Molecular characterizations of DNA methyltransferase 3 and its roles in temperature tolerance in the whitefly, Bemisia tabaci Mediterranean.

The Bemisia tabaci Mediterranean (MED) cryptic species is an invasive pest, distributed worldwide, with high ecological adaptability and thermotolerance. DNA methylation (a reversible chromatin modification) is one possible change that may occur within an organism subjected to environmental stress. To assess the effects of temperature stress on DNA methyltransferase 3 (Dnmt3) in MED, we cloned and sequenced BtDnmt3 and identified its functions in response to high and low temperatures. The full-length cDNA of BtDnmt3 was 3913 bp, with an open reading frame of 1962 bp, encoding a 73.89 kDa protein. In situ hybridization showed that BtDnmt3 was expressed mainly in the posterior region. BtDnmt3 messenger RNA expression levels were significantly down-regulated after exposure to heat shock and significantly up-regulated after exposure to cold shock. Furthermore, after feeding on double-stranded RNA specific for BtDnmt3, both heat resistance and cold resistance were significantly decreased, suggesting that BtDnmt3 is associated with thermal stress response and indicating a differential response to high- and low-temperature stress in MED. Together, these results highlight a potential role for DNA methylation in thermal resistance, which is a process important to successful invasion and colonization of an alien species in various environments.

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.

Effects of Five Naturally Occurring Sugars on the Longevity, Oogenesis, and Nutrient Accumulation Pattern in Adult Females of the Synovigenic Parasitoid Neochrysocharis formosa (Hymenoptera: Eulophidae).

Neochrysocharis formosa (Westwood) (Hymenoptera: Eulophidae), one of the dominant natural enemies of agromyzid leafminers, is a synovigenic parasitoid. We compared the longevity, oogenesis, and nutrient levels of female wasps provided with 10% solutions of five naturally occurring sugars. All five sugars significantly increased the longevity of female wasps, which was 6.5-9.3-fold higher than that of parasitoids provided with water only. We found no significant difference in longevity of female wasps fed on glucose versus fructose or trehalose versus melezitose, but longevity of wasps fed on glucose or fructose was significantly longer than those fed on trehalose or melezitose. Also, we examined the oosorption capability of wasps fed on the five sugars. Some mature eggs were present in the ovaries of newly emerged females, but these were fully reabsorbed within 72 h when wasps were starved. Once wasps were fed with any of the sugars, the number of mature eggs increased at first and then decreased due to oosorption. The longevity and oogenesis dynamics of female wasps fed on five sugars were related with their function of hydrolysis and digestion. As female wasps have no lipogenesis capability, by acquiring exogenous sugars for oogenesis, they can either maintain or exceed the original level of capital nutrients held on adult emergence because none of the wasps' glycogen need be metabolized to burn as sugar.

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.

Including climate change in pest risk assessment: the peach fruit fly, Bactrocera zonata (Diptera: Tephritidae).

Bactrocera zonata (Saunders) is one of the most harmful species of Tephritidae. It causes extensive damage in Asia and threatens many countries located along or near the Mediterranean Sea. The climate mapping program, CLIMEX 3.0, and the GIS software, ArcGIS 9.3, were used to model the current and future potential geographical distribution of B. zonata. The model predicts that, under current climatic conditions, B. zonata will be able to establish itself throughout much of the tropics and subtropics, including some parts of the USA, southern China, southeastern Australia and northern New Zealand. Climate change scenarios for the 2070s indicate that the potential distribution of B. zonata will expand poleward into areas which are currently too cold. The main factors limiting the pest's range expansion are cold, hot and dry stress. The model's predictions of the numbers of generations produced annually by B. zonata were consistent with values previously recorded for the pest's occurrence in Egypt. The ROC curve and the AUC (an AUC of 0.912) were obtained to evaluate the performance of the CLIMEX model in this study. The analysis of this information indicated a high degree of accuracy for the CLIMEX model. The significant increases in the potential distribution of B. zonata projected under the climate change scenarios considered in this study suggest that biosecurity authorities should consider the effects of climate change when undertaking pest risk assessments. To prevent the introduction and spread of B. zonata, enhanced quarantine and monitoring measures should be implemented in areas that are projected to be suitable for the establishment of the pest under current and future climatic conditions.

Investigation of the genetic diversity of an invasive whitefly (Bemisia tabaci) in China using both mitochondrial and nuclear DNA markers.

It is often considered that reduced genetic variation due to bottlenecks and founder effects limits the capacity for species to establish in new environments and subsequently spread. The recent invasion (during the past five years) of an alien whitefly, one member of Bemisia tabaci cryptic species complex, referred to as Mediterranean (herein referred to as Q-type) in Shandong Province, China, provides an ideal opportunity to study the changes in genetic variation between its home range in the Mediterranean region and its invasion range. Using both the mitochondrial cytochrome oxidase I (mtCOI) and nuclear (microsatellite) DNA, we show that Q in Shandong likely originated in the western Mediterranean. We also found that the haplotype diversity was low compared with its presumed geographic origin, whereas microsatellite allele diversity showed no such decline. A key factor in invasions is the establishment of females and so bottleneck and founder events can lead to a very rapid and considerable loss of mitochondrial diversity. The lack of haplotype diversity in Shandong supports the interpretation that, at one or more points between the western Mediterranean and China, the invading Q lost haplotype diversity, most probably through the serial process of establishment and redistribution through trade in ornamental plants. However, the loss in haplotype diversity does not necessarily mean that nuclear allelic diversity should also decline. Provided females can mate freely with whichever males are available, allelic diversity can be maintained or even increased relative to the origin of the invader. Our findings may offer some explanation to the apparent paradox between the concept of reduced genetic variation limiting adaptation to new environments and the observed low diversity in successful invaders.

Further insights into the strange role of bacterial endosymbionts in whitefly, Bemisia tabaci: comparison of secondary symbionts from biotypes B and Q in China.

The percentage infection of secondary symbionts (SS) (Wolbachia, Arsenophonus, Rickettsia, Hamiltonella, Fritschea and Cardinium) in the exotic Bemisia tabaci (Genn.) invaders, commonly known as biotypes B and Q from China, were determined by PCR. In total, 373 biotype B and 1830 biotype Q individuals were screened for the presence of SS. Biotype B was more abundant than biotype Q from 2005 to 2006, and biotype Q was more abundant from 2007 to 2009. Each of the SS, with the exception of Fritschea, was detected in both biotypes B and Q; Fritschea was found in none of the samples examined. For biotype B, the percentage infection of Hamiltonella was the highest (92.0%) followed by Rickettsia (70.2%). For biotype Q, the percentage infection of Hamiltonella was again the highest (73.3%). Arsenophonus was the least common of the SS observed in both biotypes B and Q. The percentage infection of Wolbachia, Rickettsia and Hamiltonella in biotype B was each significantly higher than in biotype Q, whereas the percentage infection of Cardinium in biotype B was significantly lower than in biotype Q. The percentage infection of SS in biotypes B and Q varied from year to year over the period 2005-2009. Furthermore, within biotype Q, two distinct subgroups were identified which differ from each other in terms of their SS complement. We discuss these results in the light of the potentially influential factors and roles of the SS.