The expression of three opsin genes and phototactic behavior of Spodoptera exigua (Lepidoptera: Noctuidae): Evidence for visual function of opsin in phototaxis

Opsin mutants alter host plant selection by color vision in the nocturnal invasive pest Tuta absoluta

In insects, vision is crucial in finding host plants, but its role in nocturnal insects is largely unknown. Vision involves responses to specific spectra of photon wavelengths and opsins plays an important role in this process. Long-wavelength sensitive opsin (LW opsin) and blue-sensitive opsin (BL opsin) are main visual opsin proteins and play important in behavior regulation.We used CRISPR/Cas9 technology to mutate the long-wavelength-sensitive and blue wavelength-sensitive genes and explored the role of vision in the nocturnal invasive pest Tuta absoluta. Light wave experiments revealed that LW2(-/-) and BL(-/-) mutants showed abnormal wavelength tropism. Both LW2 and BL mutations affected the preference of T. absoluta for the green environment. Mutations in LW2 and BL are necessary to inhibit visual attraction. The elimination of LW2 and BL affected the preference of leaf moths for green plants, and mutations in both induced a preference in moths for white plants. Behavioral changes resulting from LW2(-/-) and BL(-/-) mutants were not affected by sense of smell, further supporting the regulatory role of vision in insect behavior. To the best of our knowledge, this is the first study to reveal that vision, not smell, plays an important role in the host-seeking behavior of nocturnal insects at night, of which LW2 and BL opsins are key regulatory factors. These study findings will drive the development of the "vision-ecology" theory.

Knockout of lws1 in zebrafish (Danio rerio) reveals its role in regulating feeding and vision-guided behavior

Long-wave sensitive (LWS) is a G protein-coupled receptor expressed in the retina, and zebrafish is a better model organism for studying vision, but the role of LWS1 in vision-guided behavior of larvae fish has rarely been reported. In this study, we found that zebrafish lws1 and lws2 are tandemly replicated genes, both with six exons, with lws1 being more evolutionarily conserved. The presence of Y277F in the amino acid sequence of lws2 may have contributed to the shift of λmax to green light. We established a lws1 knockout zebrafish model using CRISPR/Cas9 technology. Lws1-/- larvae showed significantly higher levels of feeding and appetite gene (agrp) expression than WT, and significantly lower levels of anorexia gene (pomc, cart) expression. In addition, green light gene compensation was observed in lws1-/- larvae with significantly increased expression levels of rh2-1. The light-dark movement test showed that lws1-/- larvae were more active under light-dark transitions or vibrational stimuli, and the expression of phototransduction-related genes was significantly up-regulated. This study reveals the important role of lws1 gene in the regulation of vision-guided behavior in larvae.

Identification, expression analysis, and functional verification of three opsin genes related to the phototactic behaviour of Ostrinia furnacalis

Ostrinia furnacalis is a disreputable herbivorous pest that poses a serious threat to corn crops. Phototaxis in nocturnal moths plays a crucial role in pest prediction and control. Insect opsins are the main component of insect visual system. However, the inherent molecular relationship between phototactic behaviour and vision of insects remains a mystery. Herein, three opsin genes were identified and cloned from O. furnacalis (OfLW, OfBL, and OfUV). Bioinformatics analysis revealed that all opsin genes had visual pigment (opsin) retinal binding sites and seven transmembrane domains. Opsin genes were distributed across different developmental stages and tissues, with the highest expression in adults and compound eyes. The photoperiod-induced assay elucidated that the expression of three opsin genes in females were higher during daytime, while their expression in males tended to increase at night. Under the sustained darkness, the expression of opsin genes increased circularly, although the increasing amplitude in males was lower when compared with females. Furthermore, the expression of OfLW, OfBL, and OfUV was upregulated under green, blue, and ultraviolet light, respectively. The results of RNA interference showed that the knockout of opsin genes decreased the phototaxis efficiency of female and male moths to green, blue, and ultraviolet light. Our results reveal that opsin genes are involved in the phototactic behaviour of moths, providing a potential target gene for pest control and a basis for further investigation on the phototactic behaviour of Lepidoptera insects.

