Identification and functional characterization of chemosensory genes in olfactory and taste organs of Spodoptera litura (Lepidoptera: Noctuidae)

Identification of Behaviorally Active Odorants for Adult Chilo sacchariphagus Based on the Binding Properties of Odorant-Binding Proteins toward Host Volatiles

Chilo sacchariphagus is the key pest of sugar cane. Due to the difficulty associated with pesticide application in middle and late growth stages of sugar cane, the use of odorant attractants is a beneficial alternative to pesticides. Odorant-binding proteins (OBPs) in the insect olfactory system represent excellent targets for screening odorant attractants. Here, we identified 12 OBPs from the head transcriptome of C. sacchariphagus adults, with four OBPs (CsacOBP1/2/5/12) highly enriched in adult antennae. Ligand-binding assays for the four CsacOBPs showed that they can bind with 10 of the 30 host volatiles tested. Behavioral assays revealed that (+)-cedrol and 1-hexadecanol from the 10 compounds can attract the moths of both sexes. Protein-ligand interaction analyses identified five key amino acid residues involved in CsacOBPs' binding to (+)-cedrol and 1-hexadecanol. These findings have enhanced our molecular understanding of the host plant selection in C. sacchariphagus and have facilitated the development of attractants for C. sacchariphagus.

Instar determination, development, and sexual dimorphism for Gynaephora menyuanensis (Lepidoptera: Lymantriinae) and ultrastructure of adult antennae

Gynaephora menyuanensis Yan & Zhou is one of the most devastating pests that harm the ecosystem of alpine meadows and hinder the advancement of animal husbandry. However, the current knowledge of the morphology of the different developmental stages within G. menyuanensis reveals an information deficit that needs to be addressed. This study is the first to report the life history, sexual dimorphism, and morphology of eggs, mature larvae, pupae, and adult antennal sensilla types of G. menyuanensis. This study used a K-means clustering method, based on the head width, body length, body width, and the number of crochets of larvae at each instar, to differentiate instars of G. menyuanensis; the description of the morphology of larvae, pupae, and adult antennae employed light microscopy and scanning electron microscopy photographs. The results revealed that the instar grouping was reliable and verified by the Brooks-Dyar combined with Crosby rules, revealing that the larval stage of G. menyuanensis comprises 7 instars. This species produces one generation per year in the alpine meadow, with its life cycle lasting approximately 300 d in total. The pupae and adult antennae significantly differed between the sexes, indicating sexual dimorphism in the 2 genders. Nine types and 14 subtypes of antennal sensilla were observed in male antennae (bipectinate), while only 3 types and 3 subtypes were found in female adult antennae (club-like). Our findings have implications for better understanding the life history, adaptation strategies under extreme environmental conditions on the Qinghai-Tibet Plateau and developing scientific and effective pest control methods.

Deorphanization of Pheromone Receptors and Discovery of a Novel Agonist for Sex Pheromone Communication in Diamondback Moths

Sex pheromone communication is an essential component of mate recognition in moths. In this study, we heterologously expressed male-biased pheromone receptors (PRs) of diamondback moths, Plutella xylostella, in Drosophila OR67d neurons and determined their responses toward sex pheromonal compounds. The neurons expressing PxylOR59, PxylOR13, and PxylOR46 specifically responded to three sex pheromone components, Z11-16:Ald, Z11-16:Ac, and Z11-16:OH, respectively. The most effective ligands of other three PRs, PxylOR47, PxylOR49, and PxylOR73 were Z11-14:Ac, Z9,E12-14:Ac, and Z9,E11-14:Ac, respectively. Interestingly, the last two PRs were also tuned to Z11-14:Ac, which was not present in the pheromone glandular extract of P. xylostella in previous studies. Y-tube olfactometer assays revealed that the sex pheromone blend mixed with Z11-14:Ac at a ratio of 100:0.1 attracted more virgin males compared to the sex pheromone blend. These findings improve our understanding of the olfactory coding mechanisms in this important pest and provide promising potential for enhancing insect capture of pheromone traps.

Linalool fumigation improves mating competitiveness of males for population suppression of the global fruit pest Cydia pomonella

BACKGROUND

The implementation of sterile insect technique (SIT) has proven effective in the area-wide suppression of several significant agricultural and sanitary pests by using traditional cobalt-60 (60Co-γ) as a radiation source. Recently, X-ray has been validated as a feasible alternative to 60Co-γ radiation sources. Nonetheless, higher doses of X-ray irradiation led to insect sterility but diminish mating competitiveness, thereby impacting the effectiveness of SIT applications.

