Juvenile hormone esterase activity repressive factor in the plasma of parasitized insect larvae

A proteinaceous factor that represses plasma juvenile hormone esterase activity in parasitized insect larvae has been isolated and partially characterized from last instar larvae of the armyworm Pseudaletia separata parasitized with the wasp Apantales kariyai. Purification procedures consisted of extraction with 25% ethanol, gel filtration and reversed phase high performance liquid chromatography. Plasma juvenile hormone esterase activity in Day 3 last instar larvae was repressed by 50% when larvae were injected on Days 1 and 2 with 6.5 pmol of the purified peptide, which has a molecular weight of about 4,500 Da. The application of the factor also causes more than a 2-day delay in the onset of pupation. The sequence of 23 amino acid residues at the amino terminus of the factor was determined as follows: H-Glu-Asn-Phe-Ser-Gly-Gly-Xaa-Val-Ala-Gly-Tyr-Met- Arg-Thr-Pro-Asp-Gly-Arg-Xaa-Lys-Pro-Thr-Phe-Tyr-Gln-.

Venom and viral expression products of the endoparasitic wasp Campoletis sonorensis share epitopes and related sequences

Endoparasitic wasps of lepidopteran insects must induce changes in host immunity and development to survive. Depending on the species, this may require wasp venom proteins and/or a polydnavirus. We describe an immunological and genetic relationship between the Campoletis sonorensis polydnavirus and the wasp's venom gland. Monoclonal antibodies raised against venom glands recognized epitopes conserved on several polydnavirus proteins and on multiple wasp oviduct and venom proteins. The viral envelope proteins had molecular masses of 16, 20, 45, and 50 kDa, while a complex of at least five immunoreactive venom-gland and soluble oviduct proteins ranged in size from 24 to 36 kDa. Since the conserved epitopes were present on the viral envelope, neutralization assays were performed. Monoclonal antibodies added to purified virus blocked the normal viral inhibition of host growth and development. To determine whether venom mRNA and viral genes were also related, venom-related cDNA clones were isolated from the wasp oviduct with a venom-gland cDNA probe. Venom-related viral clones were then identified and selected from a viral genomic library and from a parasitized Heliothis virescens cDNA library. Venom-related mRNAs were expressed in the venom gland, the oviduct, and the parasitized host. We propose that the immunological relationship between venom and viral proteins, and the hybridization of venom and viral genes, may reflect an evolutionary relationship in which venom gene homologs were incorporated into the viral genome, thereby allowing viral expression of venom-related genes and enhancing parasite survival.

The influence of infection with Steinernema feltiae Filipjev on the haemocyte picture of the cotton leaf worm (Spodoptera littoralis Boisduval)

Infection of Spodoptera littoralis Boisduval larvae with Steinernema feltiae Filipjev nematodes caused sharp variation in proportional percentages of differential haemocyte counts. The mean total haemocyte count per mm3 of haemolymph in control larae of S. littoralis was 6000 haemocyte mm3. After infection with 50, 100, 200 and 500 parasitic nematodes of S. feltiae, the mean total count was significantly increased to 17,250, 18,600, 21,000 and 24,000 haemocyte mm3 respectively.

Segment W of Campoletis sonorensis virus: expression, gene products, and organization

Campoletis sonorensis virus (CsV, Polydnaviridae) is a segmented double-stranded DNA virus which has an apparently symbiotic relationship with the parasitic wasp, Campoletis sonorensis. CsV replicates in the oviducts of the parasitic wasp and is injected into the wasp's host, Heliothis virescens (Lepidoptera; Noctuiidae), during oviposition. In the parasitized lepidopteran host, the virus has a dramatic effect on host physiology and viral gene products are believed to play an essential role in the survival of the parasitic wasp's egg and larva. In the current study, we used Northern blot analyses to examine expression from segment W in the parasitized host and in the parasitic wasp. Segment W hybridized primarily to two relatively abundant mRNAs (1.6 and 1.0 kb) from the parasitized host. These 1.6- and 1.0-kb mRNAs, which were previously shown to be transcribed from two closely related genes (WHv1 and WHv2) on segment W (G. W. Blissard, O. P. Smith, and M. D. Summers, 1987, Virology 160, 120-134) increased in relative abundance between 2 and 24 hr postparasitization (pp) and were detected throughout parasitization (8 days). To study the proteins encoded by these closely related genes, the open reading frame from each of the related genes was cloned into a baculovirus expression vector. By pulse labeling in the presence and absence of tunicamycin, we examined secretion and glycosylation of these CsV proteins in infected lepidopteran cells (Spodoptera frugiperda). Expression of segment W in the oviducts of the female wasp was also examined. Segment W hybridized to at least five CsV mRNAs on Northern blots of poly(A) mRNA from C. sonorensis oviducts. To identify specific CsV mRNAs and map putative viral genes expressed in wasp oviduct tissues, segment W was used to screen a cDNA library of C. sonorensis oviduct mRNAs. Three cDNAs were used to identify CsV mRNAs by Northern blot analyses and to map the locations of three putative CsV genes on segment W. Cross-hybridization within the CsV genome was examined with cloned segment W and with the three cloned cDNAs.

