Physiologische wechselbeziehungen zwischenPieris brassicae und dem endoparasitenApanteles glomeratus II. Der einfluss der parasitierung auf die ern?hrung des wirtes

Zusammenfassung Der Parasitismus vonApanteles glomeratus (L.) bewirkt bei den Larven seines Wirtes,Pieris brassicae (L.), quantitative Veränderungen des Futterkonsums, die mit der Wachstumshemmung des Wirt-Parasit-Systems eng korrelieren. In Abhängigkeit vom Alter der Parasitenlarven und von deren Individuenzahl variiert die im 5. Wirtsstadium abgegebene Kotmenge zwischen 12% und 144% der durchschnittlichen Kotmenge unparasitierter Raupen. Unternormale Fraßleistungen beruhen auf der Reduktion der täglichen Fraßmenge, übernormale auf einer Verlängerung der Fraßperiode. Die Ergebnisse deuten darauf hin, daß in parasitierten Wirten nicht nur die Futterausnutzung verbessert wird, sondern daß die Parasitenlarven auch die Nahrungsaufnahme des Wirtes steuern.

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Summary Food consumption of unparasitisedPieris larvae (A) and larvae parasitised when one day (B), 6 days (C) or 11 days old (D), respectively, was indirectly measured by dry weight of faeces produced during the 5th larval instar of the host. The general inhibition of growth of the host by parasitism, and the dependence upon parasite load of the growth of the host-parasite system has been previously ascertained. Food consumption of the host larva is also affected by parasitization, parasite age and parasite load. Thus the daily rate of faeces production is similar in A-larvae and in heavily parasitized B- and C-larvae, but is reduced in slightly to moderately parasitized hosts, making no difference between B- and C-larvae. This means that the increased food consumption of heavily parasitized C-larvae is the result of a prolonged feeding period, while the reduced uptake in slightly parasitized hosts is caused by a drop in the daily feeding rate.The increment of fresh weight of unparasitized hosts and the host-parasite system, respectively. during the 5th instar is poorly correlated with faeces dry weight in A-larvae, but the correlation is good for B- and C-larvae. Regressions of parasitized hosts, which are quite similar in B- and C-larvae, differ significantly from that of A-larvae. Although the comparison of these parameters may only permit a rather tentative interpretation, the results suggest that utilization and conversion of food follow different rules in unparasitized and parasitized hosts. The conditions in D-larvae, in which parasitization was mostly quite unsuccessful and in which parasites could only pass through embryonic development and the first days of their L₁-stage, are totally unclear.The relationship between the fresh weight gain and the faeces dry weight during the 5th instar is expressed by the preliminary conversion coefficient Qu. Its differences between the types of host larvae and its dependence upon the parasite load are demonstrated. There is no doubt thatApanteles parasitism in general and the parasite load in particular are controlling essential processes of nutrition in the host.

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Gefördert durch die Deutsche Forschungsgemeinschaft     

Endokrinologische Untersuchungen an dem Wirt-Parasit-System: Pieris brassicae-Apanteles glomeratus

Die von Apanteles glomeratus L. parasitierten Raupen von Pieris brassicae zeigen in Abhängigkeit des Parasitierungstermins eine deutliche Veränderung des Juvenilhormon (JH)-Titer-Verlaufs während des letzten Larvenstadiums. Dabei tritt ein steiler Anstieg des JH-Gehaltes der Wirtshämolymphe im Zusammenhang mit der Häutung der Parasitenlarven vom 1. zum 2. Larvenstadium auf. Aufgrund von Ligations-experimenten konnte nachgewiesen werden, daß die Parasitenlarven selbst für den erhöhten JH-Titer ihrer Wirtsraupen verantwortlich sind, indem sie während ihrer Häutungsphase anscheinend JH in die Wirtshämolymphe abgeben.Eine durch die Parasitierung gesteigerte Syntheseaktivität läßt sich aus den Befunden histologischer Schnitte der Corpora allata frühparasitierter Raupen nicht feststellen. Dagegen weisen die Prothoraxdrüsen parasitierter Raupen zur Mitte des letzten Stadiums eine deutlich kleinere Querschnittsfläche auf als unparasitierte Tiere. Eine dadurch im Zusammenhang mit dem erhöhten JH-Titer bestehende Beziehung zur Häutungsunfähigkeit parasitierter Pieris-Raupen am Ende des letzten Larvenstadiums wird diskutiert.

