Lepidopteran Host Species Research Articles

Plasticity in life features, parasitism and super-parasitism behavior of Bracon hebetor, an important natural enemy of Galleria mellonella and other lepidopteran host species.

The wasp, Bracon hebetor Say, is an important potential biocontrol agent of a wide range of lepidopteran insect species. The current study was subjected to compare these ectoparasitoid fitness traits on different host species belonging to the order Lepidoptera. Moreover, we determine the population dynamic with different host densities, sex ratio patterns, super-parasitism, longevity, paralysis success, and reproductive potential under laboratory conditions. Our results revealed that oviposition increased with an increase in host density, while the adult emergence and egg hatching were decreased due to the super-parasitism on host larvae. A higher male and female-biased population were observed when virgin and mated females offered fresh hosts. Adults' longevity was recorded more in females than males when kept only with bee honey + royal jelly + host larvae. The mean duration of egg-adult development was recorded higher on Galleria mellonella and lowest on Busseola fusca. The parasitization rate, super-parasitism, and cumulative fecundity of mated and virgin female wasps with different host species were observed higher on specific host Galleria mellonella while it was lower on Phthorimaea operculella. Furthermore, the parasitoids having mating experience preferred fresh, while the parasitoids' lack of mating experiences preferred paralyzed host under olfactometer test. Besides, this research has produced novel facts on the biology of parasitic wasp, B. hebetor that may guide the advancement of sustainable biological control programs to control lepidopteran pests.

A survey of the adventive parasitoid Meteorus pulchricornis (Hymenoptera: Braconidae) and native larval parasitoids of native Lepidoptera

ABSTRACTSince its arrival in New Zealand, Meteorus pulchricornis has parasitised adventive and native lepidopteran host species. We carried out a survey of parasitism by M. pulchricornis and native parasitoids of native lepidopteran host species in the Auckland region. From September 2013 to January 2016, parasitoids were reared from larvae collected from native host plants in habitats including urban gardens, regenerating native forest and native forest remnants. Meteorus pulchricornis was the most abundant parasitoid, accounting for 12% of parasitism, and was reared from 11 of 26 native Lepidoptera species. The host range of M. pulchricornis overlapped with eight other parasitoid species. A previously unrecorded species of Casinaria as well as M. pulchricornis were reared from Cleora scriptaria larvae collected from Te Hauturu-ō-Toi/Little Barrier Island. The parasitoid host association data collected provides preliminary information on the potential impact of M. pulchricornis on native parasitoids.

Parasitism and survival rate of Diadegma fenestrale (Hymenoptera: Ichneumonidae) and DfIV gene expression patterns in two lepidopteran hosts

The genus Diadegma is a well-known parasitoid group and some are known to have symbiotic virus, polydnavirus (PDV). A novel IV was discovered from the calyx of Diadegma fenestrale female and sequenced its genome. D. fenestrale has more than two hosts, including potato tuber moth (PTM) and diamondback moth (DBM). D. fenestrale preferred PTM to DBM as hosts based on the oviposition and survival rate. Nevertheless, the developmental period and morphology of D. fenestrale were not significantly different between PTM and DBM. We compared DfIV gene expression patterns between PTM and DBM under various conditions to understand the phenomena. DfIV genes were more widely expressed in PTM with large numbers than in DBM after parasitized by D. fenestrale, particularly at the initial point. They showed differential expression patterns between two lepidopteran hosts. This DfIV gene expression plasticity showed a dependency on the lepidopteran host species and parasitization time, suggesting that it may contribute to increase the parasitoid survival rate. This might be one of the key elements that determine the symbiotic relationship between PDV and parasitoid.

