Apterous Virginoparae Research Articles

Morph-specific fitness throughout the life cycle of the grain aphid, nonhost-alternating, holocyclic Sitobion avenae (Hemiptera: Aphididae).

Aphids exhibit seasonally alternating asexual and sexual reproductive modes. Different morphs are produced throughout the life cycle. To evaluate morph-specific fitness during reproductive switching, holocyclic Sitobion avenae were induced continuously under short light conditions, and development and reproduction were compared in each morph. Seven morphs, including apterous and alate virginoparae, apterous and alate sexuparae, oviparae, males, and fundatrices, were produced during the life cycle. The greatest proportions of sexuparae, oviparae, males, and virginoparae were in the G1, G2, G3, and G4 generations, respectively. Regardless of asexual or sexual morphs, alate morphs exhibited a marked delay in age at maturity compared with that of apterous morphs. Among the alate morphs, males had the longest age at maturity, followed by sexuparae and virginoparae. Among the apterous morphs, sexuparae were older at maturity than the fundatrices, virginoparae, and oviparae. The nymphs of each morph had equal survival potentials. For the same wing morphs, apterous sexuparae and oviparae exhibited substantial delays in the pre-reproductive period and considerable reductions in fecundity, compared with those of apterous virginoparae and fundatrices, whereas alate sexuparae and alate virginoparae had similar fecundity. The seven morphs exhibited Deevey I survivorship throughout the life cycle. These results suggest that sexual production, particularly in males, has short-term development and reproduction costs. The coexistence of sexual and asexual morphs in sexuparae offspring may be regarded as an adaptive strategy for limiting the risk of low fitness in winter.

Polyphenism in Antennal Sensilla Among Different Adult Morphs of Nonhost-Alternating, Holocyclic Sitobion avenae (Hemiptera: Aphididae).

Aphids, mainly distributed in temperate zones, exhibit seasonal generation-alternating phenomena. Across the life cycle, different morphs are produced. Sitobion avenae (Fabricius 1775) is a major pest of wheat worldwide. To elucidate olfactory perception of morph-specific behavior across their life cycle, we investigated antennal sensilla among seven morphs using scanning electron microscopy. Trichoid, placoid, coeloconic, and campaniform sensilla were identified. Trichoid sensilla, big multiporous placoid sensilla (primary rhinarium), a group of sensilla (primary rhinaria), and campaniform sensilla showed similar distribution and resemblance among morphs, whereas small multiporous placoid sensilla (secondary rhinaria) exhibited obvious differences. Compared to apterous morphs, alate morphs possessed a greater abundance of secondary rhinaria, with the greatest found in males on antennal segments III–V. Alate virginoparae and alate sexuparae ranged from six to fourteen rhinaria on antennal segment III. Fundatrices, apterous virginoparae and apterous sexuparae only had one or two secondary rhinaria on antennal segment III while they disappeared in oviparae. Secondary rhinaria, lying in a cuticle cavity, are convex or concave in their central part. In males, both forms were present, with a greater proportion of convex form than that of the concave form. Fundatrices and virginoparae had the convex form while sexuparae had the concave form. Polyphenism of secondary rhinaria might suggest their association with the olfactory functions of morph-specific behavior. These results have improved our understanding of the adaptive evolution of the antennal sensilla in nonhost-alternating, holocyclic aphids.

Mortality of Sugarcane Aphid, Melanaphis sacchari (Zehntner, Hemiptera: Aphididae), at Low Temperatures.

