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.     

Host regulation and the embryonic development of the endoparasitoid Toxoneuron nigriceps (Hymenoptera: Braconidae)

Insect endoparasitoids modulate the host physiology through the injection of maternal-derived substances into the host, inducing physiological and hormonal changes in the host's internal environment to benefit parasitoid development. These changes are direct to control host development and regulate nutrient availability to the developing parasitoid, and they are synchronized with parasitoid development. Eggs of some of these parasitoids have low yolk content and require nutrients from the host hemolymph to initiate and complete embryogenesis. We report changes in the amino acid composition and protein profile of the host hemolymph of the endoparasitoid Toxoneuron nigriceps, and improved the in vitro culture of pre-germ band stage eggs. The protein profile of parasitized larvae was similar to controls throughout the embryonic development, but total amino acid concentration decreased in the first 2 h after parasitization, significantly increasing in the following hours up to 8 h. Amino acid levels were higher in parasitized larvae from 16 to 28 h after parasitization. Comparison of single amino acids indicated amino acids involved in energy metabolism (Krebs cycle) followed a trend during parasitoid embryogenesis, and their changes were correlated with embryonic development. Improvement in the in vitro development of 6 h-old eggs of T. nigriceps was obtained by adding factors released by the host fat body to the artificial medium, while a cell lysate stimulated embryogenesis and allowed the full development of newly laid eggs in vitro.     

Influence of the braconid Glyptapanteles liparidis on the juvenile hormone titer of its larval host,the gypsy moth,Lymantria dispar

The increase in the juvenile hormone (JH) III titer in the hemolymph of Lymantria dispar larvae that were parasitized by the endoparasitoid braconid, Glyptapanteles liparidis, during the host's premolt to third instar, coincided with the molt of the parasitoid larvae to the second instar between day 5 and 7 of the fourth host instar. It reached a maximum mean value of 89 pmol/ml on day 7 of the fifth instar while it remained below 1 pmol/ml in unparasitized larvae. Only newly molted fifth instar hosts showed a low JH III titer similar to that of the unparasitized larvae. JH II, which is the predominant JH homologue in unparasitized gypsy moth larvae, also increased relative to controls in the last two samples (days 7 and 9) from parasitized fourth and fifth instars. Compared to unparasitized larvae, a generally reduced activity of JH esterase (JHE) was found in parasitized larvae throughout both larval stages. The reduction in enzyme activity at the beginning and at the end of each instar, when the JHE activity in unparasitized larvae was high, may be in part responsible for the increased JH II and JH III titers in parasitized larvae. Ester hydrolysis was the only pathway of JH metabolism in the hemolymph of unparasitized and parasitized gypsy moth larvae as detected by chromatographic assays. © 1996 Wiley-Liss, Inc.     

Regulation of Heliothis virescens prothoracic glands by Cardiochiles nigriceps polydnavirus

Heliothis virescens (F.) Larvae parasitized by the endophagous braconid Cardiochiles nigriceps Viereck fail to attain the pupal stage. This developmental alteration is caused by both an inactivation of prothoracic glands of last-instar larvae and an altered ecdysone metabolism. Decrease in ecdysteroidogenesis in vitro was already evident in glands explanted from larvae that have attained the early cell formation stage (day 4 of fifth instar), 6 h after parasitoid oviposition. Ecdysteroidogenesis nearly ceased by 24 h after parasitoid oviposition. The degree of this biosynthetic depression increased as the time between parasitization and gland dissection increased. A time-course study allowed us to determine if both the degree of phosphorylation of regulatory target proteins, the rate of general protein synthesis and ecdysteroidogenesis decreased in concert over time. The results provide further evidence in support of the hypothesis that these cellular activities in prothoracic gland cells are functionally correlated in steroidogenic responses. Treatment with calyx fluid and venom of C. nigriceps duplicates the parasitism-induced inactivation of host prothoracic glands. A 6-h conditioning in vitro of pupally committed host prothoracic glands with these parasitoid female reproductive secretions resulted in a significant depression of their ecdysteroid production. However, glands lost their sensitivity to calyx fluid and venom treatment when explanted from hosts that had already attained the cell formation stage. This was further supported by the fact that nearly all the host larvae parasitized on day 4 of fifth instar (cell formation stage) pupated, while parasitization on day 3 resulted in only 11% pupation. The coupled trioxsalen/UV irradiation treatment of C. nigriceps calyx fluid and venom eliminated their negative effect on biosynthetic activity in vitro by host prothoracic glands. This result indirectly demonstrates that C. nigriceps polydnavirus is the major regulating factor involved in the host prothoracic gland inactivation. Arch. Insect Biochem. Physiol. 38:1–10, 1998. © 1998 Wiley-Liss, Inc.     

