Megoura Viciae Buckton Research Articles

Determining the effects of life stage, shared prey density and host plant on intraguild predation of a native lacewing (Chrysoperla carnea) by an invasive coccinellid (Harmonia axyridis)

Negative impacts of non-native Harmonia axyridis (Pallas) on members of the native aphid enemy guild have been widely hypothesised but mainly only assessed with other coccinellid species, and mostly in small experimental arenas. Here we investigated the interactions between H. axyridis and Chrysoperla carnea Stephens larvae. In small-scale (Petri dish) arenas 2nd-instar C. carnea were at risk of predation from larval (2nd and 4th-instar) and adult (male and female) H. axyridis while 3rd-instar C. carnea were only at minimal risk from 4th-instar and adult female H. axyridis. Plant species, aphid species and aphid density did not affect intraguild predation of 2nd-instar C. carnea by 4th-instar and adult H. axyridis in mesocosm experiments. Chrysoperla carnea consumed similar numbers of Megoura viciae Buckton, Aphis fabae Scop. and Acyrthosiphon pisum Harris aphids while H. axyridis consumed fewer M. viciae than the other two species. The greatest suppression of A. pisum was achieved in treatments with both C. carnea and H. axyridis. Life stage and the sex of H. axyridis as well as the life stage of C. carnea are important variables affecting intraguild predation and these attributes should be considered when assessing the potential threat of other potentially invasive alien predators.

The influence of different aphid prey species on the biology and life table parameters of Propylaea japonica

The influence of three aphid prey species – Aphis craccivora Koch, Megoura viciae Buckton and Rhopalosiphum maidis (Fitch) – on the biology of Propylaea japonica (Thunberg) was studied under laboratory conditions. The development, survivorship, longevity, reproduction and life table parameters of P. japonica differed significantly among different treatments. The shortest developmental period of P. japonica (from first-instar larvae to adult) was observed on A. craccivora, whereas the longest was observed on M. viciae. The highest survivorship was observed on A. craccivora, and the lowest survivorship was observed on M. viciae. The highest sex ratio, fecundity and the shortest pre-oviposition period were observed when A. craccivora was used as prey. The longevities of P. japonica females and males did not differ significantly when reared on different aphid species. The highest values of net reproductive rate, intrinsic rate of increase and finite rate of increase were observed on A. craccivora. The results suggest that A. craccivora is a suitable prey for P. japonica among the three aphid species tested and can serve as a diet for the mass rearing of P. japonica under laboratory conditions for possible use in integrated pest management.

Honeydew volatile emission acts as a kairomonal message for the Asian lady beetle Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract The Asian lady beetle Harmonia axyridis Pallas is considered as an invasive species in most territories where it has been introduced. Because aphid honeydew acts as an attractant for many aphid predators and parasitoids, the objectives of this work were to collect and identify the volatile compounds released from the aphid excretory product to evaluate how these semiochemicals could affect the H. axyridis foraging behavior. Twelve volatile chemicals were identified from the Megoura viciae Buckton honeydew including four alcohols, three ketones, three aldehydes, a pyrazine and a monoterpene. The volatiles 3‐methyl‐1‐butanol and 3‐methyl‐butanal were highlighted as the two most abundant semiochemicals released from the M. viciae honeydew. Vicia faba L. plants treated with crude honeydew attracted more than 80% of the tested individuals with 40% of attracted beetles located on the plant. Four volatile compounds (3‐hydroxy‐2‐butanone, 3‐methyl‐butanal, 3‐methyl‐1‐butanol and limonene) were also highlighted to attract more than 75% of the coccinellids toward the odor source and to locate about 35% of them on the plants. Limonene was the most efficient attractant since 89% of the H. axyridis responded to this odor. The use of the identified semiochemicals as well as the composition of an artificial honeydew could certainly be helpful to control the dispersal of the Asian lady beetle H. axyridis.

Aphid-host plant interactions: does aphid honeydew exactly reflect the host plant amino acid composition?

