Parasitized Host Larvae Research Articles

PARASITOIDS REARED FROM THE OBLIQUEBANDED LEAFROLLER (LEPIDOPTERA: TORTRICIDAE) INFESTING RASPBERRIES

AbstractFourteen species of parasitoids (13 hymenopterans, 1 dipteran) were reared from larvae or pupae of the obliquebanded leafroller,Choristoneura rosaceana(Harris), collected from commercial raspberry fields in the Fraser Valley, British Columbia, Canada, over 3 years. Levels of parasitism ranged from 5 to 15%. Among these 14 species, five represent new host records. A polyembryonic wasp,Macrocentrus nigridorsisViereck (Hymenoptera: Braconidae), was the most abundant parasitoid. External feeding on the final host instar is obligatory forM.nigridorsisto complete development. On average, each parasitized host larva produced about 36M.nigridorsis, in either unisexual or mixed-gender groups. Overall male to female sex ratio was 1:4. Head capsules of mature parasitized host larvae were significantly larger than those of unparasitized ones, suggesting thatC.rosaceanalarvae parasitized byM.nigridorsismight have an extra larval stage.

Impact and oviposition behaviour ofAgeniaspis fuscicollis(Hymenoptera: Encyrtidae), a polyembryonic parasitoid of the apple ermine moth,Yponomeuta malinellus(Lepidoptera: Yponomeutidae)

AbstractThe distribution and extent of parasitism of the apple ermine mothYponomeuta malinellusZeller by the polyembyronic encyrtid parasitoidAgeniaspis fuscicollis(Dalman) were examined in a three year field study and related to oviposition behaviour in the laboratory.Ageniaspis fuscicollisattacks egg batches of its host and kills the final instar larvae, which feed gregariously from within tents. Host population densities in the field were low, from 1.5 to 2.2 tents per 100 leaf clusters, and parasitism increased from 7.8% to 18% over the three year period. Parasitism was independent of host density at the whole tree scale, but at the individual tent scale, the probability of a tent containing parasitized host larvae increased and percent parasitism decreased with the number of host larvae per tent. Observations on the oviposition behaviour ofA. fuscicollisin the laboratory revealed that parasitoids distributed their eggs randomly within host egg batches. On average, they spent almost two hours on an egg batch and laid 44% of their egg load of 132 eggs into the first egg batch visited, leading to a mean of 1.4 eggs laid per host egg through frequent self-superparasitism of hosts. The percentage of eggs receiving one or more ovipositions was independent of the size of an egg batch, contradicting our field observations of inverse density dependence. Factors that might account for the differences in rates of parasitism and attack distributions between laboratory and field data are discussed.

Prothoracic gland inactivation in Heliothis virescens (F.) (Lepidoptera:Noctuidae) larvae parasitized by Cardiochiles nigriceps Viereck (Hymenoptera:Braconidae)

Heliothis virescens (F.) last instar larvae parasitized by the endophagous braconid Cardiochiles nigriceps Viereck fail to attain the pupal stage, due to a parasitoid-induced alteration of ecdysteroid biosynthesis and metabolism. Currently available information on host prothoracic gland inactivation in this host-parasitoid system is reported here. Prothoracic glands of H. virescens mature larvae show a depressed biosynthetic activity, without undergoing gross morphological disruption. The ultrastructure of gland cells is characterized by minor parasitoid-induced changes, with the rough endoplasmic reticulum appearing more developed and electrondense than in nonparasitized controls. Eventually, the cells of prothoracic glands of parasitized host last instar larvae die but maintain their structural integrity. The inactivation of pupally committed host prothoracic glands is achieved through the disruption of the PTTH signal transduction pathway. The second messenger cAMP appears to be normally produced in response to PTTH stimulation of glands explanted from parasitized host larvae, however the downstream activation of the cAMP-dependent protein kinase does not appear to occur. In fact, a marked underphosphorylation of regulatory target proteins is observed. This underphosphorylation is associated with a significant reduction in general protein synthesis, which appears to be blocked at the translational level, to a redirection of specific protein synthesis and to a drastic suppression of ecdysteroidogenesis. These parameters appeared to be correlated in a kinetic time-course study, confirming their functional link. C. nigriceps polydnavirus (CnPDV) plays a major role in the inactivation of pupally committed host prothoracic glands, while putative factors occurring in the host haemolymph do not seem to be of particular importance at that developmental stage. Southern blot hybridization indicates the occurrence of PKI(protein kinase inhibitor)-like genes in the C. nigriceps genome, which, in contrast, are undetectable in H. virescens.

