Development of teratocytes associated with Microctonus aethiopoides Loan (Hymenoptera: Braconidae) in natural and novel host species

A laboratory study investigated development of teratocytes derived from the parasitoid Microctonus aethiopoides Loan in the natural host, Sitona discoideus Gyllenhal, and in three novel hosts, the introduced weed biological control agent Rhinocyllus conicus (Froehlich), and two New Zealand native species Nicaeana cervina Broun and Irenimus stolidus Broun. Weevils were exposed to parasitoids and then examined 6, 10 and 15 days post-parasitism for parasitoid stage and size, and teratocyte number and size. In all hosts, teratocyte numbers decreased and size increased as parasitoid development progressed, although 6 days after parasitism, fewer, larger teratocytes were found in I. stolidus than S. discoideus or N. cervina. In weevils containing second-third instar parasitoid larvae, the most permissive hosts, S. discoideus and N. cervina contained more teratocytes than the least permissive hosts I. stolidus and R. conicus. Host gender influenced some aspects of parasitoid and teratocyte development. Total teratocyte volume was greater in female than male S. discoideus at all sampling times, and at 10 days post-parasitism in N. cervina. A possible relationship between host suitability and teratocyte development is discussed.     

Teratocytes growth pattern reflects host suitability in a host–parasitoid assemblage

Abstract.  In some parasitoid species, the serosa membrane breaks apart at hatching and produces teratocyte cells that assume various functions (immunossupression, secretion and nutrition) mediating host–parasitoid relationships. Teratocyte growth pattern may thus reflect the host suitability for a parasitoid. The teratocyte growth pattern (increase in size and number of teratocytes as a function of time) is studied and used as an indirect measure of fitness to compare the development of the endoparasitoid Dinocampus coccinellae in a marginal host, the coccinellid Harmonia axyridis , and in a suitable host, Coleomegilla maculata . Indirect measures of fitness recorded in both host species confirm that C. maculata is a suitable host for D. coccinellae contrary to the marginal host H. axyridis. According to regression analysis, teratocyte numbers decrease linearly whereas teratocyte size increases linearly with time in the suitable host C. maculata (larvae or adults). In the marginal host, parasitism occurs only in the larval stage where a delay in the parasitoid larval development is observed. Increase in teratocyte size is also highly variable. The teratocyte growth pattern of the parasitoid in the marginal host does not follow the linear model found in the suitable host. Teratocyte growth pattern may be a useful criterion to evaluate host-suitability and host range of parasitoids.     

Extended in vitro culture of Microplitis croceipes teratocytes and secretion of TSP14 protein

Teratocytes, cells which originate from the serosal membrane of some Braconidae and Scelionidae, can be found in the hemocoel of permissive hosts during part or all of the developmental time of the parasitoid larva. Teratocytes from Microplitis croceipes are known to secrete biologically active proteins, which contribute to developmental arrest and failure to pupate of Heliothis virescens larvae. One such protein, which has a molecular weight of approximately 14 kDa is called TSP14. The presence of parasitoid larvae is essential to maintain teratocytes under in vitro conditions with protein-free EX-CELL 400. The teratocyte viability was maintained in vitro for at least 12 days in the presence of larvae when medium was exchanged every three days. Western blots show that TSP14 was secreted during the entire period of exchanges. In the absence of parasitoid larvae, teratocyte viability was only 30% by day 6 and no TSP14 had been secreted. In the absence of parasitoid larvae, teratocytes maintained in vitro in EX-CELL 400 medium supplemented with 10% FBS remained viable for at least nine days and secreted TSP14 for at least six days. This suggests that parasitoid larval secretions are sufficient but not uniquely essential to maintain teratocyte viability. Parasitoid larvae maintained in the absence of teratocytes did not secrete TSP14 and their secretory products did not inhibit pupation of H. virescens larvae.     

