On the life cycle of Brachymeria podagrica (Fabricius, 1787) (Hymenoptera: Chalcididae) - a parasitoid of sacrophagid, calliphorid, and muscid flies.

The lifecycle of Brachymeria podagrica, a parasitic wasp with a worldwide distribution, was studied under laboratory conditions using the flesh fly, Sarcophaga dux, as a host. Two hundred parasite-free 3rd instars of S. dux were exposed for 24 h to 20 female B. podagrica. In daily intervals, maggots and later pupae were examined for developmental stages of the parasitoid. The whole pre-imaginal development at a temperature of 26 °C lasted 21 to 26 days. Three morphologically different instars, followed by a prepupal and a pupal stage, were described using light and scanning electron microscopy. In a second experiment with 100 3rd stage Sarcophaga larvae and 10 parasitoids, a total of 70 wasps emerged 20 to 25 days after exposure. Two fly larvae did not pupate and dried out, while 28 pupae contained a dry or caseous content, dead wasp imagos, or their larval stages. No fly imagines emerged from exposed groups, while all 100 unexposed larvae pupated and adults eclosed between day 12 and day 14 after the start of the experiment, while the imagoes of the parasitoids appeared 8 to 12 days later.

A salivary chitinase of Varroa destructor influences host immunity and mite's survival.

Varroa destructor is an ectoparasite of honey bees and an active disease vector, which represents one of the most severe threats for the beekeeping industry. This parasitic mite feeds on the host's body fluids through a wound in the cuticle, which allows food uptake by the mother mite and its progeny, offering a potential route of entrance for infecting microorganisms. Mite feeding is associated with saliva injection, whose role is still largely unknown. Here we try to fill this gap by identifying putative host regulation factors present in the saliva of V. destructor and performing a functional analysis for one of them, a chitinase (Vd-CHIsal) phylogenetically related to chitinases present in parasitic and predatory arthropods, which shows a specific and very high level of expression in the mite's salivary glands. Vd-CHIsal is essential for effective mite feeding and survival, since it is apparently involved both in maintaining the feeding wound open and in preventing host infection by opportunistic pathogens. Our results show the important role in the modulation of mite-honey bee interactions exerted by a host regulation factor shared by different evolutionary lineages of parasitic arthropods. We predict that the functional characterization of Varroa sialome will provide new background knowledge on parasitism evolution in arthropods and the opportunity to develop new bioinspired strategies for mite control based on the disruption of their complex interactions with a living food source.

Effect of Drosophila suzukii on Blueberry VOCs: Chemical Cues for a Pupal Parasitoid, Trichopria anastrephae.

Biocontrol agents such as parasitic wasps use long-range volatiles and host-associated cues from lower trophic levels to find their hosts. However, this chemical landscape may be altered by the invasion of exotic insect species. The spotted-wing drosophila (SWD), Drosophila suzukii (Diptera: Drosophilidae), is a highly polyphagous fruit pest native to eastern Asia and recently arrived in South America. Our study aimed to characterize the effect of SWD attack on the volatile organic compounds (VOCs) of blueberries, a common host fruit, and to correlate these odor changes with the olfactory-mediated behavioral response of resident populations of Trichopria anastrephae parasitoids, here reported for the first time in Uruguay. Using fruit VOC chemical characterization followed by multivariate analyses of the odor blends of blueberries attacked by SWD, we showed that the development of SWD immature stages inside the fruit generates a different odor profile to that from control fruits (physically damaged and free of damage). These differences can be explained by the diversity, frequency, and amounts of fruit VOCs. The behavioral response of T. anastrephae in Y-tube bioassays showed that female wasps were significantly attracted to volatiles from SWD-attacked blueberries when tested against both clean air and undamaged blueberries. Therefore, T. anastrephae females can use chemical cues from SWD-infested fruits, which may lead to a successful location of their insect host. Since resident parasitoids are able to locate this novel potential host, biological control programs using local populations may be plausible as a strategy for control of SWD.

Variation in Parasitoid Virulence of Tetrastichus brontispae during the Targeting of Two Host Beetles.