Venom of ectoparasitoid,Euplectrus sp near plathypenae (Hymenoptera: Eulophidae) regulates the physiological state of Pseudaletia separata (Lepidoptera: Noctuidae) host as a food resource

Euplectrus sp. near plathypenae is an ectoparasitoid that can parasitize from 3rd to day 0-6th instar Pseudaletia separata. The developmental period of the parasitoid from the egg to the pupal stage is about 13 days. Parasitized hosts are developmentally arrested and never molt to the next stadium. The injection of venom fluid results in similar effects on P. separata larvae as does parasitization. The inhibitory effect of the venom on molting was dose dependent. Injection of 0.3 female equivalents of venom into day 0-5th host instar resulted in a similar developmental arrest as seen in parasitized hosts. The amount of total lipid in the hemolymph of the host increased as a function of the amount of venom injected, while the lipid content of the fat body was similar to lipid levels in the fat body of parasitized larvae. The amount of total protein in the hemolymph also increased when venom was injected, whereas the protein level of the fat body did not increase. The lipid concentration within the parasitoid larva was maintained at the same level throughout larval development, but increased before pupation. We conclude that the injected venom increased the hemolymph content of lipid and protein to support the growth and development of the ectoparasitoid larva.     

Manipulation of fifth-instar host (Manduca sexta) ecdysteroid levels by the parasitoid wasp Cotesia congregata

Although 5th (last) instar parasitized Manduca sexta larvae undergo developmental arrest and do not wander, they exhibit a small hemolymph ecdysteroid peak (300-400pg/&mgr;l) which begins one day prior to the parasitoid's molt to the 3rd (last) instar and concomitant emergence from the host. Ecdysteroids present in this peak were 20-hydroxyecdysone, 20,26-dihydroxyecdysone and one or more very polar ecdysteroids, as well as small amounts of 26-hydroxyecdysone and ecdysone. In parasitized day-1 and -2 5th instars ligated just behind the 1st abdominal proleg, hemolymph ecdysteroid levels increased in both anterior and posterior portions (100-500pg/&mgr;l), while in unparasitized larvae, hormone levels only increased in the anterior portion (100-350pg/&mgr;l). Thus, the ecdysteroid peak observed in host 5th instars was probably produced, at least in part, by the parasitoids. It may serve to promote Cotesia congregata's molt from the second to the third instar and/or to facilitate parasitoid emergence from the host. In parasitized day-1 and -2 5th instars ligated between the last thoracic and 1st abdominal segments, hemolymph ecdysteroid titers reached much higher levels (500-3500pg/&mgr;l) in the anterior portion (no parasitoids present) than in the posterior portion (150-450pg/&mgr;l). Therefore, it appears that the parasitoid's regulation of hemolymph ecdysteroid titers occurs at two levels. First, parasitization neutralizes the host's ability to maintain its normal hemolymph ecdysteroid levels. Second, in a separate action, the parasitoid manipulates the ecdysteroid-producing machinery so that hemolymph levels are maintained at the 200-400pg/&mgr;l characteristic of day 3-4 hosts. This is the first report of a parasitoid's ability to interfere with the normal inhibitory mechanisms which prevent prothoracic gland production of ecdysteroid at inappropriate periods of insect growth and development.     

