The visual responses of free-flying summer and autumn forms of the black bean aphid, Aphis fabae, in an automated flight chamber

ABSTRACT Summer (virginoparae) and autumn (gynoparae) winged forms of Aphis fabae were flown in an automated flight chamber for up to 100 min, while being exposed to a small green target at their own level for 5 s of each minute. Virginoparae climbed more slowly than gynoparae and responded to the target by turning towards it throughout experimental flights. Gynoparae, on the other hand, were almost completely unresponsive to the target, although some individuals began to respond after an hour or more of flight. The differences between the two migratory forms are discussed with reference to previous work on aphid flight behaviour in the field and the laboratory.     

Flight behaviour of the bird cherry aphid, Rhopalosiphum padi

Abstract Seasonal winged forms of the bird cherry aphid, Rhopalosiphum padi L., were flown in an automated flight chamber. During their maiden flights, autumn migrants (gynoparae) had a greater initial rate of climb than summer (exules) and spring migrants (emigrants). Autumn migrants, presented with a laterally-positioned green-illuminated target for 2.5 s during each minute of flight, flew for a longer period before responding to the target (110 min) than summer migrants (36 min), while spring migrants responded after an intermediate time (72 min). This period is equivalent to the migratory phase of flight. The summer migrants were maximally responsive to targets illuminated by green monochromatic light (X, 555 nm). Targets illuminated with ultraviolet (γλ 360 nm) were attractive during the migratory and green-responsive phases of flight, but infrared (γλ700 nm) wavelengths were not attractive. The results are discussed with respect to aphid behaviour in the field.     

Reproductive, morphological and behavioural affinities between the alate gynopara and virginopara of the aphid, Aphis fabae

ABSTRACT. 'Normal' alate virginoparae reared under long day conditions (LD 16:8) with postnatal crowding, and 'normal' gynoparae reared in un-crowded, short day conditions (LD 12:12) over two generations were compared in respect of the morph of the progeny, the frequency distribution of secondary rhinaria (placoid sensilla) on the third and fourth antennal segments, and preferred larviposition sites. Although in Aphis fabae the two morphs closely resemble one another morphologically, they differed in each of the above characters. Progeny sequences were analysed after transfer to the opposite photoperiodic regime at various times during postnatal development of the alate mothers. Transfer of presumptive gynoparae from short to long days induced the appearance of virginoparous progeny even when the transfer was made just after the final moult. Transfer of presumptive alate virginoparae from long to short days was effective in inducing oviparous offspring, only if the transfer was made during the first instar; oviparae were always first born. Intermediates between oviparae and viviparae were found at the time when the morph of the progeny changed. Transfer from long to short days also induced gynopara production but there appeared to be an intrinsic mechanism which prevented exclusive gynopara production by alates. When first instar, presumptive gynoparae were transferred to long days, the resulting adults would be described both reproductively and behaviourally as alate virginoparae; the opposite switch, of presumptive alate virginoparae to short days, resulted in adult gynoparae on the same criteria. However, the numbers of secondary rhinaria were influenced more by the prenatal than by the postnatal photoperiodic regime. There was an asymmetry of response in that a switch from short to long days had a greater effect on all three characters monitored than did the opposite switch from long to short days.     

A transgenerational interval timer inhibits unseasonal sexual morph production in damson-hop aphid, Phorodon humuli

Abstract.  The induction of sexual and parthenogenetic morphs of the damson-hop aphid, Phorodon humuli , on hops is controlled by daylength. The ability of P. humuli , to produce winged pre-sexual females (gynoparae) in the short-day conditions of spring is inhibited by an interval timer present in generations immediately after hatching of the overwintering egg. The inhibition expires after three generations when nymphs are born and reared in short days (LD 12 : 12 h), irrespective of whether their parents are reared in short or long days (LD 18 : 6 h). No gynoparae are produced by aphids maintained for 13 generations in long days. Two wingless aphids from 35 survive transfer from Prunus spinosa to hops. No winged females are produced during nine generations among their progeny maintained in long days on hops, but gynoparae, followed by males, are produced one generation after these aphids are transferred to short days.     

