Tandemly expanded OR17b in Himalaya ghost moth facilitates larval food allocation via olfactory reception of plant-derived tricosane

Herbivorous insects utilize intricate olfactory mechanisms to locate food plants. The chemical communication of insect-plant in primitive lineage offers insights into evolutionary milestones of divergent olfactory modalities. Here, we focus on a system endemic to the Qinghai-Tibetan Plateau to unravel the chemical and molecular basis of food preference in ancestral Lepidoptera. We conducted volatile profiling, neural electrophysiology, and chemotaxis assays with a panel of host plant organs to identify attractants for Himalaya ghost moth Thitarodes xiaojinensis larvae, the primitive host of medicinal Ophiocordyceps sinensis fungus. Using a DREAM approach based on odorant induced transcriptomes and subsequent deorphanization tests, we elucidated the odorant receptors responsible for coding bioactive volatiles. Contrary to allocation signals in most plant-feeding insects, T. xiaojinensis larvae utilize tricosane from the bulbil as the main attractant for locating native host plant. We deorphanized a TxiaOR17b, an indispensable odorant receptor resulting from tandem duplication of OR17, for transducing olfactory signals in response to tricosane. The discovery of this ligand-receptor pair suggests a survival strategy based on food location via olfaction in ancestral Lepidoptera, which synchronizes both plant asexual reproduction and peak hatch periods of insect larvae.

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.

Ecological niche shift and suitable area expansion of a globally invasive species Phthorimaea operculella

Phthorimaea operculella is a major potato pest of global importance, early warning and detection of which are of significance. In this study, we analyzed the climate niche conservation of P. operculella during its invasion by comparing the overall climate niche from three dimensions, including the differences between native range (South America) and entire invaded region (excluding South America), the differences bwtween native range (South America) and five invaded continents (North America, Oceania, Asia, Africa, and Europe), as well as the differences between native region (South America) and an invaded region (China). We constructed ecological niche models for its native range (South America) and invaded region (China). The results showed that the climatic niche of the pest has expanded to varying degrees in different regions, indicating that the pest could well adapt to new environments during the invasion. Almost all areas of South America are suitable for P. operculella. In China, its suitable area is mainly concentrated in Shandong, Hebei, Tianjin, Beijing, Henan, Hubei, Yunnan, Guizhou, Sichuan, Hainan, northern Guangxi, southern Hunan, Anhui, Guangdong, Jiangsu, southern Shanxi, and southern Shaanxi. With increasing greenhouse gas emissions and global temperature, its suitable area will decrease at low latitude and increase gradually at high latitude. Specifically, the northern boundary will extend to Liaoning, Jilin, and the southeastern region of Inner Mongolia, while the western boundary extends to Sichuan and the southeast Qinghai-Tibet Plateau. The suitable area in the southeast Yunnan-Guizhou Plateau, Hainan Island, and the south of Yangtze River, will gradually decrease. The total suitable habitat area for P. operculella in China is projected to increase under future climate condition. From 2081 to 2100, under the three greenhouse gas emissions scenarios of ssp126, ssp370, and ssp585, the suitable area is expected to increase by 27.78, 165.54, and 140.41 hm2, respectively. Therefore, it is crucial to strengtehen vigilance and implement strict measures to prevent the further expansion of P. operculella.

HDAC1: An Essential and Conserved Member of the Diverse Zn2+-Dependent HDAC Family Driven by Divergent Selection Pressure

Zn2+-dependent histone deacetylases (HDACs) are enzymes that regulate gene expression by removing acetyl groups from histone proteins. These enzymes are essential in all living systems, playing key roles in cancer treatment and as potential pesticide targets. Previous phylogenetic analyses of HDAC in certain species have been published. However, their classification and evolutionary origins across biological kingdoms remain unclear, which limits our understanding of them. In this study, we collected the HDAC sequences from 1451 organisms and performed analyses. The HDACs are found to diverge into three classes and seven subclasses under divergent selection pressure. Most subclasses show species specificity, indicating that HDACs have evolved with high plasticity and diversification to adapt to different environmental conditions in different species. In contrast, HDAC1 and HDAC3, belonging to the oldest class, are conserved and crucial in major kingdoms of life, especially HDAC1. These findings lay the groundwork for the future application of HDACs.

Gene Expression Analysis Reveals Potential Regulatory Factors Response to Temperature Stress in Bemisia tabaci Mediterranean

Exposure to extreme temperatures can hinder the development of insects and even reduce their survival rate. However, the invasive species Bemisia tabaci exhibits an impressive response to different temperatures. This study aims to identify important transcriptional changes of B. tabaci occupying different temperature habitats by performing RNA sequencing on populations originating from three regions of China. The results showed that the gene expression of B. tabaci populations inhabiting regions with different temperatures was altered and identified 23 potential candidate genes that respond to temperature stress. Furthermore, three potential regulatory factors' (the glucuronidation pathway, alternative splicing, and changes in the chromatin structure) response to different environmental temperatures were identified. Among these, the glucuronidation pathway is a notable regulatory pathway. A total of 12 UDP-glucuronosyltransferase genes were found in the transcriptome database of B. tabaci obtained in this study. The results of DEGs analysis suggest that UDP-glucuronosyltransferases with a signal peptide may help B. tabaci resist temperature stress by sensing external signals, such as BtUGT2C1 and BtUGT2B13, which are particularly important in responding to temperature changes. These results will provide a valuable baseline for further research on the thermoregulatory mechanisms of B. tabaci that contributes to its ability to effectively colonize regions with considerable temperature differences.

Behavioural regulator and molecular reception of a double-edge-sword hunter beetle

BACKGROUND

The black carabid beetle Calosoma maximoviczi is a successful predator that serves as both a beneficial insect and a severe threat to economic herbivores. Its hunting technique relies heavily on olfaction, but the underlying mechanism has not been studied. Here, we report the electrophysiological, ecological and molecular traits of bioactive components identified from a comprehensive panel of natural odorants in the beetle-prey-plant system. The aim of this work was to investigate olfactory perceptions and their influence on the behaviours of C. maximoviczi.

RESULTS

Among the 200 identified volatiles, 18 were concentrated in beetle and prey samples, and 14 were concentrated in plants. Insect feeding damage to plants led to a shift in the emission fingerprint. Twelve volatiles were selected using successive electrophysiological tests. Field trials showed that significant sex differences existed when trapping with a single chemical or chemical mixture. Expression profiles indicated that sex-biased catches were related to the expression of 15 annotated CmaxOBPs and 40 CmaxORs across 12 chemosensory organs. In silico evaluations were conducted with 16 CmaxORs using modelling and docking. Better recognition was predicted for the pairs CmaxOR5-(Z)-3-hexenyl acetate, CmaxOR6-β-caryophyllene, CmaxOR18-(E)-β-ocimene and CmaxOR18-tetradecane, with higher binding affinity and a suitable binding pocket. Lastly, 168Y in CmaxOR6 and 142Y in CmaxOR18 were predicted as key amino acid residues for binding β-caryophyllene and tetradecane, respectively.

CONCLUSION

This work provides an example pipeline for de novo investigation in C. maximoviczi baits and the underlying olfactory perceptions. The results will benefit the future development of trapping-based integrated pest management strategies and the deorphanization of odorant receptors in ground beetles. © 2022 Society of Chemical Industry.

Characterization of Chromatin Remodeling Genes Involved in Thermal Tolerance of Biologically Invasive Bemisia tabaci

As an invasive species, Bemisia tabaci Mediterranean (MED) has notable potential to adapt to a wide range of environmental temperatures, which enables it to successfully spread after invasion and occupy habitats over a wide latitude range. It has been postulated that chromatin remodeling mechanisms are related to the rapid acquisition of adaptive traits and thermal resistance in invasive species; however, relevant experimental evidence is scarce. To identify the molecular characteristics and assess the role of chromatin remodelers in thermal stress within invasive MED and native Asia II 1 of the B. tabaci species complex, we identified 13 switching defective/sucrose non-fermenting (SWI/SNF) and 10 imitation switch (ISWI) family members in the B. tabaci genome, analyzed their molecular characteristics and structures, and identified key mutation sites between MED and Asia II 1, then cloned the catalytic subunits, and revealed the difference in thermal tolerance function. The results showed that the expression levels of Bt-BRM-1 and Bt-BRM-2 were significantly higher in MED than in Asia II 1 during heat stress, and Bt-BRM-2 expression was significantly higher during cold stress. In addition, RNA interference results indicated that the two target genes had similar temperature tolerance function in the both two cryptic species. This study is the first to identify and analyze the molecular characteristics of SWI/SNF and ISWI family members and reveal their potential key roles in temperature tolerance in poikilothermic ectotherms. The results will assist in understanding the underlying temperature adaptation mechanism of invasive insects and will enrich stress adaptation research systems from an epigenetic perspective.

