BioControl 44: 263280, 1999. 1999 Kluwer Academic Publishers. Printed in the Netherlands.

Larval morphology and development of Copteraoccidentalis

Mria KAZIMROV1; and Vladimr VALLO21Institute of Zoology, Slovak Academy of Sciences, Dbravsk Cesta 9, SK-84206 Bratislava,Slovakia; 2Dobsinskho 12, SK-90028 Ivanka pri Dunaji, Slovakia; author forcorrespondence (e-mail: uzaemkaz@savba.savba.sk)

Received 9 March 1999; accepted in revised form 19 July 1999

Abstract. The morphology and development of immature stages of the solitary internal para-sitoid Coptera occidentalis were studied within the pupae of their factitious host, Ceratitiscapitata. Parasitoid eggs are of the hymenopteriform type. Three larval instars are described.The first instar is of the mandibulate type bearing prominent submandibular appendages anda pair of terminal lobes on the last abdominal segment. The terminal lobes are covered withcuticular spines. The integument also bears cuticular spines arranged in paired dorsal welts oneach of body segments VIX. The second and third instar larvae are hymenopteriform withsimple mandibles, reduced submandibular appendages and smooth integument. The third in-star has an open tracheal system with three pairs of spiracles on segments IIIV. Considerablevariation in development rates of parasitoid immature stages and high percentage of super-parasitism were observed. Parasitoid eggs nearly doubled in size during the 96-h incubation.Development from egg to pupa took minimum 25 days and emergence of imagines started onday 42 after parasitization. Superparasitism was recorded in 56% of the examined hosts. Theaverage number of eggs/host was 5.04 (range 122). Supernumerary occurrence of successivelarval instars per one host was also observed.

Key words: Diapriidae, head capsule, larva, pupal parasitoid, superparasitism

Introduction

Attempts to use pupal parasitoids for biological control of economicallyimportant fruit flies date back to the beginning of this century. In 1913 anunsuccessful experiment was made to establish the African species, Copterasilvestrii (Kieffer) to control Ceratitis capitata Wiedemann (Diptera, Teph-ritidae) in Hawaii. These early studies also provided basic data on themorphology and biology of diapriids (Silvestri, 1913; Pemberton and Willard,1918). Recently, another diapriid, Coptera haywardi Oglobin attacking theMexican fruit fly, Anastrepha ludens (Loew.) has become a target speciesfor biological control of tephritid fruitflies (Sivinski et al., 1998). Never-

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theless, the knowledge about the developmental biology and host-parasitoidrelationships of internal parasitoids of pupal Diptera still remains limited.

Coptera occidentalis Muesebeck (Diapriidae, Diapriinae) is a solitaryinternal parasitoid of pupal Tephritidae (Diptera). The species was describedbased on imagines recovered from Rhagoletis completa Cresson collected inCalifornia (USA) (Muesebeck, 1980). C. occidentalis was originally intro-duced from the USA to Slovakia as a potential agent for biological controlof Rhagoletis cerasi L. (Vallo, 1989). The laboratory rearing of the parasitoidwas well established using the factitious host, C. capitata (Vallo, 1990; Kazi-mrov and Vallo, 1992). First instar C. occidentalis larvae were found tooverwinter in diapausing R. cerasi (Kazimrov, unpublished data), whereasthe species develops continually in laboratory non-diapausing host.

Earlier studies on C. occidentalis considering longevity and fecundityshowed that the species had an arrhenotokous reproduction and adultssurvived in laboratory for up to 65 days. However, at permanent host delivery,oviposition yielding maximum progeny occurred between day 46 afteremergence and fecundity of wasps (number of living progeny/female) variedbetween 8.231 (Vallo, 1990; Kazimrov, 1996; Kazimrov et al., 1997).This study was designed to provide basic information on morphology anddevelopment of immature stages of C. occidentalis while confined in theirlaboratory host.