Comparison of the developmental time of Bracon hebetor (Hymenoptera: Braconidae) reared on five different lepidopteran host species and its relationship with digestive enzymes

Bracon (Habrobracon) hebetor Say is a polyphagous parasitoid of lepidopteran larvae, including those of the family Pyrali- dae. There are many reports that this parasitoid attacks the larvae of stored product and field crop pests. However, there is little infor - mation on the biological parameters of this parasitoid attacking different lepidopteran hosts or the effect of the hosts on the digestive enzymes of the parasitoid. Hence, in the current study the effect of different lepidopteran hosts, Ectomyelois ceratoniae, Plodia inter- punctella, Ephestia kuehniella, Helicoverpa armigera and Malacosoma disstria, on the biological parameters and digestive enzymes (α-amylase and proteases) of this parasitoid were investigated. The parasitoid performed better on stored product pests, such as E. kue- hniella and P. interpunctella, than field crop pests, such as H. armigera and M. disstria. For example, in terms of percentage egg hatch, rate of development, off-spring sex ratio and adult dry mass Bracon hebetor did much better when it parasitized stored product insects than field crop insects (P < 0.05). Interestingly, the quality and quantity of the proteases and α-amylase of the parasitoid larvae parasitiz - ing stored product and field crop pests differed. The greatest activity of these enzymes was recorded in the gut of those parasitoids that were reared on stored product insects (P. interpunctella and E. kuehniella). It is concluded that stored product insects, which feed on a diet rich in sugar and glycogen, provide physiological conditions that are more suitable for the parasitoid than field crop insects, which feed on diet rich in terpenes and tannins.

Extensive transcription analysis of the Hyposoter didymator Ichnovirus genome in permissive and non-permissive lepidopteran host species.

Ichnoviruses are large dsDNA viruses that belong to the Polydnaviridae family. They are specifically associated with endoparasitic wasps of the family Ichneumonidae and essential for host parasitization by these wasps. We sequenced the Hyposoter didymator Ichnovirus (HdIV) encapsidated genome for further analysis of the transcription pattern of the entire set of HdIV genes following the parasitization of four different lepidopteran host species. The HdIV genome was found to consist of at least 50 circular dsDNA molecules, carrying 135 genes, 98 of which formed 18 gene families. The HdIV genome had general features typical of Ichnovirus (IV) genomes and closely resembled that of the IV carried by Hyposoter fugitivus. Subsequent transcriptomic analysis with Illumina technology during the course of Spodoptera frugiperda parasitization led to the identification of a small subset of less than 30 genes with high RPKM values in permissive hosts, consisting with these genes encoding crucial virulence proteins. Comparisons of HdIV expression profiles between host species revealed differences in transcript levels for given HdIV genes between two permissive hosts, S. frugiperda and Pseudoplusia includens. However, we found no evident intrafamily gene-specific transcription pattern consistent with the presence of multigenic families within IV genomes reflecting an ability of the wasps concerned to exploit different host species. Interestingly, in two non-permissive hosts, Mamestra brassiccae and Anticarsia gemmatalis (most of the parasitoid eggs were eliminated by the host cellular immune response), HdIV genes were generally less strongly transcribed than in permissive hosts. This suggests that successful parasitism is dependent on the expression of given HdIV genes exceeding a particular threshold value. These results raise questions about the mecanisms involved in regulating IV gene expression according to the nature of the lepidopteran host species encountered.

Effect of temperature and host species on parasitism, development time and sex ratio of the egg parasitoid Trichogrammatoidea lutea Girault (Hymenoptera: Trichogrammatidae)

The developmental biology of Trichogrammatoidea lutea Girault (Hymenoptera: Trichogrammatidae) was studied at six constant temperatures (18, 21, 24, 27, 30 and 35°C) on eggs of three lepidopteran host species: Helicoverpa armigera (Hübner) (Noctuidae), Chilo partellus (Swinhoe) (Crambidae) and Cadra cautella (Walker) (Pyralidae). T. lutea did not complete development at 35°C on any of the three host species. Parasitism levels were highest on H. armigera at 27°C (58%), C. cautella at 27 and 30°C (31% and 28%) and C. partellus between 24 and 30°C (13–17%). Realized progeny of T. lutea per parasitized host egg was influenced by host size. The number of progeny of T. lutea per parasitized host egg was highest on H. armigera, followed by C. partellus and lowest on C. cautella. The sex ratio was female biased on C. partellus, female biased on C. cautella with the exception of 21°C and close to 1:1 on H. armigera. The rate of development from egg to pupa and egg to adult was fastest on H. armigera and slowest on C. partellus. Lower thresholds for development and degree days (DD) of T. lutea from egg to adult were 12.8°C and 105.4DD on H. armigera, 11.3°C and 141.6DD on C. partellus and 12.9°C and 118.2DD on C. cautella, respectively. Based on these results, H. armigera is the most suitable host for mass rearing of T. lutea for biological control of Lepidoptera pests because of the relatively high parasitism levels, short development time, greater clutch size and balanced sex ratio. C. cautella may also be used although longer exposure times might be required due to lower parasitism levels.

