Sublethal Concentration of Beta-Cypermethrin Influences Fecundity and Mating Behavior of Carposina sasakii (Lepidoptera: Carposinidae) Adults

Nanoparticle-delivered RNAi-based pesticide target screening for the rice pest white-backed planthopper and risk assessment for a natural predator

Vacuolar-type (H+)-ATPase (vATPase) is a conserved multi-subunit eukaryotic enzyme composed of 14 subunits that form a functional complex consisting of an ATP-hydrolytic domain (V1) and a proton-translocation domain (V0). ATP hydrolysis and subsequent H+ translocation rely heavily on a fully assembled V1/V0 complex. Since vATPase is crucial for insect survival, it is a viable molecular target for pest control. However, detailed functional analyses of the 14 subunits and their suitability for pest control have not been fully explored in a single insect species. In this study, we identified 22 vATPase subunit transcripts that correspond to 13 subunits (A1, A2, B, C, D, E, F, G, H, a1, a2, c and d) in the white-backed planthopper (WBPH), Sogatella furcifera, a major hemipteran pest of rice. RNAi screens using microinjection and spray-based methods revealed that the SfVHA-F, SfVHA-a2 and SfVHA-c2 subunits are critical. Furthermore, star polymer (SPc) nanoparticles were utilized to conduct spray-induced and nanoparticle-delivered gene silencing (SI-NDGS) to evaluate the pest control efficacy of RNAi targeting the SfVHA-F, SfVHA-a2 and SfVHA-c2 transcripts. Target mRNA levels and vATPase enzymatic activity were both reduced. Honeydew excreta was likewise reduced in WBPH treated with dsRNAs targeting SfVHA-F, SfVHA-a2 and SfVHA-c2. To assess the environmental safety of the nanoparticle-wrapped dsRNAs, Cyrtorhinus lividipennis Reuter, a major natural enemy of planthoppers, was also sprayed with dsRNAs targeting SfVHA-F, SfVHA-a2 and SfVHA-c2. Post-spray effects of dsSfVHA-a2 and dsSfVHA-c2 on C. lividipennis were innocuous. This study identifies SfVHA-a2 and SfVHA-c2 as promising targets for biorational control of WBPH and lays the foundation for developing environment-friendly RNAi biopesticides.

Life Table Construction under Different Temperatures and Insecticide Susceptibility Analysis of Uroleucon formosanum (Hemiptera: Aphididae)

Simple Summary

Aphids are major crop pests worldwide, and in China, Uroleucon formosanum is a common aphid pest of lettuce. However, there is little basic and applied information on the control of this pest. To obtain the basic information of this pest, a life table of U. formosanum under different temperatures was constructed. Also, the susceptibility of U. formosanum to six common-used insecticides (chlorpyrifos, abamectin, beta-cypermethrin, imidacloprid, nitenpyram, and thiamethoxam) was evaluated. Results showed that U. formosanum was not suitable to a lower temperature (17 °C), and U. formosanum was relatively sensitive to all six test insecticides. These data may help us to develop integrated management strategies for better population control of U. formosanum.

Abstract

Uroleucon formosanum is an important aphid pest of lettuce, but basic information on its biology is scarce. In this study, effects of three constant temperatures (17, 21, and 25 °C, simulating the mean temperature range in greenhouses) on the development and fecundity of U. formosanum were analyzed by constructing a life table. U. formosanum could develop and reproduce under all three temperatures, but the survival rate, development, and fecundity of U. formosanum were affected by temperature. The intrinsic rate of increase was lowest at 17 °C (0.17) and it was significantly less than at 21 °C (0.20) and 25 °C (0.23). Furthermore, U. formosanum had the lowest finite rate of increase (1.19) and the largest mean generation time (20.21) at 17 °C. These results mean that U. formosanum is less adapted to the lower temperatures (17 °C) among these three set temperatures. To screen insecticides for control, susceptibility of U. formosanum to six insecticides including chlorpyrifos, abamectin, beta-cypermethrin, imidacloprid, nitenpyram, and thiamethoxam was evaluated. U. formosanum was relatively sensitive to all six test insecticides. Chlorpyrifos had the highest toxicity to U. formosanum (LC₅₀ = 3.08 mg/L). These data may help to develop integrated management strategies for better population control of U. formosanum.