Plants provide aphids with unbalanced and low concentrations of amino acids. Likely, intracellular symbionts improve the aphid nutrition by participating to the synthesis of essential amino acids. To compare the aphid amino acid uptakes from the host plant and the aphids amino acid excretion into the honeydew, host plant exudates (phloem + xylem) from infested and uninfested Vicia faba L. plants were compared to the honeydew produced by two aphid species (Acyrthosiphon pisum Harris and Megoura viciae Buckton) feeding on V. faba. Our results show that an aphid infestation modifies the amino acid composition of the infested broad bean plant since the global concentration of amino acids significantly increased in the host plant in response to aphid infestations. Specifically, the concentrations of the two amino acids glutamine and asparagine were strongly enhanced. The amino acid profiles from honeydews were similar for the two aphid species, but the concentrations found in the honeydews were generally lower than those measured in the exudates of infested plants (aphids uptakes). This work also highlights that aphids take large amounts of amino acids from the host plant, especially glutamine and asparagine, which are converted into glutamic and aspartic acids but also into other essential amino acids. The amino acid profiles differed between the host plant exudates and the aphid excretion product. Finally, this study highlights that the pea aphid, a “specialist” for the V. faba host plant, induced more important modifications into the host plant amino acid composition than the “generalist” aphid M. viciae.

Occurrence of nitric oxide synthase in Megoura viciae Buckton(Homoptera, Aphididae): an histochemical and immunohistochemical localisation

Nitric oxide (NO) is known to be involved in many physiological reactions of insects. We analysed NOS localisation in aphids of the species Megoura viciae by means of histochemical reaction for the NADPH-diaphorase activity and immunohistochemical methods for uNOS, nNOS and iNOS. The obtained data provided a complex and peculiar pattern of NOS distribution in cells and tissue of M. viciae. The histochemical reaction for NADPH-diaphorase was an indicative, but not exact marker of NOS localisation in aphids. The use of anti uNOS antiserum (frequently applied in insects) was of limited value in our specimens, whereas more satisfactory results were obtained with anti nNOS and iNOS antisera of human origin. The results of Western blot analysis confirmed the immunohistochemical ones, showing an aphid protein that reacted strongly with the polyclonal antibody anti-iNOS and anti-nNOS while a similar protein band was weakly immunoreactive with the polyclonal antibody anti-uNOS. Our results suggest that NO, prevalently synthesised by calcium/calmodulin-dependent isoform, plays important physiological roles both in adult and embryological stages of aphids. The data of principal interest was NOS presence in bacteriocytes, cells that host symbiotic prokaryotes belonging to the species Buchnera aphidicola, and in nuclei of adipocytes and gut cells.

The influence of natural enemies on wing induction in Aphis fabae and Megoura viciae (Hemiptera: Aphididae)

Previous studies have shown that the aphid species, Aphis fabae Scopoli and Megoura viciae Buckton, do not produce winged offspring in the presence of natural enemies, in contrast to results for the pea aphid (Acyrthosiphon pisum (Harris)) and the cotton aphid (Aphis gossypii Glover); but these studies did not involve exposing aphids directly to natural enemies. We exposed colonies of both A. fabae and M. viciae to foraging lacewing (Chrysoperla carnea (Stephens)) larvae and found that the predators did not induce winged morphs among offspring compared to unexposed controls. Colonies of A. fabae responded to an increase in aphid density with increasing winged morph production, while such response was not found for M. viciae. We suggest that different aphid species differ in their susceptibility to natural enemy attack, as well as in their sensitivity to contact.

Predatory hoverflies select their oviposition site according to aphid host plant and aphid species

AbstractThe hoverfly Episyrphus balteatus De Geer (Diptera: Syrphidae) is an abundant and efficient aphid‐specific predator. Several aphidophagous parasitoids and predators are known to respond positively to aphid‐infested plants. Semiochemicals from the latter association usually mediate predator/parasitoid foraging behavior toward sites appropriate for offspring fitness. In this study, we investigated the effect of aphid host plant and aphid species on foraging and oviposition behavior of E. balteatus. Behavioral observations were conducted using the Noldus Observer v. 5.0, which allows observed insect behavior to be subdivided into different stages. Additionally, the influence of aphid species and aphid host plant on offspring fitness was tested in a second set of experiments. Acyrthosiphon pisum Harris and Megoura viciae Buckton were equally attractive for E. balteatus whereas Aphis fabae Scopoli (all Homoptera: Aphididae) were less attractive. These results were correlated with (i) the number of eggs laid, which was significantly higher for the two first aphid species, and (ii) the fitness of hoverfly larvae, pupae, and adults. Two solanaceous plant species, Solanum nigrum L. and Solanum tuberosum L. (Solanaceae), which were infested with Myzus persicae Sulzer (Homoptera: Aphididae), were also compared using the same approach. Discrimination between these two M. persicae host plants was observed, with S. tuberosum being preferred as an oviposition site by the predatory hoverfly. Larval and adult fitness was correlated with the behavioral observations. Our results demonstrated the importance of the prey–host plant association on the choice of the oviposition site by an aphid predator, which is here shown to be related to offspring fitness.