Genetic variation and virulence of Autographa californica multiple nucleopolyhedrovirus and Trichoplusia ni single nucleopolyhedrovirus isolates

To determine the genetic diversity within the baculovirus species Autographa calfornica multiple nucleopolyhedrovirus (AcMNPV; Baculoviridae: Alphabaculovirus), a PCR-based method was used to identify and classify baculoviruses found in virus samples from the lepidopteran host species A. californica, Autographa gamma, Trichoplusia ni, Rachiplusia ou, Anagrapha falcifera, Galleria mellonella, and Heliothis virescens. Alignment and phylogenetic inference from partial nucleotide sequences of three highly conserved genes (lef-8, lef-9, and polh) indicated that 45 of 74 samples contained isolates of AcMNPV, while six samples contained isolates of Rachiplusia ou multiple nucleopolyhedrovirus strain R1 (RoMNPV-R1) and 25 samples contained isolates of the species Trichoplusia ni single nucleopolyhedrovirus (TnSNPV; Alphabaculovirus). One sample from A. californica contained a previously undescribed NPV related to alphabaculoviruses of the armyworm genus Spodoptera. Data from PCR and sequence analysis of the ie-2 gene and a region containing ORF ac86 in samples from the AcMNPV and RoMNPV clades indicated a distinct group of viruses, mostly from G. mellonella, that are characterized by an unusual ie-2 gene previously found in the strain Plutella xylostella multiple nucleopolyhedrovirus CL3 (PlxyMNPV-CL3) and a large deletion within ac86 previously described in the AcMNPV isolate 1.2 and PlxyMNPV-CL3. PCR and sequence analysis of baculovirus repeated ORF (bro) genes revealed that the bro gene ac2 was split into two separate bro genes in some samples from the AcMNPV clade. Comparison of sequences in this region suggests that ac2 was formed by a deletion that fused the two novel bro genes together. In bioassays of a selection of isolates against T. ni, significant differences were observed in the insecticidal properties of individual isolates, but no trends were observed among the AcMNPV, TnSNPV, or RoMNPV groups of isolates. This study expands on what we know about the variation of AcMNPV, AcMNPV-like and TnSNPV viruses, provides novel information on the distinct groups in which AcMNPV isolates occur, and contributes to data useful for the registration, evaluation, and improvement of AcMNPV, AcMNPV-like, and TnSNPV isolates as biological control agents.

Suitability of Different Lepidopteran Host Species for Development ofBracon hebetor(Hymenoptera: Braconidae)

