Venom of the egg-larval parasitoid Chelonus inanitus is a complex mixture and has multiple biological effects

The egg-larval parasitoid Chelonus inanitus injects bracoviruses (BVs) and venom along with the egg into the host egg; both components are essential for successful parasitoid development. All stages of eggs of its natural host, Spodoptera littoralis, can be successfully parasitized, i.e. from mainly a yolk sphere to a fully developed embryo. Here, we show that the venom contains at least 25 proteins with masses from 14 kDa to over 300 kDa ranging from acidic to basic. The majority is glycosylated and their persistence in the host is short when old eggs are parasitized and much longer when young eggs are parasitized. Physiological experiments indicated three different functions. (1) Venom synergized the effect of BVs in disrupting host development when injected into third instar larvae. (2) Venom had a transient paralytic effect when injected into sixth instar larvae. (3) In vitro experiments with haemocytes of fourth instar larvae suggested that venom alters cell membrane permeability. We propose that venom promotes entry of BVs into host cells and facilitates placement of the egg in the embryoʹs haemocoel when old eggs are parasitized. The multifunctionality of the venom might thus be essential in enabling parasitization of all stages of host eggs.