Selectivity of deltamethrin doses on Palmistichus elaeisis (Hymenoptera: Eulophidae) parasitizing Tenebrio molitor (Coleoptera: Tenebrionidae).

Insecticides are the main method of controlling lepidopteran pests of eucalyptus plantations and those selective to natural enemies, such as the endoparasitoid Palmistichus elaeisis Delvare et LaSalle (Hymenoptera: Eulophidae), are preferable. The objective of this study was to evaluate the selectivity and effects on biological parameters of the insecticide deltamethrin, registered for the control of defoliator caterpillars of eucalyptus, to the parasitoid P. elaeisis aiming the rational use of this insecticide and its compatibility with parasitoids. The experiment was in a completely randomized design. The treatments were the doses of 0.64, 1.40, 3.10, 6.83, 15.03, 33.05, 72.7 and 160 mg a.i./L of deltamethrin and the control (distilled water) with 10 replications, each with a pupae of the alternative host Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae) exposed by the immersion method. The parasitism, biological cycle, emergence, longevity, head width and metatibia length of the natural enemy were evaluated. Deltamethrin reduced parasitism and the emergence rates of P. elaeisis. The duration of the biological cycle of this parasitoid, emerged from T. molitor pupae exposed to 15.03 mg a.i./L of deltamethrin, was higher. The morphometric parameters of P. elaeisis exposed to the doses of 0.64 and 1.40 mg a.i./L of the insecticide were lower. However, the morphometric parameter values were higher with the doses above 3.10 mg a.i./L than in the control. The parasitism and emergence of P. elaeisis were also reduced by the deltamethrin doses lower than the commercially recommended one and therefore, this insecticide is not selective for this natural enemy.

Tolerance of the mealworm beetle, Tenebrio molitor, to an entomopathogenic nematode, Steinernema feltiae, at two infection foci, the intestine and the hemocoel.

An entomopathogenic nematode, Steinernema feltiae K1, exhibits pathogenicity in various insect hosts, however, its virulence among the target insect species varies. Specifically, a coleopteran insect, Tenebrio molitor, is less susceptible to S. feltiae than are lepidopteran insects. We analyzed the low virulence of S. feltiae against T. molitor sequentially, in entering the gut lumen and penetrating the hemocoel, and in hemocoelic immune defenses by comparing the responses to those of a lepidopteran insect, Spodoptera exigua. Infective juveniles (IJs) of S. feltiae exhibited higher virulence and produced more progeny IJs in S. exigua than in T. molitor. The difference in IJ behavior was observed in the IJ invasion rate (IJs in gut lumen/IJs treated) after treatment, in which a lower rate was observed in T. molitor (20.4%) than in S. exigua (55.5%). Also, a lower hemocoelic penetration rate of IJs (IJs in hemocoel/IJs in gut) was observed in T. molitor (54%) than in S. exigua (74%) 24 h after feeding treatment. To investigate the immune defense in the hemocoel, insect hemolymph samples were incubated with IJs. The encapsulation behavior and phenoloxidase activity was higher in T. molitor hemolymph than in S. exigua hemolymph, which resulted in a significantly higher nematicidal activity in S. exigua. The humoral immune responses against S. feltiae were also different between the two species. The expression of two antimicrobial peptides, cecropin and attacin 1, was much higher in T. molitor. Furthermore, eicosanoid biosynthetic activity against S. feltiae was different in the two host species; sPLA2 activity was highly inducible in T. molitor but not in S. exigua. These results suggest that variability of the immune defense in the target insects, as well as in the invasion and penetration rates of IJs to the hemocoel, plays a crucial role in determining the insecticidal virulence of S. feltiae.

Timing of sub-lethal insecticide exposure determines parasite establishment success in an insect-helminth model.

