Litura Populations Research Articles

The impact of lethal and sub-lethal exposure of emamectin benzoate on populations of Spodoptera litura (Lepidoptera: Noctuidae) under laboratory conditions

Emamectin benzoate is an avermectin bio-insecticide commonly used for managing several insect pests including Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae), a major polyphagous pest of many cultivated crops. The current study was conducted to evaluate the effects of emamectin benzoate on the fitness of S. litura populations exhibiting differential susceptibility to insecticide. The selection process and all the bioassays were carried out using 6-day-old 2nd instar larvae of S. litura. A field-collected population of S. litura was divided into two groups: one selected with emamectin benzoate for eight generations (EB-Sel) and the other kept unexposed (Unsel-Lab) to insecticide in the laboratory. An increase in resistance ratio from 1.71-fold in the F1 generation to 22.54-fold in the F8 generation of the EB-Sel population was observed compared to the Unsel-Lab (F8) population. The EB-Sel and Unsel-Lab populations were treated with their respective lethal and sub-lethal concentrations which resulted in an extended development period, decreased larval survival, and adult emergence along with increased morphological abnormalities in adults. Significant reductions were observed in both male and female longevity, fecundity, egg hatching, net reproductive rate (R0), intrinsic rate of increase (rm), and finite rate of increase (λ) in EB-Sel and Unsel-Lab populations. Higher concentrations of the insecticide also reduced the relative fitness (Rf) of S. litura larvae, with maximum effect at LC50 of the EB-Sel population where the Rf value was 0.32 compared to the Unsel-Lab population. Both populations have been affected by emamectin benzoate exposure, however, the impact was more pronounced in the EB-Sel population indicating fitness costs. Our results suggested the fitness cost linked to emamectin benzoate resistance in S. litura which might favor managing insecticide resistance by reducing the frequency of resistant alleles by removing selection pressure. Consequently, our research provides significant insights to devise better pest management strategies for S. litura.

Biochemical Mechanism of Insecticide Resistance in <i>Spodoptera litura</i> (F) Populations from Uttarakhand

Spodoptera litura populations were collected from different lowland areas and doon valley situated in Uttarakhand and insecticide resistance effect was studied for indoxacarb 14.5% SC, chlorantraniliprole 18.5%SC, fipronil 5% SC, chlorpyriphos 50%+cypermethrin 5% EC and profenofos 40%+cypermethrin 4% EC, also the specific activity of carboxylesterase, acetyl choline esterase, mono-oxygenase and glutathione-s-transferase was studied for biochemical analysis of detoxification enzymes. The scale of infestation was measured and related to temperature and humidity. High infestation has been observed in areas with optimum temperature and humidity. Highest resistance in the study was found against profenofos 40%+chlorpyriphos 4% and fipronil 5%SC with LC50 243.63 µg/ml and 214.22 µg/ ml respectively. On biochemical analysis of detoxification enzymes, it was observed that the highest activity of all the enzymes was observed in Mota Haldu population. Hence, overproduction of detoxification enzymes was found to be responsible for insecticide resistance in S. litura populations studied.

Monitoring and characterization of field‐evolved resistance to diamide insecticides in Spodoptera litura collected from eastern China

AbstractSpodoptera litura is a notoriously destructive pest, which infests horticultural plants and economically important crops worldwide. Several generations of diamide insecticides have been used to combat S. litura throughout the world, causing various levels of resistance to this class of insecticides among wild S. litura populations. In this work, we monitored resistance to five diamide insecticides among 10 S. litura populations sampled from eastern China in 2022. In comparison with Lab‐S the susceptible strain, five of the tested populations displayed high susceptibility to three of the five diamide insecticides (cyantraniliprole, broflanilide and tetraniliprole). In contrast, there was significant resistance to the other two tested diamide insecticides, flubendiamide and chlorantraniliprole, in seven of the field‐collected populations. The Shanghai (SH) population showed high resistance to chlorantraniliprole (77.0‐fold), flubendiamide (25.5‐fold) and cyantraniliprole (27.8‐fold), respectively, than the strain of Lab‐S. Results of synergism tests in the SH population revealed that diethyl maleate (DEM) and piperonyl butoxide (PBO) greatly inhibited chlorantraniliprole resistance. The progeny of reciprocal crosses between the Lab‐S and SH populations presented dominance degrees of F1 progenies, suggesting that the chlorantraniliprole resistance was autosomal and incompletely recessive in SH. Above results of the current work offer useful knowledge for future formulation of field pest management strategies, allowing farmers to delay the development of resistance to diamide insecticides and thus promote sustainable management of S. litura.