Host regulation effects on Heliothis virescens (F.) larvae inducd by teratocytes of Cardiochiles nigriceps Viereck (Lepidoptera,Noctuidae-Hymenoptera,Braconidae)

Teratocytes deriving from the serosal membrane of Cardiochiles nigriceps Viereck, obtained “in vitro” from embryos hatched on a semidefined medium, were injected at different numbers and in different developmental stages of nonparasitized Heliothis virescens (F.) last instar larvae. Host development was affected by teratocyte injections and the responses registered ranged from normal to complete inhibition of pupation, according to the number of teratocytes injected and the developmental stage of the larva at time of injection. Complete pupation failure was observed when teratocytes derived from 4C nigriceps embryos were injected into 1st day 5th instar (new-slender stage) host larvae. Complete pupation occurred when teratocytes from 2 embryos were injected into 3rd or 4th day 5th instars (burrow-digging or day 1 cell formation stage). Intermediate responses, such as the formation of pupal cuticle without ecdysis or with only partial ecdysis, were obtained with intermediate teratocyte numbers, or host developmental stages. All pupae derived from teratocyte injected larvae failed to develop into adults normally obtained from control injected larvae. The larval weight just before pupation was negatively affected only when teratocyte injections were performed on 1st day 5th instar H. virescens larvae. Teratocyte injections altered the hemolymph protein titer to a level similar to that occurring in parasitized larvae. At the same time the ecdysteroid titer was characterized by a late significant increase, which reached values almost 3 times greater than found in normally parasitized larvae, and also surpassed the highest values registered for nonparasitized larvae. Ligation of parasitized larvae between the meso- and metathorax demonstrated that when the prothoracic glands were excluded, there was almost no ecdysteroid production posterior to the ligation. Ligations performed on parasitized larvae to isolate parasitoid eggs before hatching in the last abdominal segments, demonstrated that only virus and venom determined a reduction of the ecdysteroid titer. On the basis of these results the possible role of teratocytes in affecting the biological activity of ecdysteroids is postulated and discussed in a wider context of host-parasitoid physiological interactions.     

Teratocytes of the solitary endoparasitoid Meteorus gyrator (Hymenoptera: Braconidae): morphology, numbers and possible functions

Abstract. Laboratory studies investigated the development of teratocytes derived from the eggs of the parasitoid Meteous gyrator (Thun.) in its host, the tomato moth Lacanobia oleracea (L.). At hatching, each parasitoid egg produced an average of approximately 1000 teratocytes, but this number declined to approximately 400 during the course of parasitism. The teratocytes increased in size markedly, such that 7 days after egg hatch their mean diameter was approximately four times that of the cells immediately after dissociation. The haemolymph of parasitized hosts had reduced phenoloxidase activity, and teratocytes inhibited phenoloxidase activity when coincubated with plasma from nonparasitized hosts. The injection of teratocytes into nonparasitized fifth‐instar L. oleracea larvae suppressed growth and induced a supernumerary moult in some larvae. A number of parasitism‐specific proteins were detected in the haemolymph of parasitized hosts, and incubation of teratocytes in culture media indicated that these cells were a source of at least two of these proteins.     

Characterization of a cDNA encoding a putative chitinase from teratocytes of the endoparasitoid Toxoneuron nigriceps

Females of insect endoparasitoids inject substances along with the egg at oviposition, which can regulate or induce changes in a number of host physiological processes to benefit the developing parasitoid. These changes can be caused by substances such as venoms, calyx fluids, or symbiotic‐associated virus particles (polydnavirus), which are injected by females along with their eggs, and by substances secreted by parasitoid‐derived tissues (teratocytes) or the developing parasitoid larvae. Teratocytes (dissociated cells of the serosal membrane after parasitoid eclosion) release substances that have roles (i) in parasitoid nutrition, (ii) in the digestion of host tissues, and (iii) in the regulation of host development. Teratocytes of Toxoneuron nigriceps (Viereck) (Hymenoptera: Braconidae) have been implicated in the arrestment of the host development and in the regulation of circulating levels of host ecdysteroids. Here we describe the cDNA of a teratocyte‐secreted chitinase and its expression during parasitoid development, and discuss its putative role in this host–parasitoid association.     