Effect of the parasitoid,Cardiochiles nigriceps,on the nitrogen excretion of its host,Heliothis virescens

Excretion of nitrogenous products by larvae of the tobacco budworm, Heliothis virescens, and the effect of parasitism by the parasitoid, Cardiochiles nigriceps, on the host's excretory products were investigated. The dry weight of faeces produced after parasitism declined although the per cent of total nitrogen in the faeces did not differ significantly between non-parasitized and parasitized larvae. No free ammonia and only small amounts of ammonium nitrogen were found in the faeces. Uric acid was the only purine found and parasitism significantly decreased its excretion. Parasitism apparently had no qualitative effect on the presence of amino acids in the faeces.Amino nitrogen was the major contributor of faecal nitrogen and was reduced in parasitized larvae. Parasitism significantly increased the excretion of proteins in H. virescens larvae. One pteridine was identified in H. virescens and parasitism had no qualitative effect on the pteridines found in host faeces.The major nitrogenous compounds in the faecal material from the parasitoid were uric acid, amino nitrogen, and protein. In addition several pteridines were identified.     

Microplitis croceipes teratocytes cause developmental arrest of Heliothis virescens larvae

Microplitis croceipes teratocytes placed into nonparasitized Heliothis virescens larvae survived in the absence of a parasitoid larva and caused developmental changes in the host. Expressions of these changes included delayed larval mortality, incomplete larval-pupal ecdysis, or delayed pupation. Two day old 4th stadium H. virescens larvae were more sensitive to injected teratocytes than were 5th stadium larvae. Three day old teratocytes were more effective than were 6 day old teratocytes. The degree of response was related to the number of injected teratocytes. For example, 750 three day old teratocytes (the approximate number from a single parasitoid egg) caused delayed larval mortality in 96% of the treated larvae whereas 175 three day old teratocytes caused delayed larval mortality in only 33% of the treated larvae. Even a dose of 80 teratocytes resulted in 15% incomplete larval-pupal ecdysis compared to 0% for controls. Treatment with hemocyte-and teratocyte-free hemolymph from parasitized larvae, hemocytes from nonparasitized H. virescens, unfertilized M. croceipes eggs, Cotesia congregata teratocytes, or Micrococcus lysodeikticus cells all had very little effect either on larval growth or development time.     

Polydnavirus of Microplitis croceipes prolongs the larval period and changes hemolymph protein content of the host,Heliothis virescens

Polydnaviruses from certain parasitoid Hymenoptera have been reported to interfere with both host immunity and host development. Heliothis virescens larvae injected with either calyx fluid or sucrose gradient-purified polydnavirus from Microplitis croceipes (McPDV) gained less weight than saline-injected larvae. The active feeding portion of the fifth stadium larva (time to reach the burrowing-digging stage) was doubled (7.0 vs. 3.4 days) when a 0.25 wasp equivalent (WE) of sucrose gradient-purified McPDV was injected into a newly ecdysed fifth stadium host. Many of the treated larvae were unable to pupate, successfully and died at a point of incomplete larval-pupal ecdysis. Pupae that did result from the treated larvae weighed significantly less than controls, even at 0.025 WE. The rate of weight gain and extent of delay of development were dose-dependent; as little as 0.1 WE extended the time of active feeding by 1.5 days and yielded only 25% adults. A 0.05 WE dose yielded 78% adults compared to 95% for controls. The total protein content of hemolymph from individuals injected with McPDV was significantly less than that of controls at any McPDV dose equal to or greater than 0.1 WE. SDS-PAGE profiles of hemolymph proteins from control and McPDV-injected larvae revealed a marked inhibition of the normal accumulation of storage proteins during the fifth stadium and a lesser reduction of serine protease inhibitor protein. Thus, McPDV-injected larvae exhibited some symptoms (less total hemolymph protein and reduced amounts of storage protein) similar to those shown by both parasitized larvae and by larvae injected with M. croceipes teratocytes. However, McPDV affected development during the active feeding stage of the larva, while teratocytes primarily impacted larvae at the time when larval-pupal transformation processes are initiated. © 1995 Wiley-Liss, Inc.     

