Serratia marcescens as a rapid indicator of Microctonus hyperodae oviposition activity in Listronotus maculicollis and potential application of the technique to host-specificity testing

Listronotus maculicollis (Dietz) (Coleoptera: Curculionidae) is a potential novel host of the braconid parasitoid Microctonus hyperodae Loan, but initial studies have shown that levels of parasitism are lower than in the natural host L. bonariensis (Kuschel). A novel bacterial indicator test was used to determine whether the lower level of parasitism was due to behavioural factors, lack of oviposition, or host resistance. The incidence of ovipositor penetration by the parasitoid M. hyperodae into adult L. maculicollis was measured by immersing the ovipositor of the parasitoid in the facultative pathogen, Serratia marcescens Bizio. Adult weevils were then exposed to parasitoids for up to 72 h and rapid mortality used as an indicator of oviposition penetration. Survival was assessed after six days and surviving weevils were dissected and examined for parasitoid larvae. Mortality among L. maculicolis exposed to parasitoids treated with S. marcescens was significantly higher (P<0.001) than the controls but significantly lower (P<0.001) than in the natural host, L. bonariensis. Dissection of weevils exposed to uncontaminated parasitoids revealed that parasitism in L. maculicolis was significantly (P<0.001) less than parasitism in L. bonariensis. Serratia marcescens-induced mortality plus parasitism of surviving weevils in the parasitoid plus bacteria treatments produced a similar overall effect. Application of bacteria to the parasitoid ovipositor provided a rapid, simple test for ovipositor penetration, which shows potential for separation of behavioural and physiological defence mechanisms in parasitoid/host range studies.     

Microsatellites and 16S sequences corroborate phenotypic evidence of trans-Andean variation in the parasitoid Microctonus hyperodae (Hymenoptera: Braconidae)

Eight South American geographical populations of the parasitoid Microctonus hyperodae Loan were collected in South America (Argentina, Brazil, Chile and Uruguay) and released in New Zealand for biological control of the weevil Listronotus bonariensis (Kuschel), a pest of pasture grasses and cereals. DNA sequencing (16S, COI, 28S, ITS1, beta-tubulin), RAPD, AFLP, microsatellite, SSCP and RFLP analyses were used to seek markers for discriminating between the South American populations. All of the South American populations were more homogeneous than expected. However, variation in microsatellites and 16S gene sequences corroborated morphological, allozyme and other phenotypic evidence of trans-Andes variation between the populations. The Chilean populations were the most genetically variable, while the variation present on the eastern side of the Andes mountains was a subset of that observed in Chile.     

Host preference and host suitability in an egg-pupal fruit fly parasitoid, Fopius arisanus (Sonan) (Hym., Braconidae)

The relative oviposition rate of the parasitoid Fopius arisanus (Sonan) was investigated across three frugivorous tephritid species, Bactrocera tryoni Froggart, Bactrocera jarvisi (Tryon) and Bactrocera cucumis French. Choice and no-choice tests were both used. The suitability of these three species for sustaining larval development and survival to the adult stage was also assessed. Fopius arisanus parasitized all three tephritid species, regardless of the method of exposure, but showed stronger preference for B. tryoni and B. jarvisi over B. cucumis. Superparasitism was extremely rare. Successful development of F. arisanus varied across host species. Bactrocera tryoni yielded significantly more parasitoids than B. jarvisi, but no wasps emerged from B. cucumis puparia. Tests were set up in replicated trials, but results were not homogeneous across trials. We discuss the host relationships of F. arisanus with reference to this variation and in relation to host suitability for larval development.     

