The identification of an aphid juvenile hormone, and its titre in relation to photoperiod

ABSTRACT. Whole body extractions from larval and adult apterous forms of Megoura viciae , and from adult Aphis fabae , were analysed for the known insect juvenile hormones (JHs) by a gas chromatography-mass spectrometric method. Low levels of JH III were detected in both aphid species, the first identification of a juvenile hormone from an homopteran insect. Although the mean titre in adult M. viciae is higher in long-day than in short-day reared insects (0.12±0.03 v. 0.04±0.01 ng/g), titres were variable and measurements overlapped. The results are discussed in the context of the hormonal control of aphid polymorphism and the question of identity of homopteran and hemipteran JH.     

Inhibition by kinoprene of photoperiod-induced male production by apterous and alate viviparae of the aphid Myzus persicae

Photoperiod-induced male production by apterous and alate viviparae of the green peach aphid. Myzus persicae, was reduced or prevented by treating the aphids with the JH analog kinoprene (Zoecon's insect growth regulator ZR 777). Concomitant with this reduction in the number of males was an increase in the production of females. This was most clearly demonstrated for apterous viviparae that had been raised from birth under weak long-night regimes of 10–10.5 hr dark day, and exposed to 0.1% kinoprene-treated radish seedlings for 2–3 days on reaching the fourth larval instar or adulthood.Male production by alate viviparae, whose apterous mothers were born and raised for 5 days under a long-night regime of 15 hr dark day and then maintained under a short-night regime of 8 hr dark day, was completely inhibited by exposing them to kinoprene-treated plants for 2–3 days when they had reached the fourth instar.It is concluded that the kinoprene treatment affects sex chromosome replication in the oögonia of an aphid so that these germ cells develop parthenogenetically into females (2n = 12 with two X chromosomes) rather than males (2n = 11 with one X chromosome). This may result either from a direct action of absorbed kinoprene on the oögonia or from an indirect action whereby the kinoprene stimulates the insect's hormonal system to produce a hormone that stimulates development of the oögonia into females.     

Photoperiodic induction of winged females in the black bean aphid. Aphis fabae

Abstract. The Photoperiodic of winged females (alatae) in the black bean aphid, Aphis fabae Scop. (Homopetera: Aphididae), is investigated in detail with emphasis on the interaction of the maternal and embryonic/young larval photoperiodic clocks. Previous work had shown that in uncrowded conditions the induction of gynoparae (winged females that produce sexual females) requires both prenatal and postnatal exposure to long-night (12 h) Photoperidic cycles: present results show that sole postantal exposure to long nights of any lenght does not induce wing formation in early-born aphids.
When aphids were exposed to experimental light-dark cycles postanatally only, their daughters developed as alate in long nights and as apterae in short nights: the critical night lenght (CNL) was 11:1 h. Additional prenatal exposure to experimental regimes resulted in a significantly shorter CNL (10.6 h). This difference could be accounted for by the fact that more experimental light-dark cycles were experienced in the latter case.
Apterous aphids transferred from LD 16:8 h to LD 12:12 h as either third-or fourth-stadium larvae, or young adults, switched for aptera-production to alata-production. The transition form aptera- to alata-production was rather abrupt in third-stadium transfers but more gradual when transfers occurred as fourth-stadium larvae and adults. Moreover, s the number of days required for 50% of the aphids to become alata-producers increased from 7–8 in third-stadium transfers, to 9–10 and 11–12 in the later transfers.     

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.     

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.     

The occurrence of a juvenile hormone binding protein and in vitro synthesis of juvenile hormone by the serosa of Locusta migratoria embryos

Summary At the end of blastokinesis, serosal epitheliae of 4- to 5-day-old embryos of Locusta migratoria contain an immunohistologically detectable cytosolic protein (M_r 240 kDa) which is related to the juvenile hormone carrier-protein in the haemolymph of the same species and which binds tritiated juvenile hormone 3 (JH3) (K_d10^–8 M). At this early stage of development the corpora allata of the embryo are not yet fully differentiated and do not synthesize JH3 in organ cultures. The earliest detectable JH3 production by corpora allata in isolated heads is on day 6. On the other hand, serosal epitheliae of 4- to 5-day-old embryos produce JH3 in organ cultures, as has been shown by methylation of (10-³H)-JH3-acid to (10-³H)-JH3, and by incorporation of tritiated CH₃ from l-(methyl-³H)-methionine into JH3. Isolated heads and abdomens of the embryos used as donors for the serosal preparations did not show methyl transferase activity responsible for JH3 biosynthesis. The serosal cells represent a hitherto unrecognized source of methyl transferase activity and of JH3 production. Degradation of JH3 to JH3-acid was also observed.Dedicated to Professor Herbert Röller on the occasion of his 60th birthday     

Juvenile Hormone Stimulation of Oocyte Development and Embryogenesis in the Parthenogenetic Ovaries of an Aphid,Aphis fabae

Summary

The parthenogenetic ovaries of the black bean aphid, Aphis fabae, contain developing embryos. When reared at 15°C in long days (LD 16:8) oocyte development begins within the ovaries of the largest embryos of a fourth instar mother 24–48 hr after her ecdysis from the third instar. Starvation, decapitation and precocene III treatment inhibit embryonic oocyte development; juvenile hormone treatment reverses this inhibition. A method for the in vitro culture of embryos is described and under these conditions juvenile hormone again stimulates oogenesis. Embryogénie growth in vivo, as measured by the increase in length of the oldest daughter embryos, is also stimulated by juvenile hormone treatment. The results are discussed in relation to other roles proposed for juvenile hormone in aphid development.     