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Summary The effects of parasitism by Apanteles glomeratus on the hemolymph juvenile hormone (JH) titers of Pieris brassicae during the last larval instar were determined using the Galleria bioassay.Depending on the time of parasitization, a significant increase of the JH titer could be observed when moulting of the parasites from the first to the second larval instar occurred.As neck-ligatured, parasitized Pieris larvae showed a similar increase of the JH titer at this time, it is concluded that the parasite larvae themselves are responsible for the elevation of the titer by delivering JH during their ecdysis into the host's hemolymph.This is supported by histological results from the corpora allata of parasitized and unparasitized caterpillars at the first and third day of the last larval instar, indicating no differences in its secretory activity. The prothoracid glands of parasitized host larvae, however, appear significantly smaller than those of comparable unparasitized ones in the middle of the last instar. A reduced secretory activity at this time, which is assumed from their decreased size, combined with an elevated JH titer may explain why parasitized larvae fail to moult at the end of their larval development.

     

PARASITÄRE VERÄNDERUNGEN DER WIRTSKUTIKULA BEI PIERIS BRASSICAE UND CYDIA POMONELLA DURCH ENTOMOPHAGE ENDOPARASITEN

Zusammenfassung An den Wirt-Parasit-Systemen Pieris brassicae-Apanteles glomeratus sowie Cydia pomonella-Ascogaster quadridentatus wurde der parasitäre Einfluß auf die Kutikula der Wirtsraupen im 5. Stadium histologisch und chemisch untersucht. Die Dickenentwicklung der Exo-und insbesondere der Endokutikula unterliegt einer starken parasitären Hemmung, die bei beiden Wirt-Parasit-Systemen schließlich in einer Reduktion der Dicke und des Trockengewichts um etwa 50% bis 58% resultiert. Der Parasitismus von Apanteles wirkt sich schon in der frühen Aufbauphase der Kutikula auf deren Wachstum und Eigenschaften aus und verändert auch im weiteren Verlauf die Kutikulaentwicklung. Qualitative Veränderungen betreffen die Dichte und chemische Zusammensetzung. Besondere Gewichtsdefizite beim Stickstoff sowie bei der alkalilöslichen Fraktion zeigen an, daß insbesondere der Einbau von Proteinen, aber auch die chemische Stabilisierung des Chitin-Protein-Komplexes gehemmt sind.

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Summary Parasitism by Apanteles glomeratus and Ascogaster quadridentatus affects the development of cuticle of the host larvae, Pieris brassicae and Cydia pomonella, respectively. Inhibitory parasitic effects on cuticular growth of the host during its last larval instar are evident in differences in surface area, thickness and dry weight of the integument. They amount to 32% reduction in surface area, 56% of thickness and 54% of dry weight in Pieris and to 37%, 50% and 58% in Cydia. Thickness of endocuticle is reduced much more than that of exocuticle. This may be due to the continuous influence of the parasite larvae on the deposition of endocuticular material during the intermoult period.Extraction of cuticles with hot water and hot 5% aqueous potassium hydroxide revealed changing differences between the relative amounts of the three fractions, obtained by this treatment. Relative gain of dry weight is less in the alkali-soluble fraction of parasitized Pieris and Cydia. Deficiency of nitrogen (29% to 62% in water extract and 56% to 75% in alkali extract) is generally greater than reduction of total cuticle dry weight. This is more pronounced in the alkali-soluble fraction than in the water extract.These data suggest that the presence of parasites has greatest effect on incorporation of nitrogenous compounds. Moreover, chemical stabilization of the chitin-protein complex seems to stop earlier and to be less perfect in parasitized caterpillars. Since specific gravity of dry cuticle is also subject to effects of parasites, it is assumed that in the investigated hostparasite associations the cuticle of parasitized hosts differs from unparasitized ones in quantity, physical quality and chemical composition.