Effect of mating status and age of Microplitis rufiventris (Hym., Braconidae) females on the growth pattern and number of their teratocytes

The effect of mating status and age of the female of Microplitis rufiventris parasitoid on the growth pattern of its teratocytes during the larval development is described as well as the changes in the number of these cells. The growth pattern of teratocytes derived from haploid eggs significantly differed from that of eggs deposited by mated females. Both cell diameter and the number of maturing M. rufiventris teratocytes was fertilization-dependent. Following the parasitization of Spodoptera littoralis larvae with virgin parasitoid females, the host larvae hosted a large number of cells of smaller size at the end of parasitoid development. The opposite effect was seen when the host larvae contained female parasitoid larvae. The age of the female at parasitization had an effect on the maximum cell size attained prior to parasitoid emergence. It seems that there are two factors other than mating which affect the number of teratocytes: degeneration inside the host haemolymph and to some degree accidental ingestion by parasitoid larva.     

Prediction studies on number of teratocytes and eggs of Microplitis rufiventris Kok. (Hym., Braconidae) parasitoid in superparasitized host larvae

Microplitis rufiventris Kok. (Hym., Braconidae) is an internal solitary parasitoid of many noctuid caterpillars including the cotton leafworm Spodoptera littoralis (Boisd.) ( Kokujev 1914 ; Hammad et al. 1965 ; Gerling 1969 ), the lesser cotton worm S. exigua Hbn. ( Meier 1929 ; Thompson 1946 ; El-Minshawy 1963 ); S. latebrosa Lederer ( Hammad et al. 1965 ) and American bollworm Heliothis armigera Hbn. ( Meier 1929 ; Ibrahim & Tawfik 1975 ). When the egg of M. rufiventris hatches in its host, S. littoralis, spherical cells from the serosa that envelope the parasitoid embryo are released into the host’s haemolymph. Approximately 400 cells are liberated from an egg of the parasitoid. These cells increase in size, reaching a maximum average diameter of 137 μm at the completion of parasitoid development ( Khafagi 1997 ). These cells are most frequently called ‘teratocytes’ ( — 1968 , 1971; Vinson 1970 ). It is reported that the presence of large numbers of the teratocytes is indicative of superparasitism but their number does not give an indication to the exact number of parasitoid eggs from which the cells have been derived ( —, — Khafagi et al. 1998 ) . Therefore, it was of interest to initiate prediction studies on egg and teratocyte numbers in superparasitized host larvae.     

Quantification and development of teratocytes in novel-association host-parasitoid combinations

We studied the development of teratocytes derived from two congeneric gregarious endoparasitic species, Cotesia chilonis and C. flavipes, parasitizing two congeneric novel hosts, Diatraea saccharalis and D. grandiosella. The host-parasitoid combinations studied allowed us to investigate relationships between host suitability and teratocyte development. D. saccharalis was a suitable host for both parasitoids, whereas D. grandiosella was suitable for C. chilonis development but often encapsulated C. flavipes progeny. Encapsulation of C. flavipes by D. grandiosella commenced around the time of parasitoid egg hatch, when teratocytes were released into the host's hemolymph. The gregarious parasitoids studied here released about 200 teratocytes per egg. Both absolute and normalized (teratocytes/parasitoid) numbers decreased over time. D. saccharalis supported more C. flavipes-derived teratocytes than D. grandiosella, possibly because of the unsuitability of the latter host. On intermediate assay days the number of C. flavipes-derived teratocytes was greater than for C. chilonis. However, C. chilonis-derived teratocytes grew larger than C. flavipes. Teratocytes in all host-parasitoid combinations doubled in size during parasitoid development. Teratocytes generally grew larger in D. grandiosella, which was a less suitable host.     

