The present invention relates to the use of increased culture pH, relative to standard insect cell culture conditions, during baculovirus infection of lepidopteran insect cells to enable production of recombinant chikungunya (CHIKV) virus like particles (VLPs). The invention further relates to adapted insect cell lines derived from insect cells such as Sf21, which can grow robustly at elevated culture pH, the use of said cell lines to recombinantly produce pH sensitive proteins in the correct conformation and increase expression of recombinant proteins relative to standard insect cell lines. In some embodiments of the invention, the cells are useful for recombinant production of CHIKV VLPs. The invention also relates to a method for the production of a pH-adapted lepidopteran insect cell line. In some embodiments of said method, the cell line is produced and/or maintained in reduced phosphate serum-free insect cell media.