Cuticular Hydrocarbon Trails Released by Host Larvae Lose their Kairomonal Activity for Parasitoids by Solidification

Successful host search by parasitic wasps is often mediated by host-associated chemical cues. The ectoparasitoid Holepyris sylvanidis is known to follow chemical trails released by host larvae of the confused flour beetle, Tribolium confusum, for short-range host location. Although the hexane-extractable trails consist of stable, long-chain cuticular hydrocarbons (CHCs) with low volatility, the kairomonal activity of a trail is lost two days after release. Here, we studied whether this loss of kairomonal activity is due to changes in the chemical trail composition induced by microbial activity. We chemically analyzed trails consisting of hexane extracts of T. confusum larvae after different time intervals past deposition under sterile and non-sterile conditions. GC-MS analyses revealed that the qualitative and quantitative pattern of the long-chain CHCs of larval trails did not significantly change over time, neither under non-sterile nor sterile conditions. Hence, our results show that the loss of kairomonal activity of host trails is not due to microbially induced changes of the CHC pattern of a trail. Interestingly, the kairomonal activity of trails consisting of host larval CHC extracts was recoverable after two days by applying hexane to them. After hexane evaporation, the parasitoids followed the reactivated host trails as they followed freshly laid ones. Cryo-scanning electron microscopy showed that the trails gradually formed filament-shaped microstructures within two days. This self-assemblage of CHCs was reversible by hexane application. Our study suggests that the long-chain CHCs of a host trail slowly undergo solidification by a self-assembling process, which reduces the accessibility of CHCs to the parasitoid’s receptors as such that the trail is no longer eliciting trail-following behavior.

The Importance of Methyl-Branched Cuticular Hydrocarbons for Successful Host Recognition by the Larval Ectoparasitoid Holepyris sylvanidis

Cuticular hydrocarbons (CHCs) of host insects are used by many parasitic wasps as contact kairomones for host location and recognition. As the chemical composition of CHCs varies from species to species, the CHC pattern represents a reliable indicator for parasitoids to discriminate host from non-host species. Holepyris sylvanidis is an ectoparasitoid of beetle larvae infesting stored products. Previous studies demonstrated that the larval CHC profile of the confused flour beetle, Tribolium confusum, comprises long chain linear and methyl-branched alkanes (methyl alkanes), which elicit trail following and host recognition in H. sylvanidis. Here we addressed the question, whether different behavioral responses of this parasitoid species to larvae of other beetle species are due to differences in the larval CHC pattern. Our study revealed that H. sylvanidis recognizes and accepts larvae of T. confusum, T. castaneum and T. destructor as hosts, whereas larvae of Oryzaephilus surinamensis were rejected. However, the latter species became attractive after applying a sample of T. confusum larval CHCs to solvent extracted larvae. Chemical analyses of the larval extracts revealed that CHC profiles of the Tribolium species were similar in their composition, while that of O. surinamensis differed qualitatively and quantitatively, i.e. methyl alkanes were present as minor components on the cuticle of all Tribolium larvae, but were absent in the O. surinamensis CHC profile. Furthermore, the parasitoid successfully recognized solvent extracted T. confusum larvae as hosts after they had been treated with a fraction of methyl alkanes. Our results show that methyl alkanes are needed for host recognition by H. sylvanidis.

Color Preference of Three Parasitoids Imported to the Americas for the Biological Control of the Coffee Berry Borer (Curculionidae: Scolytinae)

The African parasitoids Cephalonomia stephanoderis Waterston (Bethylidae: Hymenoptera), Prorops nasuta Betrem (Bethylidae: Hymenoptera), and Phymastichus coffea LaSalle (Eulophidae: Hymenoptera) are biological control agents of the coffee berry borer (Coleoptera: Curculionidae). In this study, we investigated in laboratory the female behavioral responses of these parasitoids to 14 different wavelengths (340-670 nm) against a control (570 nm, yellow). When nonchooser females were included in the analysis, none parasitoids species showed a preference between 340, 350, 370, 460, 490, 520, 540, 590, 640, and 650 nm with respect to the control wavelength. In contrast, the three species of parasitoids were more attracted to wavelengths of 380, 400, and 420 nm than the control wavelength. Phymastichus coffea and P. nasuta were more attracted to the wavelength of 400 and 420 nm compared to C. stephanoderis. At 380 nm, P. coffea and C. stephanoderis wasps showed the higher responses in comparison to P. nasuta females. When nonchooser wasps were excluded from the analysis, we observed other differences among the parasitoid species. For instance, P. coffea were more attracted to 490-540 nm than to 570 nm, whereas the bethylids did not discriminate between 490-540 nm or 570 nm. Our results are discussed in relation to possible implications associated with the vision of these parasitoid species.