We conditioned colonies of Melanaphis sacchari (Zehntner, Hemiptera: Aphididae) to three different temperature regimes over a period of 2 mo: 30°C, 25°C, and a cycle of 18/8°C (L:D), all under a diurnal photoperiod of 12:12 (L:D). Plants of susceptible sorghum, 85Y40, were grown to the five-leaf stage in 4-liter pots, 2 per pot, and then infested with mixtures of second-fourth instar M. sacchari nymphs, either 50 (18/8°C treatment) or 100 (25 and 30°C treatments) aphids per plant. In each run of the experiment, a series of two to four plants of each treatment group were lowered to the desired cold temperature (4.0, 2.0, 0.0, -2.0, and -4.0°C) in a climate-controlled chamber and then evaluated for aphid survival after 12 h in complete darkness. Results revealed substantial survival of aphids from the 18/8 and 25°C conditioned treatments, even at -4.0°C, a temperature sufficient to kill the plants, and >90 and 60% survival, respectively, at 0.0°C. In contrast, aphids conditioned to 30°C experienced about 50% mortality at 4.0°C, and complete mortality at 0.0°C. Our results indicate that M. sacchari is able to survive periods of sub-freezing temperatures quite easily and will not suffer 'cold-shock' mortality unless subjected to a rapid drop in temperature from very warm conditions (e.g., 30°C or higher). Therefore, only temperatures that are cold enough to kill sorghum plants are likely to kill all apterous virginoparae of M. sacchari.

Bt 양배추가 복숭아혹진딧물의 발육과 기주선택에 미치는 영향

해충저항성 유전자변형 작물은 대상 해충에 대한 방제 효과를 증진시킬 수 있는 효과적인 수단이 될 수 있지만, 생태계 내의 다른 비표적 생물에 부정적인 영향을 줄 가능성 또한 있기 때문에 상업적인 재배에 앞서 이에 대한 충분한 연구가 이루어져야 한다. 본 연구에서는 배추좀나방내성 유전자변형 Bt (Cry1Ac1)양배추가 비표적 곤충인 복숭아혹진딧물에 미치는 영향을 알아보기 위한 기초적인 실험으로서 기주선택실험 및 성장실험을 실시하였다. 기주선택실험에서, 두 개체씩의 Bt 양배추와 모본 양배추에 각각 10마리의 유시 성충(alate virginoparae)을 접종하고, 사흘간 생식(reproduction) 기회를 제공한 후 생산한 약충의 마리수를 측정한 결과, Bt 양배추와 모본 양배추에 낳은 약충의 수가 각각 <TEX>$21.9{\pm}1.8$</TEX>와 <TEX>$22.5{\pm}2.2$</TEX>로 비슷하였다. 성장실험에서, 갓 태어난 무시 약충(apterous virginoparae)을 Bt 양배추 및 모본 양배추를 기주로 하여 키웠을 때, 성충이 될 때까지 걸린 시간은 Bt 양배추와 모본 양배추에서 각각 <TEX>$5.8{\pm}0.2$</TEX>, <TEX>$5.9{\pm}0.1$</TEX> 일(day)로 통계적으로 유의한 차이가 없었고, 개체군 생장률(rm) 또한 <TEX>$0.7{\pm}0.1$</TEX>, <TEX>$0.8{\pm}0.1$</TEX>로 유사하였다. 이상의 결과들로 볼때 Bt 양배추가 복숭아혹진딧물에 미치는 영향이 없거나 미미함을 알 수 있으나, 다양한 관점에서의 보완 연구가 더 필요하다. Transgenic crops that produce insecticidal toxins have a great potential for controlling target pest insects, but there is a growing concern about unintended influences on non-target species. In the present study, the preferences and performance of non-target green peach aphid, Myzus persicae (Sulzer), on transgenic cabbages (Brassica oleracea) that produce Bt toxin (Cry1Ac1) and untransformed control plants were investigated as a part of risk assessment. In a free-choice situation, the number of nymphs larviposited by 10 winged adults over 3 days was <TEX>$21.9{\pm}1.8$</TEX> and <TEX>$22.5{\pm}2.2$</TEX> on transgenic and the control plants, respectively, indicating that the aphids did not discriminate between the two types of plants. In a performance assay, the development time (D) and intrinsic rate of increase (rm) of wingless aphids reared on transgenic and control plants were also similar (D, <TEX>$5.8{\pm}0.2$</TEX> and <TEX>$5.9{\pm}0.1$</TEX> (days) and rm, <TEX>$0.7{\pm}0.1$</TEX> and <TEX>$0.8{\pm}0.1$</TEX>, for transgenic and control plants, respectively). These results suggest that M. persicae is not significantly affected by transgenic Bt cabbage.

