Shao-Jian Li

Host plants and natural enemies of Bemisia tabaci (Hemiptera: Aleyrodidae) in China

Abstract  The sweetpotato whitefly, Bemisia tabaci, has been a destructive pest in China for over the past two decades. It is an extremely polyphagous insect, being recorded feeding on hundreds of host plants around the world. Potential host plants and natural enemies of B. tabaci in the south, southeast, middle, north and northwest of China were investigated during the last decade. In total 361 plant species from 89 families were recorded in our surveys. Plants in the families Compositae, Cruciferae, Cucurbitaceae, Solanaceae and Leguminosae were the preferred host species for B. tabaci, which therefore suffered much damage from this devastating pest due to their high populations. In total, 56 species of parasitoids, 54 species of arthropod predators and seven species of entomopathogenic fungi were recorded in our surveys. Aphelinid parasitoids from Encarsia and Eretmocerus genera, lady beetles and lacewings in Coleoptera and Neuroptera were found to be the dominant arthropod predators of B. tabaci in China. The varieties of host plant, their distribution and the dominant species of natural enemies of B. tabaci in different regions of China are discussed.

The intracellular bacterium Wolbachia uses parasitoid wasps as phoretic vectors for efficient horizontal transmission.

Facultative bacterial endosymbionts are associated with many arthropods and are primarily transmitted vertically from mother to offspring. However, phylogenetic affiliations suggest that horizontal transmission must also occur. Such horizontal transfer can have important biological and agricultural consequences when endosymbionts increase host fitness. So far horizontal transmission is considered rare and has been difficult to document. Here, we use fluorescence in situ hybridization (FISH) and multi locus sequence typing (MLST) to reveal a potentially common pathway of horizontal transmission of endosymbionts via parasitoids of insects. We illustrate that the mouthparts and ovipositors of an aphelinid parasitoid become contaminated with Wolbachia when this wasp feeds on or probes Wolbachia-infected Bemisia tabaci AsiaII7, and non-lethal probing of uninfected B. tabaci AsiaII7 nymphs by parasitoids carrying Wolbachia resulted in newly and stably infected B. tabaci matrilines. After they were exposed to infected whitefly, the parasitoids were able to transmit Wolbachia efficiently for the following 48 h. Whitefly infected with Wolbachia by parasitoids had increased survival and reduced development times. Overall, our study provides evidence for the horizontal transmission of Wolbachia between insect hosts by parasitic wasps, and the enhanced survival and reproductive abilities of insect hosts may adversely affect biological control programs.

Inactivation of Wolbachia Reveals Its Biological Roles in Whitefly Host

Background The whitefly Bemisia tabaci is cryptic species complex composed of numerous species. Individual species from the complex harbor a diversity of bacterial endosymbionts including Wolbachia. However, while Wolbachia is known to have a number of different roles, its role in B. tabaci is unclear. Here, the antibiotic rifampicin is used to selectively eliminate Wolbachia from B. tabaci so as to enable its roles in whitefly development and reproduction to be explored. The indirect effects of Wolbachia elimination on the biology of Encarsia bimaculata, a dominant parasitoid of B. tabaci in South China, were also investigated. Methodology/Principal Finding qRT-PCR and FISH were used to show that after 48 h exposure to 1.0 mg/ml rifampicin, Wolbachia was completely inactivated from B. tabaci Mediterranean (MED) without any significant impact on either the primary symbiont, Portiera aleyrodidarum or any of the other secondary endosymbionts present. For B. tabaci MED, Wolbachia was shown to be associated with decreased juvenile development time, increased likelihood that nymphs completed development, increased adult life span and increased percentage of female progeny. Inactivation was associated with a significant decrease in the body size of the 4th instar which leads us to speculate as to whether Wolbachia may have a nutrient supplementation role. The reduction in nymph body size has consequences for its parasitoid, E. bimaculata. The elimination of Wolbachia lead to a marked increase in the proportion of parasitoid eggs that completed their development, but the reduced size of the whitefly host was also associated with a significant reduction in the size of the emerging parasitoid adult and this was in turn associated with a marked reduction in adult parasitoid longevity. Conclusions/Significance Wolbachia increases the fitness of the whitefly host and provides some protection against parasitization. These observations add to our understanding of the roles played by bacterial endosymbionts.