First Report on CRISPR/Cas9-Based Genome Editing in the Destructive Invasive Pest Tuta Absoluta (Meyrick) (Lepidoptera: Gelechiidae)

The tomato leaf miner Tuta absoluta (Meyrick) is one of the world’s most destructive pests of tomato, and because of its severe economic impacts, as well as the development of pesticide resistance, the species has been intensively studied, especially in regard to the identification of targets for T. absoluta control. However, functional genomic studies of T. absoluta have been constrained by a lack of effective genetic tools. Therefore, the aim of the present study was to develop a CRISPR/Cas9 zygote microinjection protocol for generating heritable mutations in T. absoluta, using the ommochrome synthesis gene cinnabar as an easily evaluated target gene. The injection of fertilised eggs with Cas9 protein and four sgRNAs, which targeted cinnabar exon 3, resulted in a mutagenesis rate of 31.9% for eggs reaching adulthood, and cinnabar mutagenesis resulted in either red or mosaic eye colour phenotypes. As such, this study is the first to report a complete and detailed CRISPR/Cas9 workflow for the efficient genome editing of the globally important invasive pest T. absoluta. The application of this robust genome-editing tool to T. absoluta will greatly facilitate the discovery of suitable RNAi control targets and the subsequent development of novel control strategies.

Outbreak of the South American tomato leafminer, Tuta absoluta, in the Chinese mainland: geographic and potential host range expansion

BACKGROUND

In 2017 Tuta absoluta was identified as an invasive species in China. Due to its rapid geographic expansion and the severe crop damage it causes, T. absoluta poses a serious threat to China's tomato production industry. To determine its geographic distribution and host range, intensive surveys and routine monitoring were conducted across the Chinese mainland between 2018 and 2019. The population colonization coefficient (PCC; ratio of colonized sites and prefectures) and population occurrence index (POI; ratio of infested host species and PCCs) were calculated.

RESULTS

In northwestern China, T. absoluta populations established in Xinjiang exhibited a medium PCC value (~0.03). In southwestern China, populations in Yunnan and its five neighboring provinces exhibited high (~0.50 in Yunnan and Guizhou), or low (<0.02 in Guangxi, Sichuan, Hunan, and Chongqing) PCC values. In the Chinese mainland, infestations of four crop plant species (tomato, eggplant, potato, and Chinese lantern) and two wild plant species (black nightshade and Dutch eggplant) were identified; tomatoes were infested in every colonized province. Chinese lantern and Dutch eggplant are potentially novel hosts. Yunnan, Guizhou, and Xinjiang experienced the most serious damage (POI). In southwestern China, observed damage significantly decreased with increased distance from the first discovery site of T. absoluta to the farthest county of an infested province increased.

CONCLUSION

T. absoluta populations are well-established and could potentially spread to other regions of China. The present study helps to inform the establishment of better pest management guidelines and strategies in China and tomato-producing regions worldwide. © 2021 Society of Chemical Industry.

Establishment and characterization of the Bactrocera dorsalis (Diptera: Tephritidae) embryonic cell line QAU-Bd-E-2

In this study, we successfully established a Bactrocera dorsalis (Diptera: Tephritidae) embryonic cell line, i.e., QAU-Bd-E-2, from the insect eggs. The cells have been stably passaged for more than 60 times in TNM-FH medium with 10% fetal bovine serum (FBS). QAU-Bd-E-2 cells are adherent cells. Most of the cells were round, spindle-shaped, and rod-shaped. Round cells accounted for 82.3%, with a diameter of 13.9 ± 2.6 µm; spindle-shaped cells accounted for 9.8%, with the size of 51.2 ± 11.2 µm × 10.3 ± 3.1 µm; the rod-shaped cells accounted for 7.9%, with the size of 35.2 ± 9.4 µm × 12.0 ± 2.5 µm. The mitochondrial cytochrome oxidase I subunit (CoI) gene from QAU-Bd-E-2 cells was amplified, and the 657 bp fragment had a 100% similarity with the CoI gene of B. dorsalis, suggesting that the cell line was derived from B. dorsalis. The chromosome number of QAU-Bd-E-2 cells was mostly 12, which is the same as the B. dorsalis chromosome number. The cell density of QAU-Bd-E-2 cells reached the maximum (3.4 × 10⁶ cells/mL) at 192 h, and the population doubling time was 31.9 h. Bactrocera dorsalis cripavirus (BdCV) could replicate in QAU-Bd-E-2 cells, suggesting that this cell line could be used for in-depth study of the relationship between virus and host.

Screening Potential Reference Genes in Tuta absoluta with Real-Time Quantitative PCR Analysis under Different Experimental Conditions

Tuta absoluta is one of the most significant invasive pests affecting tomato plants worldwide. RT-qPCR has emerged as one of the most sensitive and accurate methods for detecting gene expression data. The screening of stable internal reference genes is the most critical step for studying the molecular mechanisms of environmental adaptability. The stable reference genes expressed in T. absoluta under specific experimental conditions have not yet been clarified. In this study, seven candidate reference genes (RPL27, RPS13, RPS15, EF1-α, TUB, TBP, and β-actin) and their optimal numbers were evaluated under biotic (developmental stages and adult tissues) and abiotic (insecticide, temperature, and plant VOC) conditions using four software programs. Our results identified the following reference genes and numbers as optimal: three genes (EF1-α, RPS13, and RPL27) for different developmental stages (egg, larva, pupa, unmated adult), two genes (RPS13 and TBP) for adult tissues (antenna, head, thorax, abdomen, leg), two genes (TBP and RPS13) for insecticides (Bacillus thuringiensis, chlorpyrifos, abamectin-aminomethyl, and chlorantraniliprole), two genes (RPL27 and TUB) for temperature-induced stresses (0, 25, and 40 °C), and two genes (RPS13 and TUB) for VOC-induced stresses (nonanal, α-phellandrene, and tomato leaves). Our results provide a reference for selecting appropriate reference genes for further study of the functional genes of T. absoluta under different experimental conditions.

Molecular Characterization of TRPA Subfamily Genes and Function in Temperature Preference in Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

To reveal the mechanism of temperature preference in Tuta absoluta, one of the top 20 plant pests in the world, we cloned and identified TaTRPA1, TaPain, and TaPyx genes by RACE and bioinformatic analysis, and clarified their expression profiles during different development stages using real-time PCR, and revealed their function in preference temperature by RNAi. The full-length cDNA of TaPain was 3136 bp, with a 2865-bp open reading frame encoding a 259.89-kDa protein; and the partial length cDNA of TaPyx was 2326-bp, with a 2025-bp open reading frame encoding a 193.16-kDa protein. In addition, the expression of TaTRPA1 and TaPyx was significantly lower in larvae than other stages, and it was significantly higher in pupae and newly emerging males for TaPain. After feeding target double-stranded RNA (dsRNA), the preferred temperature decreased 2 °C more than the control group. In conclusion, the results firstly indicated the molecular characterization of TRPA subfamily genes and their key role in temperature perception in T. absoluta, and the study will help us to understand the temperature-sensing mechanism in the pest, and will provide some basis for study of other Lepidoptera insects’ temperature preference. Moreover, it is of great significance in enriching the research progress of “thermos TRP”.

Complete mitochondrial genome of a predominant parasitoid, Necremnus tutae (Hymenoptera: Eulophidae) of the South American tomato leafminer Tuta absoluta (Lepidoptera: Gelechiidae)

The complete mitochondrial genome of a predominant parasitoid, Necremnus tutae (Hymenoptera: Eulophidae) (GenBank accession number MT916846) is 15,252 bp in length, and contains 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes, and an A + T-rich region. The overall base composition is 38.86% for A, 7.14% for C, 8.57% for G, and 45.43% for T, with a high AT bias of 84.29%. ATA, ATT, ATG were initiation codons and TAA and T were termination codons. All the 22 tRNAs displayed a typical cloverleaf secondary structure, except for trnS₁ and trnR which lacked the dihydrouracil (DHU) arm. Phylogenetic analyses were performed using 13 PCGs showed that N. tutae is closely related to Tenthredo tienmushana, which in accordance with the traditional classification.