Role of virus-like particles in parasitoid-host interaction of insects

Insect endoparasitoids are capable of suppressing the immune reaction of their habitual hosts in a specific way. Salt (1968) characterized some of the implications: This seeming contradiction--that defence reactions against all kinds of foreign bodies are available to insects and that endophagous parasitoids are nevertheless able to develop in insect hosts--is resolved by recourse to one of the principles of host specificity. Although insects as a group react to every foreign body in the sense that any organism or substance evokes a reaction in most insects, each species of insect fails to make a reaction (or makes an ineffective reaction) to a small group of organisms, its habitual parasites. It is the common paradox of parasitology that defence reactions are least effective against the most noxious parasites, involving the tautology that the most noxious parasites are those against which defence reactions are least effective. Recently, VLP of hymenopteran wasps have been shown to play a crucial part in suppressing the cellular encapsulation reaction (Stoltz and Vinson, 1979a). In some parasitoid wasps, polydnavirus particles are involved in the phenotypic transformation of hemocytes, reducing the capability of the host to mount an immune reaction towards the parasitoid egg (Stoltz and Guzo, 1986; Davies et al., 1987). However, at least in Venturia, the eggs are effectively protected by VLP that lack significant amounts of nucleic acids, precluding any virus expression in the host. The question was raised whether VLP could have acquired properties of the host immune system, which allows specific suppression of the immune response. The finding of structural similarities between VLP proteins and a host component indicated that a host function is expressed in VLP (Feddersen et al., 1986) and this observation has subsequently permitted the identification and characterization of a protein in caterpillars, which appears to inhibit cellular defense reactions (Berg et al., 1987). On the basis of these results we continue to approach this parasitoid-host interaction, assuming that VLP have evolved in the host organism and eventually acquired the coding sequences of a host protein with properties of an inhibitor of encapsulation. Although there are several ways to explain the emergence of VLP in endophagous parasitoid wasps, a simple proposal would be that such hypothetical viruses, which were able to suppress immune reaction in lepidopteran hosts, were incorporated into a parasitoid wasp to become part of the life cycle of the parasitoid.(ABSTRACT TRUNCATED AT 400 WORDS)

The parasitoid Apanteles kariyai inhibits pupation of its host, Pseudaletia separata, via disruption of prothoracicotropic hormone release

When the parasitoid Apanteles kariyai laid eggs into host Pseudaletia separata larvae, before prothoracicotropic hormone (PTTH) was released in the last instar preparatory to metamorphosis, the host did not pupate and the larvae of the wasps emerged. The ecdysteroid titer of unparasitized intact larvae increased up to 1 microgram/ml 1 day before pupation, whereas the titer of parasitized larvae was maintained at a low level without the surge. Isolated prothoracic glands from intact larvae synthesized much more ecdysone than those of parasitized larvae both in vivo and in vitro. Administration of exogenous PTTH caused the activation of the prothoracic glands seen during parasitization. Injection of 20-hydroxyecdysone (20-HE) into the parasitized larvae caused by host's pupation, but did not affect the development of the wasp larvae. However, the sensitivity of the integument to 20-HE was lower in parasitized than in unparasitized larvae. Injection of a mixture of adult wasp calyx and venom fluids into last instar unparasitized larvae delayed their pupation, suggesting that calyx and venom fluids are factors contributing to disturbance of the normal function of brain-prothoracic gland system. These results show that parasitization inhibits secretion and/or synthesis of PTTH and also delays the larval-pupal commitment of the integument by keeping the ecdysteroid level low.