Bracon hebetor Say (Hymenoptera: Braconidae) is a gregarious larval ectoparasitoid of several species of Lepidoptera that are associated with stored products. The suitability of 12 potential lepidopteran host species representing four families was studied in this study for the development and reproduction of B. hebetor. The Lepidoptera species used were the Indianmeal moth, Plodia interpunctella (Hübner), Mediterranean flour moth, Ephestia kuehniella (Zeller), almond moth, E. cautella (Walker), rice moth, Corcyra cephalonica (Walker), navel orangeworm, Amyelois transitella (Stainton), greater wax moth (laboratory reared and commercial), Galleria mellonella (Linnaeus) (all Pyralidae); tobacco budworm, Heliothis virescens (Fabricus), corn earworm, Helicoverpa zea (Boddie), beet armyworm, Spodoptera exigua (Hübner) (all Noctuidae); webbing clothes moth, Tineola bisselliella (Hummel) (Tineidae); and Angoumois grain moth, Sitotroga cerealella (Olivier) (Gelichiidae). Experiments were conducted using petri dishes (100 by 15 mm) as experimental arenas at 29 +/- 1 degrees C, 65 +/- 5% RH, and a photoperiod of 14:10 (L: D) h. B. hebetor females were introduced singly into arenas and given a full-grown host larva every day for 5 consecutive d. Paralysis of the host larvae and oviposition by B. hebetor females were significantly affected by host species. The cumulative fecundity in the 5-d period was highest on A. transitella (106.42 +/- 5.19) and lowest on T. bisselliella (9.64 +/- 1.28). The egg-to-adult survivorship and progeny sex ratio were also significantly affected by the host species. The highest percentage of parasitoid survival to the adult stage was on A. transitella (84.07 +/- 2.26) and zero on T. bisselliella. Egg to adult development time was shortest on E. cautella (9.75 +/- 0.25 d) and longest on G. mellonella (12.63 +/- 0.28 d). Results from these studies suggest that B. hebetor females can use a wide range of lepidopteran hosts for paralysis and oviposition. However, B. hebetor cannot necessarily develop and reproduce on all host species that it can paralyze and oviposit on, and optimum reproduction is with the stored-product pyralid hosts.

Autographa californica multiple nucleopolyhedrovirus ODV-E56 envelope protein is required for oral infectivity and can be substituted functionally by Rachiplusia ou multiple nucleopolyhedrovirus ODV-E56

The Autographa californica multiple nucleopolyhedrovirus (AcMNPV) odv-e56 gene encodes an occlusion-derived virus (ODV)-specific envelope protein, ODV-E56. In a previous analysis, the odv-e56 gene was found to be under positive selection pressure, suggesting that it may be a determinant of virus host range. To assess the role of ODV-E56 in oral infectivity and host range, we constructed recombinant AcMNPV clones (Ac69GFP-e56lacZ and AcIEGFP-e56lacZ) in which ODV-E56 protein synthesis was eliminated by inserting a beta-galactosidase (lacZ) expression cassette into the odv-e56 open reading frame. We also constructed a recombinant virus, Ac69GFP-Roe56, in which the native AcMNPV odv-e56 coding sequence was replaced with that of Rachiplusia ou multiple nucleopolyhedrovirus (RoMNPV), a closely related virus that is significantly more virulent towards some host species than AcMNPV. The odv-e56 recombinant viruses exhibited no alterations in polyhedron production and morphogenesis or in the production of infectious budded virus in cell culture. In bioassays using three lepidopteran host species, the oral infectivities of the odv-e56 mutant viruses Ac69GFP-e56lacZ and AcIEGFP-e56lacZ were profoundly impaired compared with those of wild-type and control recombinant viruses. Oral infectivity was restored fully by marker rescue of the odv-e56 mutant viruses with either the AcMNPV or the RoMNPV odv-e56 gene. In bioassays using two host species that are more susceptible to RoMNPV than to AcMNPV, Ac69GFP-Roe56 killed larvae with LC50 values similar to those of recombinant viruses expressing AcMNPV ODV-E56. This result indicated that replacement of the AcMNPV odv-e56 gene with the RoMNPV orthologue did not increase virulence against these two species.

Development of Meteorus pulchricornis and regulation of its noctuid host, Pseudaletia separata