Behavioural Acceptability of Sitona lepidus (Coleoptera: Curculionidae) to the Parasitoid Microctonus aethiopoides (Hymenoptera: Braconidae) Using the Pathogenic Bacterium Serratia marcescens Bizio

Microctonous aethiopoides Loan has been introduced into New Zealand to control the lucerne pest Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Sitona lepidus Gyllenhal (Coleoptera: Curculionidae) a pest of clover ( Trifolium spp.), has recently established in New Zealand. Laboratory experiments to test the potential of M. aethiopoides to parasitize S. lepidus has resulted in very low levels of parasitism. To investigate whether there were behavioural or physiological barriers to successful parasitism, two experiments were conducted using the insect pathogenic bacterium. Serratia marcescens Bizio as a marker for parasitoid ovipositor penetration. Firstly, M. aethiopoides 'treated' with S. marcescens were exposed to weevils and rapid weevil mortality was used to indicate ovipositor penetration. Up to 50% mortality of S. lepidus occurred, which was comparable with mortality observed in the permissive host Listronotus bonariensis . Dissection of S. lepidus exposed to parasitoids treated with distilled water showed that ca. 21% contained parasitoid eggs of which 98% were nonviable. In the second experiment, exposure periods of 24, 48 and 72 h to S. marcescens -treated parasitoids produced an increase in S. lepidus mortality of 14, 28 and 38%, respectively. There was 3% successful parasitoid development in weevils exposed for 72 h to parasitoids treated with distilled water. M. aethiopoides has been shown to develop successfully in a wide range of non-target weevil species both in the laboratory and field. Possible reasons for poor survival of M. aethiopoides immature stages in S. lepidus are discussed.     

Mass-rearing biology of Fopius vandenboschi (Hym., Braconidae)

Abstract:   Basic biological information concerning the reproductive activities of Fopius ( Biosteres ) vandenboschi (Fullaway) (Hym., Braconidae, Opiinae) were determined to facilitate insectary mass production. Mean (±SE) progeny production per generation (yield) of 200 ♀♀ F. vandenboschi was 6835.8 ± 433.2 and 3755.8 ± 112.4 parasitoids, with 24-h exposure to second instar Bactrocera dorsalis (Hendel), and Ceratitis capitata (Wiedemann), respectively. Ceratitis capitata as a factitious host was more sensitive to parasitism, producing a significantly higher percentage of uneclosed host puparia frequently containing parasitoid cadavers (22.5 ± 0.8%), than B. dorsalis (3.4 ± 0.2%). The overall mean production of female offspring was ≥50%♀♀ in both host species. Unlike several other opiine parasitoids, young (5-day-old) females of F. vandenboschi produced low proportion of daughters (26–37%♀♀) and significantly shifted production to female-biased offspring (53–71%♀♀) at older age intervals (16–30 days). Based on the parasitoid yield data with a 24-h exposure period to second instar host larvae of B. dorsalis , about 150 cage replicates (of 200 ♀♀ each) may be sufficient to mass produce about 1 million parasitoids of F. vandenboschi during the reproductive period of 5–30 days, with an average of 56% female offspring. A short oviposition exposure period of 6 h was not optimal for mass production of F. vandenboschi . Total yield at 6 h exposure was one-fifth the production at 24-h exposure, using B. dorsalis hosts.     

Interaction between MbMNPV and the braconid parasitoid Habrobracon hebetor (Hym., Braconidae) on larvae of beet armyworm,Spodoptera exigua (Lep., Noctuidae)

The survival of a braconid parasitoid Habrobracon hebetor was investigated on nucleopolyhedrovirus (NPV)-infected Spodoptera exigua larvae. The second-instar larvae were exposed to 30, 51.4 and 180 PIB/mm² of Mamestra brassicae NPV (MbMNPV) as under-LD₅₀, LD₅₀ and over-LD₅₀ values, respectively. They were accessible to be parasitized by H. hebetor after 24, 48 and 72 h post-treatment. Infection of the larvae with MbNPV was deleterious to the survival and parasitism of H. hebetor. The survival of H. hebetor in MbNPV-infected S. exigua larvae was dependent on the interval between viral infection and parasitization, as well as on the treatment dose of MbMNPV; very few adults of parasitoid emerged from infected hosts when host larvae were exposed to 180 PIB/mm² of MbNPV on 72-h interval treatment. The inoculation dose of MbNPV and the timing of parasitoid release had significant effect on the development of H. hebetor on virus-infected hosts. Field applications of virus for biocontrol of S. exigua may lead to substantial mortality of immature parasitoids.     