Effect of insecticides on locomotory behaviour and enzyme activity of Spodoptera litura (Fabricius) populations from Punjab

Aim: The variations in locomotory behaviour and enzyme activity, i.e., acetylcholinesterase and general esterases of Spodoptera litura Fabricius larval populations collected from different regions of Punjab, i.e., Amritsar, Kapurthala and Ludhiana were investigated in the laboratory prior exposure to different insecticides. Methodology: The test larvae were exposed to sublethal doses of different insecticides via surface and food treatment. For locomotory behaviour, they were allowed to move on treated surface and their movements were recorded with an automated video tracking system, Ethovision while on other hand food treatment was opted for observing the influence on enzyme activity. Results: The pronounced variations were observed in the locomotor behaviour of S. litura upon surface exposure of different insecticides. The larva travelled more distance with higher speed and larger turn angle on insecticide-treated surfaces than the untreated ones, while on comparison of different larval populations, the Amritsar population larvae travelled less distance with low speed and maximum turnings. The decrease in acetylcholinesterase and general esterase activity was recorded in treated larvae than untreated ones. The influence of emamectin benzoate was recorded more on locomotion and enzyme activity of S. litura as compared to the remaining insecticides and the Amritsar population was least affected. Interpretation: The sublethal doses of insecticides influenced the overall behavioural physiology of S. litura and this biological parameter could be useful in designing the management strategies for S. litura. Key words: Acetylcholinesterase, Esterases, Insecticides, Locomotory behaviour, S. litura

Baseline Susceptibility, Cross-Resistance, and Sublethal Effects of Broflanilide, a Novel Meta-Diamide Pesticide, in Spodoptera litura

Spodoptera litura is a damaging and notorious insect pest of agricultural crops that has developed resistance to various insecticides. Broflanilide is a novel pesticide with a unique mode of action that displays high efficiency against lepidopterous larvae. We here determined the baseline susceptibility of a laboratory strain of S. litura to broflanilide and 10 other popular insecticides. Furthermore, we measured susceptibility and cross-resistance using three common insecticides in 11 field-collected S. litura populations. Broflanilide caused the highest toxicity among all tested insecticides, with the laboratory strain and all field-collected populations showing high susceptibility. Moreover, no cross-resistance was detected between broflanilide and the other tested insecticides. We subsequently evaluated the sublethal effects of broflanilide and found that treatment with the 25% lethal concentration (LC25) prolonged the development duration in the larvae, reduced the pupation rate and pupae weight, and decreased egg hatchability. Finally, the activities of three detoxifying enzymes were measured in S. litura after treatment with the LC25 dose. The results suggested that enhanced cytochrome P450 monooxygenase (P450) activity could be involved in broflanilide detoxification. Overall, these findings demonstrate the strong toxicity and significant sublethal effects of broflanilide in S. litura and suggest that increased P450 activity may be associated with broflanilide detoxification.

Effects of wild, local, and cultivated tobacco varieties on the performance of Spodoptera litura and its parasitoid Meteorus pulchricornis.