The solitary endoparasitoid Meteorus pulchricornis can parasitize many lepidopteran host species successfully. In the case of parasitization of Pseudaletia separata, developmental duration of M. pulchricornis was 8–9 days from egg to larval emergence and 6 days from prepupa to adult emergence. Successful parasitism by M. pulchricornis decreased with host age. Following parasitization of day-0 4th host instar, the parasitoid embryo, whilst still enclosed in serosal cell membrane, hatched out of the egg chorion 2 days after oviposition. Subsequently, the 1st instar parasitoid emerged from the surrounding serosal cell membrane. Serosal cells dissociated and developed as teratocytes 3.5 days after oviposition. One embryo of M. pulchricornis gave rise to approximately 1200 teratocytes, a number that remained constant until 6 days after parasitization, but decreased drastically to 200 at 7 days post-oviposition. The teratocytes of M. pulchricornis were round- or oval-shaped and grew from 65 μm at 4 days to 200 μm in the long axis at 6 days post-parasitization. At 4 days post-parasitization, many cells or cell clusters with lipid particles were observed in the hemocoels of parasitized hosts. In addition, paraffin sections of parasitized hosts revealed that many teratocytes were attached to the host's fat body and contributed to disrupting the fat body tissue. Further, examination of the total hemocyte count (THC) during parasitization revealed that THC was maintained at low levels. Surprisingly, a temporal decrease followed by restoration of THC was observed in hosts injected with virus-like particles of M. pulchricornis (MpVLPs) plus venom, which contrasts with the constant THC suppression seen in parasitized hosts. This indicates that MpVLP function is temporal and is involved in regulation of the host during early parasitism. Therefore, teratocytes, a host regulation factor in late parasitism, could be involved in keeping THC at a low level.

The comparative biology of the solitary endoparasitoid Meteorus gyrator (Hymenoptera: Braconidae) on five noctuid pest species

The comparative biology of the solitary endoparasitoid Meteorus gyrator (Thun.) was investigated in five noctuid pest species. Meteorus gyrator parasitized all larval stages of the noctuid pests Lacanobia oleracea, Mamestra brassicae, Spodoptera exigua, Spodoptera littoralis and Chrysodeixis chalcites. When female parasitoids were offered host larvae of all developmental stages, host larvae in their third stadium were parasitized most frequently in all species. When the parasitoid was offered a choice of third stadium larvae from each of the five lepidopteran host species, L. oleracea was the most frequently parasitized, followed by M. brassicae. The growth of L. oleracea and M. brassicae was markedly reduced when larvae were parasitized by M. gyrator, with the effect of parasitism on the remaining species being much less pronounced. In excess of 94% of parasitized hosts gave rise to live wasps in L. oleracea, whilst in M. brassicae only 52% of parasitized hosts gave rise to a live wasp, the remainder dying (44.6%) or pupating (3.1%). The larval development of the parasitoid was also strongly influenced by the host species. Thus, the development (egg to cocoon) of female wasps was most rapid in C. chalcites (9.7 ± 0.09 days), and longest in M. brassicae (17.2 ± 1.08 days). The cocoon weight of wasps was also significantly affected by host species, with the heaviest female cocoons being derived from C. chalcites (10.4 ± 0.16 mg) and the lightest female cocoons being derived from M. brassicae (7.0 ± 0.14 mg). In all cases, the development times and cocoon weights of male parasitoids were less than those of female wasps.

Biological studies on Encarsia porteri (Mercet) (Hymenoptera: Aphelinidae) an heterotrophic parasitoid of the Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) complex

Abstract Encarsia porteri is an heterotrophic species. Female progeny develop as primary parasitoids of whiteflies, whereas male progeny occur as primary parasitoids of lepidopteran eggs. This parasitoid was found parasitizing the local biotype of Bemisia tabaci (ARG1) on cotton, soybean and alfalfa in Argentina. The main biological parameters of E. porteri were recorded under laboratory conditions. Preimaginal developmental time of females on whitefly nymphs was significantly faster ( P P >0.05) (tomato: 18.85 ± 2.49 days, cotton: 20.52 ± 0.94 days) at 21.4 ± 0.4 °C. Developmental time and longevity for E. porteri males were estimated on five lepidopteran host species ( Anticarsia gemmatalis , Cydia pomonella , Diatraea saccharalis , Crocidosema aporema , and Sitotroga cerealella ). Males developed more quickly on A. gemmatalis than they did on D. saccharalis and C. pomonella eggs, whereas no differences were observed with C. aporema and S. cerealella ( P P >0.05). Preference of E. porteri females for some lepidopteran eggs ( A. gemmatalis , C. pomonella , D. saccharalis , and S. cerealella ) was also studied. The eggs of the noctuid A. gemmatalis were preferred by E. porteri females for allocating their male progeny ( P A. gemmatalis is the most suitable host for E. porteri males among the species tested.