Extraembryonic membrane of the polyembryonic parasitoid Macrocentrus cingulum Brischke (Hym., Braconidae) is essential for evasion of encapsulation

Abstract:  The wasp Macrocentrus cingulum (Hymenoptera) is an endoparasitoid that uses larvae of the Asian corn borer Ostrinia furnacalis as one of its hosts. The wasp is polyembryonic and a single wasp egg gives rise to several dozens of embryos. Earlier studies showed that the fibrous layer on the surface of M. cingulum eggs protects them from the immune system of the moth larvae. However, the way in which the embryos of the parasitoid avoid being encapsulated remained unknown. In this paper, we show that the evasion of encapsulation is mediated through the extraembryonic membrane. We also show that M. cingulum embryos developed normally in the larvae of O. furnacalis but were encapsulated when injected into the larvae of Helicoverpa armigera , which is not a host species for the wasp larvae. When the extraembryonic membrane was removed, either chemically using the enzyme dispase or mechanically using a dissecting needle, the 'unprotected' embryos were also encapsulated both in vivo and in vitro by the haemocytes of the normal host O. furnacalis . It was also shown that the extraembryonic membrane was labelled strongly with fluorescein isothiocyanate (FITC)-conjugated Helix pomatia ( H.p. ) lectin. This suggests that a chemical in, or on, the extraembryonic membrane, that helps the embryos of M. cingulum to avoid encapsulation, is possibly a glycodeterminant produced in the haemocoel of the wasp.     

Electroantennogram responses of Apanteles obliquae (Hym., Braconidae) to various infochemicals

Abstract:   The electroantennogram recording technique (EAG) was used to study the olfactory sensitivity of Apanteles obliquae (Hym., Braconidae), a gregarious larval endoparasitoid of Spilosoma obliqua (Walker) (Lep., Arctiidae), to 25 general plant volatiles belonging to alcohol, aldehyde and terpenoid groups and also to volatiles from the host and plant–host complex. The EAG data indicated different olfactory sensitivity between the sexes, not only to individual plant volatiles but also to the volatiles from host and plant–host complex. Females were found to be more responsive than males. However the synthetic sex pheromone blend of the host insect elicited similar EAG responses in both sexes. The EAG data of the present study is correlated with the reported behaviour observed in other parasitoids.     

A Morphometric Method to Assist in Defining the South American Origins of Microctonus hyperodae Loan (Hymenoptera: Braconidae) Established in New Zealand

In 1991, Microctonus hyperodae Loan (Hymenoptera: Braconidae, Euphorinae), collected from eight diverse South American locations, was released in New Zealand as a biological control agent of the pasture pest Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). Equal numbers of each South American geographical population of this thelytokous endoparasitoid of adult hosts were released in New Zealand. A morphometric method described in this paper provided a means of classifying M. hyperodae adults as originating from either east or west of the Andes. Analysis revealed that, on average, specimens collected in Chile had significantly more antennal segments, narrower stigmas and longer radial cells than those collected in Brazil, Uruguay and Argentina. Significant differences between populations originating from each side of the Andes were also recorded in the dimensions of metasomal tergum one and basitarsus three. The morphometric method should, therefore, assist in defining the origins of M. hyperodae established in New Zealand. This information will be used in attempts to ascertain the importance of climate matching and host-parasitoid co-evolution to the outcome of the L. bonariensis biological control programme.     

Influence of crucifer cropping system on the parasitism ofPlutella xylostella (Lep., Yponomeutidae) byCotesia plutellae (Hym., Braconidae) andDiadegma semiclausum (Hym., Ichneumonidae)

Field experiments were conducted to study the influence of cabbage monoculture and mixed cropping on the parasitism of diamondback moth,Plutella xylostella (L.), a destructive pest of all crucifers, by 2 larval parasites,Diadegma semiclausum Hellén andCotesia plutellae Kurdjumov. There was no significant difference in parasitism by either species whether cabbage was planted in insecticide-free monoculture or in mixed cropping with 8 noncrucifers which were sprayed twice a week with chemical insecticides mevinphos, methamidophos and permethrin. Population ofP. xylostella increased as the cabbage plants grew older. Parasitism byC. plutellae was higher soon after cabbage transplanting but decreased as the plants grew older. Parasitism byD. semiclausum was very low soon after cabbage planting but increased as the plants grew older. A significant negative correlation was found betwen parasitism byC. plutellae andD. semiclausum. In a caged field study where only one parasite species was used in an individual cage, parasitism ofP. xylostella by both species decreased as theP. xylostella population increased. This is believed to be due to the absence of competition between the two parasites inside the cage. There was no relationship between host-plant age and parasitism ofP. xylostella larvae by either parasite species.     