Environmental toxicants are pervasive in nature, but sub-lethal effects on non-target organisms and their parasites are often overlooked. Particularly, studies on terrestrial hosts and their parasites exposed to agricultural toxicants are lacking. Here, we studied the effect of sequence and timing of sub-lethal exposures of the pyrethroid insecticide alpha-cypermethrin on parasite establishment using the tapeworm Hymenolepis diminuta and its intermediate insect host Tenebrio molitor as a model system. We exposed T. molitor to alpha-cypermethrin (LD20) before and after experimental H. diminuta infection and measured the establishment success of larval tapeworms. Also, we conducted in vitro studies quantifying the direct effect of the insecticide on parasite viability. Our results showed that there was no direct lethal effect of alpha-cypermethrin on H. diminuta cysticercoids at relevant concentrations (LD10 to LD90 of the intermediate host). However, we observed a significantly increased establishment of H. diminuta in beetles exposed to alpha-cypermethrin (LD20) after parasite infection. In contrast, parasite establishment was significantly lower in beetles exposed to the insecticide before parasite infection. Thus, our results indicate that environmental toxicants potentially impact host-parasite interactions in terrestrial systems, but that the outcome is context-dependent by enhancing or reducing parasite establishment depending on timing and sequence of exposure.

A parasitological evaluation of edible insects and their role in the transmission of parasitic diseases to humans and animals.

From 1 January 2018 came into force Regulation (EU) 2015/2238 of the European Parliament and of the Council of 25 November 2015, introducing the concept of "novel foods", including insects and their parts. One of the most commonly used species of insects are: mealworms (Tenebrio molitor), house crickets (Acheta domesticus), cockroaches (Blattodea) and migratory locusts (Locusta migrans). In this context, the unfathomable issue is the role of edible insects in transmitting parasitic diseases that can cause significant losses in their breeding and may pose a threat to humans and animals. The aim of this study was to identify and evaluate the developmental forms of parasites colonizing edible insects in household farms and pet stores in Central Europe and to determine the potential risk of parasitic infections for humans and animals. The experimental material comprised samples of live insects (imagines) from 300 household farms and pet stores, including 75 mealworm farms, 75 house cricket farms, 75 Madagascar hissing cockroach farms and 75 migrating locust farms. Parasites were detected in 244 (81.33%) out of 300 (100%) examined insect farms. In 206 (68.67%) of the cases, the identified parasites were pathogenic for insects only; in 106 (35.33%) cases, parasites were potentially parasitic for animals; and in 91 (30.33%) cases, parasites were potentially pathogenic for humans. Edible insects are an underestimated reservoir of human and animal parasites. Our research indicates the important role of these insects in the epidemiology of parasites pathogenic to vertebrates. Conducted parasitological examination suggests that edible insects may be the most important parasite vector for domestic insectivorous animals. According to our studies the future research should focus on the need for constant monitoring of studied insect farms for pathogens, thus increasing food and feed safety.

Hydrocarbons catalysed by TmCYP4G122 and TmCYP4G123 in Tenebrio molitor modulate the olfactory response of the parasitoid Scleroderma guani.

Hydrocarbons (HCs) present on the epicuticle of terrestrial insects are not only used to reduce water loss but are also used as chemical signals. The cytochrome p450 CYP4G gene is essential for HC biosynthesis in some insects. However, its function in Tenebrio molitor is unknown. Moreover, it is not yet known whether CYP4G of a host can modulate the searching behaviours of its parasitoid. Here, we explore the function of the TmCYP4G122 and CYP4G123 genes in T. molitor. The TmCYP4G122 and CYP4G123 transcripts could be detected in all developmental stages. Their expression was higher in the fat body and abdominal cuticle than in the gut. Their transcript levels in mature larvae under desiccation stress [relative humidity (RH) < 5%] was significantly higher than that in the control (RH = 70%). Injection of dsCYP4G122 and dsCYP4G123 caused a reduction in HC biosynthesis and was associated with increased susceptibility to desiccation. Individuals of the parasitoid Scleroderma guani that emerged from mealworm pupae showed host preference for normal pupae whereas S. guani that emerged from pupae lacking CYP4G122 or/and CYP4G123 lost this searching preference. The current results confirm that CYP4G122 and CYP4G123 regulate the biosynthesis of HCs and modulate the olfactory response of its parasitoid S. guani.

