It has been suggested that nutrient- or light-deficient algal populations are
more susceptible to fungal infections (Canter and Lund, 1969; Reynolds, 1984),
but studies on chytrid infections of freshwater diatoms had shown that phosphorus-
limited host cells were less susceptible to infections than non-limited host
cells (Bruning, 1991b). Since light-deficient Coscinodiscus cultures were more
rapidly infected by P.diadema, it appeared that in this case the hypothesis of
increased susceptibility under unfavourable growth conditions might hold true.
Experiments were carried out to investigate the (i) interspecific and (ii) intraspecific
infection behaviour of the parasitoids.