Characterization of polydnavirus-encoded mRNA in parasitized armyworm larvae

We have isolated five cDNA clones encoding Cotesia kariyai polydnavirus (CkPDV) mRNAs transcribed in parasitized host larvae of Pseudaletia separata. One of the cDNAs encoding the longest 2.0 kb CkPDV mRNA was sequenced and characterized. Southern hybridization analyses using the cloned cDNA as a probe showed that CkPDV mRNA was homologous to one of CkPDV DNA segments, 5.6 kbp DNA segment A. The 2.0-kb mRNA was demonstrated as being expressed in the parasitized host larvae by Northern-blot analyses. When specific host tissues were examined, the 2.0-kb mRNA was detected mainly in haemocytes. This RNA increased in relative abundance after 2 and 4 h post-parasitization when the immune response of host haemocytes appeared compromised.

Biological Basis for Mass Propagation of Catolaccus grandis (Hymenoptera: Pteromalidae): Effects of Parasitoid Densities and Host–Parasitoid Ratios

We studied the effects of densities of ectoparasitoids (per liter of cage volume) and host-parasitoid ratios on the reproductive potential of parasitoid females. Ectoparasitoid, Catolaccus grandis (Burks), densities were varied from 3.8 to 37.7 females per liter volume of oviposition cages (petri dishes). Host-parasitoid ratios ranged from 0.2 to 20 3rd instars of the boll weevil, Anthonomus grandis grandis (Boheman), per parasitoid female per days. Fecundity of C. grandis females was not affected by changes in the density of female adults in oviposition cages. However, adult mortality increased when female parasitoid density exceeded 15 females per liter of cage volume. Mean percentage of parasitism of the boll weevil hosts decreased from 100 to 33% when the host-parasitoid ratio increased from 0.2 to 20.0 weevil larvae per C. grandis female per day. Parasitoid fecundity was inversely proportional to the percentage of parasitized host larvae. A higher proportion (69-75%) of fertilized eggs were oviposited when host-parasitoid ratios were between 1 and 20 host larvae per C. grandis female than when ratios were <1 host per female (40-41%). Low host-parasitoid ratios reduced the rate of reproduction in C. grandis, whereas high parasitoid densities increased intraspecific competition and parasitoid mortality. Under laboratory conditions, the most efficient host-parasitoid ratio was 5-15 host larvae per female parasitoid per day.

Morphology and ultrastructure of the serosal cells (teratocytes) in Cardiochiles nigriceps Viereck (Hymenoptera : Braconidae) embryos

The morphogenetic changes of the serosal membrane during embryonic development of Cardiochiles nigriceps Viereck (Hymenoptera : Braconidae) were investigated. Eggs observed soon after oviposition into the natural host Heliothis virescens (F.) (Lepidoptera, Noctuidae) showed a transparent chorion and a uniform texture. After 5 hr, the embryo exhibited a distinct granular appearance and by 12 hr attained the germ band stage. A serosal membrane originated from the anterior pole of the embryo between 14 and 15 hr after the egg was laid, eventually forming with the cells both in the anterior and posterior pole a continuous envelope around the developing embryo. Ultrastructural observations revealed that the serosal cells in contact with the abdominal region of the embryo, beginning 24–25 hr after oviposition, formed a syncytium. However, the syncytial tissue did not extend to the cells around the head and thorax. The serosal cells at both embryo poles increased in size without losing their structural organization, and developed into teratocytes when the larva hatched. In contrast, the serosal cells surrounding the body of the embryo persisted longer on the head and thorax region of the newly hatched larva, while the syncytial tissue degraded more rapidly after hatching. In vitro rearing experiments showed that C. nigriceps embryos removed from parasitized host larvae just before and just after serosa formation, hatched only when the medium used was formulated with the addition of fetal bovine serum. Embryos did not develop or hatch when placed in a serum-free medium. Once the syncytium deriving from the serosal membrane became evident, embryos readily developed and hatched in serumfree media. The results of this study seem to suggest that the serosal embryonic membrane could have a nutritional role for the developing parasitoid embryo.

