Since the diploid number of mosquitoes is six, that means that there are 6 chromosomes in every somatic (non-reproductive) cell, including the cells that make up the stomach. The six chromosomes represent two three-chromosome sets; the mosquito received one set of three chromosomes from the egg cell of the mother and a similar set of three chromosomes from the sperm cell of the father.
The only exception to the six chromosomes per cell rule for mosquitoes would be the gametes, or sex cells. When cells in the ovary or teste undergo meiosis, the result is egg or sperm cells which are haploid, meaning that they have just one copy of each chromosome, for a total of three chromosomes.
Interestingly, in some colonial insect species such as bees, wasps, and ants, only the females are diploid, and the males are entirely haploid. This is an unusual variation on the normal haploid gamete/diploid somatic cell condition that exists in most animals.