Homozygous spen^GE10359 mutant adults are more sensitive to fungal infection (B. bassiana) than wild type controls. This increase in sensitivity is seen following both natural infection and infection through septic injury. However a minor increase in survival is also seen when spen^GE10359 mutant flies are wounded with a sterile tungsten needle and in response to infection with Gram-negative bacteria (Ecc-15). A fall in survival rate is also seen in response to Gram-positive bacteria (M. luteus or S. aureus). An increased number of hemocytes are seen in spen^GE10359 mutants compared to wild type, but these hemocytes are defective in the uptake of B. bassiana fungal spores. Defects are also seen in the phagocytic uptake of E. coli and S. aureus. An increased number of plasmatocytes and a reduced number of crystal cells are seen in third instar larvae. Less melanisation occurs following injury compared to wild type.