Pteromalus puparum is a predominant endoparasitoid wasp of Pieris rapae. Its venom is the only active factor injected into host associated with oviposition. In this report, we explored whether the venom alone from this wasp affects the endocrine system of its host or not. We monitored the changes of hemolymph juvenile hormone (JH; only JH III detected), ecdysteroid, and juvenile hormone esterase activity (JHE) over 72 h in parasitized and venom-microinjected P. rapae pupae. Non-parasitized and PBS-microinjected P. rapae served as controls. Results showed that JH titers were significantly higher in parasitized and venom-microinjected pupae than that in control pupae during 24 to 72 h. After 12 h, JH titers were significantly promoted by parasitization and venom microinjection. JHE activities of non-parasitized and PBS-microinjected pupae were significantly higher than that of parasitized and venom-microinjected pupae, which was with a peak at 12 h (parasitized pupae) or 24 h (venom-microinjected pupae) during 6 to 48 and 12 to 36 h, respectively. The hemolymph titers of ecdysteroid in non-parasitized and PBS-microinjected pupae increased rapidly during 12 to 36 h with a peak at 36 h, and were higher than treatments before 48 h, while presenting a significant difference at 24 to 48 h between the treatments and controls. The results demonstrate that venom alone of this parasitoid wasp can disrupt its host's endocrine system.
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