Interspecific competition between Diadegma semiclausum Hellen (Hym., Ichneumonidae) and Cotesia plutellae (Kurdjumov) (Hym., Braconidae) in parasitizing Plutella xylostella (L.) (Lep., Plutellidea)

Abstract:  Interspecific competition between Diadegma semiclausum and Cotesia plutellae was investigated at 25°C in the laboratory, by exposing the third instar larvae of the diamondback moth, Plutella xylostella to both species together, either species alone or by exposing the host larvae already parasitized by one species, at different intervals, to the other. When host larvae were exposed simultaneously to two species in one arena, parasitism rates of the host by each species were not reduced by the presence of the other species; joint parasitism rate by two species was not significantly higher than that by either parasitoid alone. Both parasitoids could lay eggs into the host larvae which had previously been parasitized by the other species, leading to the occurrence of multiparasitized hosts. When host larvae were parasitized first by D. semiclausum and then being followed within 1–2 h by exposing to C. plutellae , or vice versa, ensuing parasitoid cocoons from the multiparasitized host larvae were nearly all C. plutellae . When host larvae were parasitized initially by C. plutellae and then being followed by D. semiclausum two or more days later, all parasitoids ensued from the multiparasitized hosts were C. plutellae . In contrast, when host larvae were parasitized initially by D. semiclausum and then being followed by C. plutellae two or more days later, most host larvae could not survive to prepupae and most of the ensuing parasitoid adults from the surviving hosts were D. semiclausum . Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that development of both parasitoids in multiparasitized hosts were somewhat arrested, and that the first instar larvae of C. plutellae could initiate a physical attack on the larvae of D. semiclausum and remove the latter.     

Additive effect of teratocyte and calyx fluid from Cotesia plutellae on immunosuppression of Plutella xylostella

Abstract.  Teratocytes are cells that originate from the extra-embryonic tissues of some hymenopteran parasitoids, typically dissociate upon hatching, and develop in the host haemolymph. They are considered to be involved in parasitoid larval nutrient uptake, host immunosuppression and/or repression of competing parasitoid development. Teratocytes of the parasitoid, Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) are found in its natural host, Plutella xylostella (Linnaeus) (Lepidoptera: Yponomeutidae) and can be cultured in vitro . The present study demonstrates that teratocytes of C. plutellae possess a significantly depressive effect on host cellular immunity. When the hosts are preinjected with 200 cultured teratocytes (corresponding to the normal number of teratocytes released during wasp hatching), haemocyte nodulation is inhibited by approximately 40%, with younger teratocytes being more potent than older ones. Similarly, the medium in which teratocytes are cultured has similar immunosuppressive properties. In comparison, calyx fluid extracted from the C. plutellae ovary also has an immunosuppressive effect on P. xylostella . These two maternal (calyx fluid) and embryonic (teratocytes) factors are additive and result in a reduced level of nodule formation equivalent to that induced by natural parasitization. However, the immunosuppression of the parasitized P. xylostella does not appear to be due to inhibition of phospholipase A₂, an immune mediator, because injection of arachidonic acid failed to restore haemocyte nodulation capability.     

Possible bases of pseudoparasitism in Spodoptera littoralis larvae stung by Microplitis rufiventris

The effects of host age and parasitoid female age on the occurrence of 'Pseudoparasitism', using the Spodoptera littoralis-Microplitis rufiventris host-parasitoid system were investigated. The first four larval instars of the host are not equally suitable for parasitoid development. The proportion of pseudoparasitized hosts significantly increases when: (1) the age of the female parasitoid increases; (2) oviposition occurs mostly in fourth instar larvae; (3) a later age of the host instar is used; (4) the mandibles of the newly hatched parasitoid larvae mistakenly attack host interior organs (e.g. Malpighian tubules); and (5) an imperfect growth pattern of teratocytes occurs. The reluctance of female wasps to parasitize fourth instar host larvae is not due to the thickness of host cuticle but possibly due to the unfavourable physiological state of the host larvae. The age of host larvae at the time of parasitization may influence the adverse effects of parasitoid factors (e.g. polydnavirus, venom and teratocytes) on the growth of host larvae. It is suggested that females of M. rufiventris are able to determine the suitability of a potential host instar for the development of their offspring. The cell diameter of M. rufiventris teratocytes increases with increasing age of host larvae at the time of oviposition. The association within the host of living parasitoid larvae and functional teratocytes may be important for the survival of each other and consequently for successful parasitism.     

