Effect And Mechanism Of Endosymbiots On Formation And Development Of Bemsia Tabaci

The sweet potato whitefly, Bemisia tabaci (Gennadius)(Hemiptera:Aleyrodidae), is an important cosmopolitan insect pest all over the world. B. tabaci is a species complex composed of numerous biotypes, which are morphologically indistinguishable. Among the numerous B. tabaci biotypes, B and Q biotypes are widely distributed and well-studied. Many researches proved that B. tabaci Q biotype has better survival than B biotype due to higher tolerance to extreme temperature and greater resistance to insecticides, and Q biotype has spread worldwidely. In addition to the essential intracellular symbiotic bacterium Portiera, several facultative secondary symbionts (S-symbionts) including Hamiltonella, Rickettsia, Wolbachia, Cardinium, Fritschea, and Arsenophonus have been identified from B. tabaci. To verify the correlation between the geographical distribution of S-symbiont communities and population proportions of B and Q biotypes, S-symbiont infection frequencies of58Chinese geographical populations of B and Q biotypes were determined by a specific PCR detection technique. The main results and conclusion were as follows,1. Hamiltonella was detected in all populations. The infection frequencies of Rickettsia, Wolbachia and Fritschea were93.3%,33.3%and11.1%in B biotype populations, respectively. And in Q biotype populations, Rickettsia, Cardinium and Fritschea showed infection frequencies of4.3%,31.9%and19.1%, respectively. None of the populations screened tested positive for the presence of Arsenophonus.2. Nine S-symbiont combinations were found among B biotype individuals, and seven among Q biotype individuals. In some geographical populations, all basic infection types were detected sympatrically. The composition and frequency of S-symbionts often differed greatly among closely located populations. Multiple infections with the S-symbionts within all the B and Q biotype individuals examined were approximately48.9%and15.8%, respectively.3. The S-symbionts exhibited characteristic geographical distribution patterns, such as Hamiltonella at high frequencies in all localities, Rickettsia at high frequencies mainly in B biotype in all localities, while Wolbachia, Cardinium and Fritschea were found at low frequencies sporadically in the southeastern part of China.4. A statistically significant positive correlation was detected between the Rickettsia infection and the environmental factors. The following tendencies were identified:(1) Rickettsia infection tends to be found on Brassicaceae more than on Leguminosae;(2) higher frequency of Rickettsia is associated with higher mean annual temperature at the locality;(3) higher frequency of Rickettsia is associated with greater mean annual precipitation at the locality.5. B biotype was dominant in higher latitude regions and Q biotype was dominant in lower latitude regions. Mean annual temperature and mean annual precipitation were highly correlated with the B biotype distribution proportions. The following tendencies were identified:(1) a lower B biotype distribution proportion, by locality is associated with higher mean annual temperature;(2) a lower B biotype distribution proportion is associated with greater mean annual precipitation at the locality.6. Rickettsia increased susceptibility to insecticidal compounds of B. tabaci. A lower B biotype distribution proportion is associated with greater infection frequency of Rickettsia. Differences in insecticide resistance induced by Rickettsia might be the main factor affecting population proportions of B and Q biotypes in China.In order to understand the functions of endosymbionts, and then reveal their biological significance for invasive mechanism of B. tabaci Q biotype in China. We extracted total DNA of endosymbionts from whiteflies and the comprehensive metagenomic analysis is ongoing. The research results will be helpful for the pest control.