Invasive Whitefly Research Articles

Draft mitochondrial DNA genome of a 1920 Barbados cryptic Bemisia tabaci ‘New World’ species (Hemiptera: Aleyrodidae)

Identification of invasive whitefly Bemisia tabaci cryptic species is best achieved by an integrated approach combining mating and genomic studies including complete mitochondrial DNA genomes (mitogenomes) characterization. We present the draft mitogenome of a 1920 historical B. tabaci specimen obtained using High Throughput Sequencing (HTS) technology. Our B. tabaci partial mtCOI gene best matched the B. tabaci ‘NW’ (New World) cryptic species (e.g. to AY057133; nucleotide identity: 99.85%). It has a circular genome of ca. 15,325bp with 13 protein-coding genes (PCGs), 22 tRNA’s, and two rRNA genes. A total of 43 amino acid residues differed between a Sanger-sequenced ‘NW’ mitogenome (AY521259.2) and this HTS-generated ‘NW’ mitogenome. High intra-specific amino acid conservation was observed across the partial 657 bp mitochondrial DNA COI (mtCOI) gene region used in species identification (i.e. from nucleotides 782 to 1438) when compared between both ‘NW’ (MK386668, AY521259.2) species.

The functions of caspase in whitefly Bemisia tabaci apoptosis in response to ultraviolet irradiation.

Whiteflies (Bemisia tabaci) are phloem feeders, and some invasive species are composed of cryptic species complexes that cause extensive crop damage, particularly via the direct transmission of plant viruses. Apoptosis is a type of programmed cell death essential for organismal development and tissue homeostasis. The caspases belong to a family of cysteine proteases that play a central role in the initiation of apoptosis in many organisms. Here, we employed a comprehensive genomics approach to identity caspases in B. tabaci Middle East Asia Minor1 (MEAM1), an invasive whitefly that carries a cryptic species complex that is devastating to crops. Four caspase genes were identified, and their motif compositions were predicted. Structures were relatively conserved in both putative effector and initiator caspases. Expression patterns of caspase genes differed across insect developmental stages. Three caspase genes were induced immediately after ultraviolet (UV) treatment. Expression levels of Bt-caspase-1 and Bt-caspase-3b increased in the midgut and salivary glands during apoptosis induced by UV treatments, whereas silencing of both genes reduced UV-triggered apoptosis. Our study demonstrates that Bt-caspase-1 and Bt-caspase-3b, respectively, act as putative initiator and effector apoptotic caspases in the MEAM1 whitefly.

Temperature-Dependent Development and Survival of Giant Whitefly Aleurodicus dugesii (Hemiptera: Aleyrodidae) Under Constant Temperatures.

The invasive giant whitefly Aleurodicus dugesii Cockerell (Hemiptera: Aleyrodidae) is a pest of over 300 plants species in the United States, many of which are economically important ornamentals and crops. Development and survival of A. dugesii was assessed at seven constant temperatures ranging from 10 to 35°C to provide a basis for phenological forecasting and assist in enhancing current biological control strategies. Complete development occurred from 15 to 28°C, with partial development occurring at 30°C. Development time differed between sexes, with males developing 2 (at 25°C) to 6 (at 15 and 28°C) d faster than females. Adult survival was highest at 25°C (65.4%), with survival rate declining rapidly at other temperatures. The relationship between temperature and development was evaluated using five nonlinear models (Lactin-2, Brière-1 and 2, Beta, and LRF). Additionally, the simple linear regression was used to calculate developmental degree-days (DDs). While all five nonlinear models evaluated fit the data well, the Brière-1 model provided the best fit of the data and estimated the optimal (25.3°C), lower (9.9°C), and upper (30.0°C) developmental thresholds for male and female complete development. Using linear regression, DDs for complete development were calculated as 408 and 435 for males and females, respectively. The results of this study emphasize A. dugesii survival and development under varied temperature conditions.