Discovery of three woolly apple aphid Eriosoma lanigerum (Hemiptera: Aphididae) biotypes in Australia: the role of antixenosis and antibiosis in apple tree resistance

AbstractThe woolly apple aphid (WAA), Eriosoma lanigerum Hausmann, is a worldwide pest of apple orchards that has become widespread in apple‐growing regions of Australia. Several WAA populations that are geographically distant may have evolved into biotypes having different fitness (e.g. fecundity) in similar biotic and abiotic conditions. In this study, we investigated the performance of four different lines of WAA (designated as ALB, STA, BAT and YAR) originating from four locations in Victoria and New South Wales (Australia). Nymph establishment, nymph development to adult, nymph developmental time, female fecundity and adult weight of apterous virginoparae on apple trees (cv Granny Smith) were monitored under glasshouse conditions. Results showed that at least three lines examined here differ significantly in one or more performance parameters. Nymphs of the STA lineage showed a significantly higher establishment success after 7 days (64.3%) compared with lines BAT (53.1%) and YAR (43.6%). Nymph development to adulthood followed a similar trend. The average fecundity/female/7 days of the ALB lineage (19.7 ± 1.6 nymphs) was the lowest and significantly reduced relative to all other lines (from 36.6 to 40.5 nymphs). These results demonstrate the existence of at least three different biotypes in Australia. Antibiosis and antixenosis, respectively, could explain lower aphid establishment and lower female fecundity once settled. The characterisation of different WAA biotypes could have important implications for WAA management, and further studies should evaluate the overall diversity of biotypes, their geographical distribution and their growth characteristics to fully optimise pest control strategies.

Survey for Resistance to Four Insecticides in &lt;I&gt;Myzus persicae&lt;/I&gt; Clones from Peach Trees and Weeds in South-Central Washington

The insecticides esfenvalerate, endosulfan, imidacloprid, and methamidophos were screened against 74 clonal populations of the green peach aphid, Myzus persicae (Sulzer), collected as fundatrices from peach (Prunus spp.) and as apterous virginoparae from various weeds near potato (Solanum spp.) fields in the Yakima Valley and Columbia Basin regions of Washington state. Response to diagnostic concentration of four insecticide products demonstrated a bimodal pattern of survival to endosulfan (Phaser), suggesting two phenotype classes responding to this insecticide. This pattern was not observed with the other products. Moderately significant correlations in mortality of aphid clones treated with diagnostic concentrations of endosulfan versus clones treated with methamidophos and similarly with the correlation of mortalities for imidacloprid-treated versus methamidophos-treated clones suggested modest levels of cross tolerance. No significant correlations were observed with the remaining four possible comparisons. Concentration-response bioassays were conducted on 16 clones with the four insecticides. The greatest difference between resistant and susceptible clones (expressed as the ratio of lethal concentrations producing 50% mortality; RR) was only seven-fold observed in the endosulfan-treated clones. The greatest RR was five-fold for imidacloprid, four-fold for esfenvalerate, and three-fold for methamidophos-treated clones. Only the endosulfan response is likely to be ofbiological significance and reflects the same cyclodiene resistance discovered in this region over a decade ago.

Resistance to Biotype 2 Russian Wheat Aphid (Homoptera: Aphididae) in Two Wheat Lines