Winter ecology of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae: Aphidiidae)

Abstract:  Flower strips near crops may stimulate natural enemies by the provision of nectar and hibernation sites. However, these habitats may also be beneficial for potential pest species. We investigated the dynamics of the cabbage aphid Brevicoryne brassicae (L.) (Homo., Aphididae) and its primary parasitoid Diaeretiella rapae (McIntosh) (Hym., Braconidae) in brussels sprout fields and adjoining flower plots in winter. A wide variety of 14 plant species were included in the study, each established as monoculture plots. Brussels sprout fields and flower plots were established at two sites. One site was located in an open agricultural landscape, the other in a landscape dominated by mixed forest. Brevicoryne brassicae and D. rapae were found on brussels sprout plants but not in the flower plots. Brevicoryne brassicae was initially more abundant in the open landscape, but as their densities declined rapidly in time, no living aphids were recovered at both sites by February. The density of aphids parasitized by D. rapae showed a similar trend, but densities of eight mummies per brussels sprout plant were still present by the end of February. These findings suggest that (i) flower species under investigation do not function as sources of B. brassicae and (ii) brussels sprout plants that are not harvested may not only harbour D. rapae populations that may sustain biological control, but are also likely to act as sources of B. brassicae infestation.     

Comparison of development and demographic parameters of Diuraphis noxia (Hem., Aphididae) and its parasitoid,Diaeretiella rapae (Hym., Braconidae: Aphidiinae)

Demographic parameters of Diuraphis noxia (Mordvilko) and its parasitoid, Diaeretiella rapae (McIntosh) were investigated under laboratory conditions at temperatures of 20 ± 1°C, 60 ± 5% relative humidity of 60 ± 5% and a photoperiod of 16: 8 (light: dark) hours. The survival rates (l_x ) and the life expectancy (e_x ) at the beginning of adult emergence were 86% and 25.81 days for D. noxia and 100% and 7.36 days for D. rapae, respectively. Based on the Weibull distribution parameters, the survival curves were type I for both D. noxia and D. rapae, which indicates that mortality mostly occurred in older stages. The r _m-values in aphid and parasitoid were obtained as 0.22 ± 0.002 and 0.19 ± 0.003 day^?1, respectively. Mean generation time (T) and doubling time (DT) were 15.93 ± 0.202 and 3.15 ± 0.031 days for the aphid and 15.33 ± 0.071 and 3.67 ± 0.054 days for the parasitoid, respectively. The R₀ -values of D. noxia and D. rapae were evaluated 33.19 ± 0.961 and 18.07 ± 0.761 females/female/generation, respectively. The gross and net fecundity rates were 59.21 ± 1.94 and 32.825 ± 0.972 nymphs/female/day for the aphid and 37.59 ± 1.46, and 33.8 ± 1.51 eggs/female/day for the parasitoid, respectively. The results of this research indicated that D. rapae is an adequate parasitoid for control of Russian wheat aphid.     

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

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

Host specificity testing and suitability of the parasitoidMicroctonus hyperodae (Hym.: Braconidae,Euphorinae) as a biological control agent ofListronotus bonariensis (Col.: Curculionidae) in New Zealand

The behaviour of the parasitoidMicroctonus hyperodae Loan was studied under quarantine conditions to determine its likely host range in New Zealand. The species was imported from South America as a potential biological control agent of Argentine stem weevil,Listronotus bonariensis (Kuschel). The study involved systematic evaluation of the parasitoid's behaviour when exposed to 24 non-host weevil species; all but three of these were native to New Zealand. Of those tested, four were found to sustain someM. hyperodae development. However, further examination showed that in all but one species,Irenimus aequalis (Broun), parasitoid development was impeded, with up to 50% of the larvae becoming encapsulated. Overall, those weevil species that were attacked produced only 19% of the parasitoids derived fromL. bonariensis controls. As an adjunct to this quarantine study, a review of the habitats of the native weevil and target pest populations indicated that refugia would probably exist for native alpine species. I. aequalis was not considered to be threatened byM. hyperodae as this weevil has benefited from the advent of European agricultural systems to the extent that it is now recognised as a minor pest. In view of its relatively oligophagous behaviour, the parasitoid was recommended as suitable for release.      