Material and methods

Coptera occidentalis was originally recovered from pupae of Rhagoletiscompleta in California and provided by former co-workers of the Universityof California, Berkeley (USA). The parasitoid has been maintained on pupaeof Ceratitis capitata at the Institute of Experimental Phytopathology andEntomology at Ivanka pri Dunaji (Slovakia) since the beginning of the 1980sas described by Kazimrov and Vallo (1992). At the time of experiments, thecolony of C. occidentalis had completed102 generations. For parasitizationexperiments, ca. 5000 pupae of C. capitata 34 days after pupariation wereexposed to groups of ca 500 mated parasitoid females for 6 h (for details seeVallo, 1990; Kazimrov and Vallo, 1992; Kazimrov, 1996) and then placedin a controlled room at 231 C, 65% RH and 16L:8D photoperiod. At theseconditions flies emerged from unparasitized pupae in about 1011 days. Thehost pupae exposed to female parasitoids were regularly examined for thepresence of parasitoid developmental stages. Dissections were carried out in8-, 12- and 24-h intervals, respectively, until 96 h, 15 days and 44 days afterparasitization. After the onset of adult emergence (day 44), emerging wasps

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were recorded for a sample of 250 parasitized pupae. Pupae from which nowasps emerged were examined for the presence of dead parasitoids or flies.

Host samples had been selected randomly and dissected until at least 20immature parasitoids were found in each case. Data beginning with day 8were then pooled in 23 day intervals. The duration of each developmentalstage was recorded based on the above dissections. Parasitoid immaturestages were removed from hosts to insect saline and then mounted in lacto-fuchsin on microscope slides. Measurements (maximum body length andwidth) of at least 15 individuals were taken at each dissection time usinga light microscope or stereomicroscope equipped with an ocular micrometer.Additionally, size of developing parasitoid eggs dissected from hosts, firstinstar larvae head capsule length and width as well as length and width ofsuccessive larval instars and pupae were measured in 15 randomly selectedspecimens. Parasitoid female ovaries were dissected in saline, mounted inlactofuchsin and the measurements of fully developed ovarian eggs wererecorded. External morphology of eggs and larvae was studied using light andscanning electron microscopy (SEM). Light micrographs were taken usingNikon Eclipse E600 microscope and Nikon FDX-35 photoequipment. ForSEM studies, parasitoid larvae were dissected in saline, rinsed in distilledwater, killed in hot distilled water, progressively dehydrated in alcohol andplaced in chloroform. Following drying the specimens were mounted onstubs, gold/platinum coated and observed with the SEM Tesla BS301 or thefield emission SEM Hitachi S800.

Classification of egg and larval types was adapted according to Clausen(1940) and Hagen (1964). Voucher specimens of C. occidentalis are depositedin The Museum of Reading, UK.

Results

Morphology

EggFully developed ovarian eggs are typically hymenopteriform in shape withsmooth, transparent and thin chorion (Figure 1A). The mean length and widthare 0.35 0.004 mm and 0.13 0.003 mm (mean SE, N = 15). Eggs beginto increase in size 48 h after parasitization. Prior to hatching they becomeround in form and attain a size of 0.48 0.03 mm by 0.34 0.02 mm (N =15). At this stage, the fully developed first instar larva is visible (Figure 1B).

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Figure 1. Coptera occidentalis egg (AB) and first instar larva (CG). A. Fully developedovarian egg. B. Egg with the first instar larva 96 h following parasitization. C. Head capsulewith anterior rostrum Ar, mandibles Md and submandibular appendages Sa. D. Dorsal viewof the abdomen with dorsal cuticular spines Ds and terminal lobes Tl. E. Lateral view offirst instar larva. F, G. Frontal and dorsolateral view of the head showing anterior rostrum Ar,mandibles Md, submandibular appendages Sa and submandibular cuticular processes Sp.