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.     

Photoperiodic determination of gynoparae and males of damson-hop aphid Phorodon humuli

Abstract. Sexual morph production in Phorodon humuli is controlled by daylength. Wingless aphids reared from birth in short-day conditions (LD 12 : 12 h) and transferred when adult to long-day conditions (LD 18 : 6 h) produce only gynoparae and males until death some 7 weeks later, whereas those reared in long days and transferred to short days produce 20% wingless parthenogenetic females, 50% gynoparae and 30% of males in an overlapping sequence. No winged morph capable of re-infesting hop is produced. Less mature embryos are more sensitive to short days than older embryos because 100% of the former became gynoparae after 4 days of exposure of their mothers, and 59% when their mothers were exposed for the 4 days immediately preceding the birth of their offspring. Two days of exposure to short days switches 94% of young embryos from wingless to gynopara production when mature. The response to short days is irreversible. Wingless aphids reared from birth to adult in short days produce 30% fewer offspring than those reared to the same stage in long days and are male-biased, with 76–78% of their offspring being male.     

Photoperiodic regulation of the development of winged gynoparae in the aphid, Aphis fabae

ABSTRACT. In uncrowded rearing conditions, determination of the winged gynopara of the Aphis fabae Scopoli is dependent upon both pre- and postnatal short days (LD 12:12). Extension of the photophase to produce longday (LD 16:8) conditions localized on the head or abdominal region, showed that during the early larval instars of the parent generation (G1) there is a maternally-controlled induction of gynoparae. However, during later stages of embryonic development the presumptive gynoparae respond directly to photoperiod through the mother's abdominal wall. During early postnatal development, presumptive gynoparae (G2) remain sensitive to photoperiodic conditions; the photoperiodic receptors lie in the head. These results are discussed with respect to possible endocrine mediators of this photoperiodically controlled polymorphism.     

The time of determination of gynoparae and males in the bird cherry–oat aphid, Rhopalosiphum padi

Apterous exules of Rhopalosiphum padi which experienced short photoperiods only during the first half of their nymphal life all produced gynoparae which made up 57% of the offspring produced in the first 7 days of the mother's reproductive life. Short photoperiods during the second half of a mother's nymphal life did not induce the production of gynoparae. However, when short photoperiods were experienced throughout a mother's nymphal life significantly more gynoparae (82%) were produced. Ten per cent of the offspring of mothers that experienced short photoperiods only during their adult life developed into gynoparae. Of the offspring reared in short photoperiods, but born to mothers reared and kept in long photoperiods, 30% developed into gynoparae. When mothers were exposed to short photoperiods in their adult life and their offspring so treated, then 90% of the offspring developed into gynoparae. Males only occurred amongst the last offspring of mothers that experienced short photoperiods in either the first or the second half of their nymphal life.     

Juvenile hormone and photoperiodically controlled polymorphism in Aphis fabae: Prenatal effects on presumptive oviparae

All three naturally occurring juvenile hormones (JH's) were shown to have effects on the parthenogenetic/gamic polymorphism of Aphis fabae; they mimicked long day conditions by inducing parthenogenetic forms. When topically applied to fourth instar gynoparae, JH caused the appearance of oviparous/viviparous intermediate morphs in the progeny. JH induced both wing development and embryogenesis in embryonic, presumptive oviparae. Embryogenesis was induced by lower doses of JH. Adult, embryo-containing alatae produced by treatment with high JH doses were capable of flight, and whilst reluctant to reproduce, their few viable progeny were oviparae. They did, however, differ from normal gynoparae in size, occasional presence of scent plaques on the metathoracic tibiae, numbers of secondary rhinaria on the antennae and morphogenetic response to postnatal rearing in long day conditions. The presumptive, oviparous embryos most sensitive to JH treatment were shown to be ca 323 μm in length, close to the stage where their germaria differentiate as parthenogenetic or gamic. Similar effects were observed in the progeny of JH-treated, teneral adult gynoparae but there was no effect on the morph of progeny of long day, alate virginoparae. The JH's differed in potency in the order JH I > JH II > JH III. The treatment of fourth instar gynoparae also induced a terminal batch of apparently normal viviparous progeny in a number of aphids. This result was obtained even at JH doses below threshold for the appearance of oviparous/viviparous intermorphs.     