Unraveling the G protein-coupled receptor superfamily in aphids: Contractions and duplications linked to phloem feeding

The G Protein-Coupled Receptor (GPCR) superfamily is the largest and most diverse transmembrane receptor family, playing crucial roles in regulating various physiological processes. As one of the most destructive pests, aphids have been subject to previous studies, which revealed fewer GPCR superfamily members in Acyrthosiphon pisum and Aphis gossypii and the loss of multiple neuropeptide GPCRs. To elucidate the contraction patterns and evolutionary features of the aphid GPCR superfamily, we identified 97, 105, and 95 GPCR genes in Rhopalosiphum maidis, A. pisum, and A. gossypii, respectively. Comparative analysis and phylogenetic investigations with other hemipteran insects revealed a contracted GPCR superfamily in aphids. This contraction mainly occurred in biogenic amine receptors, GABA-B-R, and fz families, and several neuropeptide receptors such as ACPR, CrzR, and PTHR were completely lost. This phenomenon may be related to the parasitic nature of aphids. Additionally, several GPCRs associated with aphid feeding and water balance underwent duplication, including Lkr, NPFR, CCHa1-R, and DH-R, Type A LGRs, but the SK/CCKLR that inhibits feeding was completely lost, indicating changes in feeding genes that underpin the aphid's prolonged phloem feeding behavior. Furthermore, we observed fine-tuning in opsins, with reduced long-wavelength opsins and additional duplications of short-wavelength opsin, likely associated with daytime activity. Lastly, we found variations in the number of mthl genes in aphids. In conclusion, our investigation sheds light on the GPCR superfamily in aphids, revealing its association with diet lifestyle and laying the foundation for understanding and developing control strategies for the aphid GPCR superfamily.

Expression and function of opsin genes associated with phototaxis in Zeugodacus cucurbitae Coquillett (Diptera: Tephritidae)

BACKGROUND

Zeugodacus cucuribitae is a major agricultural pest that causes significant damage to varieties of plants. Vision plays a critical role in phototactic behavior of herbivorous insects. However, the effect of opsin on the phototactic behavior in Z. cucuribitae remains unknown. The aim of this research is to explore the key opsin genes that associate with phototaxis behavior of Z. cucurbitae.

RESULTS

Five opsin genes were identified and their expression patterns were analyzed. The relative expression levels of ZcRh1, ZcRh4 and ZcRh6 were highest in 4-day-old larvae, ZcRh2 and ZcRh3 were highest in 3rd-instar larvae and 5-day-old pupae, respectively. Furthermore, five opsin genes had the highest expression levels in compound eyes, followed by the antennae and head, whereas the lower occurred in other tissues. The expression of the long-wavelength-sensitive (LW) opsins first decreased and then increased under green light exposure. In contrast, the expression of ultraviolet-sensitive (UV) opsins first increased and then decreased with the duration of UV exposure. Silencing of LW opsin (dsZcRh1, dsZcRh2, and dsZcRh6) and UV opsin (dsZcRh3 and dsZcRh4) reduced the phototactic efficiency of Z. cucurbitae to green light by 52.27%, 60.72%, and 67.89%, and to UV light by 68.59% and 61.73%, respectively.

CONCLUSION

The results indicate that RNAi inhibited the expression of opsin, thereby inhibiting the phototaxis of Z. cucurbitae. This result provides theoretical support for the physical control of Z. cucurbitae and lays the foundation for further exploration of the mechanism of insect phototaxis. © 2023 Society of Chemical Industry.

Effect of monochromatic light on light adaptation and opsin expression in Ectropis grisescens

Light has a substantial effect on the behaviour and physiology of nocturnal moths. Ectropis grisescens is a major nocturnal tea pest in China, and light traps are commonly used to control geometrid moths because of their positive phototaxis. However, some moths gather around light traps and enter the light adaptation state, which decreases the efficacy of light traps in controlling this pest. We identified opsin genes and the spectral sensitivities of the photoreceptors of E. grisescens moths. We also determined the effects of several monochromatic lights on opsin gene expression and light adaptation. We detected three types of opsin genes and six spectral sensitive peaks (at 370, 390, 480, 530, 550, and 580 nm). We also observed significant changes in the diurnal rhythm of opsin gene expression under different light conditions. When active males were suddenly exposed to different monochromatic lights, they quickly entered the light adaptation state, and the adaptation time was negatively correlated with the light intensity. Males were most sensitive to 390 nm wavelengths, followed by 544 nm, 457 nm, and 593 nm. Red light (627 nm) did not affect the activity of E. grisescens males but had detectable physiological effects.