Using RNA Interference to Reveal the Function of Chromatin Remodeling Factor ISWI in Temperature Tolerance in Bemisia tabaci Middle East-Asia Minor 1 Cryptic Species

Invasive species often encounter rapid environmental changes during invasions and only the individuals that successfully overcome environmental stresses can colonize and spread. Chromatin remodeling may be essential in environmental adaptation. To assess the functions of imitation switch (ISWI) in invasive Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) cryptic species, we cloned and characterized the MEAM1 BtISWI gene and determined its functions in response to thermal stress. The full-length cDNA of BtISWI was 3712 bp, with a 3068 bp open reading frame (ORF) encoding a 118.86 kDa protein. BtISWI mRNA expression was significantly up-regulated after exposure to heat shock or cold shock conditions, indicating that BtISWI expression can be induced by thermal stress. After feeding double-stranded RNA (dsRNA), specifically for BtISWI, resistance to both heat and cold decreased significantly, suggesting that BtISWI may function directly in the thermal tolerance of MEAM1. Moreover, the preferred temperature of MEAM1 adults fed dsRNA was 1.9-3.5 °C higher than the control groups. Taken together, our findings highlight the importance of epigenetic gene regulation in the thermal response or thermal adaptation of invasive Bemisia tabaci (B. tabaci), and provide a new potential target for establishing sustainable control strategies for B. tabaci.

Induced Thermotolerance and Expression of Three Key Hsp Genes (Hsp70, Hsp21, and sHsp21) and Their Roles in the High Temperature Tolerance of Agasicles hygrophila

Thermal adaptation plays a fundamental role in the expansion and distribution of insects, and heat shock proteins (Hsps) play important roles in the temperature adaptation of various organisms. To determine the roles of Hsp genes (Hsp70, Hsp21, and sHsp21) on the high temperature tolerance of Agasicles hygrophila, we obtained complete cDNA (complementary DNA) sequences for Hsp70, Hsp21, and sHsp21 by rapid amplification of cDNA ends (RACE), analyzed their expression profiles under different high temperature treatments by quantitative reverse transcription polymerase chain reaction (RT-qPCR), and performed functional verification by RNA interference (RNAi). The open reading frames of Hsp70, Hsp21, and sHsp21 were 1940, 543, and 567 bp, encoding 650, 180, and 188 amino acids, respectively. Their molecular weights (MWs) were 71.757, 20.879, and 21.510 kDa, and the isoelectric points were 5.63, 6.45, and 6.24, respectively. Phylogenetic tree analysis showed that the Hsp70, Hsp21, and sHsp21 genes of A. hygrophila were relatively conserved in evolution. The Hsp70 and Hsp21 genes in A. hygrophila were homologous to those in Leptinotarsa decemlineata (87 and 79% similarity, respectively), and the sHsp21 gene in A. hygrophila was homologous to that in Lissorhoptrus oryzophilus (74% similarity). The amino acid polypeptide chain had highly conserved sequences of DLGGGTFD, VLVGGSTR, and GPTIEEVD. The sequence of EEVD was the characteristic motif of cytoplasmic Hsp70, and the highly conserved sequences of MALFR and MSLLP were characteristic sequences of Hsp2 and sHsp21, respectively. Relative quantitative real time PCR showed that the three Hsps could be induced by 4-h treatment at high temperatures. Significant upregulation of these Hsps was observed when the temperature was further increased. The RNAi results showed that the injection of the three Hsps' dsRNA could suppress the expression at the gene level significantly. Compared with the control group, high temperature heat shock reduced the fecundity of A. hygrophila significantly, and the fecundity decreased with the increase in temperature. Our results suggest that Hsp70, Hsp21, and sHsp21 might play key roles in high temperature adaptation of A. hygrophila and help improve our understanding of their mechanism of thermotolerance.

The potential of trap and barrier cropping to decrease densities of the whitefly Bemisia tabaci MED on cotton in China

BACKGROUND

The whitefly, Bemisia tabaci (Gennadius) MED, is a destructive insect pest in many countries of the world. Although the use of insecticides for controlling B. tabaci has been effective to a certain extent, pesticides are not an acceptable long-term control method, and alternatives should be sought. This paper focuses on the possibility of controlling B. tabaci on cotton using trap and barrier crops. We performed field experiments using cantaloupe (Cucumis melo) and sunflower (Helianthus annuus) as trap crops, and maize (Zea mays) as a barrier crop in various configurations in Hebei Province, North China.

RESULTS

The main activity periods were shortest on cantaloupe and ranged between 16-32 days for immatures and 14-33 days for adults. Adult whitefly densities were not significantly reduced by any treatment. During the main activity period, maize intercropping reduced densities of immature whiteflies from 24.2 individuals (ind.) 100 cm^-2 to 4.0 ind.100 cm^-2 , but all treatments were successful in significantly reducing immature B. tabaci densities. This resulted in a significant yield premium.

CONCLUSIONS

Intercropping reduced B. tabaci densities on cotton more than perimeter planting. Maize was more effective to reduce densities of immature whiteflies on cotton than cantaloupe. The results will contribute to the development of more effective and practical approaches for protecting cotton from B. tabaci and lowering chemical pressure on this crop. © 2019 Society of Chemical Industry.

Comparative analysis of eight DNA extraction methods for molecular research in mealybugs

For molecular research, the quality and integrity of DNA obtained will affect the reliability of subsequent results. Extracting quality DNA from scale insects, including mealybugs, can be difficult due to their small body size and waxy coating. In this study, we evaluate eight commonly used DNA extraction methods to determine their efficacy in PCR analysis across life stages and preservation times. We find that fresh samples, immediately upon collection or after 2 wks, resulted in the most effective DNA extraction. Methods using the DNeasy Blood & Tissue kit, NaCl, SDS-RNase A, and SDS isolated DNA of sufficient quality DNA. The SDS method gave high DNA yield, while the NaCl and SDS-RNase A methods gave lower yield. NaCl, SDS-RNase A, SDS, chloroform-isopentyl alcohol, and the salting-out methods all resulted in sufficient DNA for PCR, and performed equal to or better than that of the DNeasy Blood & Tissue kit. When time and cost per extraction were considered, the SDS method was most efficient, especially for later life stages of mealybug, regardless of preservation duration. DNA extracted from a single fresh sample of a female adult mealybug was adequate for more than 10,000 PCR reactions. For earlier stages, including the egg and 1st instar nymph samples, DNA was most effectively extracted by the Rapid method. Our results provide guidelines for the choice of effective DNA extraction method for mealybug or other small insects across different life stages and preservation status.

Effects of Simulated Heat Waves on Life History Traits of a Host Feeding Parasitoid

The frequency and amplitude of heat waves are predicted to increase under future climate change conditions. We still lack a detailed understanding of how changes in the frequency and amplitude of heat waves are linked to the life history traits and biocontrol efficiency of host-feeding parasitoids. In the present study, we simulated a series of heat waves as a function of amplitude and frequency to investigate the effects on the life history traits of the host-feeding parasitoid Eretmocerus hayati. We found that both the amplitude and frequency of heat waves significantly affected the adult phenotypes. In the low-amplitude heat wave group, the frequency of heat waves did not change the life history traits of the parasitoid; however, when the heat amplitude reached 42 °C, medium (four times/week) and high frequencies (seven times/week) of heat waves detrimentally affected these parameters. Hence, these findings suggest that to obtain optimal biological control with this parasitoid, we need to carefully monitor heat wave pattern (especially the amplitude and frequency) over the short term (usually 7-10 days) before releasing a host-feeding parasitoid.

Variable temperatures across different stages have novel effects on behavioral response and population viability in a host-feeding parasitoid

Parasitoids are insects (usually wasps or flies) that lay eggs within or on other insects (their hosts). Host-feeding parasitoids lay eggs to parasitize the host and feed directly on the host for nourishment. Temperature is the most critical factor affecting insect behavioral responses. Few studies have focused on the impacts of variable temperatures across different life stages on the behaviors of host-feeding parasitoids. This study investigated the effects of temperature experienced during the preadult and adult stages on the life history traits and life table parameters of females of a host-feeding parasitoid, Eretmocerus hayati. Our results show that the temperatures experienced during the preadult and adult stages significantly change life history traits (immature development, adult longevity, host feeding and fecundity). Increasing the preadult temperature resulted in shorter development times for immature stages of the parasitoid, and decreasing the temperature during the adult stage increased reproduction and longevity. Most importantly, we found that host-feeding events changed with temperature rather than life stage. The daily host-feeding ability of the parasitoid increased with increasing temperature at all temperatures except the stress temperature (34 °C). Furthermore, switching temperatures at the immature stage and adult stage can increase the values of life table parameters, with the highest intrinsic rate of increase (r) occurring in the 30/26 °C treatment. This study provides new insight into the mass rearing of parasitic natural enemies.