In host-parasitoid interactions, antagonistic relationship drives parasitoids to vary in virulence in facing different hosts, which makes these systems excellent models for stress-induced evolutionary studies. Venom compositions varied between two strains of Tetrastichus brontispae, Tb-Bl and Tb-On. Tb-Bl targets Brontispa longissima pupae as hosts, and Tb-On is a sub-population of Tb-Bl, which has been experimentally adapted to a new host, Octodonta nipae. Aiming to examine variation in parasitoid virulence of the two strains toward two hosts, we used reciprocal injection experiments to compare effect of venom/ovarian fluids from the two strains on cytotoxicity, inhibition of immunity and fat body lysis of the two hosts. We found that Tb-Onvenom was more virulent towards plasmatocyte spreading, granulocyte function and phenoloxidase activity than Tb-Blvenom. Tb-Blovary was able to suppress encapsulation and phagocytosis in both hosts; however, Tb-Onovary inhibition targeted only B. longissima. Our data suggest that the venom undergoes rapid evolution when facing different hosts, and that the wasp has good evolutionary plasticity.

Insights into the Interaction between the Monophagous Tephritid Fly Anastrepha acris and its Highly Toxic Host Hippomane mancinella (Euphorbiaceae).

Despite their enormous economic importance and the fact that there are almost 5000 tephritid (Diptera) species, fruit fly - host plant interactions are poorly understood from a chemical perspective. We analyzed the interactions among Anastrepha acris (a little studied monophagous tephritid) and its highly toxic host plant Hippomane mancinella from chemical, ecological and experimental perspectives, and also searched for toxicants from H. mancinella in the larval-pupal endoparasitoid Doryctobracon areolatus. We identified 18 phenolic compounds from H. mancinella pulp belonging to different chemical groups including phenylpropanoids, flavonoids, chalcones and coumarins. No traces of Hippomanin A were detected in larvae, pupae or A. acris adults, or in D. areolatus adults, implying that A. acris larvae can metabolize this toxicant, that as a result does not reach the third trophic level. We tested the "behavioral preference - lack of larval specialization-hypothesis" via feeding experiments with a larval rearing medium containing H. mancinella fruit (skin + pulp or pulp alone). The high toxicity of H. mancinella was confirmed as only two (out of 2520 in three experiments) A. ludens larvae (a polyphagous pest species that preferentially feeds on plants within the Rutaceae) survived without reaching the adult stage when fed on media containing H. mancinella, whereas A. acris larvae developed well and produced healthy adults. Together, these findings open a window of opportunity to study the detoxification mechanisms used by tephritid fruit flies.

A venom protein, Kazal-type serine protease inhibitor, of ectoparasitoid Pachycrepoideus vindemiae inhibits the hemolymph melanization of host Drosophila melanogaster.

Parasitic wasps inject various virulence factors into the host insects while laying eggs, among which the venom proteins, one of the key players in host insect/parasitoid relationships, act in host cellular and humoral immune regulation to ensure successful development of wasp progeny. Although the investigations into actions of venom proteins are relatively ample in larval parasitoids, their regulatory mechanisms have not been thoroughly understood in pupal parasitoids. Here, we identified a venom protein, Kazal-type serine protease inhibitor, in the pupal ectoparasitoid Pachycrepoideus vindemiae (PvKazal). Sequence analysis revealed that PvKazal is packed by a signal peptide and a highly conserved "Kazal" domain. Quantitative polymerase chain reaction analysis recorded a higher transcript level of PvKazal in the venom apparatus relative to that in the carcass, and the PvKazal messenger RNA level appeared to reach a peak on day 5 posteclosion. Recombinant PvKazal strongly inhibited the hemolymph melanization of host Drosophila melanogaster. Additionally, the heterologous expression of PvKazal in transgenic Drosophila reduced the crystal cell numbers and blocked the melanization of host pupal hemolymph. Our present work underlying the roles of PvKazal undoubtedly increases the understanding of venom-mediated host-parasitoid crosstalk.

Tropilaelaps species identification and viral load evaluation of Tropilaelaps and Varroa mites and their Apis mellifera hosts in Palawan, Philippines.