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First instar larvaThe first instar is of the mandibulate type with 12 body segments (Figure1E). The head is heavily sclerotized and bears a pair of large sickle-shapedmandibles, an anteriorly divided rostrum-like extension protruding from thelabrum (Figures 1C, F and G), a pair of prominent cylindrical submandibularappendages (Figures 1F, G and 2C) and a pair of triangular cuticular processeslateroventrally of the submandibular appendages (Figures 1F and 2B). Thereare paired welts bearing 27 cuticular spines dorsally on each of bodysegments VIX (Figures 1D and 2D, E). The number of spines/welt variesconsiderably within segments and individuals. The last abdominal segmentbears a pair of anal processes (= terminal lobes, see Clausen, 1940) whichare covered by a number of slightly hooked spines (Figures 1D, E and 2A).Shortly after hatching the larvae measure 0.80 mm 0.15 mm (body length width) and increase to a size of 0.89 mm 0.18 mm before moulting(Table 1). The mean length and width of the first instar head capsule are 0.18 0.007 mm and 0.24 0.004 mm (mean SE, N = 15).Second instar larvaThe second instar is hymenopteriform with 12 body segments (Figure 2F).Cephalic structures are reduced. Mandibles are simple and lightly sclerotized.Submandibular appendages are conical and reduced in length as compared tothe first instar (Figure 2G). Antennal features become distinct (Figure 2I).The cuticle appears smooth, bearing no spines or processes. The mean bodylength and width are 2.42 0.13 mm and 0.73 0.05 mm (mean SE, N =15), with a maximum size of 2.61 mm 0.88 mm before moulting (Table 1).Third instar larva and prepupaThe third final instar is hymenopteriform with 12 segments (Figure 2H). Thehead bears simple acute mandibles with heavily sclerotized blades (Figure3A, B). Further reduction in the length of the submandibular appendages isevident; they are cylindrical, disc-like in shape (Figure 3A). Large antennaldiscs projecting from the surface of the head are present (Figure 3A). Thecuticle is smooth bearing no spines. This instar has an open tracheal systemwith 3 pairs of spiracles on body segments IIIV (Figure 3C). The averagebody length and width are 3.86 0.12 mm and 1.83 0.07 mm (mean SE, N = 15). After the host is fully consumed, larvae reach a maximumsize of 4.23 mm 2.04 mm (Table 1). The midgut is filled with wastematerial. In the prepupal stage, faecal pellets are discharged, the thoracicregion becomes narrower and imaginal eyes appear. The caudal end of theabdomen is rounded and lies embedded in the meconium that is formed ofnumerous greyish, ovoid pellets. Prepupae are reduced in size in comparisonwith full-grown third instar larvae (Table 1).

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Table 1. Measurements (in mm) of Coptera occidentalis larvae, prepupae and pupae at specified intervals after parasitization

First instar Second instar Third instar Prepupa PupaDays after N Length Width N Length Width N Length Width N Length N Lengthparasitization (Mean SE) (Mean SE) (Mean SE) (Mean SE) (Mean SE) (Mean SE) (Mean SE) (Mean SE)

4 17 0.80 0.01 0.15 0.0045 22 0.80 0.01 0.15 0.0046 44 0.82 0.01 0.15 0.0037 46 0.86 0.01 0.17 0.0048 51 0.85 0.02 0.17 0.005

10 87 0.79 0.01 0.15 0.002 14 1.59 0.02 0.37 0.0312 58 0.89 0.03 0.16 0.003 56 1.74 0.02 0.46 0.0114 39 0.81 0.02 0.17 0.006 71 2.35 0.04 0.68 0.0117 43 0.83 0.01 0.17 0.004 62 2.29 0.05 0.71 0.02 36 3.26 0.073 1.23 0.0220 17 0.80 0.02 0.15 0.006 34 2.56 0.09 0.78 0.02 72 4.01 0.04 1.98 0.0222 27 0.84 0.02 0.17 0.006 19 2.61 0.14 0.88 0.05 59 3.99 0.03 1.88 0.03 7 3.78 0.0925 15 0.83 0.03 0.17 0.007 12 2.38 0.14 0.75 0.07 30 4.23 0.03 2.04 0.02 42 3.84 0.03 6 3.82 0.0628 18 0.84 0.03 0.17 0.01 2 2.80 0.20 0.77 0.02 15 4.09 0.04 1.92 0.05 24 3.85 0.05 43 3.82 0.0232 35 0.83 0.02 0.15 0.003 7 2.44 0.17 0.86 0.05 17 4.07 0.04 1.95 0.04 20 3.84 0.06 98 3.76 0.0235 21 0.76 0.02 0.14 0.002 2 2.42 0.18 0.97 0.02 7 4.02 0.06 2.00 0.05 9 3.91 0.09 80 3.59 0.0238 16 0.76 0.01 0.14 0.004 1 2.6 0.95 4 4.05 0.10 1.97 0.06 5 3.90 0.11 53 3.43 0.0244 12 0.76 0.01 0.14 0.003 2 2.42 0.18 0.77 0.02 6 4.02 0.08 1.95 0.04 76 3.41 0.02

Note: width of prepupae and pupae was not measured.