Juvenile hormone and photoperiodically controlled polymorphism in Aphis fabae: Postnatal effects on presumptive gynoparae

Long days (short nights) (LD 16:8) and high temperatures (> 15°C) have an apterizing effect on the short day (LD 12:12) induced, presumptive gynopara of Aphis fabae. Transfer of presumptive gynoparae to long days (15°C) or to 25°C (short days) at varying times during postnatal development demonstrate that the adult form is determined by the second day of the second instar, i.e. 5 days after birth at 15°C. Transfer on day 1 induces maximum apterization with the proportion of aphids affected decreasing with age at transfer.Apterization induced by long days immediately after birth can, to some extent, be cancelled by return to short days but only up to day 4. Thus long days are morphogenetically more potent than short days at the beginning of larval development. At temperatures above 15°C the proportion of aphids apterized increases almost linearly.Apterized insects can be distinguished from juvenilized insects in the fifth-instar. Topical application of juvenile hormone (JH) induces both apterization and juvenilization of presumptive gynoparae but at different times during larval development, JH treatment during the early-instars promotes apterization but induces little juvenilization, whereas maximum juvenilization, without apterization, is produced by middle-instar treatment. The apterizing effects of JH are, thus, not due to its neotenic action.The response profile of JH-induced apterization is similar to that observed with long days and 25°C. It is suggested that such conditions increase endogenous JH levels in A. fabae. The three naturally occurring JH's differ in activity in the order JH I > JH II > JH III. Both long-day and JH-apterized insects switch from the normal ovipara production of the adult gynopara to vivipara production.     

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.     

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.     

Wing development and parthenogenesis induced in progenies of kinoprene-treated gynoparae of Aphis fabae and Myzus persicae

Presumptive gynoparae of Aphis fabae and Myzus persicae were exposed to various levels of kinoprene (Zoecon's ZR 777) by being placed as 4th-instar alatiform larvae on bean or radish seedlings that had been sprayed with different concentrations of kinoprene in an acetone-tween-water emulsion. Larvae exposed to the highest (0.1%) concentration tested developed into adults 1 to 2 days sooner than those on control plants. The adults on the treated plants had variously deformed wings, reduced sclerotization (and pigmentation in the case of M. persicae) and other apteriform features. On reaching adulthood the affected aphids settled to feed and started to larviposit some days earlier than the control aphids. After two weeks as adults, treated gynoparae of M. persicae produced more larvae than the 7 to 9 typically deposited by control gynoparae under the short-day and cool temperature conditions employed in these tests.Whereas most or all of the larvae produced by the control gynoparae developed into oviparae (apterous, egg-laying, sexual females), gynoparae exposed to 0.1% kinoprene-treated plants predominantly produced alatiform viviparous offspring. If the latter were allowed to develop on untreated plants they deposited a few oviparous larvae. Alatiform virginoparae of M. persicae (from the same holocyclic strain that produced the gynoparae) also responded to kinoprene by developing wing deformities and by producing alatiform offspring. In contrast, alatiform virginoparae from an androcyclic strain of M. persicae, although developing wing deformities, produced only apterous progeny.The stimulation by kinoprene of wing development and parthenogenesis in the progeny of treated gynoparae is discussed in the light of our present knowledge of these aspects of aphid polymorphism.     