Plant domestication can alter plant and insect interactions and influence bottom-up and top-down effects. However, little is known about the effects of wild, local, and cultivated varieties of the same plant species in the same region on herbivores and their parasitoids. Here, six tobacco varieties were selected: wild Bishan and Badan tobaccos, local Liangqiao and Shuangguan sun-cured tobaccos, and cultivated Xiangyan 5 and Cunsanpi. We examined how wild, local, and cultivated tobacco types affect the tobacco cutworm herbivore Spodoptera litura and its parasitoid Meteorus pulchricornis. Levels of nicotine and trypsin protease inhibitor in leaves and the fitness of S. litura larvae varied significantly among the varieties. Wild tobacco had the highest levels of nicotine and trypsin protease inhibitor, which reduced the survival rate and prolonged the development period of S. litura. The tobacco types significantly influenced the life history parameters and host selection of M. pulchricornis. The cocoon weight, cocoon emergence rate, adult longevity, hind tibia length, and offspring fecundity of M. pulchricornis increased, whereas the development period decreased from wild to local to cultivated varieties. The parasitoids were more likely to select wild and local varieties than cultivated varieties. Domestication of tobacco resulted in reduced resistance to S. litura in cultivated tobacco. Wild tobacco varieties suppress S. litura populations, adversely affect M. pulchricornis, and may enhance bottom-up and top-down control of S. litura. © 2023 Society of Chemical Industry.

Resistance Level and Enzyme Activity of Spodoptera litura F. to Chlorpyrifos and Their Sensitivity to the Oil Formulation of Azadirachta indica Juss. and Cymbopogon nardus (L.) Rendl.

This study aimed to obtain resistance information of S. litura from Karangpawitan and Lembang districts (West Java, Indonesia) against chlorpyrifos insecticides (200 g/l) and their sensitivity to oil mixture of A . indica and C . nardus (1:1) using feeding and topical assay. The activity of acetylcholinesterase, esterase, and glutathione s-transferase from S. litura larvae in both populations were tested to determine their role in insect resistance. Results showed that S. litura population from Lembang had a higher level of resistance to chlorpyrifos compared to Karangpawitan. The sensitivity of the two S. litura populations had a relatively similar resistance ratio (RR) value of less than 1 to botanical insecticide. These indicated that resistant population could be controlled by a mixture of this botanicals insecticide. Enzyme activity test indicated that chlorpyrifos at a concentration of 0.26% could inhibit the acetylcholinesterase activity of insect population from Karangpawitan by 98.66% while those from Lembang, it was only 35.31%. Specific activity of esterase from Karangpawitan was 13.37 units/mg while Lembang population was 119.65 units/mg. The specific activity of the Glutathione S-Transferase (GST) of Karangpawitan population was 1140.82 units/mg while Lembang population was 793.73 units/mg. The high activity of the three enzymes could be responsible for resistance of S. litura larvae to chlorpyrifos.

Resistance in Spodoptera litura (F.) to Insecticides and Detoxification Enzymes

Standard leaf dip bioassay experiments were conducted to study the insecticide resistance in Spodoptera litura (F.) in soybean. Chlorantraniliprole was the most toxic while, cypermethrin and organophosphates (profenophos and triazophos) recorded least toxicity against S. litura populations. Field population of S. litura showed the highest resistance to cypermethrin with resistance ratios (RRs) ranging from 244 to 376. The field populations collected from three locations of Southern Rajasthan exhibited low resistance to newer insecticides, chlorantraniliprole and spinetoram with Lab-SS strain. All the enzyme activities were significantly higher in the whole larval extracts and midgut extracts of S. litura larvae when compared to the Lab-SS strain. Analysis of the carboxyl esterase enzyme in the native PAGE assay revealed that the electrophoretic profiles showed presence of different band regions (EST 1 to EST 7) with esterase activity in the field populations along with the laboratory susceptible strain. The susceptibility of three field populations to different group of insecticides along with the profile of detoxification enzymes indicate the need to formulate a region-specific insecticide resistance management (IRM).