First Record of the Invasive Pest Pseudococcus jackbeardsleyi (Hemiptera: Pseudococcidae) on the Chinese Mainland and Its Rapid Identification Based on Species-Specific Polymerase Chain Reaction

The Jack Beardsley mealybug, Pseudococcus jackbeardsleyi Gimpel & Miller (Hemiptera: Pseudococcidae), a globally devastating, invasive polyphagous insect, causes great damage to many fruits, ornamentals, vegetables, and food crops worldwide. It is of Neotropical origin and has invaded throughout America and in parts of Asia, Africa and Oceania, and is still expanding its invasion ranges. Therefore, a method for quick and correct identification of this invasive species is crucial for quarantine and spreading interruption of it. In present study, we report the first record of P. jackbeardsleyi on the Chinese mainland, which would cause great damage to many crops. The identification of P. jackbeardsleyi was verified via morphological characters and DNA barcoding. One pair of species-specific polymerase chain reaction (SS-PCR) primers was designed based on variations in the sequences of the mitochondrial cytochromecoxidasesubunitI gene among P. jackbeardsleyi and 28 other mealybug species. No cross-reaction was detected among 21 closely related species using this SS-PCR assay, demonstrating the specificity of this marker. Furthermore, this method was successfully applied to detect individuals from different developmental stages and adult debris across four geographic populations of P. jackbeardsleyi, showing the high stability of the assay. Additionally, the detection limit of the marker was 55.94 ± 5.05 pg/µl of P. jackbeardsleyi DNA, illustrating the high sensitivity of the assay. The SS-PCR assay developed in this study provides a rapid, simple and reliable method for the identification of P. jackbeardsleyi, which should be crucial in the plant quarantine, early detection and sustainable management of this globally invasive pest.

Comparison of demographic fitness and biocontrol effectiveness of two parasitoids, Encarsia sophia and Eretmocerus hayati (Hymenoptera: Aphelinidae), against Bemisia tabaci (Hemiptera: Aleyrodidae)

BACKGROUND

The autoparasitoid Encarsia sophia and the primary parasitoid Eretmocerus hayati are two important parasitoids used against the whitefly Bemisia tabaci, with different reproductive strategies. To incorporate these two parasitoids into a sustainable whitefly control program, it is necessary to evaluate and compare their fitness and biocontrol effectiveness under identical experimental conditions. The demographic characteristics, parasitism rate and host-feeding rate of En. sophia and Er. hayati were analyzed using an age-stage, two-sex life table and the CONSUME-MSChart computer program.

RESULTS

The mean fecundity of Er. hayati (211.4 offspring per female) was significantly higher than that of En. sophia (101.6 offspring per female), although the oviposition days of En. sophia was longer than that of Er. hayati. No significant difference was found in the intrinsic rate of increase (r), finite rate of increase (λ) or net reproduction rate (R0 ) between the two parasitoid species, but the mean generation time (T) of En. sophia (18.8 days) was significantly shorter than that of Er. hayati (20.5 days). The net host feeding rate (C0 ) of En. sophia was 84.1 whiteflies per individual, significantly higher than the 17.6 whiteflies per individual consumed by Er. hayati. The finite killing rate (ν) of En. sophia (0.6713) for whitefly was significantly greater than that produced by Er. hayati (0.3652).

CONCLUSION

The En. sophia population can increase faster and have a higher killing potential than the Er. hayati population. Taking both the demographic fitness and killing potential of the two parasitoids into consideration, En. sophia would be the preferred choice to release in a biological control program. © 2018 Society of Chemical Industry.

Thermal Discrimination and Transgenerational Temperature Response in Bemisia tabaci Mediterranean (Hemiptera: Aleyrodidae): Putative Involvement of the Thermo-Sensitive Receptor BtTRPA

Anthropogenic climate change and global warming are expected to alter the geographic distribution and abundance of many ectothermic species, which will increase the invasion of new areas by exotic species. To survive in variable or fluctuating temperature conditions, insects require sensitive thermal sensory mechanisms to detect external thermal stimuli and induce the appropriate behavioral and physiological responses. TRPA, a thermal-activated transient receptor potential (TRP) family ion channel, is essential for thermotaxis in insects. Here, we investigated the potential role of BtTRPA in short-term and long-term thermal stress in Bemisia tabaci Mediterranean (Gennadius; Hemiptera: Aleyrodidae). We found that BtTRPA was mainly expressed in the head, where the antennae are located. Under short-term thermal stress, the BtTRPA gene was robustly expressed after exposure to acute low or high temperatures, BtTRPA expression reached the highest levels after exposure to 0°C for 3 h and 40°C for 5 h, but was relatively low after exposure to milder stimuli (12 and 35°C). These results demonstrated that BtTRPA could discriminate between innocuous and noxious temperature stimuli. Under long-term thermal stress, the highest expression level of BtTRPA occurred at G1 exposed to mild innocuous temperature of 21 and 31°C, along with BtTRPA sharply increased and peaked in adult females, implying that mild innocuous long-term thermal exposure could cause transgenerational expression effects to enhance the ability of offspring to cope with the same stress. This study demonstrates that the channel BtTRPA is important in temperature sensing and provides a molecular basis for thermosensation regulation in response to varied environmental temperature in B. tabaci Mediterranean.

Ecology, Worldwide Spread, and Management of the Invasive South American Tomato Pinworm, Tuta absoluta: Past, Present, and Future

The South American tomato pinworm, Tuta absoluta (Meyrick), is native to the western Neotropics. After invading Spain in 2006, it spread rapidly throughout Afro-Eurasia and has become a major threat to world tomato production. Integrated pest management (IPM) strategies have been developed, but widespread insecticide use has caused selection for insecticide resistance as well as undesirable effects on key beneficial arthropods. Augmentation and conservation biological control relying on omnivorous mirid predators has proved successful for management of T. absoluta, where implementation is dependent on abiotic, biotic (e.g., alternative prey), and anthropogenic factors (e.g., pesticides). Research has been carried out on larval parasitoids, showing potential for further development of sustainable control. The development of resistant tomato varieties is ongoing, but they are not commercially available yet. Knowledge gaps remain to be filled to optimize IPM packages on tomato crops and to help prevent further spread worldwide.

The homology gene BtDnmt1 is Essential for Temperature Tolerance in Invasive Bemisia tabaci Mediterranean Cryptic Species

The Bemisia tabaci Mediterranean (MED) cryptic species has been rapidly invading most parts of the world owing to its strong ecological adaptability, particularly its strong resistance to temperature stress. Epigenetic mechanisms play important roles in mediating ecological plasticity. In particular, DNA methylation has been the focus of attempts to understand the mechanism of phenotypic plasticity. The relationship between temperature and DNA methylation and how it affects the adaptability of invasive insects remain unknown. To investigate the temperature resistance role of DNA methyltransferase 1 (Dnmt1) in MED, we cloned and sequenced BtDnmt1 homology and identified its functions under various temperature conditions. The full-length cDNA of MED BtDnmt1 homology was 5,958 bp and has a 4,287 bp open reading frame that encodes a 1,428-amino-acid protein. BtDnmt1 mRNA expression levels were significantly down-regulated after feeding with dsRNA. Furthermore, after feeding with dsBtDnmt1, the MED adults exhibited significantly higher mortality under temperature stress conditions than the controls, suggesting that MED BtDnmt1 homology plays an essential role in the temperature tolerance capacity of MED. Our data improve our understanding of the temperature resistance and temperature adaptability mechanisms that have allowed the successful invasion and colonization of various environments by this alien species.

Adaptability of small brown planthopper to four rice cultivars using life table and population projection method

In this study, we evaluated the adaptability of the small brown planthopper (SBPH), Laodelphax striatellus (Hemiptera: Delphacidae) to four rice cultivars including Shengdao13 (SD13), Shengdao14 (SD14), Shengdao15 (SD15), and Zixiangnuo (ZXN) using the age-stage, two-sex life table with a simplified method for recording egg production (i.e., every five days vs. daily). The intrinsic rate of increase (r) of the SBPH was the highest (0.1067 d⁻¹) on cultivar SD15, which was similar to the rate on SD14 (0.1029 d⁻¹), but was significantly higher than that occurring on ZXN (0.0897 d⁻¹) and SD13 (0.0802 d⁻¹). The differences of the finite rate of increase (λ) on the four rice cultivars were consistent with the r values. Population projection predicted an explosive population growth of the SBPH occurring in a relatively short time when reared on SD14 and SD15. These findings demonstrated that the SBPH can successfully survive on the four rice cultivars, although there were varying host adaptabilities.