Diversity and evolution of the endosymbionts of Bemisia tabaci in China.

The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a cryptic species complex, including members that are pests of global importance. This study presents a screening of B. tabaci species in China for infection by the primary endosymbiont, Portiera aleyrodidarum, and two secondary endosymbionts, Arsenophonus and Cardinium. The results showed that P. aleyrodidarum was detected in all B. tabaci individuals, while Arsenophonus was abundant in indigenous species of B. tabaci Asia II 1, Asia II 3, and China 1 but absent in the invasive species, Middle East-Asia Minor 1 (MEAM1); Cardinium presented in the Mediterranean (MED), Asia II 1 and Asia II 3 species but was rarely detected in the MEAM1 and China 1 species. Moreover, phylogenetic analyses revealed that the P. aleyrodidarum and mitochondrial cytochrome oxidase 1 (mtCO1) phylograms were similar and corresponding with the five distinct cryptic species clades to some extent, probably indicating an ancient infection followed by vertical transmission and subsequent co-evolutionary diversification. In contrast, the phylogenetic trees of Arsenophonus and Cardinium were incongruent with the mtCO1 phylogram, potentially indicating horizontal transmission in B. tabaci cryptic species complex. Taken together, our study showed the distinct infection status of endosymbionts in invasive and indigenous whiteflies; we also most likely indicated the co-evolution of primary endosymbiont and its host as well as the potential horizontal transfer of secondary endosymbionts.

Assessing Compatibility of Isaria fumosorosea and Buprofezin for Mitigation of Aleurodicus rugioperculatus (Hemiptera: Aleyrodidae): An Invasive Pest in the Florida Landscape.

Rugose spiraling whitefly (RSW), Aleurodicus rugioperculatus Martin (Hemiptera: Aleyrodidae) is a new invasive whitefly pest in the Florida landscape, known to feed on a wide range of plants including palms, woody ornamentals, shrubs, and fruits. With the objective to find an alternative to neonicotinoid insecticides, and develop an ecofriendly management program for RSW, in the current study we evaluated the efficacy of a biopesticide containing the entomopathogenic fungi, Isaria fumosorosea Wize (Hypocreales: Clavicipitaceae), and an insect growth regulator buprofezin applied alone and in combination under laboratory and field conditions. Before assessing the two products, their compatibility was studied at six different concentrations of buprofezin. No significant inhibitive effect of buprofezin was observed on I. fumosorosea spore germination, and the average linear growth of the colony measured 14 d postinoculation. Under laboratory conditions, I. fumosorosea treatments (alone or mixed with buprofezin) provided higher RSW mortality than buprofezin alone. However, in both outdoor cage studies, the efficacy of buprofezin treatments (alone or mixed with I. fumosorosea) was higher than I. fumosorosea alone. A significant reduction in RSW population was reported for more than 5 wk in buprofezin alone and more than 7 wk in the combination treatments. In fall of 2014 and summer of 2015, the mean whitefly mortality observed during the 10-wk assessment period was 52.4 and 42.1% for I. fumosorosea, 79.6 and 79.0% for buprofezin, and 87.6 and 84.3% in mixed treatments, respectively. Results suggest that buprofezin can offer an effective alternate in the battle against invasive whiteflies such as RSW in Florida ecosystems, either as a stand-alone strategy or in an integrated approach.

New cost-effective bioconversion process of palm kernel cake into bioinsecticides based on Beauveria bassiana and Isaria javanica.