Pantethine inhibits cholesterol and fatty acid syntheses and stimulates carbon dioxide formation in isolated rat hepatocytes

The effects of pantethine on cholesterol and fatty acid metabolism were investigated in isolated rat hepatocytes. Preincubation of the cells with pantethine induced a concentration-dependent decrease of the radioactivity incorporated into carbon dioxide and lipids in incubations with [2-14C]acetate. When pantethine and the labeled substrate were simultaneously added to the cell suspension, there was an enhancement of carbon dioxide radioactivity at short incubation time (5 min) whereas, at longer incubation time, values were comparable to those of controls; lipid radioactivity, instead, was dramatically reduced by pantethine even at short incubation time and decreased further during the incubation, being 23% of that of controls at 60 min. Analysis of the incubation medium showed that pantethine induced a concentration- and time-dependent release of acetate into the medium. Results of the effect of the acetate concentration on the incorporation of [2-14C]acetate radioactivity into CO2 and lipids in control hepatocytes allowed the conclusion that the above-described modifications induced by pantethine are only partially attributable to the dilution of the labeled substrate, and that catabolism of acetate to carbon dioxide is stimulated by the disulphide pantethine, whereas cholesterol and fatty acid syntheses are inhibited.     

The effect of light on nitrate and nitrite assimilation by chlorella and ankistrodesmus

Light stimulates the assimilation of nitrate and nitrite by two green algae, Chlorella pyrenoidosa and Ankistrodesmus braunii. Assimilation can be observed when the algae are illuminated in the absence of carbon dioxide under both aerobic and anaerobic conditions. The rates of assimilation by Chlorella do not depend on the presence of carbon dioxide, but Ankistrodesmus assimilates nitrate and nitrite more rapidly when cultures are illuminated in the presence of carbon dioxide than in its absence. The ratios of O(2) : NO(3') and O(2) : NO(2') vary from one experiment to the other and, with the exception of Chlorella cultures reducing nitrite they are higher than the 'expected' values of 2.0 and 1.5 respectively. Oxygen evolution accompanying nitrate and nitrite by algae illuminated in the absence of carbon dioxide is completely inhibited by DCMU at concentrations of 4 × 10(-6) M. However, nitrite assimilation by both Ankistrodesmus and Chlorella and nitrate assimilation by Ankistrodesmus are less sensitive to the inhibitor.     

An interval timer controls the production of sexual morphs in Myzus persicae (Homoptera: Aphididae)

Abstract The interval timer mechanism was examined in two clones of Myzus persicae (Sulzer) originating from peach in Naousa, North Greece. Overwintering eggs were collected in April 1997 and after egg hatch the morphs of progeny were recorded at LD 10 : 14 h and 17 °C until the appearance of sexuals. In one clone, observations were continued until the 21st generation after egg hatch. In addition, the production of sexual morphs was examined in two other clones originating from Lehonia, Central Greece, when apterae (wingless females) were transferred from long to short days and 17 °C in the second and eighth generation of parthenogenetic rearing after their collection from peach trees. In clones from Naousa, the first gynoparae appear and comprise 10% of alate (winged) females in the second half of the third generation after egg hatch. The percentage of gynoparae increased in each consecutive generation, reaching 100% in fifth and seventh generations in clones Nb and Na, respectively. First males appeared later than gynoparae, in fifth and sixth generation in clones Nb and Na, respectively. In clone Nb, the number of males, after their appearance in fifth generation, was relatively constant from the sixth to the ninth generation (10.8–12.3). Then a significant increase was observed in the 10th generation, thereafter remaining relatively constant until the 21st generation (18.1–19.8). A similar trend in the number of males produced was observed in clones deriving from Lehonia.     

Morph determination in the bird cherry-oat aphid, Rhopalosiphum padi L

Both crowding and poor nutrition induce the appearance of emigrants in Rhopalosiphum padi L. No emigrants developed when the aphid was reared in isolation for six successive generations on actively growing leaves of bird cherry. However, emigrants developed as soon as the leaves ceased to grow or when the aphids became crowded. Crowding of mothers and postnatal crowding of the nymphs of apterous exules both influenced the induction of alate exules. The highest proportion of alate exules developed when both mother and offspring were crowded. Short day-length induced the appearance of gynoparae and males. For 50% production of gynoparae and males, over the range of temperature 10–18d?C, a 1.75 h reduction in day-length is required for every 4d? increase in temperature. At 18 d?C, even at day-lengths as short as 6 h, exposure for three generations is required before all offspring become gynoparae or males. Low temperature and short day-length was ineffective in inducing the development of gynoparae or males in the first three generations developing from the fundatrix.     