Heterorhabditis spp. and Steinernema (= Neoaplectana) spp.: temperature, and aspects of behavior and infectivity

The infectivity of several species/strains of nematodes of the genera Heterorhabditis and Steinernema for postfeeding, 3rd instar larvae of the sheep blowfly, Lucilia cuprina, was tested in sand at various temperatures. Of the two genera, the steinernematids were more active at lower temperatures and parasitized L. cuprina over a greater temperature range. The temperature range of infectivity for L. cuprina differed between nematodes of the same genus and between strains of the same species. Parasitization of L. cuprina and Galleria mellonella occurred in a temperature range that was greater than that permitting nematode development and reproduction. Different strains of the same species were found to have different temperature limits for development and reproduction. Developmental rate was different for each nematode species tested with the heterorhabditids taking longer to complete their life cycle than did the steinernematids.

Effect of host insect sterols on the development and sterol composition of Steinernema feltiae

Steinernema feltiae (= Neoaplectana carpocapsae), 'All' strain, was propagated in larvae of the corn earworm, Heliothis zea, which contained various sterols, in order to determine how the sterol composition of the host affects the growth, development and sterol composition of this insect-parasitic nematode. S. feltiae completed its life cycle normally in insects containing primarily cholesterol, cholestanol or 7-dehydrocholesterol, although the sterol composition of the dauer stage was affected by the sterol composition of the host. When the nematode was reared in insects containing primarily cholesterol, 55% of the sterol in the dauers was cholesterol and the other 46% was lathosterol. In contrast, cholestanol (70%) and lathostetrol (31%) were the sterols present in nematodes reared in H. zea containing primarily cholestanol. Cholestanol (43%), lathosterol (34%), campestanol and/or another 24-methylsterol (23%) and cholesterol (1%) were the sterols present in nematodes reared in H. zea containing campestanol and cholestanol as its major sterols. Lathosterol was the major sterol present in nematodes reared in H. zea containing principally 7-dehydrochlesterol. Therefore, in each case, S. feltiae metabolized some host sterol to lathosterol but the relative percentage of lathosterol in the nematode increased as it was exposed to delta 0-, delta 5- and delta 5,7-sterols, respectively. The ability of S. feltiae to utilize different host sterols may, in part, explain its success in parasitizing a wide variety of insects.

Chelonus sp.: suppression of host ecdysteroids and developmentally stationary pseudoparasitized prepupae

When eggs of the caterpillar Trichoplusia ni are stung by Chelonus sp. (near C. curvimaculatus) (Braconidae), the developing host larvae precociously spin a cocoon but then remain developmentally stationary in the prepupal stage. The latter event happens even in hosts which were stung and precociously spin cocoons but which, upon dissection, contain no obvious parasite. Injection of radiolabeled ecdysone into either pseudoparasitized or allatectomized larvae demonstrates suppressed rates of conversion of ecdysone to 20-hydroxyecdysone when compared with controls. The data indicate that the occurrence of developmentally stationary pseudoparasitized prepupae is due to less production of ecdysteroid and less conversion of ecdysone to 20-hydroxyecdysone, both probably as a result of suppressed juvenile hormone titer.

Precocious expression of the final larval instar developmental pattern in larvae of Trichoplusia ni pseudoparasitized by Chelonus spp

The present study has used a number of electrophoretic approaches to analyze the proteins in normal Trichoplusia ni larvae and those pseudoparasitized by Chelonus spp. A number of feeding-stage, hemolymph proteins appear or increase dramatically only during the final larval stadium. Other proteins highly abundant only during the penultimate stadium disappear or decrease dramatically during the final stadium. The comparative protein profiles of penultimate instar, pseudoparasitized larvae are very similar to those of last instar larvae. These changes in hemolymph proteins are seen on gels resulting from electrophoresis, isoelectric focusing (wide range and narrow range Ampholine and very narrow range Immobiline gels) and SDS-disc electrophoresis. It is concluded that the entire last instar developmental pattern of protein gene products is occurring precociously in pseudoparasitized larvae.