Optimized pupal age of Tenebrio molitor L. (Coleoptera: Tenebrionidae) enhanced mass rearing efficiency of Chouioia cunea Yang (Hymenoptera: Eulophidae).

Chouioia cunea Yang (Hymenoptera: Eulophidae) has been widely used for biological control of the fall webworm, Hyphantria cunea (Drury) (Lepidoptera: Arctiidae), in China. The yellow mealworm, Tenebrio molitor L. (Coleoptera: Tenebrionidae), an important resource insect species distributed worldwide, is considered to be a potential alternative host for mass rearing of C. cunea to the Chinese oak silkworm, Antheraea pernyi (Guerin-Meneville) (Lepidoptera: Saturniidae), which is currently used. In this study, we investigated the effects of host age on C. cunea mass rearing by measuring parasitism, development and adult fertility of C. cunea on T. molitor pupae of different ages. The results showed no significant differences in the percentage of parasitized hosts and developmental time of C. cunea in pupae of different ages. However, the number of C. cunea adults (137.2-154.7 adults per host) that emerged from 0, 1, and 2-day-old pupae was significantly higher than that from 4-day-old pupae. The lowest percentages of unemerged adults were found in 2-day-old (1.2%) and 3-day-old (1.4%) pupae, which were significantly lower than that of 4-day-old pupae (10.3%). The emergence of adult females from 0 to 2-day-old pupae (120.2-142.3 per pupa) was significantly higher than that from 4-day-old hosts (64.6). Adult females emerging from 2-day-old pupae carried significantly more eggs (258.2 eggs/female) than those from 0 and 1-day-old pupae (178.4-178.9 eggs/female). Our findings indicated that 2-day-old pupae of T. molitor were most suitable to rear C. cunea. Overall, this research provided valuable information to optimize pupae for the mass rearing of C. cunea on host T. molitor.

Transient anoxia during Metarhizium robertsii growth increases conidial virulence to Tenebrio molitor.

Little is known about the phenotypic effects of hypoxia and transient anoxia on the virulence of an entomopathogenic fungus. Conidia of Metarhizium robertsii were produced on: (1) potato dextrose agar medium (PDA) under normoxia; (2) PDA medium under continuous hypoxia; (3) PDA medium under transient anoxia; and (4) minimal medium with lactose (MML) under normoxia. Conidia produced under transient anoxia and produced on MML were the most virulent to Tenebrio molitor. Conidia produced under normoxia and hypoxia were the least virulent. Conidial production and germination speed of conidia produced under normoxia, hypoxia, and transient anoxia were similar; however, MML produced less conidia, but germinated faster than any other treatments.

Parasitism and venom of ectoparasitoid Scleroderma guani impairs host cellular immunity.

Venom is a prominently maternal virulent factor utilized by parasitoids to overcome hosts immune defense. With respect to roles of this toxic mixture involved in manipulating hosts immunity, great interest has been mostly restricted to Ichneumonoidea parasitoids associated with polydnavirus (PDV), of which venom is usually considered as a helper component to enhance the role of PDV, and limited Chalcidoidea species. In contrast, little information is available in other parasitoids, especially ectoparasitic species not carrying PDV. The ectoparasitoid Scleroderma guani injects venom into its host, Tenebrio molitor, implying its venom was involved in suppression of hosts immune response for successful parasitism. Thus, we investigated the effects of parasitism and venom of this parasitoid on counteracting the cellular immunity of its host by examining changes of hemocyte counts, and hemocyte spreading and encapsulation ability. Total hemocyte counts were elevated in parasitized and venom-injected pupae. The spreading behavior of both granulocytes and plasmatocytes was impaired by parasitization and venom. High concentration of venom led to more severely increased hemocyte counts and suppression of hemocyte spreading. The ability of hemocyte encapsulation was inhibited by venom in vitro. In addition to immediate effects observed, venom showed persistent interference in hosts cellular immunity. These results indicate that venom alone from S. guani plays a pivotal role in blocking hosts cellular immune response, serving as a regulator that guarantees the successful development of its progenies. The findings provide a foundation for further investigation of the underlying mechanisms in immune inhibitory action of S. guani venom.