Plantmediated horizontal transmission of Wolbachia between whiteflies

Maternal transmission is the main transmission pathway of facultative bacterial endosymbionts, but phylogenetically distant insect hosts harbor closely related endosymbionts, suggesting that horizontal transmission occurs in nature. Here we report the first case of plant-mediated horizontal transmission of Wolbachia between infected and uninfected Bemisia tabaci AsiaII7 whiteflies. After infected whiteflies fed on cotton leaves, Wolbachia was visualized, both in the phloem vessels and in some novel ‘reservoir’ spherules along the phloem by fluorescence in situ hybridization using Wolbachia-specific 16S rRNA probes and transmission electron microscopy. Wolbachia persisted in the plant leaves for at least 50 days. When the Wolbachia-free whiteflies fed on the infected plant leaves, the majority of them became infected with the symbiont and vertically transmitted it to their progeny. Multilocus sequence typing and sequencing of the wsp (Wolbachia surface protein) gene confirmed that the sequence type of Wolbachia in the donor whiteflies, cotton phloem and the recipient whiteflies are all identical (sequence type 388). These results were replicated using cowpea and cucumber plants, suggesting that horizontal transmission is also possible through other plant species. Our findings may help explain why Wolbachia bacteria are so abundant in arthropods, and suggest that in some species, Wolbachia may be maintained in populations by horizontal transmission.

Comparison of biological parameters between the invasive B biotype and a new defined Cv biotype of Bemisia tabaci (Hemiptera: Aleyradidae) in China.

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is a widely distributed and destructive agricultural pest on various host plants. The biology of two biotypes of B. tabaci: the invasive B and a new defined Cv biotype, on a range of host plants (hibiscus, laurel, poinsettia, collard, cucumber and tomato) were studied in the laboratory. Results revealed that the developmental periods of the B biotype immatures were not significantly different on the tested host plants except those between laurel and collard. The Cv biotype immatures developed significantly slower on cucumber and tomato than on the other plants. B. tabaci B biotype had the highest survivorship on collard (68.55%), and the lowest on laurel (33.24%), while the Cv biotype had the highest and lowest survivorships on laurel (61.63%) and tomato (36.74%). Host plants did not significantly affect the pre-ovipostion period regardless of biotype. The longest averaged longevity and highest fecundity of B biotype were both recorded on collard: 25.15 days and 143.0 eggs. The highest fecundity of Cv biotype was 196.49 eggs on laurel and its longest longevity was on hibiscus (19.62 days). The intrinsic rate of natural increase (rm) of B biotype on the three vegetables were all higher than those on the three ornamentals whereas the rm of Cv biotype on the three ornamentals were all higher that those on the three vegetables. Our research indicates that B. tabaci B and Cv biotypes have different host plant suitabilities. The three tested vegetables were more suitable for B biotype while the three tested ornamental plants were more suitable for Cv biotype. The potential mechanism for the different suitability of B and Cv biotypes on various host plants is also discussed.

Efficiency of plant induced volatiles in attracting Encarsia formosa and Serangium japonicum, two dominant natural enemies of whitefly Bemisia tabaci in China

BACKGROUND Whitefly Bemisia tabaci is a globally distributed and most destructive pest to agriculture. Owing to increasing chemical resistance, a long-lasting strategy to manage this pest must involve biological control. Herbivore-induced plant volatiles (HIPVs) usually play a profoundly important role in the foraging behaviour of natural enemies. Here, the effects of HIPVs from Chinese broccoli on the foraging behaviour of two dominant natural enemy species of B. tabaci in China, Encarsia formosa and Serangium japonicum, were investigated using a four-arm olfactometer, and exogenous jasmonic acid (JA) was used to induce plant volatiles to mimic the damage of the herbivore pest. RESULTS The parasitoid E. formosa was found to be more attracted by the volatiles from JA-induced broccoli than those from control plants. The residence times of E. formosa in the final-choice areas closed to volatiles from shoot JA (SJA)- and root JA (RJA)-induced plants were 119.8 ± 35.2 s and 99.8 ± 34.7 s respectively in the dual-choice experiments, and 123.8 ± 32.0 s and 102.3 ± 28.7 s respectively in the three-choice experiment. All are significantly longer than those spent in the final-choice area closed to volatiles from control plants (CON). JA-induced volatiles were also only a little more attractive to the predator S. japonicum. However, there was no significant difference between each of the two natural enemies in residence time spent in the final-choice areas closed to SJA, RJA or CON volatiles in both the dual- and three-choice experiments. Furthermore, the number of times that the parasitoid or predator entered the SJA, RJA and CON final-choice areas was not significantly different in any of the experiments. CONCLUSION The present results indicate that RJA- and SJA-induced plant volatiles have higher efficiencies in attracting the natural enemies of whitefly B. tabaci. The attractive efficiencies varied according to the plant volatiles that JA induced, and also depended on the natural enemy species. The parasitoid E. formosa seems to be more sensitive to and attracted by the induced volatiles than the predator S. japonicum.