Effects of Periodically Repeated Heat Events on Reproduction and Ovary Development of Agasicles hygrophila (Coleoptera: Chrysomelidae)

Insect development occurs within a specific temperature range. Constant temperature studies may produce misleading information on the eco-physiological impacts of temperature on the population dynamics of an insect species, as in most natural environments, temperature usually undergoes daily variation. In China, field surveys showed that the decline in the Agasicles hygrophila (Selman & Vogt) (Coleoptera: Chrysomelidae) population from early August to late September in summer resulted in difficulties in effectively controlling the population of Alternanthera philoxeroides (Mart.) Griseb (Amaranthaceae). Previous studies have largely ignored more natural, fluctuating conditions. In our study, we first investigated the impacts of different temperature conditions (25°C constant temperature for 20 h with a 4-h period of a high temperature of either 30°C, 33°C, 36°C, or 39°C) on adult reproduction and longevity, egg development time, egg hatch rate, female ovarian development, and oogenesis of A. hygrophila. Our results indicated that high temperatures of 30°C and 33°C did not affect the female ovarian development and oogenesis of A. hygrophila Contrarily, high temperatures of 36°C and 39°C negatively affected the population development of A. hygrophila. At 36°C and 39°C, the egg hatch rates were very low, and the egg development times significantly lengthened. The frequency of abnormal ovaries significantly rose at 39°C. We concluded that the decline in the A. hygrophila population during August and September may be related to the extreme high temperatures that frequently occur in summer. These results help provide a better understanding of A. hygrophila population dynamics under natural conditions.

A new cell line derived from embryonic tissues of Holotrichia parallela (Coleoptera:Scarabaeidae)

Holotrichia parallela is an important agricultural underground insect pest and also an edible and medicinal insect. Establishing a new cell line of H. parallela will provide a rapid and convenient tool for the studies on its physiology, pathology, and gene functions. In this study, by using the embryonic tissue of H. parallela as the material, we established a new cell line named Hp-E-1. The microscopic observation of its morphological characteristics revealed that its cellular morphology was mainly in the spherical morphology with a mean cellular diameter of 17.71 ± 2.34 μm, accounting for 67% of the total cells. The spindle-shaped cells accounted for 33% of the total cells with a mean size of 23.51 ± 4.37 × 13.98 ± 2.05 μm. The chromosomal number varied from 7 to 40, with about 50% of the cells having a diploid chromosome number of 2n = 20. Random amplified polymorphic DNA (RAPD) analysis indicated that the profiles of PCR-amplified fragments of this cell line were basically similar to those of the embryonic tissues of H. parallela but were obviously different from those of cell line BTI-Tn5B1-4 of Trichoplusia ni and cell line Sf-9 of Spodoptera frugiperda. The DNA fragment encoding mitochondrial cytochrome C oxidase subunit I (COI) gene of this cell line shared 99.7% homology with that of the embryonic tissue of H. parallela, confirming that this cell line is indeed derived from H. parallela. The results of growth curve measurement indicated that the population doubling time of this cell line was 136.7 h. Cell line Hp-E-1 could not be infected by three viruses Autographa californica multiple nucleopolyhedrovirus (AcMNPV), Bombyx mori nucleopolyhedrovirus (BmNPV), and Spodoptera exigua multiple nucleopolyhedrovirus (SeMNPV).

Effects of Host Plant Factors on the Bacterial Communities Associated with Two Whitefly Sibling Species

Background

Although discrepancy in the specific traits and ecological characteristics of Bemisia tabaci between species are partially attributed to the B. tabaci-associated bacteria, the factors that affect the diversity of B. tabaci-associated bacteria are not well-understood. We used the metagenomic approach to characterize the B. tabaci-associated bacterial community because the approach is an effective tool to identify the bacteria.

Methodology and Results

To investigate the effects of the host plant and a virus, tomato yellow leaf curl virus (TYLCV), on the bacterial communities of B. tabaci sibling species B and Q, we analyzed the bacterial communities associated with whitefly B and Q collected from healthy cotton, healthy tomato, and TYLCV-infected tomato. The analysis used miseq-based sequencing of a variable region of the bacterial 16S rDNA gene. For the bacteria associated with B. tabaci, we found that the influence of the host plant species was greater than that of the whitefly cryptic species. With further analysis of host plants infected with the TYLCV, the virus had no significant effects on the B. tabaci-associated bacterial community.

Conclusions

The effects of different plant hosts and TYLCV-infection on the diversity of B. tabaci-associated bacterial communities were successfully analyzed in this study. To explain why B. tabaci sibling species with different host ranges differ in performance, the analysis of the bacterial community may be essential to the explanation.

Functional response, host stage preference and interference of two whitefly parasitoids

The functional responses of two parasitoids, Eretmocerus hayati Zolnerowich & Rose and Encarsia sophia Girault & Dodd, of whitefly Bemisia tabaci Gennadius Middle East-Asia Minor 1 were studied under laboratory conditions. In addition, the influence of host density and host stage on the competitive interactions between the two parasitoids, and biological control effect on whitefly were evaluated. In the functional response study, adult parasitoids were tested individually, with a conspecific or heterospecific competitor. Both Er. hayati and En. sophia exhibited a type II response to increasing host density, whether a conspecific or heterospecific competitor was present or not. Difference of searching rates and handling times between treatments suggested interference interactions existed between two parasitoid species. In the host stage preference study, two parasitoid species were jointly tested. Er. hayati had a competitive advantage over En. sophia when provided young host instars (first and second instar), whereas no advantage was found on old host instars (third and fourth instar). The biological control effect of Er. hayati and En. sophia in different introductions varied with host density. However, the effect of host instar on host mortality was not significant. These findings provide information for the practice of biological control and give better insight into how parasitoid species may coexist in diverse environments.

Analysis of expressed sequence tags (ESTs) from a normalized cDNA library and isolation of EST simple sequence repeats from the invasive cotton mealybug Phenacoccus solenopsis

The cotton mealybug, Phenacoccus solenopsis Tinsley, is a serious and invasive pest. At present, genetic resources for studying P. solenopsis are limited, and this negatively affects genetic research on the organism and, consequently, translational work to improve management of this pest. In the present study, expressed sequence tags (ESTs) were analyzed from a normalized complementary DNA library of P. solenopsis. In addition, EST-derived microsatellite loci (also known as simple sequence repeats or SSRs) were isolated and characterized. A total of 1107 high-quality ESTs were acquired from the library. Clustering and assembly analysis resulted in 785 unigenes, which were classified functionally into 23 categories according to the Gene Ontology database. Seven EST-based SSR markers were developed in this study and are expected to be useful in characterizing how this invasive species was introduced, as well as providing insights into its genetic microevolution.

Host selection by the autoparasitoid Encarsia pergandiella on primary (Bemisia tabaci) and secondary (Eretmocerus mundus) hosts

In autoparasitoids, females are generally primary endoparasitoids of Hemiptera, while males are hyperparasitoids developing in or on conspecific females or other primary parasitoids. Female-host acceptance can be influenced by extrinsic and/or intrinsic factors. In this paper, we are concerned with intrinsic factors such as nutritional status, mating status, etc. We observed the behavior of Encarsia pergandiella Howard (Hymenoptera: Aphelinidae) females when parasitizing primary (3rd instar larvae of Bemisia tabaci Gennadius [Homoptera: Aleyrodidae]) and secondary hosts (3rd instar larvae and pupae of Eretmocerus mundus Mercet [Hymenoptera: Aphelinidae]) for a period of 1 h. Females had different reproductive (virgin or mated younger) and physiological (fed elder or mated elder) status. Virgin females killed a large number of secondary hosts while investing a long time per host. However, they did not feed upon them. Mated females killed a lower number of secondary hosts and host feeding was observed in both consuming primary and secondary hosts. It was common to observe host examining females of all physiological statues tested repeatedly stinging the same hosts when parasitizing, killing or rejecting them. Fed elder females parasitized more B. tabaci larvae than E. mundus larvae or pupae, while investing less time on the primary host than on the secondary host. They also parasitized more B. tabaci larvae than mated elder females, while investing less time per host. The access of females to honey allowed them to lay more eggs.

