Laboratory and field performance of in vitro and in vivo reared Exorista larvarum (L.), a natural enemy of cork oak defoliators

Exorista larvarum (L.) (Diptera: Tachinidae) was reared for 1 generation on artificial diet composed of skimmed milk, chicken egg yolk, yeast extract and saccharose. The laboratory and field efficacy of in vitro-cultured E. larvarum was compared with that of parasitoids reared on the factitious host G. mellonella. In the laboratory, the effectiveness of in vitro and in vivo-reared tachinids against the natural host Lymantria dispar (L.) was tested. For in vitro-reared E. larvarum the percentage of successfully parasitized larvae was 19.8% compared with 22.7% for parasitoids reared on the host. No significant difference was found between the in vitro and the in vivo-reared flies. In a cork oak forest in northern Sardinia (Italy), parasitism of L. dispar and Malacosoma neustrium (L.) by E. larvarum cultured in vitro or in vivo was also evaluated. The in vitro-reared females oviposited a significantly lower number of eggs on L. dispar larvae. Nevertheless, no difference in percentages of successfully parasitized larvae was recorded between the two rearing methods. No eggs were laid on M. neustrium larvae by the in vitro-reared females. No puparia formed in M. neustrium larvae, not even in those exposed to in vivo-reared flies.