Volatiles from cotton aphid (Aphis gossypii) infested plants attract the natural enemy Hippodamia variegata

The Aphis gossypii is a major threat of cotton worldwide due to its short life cycle and rapid reproduction. Chemical control is the primary method used to manage the cotton aphid, which has significant environmental impacts. Therefore, prioritizing eco-friendly alternatives is essential for managing the cotton aphid. The ladybird, Hippodamia variegata, is a predominant predator of the cotton aphid. Its performance in cotton plantation is directly linked to chemical communication, where volatile compounds emitted from aphid-infested plants play important roles in successful predation. Here, we comprehensively studied the chemical interaction between the pest, natural enemy and host plants by analyzing the volatile profiles of aphid-infested cotton plants using gas chromatography-mass spectrometry (GC-MS). We then utilized the identified volatile compounds in electrophysiological recording (EAG) and behavioral assays. Through behavioral tests, we initially demonstrated the clear preference of both larvae and adults of H. variegata for aphid-infested plants. Subsequently, 13 compounds, namely α-pinene, cis-3-hexenyl acetate, 4-ethyl-1-octyn-3-ol, β-ocimene, dodecane, E-β-farnesene, decanal, methyl salicylate, β-caryophyllene, α-humulene, farnesol, DMNT, and TMTT were identified from aphid-infested plants. All these compounds were electrophysiologically active and induced detectable EAG responses in larvae and adults. Y-tube olfactometer assays indicated that, with few exceptions for larvae, all identified chemicals were attractive to H. variegata, particularly at the highest tested concentration (100 mg/ml). The outcomes of this study establish a practical foundation for developing attractants for H. variegata and open avenues for potential advancements in aphid management strategies by understanding the details of chemical communication at a tritrophic level

Laboratory Bioassay of Iranian Isolates of Entomopathogenic Fungus Metarhizium anisopliae (Metsch.) Sorokin (Ascomycota: Hypocreales) against two Species of Storage Pest

The susceptibility of adults of Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis L. (Coleoptera: Silvanidae) to three Iranian Isolates of the entomopathogenic fungi Metarhizium anisopliae (Metsch.) Sorokin was evaluated through bioassays with direct immersion under laboratory conditions. For each isolates, five aqueous suspensions were prepared in a logarithmic series in Tween 80 (0.05% v/v). Results showed that adult of both species were susceptible to all isolates of M. anisopliae. For all three isolates, mortality percentage of the two species increased with increasing conidial concentration and significant difference was observed between concentrations. The corrected cumulative mortality of adult of O. surinamensis 10 days after immersion ranged from 12.38 to 85.84%, 18.6 to 62.83% and 10.63 to 77.87% for different concentrations of DEMI001, IRAN 715C and IRAN 1018C, respectively. These amounts for T. castaneum varied from 31.07 to 74.78%, 26.02 to 75.61% and 23.33 to 89.99% for different concentrations of DEMI001, IRAN 715C and IRAN 1018C, respectively. The parameters of probit analysis demonstrated non-overlap of 95% confidence limits of LC50 and LC95 and significant difference was observed among three isolates tested against each insect. The lowest and the highest LC50 and LC95 values were observed in the isolates DEMI001 for O. surinamensis (3/1×105 and 1/5×108) and IRAN 715C for T. castaneum (6.2×108 and 6.9×1014), respectively. This observation highlights the importance and need of screening for more virulent isolates against storage pests for use in the management of these pests

Laboratory Bioassay of Iranian Isolates of Entomopathogenic Fungus Metarhizium anisopliae (Metsch.) Sorokin (Ascomycota: Hypocreales) against two Species of Storage Pest 36 Adel KHASHAVEH, Hamid Sakenin CHELAV

Summary Th e susceptibility of adults of Tribolium castaneum Herbst (Coleoptera: Tenebrionidae) and Oryzaephilus surinamensis L. (Coleoptera: Silvanidae) to three Iranian Isolates of the entomopathogenic fungi Metarhizium anisopliae (Metsch.) Sorokin was evaluated through bioassays with direct immersion under laboratory conditions. For each isolates, fi ve aqueous suspensions were prepared in a logarithmic series in Tween 80 (0.05% v/v). Results showed that adult of both species were susceptible to all isolates of M. anisopliae. For all three isolates, mortality percentage of the two species increased with increasing conidial concentration and signifi cant diff erence was observed between concentrations. Th e corrected cumulative mortality of adult of O. surinamensis 10 days aft er immersion ranged from 12.38 to 85.84%, 18.6 to 62.83% and 10.63 to 77.87% for diff erent concentrations of DEMI001, IRAN 715C and IRAN 1018C, respectively. Th ese amounts for T. castaneum varied from 31.07 to 74.78%, 26.02 to 75.61% and 23.33 to 89.99% for diff erent concentrations of DEMI001, IRAN 715C and IRAN 1018C, respectively. Th e parameters of probit analysis demonstrated non-overlap of 95% confi dence limits of LC 50 and LC 95 and signifi cant diff erence was observed among three isolates tested against each insect. Th e lowest and the highest LC 50 and LC 95 values were observed in the isolates DEMI001 for O. surinamensis (3/1×10 5 and 1/5×10 8) and IRAN 715C for T. castaneum (6.2×10 8 and 6.9×10 14 ), respectively. Th is observation highlights the importance and need of screening for more virulent isolates against storage pests for use in the management of these pests

Identification and Tissue Expression Profiles of Odorant Receptor Genes in the Green Peach Aphid <em>Myzus persicae</em>