Apis mellifera pupae and their parasites Tropilaelaps and Varroa destructor were collected from honey bee hives in Palawan, Philippines for species identification of the Tropilaelaps and viral analyses. Genetic analysis identified Tropilaelaps mercedesae infesting A. mellifera on the island. Viral analyses showed that all pupae and their infesting Tropilaelaps or Varroa shared the same Deformed Wing Virus (DWV) variant infections with DWV-B being more prevalent than DWV-A. Pupae infested with either Varroa or Tropilaelaps had higher levels of both DWV variants than uninfested pupae. Vigilance is needed to prevent the spread of Tropilaelaps clareae into Palawan and T. mercedesae and DWV variants from Palawan to other provinces.

Parasite-host specificity: A cross-infection study of the parasite Ophryocystis elektroscirrha.

Many parasites are constrained to only one or a few hosts, showing host specificity. It remains unclear why some parasites are specialists and other parasites are generalists. The parasite Ophryocystis elektroscirrha (OE) is a neogregarine protozoan thought to be restricted to monarch butterflies, Danaus plexippus (Nymphaliae) and D. gilippus. Recently, we found OE-like spores in other Lepidoptera, specifically in three noctuid moths: Helicoverpa armigera, H. assulta and H. punctigera, as well as another nymphalid, Parthenos sylvia. To our knowledge, this is the first report of OE-like parasite infections in species other than the genus Danaus. In sequencing 558 bp of 18S rRNA, we found the genetic similarity between OE from D. plexippus and OE-like parasite from the moths H. armigera and H. punctigera to be 95.2%. When we conducted cross-species infection experiments, we could not infect the moths with OE from D. plexippus, but OE-like parasite from H. armigera did infect D. plexippus and a closely related moth species Heliothis virescens. Interestingly, we did not find the OE-like parasite in the H. armigera population from Spain. Inter-population infection experiments with H. armigera demonstrated a higher sensitivity to OE-like infection in the population from Spain compared to the populations from Australia and China. These results suggest geographic variation in OE-like susceptibility and coevolution between parasite and host. Our findings give important new insights into the prevalence and host specificity of OE and OE-like parasites, and provide opportunities to study parasite transmission over spatial and temporal scales.

Side effects of Bacillus thuringiensis on the parasitoid Palmistichus elaeisis (Hymenoptera: Eulophidae).

The endoparasitoid wasp Palmistichus elaeisis Delvare & LaSalle (Hymenoptera: Eulophidae) is used to control defoliating lepidopteran pests. Chemical insecticides are not compatible with natural enemies, but bioinsecticides, such as Bacillus thuringiensis Berliner (Bt), have great potential for use in integrated pest management. However, interactions between Bt and P. elaeisis still need to be investigated. This study aimed to evaluate the effects of Bt on parental and first-generation P. elaeisis parasitizing Bt-susceptible and -resistant Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). An additional aim was to determine the toxicity of Bt to susceptible third-instar S. frugiperda larvae. Larvae were exposed to lethal concentrations (LC50 and LC90) of Bt and then allowed to be parasitized by P. elaeisis. Parasitoid longevity, immature production, reproductive performance, and behavioral responses were evaluated. Bt repelled P. elaeisis and reduced immature production. Parental and first filial generation parasitoids of both sexes emerged from Bt-treated larvae showed lower survivorship than controls. Parasitoids had poorer reproductive performance in Bt-susceptible and -resistant pupae than in untreated pupae. Palmistichus elaeisis emerged from Bt-susceptible and -resistant S. frugiperda showed altered host-searching behavior and reproductive parameters, which indicates low compatibility between the bioinsecticide agent and the parasitoid wasp.

Side effects of chlorantraniliprole, phosalone and spinosad on the egg parasitoid, Trichogramma brassicae.