Competition and dispersal in the pea aphid: clonal variation and correlations across traits

Abstract. 1. The presence of an across‐species trade‐off between dispersal ability and competitive ability has been proposed as a mechanism that facilitates coexistence. It is not clear if a similar trade‐off exists within species. Such a trade‐off would constrain the evolution of either trait and, given appropriate selection pressures, promote local adaptation in these traits.2. This study found substantial levels of heritable variation in competitive ability of the pea aphid, Acyrthosiphon pisum Harris (Homoptera: Aphididae), measured in terms of relative survival when reared with a single clone of the vetch aphid, Megoura viciae Buckton (Homoptera: Aphididae).3. Pea aphids can move to new patches by either flying (longer distance dispersal) or walking (local dispersal) from plant to plant. There was considerable clonal variation in dispersal ability, measured in terms of the proportion of winged offspring produced, and ability to survive away from their host plant.4. Winged individuals showed longer off‐plant survival times than wingless forms of the same pea aphid clone.5. There was no evidence of a relationship between clonal competitive ability and either measure of dispersal ability, although the power of the test is limited by the number of pea aphid clones used in the trial.6. However, there was a positive correlation between clonal fecundity and the proportion of winged offspring produced. Although speculative, it is suggested that clones that are more likely to either overwhelm their host plant or attract higher numbers of natural enemies as a result of having higher fecundity are more likely to produce winged morphs.

Effect of Aphis gossypii Glover, Brevicoryne brassicae (L.), and Megoura viciae Buckton (Hemiptera: Aphidoidea) on the development of the predator Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

Abstract Laboratory experiments were carried out to evaluate the influence of the aphids Aphis gossypii Glover, Brevicoryne brassicae (L.), and Megoura viciae Buckton on the development of the coccinellid Harmonia axyridis (Pallas). Adult H. axyridis consumed significantly more individuals of the smallest aphid, A. gossypii, than the two larger species, and females consumed twice as many of all three prey species as males. On the other hand, when aphid size (relative weights) was taken into account, it is likely that a greater weight of M. viciae was consumed. H. axyridis did not complete its development when fed exclusively on either B. brassicae or M. viciae, but when fed on A. gossypii, reproduction started about 8 days after emergence from the pupal stage. The 1st-instar larval stage was also shortest when fed on A. gossypii (1.8 days), but took 3.5 days and 4.7 days when fed on M. viciae and B. brassicae, respectively. In addition, larvae fed on A. gossypii were larger and heavier than those fed on the other two aphid species. When larvae were fed exclusively on M. viciae, all but one failed to reach the 3rd instar. However, when fed on A. gossypii during the 1st instar and then on M. viciae in subsequent instars, larval H. axyridis completed their development. It was concluded that M. viciae was either toxic to the 1st-instar larvae of H. axyridis or was an unsuitable host for their development.

Responses of the aphids Phorodon humuli and Rhopalosiphum padi to sex pheromone stereochemistry in the field.

Gynoparous female and male damson-hop aphids, Phorodon humuli (Schrank), were caught in the field by water traps that were releasing the sex pheromone of this species, (1RS,4aR,7S,7aS)-nepetalactol. No behavioral activity was elicited by (4aS,7S,7aR)-nepetalactone, the major sex pheromone component of other aphid species such as Megoura viciae Buckton, even though olfactory cells were found in the secondary rhinaria on the third antennal segment of P. humuli that responded strongly to this compound. Gynoparous female P. humuli in the field responded less strongly to (1R,4aS,7S,7aR)-nepetalactol, the sex pheromone of the bird cherry-oat aphid, Rhopalosiphum padi (L.), than they did to the (4aR,7S,7aS)-nepetalactols, but males responded only to the latter. The (4aR,7S,7aS)-nepetalactone showed no electrophysiological activity so was not used in field trials. Releasing either the (4aS,7S,7aR)-nepetalactone or the (1R,4aS,7S,7aR)-nepetalactol with the (4aR,7S,7aS)-nepetalactols did not inhibit the response of P. humuli gynoparous females and males to the latter. Males of R. padi responded as strongly to the (4aR,7S,7aS)-nepetalactols as they did to (1R,4aS,7S,7aR)-nepetalactol. Males of P. humuli and R. padi responded positively to an increased concentration of the (4aR,7S,7aS)-nepetalactols released from two vials compared with that from a single vial, as did P. humuli (in one of two experiments) and R. padi to the (1RS,4aR,7S,7aS)- and (1R,4aS,7S,7aR)-nepetalactols when released together.