Biotype 2 of the Russian wheat aphid, Diuraphis noxia (Mordvilko), was identified in the United States in 2003 and is virulent to all commercially available cultivars of winter wheat, Triticum aestivum L., that are resistant to biotype 1. We compared the development and reproduction of biotype 2 D. noxia at 21.7 ± 0.12°C on ‘Trego’ (PI 612576), a susceptible commercial cultivar, and on lines CI 2401 and 03GD1378027 that represent putative resistance sources. CI 2401 is a pure wheat line originating in the former USSR (Tajikistan), whereas 03GD1378027 is a USDA–ARS breeding line originally developed from crosses with a South African line that carried a large rye translocation conferring D. noxia resistance. Both lines previously showed resistance to biotype 1 and are currently being used in the development of D. noxia-resistant wheat cultivars. Both solitary apterous virginoparae of biotype 2 and their progeny experienced a reduction in survival and prolonged developmental times on CI 2401 and 03GD1378027 compared with Trego, but the former lines did not differ significantly from each other with respect to either measure of aphid performance. Progeny developed faster than did their foundress mothers on CI 2401 and Trego, but not on 03GD1378027. Mean foundress fecundity did not differ between CI 2401 and 03GD1378027 but was reduced on these lines relative to Trego. Foundresses also were more often found off plants of CI 2401 and 03GD1378027 than Trego. Estimates of intrinsic rate of increase were higher on Trego than on either CI 2401 or 03GD1378027, the latter two lines yielding similar values. The negative impacts of CI 2401 and 03GD1378027 on development and reproduction of biotype 2 indicate that these lines represent sources of resistance effective against this biotype.

Resistance to Biotype 2 Russian Wheat Aphid (Homoptera: Aphididae) in Two Wheat Lines

Biotype 2 of the Russian wheat aphid, Diuraphis noxia (Mordvilko), was identified in the United States in 2003 and is virulent to all commercially available cultivars of winter wheat, Triticum aestivum L., that are resistant to biotype 1. We compared the development and reproduction of biotype 2 D. noxia at 21.7 +/- 0.12 degrees C on 'Trego' (PI 612576), a susceptible commercial cultivar, and on lines CI 2401 and 03GD1378027 that represent putative resistance sources. CI 2401 is a pure wheat line originating in the former USSR (Tajikistan), whereas 03GD1378027 is a USDA-ARS breeding line originally developed from crosses with a South African line that carried a large rye translocation conferring D. noxia resistance. Both lines previously showed resistance to biotype 1 and are currently being used in the development of D. noxia-resistant wheat cultivars. Both solitary apterous virginoparae of biotype 2 and their progeny experienced a reduction in survival and prolonged developmental times on CI 2401 and 03GD1378027 compared with Trego, but the former lines did not differ significantly from each other with respect to either measure of aphid performance. Progeny developed faster than did their foundress mothers on CI 2401 and Trego, but not on 03GD1378027. Mean foundress fecundity did not differ between CI 2401 and 03GD1378027 but was reduced on these lines relative to Trego. Foundresses also were more often found off plants of CI 2401 and 03GD1378027 than Trego. Estimates of intrinsic rate of increase were higher on Trego than on either CI 2401 or 03GD1378027, the latter two lines yielding similar values. The negative impacts of CI 2401 and 03GD1378027 on development and reproduction of biotype 2 indicate that these lines represent sources of resistance effective against this biotype.

Ecology and management of Ericaphis fimbriata (Hemiptera: Aphididae) in relation to the potential for spread of Blueberry scorch virus

AbstractAphids were sampled in commercial blueberry, Vaccinium corymbosum L. (Ericaceae), fields in southwestern British Columbia, Canada, from 2001 through 2003. Ericaphis fimbriata (Richards), the dominant aphid, overwintered as eggs on blueberry and emerged in late February and March during bud break. Apterous adult fundatrices were found during April. The fundatrices produced both alate and apterous virginoparae. There was a positive curvilinear relationship between production of alatae and aphid density on flower clusters, but not on leaf terminals. Peak densities in late June or early July varied from 300 to 9000 aphids per plant in different fields, suggesting that there may be considerable variation in Blueberry scorch virus transmission rates among fields infected with the virus. Production of alate virginoparae (percentage of all fourth-instar aphids with wing pads) declined from May through August. Sexual morphs were produced in late September and October. The efficacy of postbloom insecticide applications in June, by growers, was variable. Experimental trials showed that dormant oil is not effective in preventing aphid emergence. Aphids on blueberry should be controlled before bloom, before alatae are produced and large populations occur, but the efficacy of this approach in reducing virus transmission needs to be tested.