The combined use of chemicals and biological control is not always a successful strategy owing to the potential side effects on biocontrol agents. Lethal and sublethal effects of three commonly used insecticides were assessed on adult and immature stages of the egg parasitoid Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae). Recommended field concentrations of chlorantraniliprole, phosalone and spinosad caused mortality on preimaginal stages by 24, 87, and 98%, respectively. Lethal effects on parasitoid adults exposed to the insecticide dry residues were estimated as median lethal concentrations (LC50) that were 13.28, 0.25, and 0.03 µg a.i. ml-1 for chlorantraniliprole, phosalone, and spinosad, respectively. The effect of a low lethal concentration (LC30) of the compounds was evaluated on various adult biological traits, such as longevity, fecundity, emergence rate and other life table parameters. All compounds caused detrimental effects on all the estimated demographical indexes. Chlorantraniliprole affected the net reproductive rate, mean generation time and doubling time in comparison to the control; while, phosalone and spinosad adversely affected all assessed parameters. Phosalone and spinosad significantly reduced gross reproductive rate, net reproductive rate, intrinsic rate of increase, finite rate of increase, mean generation time and doubling time and reduced longevity, fecundity, emergence rate related to other biological parameters in comparison with control. The results suggest that all compounds are not fully compatible with the activity of T. brassicae, and that the inclusion of chlorantraniprole, spinosad and phosalone into Integrated Pest Management (IPM) involving this parasitoid has to be avoided. Nevertheless, further studies in open field conditions and on a multiple generation scale are necessary for providing a more definitive conclusion on the IPM suitability of the three tested insectcides.

Performance of Trichopria drosophilae (Hymenoptera: Diapriidae), a Generalist Parasitoid of Drosophila suzukii (Diptera: Drosophilidae), at Low Temperature.

Survival and parasitism activity of Trichopria drosophilae Perkins adults, a cosmopolitan parasitoid of Drosophila spp., were studied under laboratory conditions using five constant temperatures at the lower range known for this enemy, from 4 to 20°C in 4°C increments. Drosophila suzukii Matsumura, an invasive pest of small fruits, was used as a host. Commercially available adult parasitoids were provided with 1) food and D. suzukii pupae; 2) food and no D. suzukii pupae; 3) no food and no pupae. The results show that adult females of T. drosophilae lived longer than males, and both generally benefitted from food supply. The highest level of survival was observed between 8 and 12°C for fed insects, irrespective of whether they were offered host pupae or not. The absence of food led to the highest mortality, but the parasitoid demonstrated considerably resistance to prolonged starvation. Successful parasitism increased steadily with temperature and reached the highest value at 20°C. Conversely, D. suzukii emergence rate was high after exposure of pupae to parasitoids at 4°C, while pupal mortality increased strongly with temperature until 12°C. The findings indicate that T. drosophilae is well adapted to the relatively cold conditions experienced in early spring and in autumn or at high elevations, when the host pupae could be largely available. The long lifespan of the adults and the ability to parasitize the host at low temperature make T. drosophilae potentially useful for the biocontrol of D. suzukii.

Improved Sentinel Method for Surveillance and Collection of Filth Fly Parasitoids.

Parasitoids are important natural enemies of house flies and other muscoid flies. The two most commonly used methods for collecting fly parasitoids from the field have distinct advantages and disadvantages. Collections of wild puparia depend on the ability to find puparia in sufficient numbers and are prone to localized distortions in relative species abundance because of the overrepresentation of samples from hot spots of fly larval activity. Placement and retrieval of sentinel puparia is convenient and allows consistent sampling over time but is strongly biased in favor of Muscidifurax spp. over Spalangia spp. An improved sentinel method is described that combines some of the advantages of these two methods. Fly medium containing larvae is placed in containers, topped with a screen mesh bag of puparia, and placed in vertebrate-proof wire cages. Cages are placed at sites of actual or potential fly breeding and retrieved 3-7 d later. The modified method collected species profiles that more closely resembled those of collections of wild puparia than those from sentinel pupal bags. A method is also described for isolating puparia individually in 96-well tissue culture plates for parasitoid emergence. Use of the plate method provided a substantial saving of time and labor over the use of individual gelatin capsules for pupal isolation. Puparia from the collections that were housed individually in the wells of tissue culture plates had a higher proportion of emerged Spalangia species than puparia that were held in groups.

Interaction Between Beauveria bassiana (Hypocreales: Cordycipitaceae) and Coptera haywardi (Hymenoptera: Diapriidae) for the Management of Anastrepha obliqua (Diptera: Tephritidae).

