Candidatus Liberibacter solanacearum (Lso) are phloem-restricted and unculturable Gram-negative bacteria.Presently five haplotypes have been identified worldwide;but only haplotypes A and B are associated with the vector Bactericera cockerelli ((S)ulc.) in the Americas.Previous studies showed that Lso-infection reduces B.cockerelli reproductive output and that Lso haplotype B is more pathogenic than Lso haplotype A.To understand the interaction ofLso haplotype B and B.cockerelli,the fitness of Lso-free and Lso B-infected insects,and the expression of vitellogenin (Bc Vgl-like),a gene involved directly in the insect reproduction were analyzed.Statistical differences in the number of eggs oviposited,and the total number of progeny nymphs and adults were found among crosses of insects with or without Lso.Significant differences in sex proportions were found between Lso B-infected and Lso-free crosses:a higher proportion of F1 adult females were obtained from Lso B-infected mothers.A significant reduction of BcVgl-like was observed in crosses performed with Lso B-infected females compared to the Lso-free insects.In female cohorts of different age,a significant reduction of BcVgl-like expression was measured in 7-d-old Lso B-infected females (virgin and mated) compared with 7-d-old Lso-free females (virgin and mated),respectively.The reduction of Bc Vgl-like transcript was associated with a lower number of developing oocytes observed in female’s reproductive systems.Overall,this study represents the first step to understand the interaction of Lso B with B.cockerelli,highlighting the effect of Lso B infection on egg production,Bc Vgl-like expression,and oocyte development.