Biochemical and developmental alterations of Heliothis virescens (F.) (lepidoptera, noctuidae) larvae induced by the endophagous parasitoid Cardiochiles nigriceps viereck (Hymenoptera, braconidae)

AbstractAll larval stages of Heliothis virescens (F.) parasitized by the endophagous larval parasitoid Cardiochiles nigriceps Viereck, a braconid species belonging to the subfamily Microgasterinae, exhibit developmental arrest at last instar and fail to pupate. The major part of larval development of the parasitoid is synchronized with the arrested host last larval instar and the parasitoid first molt is never observed before the host attains the late digging stage. At this time, the total ecdysteroid titer of the hemolymph of parasitized hosts is very low and subsequently shows a slow and gradual increase, characterized by a low titer of 20‐hydroxyecdysone (20‐HE) associated with consistent amounts of inactive ecdysteroid polar metabolites. Juvenile hormone esterase (JHE) activity is high in both control and parasitized host larvae at the early digging stage of development, and juvenile hormone analogs (JHA) applied to parasitized host last instar larvae appear to suppress the parasitoid molt. Concurrent with these changes was an increase in the hemolymph titer of proteins which was maintained at a high level in parasitized larvae in contrast to the observed decrease in control larvae at the cell formation stage of development. Neck‐ligation of newly molted host 5th instar parasitized larvae, prior to both JHE release and the increase in protein titers, inhibited growth and molting of the parasitoid. In contrast, ligation after JHE release and with high hemolymph protein titers resulted in parasitoid molting and growth. These data suggest that the host ecdysteroid hormones are not directly involved in the regulation of the parasitoid molt, although high juvenile hormone (JH) levels probably prevent it. More likely, molting is triggered by other biochemical changes, such as proteins or other factors occurring in the hemolymph. Molting of C. nigriceps larvae in vitro into an ecdysone‐free semidefined medium further supported the view that host ecdysone is not necessary for the molt. Teratocytes of C. nigriceps seem to play an important role in the inactivation of 20‐HE through its conversion to inactive polar metabolites, and along with female calyx fluid and venom which depress the secretory activity of the host prothoracic glands, they are the most important sources of host regulatory factors. © 1994 Wiley‐Liss, Inc.

Sequence, structure, and expression of a wasp venom protein with a negatively charged signal peptide and a novel repeating internal structure.

An expression cDNA library prepared from mRNA from the venom gland of a parasitic wasp, Chelonus sp. near curvimaculatus, was screened with polyclonal antibodies against a 33-kDa venom protein from this wasp. Immunoreactive clones were sequenced, yielding a complete inferred sequence for a protein with an NH2 terminus identical with that of the 33-kDa protein. The structure of the cDNA showed an apparent encoded signal peptide, which was unusual in possessing 2 glutamic acid residues juxtapositioned next to, or replacing, the conventional basic residues. The bulk of the mature protein sequence which follows the NH2-terminal, 5000-kDa hydrophobic domain is composed of a dozen tandem repeats of a highly charged, approximately 14-residue sequence, except for the truncated eighth repeat which terminates in the only proline in this large domain. The primary structure is not closely related to any sequence in the GenBank data bank. Secondary structure analysis identified a turn occurring at or near each of 12 invariantly conserved serine residues. Further, the codon used for this serine was invariant, whereas other serines in the protein (including a nearly invariant serine 2 residues away) used various codons. Results of epitope mapping experiments supported a proposed tertiary structure in which the NH2-terminal 5-kDa forms a hydrophobic core, overlain with the charged repeats. Northern analysis of poly(A) RNA from the venom gland of young adult female wasps showed expression of a single 1-kilobase transcript, for which there is no corresponding message in normal or parasitized host larvae. The remarkable structure of this protein and structural data on other wasp venom proteins suggest an evolutionary pattern in which some proteins critical for venom function evolve by internal tandem duplication, and which are secreted after biosynthesis by a different mechanism from that used for proteins with classical signal peptides containing basic residues.