Parasitism-induced effects of Glyptapanteles liparidis (Hym., Braconidae) on the juvenile hormone titer of its host, Lymantria dispar: the role of the parasitoid larvae

Parasitization by the gregarious larval endoparasitoid Glyptapantles liparidis induces a dramatic increase in the hemolymph juvenile hormone (JH) titer (especially JH III) of its host larva, Lymantria dispar. Here, we investigated the role of the parasitoid larvae in JH synthesis and release by in vitro and in vivo experiments. GC-MS analyses confirmed that the rising hemolymph JH titer coincided with the time at which the parasitoids molt to the second larval instar. Peak values in host hemolymph titers were observed prior to parasitoid emergence, and titers dropped to negligible levels within 24 h after parasitoid emergence. Whole body extracts from excised second instar parasitoids yielded JH III and trace amounts of JH II. The in vitro secretory activity of the corpora allata (CA) of L. dispar larvae was not enhanced by parasitization. When the host's CA were separated by neck ligation, we found elevated JH III titers, but no JH II in the hemolymph of the posterior section, which contained the parasitoids. Parasitoids that were kept in in vitro culture produced and released only JH III. The parasitoids’ ability to secrete JH and to molt independently from their host's molting cycles indicates that at least second instar parasitoids are hormonally self-reliant.     

Juvenile hormone esterase activity and ecdysteroid titer in Heliothis virescens larvae injected with Microplitis croceipes teratocytes

Juvenile hormone esterase (JHE) activity in the hemolymph of 5th-instar Heliothis virescens larvae injected with Microplitis croceipes teratocytes was inversely related to the number of teratocytes injected. JHE activity in the hemolymph of larvae injected with 750 3-day-old teratocytes (the approximate number from one parasitoid embryo) was depressed to less than 5% of those levels found in control larvae. During the latter portion of the digging stage and in the burrowing-digging (BD) stage JHE activity in larvae treated with 350 teratocytes was approximately 40% of control values. However, injection of 180 teratocytes did not significantly affect JHE titers. Two-day-old teratocytes caused the greatest reduction in JHE titer with decreasing effects observed with injections of 3- to 6-day-old teratocytes. Nevertheless, because 2-day-old teratocytes were difficult to separate from host hemocytes, 3-day-old teratocytes were used in most of these studies. Injections of nonparasitized H. virescens hemolymph plasma, Micrococcus luteus bacterial cell walls, washed M. croceipes eggs, or teratocytes from Cotesia congregata did not depress JHE titers. Teratocyte injections also significantly reduced growth of host fat body. Ecdysteroid titers in cell formation, day 2 (CF2) larvae injected as new 5th instars with 350 3-day-old teratocytes failed to increase, as compared to noninjected and saline-injected controls. An injection of 1 μg/larva of 20-hydroxyecdysone at the BD stage permitted normal pupation in 50% of the teratocyte-treated larvae as compared to 0% pupation for teratocyte-treated control larvae not treated with 20-hydroxyecdysone. Teratocytes seem to be responsible for the inhibition of JHE release and thus indirectly impact on ecdysteroid titers. © 1992 Wiley-Liss, Inc.     

菜蛾盘绒茧蜂对寄主小菜蛾幼虫营养的调节和利用

寄主小菜蛾Plutella xylostella被内寄生蜂菜蛾盘绒茧蜂Cotesia plutellae寄生后,其取食、发育及营养代谢在各种寄生因子的作用下伴随幼蜂的发育而发生很大的变化,畸形细胞作为调节因子之一也发挥了重要的作用。本实验通过比较被寄生和未被寄生小菜蛾血淋巴蛋白浓度以及两种血淋巴对菜蛾盘绒茧蜂幼蜂进行体外培养的培养液的蛋白浓度,发现被寄生小菜蛾血淋巴比未被寄生小菜蛾血淋巴的蛋白浓度略低但差异不显著,而未被寄生小菜蛾血淋巴幼蜂培养液的蛋白浓度显著低于被寄生小菜蛾血淋巴幼蜂培养液的蛋白浓度,证明畸形细胞的蛋白质分泌功能。被寄生后期, 小菜蛾体重明显大于未被寄生的小菜蛾体重,而脂肪体重量相比正好相反;通过显微染色观察,在小菜蛾念珠状脂肪体表面粘附有畸形细胞,对脂肪体进行分解破坏而使其成颗粒状; 蛋白含量和脂滴浓度测定也表明,脂肪体的可溶性蛋白含量和脂滴浓度也迅速降低,同比低于未被寄生小菜蛾。而与此同时,幼蜂正处在快速生长阶段,中肠酯酶的活性逐步上升,幼蜂得以快速消化吸收小菜蛾体内的营养直到完成幼虫发育,整个幼蜂的脂滴浓度也达到了最大值。因此寄生后期,推测在畸形细胞的协助下,幼蜂吸收了寄主小菜蛾体内的营养为自身生长发育所用。     