Functional analysis of a fatty acid binding protein produced by Aphidius ervi teratocytes

Aphidius ervi (Hymenoptera, Braconidae) is an endophagous parasitoid of various aphid species, including Acyrthosiphon pisum (Homoptera, Aphididae), the model host used in the present study. Parasitized hosts show a marked increase of their nutritional suitability for the developing parasitoid larvae. This alteration of the biochemical and metabolic profile is due to a castration process mediated by the combined action of the venom, injected at the oviposition, and of the teratocytes, cells deriving from the dissociation of the embryonic membrane. Teratocytes produce and release in the host haemocoel two parasitism-specific proteins, which are of crucial importance for the development of their sister larvae. One of the proteins is a fatty acid binding protein (Ae-FABP), which shows a high affinity for C14-C18 saturated fatty acids (FAs) and for oleic and arachidonic acids. To better define the possible nutritional role of this protein, we have studied its immunolocalization profile in vivo and the impact on FA uptake by the epidermal and midgut epithelia of A. ervi larvae. During the exponential growth of A. ervi larvae, Ae-FABP is distributed around discrete lipid particles, which are abundantly present in the haemocoel of parasitized host aphids and in the midgut lumen of parasitoid larvae. Moreover, a strong immunodetection signal is evident on the surface of the two larval epithelia involved in nutrient absorption: the parasitoid midgut epithelium and the external epidermal layer. These two epithelia can effectively absorb radiolabelled myristic acid, but the FA transport rates are not affected by the presence in the medium of Ae-FABP. The protein appears to act essentially as a vector in the host haemolymph, transferring FAs from the digestion sites of host lipids to the growing parasitoid larvae. These data indicate that the proteins produced by A. ervi teratocytes may play complementary roles in the nutritional exploitation of the host.     

Pea aphid clonal resistance to the endophagous parasitoid Aphidius ervi

The physiological mechanism of resistance to the endophagous braconid Aphidius ervi Haliday (Hymenoptera, Braconidae) by a pink clone (PC) of Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) has been investigated. Comparative data on parasitoid development and associated host biochemical changes in the resistant PC aphids and in a susceptible green clone (GC) of A. pisum are reported. When the PC aphids were attacked as early 4th instars, the developing parasitoid larvae showed a strongly reduced increase in size, compared to those synchronously developing in GC aphids, and were unable to produce a regular mummy. In contrast, parasitism of 2nd instar PC aphids, allowed completion of parasitoid development, but adults had a prolonged developmental time, due to a longer duration of parasitoid’s final (3rd) instar. In all cases, teratocytes, cells deriving from the A. ervi serosal membrane, and the proteins abundantly synthesised by them, were never found in the haemolymph of parasitised PC aphids. Host castration, as demonstrated by total protein incorporation into reproductive tissues, was total in the majority of early (2nd instar) parasitised host aphids, while it was limited when later instars (4th) of PC aphids were parasitised. This is partly due to the absence of the cytolytic activity of teratocytes on host embryos, which, through their persistence, may compete for nutritional resources with the developing parasitoid larvae. In parasitised PC aphids, this competitive effect is further aggravated for the parasitoid by the absence of the regulated amino acid titre increase in the host haemolymph, which is regularly observed in GC aphids. Failure of teratocyte development in the PC clone of the pea aphid is, then, the major functional constraint accounting for the reduction/inhibition of A. ervi larval growth. The reported results allow to assess in vivo the role of teratocytes in the host physiological redirection and nutritional exploitation by the parasitoid, and to integrate and validate the proposed physiological model of host-parasitoid interactions in the system A. pisum-A.ervi.     