Invasion and Management of Agricultural Alien Insects in China

China is the world's fourth-largest country in terms of landmass. Its highly diverse biogeography presents opportunities for many invasive alien insects. However, physical and climate barriers sometimes prevent locally occurring species from spreading. China has 560 confirmed invasive alien species; 125 are insect pests, and 92 of these damage the agricultural ecosystem. The estimated annual economic loss due to alien invasive species is more than $18.9 billion. The most harmful invasive insects exhibit some common characteristics, such as high reproduction, competitive dominance, and high tolerance, and benefit from mutualist facilitation interactions. Regional cropping system structure adjustments have resulted in mono-agricultural ecosystems in cotton and other staple crops, providing opportunities for monophagous insect pests. Furthermore, human dietary shifts to fruits and vegetables and smallholder-based farming systems result in highly diverse agricultural ecosystems, which provide resource opportunities for polyphagous insects. Multiple cropping and widespread use of greenhouses provide continuous food and winter habitats for insect pests, greatly extending their geographic range. The current management system consists of early-warning, monitoring, eradication, and spread blocking technologies. This review provides valuable new synthetic information on integrated management practices based mainly on biological control for a number of invasive species. We encourage farmers and extension workers to be more involved in training and further research for novel protection methods that takes into consideration end users' needs.

Invasion Genetics of Woolly Apple Aphid (Hemiptera: Aphididae) in China

In China, the woolly apple aphid, Eriosoma lanigerum (Hausmann), was first detected as an invasive species during the 1910s to 1930s, restricted to Shandong, Liaoning, and Yunnan Provinces. However, since the 1990s, the pest has spread into many other areas of China. To determine the possible spread routes of the recently established populations, the genetic diversity and genetic structure of 24 populations in 10 provinces were analyzed using eight microsatellite loci. Analyses using STRUCTURE software identified two genetic clusters overall. Three populations from Yunnan and Xinjiang consisted of individuals originating from a single cluster. Nineteen populations from eight northern provinces consisted only of individuals from another cluster, which formed a single large and panmictic population, resembling a distinct "supercolony" in Northern China. The other two populations from Yunnan consisted of individuals from both clusters. The possible routes of spread of the recently established populations of E. lanigerum in China were revealed as follows: 1) the populations in Northern China (including these from Henan, Hebei, Shanxi, Shannxi, Jiangsu, and Gansu) may have been introduced from Shandong or Liaoning Provinces; 2) the populations in Yunnan consisted of an early-established population and a population introduced secondarily from Shandong or neighboring areas, indicating that the population in Yunnan has at least two sources; and 3) the recently established populations of E. lanigerum in Xinjiang might not have been introduced from the "supercolony" in Northern China. Knowledge of these routes of spread is useful for avoiding further dissemination and/or additional introductions.

Establishment and characterization of three embryonic cell lines of beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

Three cell lines (QAU-Se-E-1, -2 and -3, or Se-1, -2 and -3 for short) were established from eggs of beet armyworm (Spodoptera exigua) that have been passaged stably for more than 60 times in TNM-FH medium supplemented with 10 % fetal bovine serum. The cell lines consisted of round and spindle-shaped cells. The round cells accounted for 96.82, 84.34 and 83.16 % of the cells in the three cell lines, respectively, with cell diameters of 16.21 ± 0.72, 15.63 ± 0.58 and 13.06 ± 0.44 μm. Random amplified polymorphic DNA and analysis of the CO I gene showed that the three cell lines were all derived from S. exigua. Growth curves at passage 30 were determined and the results showed that the cell population doubling times were 59.03, 49.08 and 49.91 h, respectively. The three cell lines can be infected by S. exigua multiple nucleopolyhedrovirus (SeMNPV). Se-3 was extremely susceptible to the virus with an infection rate of 97.52 % 4 days after the inoculation and produced 2.02 × 10(6) OBs per mL of culture. Flow cytometry analysis showed that some of Se-1 and Se-2 cells had apoptosis after infection, whereas Se-3 cells did not. Bioassays showed that the virulence of the SeMNPV proliferated from Se-3 was similar to that from the insect with LC50 of 5.55 × 10(5) and 2.64 × 10(5) OBs/mL. Therefore, the cell lines can be used to study the SeMNPV-host interactions and mechanisms underlying the interactions.

Asymmetric consequences of host plant occupation on the competition between the whiteflies Bemisia tabaci cryptic species MEAM1 and Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

BACKGROUND

The two common whitefly species, Bemisia tabaci (Gennadius) MEAM1 and Trialeurodes vaporariorum (Westwood), often co-occur on their host plants. The effect of host plant occupation by one species on later-arriving conspecific individuals or on the other competing species was examined.

RESULTS

Resource preoccupied by T. vaporariorum had mostly negative effects on the life history parameters of later-arriving conspecifics. Red-eyed nymph and immature survival of T. vaporariorum decreased when resource was preoccupied by conspecifics, irrespective of the previous occupation scenario. However, resource preoccupied by T. vaporariorum had only minor detrimental effects on the performance of later-arriving B. tabaci MEAM1. In the opposite colonisation sequence, previous occupation by B. tabaci MEAM1 had no significant effects on the life history parameters of later-arriving conspecifics, but severe detrimental effects were observed on the performance of later-arriving T. vaporariorum. Total immature survival of T. vaporariorum decreased in both weak and strong previous occupation situations by B. tabaci MEAM1.

CONCLUSION

The interspecific interactions between B. tabaci MEAM1 and T. vaporariorum were asymmetric, with B. tabaci MEAM1 being the superior competitor. This superiority could partially explain the rapid spread of B. tabaci MEAM1 in China.

Increased survival and prolonged longevity mainly contribute to the temperature-adaptive evolutionary strategy in invasive Bemisia tabaci (Hemiptera: Aleyrodidae) Middle East Asia Minor 1

With increasing global climate change, analyses of stress-inducing conditions have important significance in ecological adaptation and the biological distribution of species. To reveal the difference in temperature-adaptive strategy between Turpan and Beijing populations of Bemisia tabaci (Gennadius) Middle East Asia Minor 1 (MEAM1) under high-temperature stress conditions, we compared thermal tolerance and life history traits between Beijing and Turpan populations of MEAM1 after exposure to different heat shock treatments for different times. The experimental design reflected the nature of heat stress conditions suffered by MEAM1. The results showed that eggs, red-eyed pupae, and adults of the Turpan population were more heat tolerant than those of the Beijing population under the same stress conditions. Additionally, it was found that longevity and F1 adult survival rate were significantly higher in the Turpan population than in the Beijing population after heat shock stress, but egg number and F1 female ratio were not significantly different between Turpan population and Beijing population. Overall, it was suggested that heat tolerance and longevity traits were the most relevant for climate characteristics and not reproductive traits, and improved heat tolerance and prolonged longevity were important adaptive strategies that helped MEAM1 to survive in harsh high-temperature conditions such as Turpan arid desert climate. The present results provided further insight into the modes of heat tolerance and the ways in which survival and longevity traits respond to environmental selection pressures.

Effect of photoperiod on developmental fitness in Ophraella communa (Coleoptera: Chrysomelidae)

Ophraella communa LeSage (Coleoptera: Chrysomelidae) is an important biological control agent of the common ragweed, Ambrosia artemisiifolia L., in China. Development and fecundity of O. communa, and hatch rate of progeny eggs were studied at five photoperiods (8:16, 10:14, 12:12, 14:10, and 16:8 [L:D] h). The highest survival rate of eggs was 92% at the photoperiod of 16:8 (L:D) h, and those of both larvae and pupae were observed at the photoperiod of 14:10 (L:D) h (85 and 96%). The shortest developmental durations of larvae and pupae were observed at photoperiods of 14:10 and 16:8 (L:D) h. Fecundity was 1,159-1,976 eggs per female from photoperiods of 8:16 to 16:8 (L:D) h. The hatch rates of progeny eggs were 67-92% from photoperiods of 8:16 to 16:8 (L:D) h, and photoperiods did not affect developmental duration of progeny eggs. The intrinsic rate for increase (r), the net reproductive rate (r0), and the finite rate of increase (λ) reached the maximum values at 16:8 (L:D) h (0.2219 d(-1), 721 hatched eggs and 1.2484 d(-1), respectively) and 14:10 (L:D) h (0.2133 d(-1), 605.6 hatched eggs and 1.2378 d(-1), respectively). Their minimum values were observed at the photoperiod of 8:16 (L:D) h, which were 0.1731 d(-1), 212.2 hatched eggs and 0.1890 d(-1), respectively. The shortest T value was 29.7 d at a photoperiod of 16:8 (L:D) h and the longest was 31.4 d at a photoperiod of 12:12 (L:D) h. Our study shows that O. communa could survive and reproduce successfully at different photoperiods, thus may expand its distribution to regions with different photoperiods.