Endocrine alteration and precocious premetamorphic behaviors in the greater wax moth larvae,Galleria mellonella,parasitized by an endoparasitoid,Apanteles galleriae

Parasitization of Galleria mellonella (Lepidoptera: Pyralididae) larvae by a larval endoparasitoid Apanteles galleriae (Hymenoptera: Braconidae) leads to the precocious expression of premetamorphic behavior in the sixth (normally penultimate) instar host larvae prior to the parasitoid's emergence. We investigated the role of parasitization with A. galleriae on the alteration of development and/or behavior of its host. The ecdysteroid titer in the hemolymph of parasitized sixth instar larvae (the last instar of parasitized larvae) was higher than that of unparasitized ones, and the high ecdysteroid concentrations induced premetamorphic behaviors such as wandering and cocoon spinning. However, the epidermis of the parasitized larvae was not pupally committed through this stage. The activity of JH esterase in the parasitized larvae remained low, and application of a JH analogue to these larvae caused the production of a larval-type cocoon. These facts suggest that the parasitization by A. galleriae induces precocious premetamorphic behaviors of G. mellonella larvae by changing host endocrine conditions without causing the typical larval-pupal metamorphosis. Arch. Insect Biochem. Physiol. 34:257–273, 1997. © 1997 Wiley-Liss, Inc.     

The juvenile hormone titer of Trichoplusia ni and its potential role in embryogenesis of the polyembryonic wasp CopidosomaFloridanum

The hemolymph juvenile hormone (JH) titer of third through fifth stadia Trichoplusia ni parasitized by the polyembryonic parasitoid, Copidosoma floridanum, was measured by radioimmunoassay and compared to the titers of unparasitized larvae. The JH titer of parasitized larvae fluctuated from 28 pg/μl to undetectable levels. Maximum levels of hormone were present at ecdysis to the fourth and fifth stadium, and at the prepupal stage. Qualitatively, similar fluctuations were observed in unparasitized larvae. However, the titers in unparasitized larvae were much lower than those of parasitized larvae in the third and early fourth stadia, and the titer fell to undetectable levels in the fifth stadium 24 h earlier (48 h) than in parasitized larvae (72 h). Preventing the JH titer from falling during the fourth and fifth stadia by topical application of (RS)-methoprene or JH II had a juvenilizing effect on parasitized T. ni, and inhibited C. floridanum embryo morphogenesis. The effect of exogenous methoprene and JH on C. floridanum development depended on timing of application and dosage. Application of 100 pmol per day of methoprene beginning at 2 h of the host fourth stadium, prior to the large drop in the endogenous JH titer, inhibited morphogenesis in the majority of C. floridanum embryos. Application of methoprene at later times of host development did not inhibit morphogenesis although other developmental alterations were observed. The potential significance of host JH and ecdysteroid titers on polyembryonic development are discussed.     