     

Developmental interactions between the tobacco hornworm Manduca sexta and its braconid parasite Apanteles congregatus

After newly hatched Manduca sexta larvae were parasitized by Apanteles congregatus, the wasps emerged from third, fourth, fifth, or supernumerary sixth stage host larvae. The number of parasites present within a host determined the time required for Apanteles development and the final host instar. In addition, the percent of parasites within a host which successfully completed their development and emerged was determined by the parasite load. Parasitized larvae gained weight more slowly and attained lower final weights than did unparasitized control larvae; this was attributed to reduced food consumption by the parasitized larvae. Following parasitization of freshly ecdysed fifth-instar Manduca larvae, the rate of Apanteles development was accelerated with respect to that observed when young larvae served as hosts. Parasitism also induced developmental changes in Manduca larvae which encapsulated Apanteles and from which no parasites emerged. Our findings suggest that such larvae retain high juvenile titers late in larval life, preventing normal metamorphosis.

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Zusammenfassung Nachdem frischgeschlüpfte Manduca sexta Raupen durch Apanteles congregatus parasitiert worden waren, schlüpften Wespen aus dem dritten, vierten, fünften oder aus einem überzähligen sechsten Raupenstadium des Wirts. Die Zahl der Parasiten in einem Wirt bestimmte die für die Entwicklung von Apanteles erforderliche Zeit und das Endraupenstadium des Wirts. Zudem wurde der Prozentsatz der Parasiten, die in einem Wirt erfolgreich ihre Entwicklung abschlossen und schlüpften, durch die Parasitenzahl bestimmt. Parasitierte Raupen nahmen langsamer an Gewicht zu und erreichten ein geringeres Endgewicht als nichtparasitierte Vergleichsraupen; dies wurde auf geringere Futteraufnahme der parasitierten Raupen zurückgeführt. Nach der Parasitierung von Manduca Raupen direkt nach der fünften Hautung war die Entwicklungsgeschwindigkeit von Apanteles beschleunigt im Vergleich zu derjenigen in parasitierten Jungraupen. Die Parasitierung verursachte auch Entwicklungsänderungen in Manduca-Raupen, die Apanteles einkapselten und aus denen keine Parasiten schlüpften. Unsere Beobachtungen deuten an, dass solche Raupen einen hohen Juveniltiter bis spät in der Raupenentwicklung behalten, was eine normale Metamorphose verhindert.

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Presented in part at the American Society of Zoologists Meeting, New Orleans, in June 1976.     

Testis development in Pieris brassicae parasitized by Apanteles glomeratus

Testis development in Pieris brassicae (L.) parasitized as 1-day-old larvae by Apanteles glomeratus (L.) is considerably retarded from the second-instar onward. Testicular volume is only one sixth and testicular wall thickness only one quarter that of the normal testes at the end of the fifth larval instar. Nevertheless, bundles of sperm are formed in parasitized larvae. After interrupted oviposition, leading to the lowest possible level of parasitism, the effects are of the same magnitude as in more heavily parasitized hosts at comparable age. No significant correlation between number of parasitoids and retardation inflicted is found. The possible source of the effect of parasitism is discussed.

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Zusammenfassung Bei den unparasitierten Wirten läuft die gesamte Hodenentwicklung während der Larvenzeit ab. Bei parasitierten Wirten ist der Entwicklungszeitplan identisch, aber das Hodenvolumen bleibt in Larvenstadium auf einem Sechstel und die Hodenwand (Peritonealhülle und Follikelwand) auf einem Viertel in der normalen Werte. Die allmählich hervortretenden Veränderungen beginnen bereits beim zweiten Larvenstadium des Wirtes. Trotz der Veränderungen entwickeln sich auch in den parasitierten Hoden zeitplangemäss Spermienbündel, deren Fertilität jedoch nach ihrem histologischen Aussehen fragwürdig erscheint. Durch eine Unterbrechung der Eiablage des Parasitenweibchens nach 3-sekundiger Ablage konnte ein schwacher Parasitismus hervorgerufen werden, bei dem die Anzahl der Parasitenlarven pro Wirt von 1–8 variierte. Die bei diesen Wirten beobachteten Veränderungen der Hoden waren gleicher Art und gleich gross wie bei stark parasitiertem Material. Eine gute Korrelation zwischen der Zahl der Parasitlarven pro Wirt und der Intensität der pathologischen Veränderungen konnte nicht festgestellt werden. Mögliche Gründe der vom Parasitismus verursachten Veränderungen werden diskutiert. Dafür kommen vor allem die Parasitenlarven ersten und zweiten Stadiums in Frage, aber der eventuelle Anteil des eierlegenden Parasitenweibchens wird auch berücksichtigt.

