of the acquisition phase to the first cell puncture of the inoculation phase. Results presented here clearly demonstrated the importance of host plant selection and probing behavior in the transmission of nonpersistent plant viruses. They also stress the need to consider the behavior of the aphid in the design of laboratory tests of virus vector efficacy.     

Probing behavior of bird cherry-oat aphid Rhopalosiphum padi (L.) on native bird cherry Prunus padus L. and alien invasive black cherry Prunus serotina Erhr. in Europe and the role of cyanogenic glycosides

The probing behavior of bird cherry-oat aphid Rhopalosiphum padi was studied on its natural winter host in Europe, the bird cherry Prunus padus, and on the invasive black cherry Prunus serotina, on which spring generations of R. padi do not survive. The EPG-recorded behavior of R. padi on bird cherry and black cherry showed differences in crucial aspects of probing and feeding. The period of the pre-phloem penetration was twice as long and rarely interrupted in aphids on bird cherry as opposed to aphids on black cherry. On black cherry, there was a considerable delay between finding and accepting the phloem. Aphids that had sampled phloem sap either refused to ingest it or the ingestion periods were very short. Amygdalin and prunasin (cyanogenic glycosides present in leaves of Prunus) seriously impeded ingestion activities when applied in pure sucrose diet. The role of amygdalin and prunasin in winter host plant selection and host alternation in R. padi is discussed.     

Migratory and targeted flight in seasonal forms of the black bean aphid, Aphis fabae

ABSTRACT. Adult winged forms of Aphis fabae Scop., the spring migrants (fundatrigeniae; alate virginoparae), the summer migrants (alate virginoparae) and the autumn migrants (gynoparae), were flown in an automated vertical wind tunnel, with a small green target presented every 60 s. On average, targeted flight developed in the spring and summer migrants after 19 and 15 min, respectively. However, in autumn migrants targeted flight occurred after 184 min of flight. No evidence of target approach was found up to 30 min prior to this time, although some movement towards the target was observed in the 30 min before the first response of autumn migrants, suggesting that a gradual change from migratory to targeted flight occurred. No correlation was found between aphid weight and the time to first response for spring or summer migrants, but a positive correlation was found for autumn migrants. Flight patterns of autumn migrants, in the absence of a target, are described and compared with flight patterns previously reported for summer migrants.     

Differential regulations of wing and ovarian development and heterochronic changes of embryogenesis between morphs in wing polyphenism of the vetch aphid

SUMMARY In wing polyphenisms that produced alternative wing morphs depending on environmental conditions, the developmental regulations to balance between flight and reproductive abilities should be important. Many species of aphids exhibit wing polyphenisms, and the development of wing and flight muscles is thought to incur costs of reproductive ability. To evaluate the relationship between flight and reproduction, the fecundity and the wing- and ovarian development in the parthenogenetic generations were compared between winged and wingless aphids in the vetch aphid Megoura crassicauda . Although no differences in offspring number and size were detected, the onset of larviposition after imaginal molt was delayed in winged adults. The comparison of growth in flight apparatus revealed that, after the second-instar nymphs, the flight-apparatus primordia of presumptive wingless aphids were degenerated while those of winged nymphs rapidly developed. In the ovaries of winged line, the embryo size was smaller and the embryonic stages were delayed from third to fifth instars, although these differences had disappeared by the time of larviposition. It is therefore likely that the delay in larviposition in winged aphids is due to the slower embryonic development. The correlation between embryo size and developmental stage suggests that the embryos of winged aphids are better developed than similarly sized embryos in wingless aphids. These heterochronic shifts would facilitate the rapid onset of larviposition after the dispersal flight. This developmental regulation of embryogenesis in the aphid wing polyphenism is suggested to be an adaptation that compensates the delay of reproduction caused by the wing development.     