Feeding studies on gynoparae, males and apterous virginoparae of Myzus persicae on potato by electrical penetration graph

Abstract: Feeding behaviour of parthenogenetic apterae, post‐teneral gynoparae and males of a holocyclic parthenogenetic lineage of Myzus persicae (Sulzer) (Hem., Aphididae) was studied on potato plants, Solanum tuberosum L. (Solanaceae) by DC‐electrical penetration graph recording. Differences were observed between morphs during the 7‐h recordings, specifically in the first phase of subcuticular probing and in xylem and phloem‐related activities. The time required for the first penetration and first cell puncture of the non‐vascular tissues was shorter in apterae than in gynoparae and males. Apterae more often showed phloem activities and sustained sap ingestion (100%) than winged morphs (ca. 25%). In addition, phloem ingestion was much longer in apterae than in winged morphs, 3458 s and 25–70 s respectively. In contrast, winged morphs spent 14–21% of the available time ingesting sap from xylem while in apterae xylem sap uptake was only for 2% of the time. Furthermore, the data showed that males perform in general all the feeding behaviours that other conspecific morphs exhibit. The differences in feeding behaviour among morphs of M. persicae are discussed in relation to host specialization and to their possible involvement in non‐persistent transmission of viruses.

Production of sexual morphs by apterous virginoparae of Myzus persicae (Hemiptera: Aphididae) in relation to pre- and postnatal exposure to short day conditions.

The production of males and females by apterae of a holocyclic clone of Myzus persicae (Sulzer) was studied in the laboratory by transferring apterous virginoparae from long day to short day conditions at different stages of their pre- and post-natal development. Prenatal exposure was also examined in nine additional clones coming from different regions of Greece. By increasing the number of short day cycles at 17 degrees C, the aphids switched to male production earlier and produced more males. The highest mean number of male progeny was observed in apterae that were transferred to short day conditions 13-14 days prenatally. Apterae that were transferred to short day conditions after the fourth nymphal instar produced only females. Apterous virginoparae were produced by aphids that were transferred to short day conditions 0-1 days prenatally or postnatally. Aphids, given short days prenatally or in the first instar, produced alate female progeny that were all gynoparae. The later the instar aphids were transferred to short day conditions the fewer the gynoparae produced among their female progeny. A reduction in the total number of progeny and embryos per ovariole was observed as aphids were transferred to short day conditions in earlier stages of their development. The increase in male production, which follows the increase in the duration of long night exposure, was also observed in the additional eight out of nine examined clones.

Functional specialisation and polyphenism in aphid olfactory sensilla

Electroantennogram (EAG) responses to the aphid sex pheromone components, (1 R,4a S,7 S,7a R)-nepetalactol and (4a S,7 S,7a R)-nepetalactone, and a plant volatile, (E)-2-hexenal, were investigated at three different positions (5/6th, 4/5th and 3/4th inter-segmental regions) along the antennae of four different morphs in two host-alternating aphid species, Aphis fabae Scopoli and Rhopalosiphum padi (L.). Position-dependent and morph-specific EAG responses were elicited in both species. The nepetalactol and nepetalactone isomers elicited large EAG responses at all three recording positions in males of both species, such that primary rhinaria as well as secondary rhinaria appeared to respond. Asexual female morphs showed relatively smaller EAG responses to these compounds. The secondary rhinaria, which have been reported as sex pheromone receptors in males, were not very different in their number and distribution between gynoparae and alate virginoparae, but the gynoparae showed significantly larger EAG responses to nepetalactol and nepetalactone. The alate virginoparae showed EAG responses that were similar to those of apterous virginoparae, which lack secondary rhinaria. Taking the EAG response profiles together with the distribution of the secondary rhinaria, it is suggested that the function of secondary rhinaria differs between the morphs. Secondary rhinaria appear to detect sex pheromone components in males and gynoparae but not in the alate virginoparae. If they are functional in the latter morph, they are likely to play a role in detecting specific, but as yet unknown, volatile compounds. Some 30 plant volatiles were tested but none evoked an EAG response that could be allocated to the secondary rhinaria. In contrast to the very different EAG response profiles to the pheromone compounds between morphs, EAG responses to (E)-2-hexenal were similar in all forms and both species. These findings suggest that this plant volatile was detected only by the two primary rhinaria, which are common to all morphs. The present study showed that EAG responses were not a simple summation of receptor potentials between recording and reference electrodes in aphids. The localised distribution pattern of olfactory receptor neurones around the recording electrode was also likely to contribute to the EAG responses.