Autographa californicaNPV Isolates: Restriction Endonuclease Analysis and Comparative Biological Activity

To determine the genetic diversity within the baculovirus species Autographa calfornica multiple nucleopolyhedrovirus (AcMNPV; Baculoviridae: Alphabaculovirus), a PCR-based method was used to identify and classify baculoviruses found in virus samples from the lepidopteran host species A. californica, Autographa gamma, Trichoplusia ni, Rachiplusia ou, Anagrapha falcifera, Galleria mellonella, and Heliothis virescens. Alignment and phylogenetic inference from partial nucleotide sequences of three highly conserved genes (lef-8, lef-9, and polh) indicated that 45 of 74 samples contained isolates of AcMNPV, while six samples contained isolates of Rachiplusia ou multiple nucleopolyhedrovirus strain R1 (RoMNPV-R1) and 25 samples contained isolates of the species Trichoplusia ni single nucleopolyhedrovirus (TnSNPV; Alphabaculovirus). One sample from A. californica contained a previously undescribed NPV related to alphabaculoviruses of the armyworm genus Spodoptera. Data from PCR and sequence analysis of the ie-2 gene and a region containing ORF ac86 in samples from the AcMNPV and RoMNPV clades indicated a distinct group of viruses, mostly from G. mellonella, that are characterized by an unusual ie-2 gene previously found in the strain Plutella xylostella multiple nucleopolyhedrovirus CL3 (PlxyMNPV-CL3) and a large deletion within ac86 previously described in the AcMNPV isolate 1.2 and PlxyMNPV-CL3. PCR and sequence analysis of baculovirus repeated ORF (bro) genes revealed that the bro gene ac2 was split into two separate bro genes in some samples from the AcMNPV clade. Comparison of sequences in this region suggests that ac2 was formed by a deletion that fused the two novel bro genes together. In bioassays of a selection of isolates against T. ni, significant differences were observed in the insecticidal properties of individual isolates, but no trends were observed among the AcMNPV, TnSNPV, or RoMNPV groups of isolates. This study expands on what we know about the variation of AcMNPV, AcMNPV-like and TnSNPV viruses, provides novel information on the distinct groups in which AcMNPV isolates occur, and contributes to data useful for the registration, evaluation, and improvement of AcMNPV, AcMNPV-like, and TnSNPV isolates as biological control agents.

Physiological Host Specificity of Microsporidia as an Indicator of Ecological Host Specificity

For most groups of biological control agents the relationship between laboratory (physiological) host range and the host range in the field (ecological host range) has not been explored empirically. The objective of our study was to investigate this relationship using the North America gypsy moth,Lymantria dispar,as a model nontarget host for microsporidia from native North American Lepidoptera. The gypsy moth,L. dispar,a native of Europe, has been established in North America for nearly 130 years and presumably exposed to many species of microsporidia from sympatric native Lepidoptera. Nevertheless, microsporidia have never been observed in North American populations ofL. dispar.We conducted traditional laboratory feeding experiments using microsporidia from 20 lepidopteran host species and 1 coleopteran host species againstL. dispar.Microsporidia from 18 native hosts infectedL. disparlarvae. Although some of the infections were not typical of infections in the indigenous natural hosts, mature spores were produced in most of these infections. Horizontal transmission experiments, based on exposure of uninfectedL. disparlarvae to infectedL. disparlarvae, demonstrated that the microsporidia were far more host specific than the direct feeding experiments suggested. Of the three microsporidian biotypes that were horizontally transmitted between the nontargetL. disparlarvae, all were transmitted at very low levels. The results of our experiments provide additional evidence that the ecological host specificity of terrestrial microsporidia is much narrower than the physiological host specificity. Our studies establish the validity of using nonindigenous insect species with long-term data sets on natural enemies associated with them as a tool for testing hypotheses about host specificity.

Development and encapsulation of the endoparasitoid,Microplitis croceipes (Hym.: Braconidae), in six candidate host species (Lep.)