Development of the aphid parasitoid,Aphidius ervi, in asexual and sexual females of the pea aphid,Acyrthosiphon pisum, and the blackberry-cereal aphid,Sitobion fragariae

The aphid parasitoid,Aphidius ervi Haliday, overwinters in larval diapause. The possibility that the parasitoid might prefer sexual (oviparae) rather than asexual females (virginoparae) as overwintering hosts (oviparae predominate in autumn when host numbers are generally declining) was tested by comparing these aphid morphs as potential hosts. Two host species were also examined, the pea aphid,Acyrthosiphon pisum (Harris), and the blackberry aphid,Sitobion fragariae (Walker). The parasitoids took longer to develop inS. fragariae than inA. pisum but the development of non-diapausingA. ervi was similar in sexual and asexual females. This observation, together with the greater variation in the duration of the different parasitoid stadia inS. fragariae, indicated that the parasitoid is specialized on the pea aphid. In photophases of 12 h and longer, the proportion ofA. ervi entering diapause inA. pisum oviparae was higher than in virginoparae. The critical daylength (where 50% of parasitoids entered diapause) was therefore longer in oviparae (12.6 h) than in virginoparae (11.7 h) with the inference that parasitoids developing in the oviparae would enter diapause earlier in the field. InS. fragariae, critical day-lengths were similar in both aphid morphs. The duration of diapause was unaffected by host morph and emergence in short days (10:14 L:D) occurred over a long period (c. 60 days).     

Decision making by generalist and specialist aphids with the same genotype

One idea to explain the high incidence of specialisation in phytophagous insects is that their nervous systems are simple and unable to efficiently recognise multiple host plants. Here this 'neural limitations' hypothesis is tested using a generalist (the summer winged virginopara) and specialist (the autumn gynopara) morph of a single clone of the black bean aphid, Aphis fabae, that are almost identical morphologically and have the same genotype. Electrical monitoring of stylet behaviour and non-invasive behavioural observations are used to compare initial plant recognition, first reproduction, 'first registered phloem contact' and 'phloem acceptance' of the generalist and specialist on their specific host plants (generalist--herbaceous hosts, Beta vulgaris, Papaver dubium, Rumex obtusifolius, Vicia faba; specialist--woody host, Euonymus europaeus) and on the same host (E. europaeus). Additional analyses of behaviour over the first few minutes of plant contact are carried out for three mutual non-host plants: Euonymus alatus, Prunus padus and Brassica pekinensis. Few examples are found where the host-selection behaviour of the specialist on its host plant is more efficient than the generalist across its hosts and there is little difference in the behaviour of the different forms on the same host. Indeed there are several instances where the generalist is behaviourally more efficient than the specialist. These include absolute time to first reproduction by the generalist on various herbaceous hosts and the same host, E. europaeus, absolute time to first registered phloem contact by the generalist on P. dubium, and incidence of phloem acceptance by the generalist on several of its herbaceous hosts. Rejection of non-hosts is carried out more efficiently by the specialist gynopara on P. padus and B. pekinensis but not on E. alatus. For generalist and specialist morphs of the same A. fabae genotype, therefore, broad host range does not appear to be associated with a reduced ability to make plant-use decisions.     

Xylem ingestion by winged aphids

When aphids and their host plant are incorporated in a DC electrical circuit, phloem and xylem ingestion register as separate waveforms of the electrical penetration graph (EPG) signal. Aphids are primarily phloem feeders; xylem ingestion is seldom reported but can be induced experimentally by fasting the insects in desiccating conditions. In experiments with the black bean aphid, Aphis fabae Scop., young winged (alate) and unwinged (apterous) virginoparous adults were collected from their natal host plants (broad bean, Vicia faba L.) and allowed 3-h continuous EPG-recorded access to V. faba seedlings. Several aphids (47% of both morphs) showed ingestion from phloem sieve elements. Alate aphids also showed frequent xylem ingestion (60% of individuals), but no apterous aphids exhibited this activity. The EPG technique involves attachment of a fine gold wire electrode to each insect, a process that may affect normal behaviour at the plant surface. However, when the technique was modified to monitor the stylet activities of freely-settled aphids, high levels of xylem ingestion by alates were also recorded. The results suggest that the developmental physiology of winged aphids somehow predisposes them to xylem ingestion, possibly as a result of dehydration during the teneral period. Alate aphids may reduce their weight by fasting before take-off, giving aerodynamic benefits, but making rehydration, via xylem uptake, a priority following plant contact.     

The role of grasslands in the yearly life-cycle of Rhopalosiphum padi (Homoptera: Aphididae) in Sweden.