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Figure 2. Coptera occidentalis first instar (AE), second instar (F, G, I), third instar larva (H)and pupa (J). A. Body segment XII with terminal lobes and cuticular spines. B. Submandibularcuticular process. C. Submandibular cylindrical appendage. D, E. Abdominal dorsal welts withcuticular spines. F. General view of second instar larva. G. Frontal view of second instar headshowing mandibles Md and submandibular appendages Sa. H. General view of full-grownthird instar larva. I. Lateral view of second instar head with mandibles Md, antennal disc Adand antennal papilla Ap. J. General view of pupa.

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Figure 3. Coptera occidentalis third instar larva. A. Frontal view of the head showingmandibles Md, submandibular appendages Sa and antennal disc Ad. B. Mandibles Md. C.Spiracle.

PupaPupation occurs within the host puparium. The pupa is of the exarate typewith mouthparts, antennae and legs clearly visible (Figure 2J). It is white andgradually turns black. The larval exuvium is fixed to the caudal end of theabdomen. The pupa lies with its head at the anterior end of the host puparium.Wasps emerge by pushing off the dorsocephalic cap of the puparium. Pupaldimensions are given in Table 1.

Development

Larval development of C. occidentalis requires a relatively long period. Greatvariability in the duration of individual immature stages and larval instarswas recorded. Most of the eggs hatched between 96120 h after oviposition(Figure 4). However, some apparently viable eggs could be found until day20 following parasitization. No encapsulation of eggs or larvae was observed.First instar larvae were found in 86.14100% of hosts till day 10 after para-sitization. Thereafter, the percentage of hosts containing only first instarparasitoids gradually decreased but they occurred during the whole dissectionperiod (i.e. 16% of dissected host pupae contained only first instar larvae atthe time of the onset of adult emergence). First second instar larvae were

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recorded on day 9 and, similarly to the first instar, they occurred until theend of the dissection period. Moulting to the final instar began on day 15after parasitization, first prepupae were found on day 21. Final instar larvaeor prepupae occurred till day 44. First pupae were dissected on day 25. Onsetof pigmentation of eyes and thorax started on day 30 and 33, respectively;first fully pigmented individuals were found on day 36 after parasitization.Adults started to emerge on day 42 and emergence lasted for 30 days (Figure5). Males emerged first with a maximum on day 46. Female wasps started toemerge on day 48 with a peak on day 52. The overall sex ratio was 1:2.06(M:F). A summarisation of data on adult emergence and final dissection ofhost pupae is also given in Figure 5 (column indicated as Total). The resultsshow that in 6% of hosts the parasitoids did not finish their development anddied. Sixteen percent of the host pupae exposed to parasitoids contained amelanized mass in which neither living nor dead parasitoids were found andwere referred to unexplained mortality.

Superparasitism was recorded in 56% of the examined hosts. The averagenumber of eggs/host was 5.04 (range 122), whereby 10.83% of the hostscontained single eggs. 25 eggs were found in 10.8317.50% and 610 eggsin 2.506.67% of hosts. More than 11 eggs were dissected from 7.50% ofhosts. Superparasitism was also observed in the first instar (Table 2), wherebylarvae occurred along with 18 eggs in 49.78% of hosts. The presence of 23 first instar larvae/host was most frequent; maximum number of first instarrecorded per one host was 15. Supernumerary larvae were also found afterthe onset of the moulting to the second instar. Maximum number of secondinstar/host was 3, but in many hosts one second instar larva along with 16first instar larvae was recorded. After the onset of moulting to the third instarthe number of supernumeraries/host declined. The simultaneous occurrenceof third and second instar/host has not been recorded but one final instarlarva along with 12 first instar larvae/host could still be found. Very rarely(0.001% of the total number of host pupae dissected in this study) two para-sitoid pupae/host were discovered. Apart from viable larvae, we frequentlyobserved various numbers of melanized or partly destroyed first instar larvaewithin the host.

Discussion

Generally, internal parasitoids undergo great morphological changes as theydevelop through various instars. First instar is considered as the mostdistinctive parasitic stage with diverse structures and it appears that themandibulate-type larva is always solitary (Hagen, 1964). Large mandiblesprobably developed in parasitic larvae as an adaptation to kill supernumer-

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Table 2. Supernumerary occurrence of immature stages of Coptera occidentalis in pupae of Ceratitis capitata (in%) at specific intervals afterparasitization (at 23 1 C and 65% RH)

Days after parasitization13 4 5 6 7 8 910 1112 1314 1517 1820 2122 2325 2628 2932 3335 3638 3941 4244