The interaction between the entomopathogenic fungus Beauveria bassiana (Balsamo) and the parasitoid Coptera haywardi (Oglobin), as potential biological control agents for Anastrepha obliqua (Macquart) fruit flies, was evaluated under laboratory and semi-protected field cage conditions. The effects of the parasitoids and fungus were individually and jointly assessed in Plexiglas cages. Application of B. bassiana dry conidia to soil produced 40% mortality in A. obliqua adults. However, mortality was lower (21.2%) on evaluation under field cage conditions. According to the multiple decrement life table analysis, the probability of death of A. obliqua was 88% when C. haywardi parasitoids and B. bassiana conidia were used in conjunction, 89% when only C. haywardi parasitoids were released and 23% when only B. bassiana conidia were applied. These results demonstrate that no synergistic, additive or antagonistic interaction took place with the simultaneous use of these natural enemies, since the presence of B. bassiana had no effect on the C. haywardi parasitism. These results indicate that the parasitoid is a better natural enemy for the control of A. obliqua, and show that, although the two biological control agents can be used simultaneously, their joint application will not produce increased control.

Comparing four methods of rearing Varroa destructor in vitro.

The parasitic mite Varroa destructor Anderson and Trueman continues to devastate western honey bee (Apis mellifera L.) colonies throughout most of the world where they are managed. The development of a method to rear Varroa in vitro would allow for year-round Varroa research, rapidly advancing our progress towards controlling the mite. We created two separate experiments to address this objective. First, we determined which of four in vitro rearing methods yields the greatest number of Varroa offspring. Second, we attempted to improve the rearing rates achieved with that method. The four methods tested included (1) rearing Varroa on honey bee pupae in gelatin capsules, (2) rearing Varroa on in vitro-reared honey bees, (3) group rearing Varroa on honey bee pupae in Petri dishes, and (4) providing Varroa a bee-derived diet. The number of reproducing females and the number of fully mature offspring were significantly higher in the gelatin capsules maintained at 75% RH than in any other method. A 2 × 3 full factorial design was used to test combinations of gelatin capsule size (6 and 7 mm diameter) and relative humidity (65, 75, or 85%) on Varroa rearing success. Varroa reproduction and survival were significantly higher in 7-mm-diameter gelatin capsules maintained at 75% RH than in those maintained in 6-mm capsules and at the other humidities. By identifying factors that influence Varroa reproductive success in vitro, this work provides an important foundation for the development of future rearing protocols.

Biocontrol potential of Steinernema cholashanense (Nguyen) on larval and pupal stages of potato tuber moth, Phthorimaea operculella (Zeller).

The potato tuber moth, Phthorimaea operculella (Zeller), is a serious pest of potato and other commercial crops belonging to the Solanaceae family. In recent years, it has become an emerging problem in potato-growing regions of the Nilgiri hills of southern India. It is responsible for the reduced quality and quantity of marketable potatoes. In this regard, the development of an eco-friendly control method for the management of the potato tuber moth is urgently required. Therefore, in the present study, the virulence of Steinernema cholashanense CPRSUS01 originally isolated from the potato rhizosphere was tested on fourth-instar larvae and pupae of P. operculella. Steinernema cholashanense caused the greatest mortality in the fourth-instar larval stage (100%) than the pupae (30%). In addition to this, penetration and reproduction of this nematode was also studied in fourth-instar larvae of P. operculella and this is the first report of penetration and reproduction of any entomopathogenic nematode species on potato tuber moth larvae. The reproduction capacity of S. cholashanense on P. operculella is higher (702 infective juveniles mg-1 body weight). Our results indicated that S. cholashanense has good potential as an alternative tool for the management of P. operculella. But before including S. cholashanense in the integrated pest management program of P. operculella, its efficacy should be tested under field conditions.

Direct transmission by injection affects competition among RNA viruses in honeybees.

The arrival of the ectoparasitic mite Varroa destructor on the western honeybee Apis mellifera saw a change in the diversity and prevalence of honeybee RNA viruses. One virus in particular, deformed wing virus (DWV) has become closely associated with V. destructor, leading many to conclude that V. destructor has affected viral virulence by changing the mode of transmission. While DWV is normally transmitted via feeding and faeces, V. destructor transmits viruses by direct injection. This change could have resulted in higher viral prevalence causing increased damage to the bees. Here we test the effect of a change in the mode of transmission on the composition and levels of honeybee RNA viruses in the absence of V. destructor. We find a rapid increase in levels of two viruses, sacbrood virus (SBV) and black queen cell virus (BQCV) after direct injection of viral extracts into honeybee pupae. In pupae injected with high levels of DWV extracted from symptomatic adult bees, DWV levels rapidly decline in the presence of SBV and BQCV. Further, we observe high mortality in honeybee pupae when injected with SBV and BQCV, whereas injecting pupae with high levels of DWV results in near 100% survival. Our results suggest a different explanation for the observed association between V. destructor and DWV. Instead of V. destructor causing an increase in DWV virulence, we hypothesize that direct virus inoculation, such as that mediated by a vector, quickly eliminates the most virulent honeybee viruses resulting in an association with less virulent viruses such as DWV.