Long-wave opsin involved in body color plastic development in Nilaparvata lugens

BACKGROUND

As one of the components of visual photopigments in photoreceptor cells, opsin exhibits different spectral peaks and plays crucial roles in visual function. Besides, it is discovered to evolve other functions despite color vision. However, research on its unconventional function is limited nowadays. With the increase in genome database numbers, various numbers and types of opsins have been identified in insects due to gene duplications or losses. The Nilaparvata lugens (Hemiptera) is a rice pest known for its long-distance migration capability. In this study, opsins were identified in N. lugens and characterized by genome and transcriptome analyses. Meanwhile, RNA interference (RNAi) was carried out to investigate the functions of opsins, and then the Illumina Novaseq 6000 platform-based transcriptome sequencing was performed to reveal gene expression patterns.

RESULTS

Four opsins belonging to G protein-coupled receptors were identified in the N. lugens genome, including one long-sensitive opsin (Nllw) together with two ultraviolet-sensitive opsins (NlUV1/2) and an additional new opsin with hypothesized UV peak sensitivity (NlUV3-like). A tandem array of NlUV1/2 on the chromosome suggested the presence of a gene duplication event, with similar exons distribution. Moreover, as revealed by spatiotemporal expression, the four opsins were highly expressed in eyes with age-different expression levels. Besides, RNAi targeting each of the four opsins did not significantly affect the survival of N. lugens in phytotron, but the silencing of Nllw resulted in the melanization of body color. Further transcriptome analysis revealed that silencing of Nllw resulted in up-regulation of a tyrosine hydroxylase gene (NlTH) and down-regulation of an arylalkylamine-N-acetyltransferases gene (NlaaNAT) in N. lugens, demonstrating that Nllw is involved in body color plastic development via the tyrosine-mediated melanism pathway.

CONCLUSIONS

This study provides the first evidence in a Hemipteran insect that an opsin (Nllw) takes part in the regulation of cuticle melanization, confirming a cross-talk between the gene pathways underlying the visual system and the morphological differentiation in insects.

Research on Photoinduction-Based Technology for Trapping Asian Longhorned Beetle (Anoplophora glabripennis (Motschulsky, 1853) (Coleoptera: Cerambycidae)

Light traps play a crucial role in monitoring pest populations. However, the phototactic behavior of adult Asian longhorned beetle (ALB) remains enigmatic. To provide a theoretical foundation to select the suitable light emitting diode (LED)-based light sources used for monitoring ALB, we compared the effect of exposure time on the phototactic response rates of adults at wavelengths of 365 nm, 420 nm, 435 nm, and 515 nm, and found that the phototactic rate increased gradually when the exposure time was prolonged, but there was no significant difference between different exposure times. We evaluated the effect of diel rhythm and found the highest phototactic rate at night (0:00-2:00) under 420 nm and 435 nm illumination (74-82%). Finally, we determined the phototactic behavioral response of adults to 14 different wavelengths and found both females and males showed a preference for violet wavelengths (420 nm and 435 nm). Furthermore, the effect of the light intensity experiments showed that there were no significant differences in the trapping rate between different light intensities at 120 min exposure time. Our findings demonstrate that ALB is a positively phototactic insect, showing that 420 nm and 435 nm are the most suitable wavelengths for attracting adults.

Blue light stimulates light stress and phototactic behavior when received in the brain of Diaphorina citri

Blue light with a wavelength of 400-470 nm is the composition of the visible light. However, in recent years, blue light contributed the most significance to light pollution due to the artificial light at night. Previously, we have demonstrated that the Asian citrus psyllid (ACP), Diaphorina citri, an important pest in citrus production, has significant positive phototaxis with a light-emitting diode light of 400 nm. In this study, ACP with positive phototactic behavior to 400 nm light (PH) and non-phototactic behavior to 400 nm light (NP) were collected, individually. Transcriptome dynamics of head tissues of PH and NP groups were captured by using RNA-sequencing technology, respectively. Forty-three to 46 million clean reads with high-quality values were obtained, and 1773 differential expressed genes (DEGs) were detected. Compared with the NP group, there were 841 up-regulated DEGs and 932 down-regulated DEGs in the PH group. Eight pathways were significantly enriched in the PH group in the KEGG database, while 43 up-regulated pathways and 25 down-regulated pathways were significantly enriched in the PH group in the GO database. The DGE approach was reliable validated by real time quantitative PCR. Results indicated that the blue light acted as an abiotic stress causing physiological and biochemical responses such as oxidative stress, protein denaturation, inflammation and tumor development in ACPs. Additionally, the light was absorbed by photoreceptors of ACPs, and converted into electrical signal to regulate neuromodulation. This study provides basic information for understanding the molecular mechanisms of ACP in response to blue light and provides a reference for further studies to elucidate phototactic behavior.