一种中红侧沟茧蜂畸形细胞分泌的寄生特异蛋白

SDS-PAGE电泳表明,黏虫Pseudaletia separa-ta、棉铃虫 Helicoverpa armigera、小地老虎 Agrotisypsilon的幼虫受中红侧沟茧蜂Microplitis mediator寄生后,血淋巴中都出现一个98.6 kDa的寄生特异蛋白(p98.6)。畸形细胞(teratocytes)的体外培养发现,p98.6是由来自中红侧沟茧蜂胚胎浆膜层的畸形细胞分泌的。这一结果将为研究寄生蜂的寄生生理和畸形细胞在协调寄生蜂和寄主关系中的作用打下基础。     

Teratocytes: Growth and numbers in the hemocoel of Heliothis virescens attacked by Microplitis croceipes

When the egg of Microplitis croceipes hatches in its host, Heliothis virescens, spherical cells (teratocytes) from the extraembryonic membrane are released into the host's hemolymph. Approximately 750 teratocytes are liberated from the parasitoid egg, and they average 10.5 μm in diameter when released. These cells increase in size, reaching a maximum average diameter of 140 μm in 8–9 days.The developing parasitoid emerges from the host in 9 days. The host remains alive and contains approximately 750 teratocytes, indicating that the teratocytes are not consumed by the parasitoid. These results suggest that teratocytes are not a direct source of nutrition for the developing parasitoid.Observations showed that encapsulation can occur in the presence of teratocytes even following the emergence of the parasitoid. The results indicate that teratocytes do not block the host's ability to encapsulate certain foreign materials within its hemocoel.     

Host regulation and release of parasitism-specific proteins in the system Toxoneuron nigriceps-Heliothis virescens

The braconid wasp Toxoneuron nigriceps induced qualitative and quantitative changes in the protein composition of the moth Heliothis virescens host hemolymph. Total protein concentration was found to be higher in parasitized host 4 days after parasitism as compared to control hosts, mainly due to changes in a particular group of proteins. Host proteins with a molecular mass of 173 and 72 kDa were found in higher levels in the hemolymph of parasitized larvae as control hosts approached pupation, while an 80 kDa peptide was found in reduced concentration in the hemolymph of parasitized hosts. Levels of these three peptides were maintained throughout parasitoid development, while two of them (173 and 72 kDa) were cleared from the host hemolymph close to pupation. Besides the regulation of host proteins, three parasitism-specific proteins (PSPs) were released into the host hemolymph. Two of them (PSP1-MW=116 kDa, pI=6.3; PSP2-MW=114 kDa, pI=6.2) first appeared in the hemolymph of parasitized hosts soon after pupation of control host and increased in concentration as the parasitoid developed. The third PSP (PSP3-MW=56 kDa, pI=5.8) was produced towards the end of parasitoid larval development, close to parasitoid egression. Database searches based on the amino acid composition and amino terminal sequence of PSP1 and PSP2 did not produce any significant matches, while PSP3 was identified as a putative chitinase. Incubation of host derived tissues, parasitoid larvae and teratocytes in 35S conditioned media suggested PSPs were a product of teratocytes. The role of the regulation of host proteins and release of PSPs by teratocytes for the successful development of T. nigriceps are discussed.     