Haemolymph removal by Varroa mite destabilizes the dynamical interaction between immune effectors and virus in bees, as predicted by Volterra's model.

The association between the deformed wing virus and the parasitic mite Varroa destructor has been identified as a major cause of worldwide honeybee colony losses. The mite acts as a vector of the viral pathogen and can trigger its replication in infected bees. However, the mechanistic details underlying this tripartite interaction are still poorly defined, and, particularly, the causes of viral proliferation in mite-infested bees. Here, we develop and test a novel hypothesis that mite feeding destabilizes viral immune control through the removal of both virus and immune effectors, triggering uncontrolled viral replication. Our hypothesis is grounded on the predator-prey theory developed by Volterra, which predicts prey proliferation when both predators and preys are constantly removed from the system. Consistent with this hypothesis, we show that the experimental removal of increasing volumes of haemolymph from individual bees results in increasing viral densities. By contrast, we do not find consistent support for alternative proposed mechanisms of viral expansion via mite immune suppression or within-host viral evolution. Our results suggest that haemolymph removal plays an important role in the enhanced pathogen virulence observed in the presence of feeding Varroa mites. Overall, these results provide a new model for the mechanisms driving pathogen-parasite interactions in bees, which ultimately underpin honeybee health decline and colony losses.

Selection for barriers between honey bees and a devastating parasite.

Rivaling pesticides and a dearth of flowers, the parasitic mite Varroa destructor presents a tremendous threat to western honey bees, Apis mellifera. A longstanding, but minor, pest for the Asian honey bee Apis cerana, these obligate bee parasites feast on developing and adult A. mellifera across several continents. Varroa reproduction is limited to a short window when developing bee pupae are concealed in wax cells. Mated females target developing bees just before pupation and then have about one day to initiate reproduction, eventually laying one male and up to several female offspring. Female mites often fail to reproduce at all, instead waiting in cells until their bee host finishes development and then hitching dangerous rides on a succession of adult bees for up to several weeks, before scouting for a new host pupa. In this issue of Molecular Ecology, Conlon et al. (2019) have explored mite reproductive success via a clever and thought-provoking association study. In so doing, they have identified a protein whose actions could be integral to the dance between bees and their mite parasites.

A gene for resistance to the Varroa mite (Acari) in honey bee (Apis mellifera) pupae.

Social insect colonies possess a range of defences which protect them against highly virulent parasites and colony collapse. The host-parasite interaction between honey bees (Apis mellifera) and the mite Varroa destructor is unusual, as honey bee colonies are relatively poorly defended against this parasite. The interaction has existed since the mid-20th Century, when Varroa switched host to parasitize A. mellifera. The combination of a virulent parasite and relatively naïve host means that, without acaricides, honey bee colonies typically die within 3 years of Varroa infestation. A consequence of acaricide use has been a reduced selective pressure for the evolution of Varroa resistance in honey bee colonies. However, in the past 20 years, several natural-selection-based breeding programmes have resulted in the evolution of Varroa-resistant populations. In these populations, the inhibition of Varroa's reproduction is a common trait. Using a high-density genome-wide association analysis in a Varroa-resistant honey bee population, we identify an ecdysone-induced gene significantly linked to resistance. Ecdysone both initiates metamorphosis in insects and reproduction in Varroa. Previously, using a less dense genetic map and a quantitative trait loci analysis, we have identified Ecdysone-related genes at resistance loci in an independently evolved resistant population. Varroa cannot biosynthesize ecdysone but can acquire it from its diet. Using qPCR, we are able to link the expression of ecdysone-linked resistance genes to Varroa's meals and reproduction. If Varroa co-opts pupal compounds to initiate and time its own reproduction, mutations in the host's ecdysone pathway may represent a key selection tool for honey bee resistance and breeding.

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.