     

Effects of the parasitization of a braconid, Apanteles, on the blood of its host, Pieris

Parasitization of a braconid wasp, Apanteles glomeratus, of larvae of a common cabbage butterfly, Pieris rapae crucivora, caused changes in differential haemocyte count (DHC), total haemocyte count (THC), and encapsulative capacity against dead eggs of Apanteles in the fourth and fifth instar host larvae.However, no correlation could be found between the number of Apanteles eggs deposited and THC of the middle fourth instar host larvae or between the number of parasitoid larvae and specific gravity of the haemolymph from the late fifth instar host larvae.From the changes in DHC and in THC of both non-parasitized and parasitized Pieris larvae, an increase in the number of plasmatocytes of non-parasitized Pieris larvae in the early fourth instar period was supposed to be due to transformation of prohaemocytes into plasmatocytes, and a low population of plasmatocytes of parasitized larvae in the comparable period was assumed to be due to a suppression of transformation of prohaemocytes by some factor released from the parasitoid eggs.Failure of the parasitized fourth instar Pieris larvae to encapsulate injected dead eggs of Apanteles indicated that the parasitoid embryos were, in some way, actively inhibiting the encapsulation reactions of the host.The increase in THC of the parasitized fifth instar larvae could not be ascribed to a decrease in the volume of host haemolymph. Rather it could be interpreted by a suppression of adhesive capacity of haemocytes in the host haemocoel to tissue surfaces.Reduced encapsulative capacity of the parasitized fifth instar larvae might be attributed either to a depression of the adhesive activity of plasmatocytes resulting from a depletion of energy source for haemocytes in the host haemolymph by parasitization, or from an active suppression of adhesiveness of the plasmatocytes by secretions from ‘giant cells’ (teratocytes) originated from the parasitoid.     

Effect of parasitism byAscogaster reticulatus [Hym.: Braconidae] on growth of the host,Adoxophyes sp. [Lep.: Tortricidae]

The developmental interaction between the egg/larval parasitoid,Ascogaster reticulatus Watanabe (Hymenoptera: Braconidae) and its host,Adoxophyes sp. (Lepidoptera: Tortricidae) was examined. Prior to the egress of a final-instar parasitoid larva from the 4^th-instar host larva, host weight decreased by 22% from the maximum weight. The final body weight of a host larva was 27% of the maximum weight of a healthy 5^th-instar host. Food consumption was significantly reduced in both 3^rd-and 4^th-instar parasitized larvae compared with healthy ones. In the 4^th instar, a parasitized larva consumed 28% less artificial diet and produced less frass than a healthy larva. The growth rate of the endoparasitoid larvae greatly increased after their host's molt to the 4^th instar. Parasitoid larval volume increased 40 fold in the 4^th-instar host.      

斑痣悬茧蜂寄生对甜菜夜蛾幼虫取食和食物利用的影响

为研究甜菜夜蛾Spodoptera exigua幼虫被斑痣悬茧蜂Meteorus pulchricornis寄生后的取食以及食物利用情况,在室内采用重量法测定了甜菜夜蛾4龄幼虫被寄生后取食量、体重增加量、营养指标的变化。结果表明：被寄生甜菜夜蛾幼虫的取食量、生长率和食物利用效率等明显受到抑制,幼虫被寄生后第3-6 d 取食量显著小于未被寄生幼虫,寄生后第4 d 的幼虫取食量只有正常幼虫的29.89%,第5 d只有48.69%。幼虫在寄生后的第3-5 d体重增加量显著小于未被寄生幼虫,分别为正常幼虫的21.51%,38.87%和14.42%,相对生长率则也显著低于后者。被寄生甜菜夜蛾幼虫的营养利用表现也明显不同于未被寄生幼虫,反映生长和代谢效率的食物利用率（ECI）和食物转化率（ECD）均显著降低,而反映吸收效率的近似消化率（AD）则提高。虽然在寄生后第4 d出现了相反的现象,其原因可能在于第4 d取食量明显减少,而体重仍在增加。本研究表明,斑痣悬茧蜂寄生明显抑制寄主甜菜夜蛾幼虫的取食、食物利用效率和生长。     

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

The 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.     