Parasite regulation of host insect metamorphosis: a new form of regulation in pseudoparasitized larvae of Trichoplusia ni

When eggs of Trichoplusia ni (lepidoptera) are stung by a parasitic wasp, Chelonus sp., the developing host larvae precociously initiate metamorphosis ten days later. Precocious initiation of metamorphosis occurs even in 'pseudoparasitized' stung hosts which contain no living parasites at the time of symptoms of host regulation by the parasite. In feeding, penultimate instar, pseudoparasitized hosts, the corpora allata activity, hemolymph juvenile hormone esterase activity, in vivo rates of juvenile hormone metabolism and changes in hemolymph protein composition all follow the pattern of the normal last instar. This and other evidence suggests the entire developmental pattern of the last larval instar is precociously expressed in penultimate instar, pseudoparasitized hosts. The cause of precocious expression of the developmental program leading to metamorphosis is a significant decrease in the critical size parameter that, in normal larvae, signals attainment of the last instar. The induction, in preultimate instar larvae, of the entire feeding stage developmental program leading to metamorphic commitment, using either biochemical, surgical or parasitic experimental probes, has not been previously reported. The results have important implications for the study of host-parasite endocrine interaction, of normal insect metamorphosis and even of human puberty.

Antibacterial and antimycotic effect of a newly discovered secretion from larvae of an endoparasitic insect, Pimpla turionellae L. (hym.)

The larvae of Pimpla turionellae, that develop in pupae of various Lepidoptera, discharged through their anus up to 8 microliters/h of a hyaline liquid, which is termed "anal secretion". It exerted a strong bacteriostatic effect on Enterobacter cloacae, a highly virulent intestinal microorganism isolated from the midgut of the host pupa, Pieris brassicae. Growth inhibition of Escherichia coli, Micrococcus luteus and Pseudomonas phaseolicola was also evident, but less pronounced. Inhibition depended upon the concentration of the anal secretion. This was also true regarding the effect on growth of Beauveria bassiana, a fungus pathogenic on insects. The antimycotic action of the anal secretion was less effective against Chaetomium pululiferum, a soil-inhabiting fungus. Growing hyphae of B. bassiana were malformed, exhibiting the so-called "curling effect", when treated with anal secretion. Parenteral injection of a low dose of Enterobacter cloacae resulted in 100% mortality of non parasitized pupae of Pieris brassicae; however, simultaneous injection of 3 microliters of anal secretion resulted in higher survival.

[Dynamics of egg maturation in the parasitoid Lixophaga diatraeae (Diptera, Tachinidae) raised in a substitute host, Galleria mellonella (Lepidoptera, Pyralidae)]

The content of the uterus and ovaries of L. diatraeae (an ovolarviparous tachinid fly) was studied by dissecting 121 females 0 to 25 days old. Several size classes of flies (p: small; m: medium; g: big) were used, weighing 10 to 12.5 mg, 12.5 to 13.5 mg, and 13.5 to 16 mg, respectively. The mean number of ovarioles per ovary, correlated to female size, was 12.1 for p as against 12.9 for m + g females. The total mean number of eggs and oocytes changed with female age and weight. For 0, 5, 10 and 15-day old females, this number was 56, 149, 158 and 202, respectively in g flies and 51, 128, 141 and 139, respectively, in p ones. To study egg maturation dynamics, we counted the total number of eggs + oocytes per p female (Y1), the eggs in the uterus (Y2), partially embryonated eggs (Y3), and entirely embryonated eggs (Y4). The experimental results were fitted to various age functions using a non-linear adjustment program. The models fitting each datum best were asymptotic functions of the form, Y = A [1-e-K(x-D)], where A is the asymptotic value, K a speed constant of the studied phenomenon and D age at the beginning of the phenomenon. At emergence time, each female contained a mean of 50 oocytes which passed into the uterus immediately after mating. Egg production continued for at least 10 days after emergence. The rate of embryogenesis seemed to be influenced by the number of eggs in the uterus and/or the age of the fly; it was high for the first eggs then decreased progressively. In our conditions, the first eggs with a planidium ready to hatch appeared at 10 days post-emergence. To obtain a maximum number of larvae in good health, it is better to dissect 12 to 18-day old females. The egg volume increases slightly during embryogenesis.