Resistance Monitoring for Six Insecticides in Vegetable Field-Collected Populations of Spodoptera litura from China

The common cutworm, Spodoptera litura (Fabricius), is a notorious and damaging insect pest of horticultural crops in China, the management of which largely relies on chemical agents that are limited by the development of chemical resistance in target populations. As such, resistance monitoring of S. litura populations is a necessary part of management strategies of insecticide resistance. In the current work, we monitored resistance to six insecticides in field-collected populations of S. litura sampled from eleven provinces across China in 2021. The results show that S. litura populations developed significant resistance against chlorantraniliprole, cyantraniliprole, metaflumizone, and pyridalyl and low levels of resistance to chromafenozide. However, S. litura populations were susceptible or exhibited minimal resistance to tetraniliprole. Possible cross-resistances between chlorantraniliprole, cyantraniliprole, metaflumizone, pyridalyl, and chromafenozide were found by pairwise correlation, which also revealed that tetraniliprole lacked cross-resistance with all insecticides tested. Our results suggest suspending the use of chemical agents against which S. litura displayed significant field-evolved resistance, such as chlorantraniliprole, metaflumizone, and pyridalyl, in favor of pesticides against which S. litura was susceptible or exhibited minimal resistance, such as tetraniliprole and chromafenozide, which may help slow the development of insecticide resistance, and in which field management programs aimed at controlling S. litura in China would benefit from the integration of such survey-informed insecticide application strategies. Moreover, the baseline susceptibility confirmed for the six tested insecticides can contribute to design strategies of resistance management for S. litura.

Functional analysis of CYP6AE68, a cytochrome P450 gene associated with indoxacarb resistance in Spodoptera litura (Lepidoptera: Noctuidae)

Spodoptera litura (Fabricius) is a widely distributed, highly polyphagous pest that can cause severe damage to a variety of economically important crops. Various populations have developed resistance to different classes of insecticides. In this study, we report on two indoxacarb-resistant S. litura populations, namely Ind-R (resistance ratio = 18.37-fold) derived from an indoxacarb-susceptible (Ind-S) population and a population caught from a field (resistance ratio = 46.72-fold). A synergist experiment showed that piperonyl butoxide (PBO) combined with indoxacarb produced higher synergistic effects (synergist ratio = 5.29) in the Ind-R population as compared to Ind-S (synergist ratio = 3.08). Elevated enzyme activity of cytochrome P450 monooxygenases (P450s) was observed for Ind-R (2.15-fold) and the Field-caught population (4.03-fold) as compared to Ind-S, while only minor differences were noticed in the activities of esterases and glutathione S-transferases. Furthermore, expression levels of P450 genes of S. litura were determined by quantitative reverse transcription PCR to explore differences among the three populations. The results showed that the mRNA levels of CYP6AE68, a novel P450 gene belonging to the CYP6 family, were constitutively overexpressed in Ind-R (32.79-fold) and in the Field-caught population (68.11-fold). CYP6AE68 expression in S. litura was further analyzed for different developmental stages and in different tissues. Finally, we report that RNA interference-mediated silencing of CYP6AE68 increased the mortality of fourth-instar larvae exposed to indoxacarb at the LC50 dose level (increase by 33.89%, 29.44% and 22.78% for Ind-S, Ind-R and the Field-caught population, respectively). In conclusion, the findings of this study indicate that expression levels of CYP6AE68 in S. litura larvae are associated with indoxacarb resistance and that CYP6AE68 may play a significant role in detoxification of indoxacarb.

Population dynamics and forewarning models for prediction of population of tobacco leaf eating caterpillar, Spodoptera litura (Fab.) Under different sowing window and groundnut varieties

The correlation between weather parameter and population of tobacco leaf eating caterpillar, Spodoptera litura (Fab.) larva (mrl-1) on different groundnut varieties at different sowing windows and forewarning models for prediction of population of tobacco leaf eating caterpillar, Spodoptera litura (Fab.) during kharif season, 2017 and 2018. The experiment was laid out in split plot design with three replications. The treatment comprised of four varieties viz., V1: JL-501, V2: RHRG-6083 (Phule Unnati), V3: TAG-24 and V4: JL-776 (Phule Bharati) as main plot and four sowing windows viz., S1: 25rd MW (18th to 24th June), S2: 26th MW (25th June to 01st July), S­3: 27th MW (2nd to 8th July) and S4: 28th MW (09th to 15th July) as sub plot treatments. The correlation of weather parameters with incidence of Spodoptera litura showed that the population of Spodoptera litura was found to have significant and positive correlation with evening relative humidity whereas maximum temperature and rainfall showed negative correlation with seasonal incidence of Spodoptera litura. Prediction of Spodoptera litura populations in different sowing window based on regression equations (R2) 72 to 83 per cent validation based on different weather parameters for variety JL-501, (R2) 66 to 85 per cent validation based on different weather parameter for variety RHRG-6083, (R2) 71 to 87 per cent validation based on different weather parameter for variety TAG-24 and (R2) 69 to 84 per cent validation based on different weather parameter for variety JL-776 for the prediction of Spodoptera litura population.

