Abstract:
Empty and live oothecae of P. americana found in houses were separately
sampled to determine natural parasitism levels of the two oothecal parasites
E. appendigaster and T. hagenowii. When a quarter of the live oothecae at a
site was removed and sampled for 12 months, T. hagenowii was found to be
the dominant parasite with a mean parasitism level of 30.5 %, compared to
E. appendigaster with a parasitism level of 8.1 %. When all the empty oothecae
were removed from the same sites and sampled in the following 12 months
the two oothecal parasites gave equal levels of parasitism, where each species
parasitized a third of the total oothecal population. When from two separate
sites either empty or live ootheoae were removed concurrently, parasitism
levels obtained were similar to those recorded when each type of ootheca was
removed from the same sites but in two different years. The study indicates
that the removal of even a quarter of the live P. americana oothecae, which
represents a sampling method with no replacement has adverse effects on
E. appendigaster populations as compared with T. hagenowii. The adverse
effect on E. appendigaster populations due to a sampling method with no
replacement stems from the low fecundity of this species together with the
habit of laying a single egg in an oothecae that yields only a single parasite at
emergence.