Activity changes of antioxidant and detoxifying enzymes in Tenebrio molitor (Coleoptera: Tenebrionidae) larvae infected by the entomopathogenic nematode Heterorhabditis beicherriana (Rhabditida: Heterorhabditidae).

Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis are lethal parasites of many insect species. To investigate defensive mechanisms towards EPNs in relation to antioxidative and detoxifying enzymes, we chose Tenebrio molitor (Coleoptera: Tenebrionidae) as experimental insect. We studied the activity changes of superoxide dismutases (SODs), peroxidases (PODs), and catalases (CATs), as well as tyrosinase (TYR), acetylcholinesterase (AChE), carboxylesterase (CarE), and glutathione S-transferase (GSTs) for 40 h in T. molitor larvae infected with Heterorhabditis beicherriana infective juveniles (IJs) at 5 rates (0, 20, 40, 80, and 160 IJs/larva). We found that when T. molitor larvae infected with H. beicherriana at higher rates (80 and 160 IJs/larva), SOD activity quickly increased to more than 70 % higher than that control levels. The activities of POD and CAT increased after 24 h. TYR activity increased slowly at lower rates of infection for 16 h, followed by a slight decrease, and then increasing from 32 to 40 h. The other detoxifying enzymes (GST, CarE, and AChE) were enhanced at lower infection rates, but were inhibited at higher rates. Our results suggested that host antioxidative response and detoxification reactions played a central role in the defensive reaction to EPNs, and that this stress which was reflected by the higher level enzymes activity contributed to the death of hosts. Further study should explore the exact function of these enzymes using different species of EPNs and investigate the links between enzyme activity and host susceptibility to EPNs.

Efficacy of condensed tannins against larval Hymenolepis diminuta (Cestoda) in vitro and in the intermediate host Tenebrio molitor (Coleoptera) in vivo.

Natural anti-parasitic compounds in plants such as condensed tannins (CT) have anthelmintic properties against a range of gastrointestinal nematodes, but for other helminths such effects are unexplored. The aim of this study was to assess the effects of CT from three different plant extracts in a model system employing the rat tapeworm, Hymenolepis diminuta, in its intermediate host, Tenebrio molitor. An in vitro study examined infectivity of H. diminuta cysticercoids (excystation success) isolated from infected beetles exposed to different concentrations of CT extracts from pine bark (PB) (Pinus sps), hazelnut pericarp (HN) (Corylus avellana) or white clover flowers (WC) (Trifolium repens), in comparison with the anthelmintic drug praziquantel (positive control). In the in vitro study, praziquantel and CT from all three plant extracts had dose-dependent inhibitory effects on cysticercoid excystation. The HN extract was most effective at inhibiting excystation, followed by PB and WC. An in vivo study was carried out on infected beetles (measured as cysticercoid establishment) fed different doses of PB, HN and praziquantel. There was a highly significant inhibitory effect of HN on cysticercoid development (p=0.0002). Overall, CT showed a promising anti-cestodal effect against the metacestode stage of H. diminuta.

Parasitization by Scleroderma guani influences expression of superoxide dismutase genes in Tenebrio molitor.

Superoxide dismutase (SOD) is an antioxidant enzyme involved in detoxifying reactive oxygen species. In this study, we identified genes encoding the extracellular and intracellular copper-zinc SODs (ecCuZnSOD and icCuZnSOD) and a manganese SOD (MnSOD) in the yellow mealworm beetle, Tenebrio molitor. The cDNAs for ecCuZnSOD, icCuZnSOD, and MnSOD, respectively, encode 24.55, 15.81, and 23.14 kDa polypeptides, which possess structural features typical of other insect SODs. They showed 20-94% identity to other known SOD sequences from Bombyx mori, Musca domestica, Nasonia vitripennis, Pediculus humanus corporis, and Tribolium castaneum. Expression of these genes was analyzed in selected tissues and developmental stages, and following exposure to Escherichia coli and parasitization by Scleroderma guani. We recorded expression of all three SODs in cuticle, fat body, and hemocytes and in the major developmental stages. Relatively higher expressions were detected in late-instar larvae and pupae, compared to other developmental stages. Transcriptional levels were upregulated following bacterial infection. Analysis of pupae parasitized by S. guani revealed that expression of T. molitor SOD genes was significantly induced following parasitization. We infer that these genes act in immune response and in host-parasitoid interactions.