Effects of the gregarious parasitoids,Apanteles ruficrus and A. Kariyai,on host growth and development

Two gregarious parasitoids, Apanteles ruficrus and A. kariyai attack larvae of the common armyworm, Pseudaletia separata. Their growth pattern and growth rate of the parasitoids were not affected by host age at the time of oviposition, even though host weight increased exponentially with age. Consequently, the maximal weight of a single parasitoid larva was nearly constant regardless of host instar parasitized. Parasitoid females laid more eggs in later-instar hosts than in earlier-instar hosts. When parasitized at the same age, heavily parasitized hosts attained a larger mass than lightly parasitized larvae. Therefore, the ratio of the maximal weight of the host to the parasitoid mass was nearly constant. These results indicate that host growth is regulated by the parasitoids.     

The effect of mermithid parasitism on predation of nymphal Baetis bicaudatus (Ephemeroptera) by invertebrates

We investigated how infection by the mermithid nematode Gasteromermis sp. affected predation on its nymphal mayfly host, Baetisbicaudatus, by two invertebrate predators – the stonefly nymphs of Kogotusmodestus and the caddisfly larvae of Rhyacophilahyalinata. Predation trials and behavioral observations were conducted in stream-side, flow-through experimental chambers. When parasitized and unparasitized prey were offered in equal numbers, K. modestus consumed significantly more parasitized than unparasitized nymphs. R. hyalinata consumed equal numbers of both prey types. Behavioral observations of foraging K.␣modestus on parasitized and unparasitized prey suggested that the increased consumption of parasitized nymphs was due to differences in the behavior of infected mayflies in response to the predator. Specifically, parasitized nymphs drifted less often to escape an approaching predator (non-contact encounters) compared to unparasitized nymphs, which increased the number of contact encounters and attacks that occurred between K.␣modestus and parasitized prey. Because all hosts are castrated, these behavioral alterations affect only the fitness of the parasite, which is killed along with its host by invertebrate predation. We present a number of hypotheses to explain why the parasite causes increased predation on its host. These include the large size of the parasite affecting the sensory abilities of the host, the larger energetic costs of escape behavior for parasitized individuals, and natural selection from fish predation against drifting behavior by parasitized individuals. Received: 27 May 1996 / Accepted: 30 September 1996     

A putative new juvenile peptide hormone in lepidopteran insects.

A growth-blocking peptide (GBP) with repressive activity against juvenile hormone (JH) esterase has been isolated from the last (6th) instar larval plasma of the armyworm Pseudaletia separata (Lepidoptera: Noctuidae) parasitized by the parasitoid wasp Apanteles kariyai (Hymenoptera: Braconidae) (1,2). This study demonstrates that GBP not only exists in the plasma of parasitized last instar larvae, but also in the plasma of unparasitized penultimate (5th) instar larvae, while the plasma of last instar larvae does not contain any detectable amount of GBP. The detection of GBP in unparasitized penultimate instar larvae, before the final larval molt, demonstrates that this factor is naturally occurring in the insect larva before the last larval instar and is seemingly coordinating, along with JH, the regulation of juvenile characteristics. This finding suggests the existence of a new type of juvenile peptide hormone in lepidopteran insects.     