Effects of previous plant infestation on sieve element acceptance by two aphids

Probing behaviour as affected by a previous infestation was studied in two aphid species on their respective host plants. Probing behaviour by Aphis fabae (reported to have beneficial effects when living in colonies) and Rhopalosiphum padi (without known beneficial effects) was studied using the electrical penetration graph (EPG) technique. In A. fabae the main effects were longer and more continuous sap ingestion, and less salivation into sieve elements before sap ingestion. These suggest phloem factors. Nevertheless, mesophyll and non-vascular tissues are likely to be involved to a lesser extent, as reflected by fewer non-probing periods before the first phloem phase on previously colonised leaves as compared to clean leaves. Total honeydew production increased on a previously colonised leaf due to the prolonged sap ingestion periods but the excretion rate was not affected, indicating that the ingestion rate remained unaltered. R. padi did not show responses to previous colonisation. It is hypothesized that the changes in probing behaviour are due to changed plant properties, chemical contents of sieve element sap and/or physiological changes induced by the saliva from the colony.     

Identification of the juvenile hormone from the cricket, Teleogryllus commodus, and juvenile hormone titre changes

In the cricket, Teleogryllus commodus, eggs, haemolymph of 7th and 8th (last)-larval instars, and haemolymph of adults of both sexes contain only juvenile hormone III. While in the male the hormone titre is independent of previous mating experience, juvenile hormone concentration in haemolymph taken from females 36–38 hr after mating (an event which is followed by oviposition) is at a level 5 times higher than that of virgin females. Based on data gleaned from several research groups the identification of juvenile hormone III as the exclusive juvenile hormone in the Order Orthopteroidea is discussed.     

Variation and covariation of life history traits in aphids are related to infection with the facultative bacterial endosymbiont Hamiltonella defensa

Host–symbiont associations play an important role in insects. In aphids, facultative symbionts affect host plant use and increase thermal tolerance and resistance to natural enemies. In spite of these beneficial effects on aphid fitness, the frequency of facultative symbionts in aphids ranges from low to intermediate. Tradeoffs induced by symbionts could prevent the fixation of symbionts in aphid populations. Therefore, we studied the life history traits and correlations between them in 21 clones of the black bean aphid, Aphis fabae, seven of which were infected with the facultative endosymbiont Hamiltonella defensa. We found that clones harbouring H. defensa exhibited significantly higher body mass at maturity and offspring production, and a marginally higher intrinsic rate of increase. However, development time and offspring body size did not differ between symbiont‐free and infected clones. In addition, body mass at maturity was positively correlated with offspring production, offspring body size and intrinsic rate of increase, whereas development time was negatively correlated with body mass at maturity, offspring production and offspring body size. Excluding infected clones had little effect on these correlations; only correlations between body mass at maturity and offspring production, and between development time and offspring body size, became nonsignificant. Therefore, we did not find any evidence for tradeoffs between life history traits induced by symbiont infection. In fact, infected clones had higher overall fitness than symbiont‐free clones under the conditions of our experiment, suggesting that symbionts do not impose costs on aphids harbouring them. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 237–247.     

Amino acids as respiratory substrates in aphids: an analysis of Aphis fabae reared on plants and diets

Abstract. The fate of radioactively labelled amino acids injected into the haemolymph of the aphid Aphis fabae was investigated. Radioactivity from each of L-[U-¹⁴C]-glutamic acid, L-[U-¹⁴C]-serine and L-[U-¹⁴C]-threonine in the aphid tissues declined exponentially, at rates of 32, 9.3 and 1.0 pmol/aphid/min, respectively. For ¹⁴C-glutamic acid, radioactivity lost from the aphids was recovered quantitatively as carbon dioxide, and radioactivity in aphid saliva and honeydew was undetectable. When expressed on a per unit aphid biomass basis, the rate of respiratory loss of glutamic acid from aphids reared on chemically-defined diets was more than double that of aphids reared on the host plant, Vicia faba . It is concluded that respiration is a quantitatively important component to the aphid metabolism of glutamic acid and other amino acids.     

Independently regulated juvenile hormone activity and vitellogenesis in mosquitoes

Temporally distinct, head-mediated processes regulate vitellogenic development as well as juvenile hormone (JH)-mediated development of ovarian follicles of Aedes aegypti. In blood-fed adult mosquitoes, vitellogenic development is stimulated during the first day after blood is imbibed and JH secretion is stimulated 2 days later. JH secretion in recently ecdysed adult mosquitoes is stimulated during or shortly before ecdysis. These observations suggest that vitellogenesis follows blood-ingestion, whereas JH activity may secondarily be promoted by vitellogenesis. It may be that vitellogenesis and JH activity are mediated by different brain hormones     

NMR assignments of juvenile hormone binding protein in complex with JH III

A hemolymph juvenile hormone binding protein (JHBP) shuttles hydrophobic JH, a key hormone in regulation of the insect life cycle, from the site of the JH biosynthesis to the cells of target organs. We report complete NMR chemical shift assignments of Bombyx mori JHBP in the JH III-bound state.     