The present study aimed to add value to palm oil by-products as substrates to efficiently produce conidia of Beauveria bassiana and Isaria javanica (Hypocreales: Cordycipitaceae) for biological control of the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae), through a solid-state fermentation process using palm kernel cake and palm fiber as nutrient source and solid matrix, respectively. The optimum culture conditions yielded high concentrations of viable conidia after air-drying, when the fungi were grown on palm kernel cake (B. bassiana 7.65 × 109 and I. javanica 2.91 × 109conidiag-1 dry substrate) after 6days under optimal growth conditions set to 60% substrate moisture and 32°C. Both fungal strains exhibited high efficacy against third-instar whitefly nymphs, inducing mortality up to 62.9 and 56.6% by B. bassiana and I. javanica, respectively, assessed after 9days post-application in a screenhouse. Furthermore, we noted that insect mortality was strongly correlated with high atmospheric moisture, while B. bassiana appeared to require shorter accumulative hours under high moisture to kill whitefly nymphs compared to I. javanica. Our results underpin a feasible and cost-effective mass production method for aerial conidia, using palm kernel as the main substrate in order to produce efficacious fungal bioinsecticides against an invasive whitefly species in Brazil. Finally, our fermentation process may offer a sustainable and cost-effective means to produce eco-friendly mycoinsecticides, using an abundant agro-industrial by-product from Brazil that will ultimately assist in the integrated management of agricultural insect pests.

Reference gene selection for RT-qPCR analysis in two invasive whiteflies after the acquisition of vectored or non-vectored viruses

Custom reference gene selection is essential for reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) in different species of insects and various experiment conditions. In this study, 14 candidate reference genes (HSP40, HSP20, HSP70, HSP90, v-ATPase, RPL29, EF-1, SDHA, Actin, PPIA, GAPDH, MyosinL, NADH, and γ-tubulin) were analyzed using five different programs including ΔCt method, BestKeeper, geNorm, NormFinder, and ReFinder to validate their use as reference genes in two invasive whiteflies, Bemisia tabaci B and Q, after acquiring the vectored virus, Tomato yellow leaf curl virus (TYLCV), or ingesting the non-vectored virus, Tomato spotted wilt virus (TSWV), respectively. The results showed that HSP40, v-ATPase, and EF-1 were the most stable genes in B. tabaci B (B. tabaci B feeding on the healthy, TYLCV- and TSWV-infected tomato plant), PPIA, SDHA, and RPL29 were the most stable genes in B. tabaci Q (B. tabaci Q feeding on the healthy, TYLCV- and TSWV-infected tomato plant). In addition, EF-1, RPL29, and HSP20 were the most stable reference genes in B. tabaci B and Q.These findings provide the basis for future RT-qPCR-based studies on whitefly-virus interactions. Meanwhile, this report may set a precedent for reference gene selection in insects after the ingestion of non-vectored viruses.

Lethal and sublethal effects of dinotefuran on two invasive whiteflies, Bemisia tabaci (Hemiptera: Aleyrodidae)

Two invasive whitefly cryptic species, Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED), are the most invasive and notorious pests on diverse crops and have significantly impacted agricultural production systems globally. This circumstance emphasizes the need for a better approach for controlling these species. In this study, the lethal effect of six insecticides and the sublethal effects of dinotefuran on B. tabaci MEAM1 and MED were examined. Among the six insecticides tested, dinotefuran was the most toxic to both B. tabaci MEAM1 and MED adults with LC50 values of 5.54mg/L and 6.01mg/L, respectively. After treating adults of the two important species with LC25 of 1.70mg/L (MEAM1) and 2.12mg/L (MED), the transgenerational effects of dinotefuran on survival, developmental duration, and fecundity of F1 generation of B. tabaci MEAM1 and MED adults were observed respectively, which increased the developmental time and decreased survival rates of nymph, pseudopupa and adult. The fecundity of tested females was also reduced markedly. In summary, these results indicate that dinotefuran could be one excellent candidate that may effectively control two invasive whitefly populations.