Plant-mediated horizontal transmission of Rickettsia endosymbiont between different whitefly species

ABSTRACT A growing number of studies have revealed the presence of closely related endosymbionts in phylogenetically distant arthropods, indicating horizontal transmission of these bacteria. Here we investigated the interspecific horizontal transmission of Rickettsia between two globally invasive whitefly species, Bemisia tabaci MEAM1 and B. tabaci MED, via cotton plants. We found both scattered and confined distribution patterns of Rickettsia in these whiteflies. After entering cotton leaves, Rickettsia was restricted to the leaf phloem vessels and could be taken up by both species of the Rickettsia‐free whitefly adults, but only the scattered pattern was observed in the recipient whiteflies. Both the relative quantity of Rickettsia and the efficiency of transmitting Rickettsia into cotton leaves were significantly higher in MEAM1 females than in MED females. The retention time of Rickettsia transmitted from MEAM1 into cotton leaves was at least 5 days longer than that of MED. Phylogenetic analysis based on 16S rRNA and gltA genes confirmed that the Rickettsia extracted from the donor MEAM1, the cotton leaves, the recipient MEAM1 and the recipient MED were all identical. We conclude that cotton plants can mediate horizontal transmission of Rickettsia between different insect species, and that the transmission dynamics of Rickettsia vary with different host whitefly species. &NA; Graphical Abstract Figure. Cotton plants can mediate the horizontal transmission of Rickettsia between whitefly species, and the transmission efficiencies vary with different whitefly species

Hosting major international events leads to pest redistributions

Human trade and transport is a major contributor to the global spread of invasive species and biodiversity change. Much of the focus on anthropogenic spread has been the movement of species between countries with far less attention being placed on the within country spread. For invasive arthropods, trade in ornamentals is a key contributor to global spread, but the role played by the transport of ornamentals within countries has been less well explored. In China, the hosting of major international events is an important expression of national and international pride and prestige. Hosting these is associated with the substantial use of landscaping to beautify the sites, all of which need to transport considerable numbers of plants to the event sites from various parts of China. To assess the consequences of this in terms of the spread of arthropod pests we sampled ornamental plants used to landscape the 29th Olympic Games in Beijing and the 16th Asia Games in Guangzhou. Plants used to landscape the Olympic Games were transported from ten provinces from across the eastern half of China. A total of 44 species of herbivorous arthropods belonging to six orders were recorded with eight species being new records for Beijing. Plants used at the 16th Asian Games came from five provinces. In total 32 species of arthropod herbivores belonging to six orders were recorded with four being new records for Guangdong province. Our results suggested that measures need to be considered to reduce the likelihood of invasive species spread when hosting major international events.

Wolbachia Has Two Different Localization Patterns in Whitefly Bemisia tabaci AsiaII7 Species.

The whitefly Bemisia tabaci is a cosmopolitan insect species complex that harbors the obligate primary symbiont Portiera aleyrodidarum and several facultative secondary symbionts including Wolbachia, which have diverse influences on the host biology. Here, for the first time, we revealed two different localization patterns of Wolbachia present in the immature and adult stages of B. tabaci AsiaII7 cryptic species. In the confined pattern, Wolbachia was restricted to the bacteriocytes, while in the scattered pattern Wolbachia localized in the bacteriocytes, haemolymph and other organs simultaneously. Our results further indicated that, the proportion of B. tabaci AsiaII7 individuals with scattered Wolbachia were significantly lower than that of confined Wolbachia, and the distribution patterns of Wolbachia were not associated with the developmental stage or sex of whitefly host. This study will provide a new insight into the various transmission routes of Wolbachia in different whitefly species.