An LW-Opsin Mutation Changes the Gene Expression of the Phototransduction Pathway: A Cryptochrome1 Mutation Enhances the Phototaxis of Male Plutella xylostella (Lepidoptera: Plutellidae)

Plutella xylostella is a typical phototactic pest. LW-opsin contributes to the phototaxis of P. xylostella, but the expression changes of other genes in the phototransduction pathway caused by the mutation of LW-opsin remain unknown. In the study, the head transcriptomes of male G88 and LW-opsin mutants were compared. A GO-function annotation showed that DEGs mainly belonged to the categories of molecular functions, biological processes, and cell composition. Additionally, a KEGG-pathway analysis suggested that DEGs were significantly enriched in some classical pathways, such as the phototransduction-fly and vitamin digestion and absorption pathways. The mRNA expressions of genes in the phototransduction-fly pathway, such as Gq, ninaC, and rdgC were significantly up-regulated, and trp, trpl, inaD, cry1, ninaA and arr1 were significantly down-regulated. The expression trends of nine DEGs in the phototransduction pathway confirmed by a RT-qPCR were consistent with transcriptomic data. In addition, the influence of a cry1 mutation on the phototaxis of P. xylostella was examined, and the results showed that the male cry1 mutant exhibited higher phototactic rates to UV and blue lights than the male G88. Our results indicated that the LW-opsin mutation changed the expression of genes in the phototransduction pathway, and the mutation of cry1 enhanced the phototaxis of a P. xylostella male, providing a basis for further investigation on the phototransduction pathway in P. xylostella.

Comparison of Phototactic Behavior between Two Migratory Pests, Helicoverpa armigera and Spodoptera frugiperda

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is an important migratory pest, causing great losses to agricultural production. Light trapping is a pesticide-free method for pest control and is influenced by many factors, especially wavelength and light intensity. In this study, a series of phototactic behavioral assays were carried out and the physical parameters were included to identify phototactic responses of S. frugiperda, with Helicoverpa armigera as control. It was found that S. frugiperda showed the highest average phototactic rate to blue light among five different LED lights. The phototactic rates of the two moths increased gradually with light intensity and were not obviously influenced by sex. In addition, the phototactic rate of S. frugiperda was significantly lower under a low light intensity of UV light than that of H. armigera, further confirmed by the indoor simulation experiment and EC50. According to the obtained parameters, the trapping distance of S. frugiperda to blue light was smaller than that of H. armigera to UV light. Therefore, we summarized a proposal of using blue light for light traps to control S. frugiperda, with a maximum distance of no more than 108 m. These results provide an experimental and theoretical basis for improving light-trapping techniques for managing S. frugiperda.

Identification and characterization of G protein-coupled receptors in Spodoptera frugiperda (Insecta: Lepidoptera)

Spodoptera frugiperda (Insecta: Lepidoptera) is a destructive invasive pest feeding on various plants and causing serious damage to several economically-important crops. G protein-coupled receptors (GPCRs) are cellular receptors that coordinate diverse signaling processes, associated with many physiological processes and disease states. However, less information about GPCRs had been reported in S. frugiperda, limiting the recognition of signaling system and in-depth studies of this pest. Here, a total of 167 GPCRs were identified in S. frugiperda. Compared with other insects, the GPCRs of S. frugiperda were significantly expanded. A large of tandem duplication and segmental duplication events were observed, which may be the key factor to increase the size of GPCR family. In detail, these expansion events mainly concentrate on biogenic amine receptors, neuropeptide and protein hormone receptors, which may be involved in feeding, reproduction, life span, and tolerance of S. frugiperda. Additionally, 17 Mth/Mthl members were identified in S. frugiperda, which may be similar to the evolutionary pattern of 16 Mth/Mthl members in Drosophila. Moreover, the expression patterns across different developmental stages of all GPCR genes were also analyzed. Among these, most of the GPCR genes are poorly expressed in S. frugiperda and some highly expressed GPCR genes help S. frugiperda adapt to the environment better, such as Rh6 and AkhR. In this study, all GPCRs in S. frugiperda were identified for the first time, which provided a basis for further revealing the role of these receptors in the physiological and behavioral regulation of this pest.