Virus in a parasitoid wasp: suppression of the cellular immune response in the parasitoid's host

A virus that replicates in the ovary of a parasitoid wasp is injected into the parasitoid's host during oviposition. Successful development of th parasitoid egg within the host depends on the presence of th virus, which acts to suppress the host's immune response (encapsulation) toward the egg. This is an example of obligatory mutualism between a virus and a eukaryotic organism.

[Effect of DDT/lindane on the Lepidoptera parasite Eupteromalus peregrinus (Pteromalidae)]

A control action against caterpillars of Euproctis chrysorrhoea (Lep.: Lymantriidae) in spring with the insecticide "bercema-Spritzaktiv 80" (72% DDT, 7% lindane) did not destroy nor visible deteriorate a population of the hymenopterous parasite Eupteromalus peregrinus (Pteromalidae). The possible causes are discussed.

The particulate basis of the resistance of a parasitoid to the defence reactions of its insect host

Small, membrane-bound particles, about 130 nm in diameter, have been isolated from that region of the genital tract of the ichneumon Nemeritis known as the calyx. These particles have been shown to possess the ability to confer resistance to encapsulation by Ephestia, the natural host of Nemeritis, upon a surface which would otherwise be encapsulated.

North American egg parasite successfully controls a different host genus in South America

Telenomus alsophilae, a parasite of the eggs of the geometrid Alsophila pometaria in North America, was introduced into Columbia, South America, for the biological control of a pest host in another genus, Oxydia trychiata. Successful results were obtained with this unorthodox procedure to control a forest insect.

[Indirect effect of the larval food of an alternative host (Galleria mellonella L., Lepidoptera, Galleriidae) on the reproduction of an entomophagous insect (Lixophaga distraeae Towns, Dipt. Tachinidae)]

G. mellonella reared on its natural food, beeswax and pollen, is not suitable for a continuous rearing of L. diatraeae. As a matter of fact, L. diatraeae cannot be maintained for more than 10 generations on G. mellonella because the effect of adverse factors during the larval stage progressively reduces both mating rate and female fertility. But adding vitamin E to the natural larval food of G. mellonella eliminates these reproduction disturbances of the parasite, and L. diatraeae rearing can be continued on this alternative host, the diet of which has been enriched with vitamin E.

Nuclear secretory particles associated with the calyx cells of the ichneumonid parasitoid Campoletis sonorensis (Cameron)

The present study is an ultrastructural investigation of the calyx region of the ichneumonid endoparasitoid Campoletis sonorensis. It appears that synthesis of electron-dense secretory particles occurs within nuclei of calyx cells. The particles consist of an ovocylindrical electron-dense inner core and a surrounding unit membrane. After their formation the particles pass from the nucleus by budding through both membranes of the nuclear envelope. The particles, along with fully developed parasitoid eggs concentrate within the lateral oviduct lumen. Feulgen histochemical studies suggest the presence of DNA within the calyxfluid. The possible function of the particles is discussed.

[Pleistophora carpocapsae Sp. N. (Microsporidia, Nosematidae) - a parasite of the codling moth]

A new species of Microsporidia, Pleistiophora carpocapsae sp. n., a parasite of caterpillars and pupae of the codling moth, is described from Moldavia. It is noteworthy that one sporant forms pansporoblasts containing from 4 to 64 sporoblasts and then the same number of spores.

[Certain tasks in the studies of Mermithoidea for biological control of moths]

The method of "flooding" with mermitids, which was successfully used against mosquitoes, is unreal for biological control of black flies because of difficulties and unprofitableness of their laboratory maintenance and reproduction. A more probable way of solving the problem is the untroduction of effective forms of parasites. In perspective the cultivation of the adipose tissue of the host and biochemical overcoming of its protective reactions are necessary.

The fowl (Gallus domesticus) and a lepidopteran (Setomorpha rutella) as experimental hosts for Tetrameres mohtedai (Nematoda)

The life-cycle of Tetrameres mohtedai in the fowl involving a hitherto unknown intermediate host, Setomorpha rutella, is described and methods for laboratory demonstration are given. Development to infectivity in the intermediate host took less than 2 weeks under laboratory conditions. Infections could be established using infective larvae dissected from the intermediate host. The pre-patent period in the fowl averaged 36 days. Experimental evidence is given for infection of the final host by ingestion of either infected adult or infected larval Setomorpha. Development of the parasite to the infective stage does not depend on metamorphosis of the intermediate host.