Transient receptor potential is essential for high temperature tolerance in invasive Bemisia tabaci Middle East Asia minor 1 cryptic species

Temperature is an important factor in affecting population dynamics and diffusion distribution of organisms. Alien species can successfully invade and colonize to various temperature environments, and one of important reasons is that alien species have a strong resistance to stress temperature. Recently, researchers have focused on the mechanisms of temperature sensing to determine the sensing and regulation mechanisms of temperature adaptation. The transient receptor potential (TRP) is one of the key components of an organism’s temperature perception system. TRP plays important roles in perceiving temperature, such as avoiding high temperature, low temperature and choosing the optimum temperature. To assess high temperature sensation and the heat resistance role of the TRP gene, we used 3′ and 5′ rapid-amplification of cDNA ends to isolate the full-length cDNA sequence of the TRP gene from Bemisia tabaci (Gennadius) MEAM1 (Middle East Asia Minor 1), examined the mRNA expression profile under various temperature conditions, and identified the heat tolerance function. This is the first study to characterize the TRP gene of invasive B. tabaci MEAM1 (MEAM1 BtTRP). The full-length cDNA of MEAM1 BtTRP was 3871 bp, and the open reading frames of BtTRP was 3501 bp, encoding 1166 amino acids. Additionally, the BtTRP mRNA expression level was significantly increased at 35°C. Furthermore, compared with control treatments, the survival rate of B. tabaci MEAM1 adults was significantly decreased under high temperature stress conditions after feeding with dsRNA BtTRP. Collectively, these results showed that MEAM1 BtTRP is a key element in sensing high temperature and plays an essential role in B. tabaci MEAM1 heat tolerance ability. Our data improved our understanding of the mechanism of temperature sensation in B. tabaci MEAM1 at the molecular level and could contribute to the understanding of the thermal biology of B. tabaci MEAM1 within the context of global climate change.

Three Heat Shock Protein Genes from Bactrocera (Tetradacus) minax Enderlein: Gene Cloning, Characterization, and Association with Diapause

Bactrocera (Tetradacus) minax Enderlein is a major pest to wild and cultivated species of citrus. Bactrocera minax produces one generation per year with a long pupal diapause period of over 6 months, which hinders efforts to obtain vast numbers of insects under standard room conditions. Determining the mechanisms of diapause is significantly important for obtaining large quantities of these insects. To characterize the heat shock protein (Hsp) genes of B. minax and to unravel their potential contribution to diapause, we performed 3' and 5' RACE to isolate the complementary DNA (cDNA) sequences, bioinformatics to examine the phylogenetic relationships, and real-time quantitative PCR to detect the expression patterns of three Hsp genes during various developmental stages. These results represent the first characterization of the three Hsp genes of B. minax; the open reading frames of Bmhsp23, Bmhsp70, and Bmhsp90 were 510, 1,911, and 1,089 bp, encoding 170, 636, and 363 amino acids, respectively. BmHsp70 and BmHsp90 displayed high identity to previously identified Hsp70 and Hsp90 genes, respectively. BmHsp23 displayed varying similarity, from 28 to 83%, to previously identified small Hsps. Bmhsp23 messenger RNA (mRNA) expression was found to be upregulated during diapause initiation, maintenance, and termination. Bmhsp70 mRNA expression peaked during diapause initiation. Bmhsp90 mRNA expression remained at a relatively low level during deep diapause. Our present results suggest that Bmhsp70 might play an important role in diapause initiation, while Bmhsp23 in diapause initiation and maintenance and Bmhsp90 in diapause regulation. These results improve our understanding of the mechanism of diapause in B. minax at the molecular level.

Heritability and evolutionary potential in thermal tolerance traits in the invasive Mediterranean cryptic species of Bemisia tabaci (Hemiptera: Aleyrodidae)

With advancing global climate change, the analysis of thermal tolerance and evolutionary potential is important in explaining the ecological adaptation and changes in the distribution of invasive species. To reveal the variation of heat resistance and evolutionary potential in the invasive Mediterranean cryptic species of Bemisia tabaci, we selected two Chinese populations-one from Harbin, N China, and one from Turpan, S China-that experience substantial heat and cold stress and conducted knockdown tests under static high- and low-temperature conditions. ANOVAs indicated significant effects of populations and sex on heat knockdown time and chill coma recovery time. The narrow-sense heritability (h2) estimates of heat tolerance based on a parental half-sibling breeding design ranged from 0.47 ± 0.03 to 0.51 ± 0.06, and the estimates of cold tolerance varied from 0.33 ± 0.07 to 0.36 ± 0.06. Additive genetic variances were significantly different from zero for both heat and cold tolerance. These results suggest that invasive B. tabaci Mediterranean cryptic species possesses a strong ability to respond to thermal selection and develops rapid resistance to climate change.

Trade-offs between survival, longevity, and reproduction, and variation of survival tolerance in Mediterranean Bemisia tabaci after temperature stress

The invasive Mediterranean Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) has emerged as one of the most common agricultural pests in the world. In the present study, we examined the cross-tolerance, fitness costs, and benefits of thermal tolerance and the variation in the responses of life history traits after heat-shock selection. The results showed that survival and longevity of Mediterranean B. tabaci were decreased significantly after direct or cross temperature stress and that the number of eggs per female was not reduced significantly. Furthermore, heat-shock selection dramatically increased the survival of Mediterranean B. tabaci within two generations, and it did not significantly affect the egg number per female within five generations. These results indicated that there was a trade-off between survival, longevity, and reproduction in Mediterranean B. tabaci after temperature stress. The improvement in reproduction was costly in terms of decreased survival and longevity, and there was a fitness consequence to temperature stress. In addition, heat tolerance in Mediterranean B. tabaci increased substantially after selection by heat shock, indicating a considerable variation for survival tolerance in this species. This information could help us better understand the thermal biology of Mediterranean B. tabaci within the context of climate change.

Phenolics from Ageratina adenophora roots and their phytotoxic effects on Arabidopsis thaliana seed germination and seedling growth

A bioassay-directed phytochemical study was conducted to investigate potential allelochemicals in the roots of the invasive plant Ageratina adenophora. Eleven phenolic compounds, including seven new ones, 7-hydroxy-8,9-dehydrothymol 9-O-trans-ferulate (1), 7-hydroxythymol 9-O-trans-ferulate (2), 7,8-dihydroxythymol 9-O-trans-ferulate (3), 7,8-dihydroxythymol 9-O-cis-ferulate (4), methyl (7R)-3-deoxy-4,5-epoxy-D-manno-2-octulosonate 8-O-trans-p-coumarate (5), methyl (7R)-3-deoxy-4,5-epoxy-D-manno-2-octulosonate 8-O-cis-p-coumarate (6), and 3-(2-hydroxyphenyl)propyl methyl malonate (7), were isolated from a bioactive subfraction of the ethanol extract of the roots of A. adenophora. The new structures were established on the basis of detailed spectroscopic analysis. The potential phytotoxic effects of these compounds on the germination of Arabidopsis thaliana seeds were tested by a filter paper assay. Compound 7 and known compounds 3-(2-hydroxyphenyl)-1-propanol (8) and o-coumaric acid (9) remarkably showed inhibition activity against Arabidopsis seed germination at a concentration of 1.0 mM. Compounds 1, 2, 5, 6, and 10 showed slight inhibitory activity at the test concentration after treatment for 3 days, while the other compounds showed no obvious inhibitory effects. Moreover, 7-9 were further found to show obvious inhibitory activity on retarding the seedling growth of Ar. thaliana cultured in soil medium.

Competitive interactions between parasitoids provide new insight into host suppression

Understanding the dynamics of potential inter- and intraspecific competition in parasitoid communities is crucial in the screening of efficient parasitoid species and for utilization of the best parasitoid species combinations. In this respect, the host-parasitoid systems, Bemisia tabaci and two parasitoids, Eretmocerus hayati (exotic) and Encarsia sophia (existing) were studied under laboratory conditions to investigate whether interference competition between the exotic and existing species occurs as well as the influence of potential interference competition on the suppression of the host B. tabaci. Studies on interspecific-, intraspecific- and self-interference competition in two parasitoid species were conducted under both rich and limited host resource conditions. Results showed that (1) both parasitoid species negatively affect the progeny production of the other under both rich and limited host resource conditions; (2) both parasitoid species interfered intraspecifically on conspecific parasitized hosts when the available hosts are scarce and; 3) the mortality of B. tabaci induced by parasitoids via parasitism, host-feeding or both parasitism and host-feeding together varied among treatments under different host resource conditions, but showed promise for optimizing control strategies. As a result of our current findings, we suggest a need to investigate the interactions between the two parasitoids on continuous generations.