Feeding and Development ofNephaspis oculata(Coleoptera: Coccinellidae) on Rugose Spiraling Whitefly (Hemiptera: Aleyrodidae)

Abstract Nephaspis oculata (Blatchley) (Coleoptera: Coccinellidae) is a predatory lady beetle that has been studied for biological control of whiteflies. Here, we studied the feeding rate and development of this beetle on rugose spiraling whitefly, Aleurodicus rugioperculatus Martin (Hemiptera: Aleyrodidae), an invasive whitefly species that was first found in the United States in 2009. The objective of our study was to measure the feeding rate of N. oculata on rugose spiraling whitefly and compare the egg-to-adult development on eggs and nymphs. Our results showed that N. oculata is able to complete its development from egg to adult solely on rugose spiraling whitefly. At 26.7 °C, immature (1st to 4th instars combined) beetles consumed an average of 245.7 ± 14.4 rugose spiraling whitefly eggs prior to pupation. Adult beetles consumed 50.6 ± 1.8 eggs per day. There was no difference between the feeding rate of adult males and females or between immature males and females. Larvae searched for prey by sweep...

Characterization of a native whitefly vitellogenin gene cDNA and its expression pattern compared with two invasive whitefly cryptic species

The whitefly Bemisia tabaci is a species complex, of which two invasive species, called MEAM1 and MED whiteflies, have invaded many parts of the world in the past 30 years and replaced native whitefly populations in many regions of invasions including many areas in China. One of the possible reasons for the invasion is that MEAM1 and MED whiteflies are more fecund than the native species. However, factors that affect reproduction and the molecular mechanism of vitellogenesis among various B. tabaci cryptic species are not clearly known. In this study, cDNAs of vitellogenin (Vg) genes were sequenced from native B. tabaci Asia II 1 and invasive B. tabaci MED in China. The deduced amino acid sequences were 2 182 residues in Asia II 1 and 2 217 residues in MED. Compared to the Vg gene cDNA sequence of Asia II 1 species, the Vg gene in MED could be cleaved at least into four subunits, with deduced molecular weight of 50, 90, 150 and 190 kDa, respectively. However, only two different subunits were cleaved between residues 459 and 460 in the Asia II 1. In addition, more than two serine-rich stretches located in both the N-terminal and the C-terminal region in invasive species. More GHN domains were revealed only in the N-terminal region of B. tabaci MED. Vg gene expression pattern was characterized using quantitative real-time (qRT)-PCR to compare the dynamic of vitellogenin gene mRNA level. Vg gene transcription reached the peak level at 13 d after eclosion in B. tabaci Asia II 1, 3 d later than that in MED and another invasive species of the B. tabaci complex MEAM1. We assumed that the present difference of Vg gene expression pattern is due to the different regulation pattern of vitellogenesis among species of the B. tabaci complex. These results provide useful information to reveal the mechanisms of reproduction in whitefly species complex.

Differential tolerance capacity to unfavourable low and high temperatures between two invasive whiteflies.

Thermal response and tolerance to ambient temperature play important roles in determining the geographic distribution and seasonal abundance of insects. We examined the survival and performance, as well as expression of three heat shock protein related genes, of two species of invasive whiteflies, Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED), of the Bemisia tabaci species complex following exposure to a range of low and high temperatures. Our data demonstrated that the MED species was more tolerant to high temperatures than the MEAM1 species, especially in the adult stage, and this difference in thermal responses may be related to the heat shock protein related genes hsp90 and hsp70. These findings may assist in understanding and predicting the distribution and abundance of the two invasive whiteflies in the field.

Molecular evidence for multiple phylogenetic groups within two species of invasive spiny whiteflies and their parasitoid wasp.