Encapsulation and development of the endoparasitoid,Microplitis croceipes (Cresson), were studied in six atypical lepidopteran host species whose usual host isHelicoverpa zea (Boddie). The candidate hosts examined were: the fall armywormSpodoptera frugiperda (J. E. Smith); the beet armyworm,Spodoptera exigua (Hubner); the cabbage looper,Trichoplusia ni (Hubner); the greater wax moth,Galleria mellonella (L.); the Indian meal moth,Plodia interpunctella (Hubner); and the diamondback moth,Plutella xylostella (L.). BothS. exigua andT. ni were completely unsuitable forM. croceipes development due to the high rate of eggs that were encapsulated within three days after parasitism. Encapsulation inS. frugiperda included mainly parasitoid eggs and was first detected six days after parasitization at 25°C and two days at 30°C. Encapsulation inG. mellonella occurred only in the larval stage of the parasitoid. InP. interpunctella, parasitoid larvae reached the 3rd stadium, but none of them pupated. OnlyS. frugiperda andG. mellonella supported successful development ofM. croceipes from egg to adult. The percentage of parasitoids reaching the adult stage in these hosts was higher at 30°C than at 25°C (13% vs. 4% inS. frugiperda, and 21% vs. 3% inG. mellonella, respectively). However, these percentages were too low to substitute them as a more economical host for rearingM. croceipes. This biological information will be useful in additional laboratory studies directed toward reducing the rate of encapsulation (e.g., manipulation of host rearing temperature) to increase production ofM. croceipes on these hosts.

Covert iridovirus infection of blackfly larvae

Iridovirus infections are typically isolated at extremely low frequencies from invertebrate species in moist or aquatic habitats. Crystalline arrangements of virus particles in heavily infected tissues cause an iridescent hue obvious to the naked eye; diagnosis of iridovirus infection has traditionally occurred when the host appeared bright lilac or blue. Evidence is presented here to show that there are two forms of iridovirus infection in larval blackfly (Diptera: Simuliidae) populations: (i) the classical patent form which causes larvae to develop blue iridescence before death; and (ii) a covert (inapparent) form which is not lethal. Patent infections are extremely rare in Simulium populations from the River Ystwyth, Wales ( ca . 1 in 10 6 ). However, a large proportion of the population harbours the disease without obvious symptoms. Covert iridovirus infection was shown by using two techniques. First, tissue homogenates from 8 out of 30 apparently healthy Simulium larvae produced patent iridovirus infections when injected into a permissive lepidopteran host species. The DNA restriction profiles from these covert isolates showed very close similarities in fragment pattern and variability to isolates causing patent infections in the same River Ystwyth populations. Second, the presence of iridovirus DNA in host tissues was confirmed by using the polymerase chain reaction (PCR) targeted at the iridovirus major structural protein gene. The frequency of PCR-positive larvae taken from the River Ystwyth in April 1992 varied between 17% and 37%, depending on site.

The Role of Kairomones in Host Recognition and Host Acceptance Behavior of the Parasite Brachymeria intermedia 134

The role of kairomones in host recognition and host acceptance of the parasite Brachymeria intermedia (Nees) (Hymenoptera: Chalcididae) was examined using 3 lepidopteran host species: the gypsy moth, Lymantria dispar (L.) (Lymantriidae); the greater wax moth, Galleria mellonella L. (Pyralidae); and the spruce budworm, Choristoneura fumiferana (Clemens) (Tortricidae). The behavioral sequence from initial contact of the host through oviposition and departure is described. Responses to kairomones washed from host pupae with equivalent amounts of n -hexane per pupal surface area were greatest with gypsy moth, followed by spruce budworm and wax moth. When pupae were washed several times with n -hexane, there was a reduction in responses to the gypsy moth washes, with a dramatic reduction in responses to wax moth and spruce budworm washes. Females responded to gypsy moth pupae after 3 washes, but not to wax moth and spruce budworm pupae. B. intermedia females did not respond to n -hexane washes of larvae, nor to washes of combined larval frass, exuviae, and silk. Parasite males showed no response to kairomones.