The rôle of the calyx and poison gland of Cardiochiles nigriceps in the host-parasitoid relationship

Abstract

Parasitism of Heliothis virescens by Cardiochiles nigriceps reduced the growth of the host. Both the poison gland and the calyx of the female parasitoid were important in reducing the growth of the parasitized host. Injections of poison gland contents (0·04 gl/larva) or calyx fluid (0·04 gl/larva) into H. virescens larvae did not affect their growth. However, a mixture of the two glands (1:1) at this low dosage significantly reduced the weight gained by Heliothis larvae. Heliothis larvae parasitized by parasitoids from which the poison gland was removed (poi gl − females) grew significantly larger than those larvae parasitized by either a normal female or by a female from which the alkaline gland was removed (alk gl − female). The injection of poison gland material (0·04 gl/larva) into larvae which were parasitized by poi gl − females reduced the weight of these larvae to within the limits of larvae parasitized by normal females. The development of larval parasitoids which hatched from eggs of poi gl − females is abnormal. The time of larval development for the parasitoids from poi gl − females is significantly longer than that for the parasitoids from normal females or from alk gl − females. In addition 34 per cent of parasitoids from poi gl − females did not successfully complete development whereas only 10 per cent of the parasitoids from normal and alk gl − females failed to complete development. Injection of poison gland contents into a host parasitized by poi gl − females allowed normal larval development of the parasitoid. These results suggest that the poison gland material and the calyx fluid act synergistically to regulate the growth of parasitized H. virescens larvae. It is speculated that the reason for abnormal development of the larval parasitoids from poi gl − females is because of the lack of control of the host development in the absence of the poison gland material.