The invasive orange spiny whitefly (OSW) Aleurocanthus spiniferus has extended its distribution to non-native areas since the early 20th century. In a similar manner, the invasive tea spiny whitefly (TSW) A. camelliae has been expanding over East Asia in recent decades. In this study, the genetic diversity of OSW and TSW and of their important parasitoid wasp Encarsia smithi was investigated in China and Japan to enable more efficient biological control policies. We detected two phylogenetic groups (haplogroups A1 and A2) in OSW and three phylogenetic groups (haplotypes B1 and B2, and haplogroup B3) in TSW in China; however, only a single haplotype was detected in each whitefly species in Japan. Based on historical records and molecular data, OSW was considered to be native to China whereas TSW has probably expanded to China from a more southern location in the last 50 years; China appears to be the source region for OSW and TSW invading Japan. In E. smithi, two phylogenetic groups were detected in Japan: haplotype I, associated with OSW, and haplogroup II mostly associated with TSW, except in two locations. These data support the hypothesis that E. smithi parasitizing TSW in Japan did not originate from the existent population parasitizing OSW but was newly imported into Japan following the invasion of its host.

Transcriptional responses of invasive and indigenous whiteflies to different host plants reveal their disparate capacity of adaptation.

The whitefly Bemisia tabaci contains more than 35 cryptic species. The higher adaptability of Middle East-Asia Minor 1 (MEAM1) cryptic species has been recognized as one important factor for its invasion and displacement of other indigenous species worldwide. Here we compared the performance of the invasive MEAM1 and the indigenous Asia II 3 whitefly species following host plant transfer from a suitable host (cotton) to an unsuitable host (tobacco) and analyzed their transcriptional responses. After transfer to tobacco for 24 h, MEAM1 performed much better than Asia II 3. Transcriptional analysis showed that the patterns of gene regulation were very different with most of the genes up-regulated in MEAM1 but down-regulated in Asia II 3. Whereas carbohydrate and energy metabolisms were repressed in Asia II 3, the gene expression and protein metabolisms were activated in MEAM1. Compared to the constitutive high expression of detoxification genes in MEAM1, most of the detoxification genes were down-regulated in Asia II 3. Enzymatic activities of P450, GST and esterase further verified that the detoxification of MEAM1 was much higher than that of Asia II 3. These results reveal obvious differences in responses of MEAM1 and Asia II 3 to host transfer.

Effects of Host Sex, Plant Species, and Putative Host Species on the Prevalence of Wolbachia in Natural Populations of Bemisia tabaci (Hemiptera: Aleyrodidae): A Modified Nested PCR Study.

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a globally distributed pest. One of the key endosymbionts in B. tabaci is Wolbachia, an α-proteobacterium implicated in many important biological processes. Previous studies indicated that the infection frequency of Wolbachia in Middle East-Asia Minor 1 (MEAM1) and Mediterranean (MED) varied greatly among populations in different areas. However, little is known about the factors that influence the prevalence of Wolbachia in B. tabaci. In this paper, 25 field populations were collected from different locations in China, and 1,161 individuals were screened for the presence of Wolbachia using a nested polymerase chain reaction (PCR)-based method, which targets the wsp gene, to confirm Wolbachia infection status. The prevalence of Wolbachia ranged from 1.54 to 66.67% within the 25 field populations, and the infection frequency of Wolbachia was affected significantly by the putative species of B. tabaci. The infection frequency (51.55%) of Wolbachia was significantly greater in native species than in the MED (25.65%) and MEAM1 (14.37%). With the exception of host plant, all factors, including putative species, geographic location, and the sex of the host, affected the Wolbachia infection frequency in whiteflies. Six Wolbachia strains were found and clustered into four distinct clades upon phylogenetic analyses. Furthermore, Wolbachia in B. tabaci have close relationships with those from other host species, including Liriomyza trifolii (Burgess), Sogatella furcifera (Horvath), Nilaparvata lugens (Stål), and Culex pipiens L. The results demonstrated the variation and diversity of Wolbachia in B. tabaci field populations, and that the application of nested PCR extended our knowledge of Wolbachia infection in B. tabaci, especially in invasive whiteflies.

Competitive ability and fitness differences between two introduced populations of the invasive whitefly Bemisia tabaci Q in China.