Strawberry crinkle virus, a Cytorhabdovirus needing more attention from virologists

Summary Taxonomic relationship: A member of nonsegmented, negative-sense, single-stranded RNA viruses of the genus Cytorhabdovirus (type member: Lettuce necrotic yellows virus), family Rhabdoviridae, order Mononegavirales. Members of the family Rhabdoviridae can infect vertebrates, invertebrates and plants. Physical properties: Virions are bacilliform, 74-88 nm in diameter and 163-383 nm in length with surface projections probably composed of trimers of the glycoprotein G, occurring in the cytoplasm in either the coated or the uncoated form (Fig. 1). The nucleocapsid is enclosed in a host-derived envelope. Within the virion, the SCV genome consists of a single negative-sense single-stranded RNA molecule of approximately 13 kb. Viral proteins: The SCV genome encodes at least five proteins: the nucleocapsid (N) protein (45 kDa), the matrix (M) protein (77 kDa), the nonstructural protein [Ns, 55 kDa, also known as phosphoprotein (P)], the glycoprotein (G, 23 kDa) and the large (L) protein. Hosts: The natural host range of SCV is limited to species of the genus Fragaria L. Experimental hosts include Physalis pubescens L., P. floridana Rydb., Nicotiana occidentalis, N. glutinosa L. and N. clevelandi Gray. SCV also replicates in its insect vectors Chaetosiphon fragaefolii Cockerell and C. jacobi Hille Ris Lamberts. When injected as purified virus, SCV replicates in aphids Hyperomyzus lactucae (L.), Macrosiphon euphorbiae Thomas, Myzus ornatus Laing, Megoura viciae Buckton, and Acyrthosiphoa pisum (Harris).

The effect of temperature on the photoperiodic ‘clock’ and ‘counter’ of a Scottish clone of the vetch aphid, Megoura viciae

Photoperiodic response curves were determined for a Scottish clone of the vetch aphid, Megoura viciae Buckton, at three temperatures: 12.5, 15, and 17.5°C. Critical night lengths (CNLs) for ovipara (sexual female) induction were 6 h, 7 h and 8 h, respectively. High incidences of ovipara production were observed in all night lengths longer than the CNL including continuous darkness (DD), as well as in continuous light (LL) at 12.5 and 15°C. At the same three temperatures, the number of long- or short-night cycles required for half of the experimental aphids to be ovipara producers (i.e. the required day number, RDN) was determined. The RDN for long-night cycles (LD12:12) could not be determined at 12.5°C, but was temperature compensated between 15 and 17.5°C. The RDN for short-night cycles (LD20:4) could not be determined at any temperature. However, as induction of oviparae was always 100% in 12.5°C, 94–100% in 15°C and dropped from 100% to between 47 and 71% in 17.5°C, it seems that short-night accumulation was temperature dependent. When fourth-stadium larvae were transferred from LD20:4 at 20°C to the same light–dark cycle at 15°C, the aphids, when adult, switched to the production of oviparae after about 4 weeks. First-born progeny kept in LD20:4 and 15°C switched to the production of oviparae about 7 days after the moult to adult. Thus, the photoperiodic response can be directly affected by temperature, irrespective of photoperiod. Model-generated response curves using the ‘double circadian oscillator model’ for photoperiodic time measurement (Vaz Nunes, M., 1998. A double circadian oscillator model for quantitative photoperiodic time measurement in insects and mites. Journal of Theoretical Biology 194, 299–311) closely resembled the observations. Differences between these data and the results of previous experiments with an English clone of M. viciae could be accounted for by differences in the photoperiodic clocks (damping rate and period) as well as the photoperiodic counters.