The population density of the bird cherry-oat aphid (Rhopalosiphum padi) was monitored in spring sown barley and in grasslands (leys and pastures) and a suction trap was used to monitor the flight periodicity of the aphids. Emigrants from the primary host (bird cherry) colonised both grass and cereals in spring and a migration from cereals to grasses took place in mid-summer. There was a negative correlation between the sizes of summer and autumn migration. There was a positive relationship between late summer growth in leys and the size of autumn migrations. It is concluded that the size of the autumn migration is mainly dependent on aphid population growth in grasslands during late summer and autumn.     

Lipid composition in long-day and short-day forms of the black bean aphid,Aphis fabae

Long-day reared winged (alate) virginoparae from laboratory stock cultures which had been reared throughout larval development on bean stipules were significantly smaller (0.46+/-0.02 mg; mean+/-SEM) than short-day-reared gynoparae (0.69+/-0.04 mg; the winged autumn migrant) which completed development on intact beans. When winged virginoparae were raised from the third stadium on bean seedlings they grew larger (0.86+/-0.02 mg) but the gynoparae contained proportionally more total lipid (12.1+/-0.4%, gynoparae; 7.4+/-0.6%, stipule-reared virginoparae; 9.2+/-0.8%, seedling-reared virginoparae). Wingless aphids (apterae) were heavier, whether reared in short (0.99+/-0.03 mg) or long days (0.95+/-0.04 mg) but the lipid content was low (4.5+/-0.7% and 4.9+/-0.6%, respectively). The triacyl-, diacylglycerol and the phospholipid contents followed this trend but analysis of the fatty acid moieties of the triacylglycerides showed phenotypic differences. The ratios of myristic acid:palmitic acid were significantly higher in the winged forms than the wingless forms and were much higher in the gynoparae than the winged virginoparae. Short-day-reared wingless females also had a higher myristic acid:palmitic acid ratio than long-day-reared apterae, possibly reflecting the embryonic gynoparae maturing in their ovaries.     

DIFFERENCE IN PROBING BEHAVIOUR OF TEA APHID ON VEGETATIVE PARTS OF TEA PLANT AND NON‐HOST PLANTS*

Abstract Electrical penetration graph (EPG) investigation showed that the secreting (El) and sucking (E2) times of tea aphid stylet in tea phloem were much longer than that on non‐host plants such as soybean and wheat. However, non‐feeding wave (np) was shorter than that on soybean and wheat. Duration of both El and E2 of stylet in tea phloem of 1st leaf, bud, 4th leaf and tender stem occupied 30.2%, 22.3%, 9.2% and 8.2% of the total experimental time, respectively. E2 wave was accompanied by honeydew secretion, with a time lag. Tea aphid preferred the tender parts, in which amino acids and other nutritional components were very rich. While the stylet of hungry tea aphid was forced to pierce phlom of non‐host plant (soybean or wheat), El and E2 waves were also produced, but the action of stylet could be disrupted by tea shoot volatile (10–6 V/V linalool, etc.) emitted near to the antennae. It was considered that before and under probing tea aphid made use of olfactory clues.     

A morphological study on autumnal morphs of Aphis glycines (Hemiptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is one of the most important pests of soybean. The complex life cycle of A. glycines is characterized as heteroecious and holocyclic, and has seasonal polymorphisms occurring during its life cycle. In the autumn, A. glycines occur as winged and wingless virginoparae in soybeans, as gynoparae and males that migrate from soybeans to Rhamnus spp. and as gynoparae, males and oviparae on Rhamnus spp. In this study, wingless virginoparae, gynoparae, males and oviparae of A. glycines were successfully induced in the laboratory and morphological parameters of these morphs were selected for quantitation. To aid in identification of these A. glycines autumnal morphs, these aphids were imaged by microscope and significant differences in morphological characteristics were found: distal parts of hind leg femurs of gynoparae were grayish black, which were darker than those of winged virginoparae; the 4th instars of gynoparae, males and winged virginoparae differ greatly in dorsal abdomen coloration and covering. Our results provide an important guide for distinguishing adults of gynoparae and winged virginoparae, and for identifying nymphs of gynoparae, males and winged virginoparae.