High Variation in Single Nucleotide Polymorphisms (SNPs) and Insertions/Deletions (Indels) in the Highly Invasive Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Middle East-Asia Minor 1 (MEAM1)

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Middle East-Asia Minor 1 (MEAM1) is invasive and adaptive to varied environments throughout the world. The adaptability is closely related to genomic variation such as single nucleotide polymorphisms (SNPs) and insertions/deletions (indels). In order to elucidate the feature of SNPs and indels in MEAM1, and reveal the association between SNPs/indels and adaptive capacity to various environments, a computational approach with QualitySNP was used to identify reliable SNPs and indels on the basis of 9110-expressed sequence tags of MEAM1 present in the NCBI database. There were 575 SNPs detected with a density of 10.1 SNPs/kb and 6.4 SNPs/contig. Also, 237 transitions (39.3%) and 366 transversions (60.7%) were obtained, where the ratio of transitions to transversions was 0.65:1. In addition, 581 indels with a density of 14.1 indels/kb and 9.2 indels/contig were detected. Collectively, it showed that invasive MEAM1 has high SNPs density, and higher SNPs percentage than non-invasive B. tabaci species. A high SNPs density/percentage in MEAM1 yielded a high genomic variation that might have allowed it to adapt to varied environments, which provides some support to understand the invasive nature of MEAM1 at the genomic level. High levels of genomic variation are implicated in the level of adaptive capacity and invasive species are thought to exhibit higher levels of adaptive capacity than non-invasive species.

Multiple generation effects of high temperature on the development and fecundity of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B

Insects are ectotherms and their ability to resist temperature stress is limited. The immediate effects of sub-lethal heat stress on insects are well documented, but longer-term effects of such stresses are rarely reported. In this study, survival, development and reproduction of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, were compared over five consecutive generations at 27, 31 and 35 °C and for one generation at 37 °C. Both temperature and generation significantly affected the fitness of the whitefly. These impacts were more dramatic with increasing generations and temperatures. Among the experimental temperatures, the most favorable for development and reproduction were 27 °C and 31 °C. At 27 °C, survival, development and fecundity were all stable over these five generations. At 31 °C, immature survival rate was the highest in the fifth generation, but female fecundities decreased in the fourth and fifth generations. At 35 °C, egg hatching rate, immature survival rate and female fecundity decreased significantly in the fourth and fifth generations. At 37 °C, survival of B. tabaci was not adversely affected, but female fecundity at 37 °C was less than 10% of that at 27 °C or 31 °C. These results demonstrate that the lethal high temperature for B. tabaci is over 37 °C, and the whitefly population continued expanding in the five generations at 35 °C. The ability of B. tabaci biotype B to survive high temperature stress will play an important role in its population extension under global warming.

Effects of high-gossypol cotton on the development and reproduction of Bemisia tabaci (Hemiptera: Aleyrodidae) MEAM1 cryptic species

Use of plant secondary metabolic compounds is an important method for insect pest control. In this study, the survival, development, and reproduction of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) MEAM1 cryptic species were compared over two consecutive generations on three cotton cultivars of different gossypol levels. Both cotton cultivar and generation significantly affected the fitness of the whitefly. In both generations, the immature development times on the low-gossypol cultivar ZMS13 were significantly longer than those on the high-gossypol cultivar M9101 or medium-gossypol cultivar HZ401. The female fecundity and rate of population increase of the whitefly ranked in the following order: ZMS13 > HZ401 > M9101. On each cultivar, the immature development time was shorter and the immature survival rate was higher in the second generation than those in the first generation. Rate of increase was also higher in the second generation. These results demonstrated that the fitness of B. tabaci MEAM1 cryptic species on the low-gossypol cotton cultivar ZMS13 was higher than that on the medium- or high-gossypol cultivar. The comparison of the life histories of B. tabaci MEAM1 cryptic species on different cotton varieties is important for the development of an integrated pest management program of the whitefly by using plant secondary metabolic compounds.

Multi-generation life tables of Bemisia tabaci (Gennadius) biotype B (Hemiptera: Aleyrodidae) under high-temperature stress

Much attention has been focused on insects' ability to survive long-term high-temperature stress and on their resulting population distributions under global warming. In this study, life tables of the whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) biotype B, were collected over five consecutive generations at 27, 31, and 35°C and for one generation at 37°C. At 37°C, the intrinsic rate of increase (r) and the net reproductive rate (r(0)) of the whitefly were 0.0383 d(-1) and 2.8 offspring, respectively. These results demonstrate that the lethal high temperature for B. tabaci is >37°C. At 27°C, neither r(0) nor r decreased over the generations studied. However, both of these values decreased over time at 31 and 35°C, and the decrease was more evident at 35°C. Our results on the ability of B. tabaci biotype B to survive long-term high-temperature stress are important for understanding its population distribution under global warming.

Suitability changes with host leaf age for Bemisia tabaci B biotype and Trialeurodes vaporariorum

The suitability of tomato leaves of different ages for Bemisia tabaci (Gennadius) B biotype and Trialeurodes vaporariorum (Westwood) was characterized by development time, stage-specific survival, sex ratio, longevity, and fecundity. Three categories of leaf ages were tested (young: expanding leaves <2 wk old; mature: fully expanded, 4-5-wk-old leaves; old: fully expanded, 6-7-wk-old leaves). There was no significant variation in the duration of development of the two species among the three classes of leaf ages, but total survival and ratio of females to males on mature and old leaves were higher than on young leaves. For egg hatch, the reverse tendency was found. Longevity of both species was higher on mature than on young leaves, and fecundity during the first 2 wk of adult life was higher on mature than on young or old leaves. The B. tabaci B biotype developed faster through the quiescent fourth nymphal instar, had higher ratio of females to males, survived longer, and produced more eggs (in the first 2 wk of adult life) than T. vaporariorum on leaves of the same age; although on young leaves, B. tabaci B biotype survivorship was lower than that of T. vaporariorum. The index of host suitability of B. tabaci B biotype was higher on mature and old leaves than on young leaves. In T. vaporariorum, no such differences were found among these three leaf ages. The results could provide some cues why B. tabaci B biotype is spreading so vigorously.

Enhanced vitellogenesis in a whitefly via feeding on a begomovirus-infected plant

BACKGROUND

The MEAM1 (B biotype) Bemisia tabaci (Gennadius) is one of the most widespread and damaging whitefly cryptic species. Our previous studies discovered that the MEAM1 whitefly indirectly benefits from interactions with the tomato yellow leaf curl China virus (TYLCCNV) via accelerated ovarian development and increased fecundity. However, the physiological mechanism of begomoviruse-infected plants acting on the reproduction of the insect vector was unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Biochemical and molecular properties of vitellogenin (Vg) and vitellin (Vt) were characterized in the MEAM1 whitefly. In addition, kinetics of Vt levels in ovary and Vg levels in hemolymph in different stages were detected using a sandwich ELISA. The level of hemolymph Vg increased rapidly after eclosion. A significantly higher level of hemolymph Vg and ovary Vt were observed in whiteflies feeding on virus-infected tobacco plants than those feeding on uninfected plants. In order to detect the levels of Vg mRNA transcription, complete vitellogenin (Vg) mRNA transcripts of 6474 bp were sequenced. Vg mRNA level in whiteflies feeding on virus-infected plants was higher than those feeding on uninfected plants. However, virus-infection of the whiteflies per se, as demonstrated using an artificial diet system, did not produce significant changes in Vg mRNA level.

CONCLUSIONS/SIGNIFICANCE

In MEAM1 whitefly, increased levels of both vitellin and vitellogenin as well as increased transcription of Vg mRNA are associated with feeding on begomovirus-infected plants, thus providing a mechanism for accelerated vitellogenesis. We conclude that MEAM1 whitefly profits from feeding on begomovirus-infected plants for yolk protein synthesis and uptake, and thereby increases its fecundity. These results not only provide insights into the molecular and physiological mechanisms underlying the elevated reproduction of a whitefly species through its association with a begomovirus-infected plant, but also provide a better understanding of the molecular mechanisms related to whitefly reproduction.