RESULTS

In this study, we assessed the impact of various X-ray irradiation doses (ranging from 0 to 366 Gy) on the fecundity, fertility, and mating competitiveness of Cydia pomonella, a globally invasive fruit pest. Results demonstrated that the sterility rate of irradiated males increased with dose up to 200 Gy, then stabilized. Exposure to 200 Gy reduced male mating competitiveness, with competitiveness index (CI) values of 0.17 in the laboratory and 0.096 in the orchard. This decline is likely linked to the decreased expression of genes associated with sex pheromones recognition, such as CpomOR3a, CpomOR3b, and CpomOR5, post-irradiation. Fumigation of linalool at varying concentrations (70, 83, and 96 μL/m3) enhanced mating competitiveness of males, particularly at moderate levels, possibly by restoring pheromones recognition. Implementation of repeated releases of sterilized males on a pilot scale led to a notable reduction in the population of C. pomonella in the field.

CONCLUSION

These findings indicate that fumigation with plant volatiles has the potential to mitigate male sterility induced by X-ray irradiation, offering a promising approach to enhance the efficacy of SIT applications for the control of C. pomonella. © 2024 Society of Chemical Industry.

Where do all the pests go? Understanding the genomic mechanisms of crop pest dynamics during the off-season

Agroecosystems provide abundant resources to insects. However, throughout the off-season, insects must overcome resource shortages and adverse climates to survive. This off-season persistence affects pest infestations in subsequent crops or seasons. Key pest species employ diapause, migration, and local-scale dispersal to persist during the off-season. Genomic approaches have advanced our understanding of these survival mechanisms. Clock genes regulate the circadian rhythm and interact with neuropeptides and downstream pathways, such as insulin-like peptides and hormonal factors-like ecdysteroids and juvenile hormones that regulate diapause. Migrant insects must manage processes like energy metabolism, oogenesis, and flight orientation. Local-scale dispersal requires mechanisms to locate, select, and exploit the most suitable host and habitat for survival and reproduction during the off-season. Here, we present advances in genomic research on pest survival during the off-season, focusing on diapause, migration, and local-scale dispersion. Understanding these phenomena is crucial for developing and optimizing effective integrated pest management programs.

The expansion and loss of specific olfactory genes in relatives of parasitic lice, the stored-product psocids (Psocodea: Liposcelididae)

BACKGROUND

Booklice, belonging to the genus Liposcelis (Psocodea: Liposcelididae), commonly known as psocids, infest a wide range of stored products and are implicated in the transmission of harmful microorganisms such as fungi and bacteria. The olfactory system is critical for insect feeding and reproduction. Elucidating the molecular mechanisms of the olfactory system in booklice is crucial for developing effective control strategies. In this study, we aim to bridge this knowledge gap by leveraging the transcriptome and genome data from five Liposcelis species.

RESULT

Using HMMER method and manual annotation, we have identified common gene families associated with olfactory processes, including odorant binding proteins (OBPs), chemosensory proteins (CSPs), odorant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs). Specifically, we identified 94, 118, 26, 47, and 34 olfactory-related genes in L. bostrychophila, L. tricolor, L. entomophila, L. decolor, and L. yangi, respectively. Comparison of quantities revealed that the number of ORs and IRs in the genome is significantly higher than those identified in the transcriptome. This discrepancy may be due to the specific expression of these genes in certain tissues or their lack of expression during the experimental stage. Simultaneously, analysis of gene expression profiles across different developmental stages revealed varying periods of peak expression for olfactory-related genes. These results suggest that the identification of olfactory-related genes in booklice on a genome-wide scale is more feasible and reliable than using a transcriptome-based approach. Additionally, compared to parasitic lice, booklice possess significantly more olfactory-related genes. This increase may be due to the inability of parasitic lice to survive without a host, whereas booklice have a wide range of feeding habits and live in complex and variable environments. Furthermore, we observed that the IR gene family in L. tricolor has undergone a certain degree of amplification, which may facilitate its adaptation to diverse environmental conditions.

CONCLUSIONS

We identified olfactory-related genes of five Liposcelis species for the first time, providing valuable insights for future functional investigations into olfactory genes associated with pheromone and odorant recognition. These discoveries present promising targets for effectively managing psocid pests.