Physiological changes in reproduction of Spodoptera litura (fabricius) on exposure to pyriproxyfen

Effects of sub-lethal dose of pyriproxyfen on the reproduction of second instar Spodoptera litura larvae as reported. At LC30 and LC50 concentrations, pyriproxyfen influenced the pre-oviposition period (4.7 d as compared to 1.4 d in control), oviposition period (2.2 d as compared to 5.2 d in control), post-oviposition period (2.1 d as compared to 1.0 d in control), fecundity (144.9 eggs as compared to 805.8 in control), egg size (0.012 mm3 as compared to 0.027 mm3 in control), reproductive effort (1.76 as compared to 21.76 in control), egg hatchability (76% as compared to 92% in control) and survival of newly emerged larvae (66% as compared to 92% in control). Ultrastructural studies revealed reduced dimensions (0.0004 ± 0.0002 mm3) of the ovarioles in the treated females. The observed effects of pyriproxyfen on the reproductive physiology of the insect suggest that it can be used as a control tool for the management of S. litura populations.

Lethal and Sublethal Effects of Three Microbial Biocontrol Agents on Spodoptera litura and Its Natural Predator Rhynocoris kumarii.

Entomopathogenic microbes such as Spodoptera litura nucleopolyhedrovirus (SpltNPV), Metarhizium anisopliae, and Pseudomonas fluorescens are biological agents used for the control of multiple arthropod pests. The objective of this study was to assess their effects on the biological parameters of Spodoptera litura (Lepidoptera: Noctuidae) larvae, and its natural reduviid predator Rhynocoris kumarii (Hemiptera: Reduviidae) under laboratory conditions. Results suggested that P. fluorescens reduced the food consumption index, relative growth rate, approximate digestibility, the efficiency of conversion of ingested food, and the efficiency of conversion of digested food of S. litura third instar larvae compared to prey infected with M. anisopliae and SpltNPV. Both SpltNPV and M. anisopliae caused similar mortality of S. litura life stages after 96 h of observation. To observe the effect of an infected prey diet on predator behavior, infected S. litura larvae were offered to the third, fourth, and fifth instar nymphs of R. kumarii, and their prey handling time, predation rate (number/day/predator), developmental period, and the survival rate was recorded. When the life stages of R. kumarii were offered entomopathogen-infected S. litura larvae, their predation rate was comparable to or higher than the untreated control. The juvenile predator, after feeding on P. fluorescens-infected S. litura larvae, had a significantly longer developmental period (2–4 days) compared to those fed on larvae infected with other microbial control agents. However, feeding on P. fluorescens alone did not affect the predator nymphal survival rate or the adult sex ratio. Although three entomopathogens had some degree of effect on the biological parameters of R. kumarii, the outcome of this study suggests that integration of reduviids with the tested entomopathogens are a compatible and potentially effective strategy for the management of S. litura populations. However promising, this combined strategy needs to be tested under field conditions to confirm the laboratory findings.

Molecular characterization of insecticide resistance in larval population of Spodoptera litura (Fab.)