N 120 46 23 44 50 51 101 114 110 141 120 112 105 102 177 119 79 47 50Egg 100.0 67.39 4.35 8.0First instar

1 L1 13.04 65.22 70.45 72.0 68.63 61.39 27.19 20.0 17.73 5.00 12.50 9.52 10.78 15.25 14.29 15.19 8.51 16.02 L1 13.04 17.39 18.18 12.0 17.65 10.89 7.02 2.73 5.67 2.68 1.96 2.26 2.52 1.263 L1 6.52 8.70 4.55 2.0 1.96 4.95 7.02 7.27 4.25 2.50 1.79 0.95 2.94 0.56 3.804 L1 4.35 6.82 4.0 5.88 3.96 4.39 1.82 1.42 0.83 2.68 0.95 1.965 L1 2.0 3.92 2.97 1.75 3.64 0.71 0.83 0.9 0.95 0.566 L1 0.99 1.75 0.83 0.9 0.95 0.56 0.847 L1 1.96 0.99 0.88 0.83 0.98 L1 0.88 0.83 0.9 0.569 L1 0.71 0.9

Second instar1 L2 5.94 32.46 39.09 30.50 17.50 8.93 5.71 0.98 3.95 1.68 1.26 4.26 4.02 L2 2.63 0.91 4.26 1.67 0.983 L2 0.88

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Table 2. Continued

Days after parasitization13 4 5 6 7 8 910 1112 1314 1517 1820 2122 2325 2628 2932 3335 3638 3941 4244

Second + first instar1 L2 + 1 L1 7.92 7.89 16.36 7.09 1.67 4.46 1.901 L2 + 2 L1 2.63 2.13 3.33 0.951 L2 + 3 L1 0.88 5.45 2.68 0.951 L2 + 4 L1 0.88 0.91 0.83 0.901 L2 + 5 L1 0.88 0.83 0.951 L2 + 6 L1 2.50 0.952 L2 + 1 L1 1.82

Third instar1 L3 4.96 46.67 57.14 66.67 36.27 20.90 13.44 11.39 8.51 4.0

Third + first instar1 L3 + 1 L1 20.57 12.50 0.90 1.90 1.961 L3 + 2 L1 0.83 0.90

Pupa1 P 5.71 42.16 54.8 66.39 67.09 78.72 78.02 P 0.56 0.84

Adult 2.0

Key: N = numbers of dissected host pupae; L1 = first instar; L2 = second instar; L3 = third instar; P = pupa; arabic numerals in column1 indicate numbers of larvae of the corresponding instar. Data represent percentages of host pupae out of the total number of parasitizedpupae in which supernumerary occurrence of various numbers and larval instars of the parasitoid were recorded.

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Figure 4. Development of Coptera occidentalis in Ceratitis capitata pupae at 23 1 C and65% RH. Data express the percentage of pupae out of the total number of parasitized pupae (atspecific intervals after parasitization) in which older instar or stage was recorded apart fromthe presence of individuals of younger instar or stage. The development was followed untilthe emergence of first adult wasps (day 44). Numbers on top of columns indicate numbers ofexamined pupae.

aries in case of superparasitism or multiparasitism (Salt, 1961; van Baarenet al., 1997). Mandibulate-type first instars have been described in phylo-genetically unrelated groups of parasitic Hymenoptera, e.g. Ichneumonidae,Braconidae, Diapriidae (Hagen, 1964). In contrast, certain structures appearin mature hymenopteran larvae which allow separating them into taxa that arecomparable to those for adult parasitoids (Hagen, 1964). Moreover, withinphylogenetically related groups (e.g. Braconidae or Mymaridae), first instarlarvae of solitary and gregarious species present morphological differences solitary species represent fighting morphs while gregarianism seems tobe associated with the reduction of conspicuous larval structures and fightingbehaviour (Laing and Corrigan, 1987; van Baaren et al., 1997). Conspicuous

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Figure 5. Emergence pattern of Coptera occidentalis adults from Ceratitis capitata pupae.Sex ratio (M:F) at specified intervals after onset of emergence is indicated above the columns.The column indicated as Total is a summary of data (in%) on adult emergence and finaldissection of host pupae: A host pupae containing dead parasitoids; B host pupaecontaining melanized mass; C hosts containing dead flies; N = 250.

structures such as large mandibles, setae and/or caudal appendages areusually lost or greatly reduced in intermediate larval instars of parasitoidswhich are often unable to fight and usually resemble the form of the finalinstar (Hagen, 1964).