Effects of Imunit Insecticide on Biological Characteristics and Life Table Parameters of Spodoptera cilium (Lepidoptera: Noctuidae)

Simple Summary

Spodoptera cilium Guenee (Lepidoptera: Noctuidae) is one of the grass pests in some parts of the world, including the southern regions of Iran. The larvae of S.cilium feed on grasses and heavy infestations can severely destroy lawn grasses. In the present study, we monitored the effects of Imunit on some biological and demographic parameters of the offspring generation. Our results indicate that Imunit reduced the survival rate and fecundity of S. cilium and could be used in the management programs of this pest.

Abstract

Imunit is a mixture of alpha-cypermethrin + teflubenzuron, and has been launched for controlling caterpillars. In this study, the effects of Imunit at LC₅₀ and LC₃₀ were investigated on parental and offspring generation of S. cilium, according to age-stage, two-sex life table. The experiments were conducted by leaf dipping method at 25 °C and 60 ± 5% relative humidity, under a cycle of 16 h fluorescent light and 8 h darkness. LC₃₀ and LC₅₀ concentrations of Imunit increased the immature developmental time of S. cilium in the offspring generation, while the LC₅₀ of Imunit significantly reduced the developmental time of adults. The adult pre-oviposition period and total pre-oviposition period considerably increased when offspring were treated with LC₅₀ of Imunit. In offspring of S. cilium exposed to LC₅₀ and LC₃₀ concentrations of Imunit, the gross reproductive rate (GRR), net reproduction rate (R₀), the intrinsic rate of population increase (r), and the finite rate of population increase (λ) significantly reduced compared to the control. This study showed that the application of Imunit at LC₅₀ could suppress the S. cilium population and can be used in the integrated management program of this pest.

Acute and Chronic Toxicity of Indoxacarb in Two Populations of Plutella xylostella (Lepidoptera: Plutellidae)

The diamondback moth, Plutella xylostella (Linnaeus, 1758), is one of the main pests of brassicas, and various insecticides, such as indoxacarb, are used to control it. However, frequent insecticide applications favor the selection of resistant individuals. Thus, the residual and sublethal effects of indoxacarb in two populations of P. xylostella, one collected in the field (FP) and one from the laboratory (LP), were evaluated and compared. The objective of this research was to investigate the toxicity of indoxacarb at residual and sublethal levels in a field population of P. xylostella from Brazil and a population from the laboratory. Leaf-dip bioassays showed high toxicity, with LC50 values after 48 h of 3.7 and 6.9 mg/liter for the LP and FP, respectively. Sublethal effects were indicated by significant reduction in the survival of larvae, pupae, and offspring. There was an increase in foliar consumption and a decrease in adult survival in the LP, and a decrease in fecundity in the FP. For the LP and FP population, the mean values for R0, rm, and λ for the control treatment were significantly higher than for the treatment groups (CL15 and CL25). Exposure of larvae to sublethal indoxacarb concentrations significantly reduced larval and pupal survival. Larval and pupal survival decreased as the indoxacarb concentration increased. Fecundity was significantly lower for the FP at LC15 (96.2 eggs per female) and LC25 (69.2 eggs per female) concentrations compared with the other treatments.

Similar Gut Bacterial Microbiota in Two Fruit-Feeding Moth Pests Collected from Different Host Species and Locations

Simple Summary

The peach fruit moth, Carposina sasakii, and the oriental fruit moth, Grapholita molesta are two co-occurring pests in orchards. Larvae of both species bore into fruits and cause damage to fruit production. Understanding the gut microbes, as well as the influencing factors between these co-occurring pests, may provide insight into their occurrence and control. In this study, we found that the two pests shared many bacteria in their gut from the genera Pseudomonas, Gluconobacter, Acetobacter, and Pantoea. The composition of the gut microbiota is similar between the two species collected from the same host plant and orchard; however, the gut microbiota of individuals collected from different orchards of the same host plant can be different within pest species. These results show that the two fruit moth pests have similar gut bacteria and varied environment in orchards can influence their gut microbiota.