Host-handling behavior of the parasitoid,Diglyphus minoeus [Hym.: Eulophidae], parasitizing the honeysuckle leaf-miner,Phytomyza lonicerae [Dipt.: Agromyzidae

The host-handling behavior of individual female waspsDiglyphys minoeus which attack the larvae of the honeysuckle leaf-miner,Phytomyza lonicerae, include 4 types of behavior: probing, ovipositor insertion, host-feeding, and resting. Ovipositor insertion may either be injection of venom, probing of the host by the sensilla on the ovipositor's tip or egg laying. Three types of attacks were distinguished: oviposition attack for unparasitized larvae, host-feeding attack for unparasitized host larvae and host rejection for previously parasitized host larvae. Oviposition attack was characterized by frequent alternation between probing and ovipositor insertion, long duration of ovipositor insertion and resting, and the long duration of host-handling. Resting behavior is thought to protect the progeny against superparasitism, host-feeding by other wasps or hosts' recovery from paralysis. Host-feeding attack was characterized by frequent alternation between host-feeding and ovipositor insertion and long duration of host-feeding. Host rejection was composed mainly of probing and ovipositor insertion and short handling time.

Chemotherapeutic and Nontarget Side Effects of Benomyl to Orange Tortrix, Argyrotaenia citrana (Lepidoptera: Tortricidae), and Braconid Endoparasite Apanteles aristoteliae (Hymenoptera: Braconidae)

Benomyl incorporated into artificial diet and fed to nonparasitized and parasitized third-instar orange tortrix, Argyrotaenia citrana (Fernald), was nontoxic to hosts at 300 ppm, but toxic via the host to the solitary endoparasite Apanteles aristoteliae Vierek. This same concentration fed to hosts after parasitization rid hosts of parasites and significantly increased percentage of parasitized host larvae pupating as compared with control larvae. This chemotherapeutic effect was similar for hosts fed benomyl-laced diet for 24 h after parasitization versus those fed benomyl continuously. Increasing concentrations of benomyl from 150 to 1,200 ppm caused increasing percentages of parasitized hosts blocked in larval development for ≤120 d. Increased levels of blocked hosts were associated with increased levels of larvae dissected from hosts that did not pupate or produce parasites after 30 d of larval development. Percentage adult parasite emergence was reduced by all fungicide treatments. Potential uses of benomyl or like substances to study parasite/host relationships and how benomyl may impact on field populations of these insects are discussed.

Studies on polydnavirus transmission

Polydnaviruses are thought to replicate only in the ovaries of certain hymenopteran species. Nevertheless, in the present study, polydnaviral DNA was found to exist in males of the braconid parasitoid species Cotesia melanoscela and in both male and female non-ovarian tissue of an ichneumonid, Hyposoter fugitivus; preliminary results suggest that viral DNA may be present in an unintegrated form, but whether or not it is encapsidated is unknown. Using interstrain genetic crosses, we demonstrated that C. melanoscela males can apparently transmit at least some viral DNA to female progeny. We suggest that polydnavirus DNAs may be present in most if not all tissues of certain parasitoid species, and are probably maintained within parasitoid populations by vertical transmission through the germ line. In parallel experiments, manually injected eggs of the ichneumonid parasitoid ( H. fugitivus) survived and hatched in Malacosoma americanum larvae in the apparent absence of exogenous polydnavirus; female parasitoids reared in this manner nevertheless carried virus in their ovaries. Experiments utilizing different strains of C. melanoscela also suggest that per os transmission of polydnaviruses (to parasitoid larvae) does not occur, despite the fact that inoculum viral DNA can be shown to persist for several days in the tissues of parasitized host larvae.