Effect of carbon dioxide dissolved in water on carboanhydrase activity in various organs of carp

The carboanhydrase activity was studied in erythrocytes and tissues of carp gills and kidneys under conditions of exogenic hypercapnia induced by an increase in the level of carbon dioxide solved in the water medium. This enzymic activity in fish erythrocytes is established to be determined by the hypercapnia degree and does not depend on its duration. The carboanhydrase activity in the gills and kidneys is not changed under the effect of higher (within 0,16-1,10 mM) concentration of carbon dioxide for seven days.     

Effects of Nitrogen Nutrition on Leaf Expansion and Photosynthesis of Trifolium subterraneum L. 1. Comparison between Different Levels of Nitrogen Supply

Growth analysis showed that reductions in the relative growth-rateof subterranean clover plants (cv. Mt. Barker), even those dueto moderate nitrogen deficiencies, were reflected in reductionsof the leaf-area ratio and particularly of the net assimilationrate. A decline in nitrogen supply in the culture solutions was foundto depress net rates of carbon dioxide uptake per unit leafarea and leaf expansion per plant to about the same extent,even at moderate levels of nitrogen stress. Four days aftertransfer of plants grown with adequate nitrogen to solutionswithout nitrogen, leaf area and net carbon dioxide uptake haddeclined to 84 per cent and 89 per cent of the values for thecontrol plants. After a further 4 days these values had decreasedto 71 per cent and 52 per cent respectively. When net carbon dioxide uptake was expressed per unit weightof chlorophyll, the effect of changes in nitrogen supply onnet photosynthesis largely disappeared, indicating a close relationshipwith the chlorophyll content of the leaves. However, anotherand perhaps more direct effect of nitrogen on photosynthesiswas suggested by the fact that, during the early stages of recoveryfrom a severe nitrogen stress, photosynthesis began to increasebefore the chlorophyll content of the leaves.     

Upwind flight of tsetse (Glossina spp.) in response to natural and synthetic host odour in the field

Abstract. In Zimbabwe, studies were made of the flight responses of tsetse ( Glossina spp.) to synthetic and natural ox odour using arrangements of electric nets.Tsetse flying away from a target showed a significant upwind bias when a blend of carbon dioxide (2/1 min), acetone (500 mg/h), octenol (0.4 mg/h), 4-methylphenol (0.8 mg/h) and 3-n-propylphenol (0.1 ma) was dispensed 15 m upwind, with c. 35% flying upwind.Without carbon dioxide this percentage was significantly reduced to 15% which was not significantly different from that with no odour (8%).This pattern was not altered by reducing the doses of acetone, octenol and phenols by 10–100 times, to levels comparable to those produced by an ox.With natural ox odour or a synthetic equivalent of ox odour dispensed from a ventilated pit 8 m upwind of the target, c. 28% flew upwind.This was reduced significantly to 15% if carbon dioxide was removed.In studies using a 17 m line of nets arranged orthogonally across the prevailing wind line, c. 50% of the catch was caught on the downwind side in the absence of odour.This increased significantly to c.60% when acetone, octenol and phenols were dispensed 15 m upwind, with or without carbon dioxide.With a shorter line (9 m) or an incomplete one (16.5 m long with 5 times 1.5 m wide gaps along its length) there was no change in the proportion caught downwind.For all three lines, dispensing odour upwind increased the catch 2–5 times on both the up-and downwind sides of the nets.It is concluded that a stronger upwind response to host odour is elicited when carbon dioxide is present.It is suggested that in nature upwind flight is very imprecisely orientated, with tsetse making flights up and down an odour plume 'searching' for a host.