<Emphasis Type="Italic">Toxoneuron nigriceps</Emphasis> parasitization delays midgut replacement in fifth-instar <Emphasis Type="Italic">Heliothis virescens</Emphasis> larvae

We have analyzed the effects of Toxoneuron nigriceps parasitization on the midgut development of its host Heliothis virescens. In parasitized H. virescens larvae, the midgut epithelium undergoes a complete replacement, which is qualitatively not different to that observed in synchronous unparasitized larvae, with similar temporal profiles of cell death and metabolic activity. However, the whole gut replacement process is significantly delayed in parasitized larvae, with complete differentiation of the new gut epithelium being observed 4 days later than in unparasitized controls. The administration of juvenile hormone before commitment and of 20-hydroxyecdysone (20E) after commitment delays and fosters, respectively, the replacement process of the midgut epithelium; moreover, the injection of 20E into developmentally arrested and 20E-deficient host last-instar larvae parasitized by T. nigriceps immediately triggers regular gut development. These hormone-based experiments suggest that endocrine alterations in the larval host, induced by T. nigriceps parasitism, are responsible for the temporal alterations in the gut replacement process. The role of this parasitoid-induced developmental change in the host regulation process is discussed. This work was partially supported by FAR 2006–2007 (University of Insubria) to G.T., by MIUR-FIRB-COFIN (grant no. RBNE01YXA8/2004077251), and by the Centro Grandi Attrezzature (University of Insubria).     

The probable significance of tracheal tufts in the 8th abdominal segment of Heliothis virescens (F.) on the development of its parasitoid, Toxoneuron nigriceps (Viereck)

The 8th abdominal segment of Heliothis virescens (Fabricius) larvae contains aerating trachea and tracheole tufts that end in the hemocoel of the 8th segment, unlike the tracheae that invade tissues in other segments. These tracheal tufts from the 8th abdominal segment extend to the tokus region, which along with the telson cavity is known to act as a “lung” for hemocytes in Calpodes ethlius and a few other lepidopteran larvae. The goal of this research was to study the effects of these tracheal tufts in the 8th abdominal segment on parasitoid development inside the host larvae, H. virescens. The first objective was to determine if the eggs of the parasitoid, Toxoneuron nigriceps, are predominantly located among the tracheal tufts of the 8th abdominal segment compared to other body cavity regions irrespective of their oviposition site or the position of the host larvae. The results showed that several hours after oviposition most of the eggs are found in the 8th abdominal segment irrespective of the oviposition site or the position of the host larvae. The second objective was to study the effect of varying oxygen concentrations in vitro on various developmental stages of the egg. The results showed that decreasing oxygen concentrations adversely affects the parasitoid egg development in vitro. A third objective was to determine the oxygen concentration in 8th abdominal segment of the host larvae and compare it to other regions of the body using an oxygen sensor placed in vivo. The results suggested relatively high concentration of oxygen in the 8th abdominal segment compared to other regions of the host, thus supporting our hypothesis that the increased oxygen level in the 8th abdominal segment is important to the development of the parasitoid eggs.     

Developmental interaction between suboptimal instars of Spodoptera littoralis (Lepidoptera:Noctuidae) and its parasitoid Microplitis rufiventris (Hymenoptera:Braconidae)

Relative effects of parasitism by Microplitis rufiventris on the development of the third instar Spodoptera littoralis (preferable, optimal host) with the development of penultimate (5th) and last (6th) instars (suboptimal hosts) were investigated. Newly molted 6th instar hosts were more acceptable for parasitization by the wasp female than older hosts. In singly parasitized 3rd instar hosts, 82.0 +/- 3.9% of the parasitoid eggs developed to full-grown instar wasp larvae. However, parasitoid eggs deposited singly in 73.9 +/- 3.3% of 5th and 100% of 6th instar hosts failed to develop. Superparasitization in the 3rd instar hosts reduced the production of pseudoparasitized larvae and, conversely, all parasitized hosts yielded viable parasitoid offspring. In suboptimal hosts, the development interaction between the parasitoid and its host larvae was highly influenced by the age of hosts at parasitism, load of deposited eggs, and other parasitoid factors. The latter factors, e.g., mainly calyx fluid particles, might be involved in establishing parasitoid eggs in the suboptimal hosts. In the last two host instars, superparasitization significantly increased the number of parasitoid larvae successfully reaching their final instar. Variation in host quality, e.g., physiological status, might be attributed, in part, to the partial breakdown of the solitary habit observed in the earlier instars. More parasitoid eggs developed to mature parasitoid larvae in hosts superparasitized as 6th instar than parasitoid eggs laid in 5th instar hosts. Superparasitization significantly lengthened the developmental period of 5th and 6th host instars and inhibited their development to the pupal stage. Studying parasitoid development in suboptimal instars of its habitual host provided physiological insight, as shown here. The results may have implication for biological control and in vitro mass rearing programs with solitary parasitoids.     