Abstract

Numerous gut microbes are associated with insects, but their composition remains largely unknown for many insect groups, along with factors influencing their composition. Here, we compared gut bacterial microbiota of two co-occurring agricultural pests, the peach fruit moth (PFM), Carposina sasakii, and the oriental fruit moth (OFM), Grapholita molesta, collected from different orchards and host plant species. Gut microbiota of both species was mainly composed of bacteria from Proteobacteria, followed by Firmicutes. The two species shared bacteria from the genera Pseudomonas, Gluconobacter, Acetobacter, and Pantoea. When we compared two pairs of PFM and OFM populations collected from the same host species and the same orchard, there is no difference in alpha and beta diversity in gut microbiota. When we compared gut microbiota of the same species and host plant from different orchards, alpha and beta diversity was different in populations of PFM collected from two pear orchards but not in other comparisons. Our study suggests that the two pests share many features of gut microbiota and environment in orchards is a main factor influencing their gut microbiota.

Extremely low neonicotinoid doses alter navigation of pest insects along pheromone plumes

The prevailing use of neonicotinoids in pest control has adverse effects on non-target organisms, like honeybees. However, relatively few studies have explored the effect of sublethal neonicotinoid levels on olfactory responses of pest insects, and thus their potential impact on semiochemical surveillance and control methods, such as monitoring or mating disruption. We recently reported that sublethal doses of the neonicotinoid thiacloprid (TIA) had dramatic effects on sex pheromone release in three tortricid moth species. We present now effects of TIA on pheromone detection and, for the first time, navigational responses of pest insects to pheromone sources. TIA delayed and reduced the percentage of males responding in the wind tunnel without analogous alteration of electrophysiological antennal responses. During navigation along an odor plume, treated males exhibited markedly slower flights and, in general, described narrower flight tracks, with an increased susceptibility to wind-induced drift. All these effects increased in a dose-dependent manner starting at LC0.001 - which would kill just 10 out of 106 individuals - and revealed an especially pronounced sensitivity in one of the species, Grapholita molesta. Our results suggest that minimal neonicotinoid quantities alter chemical communication, and thus could affect the efficacy of semiochemical pest management methods.

Density-Dependent Demography and Mass-Rearing of Carposina sasakii (Lepidoptera: Carposinidae) Incorporating Life Table Variability

Carposina sasakii Matsumura is one of the most destructive fruit-boring pests of pome and stone fruit trees in eastern Asia. Because larvae complete their development inside a single fruit, larval density per fruit is a critical factor in their survival, development, and fecundity. The effect of larval density was examined to determine the ideal density for devising an economic and sustainable mass-rearing system for harvesting of C. sasakii. Mass production of insects of the same age of a specific stage is not only important in biological control, but also in pheromone extraction, culturing of entomopathogenic nematodes and fungi, etc. Life history data for six larval densities (1-5, 6-10, 11-15, 16-20, 21-30, and 31-40 larvae/apple) were collected at 25.5 ± 0.5°C, 75.0 ± 5.0% RH, and a photoperiod of 15:9 (L: D) h. Data were analyzed using the age-stage, two-sex life table. The results showed that the highest preadult survival rate (42.00%), fecundity (104.70 eggs), and population parameters (intrinsic rate of increase r = 0.0718 d-1, net reproductive rate R0 = 23.03 eggs, and finite rate of increase λ = 1.0744 d-1) were observed at a density of 1-5 larvae/apple. However, when the rearing costs and production rate were considered, the density of 16-20 larvae/apple was the most economical for mass-rearing C. sasakii in order to achieve a daily harvest rate of 1,000 pupae (from 273 apples per day). To ensure the sustainability of the mass-rearing system, we included the life table variability in the harvesting strategy.

Molecular characterization and functional analysis of pheromone binding proteins and general odorant binding proteins from Carposina sasakii Matsumura (Lepidoptera: Carposinidae)

BACKGROUND

The peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae), is one of the most destructive pests of pome and stone fruits, while few studies of their molecular biology and physiology have been conducted. Research into CsasPBPs (Carposina sasakii pheromone binding proteins) and CsasGOBPs (Carposina sasakii general odorant binding proteins) may provide insights in to the mechanisms of olfaction in Carposina sasakii.