Overproduction of Serratia marcescens metalloprotease (SMP) from the recombinant Serratia marcescens strains

Summary To overproduce Serratia marcescens metalloprotease(SMP), various recombinant plasmids encoding SMP gene were constructed and the SMP productivities from the recombinant S. marcescens strains were examined. The recombinant S. marcescens strains indispensably required proteinaceous substrates such as casein for the extracellular production of SMP. We obtained maximum 9,100U/ml of SMP from the culture supernatant of S. marcescens ATCC27117 containing a regulatory plasmid pTSP2 encoding SMP gene fused with a strong trc99a promoter and its repressor gene lacI^q, which is about 23 times higher than that of wild type strain. SMP produced from the recombinant S. marcescens(pTSP2) was 88.3% of total extracellular proteins.     

Impact of the parasitoid Lathrolestes ensator (Hym., Ichneumonidae, Ctenopelmatinae) as antagonist of apple sawfly Hoplocampa testudinea (Hym., Tenthredinidae)

Abstract: Lathrolestes ensator (Brauns) was the only parasitoid species reared from larvae of apple sawfly Hoplocampa testudinea (Klug) collected in Dutch orchards. The life history parameters of apple sawfly and its parasitoid L. ensator were investigated in field and semi‐field experiments. Usually, the adult parasitoids emerge in synchrony with the preferred host stage, the second instar sawfly larvae. Parasitoid females carried 120–175 eggs, but never laid more than half this number. The mortality of sawfly eggs and larvae varied from 75 and 99%. The eggs and mining larvae are most vulnerable, as the older larvae survive for 90% on average. Three factors at least determine how many of the descending larvae become adult sawfly or parasitoid next spring. The failure of descending larvae to construct a cocoon varied from 7 to 31% and was highest in clay soil. Probably a similar mechanical hindrance prohibited more emerging adults, of both sawfly and L. ensator, from attaining the surface in heavier soils next spring. Relatively more sawfly prepupae than parasitoids died in the cocoon stage, from fungus disease or other causes, but more parasitoids than hosts stayed in prolonged diapause. Mainly due to this last factor, the overall result was a decrease of the parasitoid : host ratio during the first season underground. A life table based on survival rates during various life stages yields a net reproductive rate of up to 2.4 daughters per female sawfly. It indicates that 60% of the sawfly larvae need to be parasitized to stop population growth, or correspondingly less when more than 75% of the host eggs and young larvae are killed by predators or other causes.     

Effects of two neem insecticide formulations on the attractiveness, acceptability and suitability of diamondback moth larvae to the parasitoid, Diadegma mollipla (Holmgren) (Hym., Ichneumonidae)

Abstract:  Behavioural responses of female Diadegma mollipla to volatiles from cabbage plants and host-infested [ Plutella xylostella (L.)] cabbage plants sprayed with two neem insecticide formulations were investigated in a Y-tube olfactometer. Parasitoids were significantly more attracted to volatiles from cabbage and host-infested cabbage sprayed with the powder formulation than to clean air. In contrast, parasitoid response to volatiles from cabbage and host-infested cabbage sprayed with the oil formulation was not significantly different from clean air. In choice tests between infested plants sprayed with water (control) or the powder formulation, parasitoids showed no preference for volatiles from either of the treatments. In similar tests with the oil formulation, parasitoids showed a preference for volatiles from control plants over plants sprayed with the oil formulation. In host acceptance and suitability tests, parasitism rates in the neem- and water-sprayed hosts were, with one exception, not significantly different. However, the neem-sprayed larvae died earlier than control larvae and were therefore not able to support parasitoid development. The implication of these findings for the combined use of neem insecticides and parasitoids in the management of P. xylostella is discussed.     