Entomopathogenic nematodes in insect cadaver formulations for the control of Rhipicephalus microplus (Acari: Ixodidae).

This study evaluated the efficacy of four entomopathogenic nematode (EPN) strains in insect cadaver formulations against Rhipicephalus microplus and compared the efficacy of the most virulent EPNs applied in cadavers of Galleria mellonella and Tenebrio molitor. In the first experiment, infected G. mellonela larvae were used as the source of EPNs. Engorged females of R. microplus were placed in pots filled with soil and different numbers of G. mellonella larvae infected with one of four species of nematodes. All treatments with EPNs of the genus Heterorhabditis caused significant reduction (p<0.05) in the egg mass weight and hatching percentage of larvae. The EPNs of the genus Steinernema, except for the group exposed to Steinernema carpocapsae ALL, whose source nematodes included six larvae of G. mellonella, caused a significant reduction (p<0.05) in the egg mass weight produced per female. Steinernema feltiae SN applied with two, four, and six cadavers and S. carpocapsae ALL with two cadavers caused a reduction in hatching percentage of larvae of R. microplus (p<0.05). The percentage of control was above 95% in all groups treated with Heterorhabditis bacteriophora HP88 and Heterorhabditis indica LPP1 and in the treatment with four larvae infected with S. feltiae SN. The second experiment followed the same methodology, using G. mellonella and T. molitor larvae infected by the two most virulent EPNs. H. bacteriophora HP88 and H. indica LPP1 in different formulations caused reduction in the egg mass weight and hatching percentage of larvae. The percentage of control were 82.4 and 84.9% for H. bacteriophora HP88 and H. indica LPP1, respectively, formulated in T. molitor, and reaching 99.9% in groups formulated with G. mellonella. The EPNs tested in insect cadaver formulation showed pathogenicity to engorged females of R. microplus and EPNs of the genus Heterorhabditis formulated in G. mellonella larvae were more effective.

Parasitization by Scleroderma guani influences protein expression in Tenebrio molitor pupae.

Ectoparasitoid wasps deposit their eggs onto the surface and inject venom into their hosts. Venoms are chemically complex and they exert substantial impact on hosts, including permanent or temporary paralysis and developmental arrest. These visible venom effects are due to changes in expression of genes encoding physiologically relevant proteins. While the influence of parasitization on gene expression in several lepidopterans has been reported, the molecular details of parasitoid/beetle relationships remain mostly unknown. This shortcoming led us to pose the hypothesis that envenomation by the ectoparasitic ant-like bethylid wasp Scleroderma guani leads to changes in protein expression in the yellow mealworm beetle Tenebrio molitor. We tested our hypothesis by comparing the proteomes of non-parasitized and parasitized host pupae using iTRAQ-based proteomics. We identified 41 proteins that were differentially expressed (32↑- and 9↓-regulated) in parasitized pupae. We assigned these proteins to functional categories, including immunity, stress and detoxification, energy metabolism, development, cytoskeleton, signaling and others. We recorded parallel changes in mRNA levels and protein abundance in 14 selected proteins following parasitization. Our findings support our hypothesis by documenting changes in protein expression in parasitized hosts.

Activity of eight strains of entomopathogenic nematodes (Rhabditida: Steinernematidae, Heterorhabditidae) against five stored product pests.