Systematic analysis of a wasp parasitism arsenal

Parasitoid wasps are among the most diverse insects on earth with many species causing major mortality in host populations. Parasitoids introduce a variety of factors into hosts to promote parasitism, including symbiotic viruses, venom, teratocytes and wasp larvae. Polydnavirus‐carrying wasps use viruses to globally suppress host immunity and prevent rejection of developing parasites. Although prior results provide detailed insights into the genes viruses deliver to hosts, little is known about other products. RNAseq and proteomics were used to characterize the proteins secreted by venom glands, teratocytes and larvae from Microplitis demolitor, which carries M. demolitor bracovirus (MdBV). These data revealed that venom glands and teratocytes secrete large amounts of a small number of products relative to ovaries and larvae. Venom and teratocyte products exhibited almost no overlap with one another or MdBV genes, which suggested that M. demolitor effector molecules are functionally partitioned according to their source. This finding was well illustrated in the case of MdBV and teratocytes. Many viral proteins have immunosuppressive functions that include disruption of antimicrobial peptide production, yet this study showed that teratocytes express high levels of the antimicrobial peptide hymenoptaecin, which likely compensates for MdBV‐mediated immunosuppression. A second key finding was the prevalence of duplications among genes encoding venom and teratocyte molecules. Several of these gene families share similarities with proteins from other species, while also showing specificity of expression in venom glands or teratocytes. Overall, these results provide the first comprehensive analysis of the proteins a polydnavirus‐carrying wasp introduces into its host.     

Microplitis croceipes teratocytes: in vitro culture and biological activity of teratocyte secreted protein

Teratocytes originate from the dissociation of the extraembryonic serosal membrane in some Braconidae and Scelionidae. Methods used to culture teratocytes in vitro are described and the yield of teratocyte secreted proteins (TSP) was measured. Although 90% are viable after 6 days, in vitro teratocytes reached only half the diameter (32&mgr;m) of the same age teratocytes obtained in vivo. Teratocytes cultured in vitro secrete as much as 0.7&mgr;g of protein per day per larval equivalent ( approximately 900 cells). Presence of parasitoid larvae enhanced teratocyte viability while periodic exchange of medium did not. However, medium exchange significantly increased the total amount of protein secreted. Size and viability were improved with the addition of 10% FBS to the Ex-cell 400 culture medium. Non-denaturing PAGE showed at least 15 proteins with molecular sizes estimated to be between 24 to 347kDa in medium containing teratocytes. An in vitro fat body assay was developed to measure the effect of TSP on protein synthesis and juvenile hormone esterase (JHE) activity. Crude TSP inhibited in vitro incorporation of [(35)S]-methionine into protein synthesized by the fat body. The amount of JHE released from in vitro fat body treated with crude TSP was significantly less than controls, most likely caused by the inhibition of general protein synthesis. The active fraction of TSP passed through a 30kDa molecular weight cutoff filter but was retained by a 3kDa filter. SDS-PAGE revealed four proteins with molecular weights between 8 and 20kDa not present in control medium incubated without teratocytes.     

Host regulation by the aphid parasitoid Aphidius ervi: the role of teratocytes

The biochemical profile and metabolism of Acyrthosiphon pisum(Harris) (Homoptera, Aphididae) are markedly altered and redirected in response to parasitization by the endophagous braconid Aphidius erviHaliday (Hymenoptera, Braconidae). In the present study, the role played in the host regulation process by teratocytes, cells deriving from the dissociation of the embryonic membrane of the parasitoid, is taken into consideration. The protein synthesis activity of these cells of embryonic origin is analysed in vitroand an essential characterization of those proteins de novosynthesized and released in the incubation medium is provided. Teratocytes, obtained by dissecting parasitized host aphids, 3, 4 and 5 days after parasitoid oviposition, were incubated in vitroand, at the end of the incubation period, were separated from the medium for SDS-PAGE analysis of both cellular and secreted proteins. Various cellular proteins were more abundant as the time between parasitization and teratocyte collection increased. Furthermore, two proteins, showing an approximate molecular mass of 15 kD (p15) and 45 kD (p45) respectively, were abundantly secreted in the incubation medium by 5 day-old teratocytes. Incubations in presence of ³⁵S radiolabelled amino acids indicated that p15 and p45 are both synthesized by A. erviteratocytes. The amino acid composition of these two proteins was similar to that reported for other insect proteins with a demonstrated nutritional function. The p45 protein was found to be glycosylated. A tentative physiological model describing the host regulation role played by different parasitoid-derived factors is proposed.