Host selection and reproductive success of French and Moroccan populations of the parasitoid, Microctonus aethiopoides (Hymenoptera: Braconidae)

French and Moroccan populations of the parasitoid Microctonus aethiopoides Loan were studied in the laboratory for their host selection, mating behavior, and reproductive success. The French strain, collected on Hypera postica (Gyllenhal), although capable of parasitizing and producing viable offspring on Sitona weevils, preferred Hypera weevils, its known target host. The Moroccan strain, collected on Sitona discoideus Gyllenhal, exhibited host specificity for Sitona. A partial reproductive isolation was observed between the two strains. Moroccan females mated more frequently with French males than did French females with Moroccan males. The pre-copulation time for mating pairs of opposite strains was significantly longer than that for mating pairs of the same strain. There was no significant difference in copulation time nor in larval and pupal duration between French and Moroccan strains. In summary, the French and Moroccan strains of M. aethiopoides are clearly separable by biological, behavioral, and morphometric traits and the preferred host for Hypera is the French strain and Sitona for the Moroccan strain. Consequently, geographic location and host source become important when considering this parasitoid as a potential biological control agent.     

Allozyme markers to help define the South American origins of Microctonus hyperodae (Hymenoptera: Braconidae) established in New Zealand for biological control of Argentine stem weevil

The thelytokous parasitoid, Microctonus hyperodae Loan, was collected from eight South American locations and introduced to New Zealand in 1991 for biological control of Argentine stem weevil, Listronotus bonariensis (Kuschel) (Coleoptera: Curculionidae). Parasitoids from each population were released in equal numbers at each New Zealand site to give them the same opportunities to establish. Population markers have been sought to identify the South American geographic populations that have become most successful in New Zealand. These would assist in determining the importance of concepts such as climate matching and host-parasitoid coevolution to the establishment of natural enemies in new regions for biological control. Vertical polyacrylamide electrophoresis was used to survey 16 enzymes and ten calcium binding proteins, and this paper reports variation at three putative loci. Malate dehydrogenase, a dihydrolipoamide dehydrogenase isozyme and a calcium binding protein exhibited clear genetic variation, each with two alleles. All M. hyperodae isofemale lines from east of the Andes mountains shared one genotype, all but one from west of the Andes shared another, while a population from within the Andes contained both genotypes. This variation was highly congruent with previously described morphometric variation. At two loci, the maintenance of heterozygotes, and the absence of homozygotes, within isofemale lines suggested M. hyperodae thelytoky is apomictic.     

Bioecological characteristics of Bassus tumidulus (Nees) (Hym., Braconidae), a parasitoid of the poplar twig borer, Gypsonoma aceriana (Dup.) (Lep., Tortricidae) in Bulgaria

Main aspects of biology and ecology of Bassus tumidulus (Nees), a parasitoid of Gypsonoma aceriana (Dup.), were studied during the period 1989–2000. Poplar tender shoots with G. aceriana larvae were collected at four localities in Bulgaria (Sofia, Svoge, Vardim and Pazardzhik) and examined in laboratory conditions. B. tumidulus was recovered in the Sofia and Svoge localities. It is a solitary internal parasitoid that attacks young larvae of G. aceriana (first–second instars) and kills host pre‐pupae. It develops two generations and overwinters as a larva in the host. Adult emergence of both overwintering and summer generation of B. tumidulus coincides with adult emergence of the host. In 1997, the first generation emergence of B. tumidulus was in relatively good synchrony with the first larval population of G. aceriana. However, the second generation B. tumidulus was not very well synchronized with the life cycle of G. aceriana because adult parasitoids appeared mostly in the beginning of the host larval population. The average mortality of G. aceriana, caused by this parasitoid in 1997 in Sofia, was 15.7 and 23.3% for the overwintering and summer generation, respectively. The highest level of parasitism by B. tumidulus, observed in individual study, was 61.5%, occurring during the summer generation in 1997.