外寄生性花绒寄甲的寄生选择及其发育表现

"选择-表现"假说认为,成虫应该选择有利于子代发育的高品质寄主,但在寄主选择中,除了寄主品质外,其他因素也可能影响寄主选择决策。寄主选择研究通常以成虫为对象,而对那些初龄幼虫选择寄主的寄生性昆虫很少关注。以1龄幼虫积极搜寻寄主的寄生性花绒寄甲为模式生物,采用双选试验设计,观察了花绒寄甲初孵幼虫在不同体重青杨天牛幼虫之间、在已被寄生与健康的黄粉虫蛹之间的寄生选择性;然后采用回归设计,观察了花绒寄甲寄生若干不同体重的青杨天牛幼虫后的发育表现。研究结果表明,花绒寄甲1龄幼虫对体型较大的青杨天牛幼虫的选择偏好显著大于对体型较小的寄主幼虫的选择,选择大体型幼虫的比值比是选择小体型幼虫的4.55倍;对已被寄生的寄主黄粉虫蛹的选择偏好显著大于对健康寄主蛹的选择,选择已被寄生寄主的比值比是选择健康寄主的12.57倍。寄生青杨天牛幼虫的花绒寄甲幼虫发育历期平均为11.49 d、蛹历期为26.67 d、幼虫发育至成虫的羽化率50%,这些发育表现与寄生时青杨天牛幼虫的体重没有显著关系。但刚羽化寄甲成虫体重与寄生时寄主的体重存在显著的正直线关系:寄生时的寄主体重每增大0.01 g,羽化出的寄甲成虫体重增大近0.08%;方差分析寄甲成虫体重在不同寄主体重水平之间的差异表明,从体型较大寄主中羽化的寄甲成虫体重显著大于从体型较小寄主中羽化的成虫。研究结果说明,花绒寄甲初孵幼虫在寄主选择决策时,在寄主体型大小与被寄生状态之间可能采取折衷对策,而且对体型大小不同的寄主选择与子代发育适合度表现存在一致性,从而支持"选择-表现"假说。     

Growth and development of the endoparasitic wasp Apanteles congregatus: dependence on host nutritional status and parasite load

ABSTRACT. Previously we have shown that the number of Apanteles congregatus Say (Hymenoptera, Braconidae) larvae developing in Manduca sexta (L.) (Lepidoptera, Sphingidae) larvae that are parasitized in the first instar determines the timing of emergence of the parasites from the host. Here we show that the first larval ecdysis of the wasps occurs after the host ecdyses to the terminal stage, regardless of whether that stage is the host's fourth, fifth or supernumerary sixth instar. Starvation of newly ecdysed terminal stage host larvae prevents emergence of the parasites. When starvation is begun at progressively later times, then an increasing proportion of the hosts have parasites that emerge, suggesting a period of indispensable host nutrition exists during which the host must feed to satisfy the developmental requirements of the parasites. In hosts fed ad libitum , the weight of the host plus its parasites at the time of emergence is positively correlated with the number of parasites developing in the host. When the weight of the parasites alone is subtracted from the weight of the host—parasite complex, the data show that heavily parasitized hosts have a larger host mass than lightly parasitized larvae. In contrast, the wasp larvae, and the adult males and females that develop from them, have lower individual weights after development in heavily parasitized hosts.     

Temperature and development in host-parasite relationships

Summary The effects of temperature on growth and development of the cabbage butterfly, Pieris rapae, and three wasp parasites: Apanteles rubecula, Apanteles glomeratus and Pteromalus puparum in Vancouver, Canada, and Canberra, Australia, are examined. We compare the estimates of temperature threshold for development and the number of degree-days above this threshold required to complete development for the immature stages of all species in both localities. Developmental patterns of both the host and its parasites differ between localities. Within the range of temperatures likely to be experienced during the host's breeding season, Australian parasites have longer generation times than their host at low temperatures and shorter generation times at high temperatures. Canadian parasites have shorter generation times, relative to the host, at all temperatures. This may be necessitated by the shorter breeding season available to the Canadian parasites.Besides temperature, parasite development is affected by host size and, in the gregarious species, parasite density. Host larval development is retarded by both Apanteles.All parasites are smaller at higher temperatures and males are smaller than females, but size is also affected by host size and parasite density.Although parasite size, and consequently fecundity, varies greatly, parasites experiencing similar temperatures will have closely similar developmental periods. The ecological significance of these developmental responses is discussed.     

