The Susceptibility of Bemisia tabaci Mediterranean (MED) Species to Attack by a Parasitoid Wasp Changes between Two Whitefly Strains with Different Facultative Endosymbiotic Bacteria

In this study, two strains of the mitochondrial lineage Q1 of Bemisia tabaci MED species,characterized by a different complement of facultative bacterial endosymbionts, were tested for theirsusceptibility to be attacked by the parasitoid wasp Eretmocerus mundus, a widespread natural enemyof B. tabaci. Notably, the BtHC strain infected with Hamiltonella and Cardinium was more resistant toparasitization than the BtHR strain infected with Hamiltonella and Rickettsia. The resistant phenotypeconsisted of fewer nymphs successfully parasitized (containing the parasitoid mature larva or pupa)and in a lower percentage of adult wasps emerging from parasitized nymphs. Interestingly, theresistance traits were not evident when E. mundus parasitism was compared between BtHC andBtHR using parasitoids originating from a colony maintained on BtHC. However, when we movedthe parasitoid colony on BtHR and tested E. mundus after it was reared on BtHR for four and sevengenerations, we saw then that BtHC was less susceptible to parasitization than BtHR. On the otherhand, we did not detect any difference in the parasitization of the BtHR strain between the threegenerations of E. mundus tested. Our findings showed that host strain is a factor affecting the abilityof E. mundus to parasitize B. tabaci and lay the basis for further studies aimed at disentangling the roleof the facultative endosymbiont Cardinium and of the genetic background in the resistance of B. tabaciMED to parasitoid attack. Furthermore, they highlight that counteradaptations to the variation ofB. tabaci defence mechanisms may be rapidly selected in E. mundus to maximize the parasitoid fitness.