Stored product pests are responsible for losses that can amount 10% during cereal storage in the world. Aiming to find an alternative method to the chemicals used for the stored-product pests, eight strains of entomopathogenic nematodes (EPNs) were tested against five species of stored product pests. The bioassays were conducted in microtubes containing paper, inoculated with EPNs and insect diet. All the insect species were susceptible to the EPNs strains. Anagasta kuehniella and Tenebrio molitor larvae and Acanthoscelides obtectus adults were highly sensitive to the higher doses with most species and/or strains of EPNs. Adults of Sitophilus oryzae and Sitophilus zeamais were relatively less sensitive to all EPNs. Therefore, EPNs show as potential control agents for stored products pests in prophylactic applications in warehouses.

Transcriptomic immune response of Tenebrio molitor pupae to parasitization by Scleroderma guani.

BACKGROUND: Host and parasitoid interaction is one of the most fascinating relationships of insects, which is currently receiving an increasing interest. Understanding the mechanisms evolved by the parasitoids to evade or suppress the host immune system is important for dissecting this interaction, while it was still poorly known. In order to gain insight into the immune response of Tenebrio molitor to parasitization by Scleroderma guani, the transcriptome of T. molitor pupae was sequenced with focus on immune-related gene, and the non-parasitized and parasitized T. molitor pupae were analyzed by digital gene expression (DGE) analysis with special emphasis on parasitoid-induced immune-related genes using Illumina sequencing. METHODOLOGY/PRINCIPAL FINDINGS: In a single run, 264,698 raw reads were obtained. De novo assembly generated 71,514 unigenes with mean length of 424 bp. Of those unigenes, 37,373 (52.26%) showed similarity to the known proteins in the NCBI nr database. Via analysis of the transcriptome data in depth, 430 unigenes related to immunity were identified. DGE analysis revealed that parasitization by S. guani had considerable impacts on the transcriptome profile of T. molitor pupae, as indicated by the significant up- or down-regulation of 3,431 parasitism-responsive transcripts. The expression of a total of 74 unigenes involved in immune response of T. molitor was significantly altered after parasitization. CONCLUSIONS/SIGNIFICANCE: obtained T. molitor transcriptome, in addition to establishing a fundamental resource for further research on functional genomics, has allowed the discovery of a large group of immune genes that might provide a meaningful framework to better understand the immune response in this species and other beetles. The DGE profiling data provides comprehensive T. molitor immune gene expression information at the transcriptional level following parasitization, and sheds valuable light on the molecular understanding of the host-parasitoid interaction.

[Effects of venom from Sclerodermus sichuanensis Xiao on pupa of Tenebrio molitor].

To explore the regulatory mechanisms of parasitism of Sclerodermus sichuanensis on Tenebrio molitor, the methods of natural parasitism and venom injection were adopted to investigate the effects of the venom from S. sichuanensis on the pupa of T. molitor in the parasitic process. Under venom injection, the paralytic degree of the pupa had a positive correlation with the concentration of injected venom, and the number of recovered pupa had a negative correlation with the injected venom concentration. The T. molitor pupa was in slight and reversible paralysis when injected with 0.01 VRE (venom reservoir equivalent) of venom, and in non-reversible and complete paralysis when 0.2 VRE was injected. The pupa died massively and appeared a wide range of melanization when injected with soil bacterial suspension alone, but the melanization delayed and the mortality declined significantly when the mixed liquor of bacterium and venom was injected. The bacteriostasis of the venom on Staphylococcus aureus was significantly stronger than that on Escherichia coli. Within a definite range of temperature, the paralytic activity decreased significantly with increasing temperature, the bacteriostasis on S. aureus increased significantly, while that on E. coli was opposite. This study showed that the venom from S. sichuanensis had the effects of paralysis, bacteriostasis, inhibiting exuviations, and delaying melanization.

Sophisticated adaptations of Gregarina cuneata (Apicomplexa) feeding stages for epicellular parasitism.