Modelling development time of Myzus persicae (Hemiptera: Aphididae) at constant and natural temperatures

AbstractThe development period from birth to adult of alate and apterous virginoparae of the green peach aphid, Myzus persicae (Sulzer), reared on Brassica campestrisssp. chinensis, was measured at 13 constant and five natural temperature regimes. The day–degree model, the logistic equation, and the Wang model were used to describe the relationships between temperature and development rate at constant conditions. The constant temperature–development curves derived from the three models were used with a Weibull function describing the distribution of development times, to simulate the development of individuals of cohorts reared at natural temperature regimes. Comparison of the observed with simulated distributions of adult emergence indicates that all three models can simulate the development of M. persicaevery well when the temperature does not go below 4°C, the notional low temperature threshold of the day–degree model. When accumulation of temperatures below 4°C becomes substantial, only the logistic curve with a low temperature threshold of 0°C can offer accurate simulations; the other two models give falsely longer durations of development. Methods for accurately simulating the development of M. persicae in the field are suggested. The significance of modelling insect development at low temperatures by nonlinear models is discussed.

Some Wing-Padded Larvae of Pseudoregma bambucicola (Homoptera: Aphididae: Hormaphidinae) Overwinter and Develop into Virginoparae

Pseudoregma bambucicola, an Asiatic eusocial aphid, shows a typical life cycle of host-alternating aphids in Taiwan. It sexually reproduces on primary host trees and parthenogenetically produces offspring including sterile soldiers on secondary hosts. However, in southern Japan where this aphid species is thought to have been artificially introduced with secondary host plants and where there are no candidates for primary host plants, the apterous virginoparae propagate parthenogenetically throughout the year on the secondary host, still producing numerous alate sexuparae in autumn. In the present study, I collected 18 wing-padded aphids in winter and the following spring and, by rearing them, ascertained that these abnormal individuals grew not to sexuparae but to adult virginoparae which produce "normal" first-instar larvae and soldiers on the secondary host. This suggests that natural selection favors some wing-padded aphids to abandon flight probably due to the high mortality of alate immigrants, supporting the idea that the alates may play no significant role but may be produced by phylogenic inertia in Japan.

Comparison of ecdysteroid concentration in different morphs of aphids

The amounts of ecdysteroids were determined in different morphs of holocyclic monoecious aphids ( Acyrthosiphon pisum Harris, Dysaphis devecta Walk., Lachnus roboris L., Schizolachnus pineti F.) and holocyclic heteroecious aphids ( Aphis sambuci L., Rhopalosiphum padi L.) by means enzyme immunoassay. Among the parthenogenetic morphs (fundatrices, virginoparae, and oviparae), the fundatrices have consistently higher amounts of ecdysteroids than those of other morphs of the same species. Alate and apterous virginoparae showed slight differences in their ecdysteroid titer both in heteroecious and monoecious aphids. The migrant morphs (i.e., alate fundatrices and gynoparae) have the lowest amounts of ecdysteroids within a species. With the exception of D. devecta, the oviparae of both heteroecious and monoecious aphids have the second greatest amounts of ecdysteroids among the morphs living on same host plant. Polyphenism dispersal behavior, and fecundity in connection with weight, ovariole number, and ecdysteroid concentration of different morphs of aphids are discussed.

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.