BackgroundOur long-term field survey revealed that the Cardinium infection rate in Bemisia tabaci Q (also known as biotype Q) population was low in Shandong, China over the past few years. We hypothesize that (1) the Cardinium-infected (C +) B. tabaci Q population cannot efficiently compete with the Cardinium-uninfected (C −) B. tabaci Q population; (2) no reproductive isolation may have occurred between C + and C −; and (3) the C − population has higher fitness than the C + population.Methodology and ResultsTo reveal the differences in competitive ability and fitness between the two introduced populations (C + and C −), competition between C + and C − was examined over several generations. Subsequently, the reproductive isolation between C + and C − was studied by crossing C + with C − individuals, and the fitnesses of C + and C − populations were compared using a two-sex life table method. Our results demonstrate that the competitive ability of the C + whiteflies was weaker than that of C −. There is that no reproductive isolation occurred between the two populations and the C − population had higher fitness than the C + population.ConclusionThe competitive ability and fitness differences of two populations may explain why C − whitefly populations have been dominant during the past few years in Shandong, China. However, the potential role Cardinium plays in whitefly should be further explored.

Diversity and evolution of the Wolbachia endosymbionts of Bemisia (Hemiptera: Aleyrodidae) whiteflies.

Wolbachia is the most prevalent symbiont described in arthropods to date. Wolbachia can manipulate host reproduction, provide nutrition to insect hosts and protect insect hosts from pathogenic viruses. So far, 13 supergroups of Wolbachia have been identified. The whitefly Bemisia tabaci is a complex containing more than 28 morphologically indistinguishable cryptic species. Some cryptic species of this complex are invasive. In this study, we report a comprehensive survey of Wolbachia in B. tabaci and its relative B. afer from 1658 insects representing 54 populations across 13 provinces of China and one state of Australia. Based on the results of PCR or sequencing of the 16S rRNA gene, the overall rates of Wolbachia infection were 79.6% and 0.96% in the indigenous and invasive Bemisia whiteflies, respectively. We detected a new Wolbachia supergroup by sequencing five molecular marker genes including 16S rRNA, groEL, gltA, hcpA, and fbpA genes. Data showed that many protein-coding genes have limitations in detecting and classifying newly identified Wolbachia supergroups and thus raise a challenge to the known Wolbachia MLST standard analysis system. Besides, the other Wolbachia strains detected from whiteflies were clustered into supergroup B. Phylogenetic trees of whitefly mitochondrial cytochrome oxidase subunit I and Wolbachia multiple sequencing typing genes were not congruent. In addition, Wolbachia was also detected outside the special bacteriocytes in two cryptic species by fluorescence in situ hybridization, indicating the horizontal transmission of Wolbachia. Our results indicate that members of Wolbachia are far from well explored.

Host instar suitability in two invasive whiteflies for the naturally occurring parasitoid Eretmocerus hayati in China

Knowledge about host instar suitability of a parasitoid is critical to ensure bio-control efficacy. Studies were conducted to assess parasitizing and feeding behavior of a naturally occurring parasitoid, Eretmocerus hayati, on different instar nymphs of two invasive whiteflies, Bemisia tabaci (Gennadius) cryptic species MEAM1 and MED, in China. Er. hayati parasitized and fed on all nymphal stages of the two whiteflies, but preferred to parasitize 1st, 2nd and 3rd instar hosts of B. tabaci MEAM1 and 2nd instar hosts of B. tabaci MED. Parasitoids preferred to feed on earlier instar hosts of the two species. The preimaginal development times of parasitoids were the longest on 1st instar hosts, intermediate on 2nd and 3rd instars, and the shortest on 4th instars. The immature development time on B. tabaci MED hosts were slightly shorter than on MEAM1 ones. The highest parasitoid survivorships were on 4th instars, and the lowest were on 1st instars in both host species. The sex ratios of offspring remained stable at 0.5. Er. hayati could be a more suitable biological control agent for B. tabaci MED. Our results could provide guidance for indoor mass-rearing of Eretmocerus spp. for inundative release in the field, accelerating IPM programs against B. tabaci in China.