Notes on the biology and ecology of the parasitoids of the poplar clearwing moth, Paranthrene tabaniformis (Rott.) (Lep., Sesiidae) in Bulgaria. I. Apanteles evonymellae (Bouché, 1834) (Hym., Braconidae)

Aspects of the biology and ecology of Apanteles evonymellae (Bouché), a parasitoid of the poplar clearwing moth, Paranthrene tabaniformis (Rott.), were studied during the period 1987–96. One-year-old poplar ( Populus spp.) shoots infested with P. tabaniformis larvae were collected during the winter months at 11 localities in Bulgaria and examined in the field and laboratory. Apanteles evonymellae was recorded in all areas studied in Bulgaria. The mortality of P. tabaniformis caused by this parasitoid in various regions of Bulgaria varied from 2.4 to 35.4%; the average for the country was 17.3%. Laboratory observations showed that A. evonymellae is a solitary endoparasitoid of the poplar clearwing moth. It develops in early-stage (first- to fourth-instar) host larvae and overwinters as a larva in the host. Apanteles evonymellae is bivoltine, but only the second generation is associated with P. tabaniformis . In the field, adult parasitoids of first generation appear in April about 1 month before the emergence of P. tabaniformis . The longevity of A. evonymellae adults is a maximum of 6 days. Therefore, in the spring, A. evonymellae cannot attack neonate P. tabaniformis larvae and must develop in alternative hosts. Prior to their death the parasitized P. tabaniformis larvae construct conical structures, 'refuges' of frass and silk threads over the external openings of the larval galleries. Apanteles evonymellae pupates in these refuges after the host's death. This modified behaviour of the parasitized host larvae probably protects the pupae of A. evonymellae from hyperparasites and predators.     

Experimental studies on parasitization byApanteles Glomeratus V. Relationships between growth rate of parasitoid and host age at the time of oviposition

The growth and development ofApanteles glomeratus L. eggs and larvae in the host larva (Pieris rapae crucivora Boisduval) was investigated by calculating their volume. WhenA. glomeratus eggs increase 90 fold in volume after being laid, larvae hatch from them. The larvae grow exponentially and the growth rate of the parasitoid is dependent on the host stage. Being laid in the 1st instar host, the parasitoids grow more slowly than those laid in 2nd–4th instar host. A pupal host stage prevents the parasitoids’ development. When larvae exceed the threshold size of 5.0×10⁸ μ³, they enter the 2nd instar. A few days after they attain the maximum size of 3.3×10⁹ μ³, they moult and egress from the host body.     

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.     

Interspecific competition between the braconid endoparasitoids Glyptapanteles porthetriae and Glyptapanteles liparidis in Lymantria dispar larvae

The effect of interspecific competition between the solitary endoparasitoid Glyptapanteles porthetriae Muesebeck (Hymenoptera: Braconidae) and the gregarious Glyptapanteles liparidis Bouché (Hymenoptera: Braconidae), was investigated in larvae of Lymantria dispar L. (Lepidoptera: Lymantriidae). Host larvae were parasitized by both wasp species simultaneously in premolt to the 2^nd or the 3^rd host instar or in an additional approach with a 4-day delay in parasitization by the second wasp species. Host acceptance experiments revealed that both wasp species do not discriminate between unparasitized host larvae and larvae parasitized previously by the same or the other species. In more than 90% female wasps parasitized the larva they encountered first. During the period of endoparasitic development, larvae of the competing parasitoid species never attacked the egg stage of the other species. When host larvae were parasitized simultaneously by both wasp species, the rate of successful development of both species depended on the age of the host larva at the time of its parasitization; G. liparidis emerged successfully from 44% of host larvae parasitized during the premolt to 2^nd instar, G. porthetriae from 28%, and in 20% of the hosts both parasitoid species were able to develop in one gypsy moth larva. However, when host larvae were parasitized simultaneously during premolt to the 3^rd instar, G. liparidis was successful in 90% of the hosts, compared to 8% from which only G. porthetriae emerged. In the experiments with delayed oviposition, generally the species that oviposited first succeeded in completing its larval development. Larvae of the species ovipositing with four days delay were frequently attacked and killed by larvae of the first parasitizing species or suffered reduced growth. As the secondary parasitoid species, G. porthetriae-larvae were never able to complete their development, whereas G. liparidis developed successfully in at least 12,5% of the multiparasitized host larvae. Thus, multiparasitism of gypsy moth larvae by both Glyptapanteles species corresponds to the contest type; however, G. porthetriae is only able to develop successfully as the primary parasitoid of young host larvae.