Age‐Grading Nymphal Instars of Apterous Virginoparae of Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae)

ABSTRACTA reliable method for age‐grading field‐collected nymphal instars of apterous virginoparae of Eriosoma lanigerum is reported. A classification criterion in the form of linear discriminant function analysis was developed for laboratory populations of E. lanigerum using measurements of several morphological characters. This model was cross‐validated using field‐collected aphids that had been sorted a priori into instar stages on the basis of a set of morphometric measurements. All field‐collected second instars were classified as sorted, while almost all third and fourth instars were classified as sorted. to attain this degree of accuracy in classifying individuals from field populations, measurements of the distance between cornicles, cauda width, body length and hind tibia length are required. This method was developed to obtain quantitative estimates of the effect of mortality factors and the rates of increase of field populations of E. lanigerum.

Seasonal Occurrence, Development and Reproductive Biology of the Different Morphs of Eriosoma lanigerum (Hausmann) (Hemiptera: Aphididae) in the Northern Tablelands of New South Wales

ABSTRACTAs with many other aphids, the woolly aphid, Eriosoma lanigerum (Hausmann), is polymorphic; despite the fact that in Australia its life cycle is restricted to apple trees. the different morphs are: (1) apterous virginoparae; (2) alate sexuparae or virginoparae; and (3) sexuales (males and oviparae). the apterous virginoparae occur on apple trees throughout the year. the alate aphids are the offspring of apterous virginoparae and they occur first in November and then from late January to late April. Alate aphids appearing in early November produce only virginoparae, alates appearing from late November to late January produce a mixture of virginoparae and sexuales, whereas those appearing from February to April produce exclusively sexuales. Sexuales are apterous, have degenerate mouth parts and oviparae produce non‐viable eggs. Although males and oviparae of this aphid appear seasonally, perpetuation of the species appears to be entirely parthenogenetic, and overwintering is accomplished in the form of cold‐hardy apterous virginoparae. Apterous virginoparae attain a rapid rate of nymphal development, large adult size, high fecundity and high population growth rate in the spring compared to summer, autumn and winter. However, populations peak in February‐March each year.

Spatial and Temporal Distribution Patterns of Eriosoma lanigerum (Homoptera: Aphididae) on Apple

The spatial distribution of the woolly apple aphid, Eriosoma lanigerum (Hausmann), in a 41-yr-old apple orchard was analyzed using the negative binomialparameter k, Taylor's power law, and Iwao's regression technique. All three indices indicated a highly aggregated distribution of the aphid in the apple orchard. There was a weak but significant linear relationship between the negative binomial k and the mean density for the individual aphids but not for aphid colonies. Compared with Iwao'sregression, Taylor's power law provided a better description of the relationship between the variance and mean density. Woolly apple aphid occurred on the apple trees mainly as apterous virginoparae throughout the year and showed a preference for the lower part of the canopy and the trunk. At low infestations, the aphid is confined to the trunk and large branches but disperses to establish colonies on twigs or new lateral growths during peak populations. Woolly apple aphid has a limited ability to disperse between trees. Population density appears to increase mainly within trees. The relationship between the proportion of infested trees and mean aphid density was in the form of a rectangular hyperbola with an asymptotic upper limit of 33% infestation level.

Survival, growth, and reproduction of two aphid species on sucrose solutions containing host or non‐host honeydews

AbstractAphids, like most phloem‐feeding insects, commonly exhibit a high degree of host specificity. Plant‐specific chemical compounds are likely to serve as important host selection cues for monophagous aphids and such substances could be present in aphid honeydew. Apterous virginoparae of Myzus persicae (Sulzer) and Phorodon humuli (Schrank) were reared on a buffered sucrose solution containing various aphid honeydews or a mixture of amino acids. In two separate experiments, the host‐specific P. humuli (hop aphid) could grow and reproduce only on diets containing honeydew collected from hop (Humulus lupulus L.). M. persicae (the green peach aphid, GPA) did not perform well on diets containing hop honeydew, perhaps because hop is a poor GPA host. Honeydew collected from preferred GPA host plants rape, Brassica napus L., and jimsonweed, Datura stramonium L., allowed GPA growth and reproduction. Hop aphids, however, performed poorly on rape and jimsonweed honeydew diets. Bell pepper, Capsicum annuum L., honeydew supported neither the hop aphid nor GPA. The study of aphid honeydew components may contribute towards a more complete understanding of host preference and selection phenomena in aphids.