Olfactory antennal responses to plant volatiles in apterous virginoparae of the vetch aphid Megoura viciae

AbstractElectroantennogram (EAG) responses were recorded from apterous virginoparae of the vetch aphid Megoura viciae Buckton (Homoptera, Aphididae) to more than eighty volatile compounds in order to investigate its sensory ability to perceive plant odours. The response profile of M. viciae reveals a differential sensitivity for the array of plant volatiles tested. The whole group of general green leaf volatiles is very stimulatory. In addition to (E)‐2‐hexenal, the following compounds of this group elicit large EAG responses: (E)‐2‐heptenal, 1‐octenol‐3, hexyl acetate, (Z)‐3‐hexenyl acetate, hexanol‐1, hexanal, 2‐heptanone and 3‐octanone. Relatively large EAGs are also produced by 4‐methoxybenzaldehyde (p‐anisaldehyde), hexanonitrile, heptanonitrile, 1, 6‐hexanedithiol, butyl isothiocyanate, 4‐pentenyl isothiocyanate, (‐)‐(1S)‐β‐pinene, (+)‐(S)‐carvone, (‐)‐(R)‐carvone, α‐terpineol, linalool and citronellal. The nitriles are the most effective of all plant volatiles tested. Structure‐activity relationships occur in various groups of chemicals and members of the green leaf volatiles, benzaldehydes, isothiocyanates and monoterpenes are ranked accordingly. In the group of green leaf volatiles, aliphatic aldehydes are more stimulating than the corresponding alcohols. EAG responses to series of saturated aliphatic alcohols and aldehydes reveal that C6 and C7 compounds are the most stimulatory. Dose‐response curves show that the rank order of EAG response amplitudes hardly changes at lower dosages. It is concluded that M. viciae perceives general plant volatiles as well as more‐specific components, such as nitriles and isothiocyanates, associated with the odour blends of non‐host plant species.

Dispersal of apterous aphids (Homoptera: Aphididae) from their host plant and its significance

AbstractDispersal of apterae from their natal plant was monitored for three aphid species (Myzus persicae (Sulzer), Brevicoryne brassicae (Linnaeus) and Megoura viciae Buckton), each on a different host plant. Some movement off the plant occurred even in the initial parental and second generations, when the plant appeared to be growing normally and when crowding was unlikely to be the cause. However, in most experiments the most marked increase in apterous dispersal coincided with a reduction or even cessation of plant growth. In nearly all the experiments this dispersal occurred when the population on the natal plant exceeded about 20 adults and their offspring per plant. The main emigrants were fourth instar apterae and prelarviposition adult apterae. The implications of this behaviour are discussed, and it is argued that apterous dispersal might be common in aphids, allowing a fuller utilization of the environment than would be likely by alate dispersal alone.

Structure of the trophic chamber (germarium) in virginoparae of the vetch aphid, Megoura viciae Buckton (Homoptera : Aphididae)

The structure of the germaria in the ovaries of the viginoparous morph of the vetch aphid, Megoura viciae Buckton (Homoptera : Aphididae) is described and compared to other insects, including aphids. Each consists of a syncytium of trophocytes and resting oocytes arranged around a trophic core. Trophocytes contain mitochondria, ribosomes, vacuoles and some membrane-bounded material. Golgi complexes were not found. Each trophocyte has a single spherical nucleus with “nuage-like” material confluent between nucleoplasm and cytoplasm via numerous nucleopores. The surrounding monolayer of somatic epithelial sheath cells are bounded externally by an acellular tunica propria. These cells continue into the prefollicular tissue in the base of each germarium. Cells from the prefollicular tissue envelop each oocyte as it is released from a germarium. The “previtellogenic” growth phase of oocytes is relatively short, and vitellogenesis is absent. Virginoparae are reproductively precocious, and newly born larvae have up to 3 oocytes undergoing development in their anterior ovarioles. Interovariole ovulation is asynchronous within, and partially synchronous between, the 2 ovaries.

Follicular sheath (ovarian sheath) structure in virginoparae of the vetch aphid, Megoura viciae Buckton (Homoptera : Aphididae)

The anatomy of the follicular (ovarian) sheath surrounding the embryos in the virginoparae of the vetch aphid, Megoura viciae Buckton (Homoptera : Aphididae) is described. Enlarging oocytes released from the germaria are enveloped in a monolayer of cells derived from the prefollicular tissue, which is continuous with the sheat surrounding the germarium. Each embryo is compartmentalized. Initially, the sheath cells are cuboidal, but as division and elongation of the oocytes ensue, they become progressively stretched. Sheath cells surrounding large embryos show some variability in structure. In some areas, they are little more than a pair of membranes separated by a trace of cytoplasm. In other areas, they are thicker and have a structure that indicates a role in the uptake of materials. In these areas, the cells are often invaginated, with particulate and flocculent material present in the folds, and numerous organelles in the cytoplasm. Microvilli occur around some of the sheath cells and microtubule bundles are present in cells where the sheath is folded to form areas of contact between cells. A very thin acellular tunica propria is present to the exterior of the follicular sheath cells. Two acellular “membranes” present between the sheath cells and embryonic epidermal cells may have a role in the regulation of materials transfer. The structure of the epidermal cells of the embryos indicates role in the uptake of materials.