RESULTS

In our study, results of real time quantitative polymerase chain reaction (qPCR) assays demonstrated that CsasPBP1-3 and CsasGOBP1-2 transcripts were abundantly expressed in the antennae of both sexes, suggesting they play a vital role in olfaction. In addition, to examine specific functional differences between pheromone binding proteins (PBPs) and general odorant binding proteins (GOBPs), fluorescence competitive binding assays were used to measured the binding affinities for the two sex pheromones and 18 apple plant volatiles. As a result, both PBPs and GOBPs showed stronger binding affinities to Z-7-eicosene-11-one than Z-7-nonadecene-11-one in two sex pheromones, whereas only PBP3 exhibited specific affinity towards both these two sex pheromone components, and PBP1 showed a high binding affinity to the sex pheromone components, and to other plant volatiles. In addition, GOBP1-2 displayed high binding affinity to general components of plant volatiles.

CONCLUSION

Our study suggested CsasPBPs and CsasGOBPs play distinct physiological roles in the perception of sex pheromones and host plant volatiles. © 2018 Society of Chemical Industry.

Antennal transcriptome analysis of the chemosensory gene families in Carposina sasakii (Lepidoptera: Carposinidae)

BACKGROUND

The peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae), poses a serious threat to a variety of fruits and causes significant economic loss owing to difficulties in its prevention and control. The olfactory sense is generally acknowledged to be a novel target for pest control. However, a systematic study of the olfactory genes expressed in C. sasakii has not been reported yet. Here, we reported the antennal transcriptome of C. sasakii using high-throughput sequencing and annotated the main chemosensory multi-gene families.

RESULTS

In the chemosensory gene families, 29 odorant-binding proteins, 13 chemosensory proteins, 1 sensory neuron membrane protein, 52 odorant receptors, 8 ionotropic receptors and 11 gustatory receptors were annotated in the C. sasakii antennal transcriptome. The number of olfactory genes obtained in our transcriptome was consistent with that identified in other lepidopteran insects, confirming that we basically accomplished the annotation of the chemosensory genes of C. sasakii in the adult antennal transcriptome. All sequences were annotated and analyzed by BLAST (basic local alignment search tool), and some chemosensory genes with specific functions were named according to the BLAST results and phylogenetic trees. Based on the expression profile in the transcriptome and phylogenetic analysis, differentially expressed genes (DEGs) were analyzed in both male and female adults. Finally, fluorescence quantitative real-time PCR was used to identify the male-specific or female-specific chemosensory genes that were putatively related to odor detection and recognition. Moreover, expression levels of OR33 and PBP2 were significantly higher in males than in females, indicating that these genes may interact with sex pheromones. We found some conserved antennal IRs and GRs involved in detecting sugar compounds (GR2, GR5, GR6, GR8) and carbon dioxide (GR1), which were also identified based on phylogenetic analysis.

CONCLUSIONS

There are 114 putative chemosensory proteins expressed in C. sasakii identified in this study. The identification of these proteins will make the molecular mechanism of odor recognition accessible.

Morphological differences of the reproductive system could be used to predict the optimum Grapholita molesta (Busck) control period

The oriental fruit moth (OFM), Grapholita molesta (Busck), is one of the dominant fruit-boring pests worldwide. In order to conduct integrated control of OFM effectively, it is important to predict the optimum control period. OFM populations have been monitored either by the number of trapped male moths exposed to sex pheromones or by the number of trapped male and female moths using food traps in orchards. The mating status and development stage of the trapped moths have not been characterized. The present paper studies the anatomical morphology of the OFM reproductive system at different development periods. The results revealed that OFM ovarian development can be divided into six stages. The average daily fecundity of OFM had an excellent positive correlation (r = 0.86) with the percentages of OFM in the egg maturation & oviposition stage, which could be used as an indicator in field population prediction work. There were obvious differences in the morphology of the corpus bursa and the heavy muscular area of the ductus ejaculatorius simplex before and after mating, and these differences could be used to increase the accuracy in predicting the optimum OFM control period.