Acetylcholinesterase gene activity in populations of Spodoptera litura (Fab.) collected from groundnut fields of different regions of Andhra Pradesh and Telangana was compared using a- and b-napthyl acetate as substrate for enzyme reaction. Among insecticide pre exposed S. litura population analyzed, nine out of ten populations showed elevated activities of acetylcholinesterase gene. A specific amplification product at 600 bp region indicating the presence of acetylcholinesterase gene in resistant strains of S. litura, whereas in susceptible base line strain of S. litura it was not found due to non amplification ofspecific gene at the same loci (600 bp) a phenomenon due to low copy number of gene. RAPD-PCR analysis of resistant and susceptible S. litura population revealed the existence of polymorphism. Specific amplification for acetylcholinesterase gene using custom made primers produced amplified product in resistant S. litura populations.

Genetic diversity in Spodoptera litura (Fab.) from majorsoybean growing states of India

Random Amplified Polymorphic DNA molecular markers analysis of Spodoptera litura larvae population from seven major soybean growing regions of India revealed, populations from Hyderabad and Indore, shared cent per cent similarity, Pune and Parbhani populations showed 90 per cent similarity, Adilabad population shared 83 per cent similarity with both Hyderabad and Indore populations, while Dharwad and Belagavi populations showed 72 per cent similarity. The lowest genetic similarity value was observed between Dharwad and Parbhani populations (46%). It is clear from the similarity analysis more than 46 per cent similarity between populations of the S. litura from major soybean growing states, demonstrate mediocre genetic differences between the populations. Though much genetic diversity was not observed between S. litura populations, topological and temporal factors perhaps influenced the existed diversity among the populations.

Genetic diversity in Spodoptera litura (Fab.) from majorsoybean growing states of India

Random Amplified Polymorphic DNA molecular markers analysis of Spodoptera litura larvae population from seven major soybean growing regions of India revealed, populations from Hyderabad and Indore, shared cent per cent similarity, Pune and Parbhani populations showed 90 per cent similarity, Adilabad population shared 83 per cent similarity with both Hyderabad and Indore populations, while Dharwad and Belagavi populations showed 72 per cent similarity. The lowest genetic similarity value was observed between Dharwad and Parbhani populations (46%). It is clear from the similarity analysis more than 46 per cent similarity between populations of the S. litura from major soybean growing states, demonstrate mediocre genetic differences between the populations. Though much genetic diversity was not observed between S. litura populations, topological and temporal factors perhaps influenced the existed diversity among the populations.

Genetic and phenotypic comparisons of viral genotypes from two nucleopolyhedroviruses interacting with a common host species, Spodoptera litura (Lepidoptera: Noctuidae)

Nucleopolyhedroviruses (NPVs) are known to be highly variable, both genetically and phenotypically, at several scales such as different geographic locations or a single host. A previous study using several geographic isolates indicated that two types of NPV, Spodoptera littoralis NPV (SpliNPV) and S. litura NPV (SpltNPV) types, were isolated from the common cutworm, Spodoptera litura (Fabricius), a polyphagous insect that causes serious damage to many forage crops and vegetables. That study also indicated that the SpliNPV type was widely distributed in Japan. Here, we investigated the genotypic and phenotypic variation of cloned NPVs that infect S. litura; such variation is an important resource for biological control agents, and may represent the genetic diversity of an NPV species. Eighteen genotypically distinct NPVs were cloned from four field-collected NPV isolates using an in vivo cloning technique. They were divided into two virus types according to the similarity of banding patterns of DNA fragments generated by restriction endonucleases, and Southern hybridization analysis. Partial polyhedrin gene sequences revealed that the two types corresponded to SpliNPV and SpltNPV. Bioassays seem to suggest that the SpliNPV virus type was, overall, more infectious and killed S. litura larvae faster, but yielded fewer viral occlusion bodies, than the SpltNPV type. These data provide a basis for explaining the distribution pattern of SpliNPV and SpltNPV types in S. litura populations in Japan.