The genome of the black cutworm Agrotis ipsilon

The black cutworm (BCW), Agrotis ipsilon, is a worldwide polyphagous and underground pest that causes a high level of economic loss to a wide range of crops through the damage of roots. This species performs non-directed migration throughout East and Southeast Asia seasonally. Lack of a genome information has limited further studies on its unique biology and the development of novel management approaches. In this study, we present a 476 Mb de novo assembly of BCW, along with a consensus gene set of 14,801 protein-coding gene models. Quality controls show that both genome assembly and annotations are high-quality and mostly complete. We focus manual annotation and comparative genomics on gene families that related to the unique attributes of this species, such as nocturnality, long-distance migration, and host adaptation. We find that the BCW genome encodes a similar gene repertoire in various migration-related gene families to the diural migratory butterfly Danaus plexiipus, with additional copies of long wavelength opsin and two eye development-related genes. On the other hand, we find that the genomes of BCW and many other polyphagous lepidopterans encode many more gustatory receptor genes, particularly the lineage-specific expanded bitter receptor genes, than the mono- or oligo-phagous species, suggesting a common role of gustatory receptors (GRs) expansion in host range expansion. The availability of a BCW genome provides valuable resources to study the molecular mechanisms of non-directed migration in lepidopteran pests and to develop novel strategies to control migratory nocturnal pests.

CRISPR/Cas9-mediated knockout of LW-opsin reduces the efficiency of phototaxis in the diamondback moth Plutella xylostella

BACKGROUND

Opsins are crucial for animal vision. The identity and function of opsins in Plutella xylostella remain unknown. The aim of the research is to confirm which opsin gene(s) contribute to phototaxis of P. xylostella.

RESULTS

LW-opsin, BL-opsin and UV-opsin, were identified in the P. xylostella genome. LW-opsin was more highly expressed than the other two opsin genes, and all three genes were specifically expressed in the head. Three P. xylostella strains, LW-13 with a 13-bp deletion in LW-opsin, BL + 2 with a 2-bp insertion in BL-opsin, and UV-29 with a 5-bp insertion and a 34-bp deletion in UV-opsin, were established from the strain G88 using the CRISPR/Cas9 system. Among the three opsin-knockout strains, only male and female LW-13 exhibited weaker phototaxis to lights of different wavelengths and white light than G88 at 2.5 lx due to defective locomotion, and LW-13 was defective to sense white, green and infrared lights. The locomotion of LW-13 was reduced compared with G88 at 2.5, 10, 20, 60, 80, 100, and 200 lx under the green light, but the locomotion of LW-13 female was recovered at 80, 100 and 200 lx. The defective phototaxis to the green light of male LW-13 was not affected by light intensity, while the defective phototaxis to the green light of female LW-13 was recovered at 10, 20, 60, 80, 100, and 200 lx.

CONCLUSION

LW-opsin is involved in light sensing and locomotion of P. xylostella, providing a potential target gene for controlling the pest. © 2021 Society of Chemical Industry.

The evolution of opsin genes in five species of mirid bugs: duplication of long-wavelength opsins and loss of blue-sensitive opsins

BACKGROUND

Color vision and phototactic behavior based on opsins are important for the fitness of insects because of their roles in foraging and mate choice. Related topics, including the duplication and loss of opsin genes, have been well investigated in insect orders such as Coleoptera, Lepidoptera, Hymenoptera, Odonata and Orthoptera, and the findings have been used to develop pest management strategies involving light trapping. Mirid bugs of Hemiptera, which are pests that cause heavy economic losses, show capacity for color discrimination and phototaxis. However, the opsins in mirid bugs remain uncharacterized. Herein, we examined five species to investigate the evolution of opsins in the family Miridae.

RESULTS

Using RNA-seq, we identified several contigs showing high identity with opsins, including four contigs in Apolygus lucorum and three contigs each in Adelphocoris suturalis, Adelphocoris fasciaticollis, Adelphocoris lineolatus and Nesidiocoris tenuis. Phylogenetic analyses indicated that one of these genes clustered with ultraviolet-sensitive (UV) opsins and that the others clustered with long-wavelength (LW) opsins, suggesting that duplication of LW opsins and loss of blue light-sensitive (B) opsins occurred in mirid bugs. The existence of introns in the LW opsins of mirid bugs suggested that the duplication events were DNA based. Both LW1 and LW2 opsins of mirid bugs were found to be under strong purifying selection. The LW1 opsins were significantly more highly expressed than the LW2 and UV opsins.