The morphology and biology of diapriids is poorly known. Most of theknown species are endoparasites of dipteran pupae (subfamily Diapriinae)or larvae (subfamily Belytinae) (Hoffmeister, 1989; Whitefield, 1998). Somespecies are suggested to be myrmecophilous (Huggert and Masner, 1983),but in the majority of the described species no associations to hosts couldbe determined. Diapriinae have been reported to be either solitary (e.g.representatives of the genera Coptera, Psilus, Spilomicrus, Aneurhynchus) orgregarious (e.g. species of the genera Trichopria or Diapria) (Clausen, 1940;ONeill, 1973; Hoffmeister, 1989).

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Coptera occidentalis is a solitary internal parasitoid with morphologi-cally distinct mandibulate first instar, parasitizing pupae of tephritid fruitflies.Three larval instars were described in the species, similarly as in the otherrepresentatives of Diapriinae (Clausen, 1940; Hagen, 1964). Mandibulatetype first instar bearing large mandibles and submandibular appendageswas also observed in other solitary species, e.g. C. silvestrii (Pembertonand Willard, 1918), Basalys tritomus (Thomson) (Wright et al., 1947) orSpilomicrus hemipterus Marshall (Hoffmeister, 1989). In contrast, gregariousdiapriine first instar larvae lack large mandibles (ONeill, 1973) suggestingthat, as in other parasitic groups, gregarianism leads to loss of their fightingcapacities. Submandibular appendages were described, except diapriids, inmandibulate first instar larvae of some solitary braconid larval-pupal parasi-toids (Opiinae, Alysinae) (Hagen, 1964; Cals-Usciati, 1982; Notton, 1991).In braconids the structures are interpreted as maxillary palps. However, onlydetailed morphological studies involving both scanning and transmissionelectron microscopy and complementary behavioural studies could clarify thehomology and function of these structures in diapriids.

Fighting parasitoid larvae are generally mobile and show morphologicaladaptations, such as caudal appendages and/or setae (van Baaren et al., 1997).Besides mobility, several functions have been attributed to the tail of para-sitoid larvae, e.g. respiration, absorption of food substances, balancing organ(Hagen, 1964). The function of first instar C. occidentalis terminal lobesand dorsal spines can only be guessed they are probably responsible formobility and also support the small larvae to grasp the host tissues, thuspreventing them from passive floating within the host haemolymph. Similarto C. occidentalis, paired anal processes (= terminal lobes) with cuticularspines were described in the other solitary diapriine species (Pembertonand Willard, 1918; Clausen, 1940; Wright et al., 1947; Hoffmeister, 1989).However, the occurrence of setae on other body segments, except terminallobes, was reported only for S. hemipterus (Hoffmeister, 1989). Additionally,some cuticular structures consisting of two posterior tubercles with severalteeth located on the last body segment were described in both first andsecond instar larvae of the gregarious Trichopria species (ONeill, 1973).

Second and final instar C. occidentalis larvae are typically hymenopter-iform. The prominent cephalic structures are greatly reduced in size. Themandibles of the third instar are heavier chitinized than in the second instar.Moreover, the third instar has an open tracheal system with three pairs ofspiracles on body segments IIIV, thus, showing similarity to C. silvestrii(Pemberton and Willard, 1918). In contrast, the mouthparts of the third instarof the gregarious Trichopria atrichomelinae Muesebeck bearing several oralpapilae and mandibles with accessory teeth (ONeill, 1973) differ from the

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simple acute mandibles of the other described diapriids. Final instar larvae ofthe genus Coptera were also shown to differ in some structures from larvae ofthe other genera with solitary larvae. For example, only two pairs of spiracleswere discovered in Basalys sp. (Notton, 1991), a dorsal papilla projectingfrom the second body segment was observed in B. tritomus (Wright et al.,1947) or paired cone-like projections protruding dorsolaterally behind thehead were reported in S. hemipterus (Hoffmeister, 1989). The finding of largeantennal discs in third instar Coptera larvae corresponds well with the generalcharacteristics of diapriid larvae given by Stehr (1987).