Field resistance of Spodoptera litura (Fab.) to conventional insecticides in India

The present study was carried out to evaluate conventional insecticide resistance in populations of Spodoptera litura (Fab.) from seven different soybean-growing districts (Dharwad. Belgaum, Pune, Parbani, Adilabad, Hyderabad and Indore) of India. Experimental results revealed among the three chemical insecticides bioassayed, quinolphos 25 EC registered the highest LC50 value (29.7 mg a.i./L) followed by chlorpyrifos 20 EC (18.3 mg a.i./L) while the lowest LC50 value was found for lambda-cyhalothrin 5 EC (1.3 mg a.i./L) in a susceptible population of S. litura larvae. Evaluation of the seven different populations of S. litura from India showed that populations from Adilabad and Pune exhibited elevated LC50 values for chlorpyrifos [(1622.0 mg a.i./L) and (1137.0 mg a.i./L)], quinolphos [(1892.0 mg a.i./L) and (1744.0 mg a.i./L)] and lambda-cyhalothrin [(56.4 mg a.i./L) and (41.6 mg a.i./L)], respectively. Seven different S. litura populations collected varied in their resistance ratio (RR) for three conventional insecticides used in this study. For chlorpyrifos RR values ranged from 3 to 88 fold, for quinolphos RR values ranged from 3 to 63 fold and for lambda-cyhalothrin RR values ranged from 2 to 42 fold in the seven different S. litura populations compared to the susceptible population. Based on the raised LC50 values, the resistance is quite concerning for organophosphates (chlorpyrifos and quinolphos). The present study is a warning bell suggesting the cautious use of organophosphates and lambda-cyhalothrin in soybean.

Molecular and functional characterization of a candidate sex pheromone receptor OR1 in Spodoptera litura.

Olfaction is primarily mediated by highly specified olfactory receptors (ORs). Here, we cloned and identified an olfactory receptor, named SlituOR1 (Genbank no. JN835269), from Spodoptera litura and found evidence that it is a candidate pheromone receptor. It exhibited male-biased expression in the antennae, where it was localized at the base of sensilla trichoidea, the antennal sensilla mainly responsive to pheromones in moths. Conserved orthologues of this receptor, found among known pheromone receptors within the Lepidoptera, and SlituOR1 were placed among a clade of candidate pheromone receptors in a phylogeny tree of insect OR gene sequences. SlituOR1 showed differential expression in S. litura populations attracted to traps baited with different ratios of the two sex pheromone components (9Z,11E)-tetradecadienyl acetate (Z9E11-14:OAc) and (9Z,12E)-tetradecadienyl acetate (Z9E12-14:OAc). Knocking down of SlituOR1 by RNA interference reduced the electroantennogram (EAG) response to Z9E11-14:OAc, and this result is consistent with the field trapping experiment. We infer that variation in transcription levels of olfactory receptors may modulate sex pheromone perception in male moths and could provide some of the flexibility required to maintain the functionality of communication with females when a population is adapting to a new niche and reproductive isolation becomes an advantage.

Identification and Differential Expression of a Candidate Sex Pheromone Receptor in Natural Populations of Spodoptera litura.

Olfaction is primarily mediated by highly specific olfactory receptors (ORs), a subfamily of which are the pheromone receptors that play a key role in sexual communication and can contribute to reproductive isolation. Here we cloned and identified an olfactory receptor, SlituOR3 (Genbank NO. JN835270), from Spodoptera litura, to be the candidate pheromone receptor. It exhibited male-biased expression in the antennae, where they were localized at the base of sensilla trichoidea. Conserved orthologues of these receptors were found amongst known pheromone receptors within the Lepidoptera, and SlituOR3 were placed amongst a clade of candidate pheromone receptors in a phylogeny tree of insect ORs. SlituOR3 is required for the EAG responses to both Z9E11-14:OAc and Z9E12-14:OAc SlituOR3 showed differential expression in S. litura populations attracted to traps baited with a series of sex pheromone blends composed of different ratios of (9Z,11E)-tetradecadienyl acetate (Z9E11-14:OAc) and (9Z,12E)-tetradecadienyl acetate (Z9E12-14:OAc). The changes in the expression level of SlitOR3 and antennal responses after SlitOR3 silencing suggested that SlitOR3 is required for the sex pheromone signaling. We infer that variation in transcription levels of olfactory receptors may modulate sex pheromone perception in male moths and could affect both of pest control and monitoring efficiency by pheromone application after long time mass trapping with one particular ratio of blend in the field.