The defender role of the precocious larvae ofCopidosomopsis tanytmemusCaltagirone (Encyrtidae, Hymenoptera)

AbstractA specialized larval morph, here called the precocious larvae, is present in broods of the polyembryonic encyrtid wasp,Copidosomopsis tanytmemusCaltagirone, an egg‐larval parasite of the Mediterranean flour moth,Anagasta kuehniella(Zeller). The precocious larvae are clonally derived from the same embryonic cells that produce the normal larvae. In contrast to their normal siblings, precocious larvae have well‐developed cranial structures and mouthparts, and are extremely motile. The most unusual feature of precocous larvae, however, is their failure to attain reproductive age; they invariably die in the host hemolymph as untransformed larvae. Competition experiments with the braconidPhanerotoma flavitestaceaFischer or one of the ichneumonidsVenturia canescens(Gravenhorst) andTrathalasp. showed that precocious larvae injured or killed these competitors in 74, 98, and 97%, respectively, of the observed cases of multiple parasitism.Dissection of parasitized host larvae revealed that dead parasite larvae had different fates. Although injured and dead braconid and ichneumonid parasites were encapsulated by aggregations of host lamellocytes, precocious larvae remained unencapsulated, regardless of whether death occurred normally or, rarely, resulted from injury. It is hypothesized that successful avoidance of encapsulation by both precocious and normal larvae ofC. tanytmemusis due to either or both of the host‐produced cyst or the parasite‐produced trophic membrane.The precocious larvae fulfill the requirements for the ultimate altruist predicted by kin‐selection theory. However, because they are genetically identical to the individuals whose survival they enhance, the precocious larvae paradoxically qualify as a completely selfish caste as well. It is thus pointed out that the biological role of the precocious larvae is most appropriately evaluated as that of defender.

Developmental pathology of Heliothis virescens larvae parasitized by Microplitis croceipes: Parasite‐mediated host developmental arrest

AbstractThe developmental pathology of Heliothis virescens larvae parasitized by the braconid wasp Microplitis croceipes was examined. Parasitized host larvae begin the same precise sequence of developmental events in preparation for pupation as observed in unparasitized larvae. This sequence is initiated even though the host larval weight is below the normal developmental threshold for larval‐pupal transformation. After parasite emergence, the host remains in a suspended advanced developmental state but never pupates. The developmental parameters altered by parasitization are normally under the host's endocrine control.Neck ligation of control larvae was used to identify the critical periods in parasitized and unparasitized fourth‐ and fifth‐instar larvae. Control ligated fourth‐instar larvae apparently released PTTH between 21:00 AZT of the second day of the instar and 1:00 AZT of the third day. Parasitized fourth‐instar larvae were smaller and apparently released PTTH between 18:00 and 23:00 AZT of the third day. Control ligated fifth‐instar larvae apparently released PTTH between day 1 and day 2 of the cell formation phase. Ligated fifth‐instar parasitized larvae never molted to the pupal stage. Parasite larvae were adversely affected by host neck ligation with their pupal plus cocoon weight being proportional to the age of the host at the time of ligation.

Changes in haemolymph proteins of the fall armyworm, Spodoptera frugiperda (J. E. Smith), associated with parasitism by the braconid parasitoid Cotesia marginiventris (Cresson)

Changes in haemolymph proteins of the fall armyworm, Spodoptera frugiperda, associated with parasitism by the parasitoid Cotesia (= Apanteles) marginiventris were monitored by sodium dodecyl sulphate polyacrylamide gel electrophoresis. As early as hour 4 after parasitization treatment, several electrophoretically slow-migrating, high-molecular-weight proteins were detected in the host's haemolymph. These proteins were detected earlier in haemolymph from parasitized larvae than in haemolymph from control larvae, and their concentrations were higher in heavily parasitized host larvae (≥ 3 eggs/host) than in lightly parasitized larvae (1 egg/host). Additionally, unique proteins that migrated electrophoretically with bovine serum albumin appeared in the haemolymph of parasitized larvae at hour 8 after parasitization treatment and were evident in haemolymph collected through to hour 64.