In comparison with ichneumonids or braconids, bionomics and life cyclestudies of diapriids are very scarce. The development time of the studiedsolitary diapriid species is relatively long up to 5 weeks in laboratory(Clausen, 1940; Hoffmeister, 1989). The cycle of C. occidentalis from egg toadult averages 54 days at 24 C (Kazimrov, 1996). Considerable variationin development rates of individual stages and instars was shown with 16% ofhost pupae containing only first instar larvae at the onset of adult emergence.Moreover, the results of final dissections discovered a relatively high rate ofunexplained mortality of host or parasitoid and 16% of hosts containingmelanized mass. We might guess that the first instar larvae found at the timeof adult emergence did not moult to the next instar and subsequently died.However, based on results obtained in this study, we are not able to elucidatethe causes of the unexplained mortality in Coptera.

High rate of superparasitism and intraspecific competition belong toother interesting aspects of the life history of C. occidentalis. Generally,superparasitism in solitary parasitoids can be advantageous to compete withconspecifics if hosts are scarce and, on the other hand, avoidance of super-parasitism can be adaptive when sufficient unparasitized hosts are found(van Alphen and Visser, 1990). Moreover, some degree of egg limitationis expected in parasitoid populations (Heimpel and Rosenheim, 1998). Ourprevious investigations showed that Coptera females were able to survive inlaboratory for more than 60 days, but maximum oviposition occurred betweenday 210 after emergence and no parasitoid progeny could be recovered fromhosts exposed to females older than 28 days (Kazimrov, 1996). However,we did not investigate if Coptera females laid more than one egg per oviposi-tion or if two or more females laid eggs simultaneously or subsequently in onehost. Considering the data on fecundity and superparasitism in Coptera wemight suggest that (i) Coptera females lay the maximum of their egg supple-ment within a few days at regular and abundant host supply, (ii) egg limitationoccurs in Coptera females and (iii) the number of adult progeny/female doesnot reflect the real reproduction potential of a female.

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The presence of large mandibles in first instar larvae indicates that phys-ical competition is one of the strategies to eliminate conspecifics in Coptera.The absence of large mandible in second and third instar larvae, the presenceof supernumeraries of successive instars in one host during development andthe finding of a single (exceptionally two) parasitoid pupa/host suggest that,in addition to physical competition, some kind of physiological competitionmight exist during later instars of Coptera, similarly as reported for othersolitary parasitoids (Vinson, 1985).

Diapriids are suggested to be koinobionts (Hoffmeister, 1989; Sivinskiet al., 1998). No venoms have been identified in this parasitic group but ifpresent, they probably have some complex physiological effects (Whitefield,1998). Earlier investigations on the optimal age of C. capitata for obtainingmaximum C. occidentalis progeny determined that pupae 46 days afterpupariation were most suitable (Vallo, 1990). The pupal stage of C. capitatalasts on average 11 days in laboratory while the incubation time of C. occi-dentalis eggs is 46 days. No eye pigmentation or further development wasobserved in the fruit fly pupa after parasitization with Coptera, but its circu-latory system functioned in an apparently normal way. Similar disruption ofmetamorphosis was observed in fruit fly pupae parasitized by C. haywardi(Sivinski et al., 1998) or S. hemipterus (Hoffmeister, 1989). Thus, our obser-vations might indicate that Coptera mediates some kind of developmentalarrest of its host, but further studies are necessary to explain the mechanismof this process.

In conclusion, our study adds information to the characterization ofdiapriid larvae, particularly with respect to the morphology of the first instarhead capsule and body cuticular structures. Further investigation of themorphology of solitary and gregarious species might reveal some phylogen-etic relationships within this parasitic group. Moreover, our study revealedinteresting aspects of the host-parasitoid relationship and the life history of C.occidentalis, i.e. considerably high rate of unexplained mortality and highrate of superparasitism. To explain these phenomena further investigationsinto the physiology of intraspecific competition and the physiology of thehost-parasitoid relationship are necessary.

Acknowledgements

We gratefully acknowledge the help of the staff of the Institute of Informaticsof the Slovak Academy of Sciences at studies with Hitachi SEM. My thanksgo to Prof. Antonio Belcari (Universita degli Studi, Firenze) for providingprotocols for SEM studies and Dr Jana Koznkov (Bratislava) and MrsJudita Blahutiakov (Ivanka pri Dunaji) for their helpful assistance in the

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SEM studies. Thanks are also due to Dr David Notton (The Museum ofReading, UK) for the revision of specimens of C. occidentalis and for helpfulcomments and providing literature. We are also grateful to two anonymousreviewers for helpful comments on an earlier version of this paper.

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