The cynipid wasp Pseudeucoila bochei Weld lays her eggs in the larvae of Drosophila species. One host larva always produces only one parasite, hence there must be some kind of mechanism which prevents super- parasitization or which eliminates supernumerary larvae within the host.
BAKKER et al. (1967) found that Pseudeucoila can discriminate between non-parasitized and already parasitized larvae. However, this ability does not prevent egg-laying in already parasitized hosts when there are not sufficient non-parasitized hosts available. Hence, both super- parasitization and elimination occur. According to SALT (1961) there are four ways for elimination: 1) accidental injury, 2) selective starvation, 3) physiological suppression and 4) direct physical attack. Since in Pseudeucoila one host always produces one parasite, "accidental injury "cannot be the cause of the elimination. "Selective starvation" does not come into account either, as the elimination takes place when the host provides still plenty of food for more than one parasite larva. FISHER (1961a, b; 1963) analysed interspecific competition between Horogenes chrysostictos and Nemeritis canescens in their host, Ephestia sericarium and found both physical attack and physiological suppres- sion. Physical attack took place between larvae of the same age, whereas in larvae of different ages physiological suppression of the younger larva occurred through competition for the oxygen in the haemolymph of the host larva. MEYER-GRASSMANN (1967: 422) states (from rather few observations) that physical attack is the major way for elimination in Pseudeucoila. The assumption of JENNI (1951) that elimination would take place through physiological suppression by some chemical substance was rejected by her.