Ultrastructural localization of juvenile hormone biosynthesis by insect corpora allata

Summary The conversion of exogenous ³H-farnesenic acid to ³H-methyl farnesoate and ³H-C₁₆ juvenile hormone (JH) has been followed in the corpus allatum (CA) cells of the desert locust Schistocerca gregaria by means of electron microscopic autoradiography. Aerobic and anaerobic chase incubations have been used to modify the quantities of these three compounds within the CA cells. Under all incubation conditions, radiolabel is found associated almost exclusively with the subcellular membrane systems — smooth endoplasmic reticulum (SER) and Golgi elements —and with the mitochondria. CA cells are probably similar to vertebrate steroid-synthesizing cells in that the secretory product is synthesized in the SER and mitochondria.Radiolabel was found to be present in all cells of the CA suggesting that all cells are capable of at least the final two stages of JH biosynthesis (the esterification and epoxidation of ³H-farnesenic aid). This indicates that JH biosynthesis may be regulated through changes in the biosynthetic capabilities of individual cells rather than through changes in the total number of cells engaged in biosynthesis. Radiolabel was not observed to be associated with any distinctive cellular product, a result which provides additional evidence for the suggestion that the release of JH from the CA is governed by laws of simple physical diffusion.Supported by operating grants from the National Research Council of Canada to SST and ASMS. ³H-farnesenic acid was supplied by the late Dr. A.F. White of the Unit of Invertebrate Chemistry and Physiology, A.R.C., University of Sussex. We thank Dr. G.E. Pratt for helpful discussions     

Developmental control of ultrasound sensitivity by a juvenile hormone analog in crickets (Teleogryllus oceanicus)

Cricket ears are sensitive to ultrasound as well as to lower, cricket-like sound frequencies. Ultrasound stimuli evoke negative phonotaxis in flying crickets, a behavior that has been interpreted as a defensive response against predation by echolocating bats. A recent study on a wing-dimorphic species, Gryllus texensis, showed that short-winged individuals, which are incapable of flight, are less sensitive to ultrasound, but not to lower sound frequencies, than their long-winged counterparts. The developmental decision to develop as a long- or short-winged individual is made during the last two larval instars, and there is some evidence suggesting that juvenile hormone (JH) has an instructive role, such that high levels of JH result in short-winged individuals. We show that treatment of last-instar larvae of a monomorphic long-winged species, Teleogryllus oceanicus, with a JH analog causes a decrease in sensitivity to ultrasound, but not to the lower sound frequency used for intraspecific communication.     

Ecdysis triggering hormone ensures proper timing of juvenile hormone biosynthesis in pharate adult mosquitoes

Juvenile hormones (JHs) are synthesized by the corpora allata (CA) and play a key role in insect development. A decrease of JH titer in the last instar larvae allows pupation and metamorphosis to proceed. As the anti-metamorphic role of JH comes to an end, the CA of the late pupa (or pharate adult) becomes again “competent” to synthesize JH, which would play an essential role orchestrating reproductive maturation. In the present study, we provide evidence that ecdysis triggering hormone (ETH), a key endocrine factor involved in ecdysis control, acts as an allatotropic regulator of JH biosynthesis, controlling the exact timing of CA activation in the pharate adult mosquito. Analysis of the expression of Aedes aegypti ETH receptors (AeaETHRs) revealed that they are present in the CA and the corpora cardiaca (CC), and their expression peaks 4 h before eclosion. In vitro stimulation of the pupal CA glands with ETH resulted in an increase in JH synthesis. Consistent with this finding, silencing AeaETHRs by RNA interference (RNAi) in pupa resulted in reduced JH synthesis by the CA of one day-old adult females. Stimulation with ETH resulted in increases in the activity of juvenile hormone acid methyltransferase (JHAMT), a key JH biosynthetic enzyme. Furthermore, inhibition of IP₃R-operated mobilization of endoplasmic reticulum Ca²⁺ stores prevented the ETH-dependent increases of JH biosynthesis and JHAMT activity. All together these findings provide compelling evidence that ETH acts as a regulatory peptide that ensures proper developmental timing of JH synthesis in pharate adult mosquitoes.     

Prepupal regulation of juvenile hormone esterase through direct induction by juvenile hormone

The regulation of the prepupal peak of juvenile hormorne esterase activity was investigated and found to be directly induced by juvenile hormone. Allatectomy and reimplanation as well as juvenile hormone application experiments all indicated that the appearance of prepupal juvenile hormone esterase activity was in response to a prepupal burst of juvenile hormone. Implantation experiments indicated that the effect of juvenile hormone is not mediated through the isolated brain or subesophageal ganglion.