Tyrosine and catecholamine levels in the hemolymph of tobacco hornworm larvae,Manduca sexta,parasitized by the braconid wasp,Cotesia congregata,and in the developing parasitoids

Parasitism of fifth instar Manduca sexta larvae by the gregarious parasitoid Cotesia congregata prevented normal storage of tyrosine in the hemolymph, whereas total tyrosine levels increased over eight times in the hemolymph of unparasitized larvae by day 4. Tyrosine glucoside, the hemolymph storage form of tyrosine and the precursor for pupal cuticle sclerotizing agents, was found only in trace amounts in parasitized larvae at the time of parasitoid emergence, but had increased to over 6 mM in hemolymph of unparasitized larvae. Concentrations of dopamine and N-β-alanyldopamine (NBAD), precursors for melanization and sclerotization of cuticle, respectively, had approximately doubled in the hemolymph of parasitized larvae by the day of parasitoid emergence, but not in unparasitized larvae. Catecholamine biosynthesis may be transiently stimulated for wound-healing, as black melanic pigmentation appeared around the wasp emergence holes in the host integument. C. congregata larvae accumulate tyrosine, dopamine, and NBAD by the time of emergence and cocoon spinning, either by direct uptake or by synthesis from precursors obtained from the host. NBAD increased in parasitoid larvae close to pupation, suggesting it functions as the main precursor for pupal cuticle tanning. Both dopamine and NBAD increased dramatically in pharate adult wasps just before eclosion and N-acetyldopamine (NADA) appeared for the first time. Dopamine was highest in concentration and total amount, and it can serve both as a precursor for black melanic pigmentation of adult wasp cuticle and for synthesis of NADA and NBAD, the precursors for cuticle sclerotization. Arch. Insect Biochem. Physiol. 38:193–201, 1998. © 1998 Wiley-Liss, Inc.     

In vitro rearing of Toxoneuron nigriceps (Hymenoptera: Braconidae), a larval endoparasitoid of Heliothis virescens (Lepidoptera: Noctuidae) from early second instar to third instar larvae

The early second instar larvae of Toxoneuron nigriceps, a larval endoparastioid of Heliothis virescens, were incubated in artificial rearing media, supplemented with hemolymph of the unparasitized and parasitized fifth instar larvae of the host, H. virescens. The parasitoid larvae were incubated in both a semisolid and liquid form of the artificial rearing medium, and their growth and development were evaluated. The growth in size (increase in length and width), development (molting), and survival of the incubated larvae were observed for 10 days. The incubated larvae exhibited some level of growth in all nine types of media tested, including the control (without host hemolymph). However, ingesting the semisolid rearing media supplemented with the hemolymph from the late fifth instar (day 5, 7 and 9) parasitized host resulted in 100% of the larvae molting to third instars. Some of the in vitro reared third instar larvae demonstrated behavioral changes that could be interpreted as the preparation for cocoon formation or pupation i.e. oral secretion of a whitish material and lots of twisting and turning; however, none produced a cocoon nor pupa.     

The rôle of the calyx and poison gland of Cardiochiles nigriceps in the host-parasitoid relationship

Parasitism of Heliothis virescens by Cardiochiles nigriceps reduced the growth of the host. Both the poison gland and the calyx of the female parasitoid were important in reducing the growth of the parasitized host. Injections of poison gland contents (0·04 gl/larva) or calyx fluid (0·04 gl/larva) into H. virescens larvae did not affect their growth. However, a mixture of the two glands (1:1) at this low dosage significantly reduced the weight gained by Heliothis larvae.