The green peach aphid Myzus persicae (Hemiptera: Aphididae) relies heavily on its olfactory system to locate plant hosts, find mates, and avoid parasitoids or predators. The insect odorant receptors (ORs) have been proven to play a critical role in the perception of odorants from the environment. In the present study, 33 odorant receptor candidate genes including the Orco gene were identified from the antennal, head, legs and body transcriptomes of M. persicae. Phylogenetic analysis of ORs from seven different orders of insect species suggests that ORs from different insect species are highly divergent and most ORs from the same species formed monophyletic groups. In addition, the aphid ORs were clustered into six different sub-clades in the same clade. Furthermore, the genomic structure of the OR genes also tends to be consistent, suggesting that ORs from the family Aphididae have a relatively close evolutionary relationship. Reads per kilobase per million (RPKM) and tissue expression profiles analyses revealed that 27 out of the 33 MperORs were uniquely or primarily expressed in the antennae, indicating their putative roles in chemoreception. This work provides a foundation to further investigate the molecular and ecological functions of MperORs in the aphid–aphid, aphid–plant and aphid–natural enemy interactions

Characterization and Comparative Analysis of Olfactory Receptor Co-Receptor Orco Orthologs Among Five Mirid Bug Species

The phytophagous mirid bugs of Apolygus lucorum, Lygus pratensis as well as three Adelphocoris spp., including Adelphocoris lineolatus, A. suturalis, and A. fasciaticollis are major pests of multiple agricultural crops in China, which have distinct geographical distribution and occurrence ranges. Like many insect species, these bugs heavily rely on olfactory cues to search preferred host plants, thereby investigation on functional co-evolution and divergence of olfactory genes seems to be necessary and is of great interest. In the odorant detection pathway, olfactory receptor co-receptor (Orco) plays critical role in the perception of odors. In this study, we identified the full-length cDNA sequences encoding three putative Orcos (AsutOrco, AfasOrco, and LpraOrco) in bug species of A. suturalis, A. fasciaticollis, and L. pratensis based on homology cloning method. Next, sequence alignment, membrane topology and gene structure analysis showed that these three Orco orthologs together with previously reported AlinOrco and AlucOrco shared high amino acid identities and similar topology structure, but had different gene structure especially at the length and insertion sites of introns. Furthermore, the evolutional estimation on the ratios of non-synonymous to synonymous (Ka/Ks) revealed that Orco genes were under strong purifying selection, but the degrees of variation were significant different between genera. The results of quantitative real-time PCR experiments showed that these five Orco genes had a similar antennae-biased tissue expression pattern. Taking these data together, it is thought that Orco genes in the mirid species could share conserved olfaction roles but had different evolution rates. These findings would lay a foundation to further investigate the molecular mechanisms of evolutionary interactions between mirid bugs and their host plants, which might in turn contribute to the development of pest management strategy for mirid bugs

Odorant-Binding Protein <i>HvarOBP</i>5 in Ladybird Hippodamia variegata Regulates the Perception of Semiochemicals from Preys and Habitat Plants

A total of 12 OBPs were identified in the antennae of ladybird Hippodamia variegata. HvarOBP1/2/5/6/10/11 were highly expressed in adults, whereas HvarOBP3/4/7/8/9/12 had higher expression levels in larvae. In adults, HvarOBP1/2/4/5/6/7/8/11/12 were highly expressed in antennae. Among these, recombinant HvarOBP5 strong bound with (E)-β-farnesene (EβF), (R)-(+)-limonene, (E,E)-4,8,12-trimethyltrideca-l,3,7,11-tetraene (TMTT), (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), hexyl hexanoate, and geranyl acetate. Molecular docking indicated that Leu42, Lys43, and His64 were the key binding sites of HvarOBP5. All six ligands evoked electroantennography (EAG) responses in ladybirds. Moreover, (R)-(+)-limonene and hexyl hexanoate were attractive to both sexes. After RNA interference for 72 h, the EAGs of dsRNA-injected ladybirds to DMNT and hexyl hexanoate were significantly decreased by 73.8 and 78.6%, respectively. Both dsRNA-injected males and females showed significantly lower behavioral preferences for DMNT and hexyl hexanoate. These findings suggest that HvarOBP5 in H. variegata plays an important role in the perception of semiochemical cues from preys and habitat plants

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<p>The phytophagous mirid bugs of Apolygus lucorum, Lygus pratensis as well as three Adelphocoris spp., including Adelphocoris lineolatus, A. suturalis, and A. fasciaticollis are major pests of multiple agricultural crops in China, which have distinct geographical distribution and occurrence ranges. Like many insect species, these bugs heavily rely on olfactory cues to search preferred host plants, thereby investigation on functional co-evolution and divergence of olfactory genes seems to be necessary and is of great interest. In the odorant detection pathway, olfactory receptor co-receptor (Orco) plays critical role in the perception of odors. In this study, we identified the full-length cDNA sequences encoding three putative Orcos (AsutOrco, AfasOrco, and LpraOrco) in bug species of A. suturalis, A. fasciaticollis, and L. pratensis based on homology cloning method. Next, sequence alignment, membrane topology and gene structure analysis showed that these three Orco orthologs together with previously reported AlinOrco and AlucOrco shared high amino acid identities and similar topology structure, but had different gene structure especially at the length and insertion sites of introns. Furthermore, the evolutional estimation on the ratios of non-synonymous to synonymous (Ka/Ks) revealed that Orco genes were under strong purifying selection, but the degrees of variation were significant different between genera. The results of quantitative real-time PCR experiments showed that these five Orco genes had a similar antennae-biased tissue expression pattern. Taking these data together, it is thought that Orco genes in the mirid species could share conserved olfaction roles but had different evolution rates. These findings would lay a foundation to further investigate the molecular mechanisms of evolutionary interactions between mirid bugs and their host plants, which might in turn contribute to the development of pest management strategy for mirid bugs.</p