Developmental interactions between the army wormLeucania separata [Lep.: Noctuidae] and its parasiteApanteles ruficrus [Hym.: Braconidae

The developmental interactions between the gregarious endoparasitoidApanteles ruficrus Hal. and the army worm,Leucania separata Walker were investigated. The parasitoid preferred young host larvae and developed in 9.5 days irrespective of host age at the time of parasitization. The growth of parasitized host larvae were depressed. The net maximum weight of the host larva was positively correlated with the number of parasitoid eggs laid when the 2nd instar was parasitized. And when parasitizing in 2nd instar, the weight of parasitoid was negatively correlated with the number of eggs laid. The parasitoid has an ability to regulate the size of the host and the parasitoid itself according to the number of eggs laid when the host larva is very small.

Parasitism of the Light Brown Apple Moth, Epiphyas Postvittana (Walker), by Its Larval Ectoparasite, Goniozus Jacintae Farrugia (Hymenoptera: Bethylidae), in Natural Populations in Victoria.

Host-parasitoid relationships of Epiphyas postvittana (Tortricidae) and its larval ectoparasite, Goniozus jacintae were studied for 16 generations in an apple orchard and for 10 generations in a pear orchard between 1971 and 1977. G. jacintae is arrhenotokous and parthenogenetic, with unmated females producing males. It is a multiple parasitoid laying from one to seven eggs per host larva in the field, with a mean of 1.8. Parasitism is restricted to caterpillar instars III-VI, instar IV being predominantly parasitized. The life cycles of the host and the parasitoid are well synchronized, the former having three generations a year. Parasitized host larvae are found during most months of the year; numbers are maximum from October to March, when the host larvae are also in peak numbers. E. postvittana is polyphagous, occurring both on fruit trees and on dicotyledenous weed hosts in the undergrowth. G. jacintae was found in both these situations and its occurrence was related to the presence of the host larvae rather than to any association with flora or microclimate. In general, the degree of parasitism of host generations ranged from 0 to 8.3%. The impact of G. jacintae as a mortality factor of E. postvittana was insignificant. The host-parasitoid relationship was of the delayed density-dependent type.

Polyembryony in Paraleurocerus bicoloripes (Hymenoptera: Encyrtidae)

Paraleurocerus bicoloripes Girault, a polyembryonic endoparasite, overwinters as a mature secondary polygerm in the hemocoel of Marmara fraxinicola Braun. The parasite embryos dissociate from the polygerm in spring and consume the prepupal host. An average of 24.5 parasites mature per host. The precocious larva of P. bicoloripes, a teratoid form, differs from previously described precocious larvae in possessing a rudimentary respiratory system. Field studies indicated that parasitized host larvae fed longer and grew larger than nonparasitized larvae.

Development of the Salt-Marsh Caterpillar Parasite, Exorista mella at Controlled Constant and Variable Temperatures in the Laboratory12

The rate of development of Exorista mella (Walker) was determined in larvae of the salt-marsh caterpillar, Estigmenc acrea (Drury), reared on a semisynthetic diet. The egg stage required 100 hr at 68°F to 52 hr at 86°F. The egg and larval stages together required 28.1 days at 59 to 7.9 days at 86. The pupal stage was approximately of the same duration as that of the egg and larval periods and required 27.4 days at 59°F to 7.8 days at 86°F. Thirty-nine percent of the parasite larvae emerged from host larvae, 20% from pupae, and 15% remained within the host larvae. Fifty-nine percent of the parasitized host larvae had 1 larva, 23% had 2.10% had 3.6% had 4, and 2% had 5-7.