| The whitefly Bemisia tabaci (Gennadius) is an important pest on many crops, causing considerable damage to cotton, vegetable and ornamental production, and has a worldwide distribution in over90countries and regions except the South Antarctic. Bemisia tabaci is a species complex containing over34putative cryptic species. In this species complex, MEAM1(formerly referred to as B ’biotype’) and Mediterranean (formerly referred to as Q’biotype’) are most invasive and destructive, having invaded many parts of the world in the last20years. For simplicity, we call these two whitefly species B and Q species. In China, B entered in middle1990s and was already widespread in this country by2003, while Q entered China around2003, and the two invasive species have been rapidly displacing native whiteflies in many regions. Field surveys in China after2003indicate that in many regions Q has been replacing the earlier invader B. The factors underlying this displacement are not well understood and warrant detailed investigations. Because whitefly is anpoikilothermic animal, the capacity to survive low and high temperatures in the two whitefly species is likely to play a major role in their survival, life history traits, population dynamics and competitive displacement.In this study, we used two populations of each of the two invasive species, B and Q, of B. tabaci complex, and nine different temperatures, including five unfavourable high temperatures, three unfavourable low temperatures and a control temperature of26℃, in the experiments. The performance of eggs, pupae and adults, including development, survival, reproduction and sex ratio, were observed following exposures to different temperature treatments. In addition, the expressions of heat shock protein related genes were examined by RT-PCR.(1) Survival of eggs, red-eye pupae and adults following exposures to unfavourable temperaturesThe mortality of B and Q whiteflies increased with exposures to higher temperatures at the37℃,39℃,41℃,43℃and45℃for2h respectively, compared to that at the control temperature of26℃. In particular, the mortality of B whitefly was significantly higher than that of Q whitefly following exposure to41℃and43℃. In addition, the percentages of egg hatch and adult emergence decreased with the exposure to higher temperatures, but no significant differences were observed between the B and Q whiteflies. The mortality of the B whitefly was similar to that of the Q whitefly following exposures to various low temperatures for2days.(2) Fecundity of adult whiteflies following exposures to unfavourable temperaturesFollowing exposures to41℃for2h, the fecundity of the B and Q were similarly reduced. While production of eggs by adults was reduced following exposure to high temperatures, both egg hatch and development time (all approximately21-22days) did not differ between the two species. In addition, while the female ratios in the progenies of both whiteflies appeared to be reduced following parental exposure to the high temperature, and in particular the reduction was significant in B and but not in Q. Following exposure to4℃for2h, the two species of whiteflies also performed similarly in fecundity, and egg hatch, development time and female ratio of their progenies.(3) Effect of exposure to high temperature on the expression of heat shock protein related genesThe expression of heat shock protein related genes including HSP40, HSP70and HSP90in both B and Q whitefly adults was examined using RT-PCR after exposure to41℃for2h. The results indicated that the relative expression of HSP90increased seven times compared to that at26℃, in both B and Q whiteflies. At26℃, the relative expression of HSP90of Q was higher than that of B. However, the relative expressions of both HSP40and HSP70did not increase compared to those at26℃in both whitefly species. |
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