Transcriptomic analyses reveal the adaptive features and biological differences of guts from two invasive whitefly species.

BackgroundThe gut of phloem feeding insects is critical for nutrition uptake and xenobiotics degradation. However, partly due to its tiny size, genomic information for the gut of phloem feeding insects is limited.ResultsIn this study, the gut transcriptomes of two species of invasive whiteflies in the Bemisia tabaci complex, Middle East Asia Minor 1 (MEAM1) and Mediterranean (MED), were analyzed using the Illumina sequencing. A total of 12,879 MEAM1 transcripts and 11,246 MED transcripts were annotated with a significant Blastx hit. In addition, 7,000 and 5,771 gut specific genes were respectively identified for MEAM1 and MED. Functional analyses on these gut specific genes demonstrated the important roles of gut in metabolism of insecticides and secondary plant chemicals. To reveal the molecular difference between guts of MEAM1 and MED, a comparison between gut transcriptomes of the two species was conducted and 3,910 pairs of orthologous genes were identified. Based on the ratio of nonsynonymous and synonymous substitutions, 15 genes were found evolving under positive selection. Many of those genes are predicted to be involved in metabolism and insecticide resistance. Furthermore, many genes related to detoxification were expressed at an elevated level in the gut of MED compared to MEAM1, which might be responsible for the MED’s higher resistance to insecticides and environmental stresses.ConclusionThe sequencing of MED and MEAM1 gut transcriptomes and extensive comparisons of MEAM1 and MED gut transcripts provide substantial sequence information for revealing the role of gut in whiteflies.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-370) contains supplementary material, which is available to authorized users.

Evidence for adaptive divergence of thermal responses among Bemisia tabaci populations from tropical Colombia following a recent invasion.

There is an increasing evidence that populations of ectotherms can diverge genetically in response to different climatic conditions, both within their native range and (in the case of invasive species) in their new range. Here, we test for such divergence in invasive whitefly Bemisia tabaci populations in tropical Colombia, by considering heritable variation within and between populations in survival and fecundity under temperature stress, and by comparing population differences with patterns established from putatively neutral microsatellite markers. We detected significant differences among populations linked to mean temperature (for survival) and temperature variation (for fecundity) in local environments. A QST -FST analysis indicated that phenotypic divergence was often larger than neutral expectations (QST >FST ). Particularly, for survival after a sublethal heat shock, this divergence remained linked to the local mean temperature after controlling for neutral divergence. These findings point to rapid adaptation in invasive whitefly likely to contribute to its success as a pest species. Ongoing evolutionary divergence also provides challenges in predicting the likely impact of Bemisia in invaded regions.

Location of Symbionts in the Whitefly Bemisia tabaci Affects Their Densities during Host Development and Environmental Stress

Bacterial symbionts often enhance the physiological capabilities of their arthropod hosts and enable their hosts to expand into formerly unavailable niches, thus leading to biological diversification. Many arthropods, including the worldwide invasive whitefly Bemisia tabaci, have individuals simultaneously infected with symbionts of multiple genera that occur in different locations in the host. This study examined the population dynamics of symbionts that are located in different areas within B. tabaci. While densities of Portiera and Hamiltonella (which are located in bacteriocytes) appeared to be well-regulated during host development, densities of Rickettsia (which are not located in bacteriocytes) were highly variable among individual hosts during host development. Host mating did not significantly affect symbiont densities. Infection by Tomato yellow leaf curl virus did not affect Portiera and Hamiltonella densities in either sex, but increased Rickettsia densities in females. High and low temperatures did not affect Portiera and Hamiltonella densities, but low temperature (15°C) significantly suppressed Rickettsia densities whereas high temperature (35°C) had little effect on Rickettsia densities. The results are consistent with the view that the population dynamics of bacterial symbionts in B. tabaci are regulated by symbiont location within the host and that the regulation reflects adaptation between the bacteria and insect.