CONCLUSIONS

We identified the opsins of mirid bugs using five selected mirid species as a representative sample. Phylogenetic analyses clustered one of the genes with UV opsins and the others with LW opsins, suggesting the occurrence of LW opsin duplication and B opsin loss during the evolution of mirid bugs. Intron detection suggested that the identified duplication event was DNA based. The evidence of strong purifying selection and the relatively high expression levels suggested that these opsins exhibit fundamental functions in mirid bugs.

Identification and Expression Analysis of G Protein-Coupled Receptors in the Miridae Insect Apolygus lucorum

G protein-coupled receptors (GPCRs) are the largest and most versatile family of transmembrane receptors in the cell and they play a vital role in the regulation of multiple physiological processes. The family Miridae (Hemiptera: Heteroptera) is one of the most diverse families of insects. Until now, information on GPCRs has been lacking in Miridae. Apolygus lucorum, a representative species of the Miridae, is an omnivorous pest that occurs worldwide and is notorious for causing serious damage to various crops and substantial economic losses. By searching the genome, 133 GPCRs were identified in A. lucorum. Compared with other model insects, we have observed GPCR genes to be remarkably expanded in A. lucorum, especially focusing on biogenic amine receptors and neuropeptide receptors. Among these, there is a novel large clade duplicated from known FMRFamide receptors (FMRFaRs). Moreover, the temporal and spatial expression profiles of the 133 genes across developmental stages were determined by transcriptome analysis. Most GPCR genes showed a low expression level in the whole organism of A. lucorum. However, there were a few highly expressed GPCR genes. The highly expressed LW opsins in the head probably relate to nocturning of A. lucorum, and the expression of Cirl at different times and in different tissues indicated it may be involved in growth and development of A. lucorum. We also found C2 leucine-rich repeat-containing GPCRs (LGRs) were mainly distributed in Hemiptera and Phthiraptera among insects. Our study was the first investigation on GPCRs in A. lucorum and it provided a molecular target for the regulation and control of Miridae pests.

The neuroecology of insect-plant interactions: the importance of physiological state and sensory integration

Natural behaviorally important stimuli are combinations of cues that are integrated by the nervous system to elicit behavior. Nonetheless, these cues dynamically change in time and space. In turn, the animal's internal state can cause changes in the encoding and representation of these stimuli. Despite abundant behavioral examples, links between the neural bases of sensory integration and the internal state-dependency of these responses remains an active study area. Recent studies in different insect models have provided new insights into how plasticity and the insect's internal state may influence odor representation. These studies show that complex stimuli are represented in unique percepts that are different from their sensory channels and that the representations may be modulated by physiological state.

Impact of artificial light intensity on nocturnal insect diversity in urban and rural areas of the Asir province, Saudi Arabia

Continuous urban developments have resulted in increased demand for street furniture, one of which is street light columns. Artificial light at night (ALAN) pose significant impacts on insect diversity in urban and rural areas. The ALAN is a significant driver of decline in insect diversity. This study evaluated the impact of light intensity and sky quality at night on insect diversity in rural and urban areas of the Asir province, Saudi Arabia. Insect traps were installed in both areas during night. Light intensity of nearby road lamps was measured using light meter, while sky quality was measured using sky quality meter. Rural areas exhibited low light intensity (10.33 flux/f.candle) and good sky quality (18.80 magnitude/arcsec2). Urban areas exhibited intense light (89.33 flux/f.candle) and poor sky quality (15.49 magnitude/arcsec2). Higher insect diversity was recorded for rural areas where insects belonging to seven orders (i.e., Diptera, Lepidoptera, Hemiptera, Hymenoptera, Coleoptera, Neuroptera, and Dermaptera) were collected. However, insects of four orders (i.e., Diptera, Lepidoptera, Hemiptera, and Neuroptera) were found in urban areas indicating low diversity. Lepidopteran insects were frequently recorded from rural areas indicating they are attracted to artificial light. It is concluded that excessive ALAN and poor sky quality at night disrupt insect biodiversity. Therefore, ALAN and sky quality must be considered responsible for decline in insect biodiversity along with other known factors.