BACKGROUND: Gregarines represent a very diverse group of early emerging apicomplexans, parasitising numerous invertebrates and urochordates, and are considered of little practical significance. Recently, they have gained more attention since some analyses showed that cryptosporidia are more closely related to the gregarines than to coccidia. METHODOLOGY/PRINCIPAL FINDINGS: Using a combined microscopic approach, this study points out the spectacular strategy of Gregarina cuneata for attachment to host tissue and nutrient acquisition while parasitising the intestine of yellow mealworm larvae, and reveals the unusual dynamics of cellular interactions between the host epithelium and parasite feeding stages. Trophozoites of G. cuneata develop epicellularly, attached to the luminal side of the host epithelial cell by an epimerite exhibiting a high degree of morphological variability. The presence of contractile elements in the apical region of feeding stages indicates that trophozoite detachment from host tissue is an active process self-regulated by the parasite. A detailed discussion is provided on the possibility of reversible retraction and protraction of the eugregarine apical end, facilitating eventual reattachment to another host cell in better physiological conditions. The gamonts, found in contact with host tissue via a modified protomerite top, indicate further adaptation of parasite for nutrient acquisition via epicellular parasitism while keeping their host healthy. The presence of eugregarines in mealworm larvae even seems to increase the host growth rate and to reduce the death rate despite often heavy parasitisation. CONCLUSIONS/SIGNIFICANCE: Improved knowledge about the formation of host-parasite interactions in deep-branching apicomplexans, including gregarines, would offer significant insights into the fascinating biology and evolutionary strategy of Apicomplexa. Gregarines exhibit an enormous diversity in cell architecture and dimensions, depending on their parasitic strategy and the surrounding environment. They seem to be a perfect example of a coevolution between a group of parasites and their hosts.

A nuptially transmitted ichthyosporean symbiont of Tenebrio molitor (Coleoptera: Tenebrionidae).

The yellow mealworm, Tenebrio molitor, harbors a symbiont that has spores with a thick, laminated wall and infects the fat body and ventral nerve chord of adult and larval beetles. In adult males, there is heavy infection of the epithelial cells of the testes and between testes lobes with occasional penetration of the lobes. Spores are enveloped in the spermatophores when they are formed at the time of mating and transferred to the female's bursa copulatrix. Infection has not been found in the ovaries. The sequence of the nuclear small subunit rDNA indicates that the symbiont is a member of the Ichthyosporea, a class of protists near the animal-fungi divergence.

Prerequisites for parasitism in rhabditid nematodes.

To evaluate their potential for survival in a vertebrate host, dauer larvae from 7 species of rhabditid nematodes were subjected to in vitro conditions designed to emulate those of a vertebrate digestive tract. Dauer larvae from 3 of the 7 species, selected for their ability to survive elevated temperatures and low pH, and representing differing types of phoretic associations with invertebrate hosts, were fed to frogs to examine their ability to survive passage through a vertebrate digestive system. The degree of invasiveness of the phoretic association that dauer larvae had with their invertebrate hosts did not correspond to patterns of in vitro survivorship for any of the experimental conditions. When consumed with a prey item, dauer larvae from all 3 species were recovered from frogs 72 hr postexposure, and no differences for in vivo survivorship were observed among the 3 species. The contention that invasiveness or facultative parasitism within an invertebrate host is a beneficial or necessary step toward vertebrate parasitism by rhabditid nematodes was not supported by the survivorship data.

Intraspecific variability of Steinernema feltiae strains from Cemoro Lawang, eastern Java, Indonesia.

Four strains of Steinernema feltiae from Eastern Java, Indonesia were characterized based on morphometric, morphological and molecular data. In addition, their virulence against last instar Tenebrio molitor and heat tolerance was tested. Infective juvenile have a mean body length ranging from 749 to 792 microm. The maximum sequence difference among the four strains was 7 bp (8.8%) in the ITS and 2 bp (0.3%) in D2D3 regions of the rDNA. All the strains are not reproductively isolated and can reproduce with European strain S. feltiae Owiplant. The lowest LC50 was observed for strain SCM (373) and the highest for S. feltiae strain Owiplant (458) IJs/40 T. molitor. All four strains showed relatively better mean heat tolerance when compared with S. feltiae Owiplant, both in adapted and non-adapted heat tolerance experiments.