The trophic chamber (germanium) of the ovary in oviparae of the vetch aphid, Megoura viciae Buckton (Homoptera : Aphididae)

In the germaria of oviparae of the vetch aphid, Megoura viciae Buckton (Homoptera : Aphididae), the trophocytes are syncytial and arranged around a trophic core, to which they are all joined. Resting oocytes occur in the posterior region of the germaria, and encircle the basal region of the nutritive cord. The trophocytes contain mitochondria, ribosomes, vesicles, electron-dense spheres and a single large nucleus that is highly lobed and has many nucleopores. Electron-dense, “nuage-like” materials are confluent between nucleoplasm and cytoplasm, suggesting nucleocytoplasmic transport. Exterior to the trophocytes, a unicellular sheath surrounds each germarium, bordered to the exterior by a tunica propria. The cells of the sheath are continuous with the prefollicular tissue. Only one oocyte in each ovariole undergoes vitellogenesis at a time.

Intraclonal Trade-Off between Reproductive Investment and Size of Fat Body in the Vetch Aphid, Megoura viciae Buckton

Etude de la relation entre la teneur en lipides, la taille du corps gras et l'investissement reproducteur chez les viginipares apteres de M.v.

The Organs of Adhesion in the Aphid Megoura Viciae

ABSTRACT The anatomy of the adhesive organs is described in Megoura viciae Buckton. The claws serve as grappling hooks which are locked in position by the retractor unguis tendon. The pulvilli, pliable cuticular sacs, are everted from the tibiotarsal articulation. They bear a surface adhesive, a non-volatile oil, which is secreted through the cuticle. The pulvilli are everted by blood pressure and are withdrawn inside the tibia by contraction of the tibial muscles. The adhesion of these organs to various types of surface was tested by covering over the pulvilli or by claw amputation. Pulling forces were applied by progressively loading the aphid with weights. The pulvilli perform best on relatively smooth surfaces. Aphids are dislodged from the underside of polished glass by a mass of approx. 9-14 mg (a pulling force of 8·8-13·7xl0-5N). The claws cannot engage a completely smooth surface but are highly effective on rough ones, withstanding a load of approx. 57 mg on dry filter paper. Adhesion of the pulvilli to waxy surfaces is only slightly less than on glass but is greatly reduced on surfaces with still lower free energies, such as Teflon. On a glass surface the pulvilli sometimes leave ‘footprints’ consisting of oily droplets of variable size. Nevertheless, in many instances such deposits are small or absent, indicating that the bond sometimes breaks between the adhesive and the substratum. In a selected series of footprints with large deposits, their volume was found to be sufficient to form a layer at least 17·7xl0-9m in thickness over the area of pulvillar contact. This is consistent with the view that surface tension forces would adequately account for adhesion, an additional limiting factor being the physical properties (wettability) of the substratum. Viscous forces would impede the very rapid (less than 0-02 s) removal of the pulvilli, were it not for the retraction mechanism which peels off the pulvillus from the distal edge, like a piece of adhesive tape. The ultrastructure of the pulvillar gland is described. The epidermal cells discharge into a cavity which is confluent with a further reservoir within the spongy endocuticle, itself a meshwork of dissociated cuticular microfibrils. The points of exit of the secretion appear to be the epicuticular filaments. The product of the gland, which can be collected by pricking the pulvilli, is water soluble and proteinaceous, differing entirely from the hydrophobic lipid-soluble end-product on the pulvillar surface. We presume that the lipoprotein precursor is dissociated enzymatically at the level of the inner epicuticle.

Sex Pheromone in the Aphid Megoura viciae

THE adult egg-laying females (oviparae) of most holocyclic aphid species bear on their swollen hind tibiae circular plaques or tubercles which taxonomists variously refer to as sensoria, pseudosensoria, or pseudorhinaria. It has been suggested that they aid the ovipara in fixing her eggs to the host plant1, that they are sensory receptors2, or that they produce a sex pheromone which attracts the males3–5. Pettersson6 has advanced preliminary evidence for the latter function in a species of Schizaphis. Recent studies have shown that these structures (Fig. 1) in Megoura viciae Buckton do indeed secrete a sex pheromone and, moreover, that striking changes in the daily pattern of pheromone release occur as the female ages. In this article these pseudosensoria will be referred to as “scent plaques”, an appropriate term first used by Stroyan7.