The expression and function of opsin genes related to the phototactic behavior of Asian citrus psyllid

BACKGROUND

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), is a prominent pest of citrus because it transmits Candidatus Liberibacter asiaticus associated with huanglongbing. Phototactic behavior ubiquitously exists in insects and plays essential roles in host-searching and mate-searching in ACP. However, its mechanism has remained unclear to date. In this paper, molecular assays were performed to understand the relation between opsins and the phototactic behavior of ACP.

RESULTS

We cloned five opsin genes and analyzed their expression patterns. The main three opsin genes (Dc-UV, Dc-BW and Dc-LW) displayed high expression levels in daytime, and the expression levels of the other two opsin genes (Dc-UV-like and Dc-arthropsin) increased during nighttime. In constant darkness, the expression patterns and levels of opsin genes of ACP were altered. Under starvation, the expression levels of the main three opsins were reduced (53.89-84.10%). In contrast, the expression levels in females increased (27.55-60.58%). Feeding of double-stranded RNA (Dc-UV, Dc-LW or Dc-BW) have reduced the phototactic efficiency of ACP to ultraviolet light (44.79%), green light (54.81%) and blue light (43.00%), respectively.

CONCLUSION

The results suggest that the expression levels and patterns of opsins of ACP were influenced by photoperiod and the physiological status of ACP. Our research indicates that opsins play crucial roles in phototactic behavior in ACP. © 2019 Society of Chemical Industry.

Identification and Expression Patterns of Opsin Genes in a Forest Insect, Dendrolimus punctatus

Dendrolimus punctatus walker (Lepidoptera: Lasiocampidae) is the most serious coniferous forest defoliator in China. This species has long life history, and shows different activity rhythms and light response behaviors at larval and adult stages. Insect vision system play important roles for survival and reproduction, and disturbance of photoreception may help us to control this pest. However, we know little about the visual system of D. punctatus. As opsins are the most important genes determining photoreceptor sensitivity of insects, we identified opsins of D. punctatus and analyzed their expression patterns at different development stages in this study. Four opsin genes were identified based on our transcriptome data. Phylogenetic analysis showed that there are three classical ultraviolet (UV), blue, and long-wavelength (LW) light sensitive opsin genes, and another UV-like opsin as homolog of a circadian photoreceptor, Rh7, in Drosophila melanogaster and other insects. Expression analysis indicated that the UV and UV-like opsins expression levels only fluctuated slightly during whole life stages of D. punctatus, while Blue and LW opsins were up-regulated many times at adult stage. Interestingly, the ratio of UV-opsin was much higher in eggs and larvae stages, and lower in pupa and adult stages; reversely, LW-opsin showed extremely high relative ratio in pupa and adult stages. High expression level of LW opsin in the adult stage may correlate to the nocturnal lifestyles of this species at adult stage, and different ratios of UV and LW opsins in larval and adult stages may help to explain the different visual ecologies of these two development stages of D. punctatus. This work is the foundation for further research of opsin functions and vision mechanisms of D. punctatus.

Progress in the use of genetic methods to study insect behavior outside Drosophila

In the span of a decade we have seen a rapid progress in the application of genetic tools and genome editing approaches in 'non-model' insects. It is now possible to target sensory receptor genes and neurons, explore their functional roles and manipulate behavioral responses in these insects. In this review, we focus on the latest examples from Diptera, Lepidoptera and Hymenoptera of how applications of genetic tools advanced our understanding of diverse behavioral phenomena. We further discuss genetic methods that could be applied to study insect behavior in the future.

Advances in insect phototaxis and application to pest management: a review

Many insects, especially nocturnal insects, exhibit positive phototaxis to artificial lights. Light traps are currently used to monitor and manage insect pest populations, and play a crucial role in physical pest control. Efficient use of light traps to attract target insect pests is an important topic in the application of integrated pest management (IPM). Phototactic responses of insects vary among species, light characteristics and the physiological status of the insects. In addition, light can cause several biological responses, including biochemical, physiological, molecular and fitness changes in insects. In this review, we discuss several hypotheses on insect phototaxis, factors affecting insect phototaxis, insect-sensitive wavelengths, biological responses of insects to light, and countermeasures for conserving beneficial insects and increasing the effect of trapping. In addition, we provide information on the different sensitivities to wavelengths causing positive phototactic behavior in > 70 insect pest and beneficial insect species. The use of advanced light traps equipped with superior light sources, such as light-emitting diodes (LEDs), will make physical pest control in IPM more efficient. © 2019 Society of Chemical Industry.