Review of <i>Dissomphalus</i> Ashmead (Hymenoptera, Bethylidae) from Panama, with key to the Central American species

Sixty-four species of Dissomphalus from Panama are recognized, 31 are described and illustrated as new to science: D. abarus sp. nov., D. afestus sp. nov., D. arbeius sp. nov., D. ardonius sp. nov., D. areius sp. nov., D. aretisus sp. nov., D. arteobius sp. nov., D. arteus sp. nov., D. asfartus sp. nov., D. asitius sp. nov., D. azagus sp. nov., D. borus sp. nov., D. citus sp. nov., D. ettus sp. nov., D. geortus sp. nov., D. ibocius sp. nov., D. ibrastus sp. nov., D. ilarius sp. nov., D. iozus sp. nov., D. isortus sp. nov., D. isteus sp. nov., D. racarus sp. nov., D. raziogus sp. nov., D. sartus sp. nov., D. teobus sp. nov., D. teraus sp. nov., D. terbius sp. nov., D. tisinus sp. nov., D. trisus sp. nov., D. urazius sp. nov. and D. ubracus sp. nov.. Eight species are registered for the first time from Panama: D. angulatus Azevedo, D. galeatus Alencar & Azevedo, D. infissus Evans, D. persontaus Redighieri & Azevedo, D. pilus Alencar & Azevedo, D. politus Ashmead, D. pronus Alencar & Azevedo and D. vallensis Evans. Eighteen species had their known distribution broadened in the country: D. bilobatus Azevedo, D. brasiliensis Kieffer, D. cervoides Azevedo, D. coronatus Alencar & Azevedo, D. culteratus Alencar & Azevedo, D. curvifoveatus Azevedo, D. dilatatus Azevedo, D. geniculatus Azevedo, D. gilvipes Evans, D. guttus Azevedo, D. intradentatus Azevedo, D. piscicercus Azevedo, D. plaumanni Evans, D. punctatus (Kieffer), D. rettenmeyeri Evans, D. rufipalpis Kieffer, D. strepsus Azevedo and D. unitus Azevedo. Seven species previously recorded from Panama were not found in the studied material: D. altivolans Evans, D. apertus Kieffer, Alencar & Azevedo, D. declinatus Alencar & Azevedo, D. latus Azevedo, D. ramosus Alencar & Azevedo, D. strabus Azevedo and D. subdeformis Azevedo. A key to species of Dissomphalus from Central America is provided.

Host Habitat Volatiles Enhance the Olfactory Response of the Larval Parasitoid Holepyris sylvanidis to Specifically Host-Associated Cues

Host foraging of parasitic wasps attacking insects living in stored food may be guided by volatile cues emanating from these postharvest products. However, little knowledge is available as to how habitat odor released from noninfested stored food affects the parasitoid's response to host-specific chemicals. In this study, we investigated the impact of wheat grist odor on the olfactory host search by the ectoparasitoid Holepyris sylvanidis This parasitoid attacks larvae of the confused flour beetle Tribolium confusum, a common pest of grain products. Olfactometer bioassays showed that female H. sylvanidis were attracted by volatiles released from host larval feces, whereas odor of noninfested wheat grist was neither attractive nor did it mask the host-indicating cues. We analyzed the odor of host larval feces and wheat grist by coupled gaschromatography-mass spectrometry and recorded the parasitoid's electroantennographic (EAG) responses to the detected volatiles. Two specifically host-associated components of the fecal odor, (E)-2-nonenal and 1-pentadecene, elicited strong EAG responses. Both components were attractive when tested individually, but less than larval feces. Attraction of parasitoids to these host-specific key compounds was enhanced by addition of (i) noninfested habitat substrate odor or (ii) a blend of 3 EAG-active (but not behaviorally active) volatiles that had been identified in odor of noninfested grist (benzaldehyde, 1-tetradecene, 1-hexadecene), but were also detected in the host fecal odor. The impact of these volatiles ubiquitously released in a food store by noninfested habitat substrate on the parasitoid's orientation to host-specific volatile cues is discussed.

Deciphering the main venom components of the ectoparasitic ant-like bethylid wasp, Scleroderma guani

Similar to venom found in most venomous animals, parasitoid venoms contain a complex cocktail of proteins with potential agrichemical and pharmaceutical use. Even though parasitoids are one of the largest group of venomous animals, little is known about their venom composition. Recent few studies revealed high variated venom composition existing not only in different species but also between closely related strains, impling that increasing information on the venom proteins from more greater diversity of species of different taxa is key to comprehensively uncover the complete picture of parasitoid venom. Here, we explored the major protein components of the venom of ectoparasitic ant-like bethylid wasp, Scleroderma guani by an integrative transcriptomic-proteomic approach. Illumina deep sequencing of venom apparatus cDNA produced 49,873 transcripts. By mapping the peptide spectral data derived from venom reservoir against these transcripts, mass spectrometry analysis revealed ten main venom proteins, including serine proteinase, metalloprotease, dipeptidyl peptidase IV, esterase, antithrombin-III, acid phosphatase, neural/ectodermal development factor IMP-L2 like protein, venom allergen 3, and unknown protein. Interestingly, one serine proteinase was firstly identified with rarely high molecular weight about 200 kDa in parasitoid venom. The occurrence of abundant acid phosphatase, antithrombin-III and venom allergen 3 demonstrated that S. guani venom composition is similar to that of social wasp venoms. All identified venom genes showed abundantly biased expression in venom apparatus, indicating their virulent functions involved in parasitization. This study shed light on the more better understanding of parasitoid venom evolution across species and will facilitate the further elucidation of function and toxicity of these venom proteins.